The impact of light source on discrimination ability in subjects with age-related macular degeneration

To examine the influence of light source on letter contrast sensitivity in subjects with age-related macular degeneration (AMD).

Halogen incandescent bulbs and low-energy fluorescent tubes were tested with 70 subjects with AMD. The subjects' contrast sensitivity was determined in a randomized single-blind crossover study for each light source using photopically illuminated Pelli Robson contrast sensitivity charts. The test subjects' subjective light source preference was also determined.

The mean contrast sensitivity for the incandescent light source was 1.28 ± 0.29 (mean ± SD), and for the fluorescent light source 1.17 ± 0.29, p < 0.001. The illuminance was 338 lux (± 9) for the incandescent light, and 339 lux (± 11) for the fluorescent light. Forty-nine subjects preferred the incandescent light source, while none preferred the fluorescent light source for maximum detail and clarity. Nineteen had no preference. This finding is statistically significant. Fifteen of the 19 subjects without a preference had no difference in contrast sensitivity, which supports their lack of preference. There was no significant difference with regard to sex or order of exposure to light source. Subjects with AMD had significantly reduced contrast sensitivity compared with expected normal values. We found no relationship between visual acuity and contrast sensitivity.

We are only able to recommend photopic full spectral radiance incandescent light sources to visually impaired subjects for their domestic surroundings. Furthermore, we recommend the use of full spectral radiance light sources for the illumination of Pelli-Robson contrast sensitivity charts. Given equal illuminance, as in our study, the findings show that contrast sensitivity was better by illumination with incandescent light with full spectral radiance compared with fluorescent light with interrupted spectral radiance.