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Abstract
Twenty-five patients were examined by means of several tests of visual function to determine tests best suited for early diagnosis, for evaluation of progression, and for analysis of visual capabilities. Nine patients were tested two or more times during intervals ranging from one to 34 years. In the incipient stage cone function is usually normal. Measures of the light threshold of the dark-adapted eye in a number of locations from center to periphery of the retina detect localized areas of deficient rod vision. At a later stage conventional perimetric examination of the light-adapted eye detects areas in which both cone and rod function are impaired. At a far-advanced stage the field is reduced to a small patch and visual acuity is significantly reduced. Quantitative tests of ability to read continuous text determine whether or not ordinary print can be read with ease and, if not, whether magnification can provide useful reading vision. The rate at which visual function is lost varies markedly even among members of the same family.