Improving the legibility of prescription medication labels for older adults and adults with visual impairment

The Mars Letter Contrast Sensitivity Test (initially known as the Lighthouse Letter Contrast Sensitivity Test) is similar in design to the Pelli-Robson Test but may offer several advantages. This study evaluates the repeatability of the Mars test and its agreement with the Pelli-Robson test in normal and low-vision subjects. Fifty-four subjects were tested (age 22-86 years), including 20 normally sighted young adults, 17 normally sighted older adults, and 17 adults with low vision (20/16 to 20/250). Subjects were tested with both contrast sensitivity tests and with the ETDRS visual acuity chart. After a short break, subjects were retested with an alternate form of each contrast sensitivity test. The chart forms used (two Pelli-Robson and three Mars) and the order of testing were varied systematically. Testing was monocular with habitual correction and, for subjects over 40 years of age, included appropriate near add. Letter-by-letter scoring was used for both tests. Repeatability and agreement were assessed by determining the 95% limits of agreement (LoA): +/- 1.96 standard deviations of the differences between administrations or tests. The Mars test showed excellent agreement with the Pelli-Robson test, with 95% LoA of +/- 0.21 log units for all subjects. The Mars test was similarly repeatable (95% LoA = +/-0.20 log units) to the Pelli-Robson test (95% LoA = +/-0.20 log units) among all subjects. The new Mars Letter Contrast Sensitivity Test shows excellent agreement with the Pelli-Robson test and has similar repeatability. There are subtle differences in the actual contrast levels on different forms of the Mars test, and adjusting for these differences leads to superior repeatability of the Mars test. Thus, the Mars test may be a useful alternative to the Pelli-Robson test offering several advantages, including smaller size, improved durability, and ease of use.

The purpose of this study was to ascertain the prevalence and primary causes of visual impairment in a representative Canadian population. We reviewed a representative sample of patients who attended ophthalmologists' offices in a medium-sized Canadian city between 1996 and 2001 in order to estimate the prevalence of visual impairment. Demographic data, visual diagnoses, best-corrected visual acuities (BCVA), and visual field information were recorded. Visual status was categorized based on accepted World Health Organization (WHO) and North American criteria. Population data were obtained from the Canadian census. The prevalence of low vision and blindness in our population was 35.6 and 3.8 per 10 000 individuals, according to the WHO classification, and 71.2 and 23.6 per 10 000 individuals, using the North American definition. Among individuals with some vision loss (vision worse than 20/40), cataract and visual pathway disease were the most common causes, together accounting for 40% of visual impairment. Age-related macular degeneration and other retinal diseases were the next most common causes of vision loss. Diabetic retinopathy and glaucoma were less frequently encountered as causes of visual impairment. The overall prevalence of low vision and blindness in Canada are in keeping with data from large population-based studies from other developed nations. Cataract, visual pathway disease, and macular degeneration are the leading causes of visual impairment. These results are important for enhancing our understanding of the scope of vision health in Canada and may direct future health planning and cost-utilization research.