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Several lines of evidence indicate that traditional vision tests (e.g., visual acuity) do not adequately predict elderly individuals' complaints about their vision when they are engaged in common everyday activities. Reading letters on the doctor's eye chart is not, for example, a good predictor of one's ability to read everyday printed material (e.g., newspapers, prescription labels). In other words, there appears to be a discrepancy between how well an elderly individual sees in the doctor's office and how well that same individual sees when going about their everyday activities (i.e., outside of the doctor's office).

Former Lighthouse researcher, Dr. Kent Higgins, with the help of graduate students Rita Conway Ximenez (New York University) and Dan Patanella (Fordham University), undertook research designed to investigate this apparent failure of conventional vision tests to predict visual complaints that elderly individuals have in their everyday visual activities. The basic premise of the research is that the failure of conventional vision tests to predict everyday visual problems is due to a discrepancy between light levels typically used in the clinic and those typically encountered in the outside world. Specifically, most conventional tests used by the eye doctor are "standardized" in the sense that they use daytime levels designed to reveal the "best vision" of which an individual is capable. It is well-known that human visual capabilities decline selectively and rapidly as light level decreases from the daytime levels used in the doctor's office to those likely to be encountered in the home and while driving or riding in a car at twilight or nighttime. During the course of a normal day, the outdoor light level can vary by factors as great as 108 or 1010. Thus the overall objective of this research is to evaluate the contribution of average light level to the failure of conventional vision tests to predict visual problems experienced by the elderly in their everyday activities.

A pilot study began in the fall of 1995. In this pilot study, a battery of vision tests (visual acuity, visual fields, letter contrast sensitivity, and a steady-state glare sensitivity test) was administered to each of 17 elderly volunteers at two different average light levels. The first was similar to conventional clinical testing light levels; the second was 2 log units (100 times) lower and was similar to the level of outdoor illumination on a clear day about 30-40 minutes after sunset. This lower level also approximated the level of illumination when driving at night by automotive headlights. Preliminary results of the vision tests revealed significant losses in vision from the higher to the lower light level. Further, whereas there was little evidence of any visual loss due to glare when this test was administered at the higher light level, there were significant losses due to glare when the same test was administered at the lower light level.

Volunteers for this project were also administered the Activities of Daily Vision Scale (ADVS) questionnaire to assess subjective complaints about their everyday vision. This questionnaire was previously validated by other investigators for use with a specific population of elderly individuals (i.e., individuals scheduled for cataract surgery). Briefly, the questionnaire identifies 20 visual activities which are categorized into five subscales dealing with distance vision, near vision, glare disability, night driving and daytime driving. The objective was to determine the general utility of this questionnaire as an instrument for assessing self-reported visual problems; if the utility of the questionnaire was confirmed, then the results could be related to the results of the vision tests obtained at the different light levels. In this phase of the pilot research, over 300 young and elderly volunteers completed the questionnaire and preliminary statistical analyses confirmed the general utility of this instrument for assessing self-reported vision problems in the elderly.

Unfortunately, the number of elderly individuals that completed both the visual activities questionnaire and the vision tests at the two light levels was too small (N=17) to permit a definitive assessment of the relationship between the two measures. Nonetheless, the preliminary results were encouraging and were used in support of a grant application to the Department of Veterans Affairs. This application, which represented a collaborative effort between Dr. Higgins of Lighthouse International and Dr. Janis White of the Department of Veterans Affairs (East Orange, NJ), was funded for three years beginning in April of 1997.

This project incorporated four changes from the original pilot study. First, since there were two test sites, Lighthouse International and the VA Medical Center, some of the testing systems, such as that for testing disability glare, had to be duplicated so that equivalent test batteries were available at both sites. Second, the original ADVS questionnaire was replaced by a new and improved instrument, the National Eye Institute Visual Function Questionnaire. Third, the Smith-Kettlewell Institute Low Luminance (SKILL) Card was added to the test battery to provide an assessment of low-contrast, low-luminance visual acuity. Fourth, the commercially available glare test used in the pilot study was replaced by a more sensitive, specially designed system developed at Lighthouse International. The latter was a computerized test that provided estimates of losses in vision due not only to continuous glare sources but also to transient, brief-duration glare sources like the headlights of an oncoming vehicle at night.

Over the three-year period, testing was completed on 97 elderly volunteers and 20 young control subjects. Analyses of the data suggested a number of important trends. First, elderly individuals, when compared to younger individuals, appeared to experience greater losses in vision, when measured with conventional tests, as light level was reduced. Importantly, however, there were also marked variations from one elderly individual to the next. While some elderly individuals showed marked losses in vision as light levels were reduced, some showed relatively small losses that were generally more characteristic of much younger individuals. A critical question was whether variations in vision loss within the elderly sample provided important clues concerning the difficulties that some, but not all, elderly individuals have when performing their everyday visual tasks. A preliminary report of the effects of reduced light level on conventional vision tests was presented at the International Low Vision Conference, Vision '99 and at the Vision Science and Its Applications 2000 conference.

Second, results obtained with the specially constructed glare testing system also revealed two important trends. First, when exposed to continuous glare, older individuals tended to experience somewhat greater losses in visibility than did younger individuals. This may, in part, explain why older individuals complain about visibility problems when driving at night. It seems likely, however, that there may be another important reason underlying such complaints. More specifically, our results indicated that when the glare source was transient (e.g., when it simulated the headlights of an approaching vehicle), the visibility losses in the elderly were more complex than was previously thought. Specifically, previous research suggested that the visibility losses associated with the initial onset of a glare source were smaller in elderly when compared to younger individuals. Results of our research, in contrast, indicated that the visibility loss in the elderly was as great, and possibly greater, than that in the younger subjects. Moreover, elderly individuals evidenced a markedly slower time course in the recovery of sensitivity following the initial onset of a glare source when compared to younger individuals. In other words, the headlights of an approaching vehicle would be expected to produce a more prolonged period of vision loss in an older individual than in a younger individual. At present, it is unclear whether older individuals evidence a delay in the recovery of sensitivity following the offset of a brief duration glare source. Preliminary reports summarizing our findings obtained with the glare testing system have been presented at a number of scientific conferences, including the Association for Research in Vision and Ophthalmology (1998, 2003, 2004), the Fourth International Lighting Research Symposium: Vision at Low Light Levels (1999), Vision Science and Its Applications (1999), Vision '99 (1999), the Conference on Aging Retina and Early Degeneration (2001), the American Academy of Optometry (2001, 2004), the International Conference on Low Vision (2002), the international Eye and The Auto conference (2003), and the National Highway Safety Administration's Workshop on Headlamp Safety Metrics: Balancing Visibility and Glare (2004).

Dr. Higgins and his collaborators also concluded a three-year study of transient glare adaptation and recovery. This study is funded by a three-year grant from the Department of Veterans Affairs. For this research, Dr. Higgins and his collaborators constructed a new optical system, one that permits a more precise determination of possible differences in the time course of transient glare adaptation in young and elderly individuals. Such differences, if they are large, have important implications for the design of environmental lighting systems. For example, existing American National Standards Institutes (ANSI) guidelines used by illuminating engineers in, for example, in the design of tunnel lighting systems, incorporate a transient adaptation factor that is intended to make allowance for visibility losses that accompany large, abrupt changes in light level. Unfortunately, virtually all of the test subjects used to derive this factor were under the age of 40 years. In effect, the guidelines are based on the assumption the magnitude of vision loss due to transient change in light level is the same in young and elderly individuals. In contrast, our research suggests that a transient adaptation factor based on younger individuals may underestimate the visibility loss experienced by older individuals. It would also suggest that elderly individuals' complaints about oncoming headlights when driving at night are justified.

Further Reading

Higgins, K. E., & Bailey, I. (2000). Vision disorders and the performance of specific tasks requiring vision. In B. Silverstone, M. A. Lange, B. Rosenthal, & E. Faye (Eds.), The Lighthouse handbook on vision impairment and vision rehabilitation: Vol. I. Vision impairment (pp. 287-315). New York: Oxford University Press.

Higgins, K. E., Jaffe, M. J., Coletta, N. J., Caruso, R. C., & de Monasterio, F. M. (1997). Spatial contrast sensitivity: Effects of age, test-retest, and psychophysical method. In D. Yager (Ed.), Noninvasive assessment of the visual system (pp. 2-9). Washington, DC: Optical Society of America.

Higgins, K. E., & White, J. M. (1999). Transient adaptation at low light levels: Effects of age. In Proceedings-Vision at Low Light Levels: EPRI/LRO Fourth International Lighting Research Symposium(pp. 173-185). EPRI, Palo Alto, CA; Consolidated Edison Co. of New York, Bronx, NY; and Osram-Sylvania Products, Inc., Danvers, MA: TR-110738.

Higgins, K. E., White, J. M., Asami, R., & Liu, L. (1999). Effect of age on thresholds measured against transient backgrounds: A methodological caveat. Vision science and its applications, OSA technical digest series (pp. 96-99). Washington, DC: Optical Society of America.

Higgins, K. E., White, J. M., Asami, R., Liu, L., Arditi, A., & Rosenthal, B. (1998). Effect of age on the response to transient vs. steady-state peripheral glare. Investigative Ophthalmology & Visual Science, 39 (4), S1091.

Higgins, K. E., White, J. M., Asami, R., Liu, L., & Rosenthal, B. (2000). Changes in vision test performance: Effect of age and luminance level. Vision sciences and its applications OSA technical digest series (pp. 89-91). Washington, DC: Optical Society of America.

Rinalducci, E. J., Higgins, K. E., Zavod, M., & Sadkowski W., (1999). Physiological and Psychological Basis of Mesopic Vision. Proceedings-Vision at Low Light Levels: EPRI/LRO Fourth international Lighting Research Symposium (pp. 13-24) EPRI, Palo Alto, CA; Consolidated Edison Co. of New York, Bronx, NY; and Osram-Sylvania Products, Inc., Danvers, MA: TR-110738.

 

 

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