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A study of dark adaptation in ocular hypertensives using a two-filter method Patton, Danalee Goldthwaite

Abstract

Dark adaptation thresholds have been determined for a group of ocular hypertensives and a group of equivantly aged normal controls under two separate conditions of colored pre-adaptation and test. The method relies on the Purkinje shift to obtain two dark adaptation curves for each subject that cross when the initially favored long wavelength (yellow) curve is superceded by the shorter one (blue-green): under photopic conditions, the yellow and blue-green stimuli are equally efficient in stimulating the retina, as they are equated for brightness during pre-adaptation; as dark adaptation proceeds the blue-green and yellow thresholds display an early relation wherein yellow light has the lower thresholds; then the curves cross and blue-green light displays lower thresholds. Each curve is obtained separately with a pre-adaptation of 80 ft. lamberts for 5 minutes and a centrally fixated 11° test patch that matches the spectral composition of the pre-adaptation. A variety of variables are derived from threshold intensity measurements and they are analyzed for age effects, disease effects, and their interactions. Age and disease both depress blue-green and yellow cone sensitivity, delay cross-over time, and increase the total change in sensitivity over 13 minutes of dark adaptation. Interactions magnify differences. Color discrimination is found to be associated with dark adaptation thresholds, sometimes specifically as to the type of color defect and the colored dark adaptation curve showing losses. Intraocular pressure, macular sensitivity, and diastolic blood pressure are also significantly correlated with dark adaptation thresholds. Disease and age effects are elaborated in terms of changes in the ocular media, macular pigmentation changes, as well as deterioration of rod and cone processes. In addition, aging is seen to be complicated by peculiarities in the selection of the normal population. The associations demonstrated for clinical and color vision variables with dark adaptation thresholds suggest (1) that open angle glaucoma may be caused by deficient nutrition to the optic nerve head or to the retina itself, (2) that central rod and cone vision undergo changes very early in the course of the disease. A preliminary study using the two-filter method with well-established glaucoma confirms that similar, more pronounced losses in dark adaptation take place later in the disease's development.

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