Disorders of the Cornea - a Brief Overview

What Is Cornea?

The cornea is the dark transparent circular part of the front of our eyes. It is the only structure of our body that is transparent and is the main determinant of the crystal clear vision that we have come to expect from our eyes. Just like how the cornea being a clear lens, enables us to see the world around us, the cornea is also a boon to the doctors who can visualize the internal structures of the eye and blood vessels by directly viewing through the cornea without even having to touch the patient. This remarkable ability of the cornea to maintain its own transparency is made possible by a delicate balance of water and the intracorneal pressure and hydrostatic forces which preserve this state of transparency.

Just as bad are the visual results when this delicate balance is lost by disease or otherwise where the patient's vision may go down in a matter of minutes from being able to read the fine print to just being able to detect the presence of light. Thus, the role of the cornea in our visual capacity is unmatched and is irreplaceable. Like any other part of our body, the cornea too has its own host of very fulminant diseases, which, as mentioned before, hamper our vision by disrupting this delicate balance within the cornea. This article throws some light on the common corneal disorders and ways to prevent them.

What Is the Main Reason for Cornea’s Transparency?

The main reasons for the transparency of the cornea are:

1. The State of Relative Dehydration:

The normal water content of our body is around 66 %, but the corneal water content is around 82 %. This being said, the cornea is still said to be relatively dehydrated. This is because of the water being kept at a very strict level of control by special cells called endothelial cells, which pump water out of the cornea at a constant rate. This enables the cornea to be in a constantly dehydrated state even if the overall content is more than the rest of the body.

Whenever there is a breach in the corneal barriers, this gives way for water to flood into the cornea and hamper vision. The best and most common example is a corneal ulcer, where a wound over the cornea can cause inflammation and fluid to enter into the cornea. This is usually seen as a cloudy or white area on the normally clear and transparent cornea.

2. The Cornea Has No Blood Vessels or Lymphatic Vessels:

This absence of blood vessels is a remarkable adaptation to enable clear vision. The conditions such as contact lens wear or corneal graft, or interstitial keratitis can cause a growth of blood vessels onto the cornea and disrupt the corneal clarity.

3. The Orientation of Fibers of the Cornea Is Very Precise:

The fibers in the cornea are masterfully crafted and oriented such that whatever light rays get scattered after falling on them destroy each other and get nullified by a process called destructive interference. This process causes the cornea to scatter very little light and hence improves vision. The arrangement of fibers is also such that the gap between any two of the corneal fibers is less than the wavelength of visible light, once again contributing to corneal clarity.

Under normal circumstances, the above mechanisms work like clockwork keeping the cornea crystal clear.

What Are the Common Corneal Disorders?

The under-mentioned are the most common causes affecting the cornea by hampering this mechanism and causing blindness.

1. Corneal Ulcer - A corneal ulcer usually indicates a grave problem and is considered an ocular emergency. The problem is made worse by the fact that there are no blood vessels on the cornea to facilitate the healing of the wound.

An ulcer can be caused by a variety of causative factors such as by direct trauma, by the flash of very bright objects such as an electric arc, certain chemical fumes, by infection with organisms (adenovirus, cocci, bacilli, Acanthamoeba, fungi), by autoimmune disorders (Moorhen's ulcer).

The most common of the causes are either direct trauma or contact lenses. Contact lenses act by cutting out the oxygen supply to the corneal cells and killing cells due to lack of oxygen. Like any other injury, the ulcer causes a breach in the corneal barriers and allows flooding of water into the cornea. This hampers vision and causes pain.

2. Corneal Edema - It is usually caused by the failure of the endothelial pump mechanism and is common in the elderly after the age of 50. Women are more prone to corneal edema than men. Apart from aging, contact lenses, eye surgery, medications, and herpes infections can also lead to corneal edema. Such people experience irritation in the eye, a halo around lights, pain upon touching the eye, or viewing bright lights.

3. Corneal Opacity - It is the end result of corneal disease and represents a scarred and opaque cornea. Eye injury, measles, herpes simplex viral infection, using contact lenses even at night during sleep, vitamin A deficiencies, and eye infections like conjunctivitis can cause corneal opacity.

What Are the Measures to Avoid Corneal Disease?

1. No matter how small the eye infection is, always get an ophthalmologist’s opinion. The most benign of eye problems like conjunctivitis, unless treated well, can form ulcers.

2. Never use contact lenses regularly and beyond the prescribed limits of the duration of use. Also, do not use contact lenses at night during sleep.

3. If there are any injuries to the eye, kindly get an ophthalmologist’s appointment right away.

4. For people whose work involves traveling in dust or in welders and grinding operators, always wear your safety glasses.

5. Do not rub your injured or scratchy eye.

6. If you suspect any foreign material within your eye, you can rinse it with fresh and clean water.