R. A. Clement

A METHOD FOR RAYTRACING THROUGH SCHEMATIC EYES WITH OFF-AXIS COMPONENTS

Abstract A linear algebraic method for tracing skew rays through aspheric surfaces is described. The advantage of this method is that the refracting surfaces can be translated and rotated with respect to each other. The method is used to investigate the optical factors affecting the location of Purkinje images.

A MODEL FOR RETINAL SHAPE CHANGES IN AMETROPIA

Abstract Modelling 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.

A schematic eye model for the effects of translation and rotation of ocular components on peripheral astigmatism.

Abstract The relative contributions of translation and rotation of the cornea and lens to peripheral astigmatic asymmetry have been investigated using a linear algebraic ray tracing method. It is believed that lenticular rotation is responsible for angle alpha, so bringing about peripheral astigmatic asymmetry, as normally occurs in human eyes over the temporal and nasal retina. Rotation of the cornea may be responsible for the small numbers of eyes which exhibit large amounts of peripheral astigmatic asymmetry. The effects of corneal rotation and translation on the dimensions of the entrance pupil are illustrated.

A COMPARISON OF DIFFERENT MODELS OF EXTRAOCULAR MUSCLE COOPERATION

Abstract— 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.

COMPUTER SIMULATION OF EXTRAOCULAR MUSCLE CO‐OPERATION: AN EVALUATION

Abstract This paper is concerned with specifying how extraocular muscles co‐operate in moving the eye, A set of assumptions is described which enable ibis lo be done with enough precision for: i computer model of the actions of the extraocular muscles to be set up. The behaviour of the model and its validity arc then evaluated.

Lateralisation of the flash visually evoked cortical potential in albino babies.

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.

Visual evoked cortical and subcortical potentials in human albinos

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.

Gaze Angle Explanations of the Induced Effect

Mayhew and Longuet-Higgins formulated a computational explanation of the induced effect which successfully predicts the conditions under which the induced effect will occur. Underlying their theories are the assumptions that disparity information is separated into horizontal and vertical components and that the vertical disparities are used to calculate the gaze angles. An implementation of the fusional explanation introduced by Petrov makes similar predictions for the induced effect, but does not depend on these two assumptions.

Line Correspondence in Binocular Vision

The mathematical analysis of binocular vision introduced by Helmholtz is applied to the problem of the use of disparity information to position a stimulus in depth. It is shown that matching the images from the left and right eyes along radial directions is an alternative to matching images along the horizontal direction only.

EXCURSION TESTS OF OCULAR MOTILITY

Abstract—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.