Biomedical subjects
Publications and source records attributed to R A Weale.
The elliptical shape and the physiological astigmatism of the normal neonatal human cornea are attributed to the ellipsoidal shape of the eyeball. This in turn is a feature of ocular development. The analysis is used to examine earlier observations on myopia.
Visual decrement correlated with age is often attributed to a progressive deterioration in the optical quality of the ocular media, notably the crystalline lens. Experimental evidence is presented to test the extent to which this hypothesis can be sustained. Recent data on lenticular scatter are shown to be useful in the visualisation and photography of cataract in man.
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A comparison is made between the luminances of slit-lamp images of the normal human lens in frontal view with plane polarized light, when one ocular is provided with an analyzer and the other with variable neutral density filters, the light source being polarized perpendicularly to the direction of the analyzer. The amount of extinguished light is significantly larger as seen in the former, and rises systematically with age. The effect of varying the spectral composition of the illumination is also examined. What is conventionally referred to as scattered light appears to be made up of at least two separate components. The effect which this may have for our interpretation of pathological images is discussed.
The usual trichromatic equation for a color match is converted into an algebraic equation consisting of the sum of the contrasts determined by the intensity ratios between the matching stimuli and arbitrary fractions of the proband. The senescence of the preretinal media is shown to affect color matches monotonically, but discrimination steps are affected differently. It is suggested that the senescence observed in tasks involving chromatic discrimination can be explained in terms of the nervous mechanisms subserving other types of contrast discrimination. The possibility of either simplifying or refining some clinical tests also is discussed.
Mean ocular temperature measured using a hand-held infrared thermometer was 36.54 degrees C and 36.38 degrees C for the right and left eyes of 51 premature babies; whilst for 54 fullterm controls the corresponding figures were 36.40 degrees C and 36.25 degrees C. As fetal temperature at about 38.0 degrees C is above maternal core temperature this means that the eye of the prematurely born infant experiences a thermal deficit of 1.0 to 2.0 degrees C which is never replaced postnatally. The possibility that this reduction in temperature could influence ocular growth is discussed, with particular regard to the development of myopia which people born prematurely are prone to develop.
A suggestion that protective eye gear can pose a threat either to the crystalline lens or to the retina is examined from an epidemiological point of view. It is concluded that it may accentuate a pre-existing high-risk hazard but has little significance for low-risk hazards.
When the illuminating beam of a slit-lamp is polarised and one of the viewing oculars and the camera lens are provided with crossed analysers, the image of the lens generally darkens. The effect is enhanced by the insertion of a quarter-wave plate. The contrast of lenticular discontinuities is consequently greatly accentuated. This makes it possible to quantify them.
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Conditions are described which make it possible to maintain the spectral transmissivity of human crystalline lenses in a wide age range unaltered for months on end.
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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.
The changes produced within the retina by ultraviolet and blue-violet light are discussed in relation to the increased sensitivity of aphakic and pseudophakic eyes to actinic damage.
An examination is made of possible relations between ocular morphology and refraction in man. Special attention is paid to astigmatism, prematurity, the eye at birth, and differences as between the eyes of men and women respectively. Some functional correlates are also pointed out.
Lenses of various ages were immersed in castor-oil and used to project gratings of known spatial frequency. Measurements were made of the highest frequency that could be resolved, and also of the optical power of each lens. Parameters included age, days post-mortem, and sex. The variation of the power differed appreciably as between infant and adult lenses, reflecting on the mechanical components of the lenses. Women's lenses were found to be more powerful than those of men. There was no decrease in transparency for up to seven weeks post-mortem. There was no significant variation of transparency with age, but women's lenses were somewhat less transparent than those of men.