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At least 1,513 records · Page 84Linked to original sources
PubMed1982

Central retinal artery obstruction and visual acuity.

The records of 72 patients (73 eyes) with acute central retinal arterial obstruction (CRAO) were reviewed. Three eyes (4%) were initially observed to have no light perception vision. However, two of these three were found to have concomitant posterior ciliary circulation defects on fluorescein angiography, and the third had electroretinographic evidence of both outer and inner retinal damage. Previous studies have indicated that a much higher percentage of patients with CRAO present with NLP vision. From the data presented it is the feeling of the authors that cases with obstruction of the central retinal artery alone and NLP acuity in the involved eye are most unusual. If true NLP vision is present, additional complicating factors should be suspected, particularly abnormalities of the choroidal circulation and the optic nerve.

Adult↗
PubMed1979

Striate cortex and visual acuity functions in the cat.

Using a two-choice visual discrimination paradigm, thresholds for size (gratings), parallelness (parallel vs. non-parallel lines), contour alignment (vernier offset), and angularity (polygon figures) were behaviorally determined in cats before and after ablations of portions of the geniculo-cortical system. Animals with a total loss of cortical area 17, and with a loss, in some cases, of up to 90% of areas 18 (with and without infringement into area 19), showed about a 30% reduction in grating acuity, a three-fold increase in parallelness and angularity thresholds, and a total loss of contour alignment ability. Control animals with ablations sparing area 17 showed no significant threshold changes. All animals were able to learn classic form discriminations postoperatively, but those with area 17-18 lesions at a somewhat slower than normal rate. Control procedures indicated that all tested discrimination capabilities did not depend on luminance differences between targets, local flux cues within the targets, or on the animals' use of residual portions of area 17 representing the peripheral visual field. Since the cat has multiple thalamo-cortical visual pathways, the results of the present study are consistent with the hypothesis that pathways parallel to the geniculo-striate system are capable of processing spatial information of considerable detail. The results also suggest, however, that the geniculo-striate system is uniquely necessary for the processing of the finest attributes of spatial contours.

Animals↗
PubMed1980

Ocular dominance, eye alignment and visual acuity in kittens reared with an optically induced squint.

A horizontal concomitant strabismus produced optically in kittens with prisms caused a decrease in the proportion of binocularly excitable striate neurons with approximately equal percentages of neurons being driven by each eye. In addition, preventing fusion with prisms resulted in alterations in interocular alignment and in some cases a mild strabismic amblyopia. The changes in ocular dominance were dependent on the amount and direction of the prism induced deviation; however, regardless of the type of prisms worn, the kittens which demonstrated interocular misalignments were esotropic.

Animals↗
PubMed1993

Prediction of postoperative visual acuity in patients with total glaucomatous cupping using the Potential Acuity Meter and automated perimetry.

We evaluated the effectiveness of using the Potential Acuity Meter (PAM) and automated perimetry to predict postoperative vision in 30 advanced glaucoma patients following combined cataract extraction and trabeculectomy. Using the binomial distribution at alpha = 0.05, PAM and automated perimetry individually were significantly useful in predicting postoperative vision of 20/40 or better. Automated perimetry, but not PAM, was useful in predicting worse than 20/40 vision. Used together, automated perimetry and PAM testing were significantly useful in predicting vision worse or better than 20/40.

Aged↗
PubMed1991

[Diffuse and localized glaucomatous visual field changes in light sense, flicker and visual acuity perimetry. Evidence of pressure damage].

75 eyes of 75 patients with different types of glaucoma (21 eyes with normal-tension glaucoma, 49 eyes with primary open-angle glaucoma and 5 eyes with pigmentary glaucoma) were examined by automated light-sense, flicker and resolution perimetry. All fields were classified as being "normal" (N) or having "diffuse loss" (D), "localized loss" (L) and "diffuse plus localized loss" (DL) in masked fashion. The frequency distributions for the various field loss categories against the highest intraocular pressure ever reported in the patients' records were plotted. The frequency distributions for the purely localized defects show a peak at 20 mmHg and are markedly skewed to low pressure values, while the diffuse plus localized damage and the purely diffuse loss, however, show a peak at about 30 mmHg. The data support the hypothesis that diffuse field loss may be an indicator of pressure-induced damage.

Adult↗
PubMed1981

Grating detection and visual acuity after lesions of striate cortex in hooded rats.

The ability of rats to detect high-contrast square-wave gratings over a range of spatial frequencies was measured before and after ablation of striate cortex. The animals relearnt to detect low-frequency gratings very quickly after operation, and their acuity was reduced from 1.0 c/deg to about 0.7 c/deg. These effects were in striking contrast to those produced by larger posterior cortical ablations, which included both striate and prestriate cortex (Dean 1978); after the larger lesions, rats required many weeks of retraining to detect even low-frequency gratings and their acuity was reduced to 0.3 c/deg. The difference in the effects of the two lesions suggested that the rats with striate ablation were using information about spatial contrast that was relayed either by spared remnants of the geniculo-cortical pathway, or by the pathway from superior colliculus to prestriate cortex via the lateral posterior nucleus. To try and distinguish between these possibilities, the destriate rats were given a further lesion of the superior colliculus. This second lesion severely disrupted contrast detection: the animals made about as many errors as rats with large posterior cortical removal in relearning to detect a low-frequency grating, which is about 20 to 30 times as many as after either striate cortex or superior colliculus lesions alone. This result suggests that rats, like other mammals, can use spatial information conveyed in the tectocortical path when striate cortex has been destroyed.

Animals↗
PubMed2004

Visual acuity of fly photoreceptors in natural conditions--dependence on UV sensitizing pigment and light-controlling pupil.

The effect of the UV-absorbing sensitizing pigment of fly photoreceptors on absolute, spectral and angular sensitivity was investigated with a wave-optics model for the facet lens-rhabdomere system. When sky light was used as a UV-rich light source, one sensitizing pigment molecule per rhodopsin increased the photoreceptor absorption by 14-18% with respect to pure rhodopsin, whilst two sensitizing pigment molecules per rhodopsin increased the absorption by 20-27%. Upon light adaptation, when the pupil mechanism is activated, photoreceptor absorption decreases; in the housefly, Musca, by up to 6-fold. The fully light-adapted pupil diminishes the photoreceptor's acceptance angle by a factor of approximately 0.6 due to selective absorption of higher order waveguide modes. Spatial acuity of dark-adapted photoreceptors is more or less constant throughout the visual wavelength range, including the UV, because the waveguide optics of the rhabdomere compromise acuity least at wavelengths most limited by diffraction of the facet lens. Diffraction is not the general limiting factor causative for UV sensitivity of insect eyes. Visual acuity is governed by diffraction only with a fully light-adapted pupil, which absorbs higher waveguide modes. Closure of the blue-absorbing pupil causes a UV-peaking spectral sensitivity of fly photoreceptors. The sensitizing pigment does not play an appreciable role in modifying spatial acuity, neither in the dark- nor the light-adapted state, due to the dominant contribution of green light in natural light sources.

Adaptation, Ocular↗
PubMedDate not supplied

[Possibilities of the use of visual evoked potentials in the evaluation of visual acuity in congenital myopia in children].

Studies of visual evoked potentials (EP) to chess field reversion in 80 children (147 eyes) aged 5 to 16 with congenital myopia have demonstrated significant deviations from the reference values of the P100 component to all the stimuli. The clinical groups with various changes in the fundus oculi were found to differ by the P100 component amplitude when chess fields with cells 112 and 56 angular min in size were shown. The number of discrepancies between the clinical vision acuity and its assessment from the threshold EP grew from 19% when no changes in the fundus oculi were seen to 54 and 61% when myopic and non-myopic changes were detectable in the fundus oculi. These data evidence that EP amplitude to chess field reversion better reflects the status of the retino-cortical route than the central vision acuity.

Adolescent↗