Eye Anotomy - Common Diseases and Disorders of Cornea
Know your Body

The Cornea: Guards Your Eye

Dr.Surya Rao Poodipeddi profile Authored by Dr.Surya Rao Poodipeddi on 3 Mar 2014 - 17:21.

Human cornea is a transparent dome shaped window situated in front of each eye. It’s a very powerful surface with intense ability for refraction with a capacity to provide 2/3rd of the focusing power of the eye. It can be compared to the crystal of a watch which acts like a clear window to look through.

Unlike any other organ in the human body the cornea is totally avascular meaning that there are no blood vessels in the cornea and hence has a shiny appearance. Most notable feature of the human cornea is that it has more nerve endings than anywhere else in the body

In an adult the cornea is about ½ a millimeter thick. Such a thin membrane has five layers namely epithelium, Bowman’s membrane, stroma, descemet’s membrane and the endothelium. Each layer has a distinct function:

  • The epithelium is a layer of cells capable of regenerating whenever there is any injury to the cornea.
  • Bowman’s membrane lies just beneath the epithelium and is very tough and difficult to penetrate and hence can protect the cornea from external injury.
  • The stroma consists of tiny collagen fibers running parallel to each other and provides clarity to the cornea.
  • The last two layers help pumping water from the cornea and keep it clean and clear. They are very thin and cannot regenerate if injured or diseased.

Cornea helps the eye in two ways:

1.     It helps to shield the rest of the eye from germs, dust and any other harmful matter. It does this with active help from the eyelids, eye socket, tears and the sclera (the white of the eye).

2.     It acts as the eye’s outer most lens, functioning like a window controlling and focusing the entry of light into the eye.

(The mechanism of light falling on the retina and how the rays of light are focused has been dealt in detail in a separate chapter on Retina, by the same author)

The cornea has a great capacity to cope with any minor injury or abrasions. When this highly sensitive membrane is scratched, healthy cells slide over quickly and patch up the injury to prevent entry of any infection. However, if the injury penetrates deep inside, the healing process takes a longer time. Such deep penetrating injuries result in pain, blurring of vision, tears, redness and extreme sensitivity to light. If this happens professional help must be sought. Very deep penetrating injuries may leave a scar requiring corneal transplant.

Common diseases and disorders of cornea are:

Allergies: are very common and mostly occur due to pollen, characterized by redness, itching, burning, stinging sensation and watery discharge. Antihistamines and decongestant eye drops gives relief. Other causes include allergy due to contact lens and certain medications.

Conjunctivitis: This includes a group of diseases which cause swelling, itching, blurring and redness of the conjunctiva. Judicious use of antibiotics and eye drops give prompt relief. Delay in treatment may lead to corneal inflammation and may be loss of vision.

Corneal Infections: Some are caused due to piercing injuries to the cornea. Some may be due to contamination and infection from contact lens. These conditions if not detected and treated, may lead to inflammation of cornea called Keratitis. They reduce visual clarity and might necessitate corneal transplant if there is severe visual impairment. Minor infections can be tackled with antibiotic care. Very severe inflammations may need use of steroid drops.

Dry Eye: For the eye to be healthy continuous production of tears and efficient drainage is very important. Production of tears in less quantity leads to dry eye. The dry eye condition is characterized by a feeling of sand in the eye. Pain and redness, stingy discharge and a feeling of dryness are other symptoms of dry eye. Artificial tears which lubricate the eye are the fundamental treatment for dry eye. Sterile eye ointments may be used at bedtime to keep the eyes moist. In severe cases of dry eye permanent closure of the drain for tears may be helpful.

Fuchs’ Dystrophy: This is a slowly progressive disease affecting one or both eyes and commonly affects more women than men. The main reason for deterioration of the endothelial layers of the cornea is, it causes inefficient pumping of water out of the stroma. This condition may need corneal transplant depending on the severity of the symptoms.

Corneal Dystrophies: In this condition the cornea loses its normal clarity due to a build-up of cloudy material. There are roughly 20 types of corneal dystrophies and each one shares many common features namely:

  • They are usually hereditary
  • They affect either of the eyes in equal proportions.
  • Injury or any outside factors are not responsible for this condition.
  • Most of them progress very slowly.
  • Usually they affect first one of the layers of the cornea and gradually affect the other layers.
  • Most of these conditions do not affect other parts of the body nor do they relate to other diseases.
  • They can affect a normal person of either sex
*Disclaimer: This is not medical advice. The content is for educational purposes only. Please contact your doctor for any health care issues.