THERAPEUTIC INSIGHTS

Artificial Tears and Sight

Does dry eye impact visual function?

Christine W. Sindt, O.D., Iowa City, Iowa

In treating dry eye, we are very mindful of the patient's quality-of-life. Within the last few years, clinicians and researchers have become increasingly aware that visual function loss (i.e. non-optimal dynamic visual abilities between blinks, as characterized by blurred vision, etc.) associated with dry eye can have substantial quality-of-life implications.

Patient complaints of blurred vision, difficulty performing eye-intensive tasks (e.g., reading, watching television, driving at night) and treatment-induced visual blur are prime examples of these effects.

In fact, recent research has shown that eye-intensive tasking can stress the compromised ocular surface conditions of a dry eye patient and contribute to long periods of ocular surface exposure between blinks, which further impacts visual function.^1,2 With increasing knowledge of the impact of this visual function deficit on daily life, researchers have begun to scrutinize the visual effects of dry eye treatment and have begun routinely using diagnostic tests capable of identifying visual decay.

Here, I discuss the tools currently available to assess visual function, the risk factors for visual function loss associated with dry eye and the visual effects of tear supplementation.

Visual function assessment

The tools used to assess visual function vary in their abilities to capture relevant alterations in visual function for dry eye patients. (See "Visual Function Toolbox") The first measure of visual function — visual acuity testing using standardized charts — demonstrates a good basic test, but it's limited in its ability to identify dry eye-associated decreased visual function because it's a static test.

Contrast sensitivity charts (e.g. Pelli-Robson) are geared toward capturing a slightly more sensitive measurement to dynamic changes in visual acuity by determining the level to which a patient is able to discern letters in decreasing contrast. But, these tests are also examples of static measures.³

Reading performance (e.g. reading standardized lists, menu reading, etc.) demonstrates a more sensitive measure of a patient's visual function by introducing the element of time. By measuring the length of time a patient takes to read a list of words (or alternatively the number of words a patient reads in a set amount of time), you can assess the changes in this rate at sequential visits.

Meanwhile, dynamic tests, such as the Inter-blink Interval Visual Acuity Decay (IVAD) test and the Functional Visual Acuity (FVA) measurement system, are likely the most sensitive to dynamic changes between blinks of tests available today.^1,4 Use of the rVAD test has demonstrated a significant difference in the visual acuity decay between blinks in non-dry eye patients and dry eye patients.¹ In addition, researchers have found that the FVA measurement system is effective in assessing dynamic visual acuity changes in dry eye and normal patients and in evaluating the outcome of punctum plug treatment of dry eye disease.⁵

Risk factors

Recent research has attempted to assess the relationships between visual tasking, visual function and potential treatment concerns in various populations susceptible to dry eye conditions.

For instance, reports of visual display use within the last two years demonstrate a significant association between dry eye syndrome and computer use (P <0.001), and="" increased="" prevalence="" of="" dry="" eye="" symptoms="" with="" increasing="" daily="" hours="" of="" computer="">^2,6

Also, a Japanese study found that female contact lens wearers were at risk of experiencing dry eye symptoms during visual display use (P <>⁶ Both of these studies demonstrate the interaction of visual display use and ocular discomfort associated with dry eye (e.g. burning, stinging, grittiness, foreign body sensation, tearing, ocular fatigue), suggesting that patients who frequently use computers, etc. may be at further risk for ocular surface damage. As a result, these patients may benefit from dry eye treatment and likely require a drug that doesn't limit their visual function capabilities.

Clinical experience has revealed relationships between age and ocular health deterioration, and researchers have confirmed the effects of age on visual function as well. One study demonstrated that individuals aged 90 or older performed 12 to18 times worse than young normals on glare tasks (e.g. vision in the presence of glare, glare recovery time, etc).⁷ Since increasing age is also a risk factor for dry eye, this study supports the need for a widespread use of visual function-based diagnostics.

Researchers have also found that reading performance decreases with age, suggesting that patients' dynamic functional visual acuities can differ with age, even if they demonstrate the same static visual acuity.⁷ These findings highlight the importance of functional visual acuity measurement and the need to incorporate visual function as a treatment consideration.

Visual effects of tear supplementation

An Alcon-sponsored study presented at this year's annual meeting of the Association for Research in Vision and Ophthalmology (ARVO) (Pro-gram#/Poster#: 4649/D893), demonstrated that an artificial tear containing PEG/PG 400/HP-guar extended the amount of time dry eye patients maintained visual acuity — within one line of best-corrected visual acuity (BCVA) — between blinks at 90 minutes post-instillation vs. baseline. The two-period crossover, controlled, randomized and double-masked study, which used the IVAD test, included 48 dry eye patients. (See “Additional Artificial Tear Research,” below.)

The IVAD test and results, as with the FVA measurement system, give you a sense of how long your patients may be able to maintain their BCVAs between blinks, prior to noticeable visual acuity decay.

Further research in larger sample sizes than the one in the ARVO study and with different treatments may help to elucidate relationships between artificial tears and dry eye-related visual function deficits, since dry eye patients can complain of blurring effects of treatment.

As illustrated here, a dry eye patient's quality of life isn't only contingent on symptom relief, but also on optimal visual function. Previous testing has illustrated that while the short-term effects of an artificial tear may cause decreased contrast sensitivity, long-term use may result in a lessening of this effect.⁸

To best address this, take the time to discuss symptomatology with your patients, and be especially mindful of responses regarding visual tasking or visual blurring. You want to strive to identify any visual function deficit that your dry eye patients experience and the effects of their treatments on these changes.

If a patient has increased dynamic changes between blinks (e.g. while on the computer) and experiences faster tear film break-up time (TFBUT) as a result, you should consider lengthening the time that the tear film remains intact between blinks. Options to do this include instructing the patient to consciously blink more frequently or prescribing artificial tears to lengthen TFBUT.⁸ Keep in mind that if a dry eye patient experiences visual function benefits as a result of artificial tear use, he may be more likely to continue tear usage, and, thus, experience further benefits of maintaining a hydrated ocular surface microenvironment. The benefit for you, the practitioner: improved patient loyalty and satisfaction. OM

1. Walker P, Ousler GW 3rd, Workman DA, et al. Visual function in normals compared to patients diagnosed with dry eye as measured by the inter-blink interval visual acuity decay (IVAD) test. Invest Ophthalmol Vis Sci. 2007; 48:E-abstract 422.
2. Miljavoni B, Dana R, Sullivan DA, Schaumberg DA. Impact of dry eye syndrome on vision-related quality of life. Am J Ophthalmol. 2007 Mar;143(3):409-15.
3. Pelli D. G., Robson J.G., & Wilkins, A.J. The design of a new letter chart measuring contrast sensitivity. Clin Vision Sci. 1988;2:187-99.
4. Kaido M, Dogru M, Ishida R, Tsubota K. Concept of functional visual acuity and its applications. Cornea. 2007 Oct;26(9 Suppl l):S29-35.
5. Ishida R, Kojima T, Dogru M, et al. The application of a new continuous functional visual acuity measurement system in dry eye syndromes. Am J Ophthalmol. 2005 Feb;139(2):253-8.
6. Uchino M, Schaumberg DA, Dogru M, et al. Prevalence of dry eye disease among Japanese visual display terminal users. Ophthalmology. 2008 Nov; 115(11):1982-8.
7. Brabyn J, Schneck M, Haegers-trom-Portnoy G, Lott L. The Smith-Kettlewell Institute (SKI) longitudinal study of vision function and its impact among the elderly: an overview. Optom Vis Sci. 2001 May;78(5):264-9.
8. Ridder WH 3rd, LaMotte J, Hall JQ Jr, et al. Contrast sensitivity and tear layer aberrometry in dry eye patients. Optom Vis Sci. 2009 Sep;86(9):E1059-68.
9. National Eye Institute Visual Functioning Questionnaire -25. (Interviewer Administered format) January 2000. www.nei.nih.gov/resources/visionfunction! vfq_ia.pdf. (Accessed 3 April 2009).
10. OSDIPAD. Restasis Website. www.restasisprofessional.com/documents/OSDI_PAD.pdf (Accessed 11 September 2009).

Dr. Sindt is currently an associate professor of clinical ophthalmology and director of the contact lens services at the University of Iowa Department of Ophthalmology and Visual Sciences and is vice chair for the AOA Cornea and Contact Lens Council. E-mail her at christinesindt@uiowa.edu.