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J M Enoch

Publications and source records attributed to J M Enoch.

At least 73 records · Page 4Linked to original sources
PubMed1985

Drusen of the optic nerve head. An important model.

It is proposed that drusen of the optic nerve head (ONH) may provide a useful model for the study of diseases which affect the vicinity of the optic disc. Several sensitive and revealing tests of inner retinal/optic nerve function have been applied in this investigation. Fundus Photo Perimetry has confirmed that little correlation exists between visual field defects and the location of ophthalmoscopically visible ONH drusen. The Flashing Repeat Static Test (FRST) was found to be abnormal in half of our patients, indicating probable ascending dysfunction in optic nerve fibers beyond the lamina cribrosa. Alterations in transient-like and/or sustained-like functions, found in several cases, are thought to represent effects of dysfunction descending to the retinal plexiform layers.

Adult↗
PubMed1984

Relating vernier acuity and Snellen acuity in specific clinical populations.

The relationship between vernier acuity and Snellen acuity in a group of cataract patients was examined. The vernier stimulus consisted of two small spots of light, vertically separated by a variable-sized gap. The Snellen stimulus was a standard projected Snellen chart. The form of the relation between vernier and Snellen acuity was found to depend upon the vernier gap size used. Specifically, when the smaller gaps of 4 or 8 min of arc are used, the two types of acuity are linearly related. When the gap is 16 or 32 min of arc, (or if best vernier performance irrespective of gap is considered) vernier acuity is related to Snellen acuity by a power function with an exponent less than one, within this clinical population. Thus, with increasing degrees of retinal image degradation caused by cataract, optimum vernier acuity is impaired at a slower rate than Snellen acuity. Our results in cataract patients are compared to results obtained by others within a population of strabismic and anisometropic amblyopes.

Aged↗
PubMed1984

Hyperacuity perimetry. Assessment of macular function through ocular opacities.

"Hyperacuity perimetry" provides localized measures of visual performance across the central visual field that are resistant to the retinal image degradation caused by media opacities. A normal observer, viewing a vernier stimulus through an artificial opacity (ground glass), exhibits a pronounced performance improvement with foveal viewing, relative to viewing at visual field points just 2 degrees to 4 degrees parafoveal. Patients with central lesions exhibit anomalous hyperacuity perimetric profiles, even in the presence of a simulated ocular opacity. We conclude that in patients with media opacities, hyperacuity perimetry can preoperatively evaluate the distribution and size of areas of visual loss across the central visual field and the stability and location of primary fixation. This potentially powerful test of macular function behind media opacities is as easy to apply as any static visual field measurement.

Adult↗
PubMed1984

Retinal boundaries and visual function in gyrate atrophy.

Three patients with gyrate atrophy of the retina and choroid underwent fundus photoperimetry, the combination of fundus photography and visual field analysis within the same instrument, to examine the correspondence between the funduscopically observed, scalloped margin of remaining retina and the functional limit of the peripheral visual field. The results suggest that near the border between remaining retina and atrophic areas, visual sensitivity falls off quite rapidly, producing perimetric isopters that conform closely to the scalloped retinal margin. In some instances, visual function can be demonstrated in islands of remaining retina that are totally surrounded by atrophic areas. This study demonstrates the usefulness of fundus photoperimetry in following the course of degenerative retinal diseases.

Adult↗
PubMed1984

Retinal image noise and vernier acuity.

The effects of optically produced "noise" in the retinal luminance distribution of a vernier stimulus are demonstrated in two experiments. In the first, vernier performance with a bright, two-dot target is shown to improve upon the introduction of a luminous background field, relative to performance with a completely dark background. The brighter background probably acts as an adapting field, reducing the visibility of the retinal image "noise". The second experiment demonstrates that, under defocused conditions, introduction of a low-pass spatial filter that removes phase-reversed high spatial frequency components can enhance vernier performance. Thus, high spatial frequency information may interfere with the vernier response when phase information is disturbed by defocus.

Form Perception↗
PubMed1984

The effects of image degradation by cataract on vernier acuity.

The resistance of certain types of hyperacuity tasks (eg, vernier acuity) to optical degradation of the retinal image has been demonstrated previously. This suggests that such a task might provide a means of filling the clinical need for a reliable test of retinal function in the presence of cataracts and other ocular opacities. In the present study, we measure several aspects of vernier acuity performance in cataract patients. These data provide an early basis for the development of a vernier acuity test to detect retinal/neural visual loss prior to cataract surgery. We report the results of measurements in 15 cataract patients using a two-dot vernier acuity task with variable separation between the two dots (gap). The data indicate that the shape and mean level of the vernier threshold-versus-gap function co-vary with the functional severity of the opacity as corroborated by Snellen acuity measures. Furthermore, the optical effects of the cataracts we studied are very similar to the effects of degrading the visual stimulus by interposing ground glass for a normal observer. We conclude that the shape of the vernier threshold-versus-gap function is a good indicator of the functional severity of the cataract in patients with otherwise normal vision.

Aged↗
PubMed1984

The resistance of selected hyperacuity configurations to retinal image degradation.

Traditional visual acuity is based on resolution of stimulus features, whereas hyperacuity (ie, vernier acuity) is based on relative localization of stimulus features. Since resolution acuity is influenced severely by optical degradation, it is often not a suitable measure of the status of the retinal/neural visual system in conditions of optical degradation. In the present study, the authors investigate the effect of optical degradation on various relative localization tasks. Thresholds for three types of hyperacuity stimuli (line vernier, two-dot vernier, and line tilt) were measured under various degrees of image degradation, produced by viewing the targets through ground glass. The results indicate that when a hyperacuity stimulus is optically degraded, relative localization threshold increases only slightly for certain separations of the comparison features. In comparison with resolution acuity, hyperacuity threshold at the optimum feature separation is quite resistant to image degradation. This finding demonstrates a potential for the clinical application of hyperacuity as a test of visual function in the presence of cataracts and other media opacities.

Cataract↗
PubMed1983

Perimetry, today and tomorrow.

Perimetry is clearly in an explosive stage of development. Here, an attempt is made to bring together major developments and put them into an orderly perspective. The projection-bowl-perimeters of Bern and Tübingen set the stage. Standardization provides the base for future development and data exchange. Automation and inclusion of computational procedures enhance the possibility of broad utilization for better screening and advanced testing. New test procedures make possible extremely fine localization of functions and allow superior definition of areas of involvement in pathology. New fundus perimeters make possible instantaneous fine correlations between functional changes and observed retinal anatomic lesions.

Humans↗
PubMed1983

Joseph Le Conte.

Explore the source record for details and available documents.

California↗
PubMed1982

Calculating photopic illuminance.

A procedure is proposed for computing the visual effectiveness of light incident on the retina considering the directional sensitivity of the underlying photoreceptor population. A half-sensitivity half-width measurement of the retinal directional sensitivity provides the basis for integrating a parabolic approximation to the directional sensitivity over the pupillary area penetrated by the incident light.

Humans↗