Biomedical subjects
Publications and source records attributed to C Ramsdale.
The results are described of a 10-year study of the longitudinal changes in the static response of an individual subject during the approach to absolute presbyopia. The amplitude of accommodation declines linearly with age. A new finding is that the magnitude of the slope of the linear portion of the response/stimulus curve also reduces with age, as does the level of tonic accommodation.
Experiments are described in which the steady-state accommodation response to binocularly viewed targets at various distances in the range 0.2-5 m was measured by laser optometry in normal, near-emmetropic subjects. Responses were determined with naked-eye viewing and when equal pairs of either spherical lenses or base-in or base-out prisms were placed before the eyes. Snellen acuity was also measured under the same range of conditions. The results show that, although the most accurate accommodation responses were found under natural viewing, the response accuracy was remarkably robust against both lenses and prisms. There was, however, always some change in response level to any increment in lens or prism power. The results are discussed in terms of earlier theories and data on the general relationship between accommodation and convergence.
The accommodative response of 15 myopic, 10 hypermetropic and 15 emmetropic (less than +/- 0.50 D) subjects was assessed by the laser optometer. The Snellen E target was viewed binocularly whilst the monocular response to various levels of stimuli (0 D to 5 D) was measured. The mean response/stimulus curves and resting points for each group are compared. No significant difference is present between the 3 groups. There is no correlation between a) the resting point and spectacle prescription (r = 0.20) and b) the slope of the response/stimulus curve and the spectacle prescription (r = -0.32). The effect of ametropia on the accommodative response is insignificant.
Field and laboratory studies were carried out on populations of Anopheles sicaulti and An. labranchiae from the Moroccan province of Tetouan, in order to evaluate the hypothesis of a specific rank for the former taxon, recently suggested by White (1978). The egg morphology, and particularly the exochorion pattern and the number of float ribs, showed a complete range of variation, from typical sicaulti to typical labranchiae. Females laying "intermediate" eggs are those prevailing in the study area (60.5% of the eggs collected in the Tetouan province were of this type); in some localities (Ben Karriche and Restinga) only such females were observed. The latter finding would indicate a polygenic control of the egg pattern, as the two supposed parental forms do not seem to segregate from the "intermediate" one. No pure labranchiae populations were observed in the study area, while a pure sicaulti sample was found at Kantara. More widespread appears to be the coexistence of the "intermediate" form either with sicaulti (at Mdiq and Beni Yder, in both cases with a ratio of about 1.7:1), or with both sicaulti and labranchiae (at Souk Khemis and Tatoufet, with a ratio of about 2:1:1 in the two cases). These data seem to indicate that in the considered area sicaulti interbreeds freely with labranchiae. Crossing experiments failed to evidence post-mating barriers between the two taxa; fertile hybrids were obtained in the expected numbers. The polytene chromosome studies showed no differences of diagnostic value between sicaulti and labranchiae, that have the same banding pattern. Also the genetic structure, analyzed by means of starch-gel electrophoresis on the basis of 16 gene-enzyme systems appears to be quite similar in the two forms: allele frequencies at the polymorphic loci do not show significant differences. The average Nei's genetic distance found between sicaulti and labranchiae is exceedingly low (D = 0.014); values of the same magnitude were observed between conspecific populations both in An. labranchiae and An. atroparvus (average D = 0.016 in the two cases). The polymorphic loci in the Tatoufet population, that includes the three forms: sicaulti, "intermediate" and labranchiae, are in Hardy-Weinberg equilibrium, indicating that it represents a panmictic unit. The overall picture does not favour a specific rank for sicaulti, that seems rather a local variant of An. labranchiae. The need is stressed for further investigations involving populations living in the Rabat area, from where sicaulti was originally described.
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