The cornea has five layers - epithelium, Bowman's layer, stroma, Descemet's membrane, and endothelium. The stroma makes up around 90% of the cornea thickness and contains collagen fibrils and keratocytes. The stroma's collagen is arranged in tightly packed, regularly spaced lamellae that run parallel to the corneal surface. Keratocytes maintain the stroma by synthesizing collagen and proteoglycans. The epithelium is stratified and squamous, consisting of basal, wing, and surface cells. It regenerates through cell migration from the limbus. Injury repair involves cell migration, proliferation, and remodeling.
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
The tear film constitutes Three layers :- An outermost lipid (oily) layer An aqueous (watery) layer that makes up 90% of the tear film volume; and A mucin layer that coats the corneal surface.
3. To form smooth optical surface on cornea. To keep the surface of cornea & conjunctiva moist It serve as lubricant It transfer oxygen Provide antibacterial action Wash debris out It provides a pathway for WBC in case of injury
4. Functions of lipid layer Retards evaporation of tear film Prevents the overflow of tears
5. Function of Aqueous Layer Flushes, buffers and lubricates the corneal surface Delivers oxygen and other nutrients to the corneal surface Wash out debris Delivers antibacterial enzymes and antibodies such as lysozyme.
6. Functions of Mucin Layer Spreads tears over corneal surface. Protects the cornea against foreign substances . Makes corneal surface smooth by filling in surface irregularities
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
The tear film constitutes Three layers :- An outermost lipid (oily) layer An aqueous (watery) layer that makes up 90% of the tear film volume; and A mucin layer that coats the corneal surface.
3. To form smooth optical surface on cornea. To keep the surface of cornea & conjunctiva moist It serve as lubricant It transfer oxygen Provide antibacterial action Wash debris out It provides a pathway for WBC in case of injury
4. Functions of lipid layer Retards evaporation of tear film Prevents the overflow of tears
5. Function of Aqueous Layer Flushes, buffers and lubricates the corneal surface Delivers oxygen and other nutrients to the corneal surface Wash out debris Delivers antibacterial enzymes and antibodies such as lysozyme.
6. Functions of Mucin Layer Spreads tears over corneal surface. Protects the cornea against foreign substances . Makes corneal surface smooth by filling in surface irregularities
The aqueous humour is a transparent, watery fluid similar to plasma, but containing low protein concentrations. It is secreted from the ciliary epithelium, a structure supporting the lens
The tear film is a complex mixture of substances secreted from multiple sources on the ocular surface, including the lacrimal gland, the accessory lacrimal glands, the meibomian glands, and the goblet cells.
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. The cornea, with the anterior chamber and lens, refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power.
Accommodation/ Accommodation of Eye, Measurement of Accommodation of Eye (hea...Bikash Sapkota
CLICK HERE TO DOWNLOAD FULL PPT ❤❤ https://healthkura.com/measurement-of-accommodation-of-eye/ ❤❤
Dear viewers Check Out my other piece of works at ❤❤❤ https://healthkura.com ❤❤❤
Measurement of Accommodation of eye:
Amplitude, Facility,
Relative Accommodation, Fatigue, Lag,
Dynamic Retinoscopy
Presentation Layout:
-Introduction to accommodation of eye
-Mechanism
-Components
-Measurement of accommodation of eye
- Amplitude
- Facility
- Relative accommodation
- Lag
-Dynamic Retinoscopy
Accommodation
-dioptric adjustment of the crystalline lens of the eye
- to obtain clear vision for a given target of regard
-process by which the refractive power of eye is altered
- to ensure a clear retinal image
For further reading
-Clinical Procedures in Optometry by J.D. Bartlett, J.B. Eskridge, J.F. Amos
-Primary Care Optometry by Theodere Grosvenor
-Borish’s Clinical Refraction by W.J. Benjamin
-Clinical Procedures for Ocular examination by Carlson et al
-American Academy of Ophthalmology
-Optometric Clinical Practice Guideline by American Optometric Association
-Internet
Follow me to get in touch with optometric and ophthalmic updates
1. Introduction Gross anatomy Layers Blood supply, drainage and nerve supply
2. INTRODUCTION • Sclera forms posterior 5/6th of external tunic , connective tissue coat of eyeball. • it continues with duramater and cornea • Its whole surface covered by tenon’s capsule • Anteriorly covered by- bulbar conjunctiva • Inner surface lies in contact with choroid • With a potential suprachoroidal space in between
3. Equa THICKNESS OF SCLERA
4. • Thickness varies with individual, with age • Thinner- children, elder, F> M • Thickest posteriorly • Gradually becomes thinner when traced anteriorly • Thin at insertion of extraocular muscle
The aqueous humour is a transparent, watery fluid similar to plasma, but containing low protein concentrations. It is secreted from the ciliary epithelium, a structure supporting the lens
The tear film is a complex mixture of substances secreted from multiple sources on the ocular surface, including the lacrimal gland, the accessory lacrimal glands, the meibomian glands, and the goblet cells.
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. The cornea, with the anterior chamber and lens, refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power.
Accommodation/ Accommodation of Eye, Measurement of Accommodation of Eye (hea...Bikash Sapkota
CLICK HERE TO DOWNLOAD FULL PPT ❤❤ https://healthkura.com/measurement-of-accommodation-of-eye/ ❤❤
Dear viewers Check Out my other piece of works at ❤❤❤ https://healthkura.com ❤❤❤
Measurement of Accommodation of eye:
Amplitude, Facility,
Relative Accommodation, Fatigue, Lag,
Dynamic Retinoscopy
Presentation Layout:
-Introduction to accommodation of eye
-Mechanism
-Components
-Measurement of accommodation of eye
- Amplitude
- Facility
- Relative accommodation
- Lag
-Dynamic Retinoscopy
Accommodation
-dioptric adjustment of the crystalline lens of the eye
- to obtain clear vision for a given target of regard
-process by which the refractive power of eye is altered
- to ensure a clear retinal image
For further reading
-Clinical Procedures in Optometry by J.D. Bartlett, J.B. Eskridge, J.F. Amos
-Primary Care Optometry by Theodere Grosvenor
-Borish’s Clinical Refraction by W.J. Benjamin
-Clinical Procedures for Ocular examination by Carlson et al
-American Academy of Ophthalmology
-Optometric Clinical Practice Guideline by American Optometric Association
-Internet
Follow me to get in touch with optometric and ophthalmic updates
1. Introduction Gross anatomy Layers Blood supply, drainage and nerve supply
2. INTRODUCTION • Sclera forms posterior 5/6th of external tunic , connective tissue coat of eyeball. • it continues with duramater and cornea • Its whole surface covered by tenon’s capsule • Anteriorly covered by- bulbar conjunctiva • Inner surface lies in contact with choroid • With a potential suprachoroidal space in between
3. Equa THICKNESS OF SCLERA
4. • Thickness varies with individual, with age • Thinner- children, elder, F> M • Thickest posteriorly • Gradually becomes thinner when traced anteriorly • Thin at insertion of extraocular muscle
This lecture includes anatomy and Physiology of Cornea, if u like it kindly share it with colleagues and like it. I will share more lectures related to eye anatomy and optometry.
Thank You.
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 Atlas of the eye is a B.sc. degree research
It contains three parts:
- Anatomy & Physiology of the eye
- Pathology & errors in the eye
- Photography of the eye
enjoy it!
Report Back from SGO 2024: What’s the Latest in Cervical Cancer?bkling
Are you curious about what’s new in cervical cancer research or unsure what the findings mean? Join Dr. Emily Ko, a gynecologic oncologist at Penn Medicine, to learn about the latest updates from the Society of Gynecologic Oncology (SGO) 2024 Annual Meeting on Women’s Cancer. Dr. Ko will discuss what the research presented at the conference means for you and answer your questions about the new developments.
Pulmonary Thromboembolism - etilogy, types, medical- Surgical and nursing man...VarunMahajani
Disruption of blood supply to lung alveoli due to blockage of one or more pulmonary blood vessels is called as Pulmonary thromboembolism. In this presentation we will discuss its causes, types and its management in depth.
Ethanol (CH3CH2OH), or beverage alcohol, is a two-carbon alcohol
that is rapidly distributed in the body and brain. Ethanol alters many
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is the oldest recreational drug and likely contributes to more morbidity,
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(DSM-5) integrates alcohol abuse and alcohol dependence into a single
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In the DSM-5, all types of substance abuse and dependence have been
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from mild to severe. A diagnosis of AUD requires that at least two of
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The four main behavioral effects of AUD are impaired control over
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of the prevalence and harmful consequences of AUD in the U.S.,
the systemic nature of the disease, neurocircuitry and stages of AUD,
comorbidities, fetal alcohol spectrum disorders, genetic risk factors, and
pharmacotherapies for AUD.
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These simplified slides by Dr. Sidra Arshad present an overview of the non-respiratory functions of the respiratory tract.
Learning objectives:
1. Enlist the non-respiratory functions of the respiratory tract
2. Briefly explain how these functions are carried out
3. Discuss the significance of dead space
4. Differentiate between minute ventilation and alveolar ventilation
5. Describe the cough and sneeze reflexes
Study Resources:
1. Chapter 39, Guyton and Hall Textbook of Medical Physiology, 14th edition
2. Chapter 34, Ganong’s Review of Medical Physiology, 26th edition
3. Chapter 17, Human Physiology by Lauralee Sherwood, 9th edition
4. Non-respiratory functions of the lungs https://academic.oup.com/bjaed/article/13/3/98/278874
The prostate is an exocrine gland of the male mammalian reproductive system
It is a walnut-sized gland that forms part of the male reproductive system and is located in front of the rectum and just below the urinary bladder
Function is to store and secrete a clear, slightly alkaline fluid that constitutes 10-30% of the volume of the seminal fluid that along with the spermatozoa, constitutes semen
A healthy human prostate measures (4cm-vertical, by 3cm-horizontal, 2cm ant-post ).
It surrounds the urethra just below the urinary bladder. It has anterior, median, posterior and two lateral lobes
It’s work is regulated by androgens which are responsible for male sex characteristics
Generalised disease of the prostate due to hormonal derangement which leads to non malignant enlargement of the gland (increase in the number of epithelial cells and stromal tissue)to cause compression of the urethra leading to symptoms (LUTS
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Microteaching is a unique model of practice teaching. It is a viable instrument for the. desired change in the teaching behavior or the behavior potential which, in specified types of real. classroom situations, tends to facilitate the achievement of specified types of objectives.
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Tom Selleck Health: A Comprehensive Look at the Iconic Actor’s Wellness Journeygreendigital
Tom Selleck, an enduring figure in Hollywood. has captivated audiences for decades with his rugged charm, iconic moustache. and memorable roles in television and film. From his breakout role as Thomas Magnum in Magnum P.I. to his current portrayal of Frank Reagan in Blue Bloods. Selleck's career has spanned over 50 years. But beyond his professional achievements. fans have often been curious about Tom Selleck Health. especially as he has aged in the public eye.
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Introduction
Many have been interested in Tom Selleck health. not only because of his enduring presence on screen but also because of the challenges. and lifestyle choices he has faced and made over the years. This article delves into the various aspects of Tom Selleck health. exploring his fitness regimen, diet, mental health. and the challenges he has encountered as he ages. We'll look at how he maintains his well-being. the health issues he has faced, and his approach to ageing .
Early Life and Career
Childhood and Athletic Beginnings
Tom Selleck was born on January 29, 1945, in Detroit, Michigan, and grew up in Sherman Oaks, California. From an early age, he was involved in sports, particularly basketball. which played a significant role in his physical development. His athletic pursuits continued into college. where he attended the University of Southern California (USC) on a basketball scholarship. This early involvement in sports laid a strong foundation for his physical health and disciplined lifestyle.
Transition to Acting
Selleck's transition from an athlete to an actor came with its physical demands. His first significant role in "Magnum P.I." required him to perform various stunts and maintain a fit appearance. This role, which he played from 1980 to 1988. necessitated a rigorous fitness routine to meet the show's demands. setting the stage for his long-term commitment to health and wellness.
Fitness Regimen
Workout Routine
Tom Selleck health and fitness regimen has evolved. adapting to his changing roles and age. During his "Magnum, P.I." days. Selleck's workouts were intense and focused on building and maintaining muscle mass. His routine included weightlifting, cardiovascular exercises. and specific training for the stunts he performed on the show.
Selleck adjusted his fitness routine as he aged to suit his body's needs. Today, his workouts focus on maintaining flexibility, strength, and cardiovascular health. He incorporates low-impact exercises such as swimming, walking, and light weightlifting. This balanced approach helps him stay fit without putting undue strain on his joints and muscles.
Importance of Flexibility and Mobility
In recent years, Selleck has emphasized the importance of flexibility and mobility in his fitness regimen. Understanding the natural decline in muscle mass and joint flexibility with age. he includes stretching and yoga in his routine. These practices help prevent injuries, improve posture, and maintain mobilit
Explore natural remedies for syphilis treatment in Singapore. Discover alternative therapies, herbal remedies, and lifestyle changes that may complement conventional treatments. Learn about holistic approaches to managing syphilis symptoms and supporting overall health.
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Title: Sense of Taste
Presenter: Dr. Faiza, Assistant Professor of Physiology
Qualifications:
MBBS (Best Graduate, AIMC Lahore)
FCPS Physiology
ICMT, CHPE, DHPE (STMU)
MPH (GC University, Faisalabad)
MBA (Virtual University of Pakistan)
Learning Objectives:
Describe the structure and function of taste buds.
Describe the relationship between the taste threshold and taste index of common substances.
Explain the chemical basis and signal transduction of taste perception for each type of primary taste sensation.
Recognize different abnormalities of taste perception and their causes.
Key Topics:
Significance of Taste Sensation:
Differentiation between pleasant and harmful food
Influence on behavior
Selection of food based on metabolic needs
Receptors of Taste:
Taste buds on the tongue
Influence of sense of smell, texture of food, and pain stimulation (e.g., by pepper)
Primary and Secondary Taste Sensations:
Primary taste sensations: Sweet, Sour, Salty, Bitter, Umami
Chemical basis and signal transduction mechanisms for each taste
Taste Threshold and Index:
Taste threshold values for Sweet (sucrose), Salty (NaCl), Sour (HCl), and Bitter (Quinine)
Taste index relationship: Inversely proportional to taste threshold
Taste Blindness:
Inability to taste certain substances, particularly thiourea compounds
Example: Phenylthiocarbamide
Structure and Function of Taste Buds:
Composition: Epithelial cells, Sustentacular/Supporting cells, Taste cells, Basal cells
Features: Taste pores, Taste hairs/microvilli, and Taste nerve fibers
Location of Taste Buds:
Found in papillae of the tongue (Fungiform, Circumvallate, Foliate)
Also present on the palate, tonsillar pillars, epiglottis, and proximal esophagus
Mechanism of Taste Stimulation:
Interaction of taste substances with receptors on microvilli
Signal transduction pathways for Umami, Sweet, Bitter, Sour, and Salty tastes
Taste Sensitivity and Adaptation:
Decrease in sensitivity with age
Rapid adaptation of taste sensation
Role of Saliva in Taste:
Dissolution of tastants to reach receptors
Washing away the stimulus
Taste Preferences and Aversions:
Mechanisms behind taste preference and aversion
Influence of receptors and neural pathways
Impact of Sensory Nerve Damage:
Degeneration of taste buds if the sensory nerve fiber is cut
Abnormalities of Taste Detection:
Conditions: Ageusia, Hypogeusia, Dysgeusia (parageusia)
Causes: Nerve damage, neurological disorders, infections, poor oral hygiene, adverse drug effects, deficiencies, aging, tobacco use, altered neurotransmitter levels
Neurotransmitters and Taste Threshold:
Effects of serotonin (5-HT) and norepinephrine (NE) on taste sensitivity
Supertasters:
25% of the population with heightened sensitivity to taste, especially bitterness
Increased number of fungiform papillae
2. The Cornea
The cornea is a transparent avascular tissue
with a smooth, convex outer surface and concave
inner surface, which resembles a small watch-glass.
To meet the diverse functional demands the
cornea must be:
- Transparent
- Refract light
- Contain the intraocular pressure
- Provide a protective interface
sbj
4. Contd…
Thickness:
- Centrally about 0.52 mm
- Peripherally about 0.67 mm
Surface area:
- About 1.3 cm² (one-sixth of the
globe)
Optical zone:
- Cornea is almost a sphere, the
central 1/3rd is called optical zone
about 5.4 mm
sbj
5. Contd…
Radius of curvature:
- Anterior surface – about 7.8 mm
- Post. Surface – about 6.5 mm
Refractive power: +43.1 D
(Air-tear = +43.6 D, Tear-cornea = +5.3 D, Cornea-aqueous = -5.8 D)
Refractive index: 1.376
sbj
6. Contd…
Topography:
- Shape of cornea is important for fitting of contact
lenses
- Small spherical zone of ant. curvature (2-4 mm) is
decentered up & outwards with visual axis, but
correctly centered for pupillary aperture is
termed as corneal apex or cap
- Curvature varies from apex to limbus, greater
flattening in nasally and superiorly
- Cornea is flatter in men than in women
- Cornea flattens slightly on convergence
sbj
8. Embryonic origin of Cornea:
The formation of cornea is induced by the
lens and the optic cup at the 7th weeks
ofintrauterine life.
• Corneal epithelium – Surface ectoderm
• Bowman’s membrane – Mesenchyme
• Stroma – Mesenchyme and Neural crest
• Descemet’s membrane – Synthesized by
endothelium
• Endothelium – Neural crest
sbj
9. Structure
Behind the precorneal tear film there are five
layers of cornea:
1. Epithelium
2. Bowman’s layer
3. Stroma
4. Descemet’s membrane
5. Endothelium
sbj
10. Epithelium:
The corneal epithelium is -
- Stratified, squamous and non-
keratinized
- Continuous with conjuctival
epithelium at limbus but having no
goblet cells
- 50-90 µm in thickness
- Consists of 5 or 6 layers of
nucleated cells resting on a basal
lamina, namely- a. Basal cells
b. Wing cells
c. Surface cells
sbj
11. Basal cells:
- Deepest cell layer
- Stand in a palisade manner
on basal lamina
- Germinative layer of the
epithelium
- Columner with rounded
heads and flat bases
- Nucleus is oval and oriented
parallel to the cells long axis
Contd…
sbj
12. Wing or umbrella cells:
- Second epithelial cell layer (1-2 layers of cells)
- Polyhedral cells
- Convex anteriorly forming cap over basal cells
and send processes between them
- Nucleus is oval and oriented parallel to corneal
surface
Contd…
sbj
13. Surface cells:
- Most superficial 2-3 layers of
cells
- Also polyhedral and become
wider & flattened towards the
surface
- Flattened nuclei project
backwards leaving the surface
perfectly smooth
Contd…
- Most superficial cells are mostly hexagonal in shape
and exhibit surface microvilli or microplicae
sbj
14. Ultrastructural features:
- Epithelial cells shows usual organelles like
other actively metabolizing cells
- Moderately abundant mitochondria in wings
& middle layer cells but small and scarce in
basal cells
- Wing & superficial cells have high glycogen
content
Contd…
sbj
15. - Tonofibrils: cells contain a cytoplasmic
meshwork of electrondense intermidiate
filaments composed of cytokeratins
- The plasma membrane of contiguous cells
interdigitative to each other
- Adhesion is achieved by –
• Tight junctions & desmosomes – surface cells
• Desmosomes – wings & superficial cells
• Desmosomes & Hemidesmosomes – in basal cells
Contd…
sbj
17. - In the basal cells there are anchoring
filaments which pass through the
hemidesmosomal structure to be inserted
into basal lamina
- Langerhans cells (cells of immune recognition system)
present near periphery. They are almost
absent at central cornea but aggregate in
response to infection
Contd…
sbj
18. Basal lamina:
- The basal lamina is secreted by the basal
cells
- 0.5 - 1 µm wide
- Ultrastructurally it is distinguished in to two
patrs –
i. Lamina lucida (superficial)
ii. Lamina densa (deep osmiophilc)
Contd…
sbj
19. - The lamina consist of collagen and glycoprotein
constituents which integrated with Bowman’s
layer by array of short anchoring filaments
- Lipid solvent, stromal oedema and inflamation
may loosened the cohesion between Bowman’s
zone and lamina
- With old age, in diabetes and in some corneal
disorders it becomes thickened and
multilamellar
Contd…
sbj
20. Epithelial Turnover:
- Early studies suggested that the epithelium
replaced approximately weekly by division of
basal cells and the oldest shed from the
surface
- It is now recognized that the germinative
region lies at the limbus, the stem cells, and
cells migrate at a very slower rate (123
µm/week) to the center of the cornea which
may be as long as a year
Contd…
sbj
21. - The XYZ hypothesis:
1. Thoft R. and Friend J. (1983) proposed on
the basis of experimental evidence that
both limbal basal and corneal basal cells
are the source for corneal epithelial cells,
and there is a balance among division,
migration & shedding.
Contd…
sbj
22. The corneal epithelium is maintained by a balance
among sloughing (Z) of cells from the corneal surface,
cell division (X) in the basal layer and renewal of basal
cells by centripetal migration (Y) of new basal cells
originating from the limbal stem cells.
Contd…
sbj
23. Epithelial Repair:
- Repair of corneal epithelial injury like
abration follows a distinctive sequence of
events - Injury (abration)
Cells at wound edge retract, thicken and lose attachment
Travel in an amoeboid movement to cover the defect
Cells at wound edge ruffle and send out
filopodia and lamellipodia towards the center of wound
Contd…
sbj
24. Migration process is halted by contact inhibition
They then anchor and
Mitosis resumes to re-establish epithelial thickness
Surface tight junctions re-establised
Adhesion with Bowman’s layer within 7 days (if basal lamina intact)
• The healing process occurs rapidly, rate of cell
migration is 60 – 80 µm/hr
Contd…
sbj
25. - In case of total epithelial loss including total
limbus, cornea is covered with vascularized
conjunctival type of epithelium by adjacent
conjunctiva
- If a small part of limbus with stem cell is
retained then conjunctival type of epithelium
is gradually disappear and metabolic behavior
of corneal epithelium re-established very
slowly
Contd…
sbj
26. Bowman’s layer: (Ant. Limiting lamina)
- Modified region of anterior
stroma
- Acellular homogeneous zone
- 8 – 14 µm thick
- Ant. surface is smooth &
parallel with corneal surface
- It delineates the anterior
junction between cornea
and limbus
sbj
27. Ultrastructural features:
- Ultrastructurally it is a felted meshwork of fine
collagen fibrils of uniform size in a ground
substance
- Posteriorly it becomes blended & interweaving
with fibrils of ant. stroma
- Compact arrangement of collagen gives it great
strength and relatively resistant to trauma both
mechanical and infective
Contd…
sbj
28. - Convex ridges may generate
over surface if its tension is
relaxed during indentation,
hypotony or manipulation
causes ant.corneal mosaic,
polygonal or chicken-wire
pattern over surface
- No regeneration and replaced
by coarse scar tissue
- It is perforated many places by
nerve to epithelium
Contd…
Fig.: Ant.corneal mosaic
sbj
29. Stroma: (Substantia propria)
- About 500 µm thick (about 90% of
corneal thickness)
- Consists of regularly arranged lamellae
of collagen bundles, lie in proteoglycan
ground substance with –
- 200 – 300 bundles – centrally
- 500 bundles – peripherally
- Width about 9 – 260 µm
- Height about 1.15 – 2 µm
- Small population of cells – keratocytes
present
sbj
30. - Arrangement of lamellae –
- Lamellae are arranged in layers, parallel with
each other & with corneal surface
- In deeper stroma the lamellae form strap-like
ribbons which run approximately at right angles
to those in consecutive layers
- At the periphery this right-angular arrangement
is slightly changed where it gets scleral fibres
- At the limbus the bundles appeared to take a
circular course
Contd…
sbj
32. Ultrastructural features:
- Each lamellae comprises of a band of collgen
fibrils arranged in parallel with each other
- Fibrils show typical 64 nm periodicity of
connective tissue collgens with a microperiod
of 6 nm
- There is a unique uniformity of fibril diameter,
it is 22 (±1) nm from ant. to post.
- There is remarkable regularity of seperation
both within and between lamellae
Contd…
sbj
33. - The keratocytes occupy 2.5 – 5 % of total
stromal volume and is responsible for synthesis
and maintaining of collagen & proteoglycan
substance of stoma
- Keratocytes:
- Long, thin, flattened cells (maximally 2µm thick)
running parallel to corneal surface
- Having long flattened nuclei, sparse cytoplasm
but contains full component of organells
- Position – between the lamellae
Contd…
sbj
34. - There stellate processes extened for great distance
and frequent contacts are made with other
keratocytes in same horizontal plane forming gap
junctions
- Lymphocytes, macrophages and
polymorphonuclear leucocytes (very rarely) also
found in stroma ocationally
Contd…
sbj
35. Stromal repair:
- Repair of stroma after small injuries involves: -
Keratocytes activation
Migration & transformation into fibroblasts
Production of scar tissue
Initial fibrils are large & irregular
Contd…
sbj
36. Remodelling of scar tissue occurs, it ensues –
1. Thinning of fibrils
2. Reformation of lamellae over months
3. Increase in tranperency
- Larger wounds provoke rapid vascular response
and leaving vascularised scar along with
lymphatic channels
Contd…
sbj
37. Descemet’s membrane: (Post. Limiting layer)
- It is the basal lamina of corneal endothelium
- First appears at 2nd month of gestation and
synthesis continue throughout adult life
Thickness – at birth :- 3 – 4 µm
at childhood :- about 5 µm
at adult :- 10 – 12 µm
- There is a distinct structural difference
between fetal & postnatal components
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38. - It is a strong resistant sheet
- It thickens with age and in some corneal
degenerative conditions
- Major protein of DM is Type IV collagen
Contd…
sbj
39. Ultrastructural features:
- In adult human, the anterior 1/3rd of DM
corresponds to fetal part, which is like a
laminated structure and shows an irregular
banded pattern in cross section
- In tangential section it appears to consist of
superimposed plates forming a lamellar pattern
Contd…
sbj
40. - Posterior 2/3rd formed after birth and consist of a
homogeneous fibrogranular material
- The zone adjoining the endothelium is the most
recently formed
- Modified hemidesmosomes attachment present in
between DM & endothelium
Contd…
Descemet’s membrane
sbj
41. Hassal-Henle warts:
- It is the peripheral excrescence produced by
focal overproduction of basal lamina like
material in aging cornea
- No clinical abnormality in corneal function
Descemet’s warts of central cornea is called
Cornea Guttata, it is associated with increased
permiability of endothelium
Contd…
sbj
43. Posterior embryotoxon:
• Schwalbe’s line may
hypertrophied in congenital
anomalies and appears as visible
shelf on gonioscopy, is called
posterior embryotoxon
Contd…
Schwalbe’s line:
• The peripheral rim of DM is the internal
landmark of corneal limbus and also it is the
anterior limit of drainage angle, is called
Schwalbe’ line
sbj
44. Repair of Descemet’s layer:
After traumatic interuption of DM (Path./Mech.)
Endothelium spread its cells to resurface the defect
Synthesis of fresh basal lamina
which is structurally identical to normal descemet’s layer
Contd…
sbj
45. Endothelium:
- It is a single layer of
hexagonal, cuboidal cells
attached posterior
aspect of DM
- It is nuroectodermal in
origin
- Corneal endothelial cells
production is relatively
fixed, it is about 500000
sbj
46. - Endothelial cells density –
- about 6000 cells/mm² at birth
- 26% lost in 1st year
- Further 26% lost over next 11
years
- Rate of cell loss slows and
stabilizes around middle age
and then it is about 2500
cells/mm²
- If cells density falls upto 500
cells/mm² corneal oedema
devlops and transparency
reduced
Contd…
Endothelium of a healthy cornea
Endothelium of a rigid contact
lens wearersbj
47. - At birth cells are 10 µm
in height, with age it
becomes flattened to 3-
5 µm and 18-20 µm width
- Single oval nucleus located
centrally
- Cells shape is hexagonal in
youth with age it become
polymorphic
Contd…
sbj
48. Ultrastructural features:
- The anterior cell membrane
(Basal) is attached with DM by
modified hemidesmosomes
- The posterior cell membrane
(Apical) facing Anterior
chamber shows 20-30
microvilli
- Lateral borders produce a
complex interdigitation with
neighboring cells
Contd…
Fig.: 3-D view of deep cornea
showing part of endothelium, DM,
Stroma
sbj
49. - Cell junctions with surrounding cells at lateral
surfaces –
- Ant. 2/3rd – maculae adharentes
- Post. 1/3rd & apicolateral edges – macculae
occludentes
- Endothelium is rich in subcellular organeles –
large number of mitochondria, both rough
and smooth endoplasmic reticulum, free
ribozomes, these reflects that endothelium is
extremely active metabolically
Contd…
sbj
50. Nutrition to endothelium:
- Endothelium gets its nutrition & O₂ from
aqueous
- Essential nutrients (such as glucose & amino
acids) pass across its surface to supply the
cellular needs of all the corneal layers
Contd…
sbj
51. Fluid regulation:
- The state of relative deturgescence of stroma
is maintained by this delicate monolayer of
cells by two ways –
- Providing a barrier function to the ingress of salt
and metabolites to the stroma
- Actively reducing the osmotic pressure of
stroma by metabolically pumping the
bicarbonate ions out of the stroma to aqueous
Contd…
sbj
52. Endothelial Repair:
- Physical & chemical damage to endothelium
results in loss of cells
- Neighboring cells move over to fill the gap by
sliding process and enlargement of cells occur
- Thus, after injury, the endothelial cell density
falls, the cell area increases and the cell height
decreases
Contd…
sbj
53. Blood supply of Cornea:
- The cornea is an avascular
structure
- Small loops derived from
the anterior ciliary vessels
invade its periphery for
about 1 mm.
- Actually, these loops are
not in cornea but in the
subconjunctival tissue
which overlaps the cornea.
sbj
54. Nerve supply of Cornea:
- Cornea is rich in sensory nerve supply derived
from ophthalmic division of trigeminal nerve via
anterior ciliary nerves and nerves to the
surrounding conjunctiva –
Ant.ciliary nerve enter the pericoroidal space a short distance behind the limbus
Connect with each other & conjunctival nerve and form pericorneal plexus
60-80 myelinated branches pass into cornea
sbj
55. After 1-2 mm lose myelin sheaths and divide into anterior and posterior groups
Anterior nerves (40-50) pass through stroma and form plexus
subjacent to Bowman’s layer
Nerve fibres then penetrate Bowman’s layer and form subepithelial plexus
Fibres then divide dichotomously to form a parallel network
which run for upto 2 mm
Contd…
sbj
56. And give rise to fine free nerve terminals to superficial epithelial layers
The posterior groups of nerves (40-50) pass posteriorly to
innervate the posterior stroma excluding Descemet’s membrane
Contd…
sbj
57. Sentinel of the eye:
• The adrenergic fibres from cervical
sympathetic, supply the limbus also
supply almost whole of the eye and its
appendages, giving warning of injury for
instance by a foreign body, its called
‘sentinel of eye’
Contd…
sbj
58. Corneal Nutrition & Metabolism
- Cornea requires energy for normal metabolic
activities as well as for maintaining
transparency and dehydration
- Energy is generated by the breakdown of
glucose in the form of ATP
- Most actively metabolizing layers are
epithelium & endothelium
sbj
59. Sources of Nutrients:
- Oxygen – mainly from atmosphere through
tear film, with minor amounts supplied by the
aqueous and limbal vasculature
- Normal Po₂ in tears is 155 mm Hg
- In aqueous is about 40 mm Hg
- Minimum 25 mm Hg Po₂ is needed for
maintaining deturgescent state and
transparency
Contd…
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60. - Glucose, amino acid, vitamins, and other
nutrients supplied to cornea by aqueous
humor, a lesser amounts from tears or limbal
vessels
- Glucose also derived from glycogen stores in
corneal epithelium
- Epithelium consumes O₂ 10 times faster than
stroma
Contd…
sbj
61. Metabolic pathways:
- Three processes or pathways –
1. Penntose shunt (Hexose monophosphate
shunt) – occurs both In hypoxic and normoxic
condition
- Forms NADPH and Pentose (Ribose 5-P) from gulcose
which are used in nucleic acid synthesis
2. Glycolysis (Embden meyerhof pathway) –
anaerobic process, glucose/glycogen converted
to pyruvate yelding 2 ATPs
3. TCA or Krebs or citric acid cycle – in aerobic
conditions pyruvate is oxidized to yield 36 ATP,
water, CO₂
Contd…
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63. Corneal Transparency
The cornea transmits nearly 100% of the light
that enters it. Transparency achieved by –
1. Arrangement of stromal lamellae
Two theories –
i) Maurice (1957): The transparency of the stroma
is due to the lattice arrangement of collagen fibrils.
He explained, because of their small diameter and
regularity of separation, back scattered light would
be almost completely suppressed by destructive
interference
sbj
64. ii) Goldman et al. (1968): He suggest, a perfect
crystalline lattice periodicity is not always necessary for
sufficient destructive interference. He explained, if fibril
separation and diameter is less than a third of the
wavelength of incident light, then almost perfect
transparency will ensue. This is the situation which
obtains in normal cornea.
Contd… A B
sbj
65. Other factors of corneal transparency -
2. Corneal epithelium & tear film
• Epithelial non-keratinization
• Regular & uniform arrangement of corneal epithelium
• Junctions between cells & its compactness and also
tear film maintain a homogenicity of its refractive index
3. Relative deturgescence state of normal
cornea
4. Corneal avascularity
5. Non myelenated nerve fibres
Contd…
sbj
66. Factors affecting corneal Hydration:
i. Stromal swelling pressure exerted by GAGs
ii. Barrier function of epithelium and endothelium
iii. Hydration controled by active pump mechanisms of
the corneal endothelium
• The enzyme pump systems are –
• Na⁺/K⁺ ATPase pump system
• Bicarbnate dependent ATPase
• Carbonic anhydrase enzyme
• Na⁺/H⁺ pump
iv. Evaporation of water from corneal surface
v. Intraocular pressure
sbj
67. Drug permeability across the Cornea:
Factors affecting drug penetration through the
cornea are –
1. Lipid and water solubility of the drug
2. Molecular size, weight and concentration of
drug
3. Ionic form of the drug
4. pH of the solution
5. Tonicity of the solution
6. Surface active agents
7. Pro-drug form
sbj