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R A Weale

Publications and source records attributed to R A Weale.

At least 19 recordsLinked to original sources
PubMed1992

Problems related to diffuse versus localized loss in the perimetry of glaucomatous visual fields.

The separation of diffuse loss from more localized loss in the glaucomatous visual field is desirable for a number of reasons. In previous papers, the characteristics of several methods and algorithms for distinguishing among normal visual fields and those exhibiting diffuse and localized loss have been described and compared. In particular, a new diffuse loss index has been introduced that serves to decide whether or not a diffuse loss component is present and, if so, helps to estimate the amount. Here the approaches utilized for calculating empiric probability maps (Heijl) and the pattern deviation plots (STATPAC) are compared with results obtained with the diffuse loss index algorithm. Based on 197 Octopus G1 examinations of glaucomatous visual fields, it is shown that both methods produce large differences when compared with the diffuse loss index. For this and other reasons, it is argued that both empiric probability maps and pattern deviation plots may lead the inexperienced clinician to ignore valuable information concerning actual pathology.

Algorithms↗
PubMed1991

The lenticular nucleus, light, and the retina.

Lenticular absorbance and retinal illumination are reviewed in the light of earlier observations showing that the nucleus rather than the lens as a whole is the main absorber of radiation. Corneal refraction is taken into account. Consideration is given to the Stiles-Crawford effect, and to the accumulation of lipofuscin in the retinal pigment epithelium which may be caused by illumination of the retina.

Adolescent↗
PubMed1991

A new analysis of United Nations mortality statistics.

Demographic data published by the United Nations in 1987 are analysed in terms of the Gompertz function. Projections for maximum life spans are obtained, with the data broadly divisible into three clusters. These are attributable not only to the influence of high infant mortality, but suggest also constitutional and/or environmental variations among members of the clusters. The difference between life span and life expectancy is estimated analytically. A comparison with an earlier analysis supports the view that there are important differences between the life expectancies of the sexes.

Adult↗
PubMed1990

Evolution, age and ocular focus.

A number of hypotheses has been advanced during the last 130 years to explain the progressive loss of accommodation of the human crystalline lens. None has dealt with the high initial value of accommodation which enables infants to form sharp retinal images of objects as close as 6 or 7 cm. This paper attempts to relate the initial value to the overall loss in terms of evolution and biological cost.

Accommodation, Ocular↗
PubMed1990

Retinal illumination using a wide-angle model of the eye: comment.

When the human eye is modeled, consideration must be given to three anatomical factors that are sometimes overlooked. First, the apparent pupillary area is likely to exceed the real one, particularly at large paraxial displacements. Second, the earlier assumption [J. Opt. Soc. Am. A 5, 146 (1988)] that lenticular pigment is distributed uniformly throughout the lens is no longer valid except along the visual axis. Third, as measurable reflection occurs within the eye, the polar retinal illumination is likely to receive a significant indirect quantity of light in addition to the direct light.

Eye↗
PubMed1989

Do years or quanta age the retina?

The progressive loss of visual faculties with advancing age is attributed, sometimes, mainly to allegedly inevitable optical deterioration, such as clouding of the media, or again to neurosenescence, as typified by cell-death. The relevant factors are assessed, and it is not thought likely that changes in normal ocular optics account for changes in contrast sensitivity and visual acuity with age. The role of senescent changes in the retina is analyzed. The progressive temporal and spatial patterns of the accumulation of lipofuscin in the retinal pigment epithelium (RPE) and the putative control of its concentration by the crystalline lens are examined following an earlier suggestion that lenticular UVA transmissivity may control the rate of UVA entry into the eye and so perhaps the amount of lipofuscin formed in the RPE. It is suggested that morphological changes attributed to senescence may partly be due to cumyulative effects of irradiation.

Aging↗
PubMed1979

Now let me see.

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Developing Countries↗
PubMed1978

The perimeter as a monitor of glaucomatous changes.

A small group of glaucoma patients with scotomata were compared with normal coevals. Plots were obtained of the error of each measurement as a function of retinal illumination. A statistical analysis shows the limitations of perimetry as a monitor of the progress of glaucoma. The significance of the data is discussed.

Glaucoma↗
PubMed1978

Rhodopsin and visual threshold in retinitis pigmentosa.

Rhodopsin kinetics and visual threshold were determined in three subjects with a dominant form of retinitis pigmentosa. The retinal areas studied showed varying loss of sensitivity, which correlated well with the reduction in the measured density of rhodopsin in the test region. Rhodopsin photosensitivity was normal, and there was no evidence that either rhodopsin or the cone pigments regenerated more rapidly than normal. The findings in these cases of retinitis pigmentosa, when compared with the threshold changes induced by vitamin A deficiency or photic bleaching, suggest that the disease produces an imbalance between disc removal and new disc formation, which results in a progressive shortening of the photoreceptor outer segments and, eventually, in their complete disappearance.

Adult↗