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PubMed1990

The effect of monocular defocus on binocular contrast sensitivity.

The monocular contrast sensitivity loss with defocus is well known. We measured binocular contrast sensitivity of sinewave gratings of 6 c/deg in the presence of different levels of monocular defocus. In the absence of defocus, the binocular sensitivity was about 42% higher than monocular. With increasing monocular defocus, the binocular sensitivity decreased steadily until it reached a level below the monocular, showing binocular inhibition. The clinical implications of binocular inhibition with monocular defocus are discussed.

Contrast Sensitivity↗
PubMed2002

Visual field structure in the Empress Leilia, Asterocampa leilia (Lepidoptera, Nymphalidae): dimensions and regional variation in acuity.

Male Empress Leilia butterflies ( Asterocampa leilia) use a sit-and-wait tactic to locate mates. To see how vision might influence male behavior, we studied the morphology, optics, and receptor physiology of their eyes and found the following. (1) Each eye's visual field is approximately hemispherical with at most a 10 degrees overlap in the fields of the eyes. There are no large sexual differences in visual field dimensions. (2) In both sexes, rhabdoms in the frontal and dorsal ommatidia are longer than those in other eye regions. (3) Interommatidial angles are smallest frontally and around the equator of the eye. Minimum interommatidial angles are 0.9-1 degrees in males and 1.3-1.4 degrees in females. (4) Acceptance angles of ommatidia closely match interommatidial angles in the frontal region of the eye. We conclude that vision in these butterflies is mostly monocular and that males have more acute vision than females, especially in the frontal region (large facets, small interommatidial angles, small acceptance angles, long rhabdoms, and a close match between interommatidial angles and acceptance angles). This study also suggests that perched males direct their most acute vision where females are likely to appear but show no eye modifications that appear clearly related to a mate-locating tactic.

Animals↗
PubMedDate not supplied

Surgical procedures performed after refractive surgery.

BACKGROUND: Refractive surgical procedures have been performed for over one decade. The complications that cause visual disability are abnormalities in wound healing, residual ametropia, and/or severe irregular astigmatism. Many of these complications can be manifested clinically in terms of visually disabling problems (loss of best-corrected vision, glare, monocular diplopia, etc). Some of these complications require additional standard ophthalmic or refractive surgical procedures to restore vision. However, since these secondary procedures have been performed in only a few cases, we known little about their outcome. METHODS: We report the histopathologic analysis of 132 cases that have undergone a secondary surgical procedure following a primary keratorefractive procedure. We attempt to correlate the problems encountered with such secondary intervention with histopathologic information obtained from specimens that have been submitted to our pathology laboratory and that had undergone secondary surgical procedures. RESULTS: Many specimens displayed abnormalities in wound healing associated with visual difficulties such as loss of best corrected acuity, glare, and under- and overcorrection. A short time from the initial procedure to the time of secondary intervention was common. CONCLUSIONS: The combination of a secondary surgical or keratorefractive procedure can produce unpredictable refractive results. Judicious application of a refractive procedure and an appropriate time period before a second procedure is performed may reduce unexpected refractive complications.

Adult↗
PubMed2000

Monocular versus binocular visual acuity as measures of vision impairment and predictors of visual disability.

PURPOSE: To examine the relationship between monocular and binocular visual acuities as predictors of visual disability in a population-based sample of individuals 65 years of age and older. METHODS: Two thousand five hundred twenty community-dwelling residents of Salisbury, Maryland, between the ages of 65 and 84 years of age were recruited for the study. Corrected visual acuity was measured monocularly and binocularly using ETDRS charts. Reading speed, face discrimination, and self-reported difficulty with visual tasks were also determined. RESULTS: Binocular acuity is predicted with reasonable accuracy by acuity in the better eye alone, but not by the widely used American Medical Association (AMA) weighted-average algorithm. The AMA algorithm significantly underestimates binocular acuity when the interocular acuity difference exceeds one line. Monocular acuity and binocular acuity were significantly better predictors of reading speed than the AMA weighted score or a recently proposed Functional Vision Score (FVS). Monocular acuity in the better eye, binocular acuity, and the AMA and FVS algorithms were equally good predictors of self-reported vision disability. None of the acuity measures were good predictors of face recognition ability. CONCLUSIONS: The binocular acuities of older individuals can be inferred from measures of monocular acuity. There is little evidence for binocular inhibition when the monocular acuities in the two eyes are unequal, as opposed to the widely used AMA algorithm for computing binocular visual impairment. For tasks that are strongly associated with visual acuity, such as reading, this association can be captured from measures of monocular acuity and does not require separate assessment of binocular acuity.

Aged↗
PubMed1997

A comparison of binocular summation in the peripheral visual field in young and older patients.

PURPOSE: To measure binocular and monocular thresholds to a light detection task in order to investigate binocular summation in the central and peripheral visual fields. The study also aims to investigate any differences in the magnitude of binocular summation in young and older subjects with healthy eyes. METHODS: Binocular and monocular thresholds were measured at eccentricities of 0, 5, 15, 25 and 40 degrees nasally and temporally, using the Humphrey Field Analyser. Binocular summation ratios were computed as the binocular sensitivity divided by the "best" monocular sensitivity. RESULTS: Binocular and monocular sensitivities declined with increasing eccentricity. Binocular summation ratios were shown to be significantly higher for the younger group compared to the older group at all eccentricities. CONCLUSIONS: Using this test, the binocular performance is shown to be lower for the older group at all eccentricities. Results are discussed in terms of age-related cortical cell loss and increased monocular sensitivity difference.

Adult↗
PubMed2002

Retinal and extra-retinal contribution to position coding.

Though considerable effort has been expended on demonstrating the importance of extraretinal cues in distance perception (e.g. state of vergence), recent studies have shown that enriching the visual image brings about a decrease of perceptual underestimation of distance as observed otherwise, providing that contextual information is situated in the proximal space with regard to target position. The fact that a similar effect was observed when viewing monocularly was suggesting a prevalence of retinal input in distance coding. The present study, investigating reaching movements performed monocularly or binocularly in three successive visual scenes (dark-structured-dark), gave evidence for this assumption. Whatever the vision condition, a dark environment gave rise to an underestimation of target distance, which disappeared instantaneously when a structured background was unexpectedly provided. The sudden return to the dark condition resulted in a progressive drift towards underestimation. These findings strongly suggest that structured retinal information influences widely the perception of target distance. They show in addition that retinal signals may contribute to the calibration of non-retinal sources of information. The putative implication of the posterior parietal cortex in this dual influence is discussed.

Adult↗
PubMed1994

Management of monocular cataract with long-term dilation in children.

We describe the use of long-term dilation and patching therapy in the management of three cases of pediatric monocular cataract. The cataracts were felt to be visually significant in the undilated state but consistent with good formed vision in the dilated state. One patient had a congenital cataract managed from 4 weeks of life, and two patients had late diagnosed cataracts of indeterminate onset presenting with dense deprivation amblyopia. The congenital cataract patient ultimately demonstrated recognition acuity of 20/40, and both the older children ultimately demonstrated an acuity of 20/30. We recommend considering long-term dilation and conventional amblyopia therapy rather than lensectomy in such cases if the cataract is felt to be consistent with development of good formed vision in the dilated state.

Amblyopia↗
PubMed1989

Binocular accommodation reaction and response times for normal observers.

Accommodation was recorded from right and left eyes of visually normal observers in both binocular and monocular viewing. Reaction and response times were similar in monocular and binocular viewing and are not influenced by eye dominance. Far-to-near responses were significantly quicker than near-to-far responses. The origin of this difference may be a feature of the elastic properties of the accommodation mechanism. Limited data are presented that indicate that the slowing of accommodation speed with age affects the near-to-far response disproportionally. Errors in the initial direction of response were fewer in binocular viewing in comparison with monocular viewing.

Accommodation, Ocular↗
PubMed1990

Binocular contrast sensitivity with monocular glare disability.

Glare disability plays an important part in the investigation and assessment of cataract. We investigated the effect of monocular glare disability on binocular contrast sensitivity. The magnitude of binocular summation was measured at different degrees of monocular glare disability. In the absence of glare, maximum binocular summation was shown. With increasing glare disability, the degree of binocular summation decreased steadily until binocular inhibition was produced. Binocular inhibition is defined as a reduction in binocular sensitivity to reach a level below the monocular. The clinical implications of binocular inhibition with monocular glare disability are discussed.

Adult↗
PubMed1997

Growth of the two layers of the chick sclera is modulated reciprocally by visual conditions.

PURPOSE: Although visual deprivation causes increased ocular elongation and myopia in both birds and mammals, changes in sclera appear to be in opposite directions. Because avian sclera has a cartilaginous layer as well as the fibrous layer found in mammals, we examined whether the scleral responses to various visual manipulations differ between the two layers. METHODS: To produce increases in ocular elongation and myopia, monocular diffusers or negative lenses were fitted to eyes. Conversely, to produce decreases in ocular elongation, diffusers were removed (restoring normal vision) or monocular positive lenses were fitted. Scleral layers were then dissected apart, and incorporation of labeled precursors into glycosaminoglycans (GAGs), DNA, and protein was assessed. Tissue coculture experiments were used to assess humoral interactions between scleral layers and with the choroid. RESULTS: In the cartilaginous layers, the incorporation of label into proteoglycans and DNA was significantly higher in eyes elongating faster than normal because of wearing diffusers or negative lenses and significantly lower than normal in eyes elongating slower than normal because of removal of the diffuser or wearing positive lenses. In the fibrous layers, the reverse was the case. Coculturing cartilaginous sclera from normal eyes with fibrous sclera from myopic or recovering eyes produced the same increase or decrease in sulfate incorporation into GAGs in the cartilaginous layer as though the tissue measured was from the animal providing the conditioning tissue. Coculturing with choroid, especially from recovering eyes, also inhibited cartilaginous sclera. CONCLUSIONS: The fibrous layer of the avian sclera shows changes in sulfate incorporation into GAGs during deprivation and recovery from deprivation in the same direction as does the mammalian sclera, whereas the cartilaginous layer changes in the opposite direction. The responses of the cartilaginous layer may be controlled by the fibrous layer, although they are influenced by the choroid as well.

Animals↗
PubMed1991

Effect of induced blur on visual acuity and stereoacuity.

The acuities of three subjects with good visual acuity and stereoacuity were reduced by the addition of diffusing filters placed before one or both eyes; these subjects then underwent automated stereoacuity and visual acuity tests. Results were idiosyncratic and differed from subject to subject to such an extent that no general rule sufficed to describe the effect of different degrees of blur on visual acuity and stereoacuity. It had been thought that blur degraded stereoacuity more than visual acuity but most of the results from one subject indicated the opposite effect. The effects of monocular vs. binocular blur are discussed.

Form Perception↗