How Important Is Water to Dry Eye?
Here's what research tells us about water, computers and arid climates.
Kelly Nichols, O.D., M.P.H., Ph.D.
At a recent lecture, an optometrist asked me, “Why don't lecturers ever mention hydration in their dry eye talks?” She asked the right question. We talk to patients about diagnostic tests and prescription therapeutic options, but are life-style changes left unspoken? We often recommend the use of a humidifier in the bedroom, especially in cold climates, and the use of air conditioners continuously in warmer climates where it is humid outside but not inside. We also discuss the positioning of computer monitors, airplane travel and arid environments.
What I cannot say is that I discuss hydration. Should I? Should we? And for that matter, how specifically should we discuss air travel, computers and arid environments?
For many of us, the morning starts with a favorite cup o' joe, black, espresso or grande skinny vanilla latte (ok, only when traveling). Then, a diet cola may suffice as the liquid for lunch, and then for dinner perhaps water or wine, depending on the day. Then there are those who carry a water bottle 24/7. Do these hydrating counterparts have less dry eye? Do those non-hydrating individuals, especially in a dry environment, like an airplane, have more dry eye?
Drink 64 oz. daily … really?
Surprisingly (or not), scientists claim that we all walk around under-hydrated with bodies comprised of anywhere from 45%-to-75% water, depending on the source and measurement technique. Some hypothesize that the obese have a lower hydration level. So we may well ask, could a drop in hydration be meaningful to our cells, and could this impact ocular surface status?
We've all heard of the recommended water intake, eight 8-ounce glasses per day. However, reviews of the scientific literature on the topic performed in 2002 and 2008 did not reveal any solid scientific evidence that supported this recommended intake. I can easily say I do not achieve that level every day. I'll wager (I can do that, being Nevada born) that most busy adults also do not drink the recommended volume of water.
But if we did drink more water, would it help our eyes? Surprisingly, that information would be difficult to collect, and it is clearly missing from the literature. Why?
► Water intake data rely on the valid report of patients, and it is data often not collected in studies, particularly in eye-related studies.
► Water drinkers likely have other habits that could be beneficial to overall health. For example, imagine someone who runs four miles daily, drinks water throughout the day, eats healthy foods, takes supplements, including fish oil, and tries to avoid caffeine and alcohol. We don't know if this individual is more or less likely to have dry eye. (What if this same individual was going through menopause and takes frequent flights to Australia?)
Thus, water intake data is probably confounded by other patient characteristics and habits.
Turning to environment, all of us have been on a plane in which the circulated air is low in humidity, often cool or cold, and forced through vents, and thus, drafty. This environment is often regarded as hostile to the ocular surface and can, therefore, precipitate dry eye symptoms. (After an hour or so on a plane, my contact lenses are irritating and feel like there is a layer of something on top of them, making me blink more frequently.)
Several reports have examined the effects of airplane environments on the ocular surface. A 2007 study, for instance, showed overall evaporation rates of 99.72% across all study subjects, (normal, dry eye and meibomian gland disfunction) when exposed to relatively low humidity conditions (20% to 25%), as experienced in airplane cabins during flight. (See www.ncbi.nlm.nih.gov/pubmed/17630623.) This indicates that all eyes exposed to an environment, such as that in an airplane, could “dry.” So why do only some people experience symptoms?
In a survey of more than 1,200 Australian pilots, symptoms of dry eye during flight were reported by 72.3%, while only 5.4% reported dry eye independent of flight. (See www.ncbi.nlm.nih.gov/pubmed/10 981789.) Further analyses revealed age, use of distance glasses, smoking, average weekly number of flight hours, type of aircraft usually flown and normal cruising altitude were associated with the dry eye symptoms. However, in multiple regression analyses, only large jets vs. propeller-driven planes and a higher number of flight hours demonstrated a higher risk of dry eye symptoms.
The authors concluded that self-reported symptoms of dry eye are common in pilots and are associated with type of plane and flying time. Therefore, a translation of this finding would be that longer exposure to arid, forced air environments could result in dry eye, even in those patients who do not experience dry eye in a “normal” environment.
Our day-to-day environment
If the amount of exposure time plays a role in symptoms, our daily ritual of staring at the computer monitor in a forced-air-ventilated and low-to-moderate humidity environment could result in dry eye symptoms. And if you follow the Australian pilot data, dry eye could occur even in those previously asymptomatic patients who are not using a computer. One study revealed a number of environmental (relative humidity, temperature, draft), occupational (e.g. visual display unit work) and individual (e.g. gender, use of cosmetics, and medication) risk factors were reported as associated with alteration of the precorneal tear film (PTF) and symptoms of eye irritation. (See www.sciencedirect.com/science/article/pii/S0160412008000676). The authors surmise that low relative humidity (<40%) and work with visual display units may destabilize the PTF by lower eye blink frequency and greater ocular surface exposure.
I would argue that most clinicians find the airplane data and the office environment/computer use hypotheses straightforward and routinely accepted. What is less apparent is the extent to which these issues are discussed with patients. Take, for example, the “frequent flier.” Can you recall the last time you asked about his/her frequency of air travel in your patient history?
Top 10 dry eye talking points for doctors and staff
From this research, we can revise our discussion with patients to include the following issues:
► gender-based screening (for females, ask about dry eye symptoms)
► age-based screening (> age 40, ask about dry eye symptoms)
► systemic “drying” medications (e.g. antihistamines, isotrexin)
► previous artificial tear and other treatment successes/failures
► previous dry eye diagnosis (if present, year of diagnosis)
► frequency of air travel
► home and workplace humidity levels
► daily duration of computer use
► daily duration of tablet computer and/or e-reader use
► airflow (vent placement/direction) at workplace, home or in auto
A final word about water
Medline searches for “dry eye ” and “water,” “dehydration“ or “hydration” yield zero publications about water intake or overall hydration and dry eye. Having said that, what if it did help? Consider an office promotion of a re-usable water bottle with your practice name and a dry eye/good health/go green message. Thirsty yet? OM
DR. NICHOLS IS FERV PROFESSOR (FOUNDATION FOR EDUCATION AND RESEARCH IN VISION), AT THE UNIVERSITY OF HOUSTON COLLEGE OF OPTOMETRY. SHE LECTURES AND WRITES EXTENSIVELY ON OCULAR SURFACE DISEASE AND HAS INDUSTRY AND NIH FUNDING TO STUDY DRY EYE. SHE IS ON THE GOVERNING BOARDS OF THE TEAR FILM AND OCULAR SURFACE SOCIETY AND THE OCULAR SURFACE SOCIETY OF OPTOMETRY AND IS A PAID CONSULTANT TO ALCON, ALLERGAN, INSPIRE AND PFIZER. DR. NICHOLS CAN BE CONTACTED AT KNICHOLS@OPTOMETRY.UH.EDU. TO COMMENT ON THIS ARTICLE, E-MAIL OPTOMETRICMANAGEMENT@GMAIL.COM.