Thesis (M.S.)--New England College of Optometry, 2007. / Includes bibliographical references (p. 49-53).

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two dark adaptation curves for each subject that cross when the initially favored long wavelength (yellow) curve is superceded by the shorter one (blue-green): under photopic conditions, the yellow and blue-green stimuli are equally efficient in stimulating the retina, as they are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 degree to which the normal eye can adapt to the dark is related to or dependent upon the eye's ability to regenerate visual purple. The relationship of vitamin A to the visual cycle has caused much development in improved methods of detecting vitamin A deficiency. For the most part these methods have been applied to adults and school age children. This study seeks to analyze this method as applied to pre-school age children.

Vision requires the photoreceptors in the eye to rapidly respond to changes in light intensity. These processes are accomplished within rod photoreceptors by the visual pigment rhodopsin that initiates a downstream signaling cascade called phototransduction. Rhodopsin is composed of an apoprotein opsin that is covalently bonded with light sensitive 11-cis retinal. Rhodopsin is activated when 11-cis retinal is photoisomerized into all-trans retinal. This isomerization initiates the phototransduction cascade that culminates in a change in current at the plasma membrane. Rhodopsin, once activated ("bleached"), can no longer absorb photons to activate phototransduction, and must be regenerated through the visual cycle. To enable the photoreceptors to respond to rapid changes in light intensities, phototransduction must terminate in a timely manner. Deactivation involves phosphorylation of activated rhodopsin by rhodopsin kinase, and then binding of visual arrestin. Exposing rods to daylight bleaches a large proportion of rhodopsin molecules. This exposure leads to desensitization of the photoreceptors and phosphorylation of bleached rhodopsin. Full recovery of receptor sensitivity is achieved when rhodopsin is recycled and regenerated through a series of steps to its ground state. The last step in this process is the dephosphorylation of rhodopsin. This dissertation focuses on how rhodopsin dephosphorylation affects rod sensitivity. I exploited a novel observation; mouse retinae when isolated from the retinal pigment epithelium (and eye cup), display blunted rhodopsin dephosphorylation. Isoelectric focusing followed by Western blot analysis of retinal homogenate from bleached isolated retinae showed little dephosphorylation of rhodopsin for up to four hours in darkness, even under conditions when rhodopsin was completely regenerated. Microspectrophotometric measurements of rhodopsin spectra show that regenerated phospho-rhodopsin has the same molecular photosensitivity as unphosphorylated rhodopsin and that flash responses measured by trans-retinal electroretinogram or single cell suction electrode recording displayed dark-adapted kinetics. Single quantal responses displayed normal dark-adapted kinetics, but rods were only half as sensitive as those containing exclusively unphosphorylated rhodopsin. I propose a revised model in which light-exposed retinae contain a mixed population of phosphorylated and unphosphorylated rhodopsin. Moreover, complete dark-adaptation can only occur when all rhodopsin has been dephosphorylated, a process that requires more than three hours in complete darkness.

No description available.

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

Because of the paucity of evidence with regard to dark adaptation and the vitamin A status of pre-school children, this study is made. The purpose, therefore, is to add to the available data on this subject through an investigation of the bio-photometer as a means of detecting vitamin A deficiency in pre-school children.

This study was conducted on a family of nine ranging in age from thirteen to fifty-two, to examine dark adaptation during physical activities.

Retinal diseases such as age-related macular degeneration (AMD) are the major cause of blindness in the developed world. Early diagnosis of these diseases is difficult as symptoms appear only at advanced stages. Nevertheless, several studies suggest that impairment of dark adaptation (the ability of the retina to adapt to low lighting) is a cue to AMD. Dark adaptation is the result of the regeneration of light sensitive pigments after having reacted to light (bleaching). This PhD aims at developing a tool for objective measurements of the quantity of photopigment and the kinetics of dark adaptation. This work comprises a thorough review of the absorbing and reflecting properties of the different ocular structures, giving rise to a new model of retinal (or fundus) reflectance. This model provides a detailed description of the different pathways of light through the photoreceptor layer and was able to explain measurements and findings of the literature, in particular the effect of the photoreceptor matrix interstices. An extensive study of the influence of the different model parameters on the total fundus reflectance led to the proposal of a new objective and comparable measure of quantity of photopigment (QoP). This measure is obtained by fitting a constrained version of the new model to a double density difference (DDD) measurement (i.e. the logarithmic difference between reflectances of a retinal area in bleached and dark adapted states). This approach was validated by correctly fitting several DDD measurements from the literature. Future experimental studies are needed to confirm the relevance of the new QoP measure and specify its application in clinical diagnosis. Several fundus reflectometry instruments have been able to measure the DDD in human eyes however because of practical and technological limitations none of these instruments were suitable for clinical use. Here, these limitations are discussed and two new imaging fundus reflectometers are presented. Developed respectively by 4D Optics Ltd. and the Vision Research group at the University of Manchester, these two systems, based on modified fundus cameras, are ongoing development work towards clinically suitable imaging fundus reflectometry. Example data obtained with these two instruments exhibits aberrant points and low signal to noise ratio (SNR). The main issues encountered were camera noise and stability, uneven retinal illumination, and subject’s eye movements and changes of alignment. It is believed that these issues can be overcome with current technologies. One important impediment to the use of the dark adaptation experiment in clinical practice is the time it takes for photopigments to completely regenerate (up to 40 min in normal eyes). A theoretical data analysis strategy using the new model of fundus reflectance and the Marhoo, Lamb and Pugh model of photopigment regeneration kinetics is proposed to rapidly diagnose an abnormal regeneration, hence reducing considerably the duration of the experiment. This idea has not been tested on experimental data but may become relevant once better quality measurements of DDD are obtained.

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.