Dry Eye Syndrome – A lot more than meets the eye
By Sasha L Radford, OD
You’d think that something with such a clear name as “Dry Eye Syndrome” would be pretty straightforward. The eyes are dry so let’s moisturize them. Simple, right? In fact, Dry Eye Syndrome (DES) has many inconsistencies and isn’t always easy to treat.
“How can my eyes be dry? They’re always watering!”
That’s only one of the odd things about DES. Many patients describe excessive watering of their eyes with or without other symptoms such as redness, burning, and foreign body sensation. They’re usually surprised when I tell them they actually have dry eyes and that’s why they’re watering so much. The watering is a reflex reaction. The eyes send a signal to the brain that they’re feeling dry, and the brain sends a signal to produce more tears. These are just watery tears, though – not the kind that lubricate the surface well – so it’s a vicious cycle of dryness and watering. More on lubricating tears to come.
Another peculiar thing happens during the eye exam – while checking the glasses prescription, my patient is seeing well and everything makes sense . . . then suddenly, she can’t read the same size letters on the chart that she did with the same lens a couple minutes ago!
Did her prescription really change that much while sitting here in my chair? Most likely not. I ask the patient if she’s remembering to blink during the testing and after a few blinks her vision clears to the level it was before. Dry Eye Syndrome is usually the culprit here. In fact, many patients with DES describe blurred or fluctuating vision throughout the day which isn’t correctable with glasses. When the eye’s surface isn’t smooth and well lubricated, vision won’t be optimal.
Something else that eye doctors must contend with is the variation in symptoms caused by DES. A patient can have significant symptoms of dryness, burning, and foreign body sensation, but when I look at the eyes the surface doesn’t appear to be very dry. Others will have significant dry patches on the cornea and conjunctiva but have absolutely no symptoms.
It’s not as obvious, but typically this difference in the actual appearance of the eye and the patient’s symptoms can be explained by the state of the corneal nerves. In early DES, the corneal nerves are still working well – the eye’s surface is quite sensitive to small amounts of dryness. However, in advanced DES (or other diseases that decrease corneal sensitivity, such as diabetes), the corneal nerves have long since been damaged so even a severely dry eye may feel normal to the patient.
The more we learn about DES, the more we learn that it is not always caused by a decrease in the amount of tears produced; rather, the tears that are present are of poor quality and evaporate too quickly. This is because your natural tears are actually made of three layers. There is a thin mucus layer, a thicker watery layer, and a thin oily layer. You must have the proper combination of these for your eyes to stay properly lubricated. The oily layer keeps tears from evaporating; in most cases of dry eye syndrome, it is the oily layer that is deficient, allowing the tears to evaporate and therefore causing dryness of the ocular surface.
Oil in the tears is produced by tiny glands at the eyelid margins and these glands can clog for a variety of reasons. For many people with DES, we must treat the lids as much if not more so than the surface of the eyes.
One more thing that hasn’t always been obvious about DES is that it is associated with significant inflammation of eyelids and the ocular surface. Many treatments for DES are targeted to treat inflammation, not just a decrease in the amount of tears that are produced.
There are a wide range of therapies for DES – over the counter lubricating eye drops, prescription eye drops, and even nutritional supplements and oral prescription medications. Some patients self-treat unsuccessfully because there are so many over the counter choices that can actually make DES worse. For such a seemingly inconsistent and complex disorder, treatment must be carefully tailored for each individual. What works for one person may not be effective for another. Your eye care provider is the best source of advice and treatment for what can be a frustrating experience.
Dr Radford cares for patients at Pontiac Family Eye Care and Fairbury Vision Center.