discovering dry eye
What Do Dry Eye Patients Feel?
BY BARBARA CAFFERY, OD, MS
As clinicians, we are aware of the weak association between the symptoms and signs of dry eye. We have all seen patients with severe corneal and conjunctival staining who have little ocular discomfort and those with severe symptoms who show few signs of staining
discomfort, and those with severe symptoms who show few signs of staining. Our dry eye study group decided to ask both healthy and dry eye patients what symptoms they have, how severe the symptoms are and when they feel them the most.
How Does it Feel?
At six optometric sites in North America, random patients voluntarily filled out questionnaires for either non-lens-wearing (DEQ) or contact-lens-wearing (CLDEQ) patients. Both included categorical scales to measure the prevalence, frequency, diurnal variation and intrusiveness of common ocular symptoms. Over 1,000 subjects completed the dry eye questionnaire, with 65 percent filling out the DEQ and 35 percent filling out the CLDEQ.
In the total population, discomfort was the most commonly reported and the most intense symptom. The contact lens wearers reported more frequent ocular discomfort, dryness, visual changes, soreness and irritation. The non-lens wearers reported more burning and stinging, light sensitivity and itching. All symptoms except light sensitivity grew more intense later in the day.
These results give us a wealth of information. It appears that the ocular surface can produce many distinct feelings. We have yet to determine what combination of events produces each one of these. Clinical wisdom suggests that itching is the earliest and lowest form of discomfort. Our results suggest that discomfort is more prevalent than itching and may be a unique sensation.
Lens Wearers vs. Non-Lens Wearers
Patients who wear contact lenses experience different sensations than those who do not. Lens wearers report more discomfort, dryness and irritation while the non-lens wearers experienced more burning, stinging and itching. Does the blanket coverage of the hydrogel lens mask the corneal nerve sensations and cause the conjunctival nerve endings to send the majority of the information? Does this produce the sensation of discomfort rather than stinging and burning? Hydrogel lens wearers can cut onions for far longer than non-lens wearers without experiencing the burning that occurs when oil from the onion contaminates the tear film. Perhaps a similar mechanism applied to everyday air waves and pollution explains the different symptoms in these two groups.
Where Do We Go from Here?
Research must be done to further understand the mechanism of sensations occurring on the ocular surface. Which nerves in which combination produce which symptoms? What does a contact lens do to change these symptoms? What tear film abnormalities produce nerve firing on the ocular surface? What combination of cell desquamation, thinned tear film, inflammatory factors in the tear film or ocular surface structures are necessary to create each sensation? How much does the observation of corneal and conjunctival staining relate to dry eye disease and the symptoms experienced by these patients?
While these issues are being resolved we must carry on as clinicians in the diagnosis and management of dry eye disease. The discomfort and interference with visual tasks experienced by our patients is far greater than we may believe. Our job is to listen to patient symptoms, recognize the limitations in understanding their mechanisms, observe the ocular surface, analyze the tear film and manage their cases in the best manner that we can.
Dr. Caffery has practiced optometry in Toronto, Canada, in a group setting dedicated to contact lens and tear film research since 1977.