Dry Eye and Newer Surface Disorder Surgeries
Q.1 What is meant by the term “Ocular Surface”?
A.1 By this is meant:
a) The conjunctiva, which is the transparent, thin layer that lines the inner surface of the 2 eyelids, and the sclera
(the white portion of the eye).
b) The limbus, which is the junction of the sclera and the cornea. This area contains “stem cells” which are precursor cells that differentiate throughout life to create new surface cells of the conjunctiva on one side and the epithelial cells of thecornea on the other side. Damage to this area results in faulty replacement of conjunctival and corneal cells, resulting in surface disorder.
c) The cornea, which is the transparent cover over the brown/black of the eye. This is composed of several layers. The most superficial layer, called the corneal epithelium is part of this ocular surface.
d) The tear film. The lacrimal glands produce this. Part of the tear film is also produced by glands in the eyelids (oily partof tears) and a part by cells in the conjunctiva (sticky, mucus part of the tears). This tear film is very essential for lubricating the ocular surface and protecting it by washing away harmful substances. It is produced continuously, without our realizing it! The tears we shed when we see the hero or heroine being hammered up in a Bollywood movie are "emotional tears”. These are different in composition from our regular lubricating tears and are of no use as far as properly wetting the ocular surface is concerned! Hence we may shed copious tears at the drop of a hat and yet be diagnosed by the eye surgeon as having a ‘dry eye’!
Q.2. Can a ‘normal’ person develop dry eye?
A.2. Yes, tears are 60% less at age 60 as compared to age 18. Menopause and pregnancy are also ‘normal’ events in the life of a woman that can cause decrease in tear production. Staring continuously at the computer screen results in reduction of normal blinking. This causes dry eye as more tears evaporate from the surface of the eye and the tears are not spread evenly across the ocular surface due to inadequate blinking. Prolonged use of contact lenses can sometimes result in dry eye. And of course, a whole host of allopathic drugs such as antihistaminics (taken for common colds), antacids, anti-hypertensives, anti-depressants, drugs used for Parkinson’s disease and many, many other tablets and capsules and syrups can cause drop in tear production. Certain environments contribute greatly to dry eye, such as windy, dusty, dry climates and atmospheric pollution. Also, overuse of heaters (less likely in most parts of India) and air-conditioners (most likely in most parts of India) causes the room air to become dry, promoting evaporation of our tears.
Q.3. What is meant by “amniotic membrane transplant”? When is it indicated?
A.3. In certain cases of non-healing corneal ulcers, (breaks in the superficial or epithelial layer of the cornea with infection) large perforations of the cornea, or surface irregularities of the ocular surface such as after removal of surface tumours or in cases of ocular trauma with acids, alkalis or other toxic substances, the ocular surface needs a cover. A biological tissue such as amnion can provide this. Amniotic membrane is the inner lining of the protective cover of the foetus in a mother’s womb. After a caesarian section, in a volunteer, the placenta is taken and the amniotic membrane is carefully stripped off and preserved in a special medium, for 6 months, The donor is tested for various blood borne diseases including AIDS. These tests are repeated at 6 months and if negative, the amniotic tissue can be used for covering the ocular surface.
Q.4. Is this a very new type of surgery?
A.4. Not at all! This surgery was very popular in the fifties and sixties. However, at that time, technology to preserve amniotic membrane for many months was non-existent. Hence only fresh membrane was used. This increased the complication rate and the procedure was largely abandoned, till it found favour again since about a decade.
Q.5. How long does the AM stay in place?
A.5. This depends on how inflamed or ‘angry’ the eye is. The more inflamed the eye, the faster the amniotic membrane is absorbed- sometimes even as early as one week. If there is not much inflammation, the AM may continue to provide protection for 4-6 weeks.
Q.6. What is meant by “corneal glue”? When is it used?
A.6. In case there is a tiny hole in the cornea following injury or melting of the cornea due to chemical burns or infection, a glue -similar to fevicol or araldite (I have no shares in either of the 2 products!) is used to seal the opening. This is a medical grade polymer; a drop or two is all that is required. It is quick drying but extremely irritant to the eye. Hence, after it has dried on the cornea, a bandage contact lens is applied, to keep the glue in place and to prevent the severe irritation that would occur if the glue came in contact with the lids.
Q.7. I have heard that ‘stem cells’ are used in eye surgery as well. What is this all about?
A.7. This is indeed a very exciting and fairly new development. Just like skin cells, the surface layer of cells of the cornea and the conjunctiva are being continuously shed and replaced by new cells. Until recently, we were not sure where these new cells were coming from. It has now been proved that the junction of the cornea and the sclera (the white of the eye) is home to the stem cells, which form new epithelial cells of the conjunctiva and cornea. This area is known as the limbus and so these stem cells are often referred to as limbal stem cells. The beauty of it all is that each stem cell divides into 2 daughter stem cells. The elder daughter stays at home while the younger goes on to differentiate into the corneal and conjunctival cells, which ultimately die and are cast off. This process goes on and on throughout the life of the individual, thus providing a continual supply of new cells for the cornea without a significant drop in the total stem cell population.
However, in certain diseases and in cases of chemical injuries to the eye (jilted lovers throwing acid or alkali into the eye!), these stem cells are diseased or damaged. When this happens, the regular cast off cells from the surface of the cornea are no longer replaced by stem cells, resulting in persistent defects in the epithelial layer of the cornea, which can get worse with time. This results also in loss of transparency of the cornea and drop in vision. Upto recently, these eyes were given up as lost. Even a corneal transplant is doomed to failure in such cases, as the superficial cells of the new donated cornea are soon cast off but not replaced due to the stem cell deficiency of the host (patient).
Q. 8. You are hinting that there is now hope for such cases?
A. 8. Yes. If the other eye of the patient is not damaged, we can harvest stem cells from the limbus of the second eye (leaving sufficient stem cells in the good eye, so as not to cause new problems of course!) This tissue containing the stem cells is then transplanted into the diseased eye. The stem cells soon start dividing and subdividing and can fill up the defects in the recipient cornea. Amazingly, eyes with very poor vision can have their vision restored by this relatively simple procedure.
Q.9. What if the second eye is similarly damaged or diseased as well?
A.9. Even in such cases, all is not lost. If a tiny area of normal stem cells is available in either eye, a part of that is removed and cultured in the laboratory. In a couple of weeks, this tiny bit of tissue can be made to grow to several times its original size i.e. from a few stem cells to several hundreds of stem cells. This newly grown tissue can then be transplanted into one or both eyes. Over a period of time, one or both corneas can regain sufficient population of cells to improve in vision.
Q.10. I hate to be a spoilsport, but what if there is so much damage in both eyes that no harvesting of stem cells is possible?
A.10. In such cases, stem cells can be harvested from a sibling or parent and transplanted into any one eye of the patient. In case they are unwilling or not available or not found suitable, then stem cells can be harvested from an unrelated cadaveric donated eye i.e. from a dead person who has donated his eyes to the eye bank. In both these cases however, there is always the fear of rejection, hence such patients are given immunosuppressive drugs for prolonged periods.
Q.11. In dry eye, what are our surgical options?
A.11. Generally, medical treatment in the form of tear substitutes is given first. These may be drops or ointments or both, depending on the severity. In some cases however, the eye surgeon may advise blockage of the tear drainage ducts so as to preserve the patient’s own tears in the eye for a longer time as well as to lessen the frequency required of instilling artificial tears. There are various types of ‘plugs’ available in the market. Chiefly, they are of 2 styles– a) ‘punctum’ plugs, which are inserted into the tiny openings in the upper and lower lids through which our tears drain and remain visible on the surface of the lid and b) canalicular plugs, which are inserted through the puncti into the drainage pathway and are therefore not visible to the naked eye once inserted. Both these types are inserted in an easy, no injection technique and can even be inserted in the eye surgeon’s office using only eye drop anaesthesia.
Q.12. My cousin was advised “occlusion of his puncti” to relieve his dry eye. Why do you eye surgeons use such complex phrases? What does it mean?
A.12. I thought I had explained it in the previous answer! In mild to moderate dry eye cases, we would like to conserve the patient’s own tears as much as possible. All of us have a tiny opening in the medial (near the nose) edge of our upper and lower eyelids. These openings are called ‘puncti’. Our tears normally drain out from these puncti into tiny canals (which we call canaliculi – canals is too simple a word!) into a bag called the lacrimal sac and from there into the nose through another canal called the nasolacrimal duct. Also part of the watery component of the tears evaporates from the surface of the eye during waking hours.
By blocking the openings or ‘puncti’ with plugs, much like the blocking of the washbasin drainage with a rubber bung, we reduce the amount of the patient’s own tears going ‘down the drain’. Therefore more of the patient’s own tears are available to lubricate his/her eye, reducing the dependence on lubricant drops and ointments.
Q.13. This sounds great! Why can we not use these in every case of ‘dry eye’?
A.13. In severe forms of dry eye, the quality of the patient’s own tears is lousy. Allowing the patient’s own tears (however small in quantity they may be) to remain in the eye for longer periods may prove to be detrimental –in simple English, it may do more harm than good. In not so simple English, what’s sauce for the goose is not sauce for the gander.
Q.14. In very severe dry eye, with the cornea totally opaque, and the patient virtually blind can something be done?
A.14. Yes, there is a device called a keratoprosthesis or artificial cornea. This can be inserted even in bone-dry eyes with opaque and vascularised corneas. The patient can get back useful vision. This is a major surgery, often done in 2 stages and done by less than a handful of eye surgeons in the country. (The author being one of them). It is a surgery of last resort and should be undertaken only after careful consideration of each individual case. (see chapter on keratoprosthesis)