Why dry eyes?

“LET us conduct a simple experiment,” I told members of the United for Vision club. “Why?” asked Segun. “Have you forgotten you planned to give us a lecture on Dry Eyes today?” “I never told you I was going to give you a lecture. I said we were going to discuss the problem of dry eyes and the experiment is to set the stage for this discussion,” I replied.

“Bring out three clean and dry plates. In the first two plates (A & B) gently rub a thin film of starch. Pour 5ml of water in each of the three plates. Do you notice that the water spreads evenly in plates A and B but forms droplets in plate C? In plate A put three drops of oil on the water. Do not add anything to the water in plates B and C. Then place the plates out in the blazing sun. Now let us go inside and watch the news if PHCN will permit! We will come out after the news to see the outcome of our experiment.”

Members of the United for Vision club were surprised that the water in plates B and C had disappeared by the time we came back in about 20minutes later. “What happened to the water in these two plates?” I asked them. John was quick to reply that the water had evaporated. “Why didn’t the water in plate A evaporate?” There was a spontaneous echo from all members present: “The oil prevented the evaporation!”

“Shall we now apply the knowledge gained from this experiment to the eye? Tears are secreted to lubricate the surface of the cornea and ensure clarity of vision. Tears consist of three components – the superficial oily layer which prevents evaporation; the middle layer of tear fluid proper and the deep mucous layer (like starch) which ensures that the tear fluid is evenly spread over the cornea instead of forming droplets. All three components are secreted by different glands in the lids and conjunctiva. Can you guess what would happen if any of the components is deficient?”

“Yes sir” replied Oju. “If the oily layer is deficient, tears dry up quickly and the cornea becomes dry; if the deep mucous layer is deficient, the tear fluid would not spread evenly. I notice that in plate B, the dryness is peculiar. It appears scaly. Is that what would happen to the surface of the cornea?” “No”, I said. “Starch is not the best example of the mucous layer but I couldn’t think of anything closer. When the water dries up, the mucous will roll up into threads and the surface of the cornea will become dry and uneven.

“A deficiency of tears either in quantity or quality leads to dry eyes and may cause itching and redness. The sufferer may also feel some pain, light sensitivity, gritty sensation and a feeling of having a foreign body or sand in the eye. Occasionally, a person with dry eyes may have paradoxically, watering of the eye and this could be confusing. This happens because the eye isn’t getting enough lubrication so it sends a distress signal through the nervous system for more lubrication. In response, the eye is flooded with “watery” tears to compensate for the underlying dryness. However, these tears do not have the lubricating qualities or the rich composition of normal tears. They will wash debris away, but will not coat the eye surface properly.

“What causes dry eyes?” asked Dele. “In addition to imbalance in the tear-flow system of the eye, the drying out of the tear film can be due to dry air created by air conditioning, heat, or other environmental conditions. Dry eyes can also occur as part of natural ageing process, menopause and side effects of some medications such as antihistamines and birth control pills. Diseases such as rheumatoid arthritis and collagen vascular diseases can also cause dry eyes. Structural problems with the eyes that don’t allow them to close properly can also be implicated in dry eyes”.

“How are dry eyes treated?” asked Oju. “Dry eyes cannot be cured but a number of steps can be taken to treat them and prevent serious complications. You should discuss treatment options with your ophthalmologist.