Robert Weale

Age and the transmittance of the human crystalline lens.

1. Conflicting data both on the transmission of the human crystalline lens in the ultra‐violet part of the spectrum and on its variation with age necessitate a re‐examination of the subject. 2. Twenty‐four excised lenses in the age range of 0‐85 years were studied with a Perkin‐Elmer spectrophotometer between 327 and 700 nm. 3. Some lenses were homogenized and the homogenates were similarly examined. 4. A systematic increase in absorbance with age was observed both in the visible and the ultra‐violet parts of the spectrum. 5. An exponential function describes the data, facilitating comparison with, and prediction of, other values. 6. The absorbance of homogenized material was found to be predictable from that of intact lenses, and does not support the notion that mechanical trauma may account for high values in earlier studies.

Epidemiology of refractive errors and presbyopia

Limitations in existing studies of the epidemiological aspects of refraction are attributed to both technical and statistical procedures. Early influences of ocular parameters on refraction are identified accordingly as prematurity and may or may not be involved. Attention is paid to familial and genetic influences, and infants and toddlers are examined as a group separate from schoolchildren and teenagers, who are likely to have experienced significant periods of near work. The effects of sex and geographical distribution are considered both for younger and older age ranges. Special attention is paid to anisometropia, which is shown-apparently for the first time-to increase appreciably among presbyopes. The connection between refractive errors and ocular pathologies is reviewed, and possible means of preventing early onset myopia are examined. Presbyopia is addressed with reference to its geographical distribution and hypothetical links to accommodation insufficiency.

Decreasing stromal iris pigmentation as a risk factor for age-related macular degeneration

To evaluate iris color, change of iris color, and iris pigment epithelial defects as risk factors in age-related macular degeneration, we compared 101 patients with age-related macular changes with 102 control subjects in a case-control study. Three of 101 patients (3%) and four of 102 control subjects (4%) had epithelial iris defects. Light iris color during youth was reported by 51 of 101 patients (50.5%) and 42 of 102 control subjects (41.2%) (odds ratio, 1.46; P = .184). Of the 101 patients, 26 (25.7%) noticed their iris color to have become lighter during life compared with six of 102 control subjects (5.9%) (odds ratio, 5.5; P = .0001). At present examination, 63 of 101 patients (62.4%) had light irides compared with 43 of 102 control subjects (42.2%) (odds ratio, 2.27; P = .004). These results suggest that initial light iris color and iris pigment epithelial defects are not associated with an increased risk of age-related macular degeneration, whereas decreased stromal iris pigmentation may indicate a higher risk.

Cone pigments in the normal human fovea

Abstract The method of fundus reflectometry was applied to the human fovea in a study of the effect of chromatic bleaching light intensity (Iλ) on the nature of the resulting difference spectrum. Significant differences were obtained when, for example, green and red bleaching lights were used. In the former case, the shape of the difference spectrum was virtually independent ofIgreen, whereas an increase inIred produced a systematic change. This was manifested as a progressive shift in the λred of the difference spectrum from long to shorter wavelengths with a rise inImax. The shift is attributed to the different photosensitivities to red light of the two visual pigments believed to be responsible for the bleaching effects. The results are used in the computation of photolytic action spectra and it is shown that these objective data agree well with the subjective foveal spectral sensitivity curve.

Photo-chemical changes in the dark-adapting human retina

Abstract The method of rapid fundus reflectometry was used in the measurement of pigment recovery in the living human retinal periphery following exhaustive bleaching. Difference spectra measured at various stages of dark-adaptation vary systematically with the latter: this implies that recovery is a complicated process. The half-time of the recovery is approximately 3 min and can be influenced by extraneous light.

On the retinal vasculature of the human fovea

Abstract Transillumination of the human sclera with light from a Xenon are reveals an exceedingly clear entopic picture of the retinal vascular bed. Streaks can be observed across the fixation area. Fluorescein retinal angiography indicates that these are patent blood capillaries, and it is argued that they cannot interfere with central vision.

Presbyopia Toward the End of the 20th Century

Recent advances in our understanding of the anatomy and physiology of accommodation have contributed to current concepts of the possible constituent factors in presbyopia, largely supplanting the long-held belief that presbyopia is due to sclerosis of the crystalline lens. In this review, the author examines epidemiologic, basic scientific, and clinical evidence for a multifactorial decrease in accommodative amplitude with age. Methods of measurement, oculomotor effects of presbyopia, and approaches to correcting it are also considered.

Human lenticular fluorescence and transmissivity, and their effects on vision

Measurements were made of the spectral transmissivity of freshly isolated normal human crystalline lenses. Parameters included age, sex and the intensity of the measuring radiation. The latter played a small but detectable role; age, unlike sex, was a significant factor, notably at short wavelengths. The axial fluorescence of lenses due to exposure to violet (visible) radiation was also studied with the above parameters. Absolute measurements of the fluorescent radiation made it possible to assess the influence of fluorescence on vision.

Notes on the photometric significance of the human crystalline lens

Abstract The effective pathlength of the human crystalline lens is calculated as a function of aperture and its photometric effects examined on the assumption that the distribution of yellow pigment is uniform. The data are applied to the interpretation of the age variation of the absolute visual threshold and to the spectral variation of the Stiles-Crawford effect.

Polarized light and the human fundus oculi.

1. Measurements were made of the relative fractions of diffuse and specular reflexions in the fovea and periphery of the human fundus oculi.