Corena & External Disease

Corneal and external diseases involve various parts of the eye including the cornea, iris, lens, anterior chamber, conjunctiva and eyelids. Corneal and external diseases can include corneal allergies, cataracts, infections, conjunctivitis and dry eye. There can also be refractive maladies like near sightedness, far sightedness and astigmatism. Other related disorders include keratoconus, pterygium, endophthalmitis and Fuch’s Dystrophy apart from other ailments.

The cornea is the dome-shaped, outermost, transparent layer that covers the iris and pupil. The corneal tissue itself consists of five basic layers called the epithelium, Bowman’s layer, stroma, Descemet’s membrane and endothelium in that order. Although it is transparent, the cornea contains a highly complex group of cells and proteins. However, unlike most tissues in the human body, the cornea contains no blood vessels to nourish it or to guard against infection. The cornea receives its nourishment from the aqueous humor that fills the chamber behind it. Human tears also provide the cornea with nourishment

The cornea serves two purposes: First, in tandem with the eyelid, eye socket, the tear film and the white part of the eye called the sclera, the cornea shields the eye from dust, germs and other harmful substances.

Secondly, since it is outermost lens of the eye, it serves as the point of entry for light. When a ray of light strikes the cornea, it refracts, or bends the ray onto the lens. The lens refocuses the light onto the retina, the tissue of light-sensing cells lining the anterior of the eye. Clear vision requires the cornea and lens to focus the light rays precisely on the retina. The way a camera takes a picture is modeled on this refractive process, with the cornea and lens of the eye acting like the lens of a camera. The retina is the film, if the cornea cannot focus the light properly, the retina receives a blurred image.

Any trauma like foreign projectiles, lacerations and blunting can result in scarring, which clouds the cornea. Hereditary conditions can also cause dystrophies and degenerations, which can also cause scarring. In young people, the most common hereditary corneal disorder is keratoconus, in which the cornea becomes cone-shaped. This is common in children in Down’s syndrome and in patients with allergic conjunctivitis. Such patients may be able to see with contact lenses or glasses for a period of time, but may eventually develop scarring or high astigmatism. These conditions can only be rectified with a corneal transplantation.

A corneal transplant can sometimes become necessary following cataract surgery, if bullous keratopathy occurs. In this condition, the endothelial cells at the back of the cornea decrease in number as a result of the surgery. However, with the invention of improved lens design an new techniques, bullous keratopathy is less common today.

The cornea or surface of the eye can be afflicted with a number of problems including:

These disorders can cause extensive damage to the eye surface and lead to the formation of new blood vessels. Severe scarring may result in loss of vision. Researchers at (Name of eye hospital) are exploring the possibility of normal tears being able to modulate and heal these conditions. A better understanding of the precise role of tears in the healing process may lead to the innovation of new techniques for visual recovery. It may also increase the number of successful surgeries.