The document provides an overview of the physiology of the cornea, including its embryology, optical properties, metabolism, hydration, transparency, and wound healing. Key points include that the cornea has 5 layers and gets its oxygen from the atmosphere, aqueous humor, and limbal capillaries. It maintains transparency through ordered collagen fibrils and avascularity. Hydration is regulated by the endothelial pump and stromal proteoglycans. Wound healing involves epithelial migration, proliferation, and adhesion as well as stromal scarring and endothelial remodeling.
The document summarizes key aspects of corneal physiology:
1. The cornea receives its metabolic energy from glucose in the aqueous humor and oxygen from the atmosphere, limbal blood vessels, and aqueous humor. It primarily metabolizes glucose anaerobically through the lactic acid pathway.
2. The cornea is transparent due to the ordered arrangement of collagen fibrils in the stroma and maintenance of hydration. Disruption of the spacing between fibrils or increased swelling can decrease transparency by increasing light scattering.
3. Permeability of substances across the cornea such as sodium, water, and drugs is regulated by the properties of the substances as well as the tight junctions between endothelial and
This document provides information on the anatomy and physiology of the cornea. It describes the layers of the cornea including the epithelium, Bowman's membrane, stroma, Dua's layer, Descemet's membrane, and endothelium. It discusses the transparency of the cornea, metabolic processes, drug permeability, wound healing, and the effects of contact lens wear on corneal physiology. The cornea has several specialized functions including refracting light and protecting the interior of the eye.
This document discusses the dynamics of the tear film. It covers the secretion and formation of the tear film, how it is retained and redistributed on the eye surface, the displacement phenomenon, evaporation from the tear film, drying and breakup of the tear film, and dynamics during blinking. Evaluation methods for the tear film like staining, the Schirmer test, and fluorophotometry are also mentioned. The tear film and its components help protect and lubricate the eye.
This document provides an overview of the anatomy of the uveal tract, which includes the iris, ciliary body, and choroid. It begins with an introduction and overview of the embryology and development of the uveal tract. It then discusses the anatomy and microstructure of each part of the uveal tract in detail, including their nerve and blood supply. It also briefly discusses some congenital anomalies that can affect the uveal tract.
The document discusses the anatomy and physiology of aqueous humor dynamics. It describes the structures involved in aqueous humor formation, which occurs primarily through active transport by the non-pigmented ciliary epithelium. These include the iris, ciliary body, trabecular meshwork, Schlemm's canal, and collector channels. Aqueous humor is formed at a rate of around 2.3 μl/min through diffusion, ultrafiltration and secretion across the ciliary epithelium. Various factors influence aqueous humor production and outflow through the trabecular meshwork into episcleral veins.
The tear film has three layers:
1. A mucin layer secreted by goblet cells that forms a hydrophilic barrier on the cornea.
2. An aqueous layer secreted mainly by the lacrimal gland, containing proteins, electrolytes, and other components.
3. An outer lipid layer secreted by meibomian glands that prevents evaporation and maintains tear film stability.
The tear film is regulated by hormonal and neural pathways and provides nutrients to the cornea, removes waste, lubricates the eye, and protects against infection through its biochemical composition.
The cornea is the transparent front part of the eye that allows light to enter. It has 6 layers - an epithelial layer, Bowman's membrane, a thick stromal layer, Duas layer, Descemet's membrane, and an endothelial layer. The stroma makes up around 90% of the cornea's thickness and contains collagen fibrils that give it strength and transparency. The cornea has no blood vessels and receives nutrients from vessels in the surrounding tissues. It has a rich nerve supply that provides its high sensitivity. The cornea refracts and helps focus light entering the eye and is essential for vision.
1. The tear film consists of three layers - an outer lipid layer, intermediate aqueous layer, and inner mucin layer. The lipid layer prevents evaporation while the aqueous layer nourishes the cornea and washes away debris.
2. Tears are produced both through basal secretion by accessory glands and reflex secretion by the main lacrimal gland in response to irritation. The tear film forms on the cornea through spreading of layers.
3. Diagnosis of dry eye involves tests like tear film break-up time (BUT), Schirmer's test, and Jones tests to evaluate tear production and drainage. Multiple factors can contribute to dry eye and tear film instability.
The document summarizes key aspects of corneal physiology:
1. The cornea receives its metabolic energy from glucose in the aqueous humor and oxygen from the atmosphere, limbal blood vessels, and aqueous humor. It primarily metabolizes glucose anaerobically through the lactic acid pathway.
2. The cornea is transparent due to the ordered arrangement of collagen fibrils in the stroma and maintenance of hydration. Disruption of the spacing between fibrils or increased swelling can decrease transparency by increasing light scattering.
3. Permeability of substances across the cornea such as sodium, water, and drugs is regulated by the properties of the substances as well as the tight junctions between endothelial and
This document provides information on the anatomy and physiology of the cornea. It describes the layers of the cornea including the epithelium, Bowman's membrane, stroma, Dua's layer, Descemet's membrane, and endothelium. It discusses the transparency of the cornea, metabolic processes, drug permeability, wound healing, and the effects of contact lens wear on corneal physiology. The cornea has several specialized functions including refracting light and protecting the interior of the eye.
This document discusses the dynamics of the tear film. It covers the secretion and formation of the tear film, how it is retained and redistributed on the eye surface, the displacement phenomenon, evaporation from the tear film, drying and breakup of the tear film, and dynamics during blinking. Evaluation methods for the tear film like staining, the Schirmer test, and fluorophotometry are also mentioned. The tear film and its components help protect and lubricate the eye.
This document provides an overview of the anatomy of the uveal tract, which includes the iris, ciliary body, and choroid. It begins with an introduction and overview of the embryology and development of the uveal tract. It then discusses the anatomy and microstructure of each part of the uveal tract in detail, including their nerve and blood supply. It also briefly discusses some congenital anomalies that can affect the uveal tract.
The document discusses the anatomy and physiology of aqueous humor dynamics. It describes the structures involved in aqueous humor formation, which occurs primarily through active transport by the non-pigmented ciliary epithelium. These include the iris, ciliary body, trabecular meshwork, Schlemm's canal, and collector channels. Aqueous humor is formed at a rate of around 2.3 μl/min through diffusion, ultrafiltration and secretion across the ciliary epithelium. Various factors influence aqueous humor production and outflow through the trabecular meshwork into episcleral veins.
The tear film has three layers:
1. A mucin layer secreted by goblet cells that forms a hydrophilic barrier on the cornea.
2. An aqueous layer secreted mainly by the lacrimal gland, containing proteins, electrolytes, and other components.
3. An outer lipid layer secreted by meibomian glands that prevents evaporation and maintains tear film stability.
The tear film is regulated by hormonal and neural pathways and provides nutrients to the cornea, removes waste, lubricates the eye, and protects against infection through its biochemical composition.
The cornea is the transparent front part of the eye that allows light to enter. It has 6 layers - an epithelial layer, Bowman's membrane, a thick stromal layer, Duas layer, Descemet's membrane, and an endothelial layer. The stroma makes up around 90% of the cornea's thickness and contains collagen fibrils that give it strength and transparency. The cornea has no blood vessels and receives nutrients from vessels in the surrounding tissues. It has a rich nerve supply that provides its high sensitivity. The cornea refracts and helps focus light entering the eye and is essential for vision.
1. The tear film consists of three layers - an outer lipid layer, intermediate aqueous layer, and inner mucin layer. The lipid layer prevents evaporation while the aqueous layer nourishes the cornea and washes away debris.
2. Tears are produced both through basal secretion by accessory glands and reflex secretion by the main lacrimal gland in response to irritation. The tear film forms on the cornea through spreading of layers.
3. Diagnosis of dry eye involves tests like tear film break-up time (BUT), Schirmer's test, and Jones tests to evaluate tear production and drainage. Multiple factors can contribute to dry eye and tear film instability.
This document discusses corneal nutrition, metabolism, and the effects of hypoxic conditions. There are three main metabolic processes in the cornea: 1) the pentose phosphate pathway, which produces intermediates for nucleic acid synthesis, 2) glycolysis, which converts glucose to pyruvate and yields 2 ATP per glucose molecule, and 3) the Krebs cycle, which fully breaks down glucose under aerobic conditions to produce 36 ATP per cycle. Hypoxic conditions like prolonged contact lens wear can increase lactate production and induce stromal edema, leading to clinical issues like halos and decreased visual acuity. Maintaining adequate oxygen is important for normal corneal function and health.
The document provides information about the Jackson Crossed-Cylinder (JCC) technique for determining astigmatism during eye exams. It discusses the optics and proper use of the JCC. It describes the historical origins of the JCC, how it works, and the step-by-step procedure for using it to refine the axis and power of astigmatic corrections. Common sources of error are also outlined. The JCC is presented as an important tool for optometrists to accurately measure and correct astigmatism in clinical practice.
The document provides information on the physiology and biochemistry of the cornea. It discusses the cornea's structure, composition, function, metabolism, wound healing, and factors that affect transparency. The cornea's layers are composed primarily of water, collagen, and proteoglycans. It maintains transparency through its regular stromal spacing and metabolic pumps that regulate hydration. The cornea relies on limbal stem cells and tight epithelial/endothelial barriers to replenish and prevent edema.
This document summarizes the physiology of the cornea. It discusses the cornea's gross anatomy, functions, histology, metabolism, hydration, transparency, and wound healing. Key points include that the cornea is transparent and avascular, has five layers, and maintains its structure and hydration through a balance of swelling pressure, metabolic pumping, and intraocular pressure. It obtains nutrients from tears and the aqueous humor and remains transparent through the uniform arrangement and small size of its stromal fibers.
Optics of contact lens and nomenclature copy [repaired] (1)Manjusha Lakshmi
A contact lens is an artificial device placed on the cornea or sclera for optical or therapeutic purposes. Contact lenses are classified based on their anatomical location, nature of material, and wearing schedule. Key parameters of contact lenses include the base curve, diameter, power, edge clearance, and central thickness. Contact lenses provide vision correction and can also be used for therapeutic reasons like drug delivery or treating corneal diseases.
The document discusses the anatomy, embryology, and function tests of the macula lutea. It describes the macula lutea as a 5.5mm circular area at the posterior pole of the retina that subserves central vision. It notes the macula's delayed development until 8 months gestation and specialization of the fovea which contains the highest concentration of cones. The document outlines various macular function tests used to evaluate macular diseases, including visual acuity, Amsler grid, microperimetry, and electroretinography. It provides details on the anatomy and cell layers of the fovea centralis and techniques for assessing macular integrity with tests like the Maddox rod.
The document summarizes the Amsler grid, a diagnostic tool used since 1945 to screen for and monitor macular diseases. It consists of a grid with a central dot that patients look at to detect any distortions, gaps, or blurred areas in their central vision. Various versions are available, including ones with different colors, patterns of lines, or dot sizes to test specific parts of the visual field and detect different types of visual abnormalities that could indicate conditions like macular degeneration or glaucoma. The procedure involves having patients view the grid with each eye separately at 16 inches and report any anomalies in the lines of the grid.
This document discusses coloboma, which is an embryologic defect resulting in a notch or gap in ocular structures. It can affect the iris, choroid, optic disc, or macula. Coloboma is usually sporadic but sometimes associated with genetic syndromes. Complications include retinal detachment, cataract, glaucoma, and amblyopia. Diagnosis involves examination and imaging. Management depends on the location and severity but may include treatment of refractive error, retinal detachment surgery, or cataract surgery. Prognosis depends on the structures involved, with macular or optic nerve coloboma having worse visual outcomes.
The cornea has 5 layers - epithelium, Bowman's layer, stroma, Descemet's membrane, and endothelium. It is avascular and receives nutrients from peri-limbal blood vessels, aqueous humor, and oxygen from the air. The pre-corneal tear film maintains moisture and transparency. The cornea remains transparent due to the endothelial pump regulating fluid levels. Damage to layers can cause opacity as repair tissue is irregularly arranged.
This document provides information on the anatomy and diseases of the vitreous humor. It discusses that the vitreous humor is a jelly-like structure that fills the back of the eye and provides support. Common diseases include vitreous liquefaction, detachment, hemorrhage, and opacities. Vitreous liquefaction is the most common degenerative change and causes floaters. Posterior vitreous detachment often occurs in older individuals and may lead to retinal tears or breaks. Vitreous opacities can result from inflammatory cells, aggregates, tumors or hemorrhages. Vitreous hemorrhage usually stems from retinal vessels and can cause vision loss.
This document provides information about fundus fluorescein angiography (FFA). It begins with basic principles of FFA and the dyes used, including sodium fluorescein and indocyanine green. The purpose, indications, contraindications, technique, phases, and interpretation of FFA are described. Abnormal fluorescence patterns like hyperfluorescence and hypofluorescence are discussed. Recent advances in wide-field imaging and indocyanine green angiography are also summarized.
1. Dr. Reshma Peter discusses various lenses used in ophthalmology, including those for fundus examination, gonioscopy, and contact biomicroscopy of the fundus.
2. Indirect fundus biomicroscopy uses Volk lenses of +60D, +78D, and +90D attached to a slit lamp to provide an inverted and laterally reversed view of the retina.
3. Lenses for indirect ophthalmoscopy include +30D, +20D, and +15D lenses, which provide different levels of magnification, stereopsis, and field of view.
4. Contact lenses for fundus examination include Modified Koeppe's lens and Goldmann's three mirror contact
Corneal physiology in relation to contact lens wearHira Dahal
This document discusses corneal physiology in relation to contact lens wear. It describes the layers of the cornea and its blood, nerve and oxygen supply. Maintaining corneal transparency requires adequate oxygen and metabolism. Contact lenses reduce oxygen levels, which can cause swelling, hypoesthesia, and structural changes if levels fall below what the cornea requires. The minimum oxygen needed varies from 5-17.9% depending on the activity. Soft lenses induce more swelling than RGP lenses. Hypoxia affects epithelial healing, sensitivity and metabolism.
The uvea consists of the iris, ciliary body, and choroid. It develops from both neuroectoderm and vascular mesoderm. The iris develops fully by age 5, with pigmentation continuing after birth. The ciliary body appears by 9 weeks and is fully developed by 6 months gestation. The choroid layers are seen by 5 months gestation. The uvea regulates light entry and provides blood supply to the outer retina. Congenital anomalies include heterochromia, polycoria, persistent pupillary membranes, and colobomas. Uveitis is inflammation of the uveal tract.
Corneal metabolism
1. o Cornea requires energy for normal metabolic activities as well as for maintaining transparency and dehydration o Energy is generated by the breakdown of glucose in the form of ATP o Most actively metabolizing layer are epithelium and endothelium o Sources of nutrients : o Oxygen : mainly from atmosphere through tear film , with minor amount supplied by the aqueous and limbal vasculature o Glucose , amino acid, vitamins and other nutrients supplied to cornea by aqueous humor o Glucose also derived from glycogen stores in corneal epithelium o Epithelium consumes O2 10 times faster then stroma
2. o Three process or pathways – o Pentose shunt (Hexose monophosphate shunt) –occurs both in hypoxic and normoxic condition o Glycolysis (Embden meyerhof pathway) –anaerobic process , glucose / glycogen converted to pyruvate yeilding 2 ATPs o TCA or krebs or citric acid cycle- aerobic condition pyruvate is oxidized to yield 36 ATP, water, CO2.
3. o In normal conditions all the glucose consumed by the cornea o Glucose mostly come from aqueous humor o The rate of glucose consumption by the whole cornea is approx. 100 microgram/hr/cm2. o 1 mol. of glucose will be converted to the pyruvic acid and produced 2 molecules lactic acid and 2 mol. of ATP o In the krebs cycle, 1 mol. of glucose will utilize the pyruvic acid and O2 to produced 36 mol. ATP o Epithelium and endothelium will consume the oxygen
4. o The pentose phosphate pathway is used to metabolize five carbon sugars; one ATP and 2 NADH molecules are produced from oxidation of one glucose molecule o Produced intermediates for nucleic acid synthesis and some amino acids o This process will happen in hypoxic or normoxic condition o The purpose of glucose metabolism through the pentose shunt is the production of NADPH
This document discusses methods for detecting the type and power of lenses. It covers hand neutralization techniques for spherical and astigmatic lenses using convex and concave lenses. It also describes using a Geneva lens measure and manual and automated focimeters. The manual focimeter involves aligning mires to determine spherical and cylinder power of single vision, bifocal, trifocal and progressive lenses. The automated focimeter uses a light beam to precisely measure lens parameters. Both tools have limitations, with the automated version providing more accuracy.
The document discusses factors that affect corneal transparency. The main points are:
1. The cornea's main function is to refract light to form a clear retinal image. Normal transparency results from the cornea's anatomical structure and relative dehydration.
2. Any disruption to the cornea's anatomy or physiology can cause loss of transparency. Key factors are the corneal epithelium, tear film, stromal layer arrangement, vascularization, hydration, and cellular components.
3. The corneal epithelium and tight junctions between cells contribute to transparency and act as a barrier. Disruptions to the epithelium or tear film can compromise transparency.
The cornea is the transparent front part of the eye that allows light to enter. It has 5 layers - epithelium, Bowman's layer, stroma, Descemet's membrane, and endothelium. The epithelium and endothelium help regulate hydration to maintain transparency. The stroma contains collagen fibrils that provide strength and refractive power. The endothelium actively pumps fluid from the stroma into the aqueous humor. Together, the layers and pumping action keep the cornea clear for vision. Metabolism relies on diffusion of nutrients from tear film and aqueous humor due to lack of blood vessels. Nerves innervate the cornea for high sensitivity.
The cornea is a transparent tissue with convex outer and concave inner surfaces. It has dimensions of 11.75mm horizontally and 11mm vertically on the anterior surface. The epithelium has basal, wing and flattened cells that provide a barrier and refractive function. The stroma contains collagen fibrils in a lattice arrangement. Corneal transparency requires a regular stromal arrangement, avascularity, and proper hydration maintained by endothelial pumping. Disruptions to these anatomical or physiological factors can compromise transparency.
This document discusses corneal nutrition, metabolism, and the effects of hypoxic conditions. There are three main metabolic processes in the cornea: 1) the pentose phosphate pathway, which produces intermediates for nucleic acid synthesis, 2) glycolysis, which converts glucose to pyruvate and yields 2 ATP per glucose molecule, and 3) the Krebs cycle, which fully breaks down glucose under aerobic conditions to produce 36 ATP per cycle. Hypoxic conditions like prolonged contact lens wear can increase lactate production and induce stromal edema, leading to clinical issues like halos and decreased visual acuity. Maintaining adequate oxygen is important for normal corneal function and health.
The document provides information about the Jackson Crossed-Cylinder (JCC) technique for determining astigmatism during eye exams. It discusses the optics and proper use of the JCC. It describes the historical origins of the JCC, how it works, and the step-by-step procedure for using it to refine the axis and power of astigmatic corrections. Common sources of error are also outlined. The JCC is presented as an important tool for optometrists to accurately measure and correct astigmatism in clinical practice.
The document provides information on the physiology and biochemistry of the cornea. It discusses the cornea's structure, composition, function, metabolism, wound healing, and factors that affect transparency. The cornea's layers are composed primarily of water, collagen, and proteoglycans. It maintains transparency through its regular stromal spacing and metabolic pumps that regulate hydration. The cornea relies on limbal stem cells and tight epithelial/endothelial barriers to replenish and prevent edema.
This document summarizes the physiology of the cornea. It discusses the cornea's gross anatomy, functions, histology, metabolism, hydration, transparency, and wound healing. Key points include that the cornea is transparent and avascular, has five layers, and maintains its structure and hydration through a balance of swelling pressure, metabolic pumping, and intraocular pressure. It obtains nutrients from tears and the aqueous humor and remains transparent through the uniform arrangement and small size of its stromal fibers.
Optics of contact lens and nomenclature copy [repaired] (1)Manjusha Lakshmi
A contact lens is an artificial device placed on the cornea or sclera for optical or therapeutic purposes. Contact lenses are classified based on their anatomical location, nature of material, and wearing schedule. Key parameters of contact lenses include the base curve, diameter, power, edge clearance, and central thickness. Contact lenses provide vision correction and can also be used for therapeutic reasons like drug delivery or treating corneal diseases.
The document discusses the anatomy, embryology, and function tests of the macula lutea. It describes the macula lutea as a 5.5mm circular area at the posterior pole of the retina that subserves central vision. It notes the macula's delayed development until 8 months gestation and specialization of the fovea which contains the highest concentration of cones. The document outlines various macular function tests used to evaluate macular diseases, including visual acuity, Amsler grid, microperimetry, and electroretinography. It provides details on the anatomy and cell layers of the fovea centralis and techniques for assessing macular integrity with tests like the Maddox rod.
The document summarizes the Amsler grid, a diagnostic tool used since 1945 to screen for and monitor macular diseases. It consists of a grid with a central dot that patients look at to detect any distortions, gaps, or blurred areas in their central vision. Various versions are available, including ones with different colors, patterns of lines, or dot sizes to test specific parts of the visual field and detect different types of visual abnormalities that could indicate conditions like macular degeneration or glaucoma. The procedure involves having patients view the grid with each eye separately at 16 inches and report any anomalies in the lines of the grid.
This document discusses coloboma, which is an embryologic defect resulting in a notch or gap in ocular structures. It can affect the iris, choroid, optic disc, or macula. Coloboma is usually sporadic but sometimes associated with genetic syndromes. Complications include retinal detachment, cataract, glaucoma, and amblyopia. Diagnosis involves examination and imaging. Management depends on the location and severity but may include treatment of refractive error, retinal detachment surgery, or cataract surgery. Prognosis depends on the structures involved, with macular or optic nerve coloboma having worse visual outcomes.
The cornea has 5 layers - epithelium, Bowman's layer, stroma, Descemet's membrane, and endothelium. It is avascular and receives nutrients from peri-limbal blood vessels, aqueous humor, and oxygen from the air. The pre-corneal tear film maintains moisture and transparency. The cornea remains transparent due to the endothelial pump regulating fluid levels. Damage to layers can cause opacity as repair tissue is irregularly arranged.
This document provides information on the anatomy and diseases of the vitreous humor. It discusses that the vitreous humor is a jelly-like structure that fills the back of the eye and provides support. Common diseases include vitreous liquefaction, detachment, hemorrhage, and opacities. Vitreous liquefaction is the most common degenerative change and causes floaters. Posterior vitreous detachment often occurs in older individuals and may lead to retinal tears or breaks. Vitreous opacities can result from inflammatory cells, aggregates, tumors or hemorrhages. Vitreous hemorrhage usually stems from retinal vessels and can cause vision loss.
This document provides information about fundus fluorescein angiography (FFA). It begins with basic principles of FFA and the dyes used, including sodium fluorescein and indocyanine green. The purpose, indications, contraindications, technique, phases, and interpretation of FFA are described. Abnormal fluorescence patterns like hyperfluorescence and hypofluorescence are discussed. Recent advances in wide-field imaging and indocyanine green angiography are also summarized.
1. Dr. Reshma Peter discusses various lenses used in ophthalmology, including those for fundus examination, gonioscopy, and contact biomicroscopy of the fundus.
2. Indirect fundus biomicroscopy uses Volk lenses of +60D, +78D, and +90D attached to a slit lamp to provide an inverted and laterally reversed view of the retina.
3. Lenses for indirect ophthalmoscopy include +30D, +20D, and +15D lenses, which provide different levels of magnification, stereopsis, and field of view.
4. Contact lenses for fundus examination include Modified Koeppe's lens and Goldmann's three mirror contact
Corneal physiology in relation to contact lens wearHira Dahal
This document discusses corneal physiology in relation to contact lens wear. It describes the layers of the cornea and its blood, nerve and oxygen supply. Maintaining corneal transparency requires adequate oxygen and metabolism. Contact lenses reduce oxygen levels, which can cause swelling, hypoesthesia, and structural changes if levels fall below what the cornea requires. The minimum oxygen needed varies from 5-17.9% depending on the activity. Soft lenses induce more swelling than RGP lenses. Hypoxia affects epithelial healing, sensitivity and metabolism.
The uvea consists of the iris, ciliary body, and choroid. It develops from both neuroectoderm and vascular mesoderm. The iris develops fully by age 5, with pigmentation continuing after birth. The ciliary body appears by 9 weeks and is fully developed by 6 months gestation. The choroid layers are seen by 5 months gestation. The uvea regulates light entry and provides blood supply to the outer retina. Congenital anomalies include heterochromia, polycoria, persistent pupillary membranes, and colobomas. Uveitis is inflammation of the uveal tract.
Corneal metabolism
1. o Cornea requires energy for normal metabolic activities as well as for maintaining transparency and dehydration o Energy is generated by the breakdown of glucose in the form of ATP o Most actively metabolizing layer are epithelium and endothelium o Sources of nutrients : o Oxygen : mainly from atmosphere through tear film , with minor amount supplied by the aqueous and limbal vasculature o Glucose , amino acid, vitamins and other nutrients supplied to cornea by aqueous humor o Glucose also derived from glycogen stores in corneal epithelium o Epithelium consumes O2 10 times faster then stroma
2. o Three process or pathways – o Pentose shunt (Hexose monophosphate shunt) –occurs both in hypoxic and normoxic condition o Glycolysis (Embden meyerhof pathway) –anaerobic process , glucose / glycogen converted to pyruvate yeilding 2 ATPs o TCA or krebs or citric acid cycle- aerobic condition pyruvate is oxidized to yield 36 ATP, water, CO2.
3. o In normal conditions all the glucose consumed by the cornea o Glucose mostly come from aqueous humor o The rate of glucose consumption by the whole cornea is approx. 100 microgram/hr/cm2. o 1 mol. of glucose will be converted to the pyruvic acid and produced 2 molecules lactic acid and 2 mol. of ATP o In the krebs cycle, 1 mol. of glucose will utilize the pyruvic acid and O2 to produced 36 mol. ATP o Epithelium and endothelium will consume the oxygen
4. o The pentose phosphate pathway is used to metabolize five carbon sugars; one ATP and 2 NADH molecules are produced from oxidation of one glucose molecule o Produced intermediates for nucleic acid synthesis and some amino acids o This process will happen in hypoxic or normoxic condition o The purpose of glucose metabolism through the pentose shunt is the production of NADPH
This document discusses methods for detecting the type and power of lenses. It covers hand neutralization techniques for spherical and astigmatic lenses using convex and concave lenses. It also describes using a Geneva lens measure and manual and automated focimeters. The manual focimeter involves aligning mires to determine spherical and cylinder power of single vision, bifocal, trifocal and progressive lenses. The automated focimeter uses a light beam to precisely measure lens parameters. Both tools have limitations, with the automated version providing more accuracy.
The document discusses factors that affect corneal transparency. The main points are:
1. The cornea's main function is to refract light to form a clear retinal image. Normal transparency results from the cornea's anatomical structure and relative dehydration.
2. Any disruption to the cornea's anatomy or physiology can cause loss of transparency. Key factors are the corneal epithelium, tear film, stromal layer arrangement, vascularization, hydration, and cellular components.
3. The corneal epithelium and tight junctions between cells contribute to transparency and act as a barrier. Disruptions to the epithelium or tear film can compromise transparency.
The cornea is the transparent front part of the eye that allows light to enter. It has 5 layers - epithelium, Bowman's layer, stroma, Descemet's membrane, and endothelium. The epithelium and endothelium help regulate hydration to maintain transparency. The stroma contains collagen fibrils that provide strength and refractive power. The endothelium actively pumps fluid from the stroma into the aqueous humor. Together, the layers and pumping action keep the cornea clear for vision. Metabolism relies on diffusion of nutrients from tear film and aqueous humor due to lack of blood vessels. Nerves innervate the cornea for high sensitivity.
The cornea is a transparent tissue with convex outer and concave inner surfaces. It has dimensions of 11.75mm horizontally and 11mm vertically on the anterior surface. The epithelium has basal, wing and flattened cells that provide a barrier and refractive function. The stroma contains collagen fibrils in a lattice arrangement. Corneal transparency requires a regular stromal arrangement, avascularity, and proper hydration maintained by endothelial pumping. Disruptions to these anatomical or physiological factors can compromise transparency.
The cornea has 5 layers - epithelium, Bowman's layer, stroma, Descemet's membrane, and endothelium. It maintains transparency through tightly packed collagen fibrils, tight cell junctions, and avascularity. The epithelium acts as a barrier and regulates hydration. The endothelium actively transports fluid using ion pumps such as Na+/K+ ATPase to prevent stromal swelling and maintain deturgescence. Any disruption to these layers or processes can compromise the cornea's transparency.
The document summarizes key aspects of corneal physiology:
1. It describes the structure and optical properties of the cornea, including its thickness, curvature, and role in refractive power.
2. The functions of the cornea are outlined as providing refractive power, protecting intraocular structures, and allowing images to reach the retina.
3. Factors like transparency, curvature regularity, and smoothness are described as affecting corneal function. Measurement techniques for analyzing the cornea's optical properties are also discussed.
This document discusses the physiology of the cornea. It describes the cornea's gross anatomy, functions, histology, biochemical composition, metabolism, hydration, transparency, and wound healing. Key points include that the cornea is avascular and transparent, maintains structural integrity, and refracts light. It has 5 layers including epithelium, stroma, and endothelium. The cornea's transparency relies on its precise structure and hydration state maintained by metabolic pumps and swelling pressure.
Main physiologic function of cornea is to act as a major refracting medium, so that a clear retinal image is formed. • Normal corneal transparency is result of • 1.anatomical factor such as uniform and regular arrangement of corneal epithelium, peculiar arrangement of corneal lamella and corneal vascularity 2.Physiological factor [ie] relative state of corneal dehydration.
3. • Therefore, any process which upsets the anatomy or physiology of cornea will cause LOSS OF TRANSPARENCY to some degree.
4. FACTORS AFFECTING CORNEAL TRANSPARENCY • CORNEAL EPITHELIUM &TEAR FLIM • ARRANGEMENT OF STROMAL LAMELLA • CORNEAL VASCULARIZATION • CORNEAL HYDRATION • CELLULAR FACTORS AFFECTING TRANSPARENCY
The cornea is the transparent front part of the eye that allows light to enter. It has six layers - epithelium, Bowman's membrane, stroma, Dua's layer, Descemet's membrane, and endothelium. The stroma makes up most of the thickness and contains collagen fibers. The endothelium maintains corneal hydration through a sodium-potassium pump. The cornea acts as a refracting surface and protects the inside of the eye. It receives nutrients and oxygen from the aqueous humor and perilimbal blood vessels to remain transparent.
Physiology of cornea in which you will get all the details about corneal functions, corneal metabolism, wound healing and information about contact lenses
The document discusses various aspects of corneal physiology, including permeability, metabolic processes, transparency, and age-related changes. It notes that the cornea receives oxygen mainly from the atmosphere via the tear film, as well as the limbal vasculature and aqueous humor. Carbon dioxide exits through tears or aqueous humor. Contact lenses can act as a barrier, reducing oxygen and carbon dioxide transmission. The cornea relies on glucose from the aqueous humor as its main energy source. Loss of transparency occurs when the ordered collagen fibril arrangement is disrupted by swelling. Blinking and tears are also summarized.
The cornea has five layers - epithelium, Bowman's layer, stroma, Descemet's membrane, and endothelium. It is avascular and transparent. The epithelium regenerates every 7 days. The endothelium maintains dehydration via ion pumps. Diseases like keratoconus cause thinning. Examination uses a slit lamp to assess size, shape, surface, transparency, and vascularization. Stains like fluorescein detect erosions while rose bengal finds filaments. The cornea has high innervation and refractive power of 45 diopters.
The cornea covers 1/6 of the eye's surface and is avascular and innervated. It is composed mainly of water, collagen, and proteoglycans. The cornea has five layers - epithelium, Bowman's layer, stroma, Descemet's membrane, and endothelium - which work together to maintain clarity and provide optical power. The epithelium is constantly renewed by stem cells in the limbus. The endothelium actively pumps fluid out of the stroma to prevent edema. Damage to the endothelium can compromise this pump function and clarity.
The document summarizes key details about the anatomy and physiology of the cornea. It describes the cornea's layers, thickness, curvature, cell types, refractive power, transparency mechanisms, metabolism, innervation, and role in maintaining hydration. A new potential layer called Dua's layer is also mentioned. The summary is as follows:
The document describes the anatomy and physiology of the cornea, including its layers, cells, curvature, thickness, refractive power, and mechanisms of transparency and hydration. A potential new layer called Dua's layer is also discussed.
The eye contains several anatomical structures that work together to allow for vision. The tear film has optical, mechanical, nutritional, and defensive functions and is composed of lipid, aqueous, and mucus layers secreted by various glands. The conjunctiva protects the eye and provides stem cells. The cornea and lens refract light before it reaches the retina. Within the retina are the photoreceptors, bipolar and ganglion cells. Structures like the iris, ciliary body, trabecular meshwork and optic nerve also contribute to vision and pressure regulation.
The document discusses the anatomy and physiology of the cornea. It notes that the cornea has three main functions: act as a refracting surface, protect the interior contents of the eye, and absorb topically applied drugs. It describes the layers of the cornea in detail, including the epithelium, stroma, Descemet's membrane, and endothelium. It explains that the transparency of the cornea is maintained by the regular arrangement of collagen fibrils in the stroma, as well as the avascular and aneural nature of the cornea.
The document discusses the anatomy and physiology of the cornea. It describes the cornea's key functions of refracting light and protecting the intraocular contents. The cornea has distinct layers - epithelium, stroma, and endothelium - that contribute to its optical and barrier properties. Tight cell junctions in the epithelium and organized collagen fibers in the stroma allow the cornea to remain clear. The avascular nature of the cornea is important for its immune privilege and transparency. Factors such as hydration levels, tear film, and orderly stromal structure help maintain corneal clarity.
Cornea is the clear front surface of the eye. It lies directly in front of the iris and pupil, and it allows light to enter the eye.
Cornea forms the transparent and anterior 1/6th of the external fibrous coat of the globe of the eyeball.
The cornea is the eye's most powerful structure for focusing light that provides approximately 65 to 75 percent of the focusing power of the eye.
The cornea has unmyelinated nerve endings sensitive to touch, temperature and chemicals; a touch of the cornea causes an involuntary reflex to close the eyelid.
The retina has several layers that serve important functions. The retinal pigment epithelium acts as a barrier and aids in visual pigment regeneration. The layers of rods and cones contain the light-sensitive photoreceptor cells that convert light signals into nerve impulses. Deeper retinal layers like the inner nuclear layer and ganglion cell layer contain neuron cell bodies that transmit these signals to the brain.
The cornea relies on metabolic pathways like glycolysis and the Krebs cycle to produce energy for maintaining transparency. Glycolysis converts glucose to pyruvate, yielding ATP. Under hypoxia, pyruvate is converted to lactate. The hexose monophosphate shunt produces pentoses for nucleic acid synthesis. Krebs cycle yields ATP. Corneal transparency results from the uniform arrangement of epithelial cells, avascularity, packed stromal lamellae, and relative dehydration maintained by metabolic pumping. Metabolic factors, barrier functions, and hydration levels are tightly regulated to prevent edema and maintain transparency.
Cornea anatomy and physiology PowerPoint presentationShallyGupta18
The cornea is the transparent, dome-shaped outer layer of the eye that forms the anterior portion of the fibrous coat. It has three main layers - an epithelial layer, stromal layer, and endothelial layer. The epithelial layer is made up of basal, wing, and surface cells that regenerate every 6-8 days. The stromal layer comprises around 90% of the corneal thickness and contains collagen fibers and keratocytes. The endothelial layer is a single cell layer that regulates hydration. Together, these layers and the cornea's avascular structure allow it to fulfill its main functions of refraction and protection of the inner eye.
This document provides an overview of visual field assessment in glaucoma patients. It discusses the anatomy and physiology of the visual field, common visual field defects seen in glaucoma including early defects like paracentral scotomas and advanced defects like a central island of vision. It also reviews different perimetry techniques including kinetic perimetry, static perimetry like Goldmann and Humphrey perimetry, and their interpretation. Standard automated perimetry is emphasized as the gold standard for evaluating glaucoma. Characteristics of glaucomatous visual field defects and a severity grading system are also summarized.
Peripheral ulcerative keratitis (PUK) is a destructive inflammatory disease of the peripheral cornea characterized by sloughing of the corneal epithelium and stromal melting. It begins with a crescent-shaped inflammatory lesion near the limbus and can progress circumferentially, leading to stromal thinning and potential perforation. PUK is often associated with autoimmune diseases and may be the initial presentation of an undiagnosed systemic vasculitis. Treatment involves topical immunosuppression with corticosteroids for mild cases or systemic corticosteroids and immunosuppressive drugs for more severe or progressive disease to halt inflammation and promote healing. Surgical interventions like conjunctival resection or grafting are
Dry eye syndrome is a common condition characterized by discomfort, visual disturbance, and tear film instability. It results from reduced tear production or increased tear evaporation, causing tear hyperosmolarity and ocular surface inflammation. Diagnosis involves evaluating tear production via tests like Schirmer's test and tear breakup time, and examining the ocular surface for signs of damage. Treatment focuses on replacing tears and reducing inflammation with artificial tears, cyclosporine drops, and punctal plugs. More severe cases may require procedures like tarsorrhaphy.
This document provides an overview of refractive errors and their optical correction. It begins with an introduction to optical principles and the concept of the far point. It then discusses the etiology, symptoms, and methods of correcting the main refractive errors - myopia, hyperopia, and astigmatism. Spectacle correction is covered in detail, including the effects on accommodation and binocularity. Full versus partial correction is addressed. The document emphasizes optimizing correction to relieve symptoms while avoiding side effects.
This document provides an overview of binocular vision including:
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- The three grades of binocular vision: simultaneous perception, fusion, and stereopsis.
- Development of binocular vision occurs postnatally through the coordination and maturation of the visual pathways and cortex.
- Tests that are used to clinically investigate binocular vision abilities including retinal correspondence, suppression, fusion, and stereopsis.
The vitreous body develops in three stages - primary, secondary, and tertiary. It fills the vitreous cavity and is attached at the vitreous base, posterior lens capsule, optic nerve head, macula, and around blood vessels. The vitreous is composed of a central medullary portion and outer cortical portion. The cortical vitreous contains more collagen fibers and cells. The vitreous is attached to the retina by the internal limiting membrane and vitreoretinal interface.
1. The supranuclear control centers for eye movements include the brainstem, cerebellum, basal ganglia, and cerebral cortex. The brainstem centers determine how the eyes move while the cortex determines when and where the eyes move.
2. Important brainstem centers include the PPRF, MLF, NPH, riMLF, and INC which control horizontal, vertical, and torsional eye movements through connections to the cranial nerve nuclei. Lesions can cause gaze palsies, nystagmus, and impaired gaze holding.
3. Other centers control smooth pursuit, vergence, and the vestibulo-ocular reflex. Supranuclear disorders can impair sacc
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Strategies for Effective Upskilling is a presentation by Chinwendu Peace in a Your Skill Boost Masterclass organisation by the Excellence Foundation for South Sudan on 08th and 09th June 2024 from 1 PM to 3 PM on each day.
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Odoo 17 CRM allows us to track why we lose sales opportunities with "Lost Reasons." This helps analyze our sales process and identify areas for improvement. Here's how to configure lost reasons in Odoo 17 CRM
LAND USE LAND COVER AND NDVI OF MIRZAPUR DISTRICT, UPRAHUL
This Dissertation explores the particular circumstances of Mirzapur, a region located in the
core of India. Mirzapur, with its varied terrains and abundant biodiversity, offers an optimal
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advanced technologies such as GIS (Geographic Information Systems) and Remote sensing to
analyze the transformations that have taken place over the course of a decade.
The complex relationship between human activities and the environment has been the focus
of extensive research and worry. As the global community grapples with swift urbanization,
population expansion, and economic progress, the effects on natural ecosystems are becoming
more evident. A crucial element of this impact is the alteration of vegetation cover, which plays a
significant role in maintaining the ecological equilibrium of our planet.Land serves as the foundation for all human activities and provides the necessary materials for
these activities. As the most crucial natural resource, its utilization by humans results in different
'Land uses,' which are determined by both human activities and the physical characteristics of the
land.
The utilization of land is impacted by human needs and environmental factors. In countries
like India, rapid population growth and the emphasis on extensive resource exploitation can lead
to significant land degradation, adversely affecting the region's land cover.
Therefore, human intervention has significantly influenced land use patterns over many
centuries, evolving its structure over time and space. In the present era, these changes have
accelerated due to factors such as agriculture and urbanization. Information regarding land use and
cover is essential for various planning and management tasks related to the Earth's surface,
providing crucial environmental data for scientific, resource management, policy purposes, and
diverse human activities.
Accurate understanding of land use and cover is imperative for the development planning
of any area. Consequently, a wide range of professionals, including earth system scientists, land
and water managers, and urban planners, are interested in obtaining data on land use and cover
changes, conversion trends, and other related patterns. The spatial dimensions of land use and
cover support policymakers and scientists in making well-informed decisions, as alterations in
these patterns indicate shifts in economic and social conditions. Monitoring such changes with the
help of Advanced technologies like Remote Sensing and Geographic Information Systems is
crucial for coordinated efforts across different administrative levels. Advanced technologies like
Remote Sensing and Geographic Information Systems
9
Changes in vegetation cover refer to variations in the distribution, composition, and overall
structure of plant communities across different temporal and spatial scales. These changes can
occur natural.
ISO/IEC 27001, ISO/IEC 42001, and GDPR: Best Practices for Implementation and...PECB
Denis is a dynamic and results-driven Chief Information Officer (CIO) with a distinguished career spanning information systems analysis and technical project management. With a proven track record of spearheading the design and delivery of cutting-edge Information Management solutions, he has consistently elevated business operations, streamlined reporting functions, and maximized process efficiency.
Certified as an ISO/IEC 27001: Information Security Management Systems (ISMS) Lead Implementer, Data Protection Officer, and Cyber Risks Analyst, Denis brings a heightened focus on data security, privacy, and cyber resilience to every endeavor.
His expertise extends across a diverse spectrum of reporting, database, and web development applications, underpinned by an exceptional grasp of data storage and virtualization technologies. His proficiency in application testing, database administration, and data cleansing ensures seamless execution of complex projects.
What sets Denis apart is his comprehensive understanding of Business and Systems Analysis technologies, honed through involvement in all phases of the Software Development Lifecycle (SDLC). From meticulous requirements gathering to precise analysis, innovative design, rigorous development, thorough testing, and successful implementation, he has consistently delivered exceptional results.
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Date: May 29, 2024
Tags: Information Security, ISO/IEC 27001, ISO/IEC 42001, Artificial Intelligence, GDPR
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How to Setup Warehouse & Location in Odoo 17 InventoryCeline George
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আমাদের সবার জন্য খুব খুব গুরুত্বপূর্ণ একটি বই ..বিসিএস, ব্যাংক, ইউনিভার্সিটি ভর্তি ও যে কোন প্রতিযোগিতা মূলক পরীক্ষার জন্য এর খুব ইম্পরট্যান্ট একটি বিষয় ...তাছাড়া বাংলাদেশের সাম্প্রতিক যে কোন ডাটা বা তথ্য এই বইতে পাবেন ...
তাই একজন নাগরিক হিসাবে এই তথ্য গুলো আপনার জানা প্রয়োজন ...।
বিসিএস ও ব্যাংক এর লিখিত পরীক্ষা ...+এছাড়া মাধ্যমিক ও উচ্চমাধ্যমিকের স্টুডেন্টদের জন্য অনেক কাজে আসবে ...
A workshop hosted by the South African Journal of Science aimed at postgraduate students and early career researchers with little or no experience in writing and publishing journal articles.
1. PHYSIOLOGY OF THE CORNEA
By Desta G.(MD,Optha R1)
Moderator Menen A. (MD, consultant
Ophthalmologist, corneal surgeon)
2. SEMINAR OUTLINE
• Introduction
• Embrology of the cornea
• Optical properties of cornea
• Metabolism of cornea
• Hydration of cornea
• Transparency of cornea
• Wound healing
3. Introduction
• It forms anterior 1/6th of the globe
• It is avascular, highly transparent
• It is principal optical media of
refraction=43D
• Protects intraocular structures of the eye
• It is thinner centrally than peripherally
• Has five layers
4.
5. Dimensions and Topography
• Anterior: Elliptical
Diameter
Horizontal:11.7mm
Vertical:10.6mm
Radius curvature: 7.8mm
• Central thickness ranges 440-650um(0.53mm)
• Peripheral:700um(0.71mm)
• Surface area is about 1.3cm2
01/22/19 5
• Posterior :circular
Diameter:11.7mm
Radius curvature;6.5mm
6. Embryology of cornea
• The separation of the lens vesicle from the surface
ectoderm initiates the development of the cornea
• With the separation of lens vesicle the surface
ectodermal cell proliferates to form epithelium of
cornea
7. Embryology cont.
• primate epithelium -acellularcorneal stroma, also
known as the Bowman's layer=20 wks of
gestation
• A first wave of neural crest-derived
mesodermal cell .—primitive endothelium (5th
wk)---descement membrane-- 8th week.
8. • second wave of mesoderm begins to grow
centrally from the limbus between the
epithelium and endothelium. ---cellular stroma
7wk
• At birth horizontal diameter is 9.8 mm
(surface area 102 mm2),
• 75% to 80% of adult
9. Optical properties
• The average index of refraction of the cornea
and tear film taken as a whole is about 1.376
• The refractive power for the anterior surface
of the cornea may be computed by the
following formula:
• D = n -n/r = D = 1.376-1.000/0.0078 =48.2′
10. Optical cont.
• The posterior surface of the cornea is bathed
with aqueous humor. By applying the same
formula, we
• arrive at the following value for the optical
power of the posterior corneal surface, where
n′ is the
refractive index of aqueous humor (1.336):
• D = n -n/r = 1.336-1.376/ 0.0065=-6.2′
11. • Therefore, the total optical power of the
cornea is 48.2 - 6.2, or approximately 42.0 D
• Because the cornea is thinner in the center
than in the periphery, it should act as a minus
lens but functions as a plus lens because the
12. aqueous humor neutralizes most of the minus
optical power on the posterior corneal surface.
If we compute the power of the posterior
corneal surface in air, we would find the
following:
•D=1.000-1.375/0.0065 =-96.0
13. Corneal physiology
• Primary concerned with
a.Source of energy of cornea that fuel the
corneas metabolic activity.
b. corneal transparency and its maintenance
c. Hydration status of the cornea
d.Wound healing mechanism
14. l. Corneal metabolism
• Metabolic stability depends on
a. Supply of oxygen
b.Supply of glucose
c. Supply of nutrients
Source of oxygen
l. Atmospheric oxygen dissolved in tear film=main
ll. From Aqueous humor
lll. Limbal capillaries
15. Metabolism of the epithelium
• Average temperature 34.8°c
• Main source of energy from glucose and
glycogen
• Glucose by diffusion from the aqouoes humor
and glycogen from epithelial store
• Glucose is metabolized in the corneal
epithelium primarily by anaerobic glycolysis
(Embden-Meyerhof pathway);
16.
17. • however, up to 35% of glucose enters the
hexose monophosphate (HMP)shunt.
• The HMP shunt produces nicotinamide-
adenine dinucleotide phosphate (NADPH).
• Important for production of nucleic acid
18. • Glucose in the cornea may also enter the
sorbitol pathway, which produces sorbitol
and fructose.
19. • The cornea consumes approximately 3.5 μL
of oxygen/cm2/hour
• Under aerobic conditions, pyruvate from
glycolysis can enter the tricarboxylic acid
cycle (Krebs cycle),
• Less common because of low epithelial
mitochondoria
20. • Under hypoxic conditions (e.g., during contact
lens wear), pyruvate is converted to lactate
• Cant pass through the apical epithelial barrier
cells so it accumulates within the stroma.
• Maintains the PH between 7.3-7.4
21. • Associated with this lactic acid is anoxia of the
epithelial cells,.
• The acidification of the extracellular fluid may
interfere with
• cellular metabolism and mitosis, leading to
epithelial thinning and erosion.
22. • The cytochrome P450 system is also functional
in the corneal epithelium.
• Under conditions of hypoxia or inflammation,
• Arachidonic acid is metabolized to yield 12(R)-
hydroxyeicosa-tetraenoic acid (12(R)HETE)
and 12(R)-hydroxyei-cosatrienoic acid
(12(R)HETrE)
23. • has the potential to diffuse from the
epithelium to the endothelium and inhibit
Na+/K+ ATPase
• Ultimately resulting in corneal edema
25. Endothelial metabolism
• Atmospheric oxygen is the primary source of
oxygen to the endothelium.
• glycolysis accounts for 93% of the conversion of
glucose-6-phosphate to pyruvate in the
endothelium.
• The aerobic tricarboxylic acid cycle converts 30%
of the pyruvate to ATP,
• whereas the remaining 70% is converted to lactic
acid by the anaerobic pathway
26. Corneal hydration
• Water content of cornea 78% highest by
any connective tissue in the body
• It depends upon the mechanical and
functional integrity of its cell component
Impairment of this results corneal edema and
in loss of transparency
27. Factors affecting corneal hydration
Pump mechanism of corneal endothelium and the
enzymes
•Na/k ATPase pump system
•NA/H exchanger
•Carbonic anhydrase enzyme
•Bicarbonate dependent ATPase
Evaporation of water from corneal surface
Barrier function of epethelium and endothelium
01/22/19 27
28. Hydration cont.
It can be summarized as
•Low-permeability barrier of the corneal
epithelium
•Water imbibing nature of corneal stroma
•High-permeability barrier: the corneal
endothelium
29. Low permeability nature
The epithelial cells are held together by
desmosomes, (zonula occludens ) tight
junctions at their peripheral intercellular
margins
•while the basal surface is attached to
Bowmans layer through
hemi desmosomes,
type VII collagen anchoring fibrils,
anchoring plaques
30. Zonula occludens tight junctions are
characterized by
fusion of the adjacent cell membranes
resulting in obliteration of the intercellular
space
•made up of the tight junction proteins ZO-1,
JAM-A, occludin,
and claudin-1, as well as some other claudin
subtypes.
31.
32. This barrier prevents the movement of ions
and thus
•fluid from the tears into the stroma,
•reduces some evaporation,
•and protects the cornea from infectious
pathogens
33. • The most superficial squamous cells at the
external surface form a high-resistance
(8–16 kΩ·cm2) barrier to the external
environment
35. Hydration cont.
Aquaporins
•are small integral membrane proteins
residing in the plasma membrane
•bidirectional
A. water selectives
B. glycerol selectives
36. • AQP1, AQP2, AQP4, AQP5, and AQP8 are
water selective
• AQP3, AQP7, and AQP9 transport glycerol
and perhaps other small solutes
38. Stroma.
•The stroma imbibes water because of the
large anionic proteoglycans Donan effect
•IP=IOP-SP
•Sp=55mmHg
•ensuring the hydrophilic environment in
the stroma responsible for maintaining the
regular spacing contributing to
transparency.
41. Low permeability cont…
The intercellular space is known to contain
apical hemi desmosomes (macula occludens)
tight junctions and lateral gap junctions
•thereby forming an incomplete barrier with
a preference to the diffusion of small
molecules
42. Macula occludens tight junctions are
•Characterized by partial obliteration
of the intercellular space and partial retention
of a 10-20 nm wide intercellular space
•low electrical resistance (25 Ω·cm2) barrier to
the aqueous humor flow
43.
44. At birth,
• the central endothelial cell density (ECD) of
the cornea is around 5000 cells/mm2
•decline in central ECD with age that typically
involves two phases:
a rapid and a slow component
45. • ECD decreases exponentially to about 3500
cells/mm2 by age 5 and
• 3000 cells/mm2 by age 14–20
Thereafter,
• a slow component occurs where central
ECD decreases to a linear steady rate of
0.3–0.6 percent per year,
• around 2500 cells/mm2 in late adulthood
46. Leaky pump function
studies show
3 million Na+/K+-ATPase pump sites are
present in the basolateral membrane of a single
corneal endothelial cell
average pump site density of 4.4 trillion
sites/mm2
47.
48.
49.
50. Corneal transparency
Cornea transmits nearly 85-99% of the light that enters it
which is achieved by several
1. MAURICE THEORY
‘the transparency of stroma is due to lattice type
arrangement of collagen fibrils with perfect dimensional
order’.
01/22/19 50
51.
52.
53. 2.Theory of GOLDMAN
‘Cornea is transparent because the fibrils are small in
relation to light and don’t interfere with light
transmission unless they are larger than one half
length of light’
destructive interference light scatter.
54. Ctn..
2.Corneal epithelium and tear film
• Epithelial non keratinization
• Regular and uniform arrangment of corneal
epithelium
• Junction between cells its compactness
3.Corneal avascularity
4.Non myelinated nerve fibers
5.Corneal hydration
01/22/19 54
55. Wound healing
• Epithelial wound healing.
• limbal corneal epithelial stem cells produce
the progenitor cells.
Has three distinctive steps
1)cell migration,
2)cell proliferation,
3)and cell adhesion
56. 4- to 6-hour latent phase occurs where the
epithelium responds by
desquamating damaged cells,
polymerizing actin filaments,
Synthesizing structural proteins, and
releasing all hemidesmosomal attachments
57. 1,The migratory step
independent of cell proliferation
flattened monolayer of epithelial cells slide
over the abraded areas and re-establish a
barrier
60 to 80 μm/hour
heals to normal thickness around 50 μm
approximately 1 to 4 weeks
hurricane keratopathy??
58. • What is conjuctival transdifferentiation??
• This basic knowledge of limbal syem cells has
helped to develop the concept autologes and
autograaft stem cell transplant
59. Stromal healing
• Usually heals by scaring
• The following steps are usually seen
apoptosis,
proliferation,
migration, and
possibly activation of keratocytes
along with causing stromal edema
60. corneal stromal injury is immediately followed
by
a zone of keratocyte apoptosis around the site
of stromal injury
influx of transient mixed acute and chronic
inflammatory cell infiltration
proliferation and migration of surviving
keratocytes
61. • Finally differentiation of the keratocytes into a
transiently metabolically activated cell type
called an activated keratocyte
• it synthesizes and deposits the extracellular
matrix of the stromal scar
62. Endothelium healing
• Following injury to the central endothelium,
both the central and peripheral cell densities
(cells/mm2) and percent hexagonal cells are
reduced,
• whereas the coefficient of variation of cell size
(an indicator of polymegathism) is increased
63. Steps…
• Stage 1 (0 to 3 days) is characterized by
an initial coverage of the wound by pleomorphic
spindle-shaped cells that form a functional but
incomplete barrier
• stage 2 (4 to 7 days), the cells assume a
flattened configuration, have an irregular
polygonal shape, and establish normal pump-
site density and barrier function
64. • Stage 3 (8 to 30 days) is characterized by a
continuation of the remodeling of the
monolayer
65. • Human corneal de compensation occurs when
the cell density drops below 500 cells/mm2
66. Other functions of the cornea
•Drug delivery
•Protection against UV light
67. References
• Duanes clinical ophtalmology 2012
• clinical anatomy and physiology of visual system
Remington’s 3rd edition
• ADELER’S physiology of the eye 11th
edition
• Online sources
01/22/19 67
Editor's Notes
where D equals diopters of optical power, n is the index of refraction of air (1.000), n′ is the index of
refraction of the whole cornea, and r is the radius of curvature of the anterior corneal surface in
meters
types. The fibrils in the corneal
stroma are a co-polymerization of collagen types I, III, and V molecules that form uniform 22-nm
diameter fibrils in the acellular Bowman's layer and uniform 25-nm diameter fibrils in the cellular
corneal stroma with only slight variability (Figs. 9, bottom and 10).54,55
nd each fibril scatter an individual wave light by process of destructive interference light scatter from individual fibril would be canceled by one another
Studies have shown that the distance
between areas of different refractive indices can
affect transparency. If the change in the index of refraction
occurs across a distance that is less than one half
the wavelength of visible light (400 to 700 nm), destructive
interference occurs, and light scattering is reduced
significantly
hurricane keratopathy??
The main problem with this type of conjunctival
epithelium is that it is thinner than normal, stains with fluorescein, attracts new blood vessels, and is
prone to recurrent corneal erosions
using autologous conjunctival
epithelial transplants to treat unilateral chemical injury was first described by Thoft in 1977.115 This