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The five major senses of the human body are sight, smell, hearing, touch, and taste. The eyes are responsible for the perception of sight. The cornea, iris, sclera, pupil, retina, lens, ciliary body, conjunctiva, macula, vitreous body, retinal blood vessels, and optic nerve are all crucial structures that assist the eye execute its function.
The cornea is the eye’s initial and outermost structure that comes into contact with the outside world. The cornea of the eye is the transparent, hard layer that covers the whole surface of the eye. Word comes from the Latin word cornu, which means horn or horny tissue.
Definition Cornea
The cornea is the eye’s clear front surface. It is located right in front of the iris and pupil, allowing light to pass through.
The cornea appears somewhat broader than it is tall when viewed from the front of the eye. The sclera (the “white” of the eye) spans the top and bottom of the anterior cornea slightly.
When viewed from the front, the cornea has a horizontal diameter of 12 millimetres (mm) and a vertical diameter of 11 millimetres (mm). The cornea appears circular when viewed from behind, with a constant diameter of roughly 11.7 mm. The cornea is about two-thirds the size of a dime as a result.
The cornea is made up of five layers. These layers are
.The corneal epithelium – The cornea’s outer layer is five to seven cells thick and is around 50 microns in thickness, making for little less than 10% of the overall cornea’s thickness. In the tear layer of the surface of the eye, epithelial cells are constantly generated and sloughed off. The corneal epithelium has a one-week turnover time.
.Bowman’s layer – The transition between the corneal epithelium and the underlying stroma is formed by a thin (8 to 14 microns) and dense fibrous film of connective tissue.
.The corneal stroma – The cornea’s central layer is around 500 microns thick, accounting for about 90% of the total thickness of the cornea. It is made up of collagen fibrils, which are connective tissue strands. These fibrils are uniform in size and are grouped in 200 to 300 flat bundles termed lamellae that run parallel to the cornea surface and span the whole cornea. The cornea’s flawless clarity is due to the regular arrangement and uniform spacing of these lamellae.
.Descemet’s membrane – The stroma is separated from the cornea’s underlying endothelial layer by this very thin layer. The membrane of Descemet (pronounced “DESS-eh-mays”) thickens during time, ranging from 5 microns in children to 15 microns in older adults.
.The corneal endothelium – This is the cornea’s deepest layer. The clear aqueous humour that fills the gap between the cornea and the iris and pupil bathes the back of the endothelium. The corneal endothelium is just around 5 microns thick and consists of a single layer of cells. Endothelial cells are hexagonal (six-sided) in most cases, but others have five or seven sides. The endothelial mosaic refers to the regular arrangement of these cells.
Function of Cornea
The clear cornea, as previously said, permits light to enter the eye for vision. The cornea, however, has another vital purpose: it contributes approximately 65 to 75 percent of the eye’s focusing capacity.
The crystalline lens, which is placed just behind the pupil, provides the rest of the eye’s focusing capacity.
Nearsightedness, farsightedness, and astigmatism are all caused by the cornea’s curvature or symmetry being less than ideal. Presbyopia, on the other hand, is caused by a change in the crystalline lens that occurs with age.
The clear cornea, as previously said, permits light to enter the eye for vision. The cornea, however, has another vital purpose: it contributes approximately 65 to 75 percent of the eye’s focusing capacity.
The crystalline lens, which is placed just behind the pupil, provides the rest of the eye’s focusing capacity.
Nearsightedness, farsightedness, and astigmatism are all caused by the cornea’s curvature or symmetry being less than ideal. Presbyopia, on the other hand, is caused by a change in the crystalline lens that occurs with age.
Individual regions of the cornea have specialised functions in addition to allowing light to enter the eye and supplying the majority of the eye’s focusing power:
- Corneal epithelium – The corneal epithelium creates an ideal surface for the tear film to spread throughout the eye’s surface, keeping it wet and healthy while maintaining clear, stable vision.
- Bowman’s layer – Bowman’s layer’s thick structure helps keep corneal scratches out of the stroma. Corneal abrasions that are limited to the outer epithelial layer heal without leaving permanent scars, but scratches that penetrate Bowman’s layer and the corneal stroma frequently leave permanent scars that can impair vision.
- Corneal endothelium –The endothelium, which is made up of a single layer of cells, keeps the fluid volume of the cornea in check. Swelling (edema) of the corneal endothelium can affect vision and affect corneal health.
Cornea Problems
The cornea can be harmed by a number of conditions. The following are a few of the most frequent corneal issues:
Arcus senilis – A white ring forms around the perimeter of the cornea as people get older. The most frequent ageing alteration in the cornea is known as arcus senilis (also known as corneal arcus). A patch of clear cornea usually separates the arcus senilis from the limbus. The white ring, which is made up of cholesterol and other similar chemicals, can be subtle or conspicuous.
Corneal arcus isn’t usually linked to blood cholesterol levels in older people, but if it happens in someone under the age of 40, blood testing should be done to rule out hyperlipidemia (abnormally high concentration of fats or lipids in the blood).
Corneal abrasion – A scratched cornea is extremely painful and can lead to an infection in the eye.
Pterygium – Pterygiums are fibrous growths that begin on the sclera and can spread into the peripheral cornea, causing discomfort, vision impairment, and deformity of the front of the eye.
Dry eyes – Though dry eyes are usually caused by problems with the tears gland and eyelids, they can also cause damage to the corneal epithelium, resulting in eye discomfort and vision problems.
Corneal ulcer – A corneal ulcer is a serious abscess-like infection that causes severe discomfort, scarring, and vision loss.
Corneal dystrophy – A dystrophy is a tissue weakness or deterioration. Fuch’s dystrophy, the most prevalent corneal dystrophy, affects the corneal endothelium, resulting in corneal edema, hazy vision, light sensitivity, and other issues.
Acanthamoeba keratitis – This is a serious and painful corneal infection that can result in severe pain and visual loss.
Fungal keratitis – This is yet another serious corneal infection that, like Acanthamoeba keratitis, is more common in contact lens wearers than in glasses wearers.
Keratoconus – This is a condition in which the cornea thins and deforms, resulting in visual issues that cannot be rectified with ordinary eyeglasses or contact lenses. Scleral contact lenses or hybrid contacts may be used to correct visual difficulties caused by keratoconus in some circumstances. In severe cases, however, a cornea transplant may be necessary.
Corneal ectasia – This is a rare complication following LASIK or other corneal refractive surgery that causes thinning and deformation of the cornea similar to keratoconus.
Conclusion
We can conclude that Cornea is the very important part of the eye because
Light rays are focused onto the retina of the eye by the cornea and lens working together . Light is absorbed and converted by retinal cells into electrochemical signals, which are subsequently conveyed to the brain via the optic nerve. If the cornea is damaged by disease, infection, or injury, your vision may be harmed as a result of the scars that develop. When light enters your eye, they may block or distort it. Doctors can use a laser procedure called phototherapeutic keratectomy (PTK) to reshape the cornea, remove scar tissue, and improve eyesight in some corneal dystrophies and other disorders.
