The British journal of physiological optics最新文献

The problem of the mean of refractive errors is solved using the theorems applied to the curvature of a surface. A numerical illustration of he method and a statistical sample ae included amongst the appendices.

Pseudophakic patients have been found with the ability to read both 6/6 and N5 without a reading addition. An explanation of this phenomenon is offered in terms of the depth-of-focus of the pseudophakic eye. Results of experiments to measure the depth-of-focus of the pseudophakic eye for Snellen letters are compared with theoretical predictions from earlier work, and implications in terms of visual acuity and refractive error are discussed.

An investigation was carried out in the relationship between the position of the binoculus and the depth (transmittance) of a monocular filter. The method used relied on changes in motor function and the linearity of the relationship found by previous workers, who used purely visual techniques, was confirmed. Some anomalous results were found which remain unexplained.

Experiments are described in which retinal reflectance was measured as a function of wavelength for three subjects. Two components of the reflected light were studied: that which retained polarization and that which was depolarized. Both components were found to be present at all visible wavelengths and to have magnitudes which rose at the red end of the spectrum, although the fraction of the reflected light which retained polarization was then lower. The results are compared with those of earlier studies. While there is qualitative agreement on the form of the wavelength-dependence of retinal reflectance, the magnitudes of the values deduced by different authors vary considerably. The influence of ocular birefringence on polarized-light studies of the retina is discussed, together with possible locations from the structures responsible for the observed reflectances.

An equation is presented describing the angular velocity of an image, viewed by an observer when a plane mirror is undergoing angular velocity. The image velocity is determined at the observer's entrance pupil. An expression to determine the size of the mirror aperture for a given exposure time is also presented. The results indicate that, in general, the image velocity is not constant nor twice the mirror velocity, as is usually assumed. Also, if the mirror extends to an equal length on each side of its axis of rotation, then the time in which the image appears to travel from the mirror's edge to the axis of rotation does not equal the time in which it appears to travel from the axis to the other edge.

The relative brightness of the foveal reflex between amblyopic eyes and their fellows was examined. Differences in reflex appearances were found in some patients but not in others. Equal appearance of the foveal reflexes does not eliminate the possibility of amblyopia, nor is there a difference in appearance related to the degree of amblyopia.

Closed circuit TV has proved to be a valuable aid for many patients with partial sight and a new device for magnification of printed material has been developed. This is in the form of a small camera, guided over the page by the subject's hand and incorporating a roller drive for a scanning mechanism. The scanning head fits into the hand easily; it is linked to an electronic TV receiver in the form of a mosaic. Tracking the scanner manually operates a flow of the display to the left, with new material emerging from the right of the screen. The present paper outlines an evaluation of the device under different conditions with patients.

As an exploratory study six colour vision tests were given to nine male and two female achromats from the Shankhabanik community in Bishnupur, and to two additional similar males. All thirteen subjects had severe photophobia, fixation nystagmus, extreme weakness of vision (4/24 to 3/60) and the red end of the spectrum was much shortened. This research indicates that they had a form of incomplete achromatopsia, varying from an almost complete to a very severe partial loss of colour vision. The condition is inherited as an autosomal recessive. The most likely interpretation of these cases is that they are incomplete rod achromats. Their performance on the colour vision tests is tabulated, and shows complete inability to do the Ishihara test; nearly complete inability on the HRR test, with a possible slight tendency to do better in the yellow-blue than the red-green sub-tests; on Sloan's test they show approximate accordance with her results for achromats; they have severe difficulty with the dichotomous and 100-hue tests, with a possible slight tendency to make fewer errors on the G/B sections. The anomaloscope shows little abnormality of mid-matching points, but great increases in average matching ranges above the normal, although not absolute loss of colour sense, but with extreme darkening or shortening of the red end of the spectrum. Their colour naming was carefully recorded, and was fairly good occasionally, sometimes erroneous without being wildly at fault, and most often completely wrong. The records of colour naming were made, not, of course, as a form of colour vision test, but simply to illustrate the ways in which such defectives make an effort to use colour names in general use among their friends and relatives.