CORNEA & EXTERNAL EYE DISEASESWhat is cornea?Cornea is the transparent, dome-shaped tissue covering the front of the eye. It is like the watch glass of a wrist watch. Cornea is a powerful refracting surface and provides about 2/3 of the eye’s focusing power. It gives us a clear window to look through and is very important for good vision. Diseases of the cornea lead to loss of transparency, thus interfering with vision. Injury, infection, genetic diseases and malnutrition can affect the functioning of the Cornea.What is corneal blindness/ visual impairment?The cornea becomes cloudy or warped due to disease, injury or infection. A damaged cornea distorts light as it enters the eye thereby leading to decrease of eye sight. This kind of visual impairment is called corneal blindness. This is the only type of visual impairment that can be treated by corneal transplantation. Corneal problems can afflict anyone at any age.What does Cornea Service include?The Cornea Service is dedicated to the medical and surgical treatment of problems involving the Cornea and other anterior structures of the eye like eyelids, conjunctiva, sclera, anterior chamber, iris and lens.
The clinic caters to the following Cornea & External eye diseases:
– Corneal infections
– Eye allergies Corneal complications arising from other forms of ocular surgery
– Ocular surface trauma
– Ocular surface disorders like blepharitis, meibomitis, conjunctival and scleral diseases
– Refractive errors (nearsightedness, farsightedness and astigmatism)
– Conjunctivitis (red eye)
– Dry eye syndrome
– Ectatic corneal diseases like keratoconus, keratoglobus and pellucid marginal degeneration
– Corneal dystrophies and degenerations
– Corneal Transplantation
– Keratoprosthesis (Artificial cornea)
– Scleral grafting
– Ocular Surface Reconstruction- Corneal, limbal, and amniotic membrane transplants allow ocular surface reconstruction in severe surface disease
– Tissue adhesive application to seal corneal perforation
– Specular Microscopy- Study of the corneal endothelium (cells that maintain corneal clarity)
– Pachymetry- Measurement of corneal thickness
– Corneal Topography (by Orbscan)- Mapping of the cornea
– Aberrometry- Measurement of the aberrations in the eye
1. What is a Corneal Transplant?
A corneal transplant involves replacing a diseased or scarred cornea with a clear, healthy donor cornea. For many individuals, a corneal transplant may be the only hope for vision restoration, and may be necessary when the cornea is cloudy or damaged due to disease, injury, accident, malnutrition or hereditary conditions.
Figure 1. Cornea Transplant- A clear central area allows light transmission
2. How can the cornea and ocular surface be damaged?
The cornea and ocular surface can be severely damaged by a number of problems, including:
– Chemical, mechanical and thermal injuries
– Corneal infections
– Diseases such as Stevens-Johnson syndrome and pemphigoid
– Chronic infections or inflammations
– Malnutrition (Vitamin A deficiency)
– New tissue growths such as pterygium and tumors
– Neurotrophic conditions (due to damage to the eye’s sensory nerves)
– Rare hereditary conditions such as aniridia (congenital absence of the iris)3. What is the success rate of Cornea Transplant?
Corneal transplants are one of the most common and most successful of all transplants.
The procedure may be successful in upto 90 percent of some cases. However, the success depends on a number of factors- recepient’s eye condition and corneal disease, donor cornea quality and the surgical technique and skill.
The first year after a transplant is the most crucial, because most complications, if they occur, will occur within the first year of the transplant.The more common complications include increased eye pressure which can cause damage to the eye nerve (glaucoma) and corneal graft rejection.
In the event of graft failure due to rejection, corneal transplantation may be repeated several times if previous transplants have failed. However, the success rate of repeat transplants is lower than the first time. In such repeat grafts, immunosuppressive medication may be used to prevent rejection.
4. Where does the donor cornea come from?
The healthy donor cornea used for transplantation is supplied by an Eye Bank. Eye Banks collect, evaluate, store and distribute donated corneas. The corneas are collected from human donors within a few hours of death. Stringent tests are performed to ensure the safety of the person receiving the cornea. The Eye Bank verifies the donor’s medical history and cause of death, and performs blood tests to ensure that the deceased person did not have contagious diseases like AIDS or hepatitis.
In addition to their expertise in corneal transplantation and medical management of corneal disorders, members of the Cornea Service staff also provide innovative medical and surgical procedures to wide variety of challenging corneal and ocular surface disorders such as keratoconus, corneal dystrophy, immune mediated ocular surface diseases, and congenital anomalies of the cornea and anterior segment.
Ocular Surface Disorders
1. Dry Eye Syndrome‘Dry eye’ is a condition characterized by an unstable tear film causing irritation and discomfort in the eye. This is because of either decreased quantity of tears or their increased evaporation from the eye. The symptoms are non-specific and can range from a tired or itching eye to diminished vision in severe cases.
Clinical examination along with diagnostic tests can help diagnose the condition of dry eyes. A detailed examination is done to assess the severity of the problem and other complications. The treatment includes use of preservative-free artificial tears, topical immunosuppresive medication and autologous serum.
Dry eyes can sometimes be a manifestation of an underlying systemic disease like rheumatoid arthritis. Such patients are jointly treated by the ophthalmologist and rheumatologist.
The term Conjuctivitis refers to a group of diseases that cause redness, swelling, itching or burning of the conjunctiva, the protective membrane lining the eyelids and the sclera (white of the eye). The patient may also have discharge and watering. It is essentially inflammation of the conjunctiva.
Acute infective conjunctivitis may be due to various microorganisms. The commonest organisms are various bacteria and viruses. Bacterial conjunctivitis usually requires treatment in the form of antibiotic eyedrops. Viral conjunctivitis usually does not require medication and the body’s defence mechanisms will clear the infection. Cold compresses will provide relief.
3. Limbal Stem cell deficiency
Patients suffering from ocular surface problems due to damaged limbal stem cells in the eye may benefit from limbal stem cell transplantation. This procedure helps to provide a stable ocular surface.
4. Corneal Dystrophies
Corneal dystrophies are inherited conditions, usually bilateral, in which the cornea loses its normal transparency due to opacity in the cornea.
Dystrophies can cause a decrease in vision as well as symptoms of irritation, watering and occasionally watering.
Dystrophies can be of many types. However, some of the traits shared by most dystrophies are:-
– They are usually inherited.
– They usually affect both the eyes equally.
– They are not caused by outside factors, such as injury or diet.
– Most progress gradually.
– Most usually begin in one of the five corneal layers and may later spread to nearby layers.
– Most do not affect other parts of the body, nor are they related to diseases affecting other parts of the eye or body.
– Most can occur in otherwise totally healthy people, male or female.
Some of the most common corneal dystrophies include Fuchs’ dystrophy, keratoconus, lattice dystrophy, map-dot-fingerprint dystrophy and Macular Corneal Dystrophy
A pterygium is a triangular-shaped tissue growth over the cornea varying in color from yellowish-white to pinkish in color, on the nasal side of the cornea. It may occasionally become red. Pterygia usually stop growing after a certain point but may sometimes continue to grow and advance toward the center of the eye.
The exact cause of pterygia is not known. However, it has been observed that people who have spent a significant time outdoors have a higher incidence of pterygia. Ultraviolet (UV) light is, therefore, believed to be a factor responsible for the formation of pterygia. Wearing protective sunglasses and/or hats with brims may reduce the risk of their formation.
It is a benign condition and often causes no harm other than being a cosmetic blemish. Lubricants can reduce the redness and provide relief from the chronic irritation. Surgery can remove the pterygia. However, it should be noted that, pterygia are notorious for recurrences and the recurrences are usually even more aggressive.
Dr. Ashu Agarwal, January 19, 2007–New Delhi