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Biomedical subjects

R A Crone

Publications and source records attributed to R A Crone.

15 recordsLinked to original sources
PubMed1992

The history of stereoscopy.

Ptolemy (127-148 AD) studied physiological diplopia, correspondence and the horopter. He had all the data to build a theory of depth perception through disparity detection, but left that undone. Alhazen (1000 AD) associated depth perception with the sensation of binocular convergence, just as Kepler (1611) and Descartes (1637). With the development of the concept of retinal correspondence and the fusion of the retinal images in the brain (Huygens 1667, Newton 1704) a cerebral mechanism of disparity detection became thinkable. The rise of Empiricism (Molyneux' Premise, the case of Cheselden) postponed the solution of the problem, finally reached by Wheatstone (1838). Physiological proof of Wheatstone's theory came from the experiments of Barlow et al. (1967).

Depth Perception↗
PubMed1979

What is normal binocular vision?

The vergence position of the eyes is determined by the near fixation-accommodation-miosis synkinesis and the fusion mechanism. The contribution of both systems was analysed in 30 normal subjects and 16 subjects with abnormal binocular vision. Prism fixation disparity curves were determined in three different experimental situations: the routine method according to Ogle, a method to stimulate the synkinetic convergence (Experiment I, with one fixation point as sole binocular stimulus) and a method to stimulate the fusion mechanism (Experiment II, with random dot stereograms). Experiment I produced flat curves and Experiment II steep curves. The mean diameter of the horizontal Panum area was 5 minutes of arc in Experiment I and 2 degrees in Experiment II. On the basis of these findings, it was postulated that the synkinetic system operates in the absence of fixation disparity and the fusion system in the presence of fixation disparity. In Experiment II, esodisparities of 100 minutes of arc occur in a number of normal subjects. The dividing line between normal and abnormal binocular vision therefore is blurred. Normal persons can display disparities, the order of magnitude of which is equal to that of the angle of squint in micro-strabismus.

Accommodation, Ocular↗
PubMed1976

Fundus changes in primary hyperlipaemia.

The retinal vascular change described for two relatively young men and initially diagnosed as arteritis retinalis but subsequently regarded as an analogue of retinal lipaemia stresses the importance of biochemical exploration for a possible disturbance in the fat metabolism in unclear cases of retinal vasculopathy. If a disturbance in the fat metabolism is found, rational therapy will lead to disappearance of the vascular mural changes.

Adult↗
PubMed1975

Optically induced eye torsion. II. Optostatic and optokinetic cycloversion.

Using a synoptophore and an objective photographic method, it was demonstrated that the eyes undergo a tonic cycloversion under the influence of a pattern with slanting stripes. A slight tilt with respect to the vertical had a greater effect than a tilt with respect to the horizontal. The maximum amplitude was of the order of 1 degree. This optostatic eye torsion is considered to be the optomotor analogue of the "ophthalmostatic" otolithic reflex. Optokinetic torsion was also investigated. To this end, rotating discs that were divided into sectors were presented in a synoptophore. The maximum amplitude observed in the 4 subjects was 6 degrees. Optokinetic torsion may be viewed as the optical superstructure above the semicircular canal reflex. Non-fusional cyclovergence, for which purpose counter-inclined or counter rotating contours were presented to both eyes, could not be demonstrated with certainty.

Eye Movements↗
PubMed1975

Optically induced eye torsion. I. Fusion cyclovergence.

Fusional cyclovergence was demonstrated for the first time, using ab objective photographic method. It was discovered that the results of subjective and objective measurements of cyclovergence agreed exactly. The largest fusional cyclovergence observed was 8 degrees. The cyclovergence partly cancels out the cyclodisparity presented. The greater part of the cyclodisparity usually remains. The maximum aplitude of the sensory cyclofusion is of the order of 8 degrees. The cyclovergence response is greatest when large fusion images with numerous horizontal contours are presented. The motor mechanism of cyclofusion presupposes the existence of recently demonstrated cyclodisparity detectors. The amplitude of sensory fusion is determined by the vertical diameter of the peripheral Panum areas.

Depth Perception↗