INFLUENCE OF IMAGE FREQUENCY OF CLOSED-CI RCUIT TELEVISION SYSTEMS (CCTV) ON READING COMFORT

Purpose: To compare reading speed and reading comfort between closed-c ircuit television systems (CCTVs) with different image refresh rates. Methods: Reading speed was measured with three CCTVs that only differe d in repeat frequency (50, 60 and 70 Hz) in 21 patients with age-relat ed macular degeneration and 10 controls. We compared reading speed mea sured in syllables per minute of 16 different reading templates with a bout 500 syllables each. Results: Reading speed was equal with all CCT Vs. Eighteen of 21 patients identified and disliked 50 Hz CCTVs becaus e the image quality was worse. An image quality of 70 Hz enabled patie nts to use positive contrast with the best reading speed. Conclusions: Although reading speed does not improve with increasing frequency, fl ickering of 50 Hz CCTVs is critical for low-vision patients. The prefe rence of low-vision patients for negative contrast image is more likel y due to flickering with a lower repeat rate and 70 Hz CCTVs may allow more comfortable reading in positive contrast.