The British journal of physiological optics最新文献

Available theoretical and experimental data on the dependence of the subjective refraction of the eye on spherical aberration and pupil size are reviewed and additional experimental results are presented. Under photopic conditions, refraction varies little (similar to 0.3 DS) with pupil diameter, even when substantial amounts of spherical aberration are present (similar to 1.0 DS). It is argued that this result may be attributed to the insensitivity of optimal focus to spherical aberration at the spatial frequencies involved in photopic refraction, to the Stiles-Crawford effect and to the influence of aberrations other than primary spherical aberration in the outer zones of the pupil. The signficance of these findings is indicated in relation to possible discrepancies between the results of objective and subjective refractions when large pupils are in use.

An experiment whereby a standard filled circle is exposed for 100-1000 msec on the tachistoscope for ten subjects. Each is asked to choose a comparison circle, which appears to be the same size, out of a series of eleven filled circles of various angular subtenses larger and smaller than the standard filled circle in the tachistoscope. The results indicate that exposure time has a role in the perception of size.

Astigmats, who have been fully optically corrected, show an acuity configuration highly characteristic of the uncorrected astigmatism when they are tested with gratings of different orientations. This phenomenon, which is called meridional amblyopia, has been supposed to be neural in origin. This paper attempts to show that there is evidence for a critical period in the visual system of humans. In the experiment described here twelve astigmatic subjects were tested against a control group of six non-astigmatic (emmetropic) subjects. The astigmatic subjects differed in the ages at which they had been initially optically corrected. Square-wave gratings were used to test the subjects and measures of acuity for different orientations were recorded. It was found that those astigmatic subjects corrected above the age of seven showed the usual acuity decrement while those corrected below seven showed significantly smaller meridional amblyopia. The age of seven, therefore, was taken to mark the end of a critical period in the development of the human visual system, after which the system ceases to be structurally influenced by visual input.

Comparisons between the various types of binocular and monocular visual acuity thresholds are made in this study. The results obtained in monocular resolution and binocular diplopia experiments support LeGrand's view regarding Panum's area. Thus the physiological mechanism which appears to account for both monocular resolution and binocular diplopia thresholds could also account for a spatial tolerance which gives rise to Panum's area.

The nature and magnitude of the visual difficulties of five volunteer patients with severely contracted visual field and high visual acuities was investigated by several techniques. These comprised a questionnaire providing a quantitative score of visual impairment, a specially devised visual search task, and an arbitrary method of estimating visual efficiency. Many aspects of visual impairment resulting from contract visual fields were revealed and discussed. Performance scores on the search task indicated that the field expander would probably be useful to a small number of cases for continuous wear, usually as a binocular bioptic system. Other cases might benefit from a clip-on or hand-held device for occasional use. Methods of manufacture and dispensing and difficulty in locating suitable patients were the major limiting factors in this study. The methods of assessment, and the optical system described in this study are worthy of further investigation and development for trial on a larger number of patients.

Preliminary results of an attempt to determine the sources of nerve fibers of the monkey cornea and the consequences of its denervation are reported. Keratitis neuroparalytica was observed on the second day after combined ophthalmic and maxillary neurectomies. It reached a peak on the third day and by the fifth day recovery was nearly complete without recurrence up to 106 days. Tarsorraphy delayed the development of keratitis neuroparalytica with poor recovery up to 28 days after sensory denervation. Coincidence of reduction and recovery of lacrimal secretion and corneal changes suggest that the former might be a factor in the production of keratitis neuroparalytica. Epithelial changes accompanying keratitis neuroparalytica were observed and described. Numerous stromal nerve fibers remained uanaffected four days after ophthalmic and maxillary neurectomies. There is a possibility that these fibers are from sources other than the trigeminal.