Influence of image frequency of closed-circuit television systems (CCTV) on reading comfort

Purpose: To compare reading speed and reading comfort between closed-circuit television systems (CCTVs) with different image refresh rates. Methods: Reading speed was measured with three CCTVs that only differed in repeat frequency (50, 60 and 70 Hz) in 21 patients with age-related macular degeneration and 10 controls. We compared reading speed measured in syllables per minute of 16 different reading templates with about 500 syllables each. Results: Reading speed was equal with all CCTVs. Eighteen of 21 patients identified and disliked 50 Hz CCTVs because the image quality was worse. An image quality of 70 Hz enabled patients to use positive contrast with the best reading speed. Conclusions: Although reading speed does not improve with increasing frequency, flickering of 50 Hz CCTVs is critical for low-vision patients. The preference of low-vision patients for negative contrast image is more likely due to flickering with a lower repeat rate and 70 Hz CCTVs may allow more comfortable reading in positive contrast.