Study Reveals Relationship Between Allergic Conjunctivitis Risk, Sudden Change In Temperature
Healio (7/13, Cimberle) reports, “A retrospective study” evaluating “the effect of temperature change on allergic conjunctivitis for patient visits at all U.S. Veterans Affairs clinic from January 2010 to December 2013” revealed “a statistically significant relationship between allergic conjunctivitis risk and sudden change in temperature, which can be compounded with a decline in humidity.” The findings were presented at an association meeting.
This study, as noted below, looked at why, when temperature changes occur, do we see increased itchy, red, irritated eyes. Let me give you some background.
The human eye is a remarkable engineering marvel. We blink at an average rate of roughly every 3-5 seconds—meaning about 15 blinks per minute. Doing the math, this runs to between 14,000-17,000 blinks a day. As long as your eyelids are gliding on a layer of tears, this process is largely frictionless. Further, we have the lacrimal gland that secretes the majority of your tears located over the temporal, outermost region of your eye, producing tears at the rate of between 3 and 4 microliters per hour. Towards the nasal region of your eye are located the upper and lower tear drainage ducts, which empties tears into your nasal sinuses. As your tears drain, it draws your tear film across the eye—in essence, creating a ‘streaming current’ of tears flowing across the surface of your eyes. Any pollens, dust, or other tear film debris is brought across the eyes’ surface and dropped into your sinuses, effectively protecting and maintaining the optical clarity of your eye.
Dry eye and ocular (eye) allergies are closely related. Both are mild inflammatory response mechanisms. When humidity drops, your tears can begin to evaporate. Now, when you are blinking, the lid gently rubs against the surface of your eye (called the cornea). After a while, this rubbing begins to trigger inflammation —redness, itching, burning, along with the eye’s attempt to resolve this irritation through increased tearing. At the same time, evaporation can disrupt the flowing of your tears into the sinuses. Now, instead of washing out the pollens and dust, they stagnate in the eye, irritating the eye and eyelids.
Mast cells are part of your immune system. Their primary responsibility is to act as an early warning system to alert your immune system of an imminent attack. We have approximately one million mast cells around each eye! One of the signaling chemicals these mast cells release is histamine. What do we take for allergies? Antihistamines!
So, if your tear film is adequately thick, not evaporating too quickly, and maintaining the flow across the eye— you are symptom-free! Throw in evaporation, and suddenly allergies and /or dry eye show up! The study below documents this link. Decrease humidity, and suddenly patients go from asymptomatic or mildly symptomatic to full-blown symptoms!
What can we do?
We have a host of treatments—from glasses with protective cupping behind the frame to reduce evaporation to prescription and non-Rx drops. We also have treatments that effectively combat evaporation by increasing the lipid layer of your tear film. I will discuss these in a future article.
Randall Fuerst, OD FAAO
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