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.
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.
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.
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.
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.
Fundus Flourescein Angiography( FFA ) by optometry fans.pptxoptometry fans
Fundus flourescein angiography (FFA) by optometry fans.
Fundus flourescein angiography (FFA) is a valuable procedure in ophthalmic practice to the diagnosis and management of a large number of fundus disorders.
FFA provide information by allowing the examiner to study the changes, produced by various fundus disorders, in the flow of fluorescein dye along the vasculature of the retina and choroid
indication
Diabetic retinopathy
Vascular occlusions
Eales’ disease
Central serous retinopathy (CSR)
Cystoid macular oedema (CME)
Contraindication
Cardiac disease
Renal impairment
Uncontrolled hypertension
Pregnancy
Allergic reaction
Injecting 5 ml of 10 per cent solution of sterile sodium fluorescein dye in the antecubital vein
Taking serial photographs (with fundus camera) of the fundus of the patient with pupils fully dilated.
The first photograph is taken after 5 seconds, then every second for next 20 seconds and every 3-5 seconds for next one minute. The last pictures are taken after 10 minutes.
The fundus camera has a mechanism to use blue light (420-490 nm wavelength) for exciting the fluorescein present in blood vessels and to use yellow-green filter for receiving the fluorescent light (510-530 nm wavelength) back for photography.
Read| The latest issue of The Challenger is here! We are thrilled to announce that our school paper has qualified for the NATIONAL SCHOOLS PRESS CONFERENCE (NSPC) 2024. Thank you for your unwavering support and trust. Dive into the stories that made us stand out!
How to Create Map Views in the Odoo 17 ERPCeline George
The map views are useful for providing a geographical representation of data. They allow users to visualize and analyze the data in a more intuitive manner.
Operation “Blue Star” is the only event in the history of Independent India where the state went into war with its own people. Even after about 40 years it is not clear if it was culmination of states anger over people of the region, a political game of power or start of dictatorial chapter in the democratic setup.
The people of Punjab felt alienated from main stream due to denial of their just demands during a long democratic struggle since independence. As it happen all over the word, it led to militant struggle with great loss of lives of military, police and civilian personnel. Killing of Indira Gandhi and massacre of innocent Sikhs in Delhi and other India cities was also associated with this movement.
Ethnobotany and Ethnopharmacology:
Ethnobotany in herbal drug evaluation,
Impact of Ethnobotany in traditional medicine,
New development in herbals,
Bio-prospecting tools for drug discovery,
Role of Ethnopharmacology in drug evaluation,
Reverse Pharmacology.
The French Revolution, which began in 1789, was a period of radical social and political upheaval in France. It marked the decline of absolute monarchies, the rise of secular and democratic republics, and the eventual rise of Napoleon Bonaparte. This revolutionary period is crucial in understanding the transition from feudalism to modernity in Europe.
For more information, visit-www.vavaclasses.com
The Indian economy is classified into different sectors to simplify the analysis and understanding of economic activities. For Class 10, it's essential to grasp the sectors of the Indian economy, understand their characteristics, and recognize their importance. This guide will provide detailed notes on the Sectors of the Indian Economy Class 10, using specific long-tail keywords to enhance comprehension.
For more information, visit-www.vavaclasses.com
How to Make a Field invisible in Odoo 17Celine George
It is possible to hide or invisible some fields in odoo. Commonly using “invisible” attribute in the field definition to invisible the fields. This slide will show how to make a field invisible in odoo 17.
2. Anatomy of Cornea
• Cornea is a transparent, avascular, watch-glass
like structure.
• It forms anterior one-sixth of the outer fibrous
coat of the eyeball.
3.
4. Dimensions
• Anterior surface of cornea is elliptical with an average horizontal
diameter of 11.7 mm and vertical diameter of 11 mm.
• Posterior surface of cornea is circular with an average diameter
of 11.5 mm.
• Thickness of cornea in the centre varies from 0.5 to 0.6 mm
while at the periphery it varies from 1 to 1.2 mm.
• Radius of curvature. The central 5 mm area of the cornea forms
the powerful refracting surface of the eye. The anterior and
posterior radii of curvature of this central part of cornea are 7.8
mm and 6.5 mm, respectively.
• Refractive index of the cornea is 1.376.
• Refractive power of the cornea is about 45 dioptres, which is
roughly three-fourth of the total refractive power of the eye (60
dioptres).
5. Histology
Histologically, the cornea consists of six layers.
From anterior to posterior these are:
–Epithelium,
–Bowman’s membrane,
–Substantia propria (corneal stroma),
–Pre-Descemet’s membrane (Dua’s layer),
–Descemet’s membrane and endothelium
7. Epithelium
• It is of stratified squamous type and becomes continuous
with epithelium of bulbar conjunctiva at the limbus.
• It consists of 5–6 layers of cells. The deepest (basal) layer
is made up of columnar cells, next 2–3 layers of wing or
umbrella cells and the most superficial two layers are made
of flattened cells.
• Tight junctions between superficial epithelial cells prevent
penetration of tear fluid into the stroma.
• Limbal epithelium. The basal epithelial cells of the limbal
area constitute the limbal stem cells which amplify,
proliferate, and differentiate into corneal epithelium.
• Damage to this area results in the invasion of conjunctival
epithelium on to the cornea
8. Bowmans membrane
• This layer consists of acellular mass of condensed
collagen fibrils.
• It is about 12 mm in thickness and binds the
corneal stroma anteriorly with basement
membrane of the epithelium.
• It is not a true elastic membrane but simply a
condensed superficial part of the stroma.
• It shows considerable resistance to infection. But
once destroyed, it is unable to regenerate and,
therefore, heals by scarring.
9. Stroma – Substantia Propria
• This layer is about 0.5 mm in thickness and constitutes most of
the cornea (90% of total thickness).
• It consists of collagen fibrils embedded in hydrated matrix of
proteoglycans (chondroitin sulphate and keratan sulphate).
• The lamellae are arranged in many layers. In each layer they
are not only parallel to each other but also to the corneal plane
and become continuous with scleral lamellae at the limbus.
• The alternating layers of lamellae are at right angle to each
other.
• Among the lamellae are present keratocytes (modified
fibroblasts), wandering macrophages, histiocytes and a few
leucocytes
10. Pre- Descement Membrane (Dua
Layer)
• Pre–Descemet’s membrane, also known as
Dua’s layer has been discovered in 2013 by Dr
Harminder Dua, an Indian ophthalmologist
working in Great Britain.
• Located anterior to the Descemet’s membrane,
it is about 15 micrometer thick acellular
structure which is very strong and imprevious
to air
11. Descemet Membrane
• Descemet’s membrane (posterior elastic lamina). The
Descemet’s membrane is a strong homogenous
basement membrane of the corneal endothelium
which is separated from the stroma by pre-Descemet’s
membrane. It is very resistant to chemical agents,
trauma and pathological processes. Therefore,
‘Descemetocele’ can maintain the integrity of eyeball
for long. Descemet’s membrane consists of collagen
and glycoproteins. Unlike Bowman’s membrane it can
regenerate. Normally, it remains in a state of tension
and when torn, it curls inwards on itself. In the
periphery it appears to end at the anterior limit of
trabecular meshwork as Schwalbe’s line (ring).
12. Endothelium
• Endothelium. It consists of a single layer of flat polygonal
(mainly hexagonal) epithelial cells (misnamed as
endothelium) which on slit-lamp biomicroscopy appear as a
mosaic. The cell density of endothelium is around 3000
cells/mm2 in young adults, which decreases with the
advancing age. The human endothelium cells do not
proliferate in vivo and the cell loss with age is compensated
by enlargement (polymegathism) and migration of
neighbouring cells. There is a considerable functional
reserve for the endothelium. Therefore, corneal
decompensation occurs only after more than 75% of the
cells are lost. The endothelial cells contain ‘activepump’
mechanism which keeps cornea dehydrated.
13. Physiology of cornea
The two primary physiological functions of the cornea are
(i) To act as a major refracting medium
(ii) To protect the intraocular contents.
Cornea performs these functions by maintaining its
transparency and regular replacement of its tissues
14. Corneal Transparency
• Peculiar arrangement of corneal lamellae
• Avascularity of cornea.
• Relative state of dehydration (78% water content),
which is maintained by the barrier effects of
epithelium and endothelium and the active Na+ K+
ATP ase pump of the endothelium.
• Swelling pressure (SP) of the stroma which counters
the imbibition effect of intraocular pressure (IOP).
• Corneal crystallins, i.e, water soluble proteins of
keratocytes also contribute to corneal transparency at
the cellular level. For these processes, cornea needs
some energy.
15. Metabolism of cornea
• Most actively metabolizing layers of the
cornea are epithelium and endothelium, the
former being 10 times thicker than the latter
requires a proportionately larger supply of
metabolic substrates.
16. Source of nutrients for cornea
• 1. Solutes (glucose and others) enter the cornea by
either simple diffusion or active transport through
aqueous humour and by diffusion from the perilimbal
capillaries.
• 2. Oxygen is derived directly from air through the tear
film. This is an active process undertaken by the
epithelium. Therefore, corneal hypoxia may occur with
over wear of contact lenses.
• Some oxygen may reach the superficial layers of cornea
from the perilimbal capillaries (especially when eyelids
are closed) and deeper corneal layers through the
aqueous humour
17. • Endothelium requires oxygen and glucose for
metabolic activities and proper functioning of
Na+ - K+ ATPase pump. Like other tissues, the
epithelium can metabolize glucose both
aerobically and anaerobically into carbon
dioxide and water and lactic acid, respectively.
Thus, under anaerobic conditions lactic acid
accumulates in the cornea