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two dark adaptation curves for each subject that cross when the initially favored long wavelength (yellow) curve is superceded by the shorter one (blue-green): under photopic conditions, the yellow and blue-green stimuli are equally efficient in stimulating the retina, as they are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. / Arts, Faculty of / Psychology, Department of / Graduate

The human vestibulo-ocular reflex (VOR) is known to undergo major plastic modification in coping with sensory conflict brought about by optical reversing prisms. The first phase of this study proposes a simple model to account for this modifiability in terms of known neurophysiology. To study the phenomenon further two series of experiments were conducted on long-term vision-reversed cats. For this a new computer technique was developed to analyse oculomotor responses. The first series studied the time course and amplitude dependence of adaptation; the second, the frequency response of the fully adapted system. The adaptive process exhibited strict limitations, the functional effectiveness of which is quantitatively defined. The findings as a whole suggest that adaptive mechanisms other than the VOR are at play and that far more complex interactions exist between vestibulo- and visual-motor mechanisms than originally envisaged.

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The purpose of the study is to determine the dark adaptation of second grade children in Denton, Texas.

The present study is part of a long time cooperative study of the Education and Home Economics Departments of North Texas State Teachers College begun in 1940. The purpose is to compare the dark adaptations of second and third grade children made in 1940 with those made in 1941, and to determine also the dark adaptation of a group of fifth and sixth grade children receiving vitamin A concentrate.

It is the purpose of the study to determine if the addition of Vita Yam as a source of vitamin A to the daily diet improves the dark adaptation of college-age students.

This study is the result of tests conducted to determine the adaptability of the human eye to darkness.

The present study is a part of a long-time cooperative study of the Home Economics Department of the North Texas State Teachers College, begun in 1940. The purpose is to compare the dark adaptations of second and third-grade children made in 1940 with those made of the same children in 1941 and in 1942. Also included in this study is the comparison of a group of freshmen college men made in 1940 with a group of twenty-five men made in 1942. An attempt is also made to determine whether an individual has higher dark adaptation on sunshiny days than on cloudy days.