Biomedical subjects
Publications and source records attributed to R A Clement.
Modeling ametropic retinal shape changes with an ellipsoid of constant equatorial radius has been found to produce types of peripheral astigmatism which are in good agreement with experimental findings.
Contrasting views on the actions of the extraocular muscles are discussed. The contributions made by clinicians are compared to those made by investigators with a background in physical science. It is shown that a clear understanding of the mechanics of the extraocular muscles can be used to increase the efficiency of oculomotility tests.
Three alternative excursion tests of ocular motility have been compared. A computer model of the mechanics of the extraocular muscles has been used to estimate the tensions developed by the muscles in these tests. On the basis of these calculations we recommend the transverse test in which the positions of the eyes are observed as they track a target moving from the right to the left with a fixed elevation and a fixed depression.
Albinism is a congenital condition in which hypopigmentation occurs. In addition to this abnormality there is a misrouting of the optic nerve fibers, with some fibers from the temporal retina following a crossed route at the chiasma and terminating in the contralateral cortical hemisphere. This contralateral preponderance of fibers from each eye should be recognizable from recording the visual evoked cortical potential over each hemisphere on monocular stimulation. Such a technique should produce evidence of responses of either increased amplitude or shorter latency over the contralateral hemisphere. Twenty-five human albinos (twenty-three oculocutaneous, two ocular) have been examined. Pattern appearance-disappearance visual evoked cortical potentials were used, but only on bioccipital derivations did these show clear lateralization. With the flash response the P2 component has a consistently shorter latency over the contralateral hemisphere to the eye stimulated. The visual evoked subcortical potential shows contrasting lateralization. The implications of these findings are discussed.
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Flash VECPs have been reported in 3 albino babies ranging in age from 1 to 7 months. The responses were dominated by a large positive component preceded by an earlier negative. The amplitude of this positive component measured from the peak of the preceding negative wave had a greater amplitude over the contralateral hemisphere on monocular stimulation indicative of the misrouting present in the albino visual system.
This study demonstrates that the source derivation procedure described by Hjorth (1975) reveals lateralisation of the visual evoked response to pattern reversal stimulation in accord with the anatomical data.
This study described the results of applying source derivation to the brain-stem auditory evoked potential. Unilateral stimulation gives rise to current sinks, associated with waves I and III, which are located in the vicinity of the ipsilateral mastoid. Waves II and V are associated with a pair of current sinks which appear bilaterally in the vicinity of each mastoid.
Different assumptions about the way in which the extraocular muscles act have been evaluated by comparing a set of models of extraocular muscle cooperation, each of which differ by just one assumption, against clinical data from patients with isolated nerve palsies.
The analysis by Helmholtz (1910) of the geometry of binocular vision has been modified to allow computerized calculation of specific examples of horopters. These are used to clarify the relationship between the shapes of the horopters and the physiological constraints involved.
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The versatility of a computer-based display of the extraocular muscles is demonstrated by comparing two different assumptions as to the paths of the muscles over the globe.
Investigations were undertaken to determine which particular components of the flash visual-evoked cortical potential (VECP) lateralize on monocular stimulation in human albinos. Our results demonstrate that only the major positive component shows clear lateralization. Statistical analysis revealed that the latency lateralization was significant (P less than 0.001) while the amplitude lateralization was not.
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