Enhancement of text for the visually impaired.

Previous research has established the benefits of image enhancement by spatial filtering for face perception and motion video appreciation among elderly low-vision observers [Invest. Ophthalmol. Vis. Sci. 32, 2337 (1991); J. Opt. Soc. Am. A 11, 1929 (1994)]. It has also been reported that similar enhancement could increase reading speeds by a factor of 2-4 in the same population [cf. Ophthalmology 96, 115 (1989)]. In our experiments we sought to determine what benefit, if any, was derived from spatial filtering of text for low-vision readers. Results from this series of studies indicate that 66% of patients do increase their reading rate with enhancement, but this increase is small. Change in reading rate with spatial filtering ranged from a 100% decrement to a 125% improvement, with an average 13% improvement. Only 10 of 67 subjects increased their reading rates by 50% or more. The clinical information that we gathered does not allow us to predict accurately which patients will benefit from spatial filtering. On the basis of these findings we conclude that enhancement of text by spatial filtering does not substantially increase reading rates for most low-vision patients.