Vision and Dry Eye
BY ERIC PAPAS, PHD, MCOPTOM, DIPCL, FAAO
Over 20 years ago, an Austrian ophthalmologist named Reiger suggested that the disruption of the tear film suffered by dry eyed patients may have consequences for vision and demonstrated that visual acuity did indeed improve five minutes after treating such eyes with a tear replacement drop (Reiger, 1992). The measured advantage was rather small, however, being less than three letters on average, prompting the response from one rather underwhelmed commentator at the time that “the results do not necessarily mean large numbers of dry-eyed drivers are putting themselves and others at risk by failing to use lubricating eye drops” (Lancet, 1992).
Ten years later, a different group comparing non-Sjögren’s syndrome dry eyed subjects with normal controls found differences in visual acuity that were also rather inconsequential, but went on to report alarmingly large disparities in what they called functional visual acuity (Yagi et al, 2002). This measure was taken after participants had avoided blinking for 10 to 20 seconds. Although facilitated by instilling a topical anesthetic, this finding was put forward as representing the sort of vision that would be experienced during common daily tasks such as reading, driving, or using a computer.
Soon afterward, this same group followed up by reporting markedly better functional visual acuity in a small sample of dry eyed patients who had undergone punctal plugging compared to those who were untreated. Again, the difference in traditional visual acuity was small and of no practical significance (Lovie-Kitchin and Brown, 2000).
Results like these leave us with two important impressions. The first is that conventional visual acuity is not a particularly sensitive or useful method for picking up differences between those who have dry eye and unaffected normals. As most of you have encountered cataract patients who read right down the chart in the consulting room while complaining bitterly of unacceptable vision in other situations, this will be a familiar phenomenon.
The second factor is that treating dry eye may offer visual benefits in addition to providing relief from the symptoms of dryness.
Implications of the Data
One response to these realizations was to look for alternative methods of assessing visual function and its effect on the well being or quality of life of those affected. The tools typically utilized were questionnaires. Although these take longer to administer compared to visual acuity testing, when properly designed and validated they have a multidimensional quality that permits enquiry into a range of lifestyle situations simultaneously.
Use of similar methods quickly revealed that individuals clinically diagnosed with dry eye syndrome reported significantly more problems compared to normal across several aspects of their visual activity.
For example, a study conducted in a group of menopausal women and older men (average ages 57 and 71, respectively) found that reading, carrying out professional work, and computer use all provoked complaints over three times more often by those who had dry eye than those who did not. Other problematic activities included watching television and driving during the day or at night, which were more than twice as bothersome (Miljanovic et al, 2007).
Similar studies began to build a body of evidence suggesting the importance of vision as a factor in dry eye disease. Consequently, it was reasonable that when the 2007 International Dry Eye Workshop (DEWS) produced a definition for that condition, they incorporated visual disturbance within it (Lemp et al, 2007).
In the six years since then, new data have continued to vindicate that decision. For example, one recent large study conducted among a Malay population in Singapore found that symptomatic dry eye was significantly associated with difficulty in everyday activities involving vision including navigating stairs, recognizing friends, reading road signs or newspapers, watching television, cooking, and driving at night (Tong et al, 2010).
In a similar vein, a survey of a population attending a Shanghai (China) hospital revealed that dry eye patients had reduced vision-related quality of life compared to their non-dry eyed counterparts (Gong et al, 2012). Those affected reported problems that not only impacted short- and long-distance vision (including driving), but had implications for their general health as well.
Furthermore, visual issues associated with dry eye interfered with other aspects of peoples’ lives such as the way in which they conduct social interactions and the ability to fulfill their roles within their community, workplace, or family.
Even subjects’ self-perceptions of their mental health state were adversely affected—a finding that has been corroborated in a second Shanghai study, this time conducted in a general community rather than in a hospital sample (Le et al, 2012).
While both of these efforts have relatively small sample sizes (and the first one is perhaps biased because the age of the control group was higher compared to the dry eyed cohort), they provide a suggestion of the extent of the consequences of dry eye-related vision disturbance and how profound the benefits of effective treatment can be.
Other Metrics for Evaluation
Other metrics can be helpful in assessing patients with such problems. As the post-blink period was understood to be active in tear film behavior, investigators began to wonder whether visual acuity or perhaps the ocular wavefront aberrations might actually be seen to fluctuate if they could be measured rapidly and often.
Continuous estimates of visual acuity over several minutes can in fact be achieved by repeatedly presenting a tumbling E on a monitor screen and using a psychophysical staircase approach to extract the response. Likewise, dynamic aberrometers can continuously record up to seven aberration orders at an acquisition rate of about once per second.
Use of these methods has shown that while the change over time for both attributes is very idiosyncratic, there is generally more fluctuation between the blinks of dry eyed subjects. Another intriguing observation concluded that some people in this group apparently subconsciously modify their blink rates to eliminate the largest variations, presumably in an effort to optimize vision (Wang et al, 2009).
Quality of Life
More recent work has attempted to directly link vision-related quality of life metrics with the optical characteristics of the eye (Denoyer et al, 2012). The experimental approach taken was to first administer a quality of life questionnaire specifically targeted at vision—in this case the Ocular Surface Disease Index (OSDI) was chosen. Subjects then had the aberrations of their eyes measured dynamically during a period of 10 seconds, during which time they were instructed to not blink. While no significant relationships were found between the OSDI scores and any of the individual aberrations measured (third to sixth orders), when the researchers considered the rate at which the higher-order aberrations increased during a 10-second period of non-blinking, a moderate correlation emerged: those who had more visual problems tended to have faster changing aberrations between blinks.
The suggestion from these studies is that at least in part, short-term changes occurring in the less-than-ideal tear films of many dry eyed subjects are responsible for initiating the visual disturbances that they experience as an integral part of their condition. Treatment strategies that can normalize the tear film and thus reduce or eliminate fluctuations on a suitable time scale would therefore seem to make sense. Evidently, Dr. Reiger knew that thought all along! CLS
Acknowledgement: Thanks to Dr. Cecille Maissa for her helpful suggestion at the genesis of this article.
For references, please visit www.clspectrum.com/references.asp and click on document #212.
Associate Professor Papas is executive director of Research & Development, Brien Holden Vision Institute and Vision Cooperative Research Centre, and senior visiting fellow, School of Optometry & Vision Science, University of New South Wales, Sydney, Australia. The Brien Holden Vision Institute and Vision Cooperative Research Centre have received research funds from B+L, AMO, and Allergan and have proprietary interest in products from Alcon, CooperVision, and Carl Zeiss. You can reach him at firstname.lastname@example.org.