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Biomedical subjects

R A Weale

Publications and source records attributed to R A Weale.

At least 19 recordsLinked to original sources
PubMed2005

The accommodation of lens implants.

Efforts devoted to the production of accommodative lens implants may be premature as there is conflicting information about the functional performance of the aged ciliary muscle which may determine their performance. Additional doubts exist on the performance of the ageing lenticular capsule in connection with some types of implant. Not only do these matters need resolving, but the change in the optical power of the eye needs also to be large enough for reading glasses to become unnecessary. However, not all these strictures apply to the development of accommodative lens implants for children who may be aphakic following operations, e.g. for congenital cataracts.

Accommodation, Ocular↗
PubMed2000

How the United Nations mortality tables hang together.

The mortality statistics of 80 member states of the United Nations were used to calculate Gompertz constants. When compared with a model based on the cumulant of failures of 46 human biological functions, they were found to form essentially one set, their slopes spreading out from a constant value like spokes from the axle of a wheel. Data for the longest lived regions agree with a prediction based on the above model, and those for less long lived regions are consistent with such a model having a constant normal cumulant average but increased S.D.s. Several different approaches support the view that the data are based on a probabilistic life-span.

Adolescent↗
PubMed2000

Why we need reading-glasses before a zimmer-frame.

Accommodative loss represents the fastest human biological decrement. Why? To examine this, the shape of the eye-lens during accommodation or its relaxation is analysed with special reference to age-related changes. The capsule is viewed as a force transmitter: the distribution of forces along centripetal capsular arcs and the resulting stresses and strains are calculated. The effect of zonular 'shifts' is considered. Age-related accommodative loss can be modelled successfully if changes in mechanical properties are linked to those in lenticular and capsular shape.

Accommodation, Ocular↗
PubMed1999

A logistics evaluation of visual acuity as applied to the Bailey-Lovie chart.

AIMS: To discover whether as a result of the increasing use of the Bailey-Lovie chart some classes of patients may not be affected by the crowding of the smaller test characters, whose spacing is proportional to their size; and to determine acuities with a logistic function so that all of a patient's responses may be utilized. METHODS: 112 patients were tested both with the original chart and one in which the horizontal distance is kept constant, i.e., the letters are arranged in vertical columns. All of a patient's responses were recorded so that the constants of the logistic function might be determined. RESULTS: No difference was found for very high and very low acuity scores, but, for intermediate ones, the vertical columns yielded acuity ratings increased by some 13%. CONCLUSION: The use of the logistics function was successful in that the correlation between stimulus and response was between 0.9 and 1 for some 80% of those examined. A constant horizontal spacing may be of advantage to some patients with a conventionally measured visual acuity of approximately 0.9.

Adolescent↗
PubMed1999

Lenticular fluorescence as a poisson process.

PURPOSE: To determine whether published data on lenticular fluorescence can be described in terms of the Poisson statistic. METHODS: The intensity of the Poisson function is expressed in terms of estimates of the fraction of the incident light absorbed by the human lens. Functions calculated for ages 0 to 80 years for probabilities of different numbers of quanta absorbed are compared with experimental results. RESULTS: To account for the observed data, a minimum of three exciting quanta (490 nm) absorbed has to be postulated for young lenses, but only two for older ones. At shorter wavelengths (380-450 nm), the tentative corresponding values are five and three, respectively. CONCLUSIONS: The model based on the age-related and wavelength-dependent changes in the minimum number of quanta absorbed from five to two is consistent with an age-related increase in the number of fluorophores and in their conformational changes.

Adolescent↗
PubMed1998

Age-related cataract and place of birth.

Cataract patient data from 13 Australian practitioners were analysed in order to compare the distribution of seven principal types of cataract in relation to gender, age and place of birth. Relative odds ratios were calculated for age-matched pairs of three identifiable ethnic groups and each type of cataract. The number of statistically significant relative odds ratios far exceeds the expectation due to chance. The results suggest a relatively greater risk for cortical cataract amongst younger when compared with older groups. In contrast, the relative odds ratios for nuclear cataract, independently of age, were consistently greater than unity when Australians or Northern Europeans were compared with Southern Europeans. There was no gender-based difference in cataract type distribution.

Age Distribution↗
PubMed1998

Cataract, glaucoma and season of birth amongst patients born on the Indian subcontinent.

The relation between the prevalence of open-angle glaucoma and of different types of cataract on the one hand and the patient's season of birth on the other was studied with special reference to natives of the Indian Subcontinent. Partial comparisons were made with results obtained on British-born patients. Both primary open-angle glaucoma (POAG) and the mixed nuclear/posterior-subcapsular type (NP) showed a statistically significant variation with the month of birth for the Asian patients, but only NP showed significant variation for the European patients in a month-by-month analysis. The Asian data are examined from the point of view of seasonal variations in maternal nutrition and of low birth-weight babies.

Aged↗
PubMed1997

Human biological decline and mortality rates.

Intercepts on the x (age)-axis of 107 normalized declining human biological functions were determined and assembled in 3 histograms, being placed in increasing order within each decade (10 year period). The histograms were classed accordingly as they contained properties associated with dividing cells, sensory properties and non-dividing cells respectively. Their cumulants were determined, multiple regressions calculated and compared with current death-rates for women and men respectively, for 10 amongst the longest living populations in the World. An alternative verification based on risk theory led to an estimate of an optimal life expectancy of 96 years. The survival curve turns out to be of the form (See text: Formula) where the inner integral represents the cumulant dimension (t') and the outer one age (t"). The premises underlying this study are compatible with the notion of a probable life-span, rather than a fixed one.

Adult↗
PubMed1997

Is there a link between corneal structure and the 'corneal cross'?

The 'corneal cross', observed when polarised light is reflected from the cornea and viewed through a crossed analyser, has been attributed to the fine anisotropic structure of the cornea causing birefringence or, alternatively, multiple reflections. But when plane polarised light is similarly reflected from isotropic curved surfaces and viewed through a crossed analyser, isogyres are also seen. Moreover, they vanish with a gonioscopic lens neutralising corneal curvature. This suggests that the corneal cross is not a specific attribute of corneal birefringence.

Chromium↗
PubMed1996

A theoretical link between lenticular absorbance and fluorescence.

The age-related variation of the fluorescence of the human eye lens was calculated from published data for lenticular absorbance. Only the nucleus was assumed to be involved. Simplifying assumptions for nuclear geometry yielded axial point-by-point data of absorbance for the exciting and fluorescent beam intensities. The resulting fluorescence profiles and their variation with age were computed. The model was tested on two assumptions: yellowing of the lens involves a pigment (a) already present at, or (b) one accumulating from, birth. Agreement between theory and experiment follows from hypothesis (b), and supports an earlier suggestion that the lens may yellow owing to a lifelong exposure to light.

Aging↗
PubMed1996

Risk factors and ocular senescence.

The first part of this paper is devoted to a brief survey of novel aspects of ocular senescence which are shown to fit into the general, apparently genetic, non-pathological framework of senescence. This is followed by an analysis of recent work on presbyopia, the sight of the elderly, which is easily remedied by the provision of reading glasses and, incidentally, seems to be an example of growth rather than senescence. A consideration of graver consequences of senescence in the eye lens is presented next in a detailed analysis of cataracts. Age-related afflictions of the retina conclude the survey.

Aging↗
PubMed1996

Odds ratios for different types of age-related cataract: ethnicity and environment.

Ethnic and environmental influences on cataract type are examined using patient data collected from an Australian region. Three ethnic groups are identified: native Australian Caucasians, southern and other Europeans. The Australians are further subdivided into 2 age groups. Apart from effects due to age, the following differences were found: the younger Australian group shows a greater relative risk for cortical cataracts; there is a gender-based difference among the southern European ethnic group; the Australian total has a lower relative risk for cortical cataracts than southern Europeans and a lower relative risk for cortical and mixed cataract than the European group. A comparison made with data published earlier for comparable groups in Britain shows that all Australian groups have a lower relative risk for nuclear but a higher one for cortical cataract and its combinations.

Aged↗
PubMed1995

The optics of the eye-lens and lenticular senescence. A review.

Although the lens of the eye is structurally a biological tissue, it functions as an optical element providing one third of the refracting power of the human eye, and a variable focus in younger years. Throughout a life-time the optical properties of the eye-lens alter, resulting in changes in function: there is a gradual depletion of the focussing amplitude from infancy to middle age, and a loss of transmittance in the later decades of life. The optical properties of the lens depend on its power, which in turn is determined by its physical dimensions (curvatures and thickness) and its refractive index as well as transmissivity and the organization of its internal components. The power of the functional lens is, however, modifiable by virtue of the lens being attached via the zonule to the ciliary muscle. The contraction and relaxation of the latter respectively increases and decreases lens power in accordance with innervations determined by the physical distance of external objects to be imaged on the retina. This review will consider many of these features and how alterations in any of them may lead to changes in lenticular function. However, as we have recently devoted a detailed study to presbyopia [1] its mechanism will not be considered here.

Accommodation, Ocular↗
PubMed1995

Polarising light biomicroscopy and the relation between visual acuity and cataract.

The use of polarised light in biomicroscopy allows discrimination of lenticular features which are not discernible using standard biomicroscopic techniques. However, just as is true of most brightness-dependent photographic methods testing the effect of filters, past uses of polarised light did not involve any control of illumination. The present study involved the use of polarised light in the photo-biomicroscopy of the anterior segment in cataract patients, the consequential loss in illumination being mimicked with different neutral density filters. This served to distinguish between polarisation and attentuation. The patients were refracted and their corrected visual acuity was recorded. A qualitative scale was drawn up ranking weights of lenticular opacities. Spearman's rank correlation was applied to the photographs obtained with conventional and polarised-light biomicroscopy in turn. Brightness control served to confirm that biomicroscopy with polarised light offers some advantages over conventional methods, and correlates with visual acuity better than is true of conventional biomicroscopy. The Spearman ranks derived from the results obtained with polarised light correlate significantly with the patient's visual acuity. It is concluded that polarised light biomicroscopy, in conjunction with the standard examination, can improve the diagnosis of cataract and assist in relating it to a patient's visual acuity.

Aged↗