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PubMed1999

Detectors for polarized skylight in insects: a survey of ommatidial specializations in the dorsal rim area of the compound eye.

Apart from the sun, the polarization pattern of the sky offers insects a reference for visual compass orientation. Using behavioral experiments, it has been shown in a few insect species (field crickets, honey bees, desert ants, and house flies) that the detection of the oscillation plane of polarized skylight is mediated exclusively by a group of specialized ommatidia situated at the dorsal rim of the compound eye (dorsal rim area). The dorsal rim ommatidia of these species share a number physiological properties that make them especially suitable for polarization vision: each ommatidium contains two sets of homochromatic, strongly polarization-sensitive photoreceptors with orthogonally-arranged analyzer orientations. The physiological specialization of the dorsal rim area goes along with characteristic changes in ommatidial structure, providing actual anatomical hallmarks of polarized skylight detection, that are readily detectable in histological sections of compound eyes. The presence of anatomically specialized dorsal rim ommatidia in many other insect species belonging to a wide range of different orders indicates that polarized skylight detection is a common visual function in insects. However, fine-structural disparities in the design of dorsal rim ommatidia of different insect groups indicate that polarization vision arose polyphyletically in the insects.

Animals↗
PubMed1989

Difficulties in the definition of 'stereoscotoma' using temporal detection of thresholds of dynamic random dot stereograms.

Temporal detection thresholds are reported from two subjects to dynamic random dot stereograms (DRDSs) of both crossed and uncrossed disparity. The stimuli were 1 degree square, of 0.25 degrees disparity and were presented at 81 positions in a 9 degree square central region. In both subjects crossed disparity stimuli were detected at shorter durations. One subject displayed particularly acute stereoscopic vision and presented a pattern of temporal thresholds increasing gradually with eccentricity. The other subject displayed evidence, particularly in response to uncrossed stimuli, of a 'stereo-scotoma' which was not evident in monocular testing or ophthalmologic examination. Criteria used to define 'stereo-scotoma' are discussed. It was concluded that, although left-right field differences may be found with a large subject sample, individual factors may be more important in the distribution of stereo sensitivity throughout the portion of visual field tested.

Adult↗
PubMed1989

Patient-physician communication when blindness threatens.

The threat of blindness creates a difficult and challenging environment for communication between patients and their ophthalmologists. This study examined concordance between what patients want to know from their physicians about their eye condition and what physicians believe their patients need to know. Eight retinal specialists and 24 of their patients with proliferative diabetic retinopathy and at risk of blindness were interviewed using parallel-constructed instruments. Although all recognized that blindness was the patients' greatest concern, disparities were noted that involved the desire/need to know about the possibility of vision loss, the causes of the eye condition, the results of each eye exam, and the extent of patient confusion. Physicians, while conscientious about informed consent, described various communication behaviors to avoid discussing bad news.

Adult↗
PubMed2005

Ophthalmologic disorders in minority populations.

Race- and ethnicity-related differences in prevalence of a number ofophthalmologic disorders have been documented. More importantly, blackand Hispanic Americans share a disproportionate share of morbidity, asmeasured by visual impairment and blindness, when compared with whiteAmericans. The reasons for this health disparity are complex andmultifactorial. If the unequal, individual, and societal burden of avoidable vision lossamong black and Hispanic Americans is to be decreased, it is essential tounderstand the apparent barriers to accessing timely and appropriateophthalmologic monitoring and care for these minority populations. Forthose who do gain access to ophthalmologic care, it is important tounderstand better the determinants leading to different treatment of blackand Hispanic Americans compared with white Americans. Opportunities for decreasing vision-related morbidity caused by cataract,diabetic retinopathy, and glaucoma for these minority groups clearly exist. Strategies for each of these ophthalmologic disorders may differ. Cataract isa reversible cause of visual impairment and removal of cataract improvesquality of life. Cataract surgery should be offered to all who can potentiallybenefit from this treatment. Earlier diagnosis, before the disease hasprogressed to loss of vision, should be a goal in both glaucoma and diabeticretinopathy. Strategies for screening high-risk groups may be particularlyrelevant in this regard. Additionally, with diabetic retinopathy, improvedmanagement of contributing risk factors, such as blood glucose control andblood pressure control, is important. Asian Americans are increasingly becoming a sizable minority group inthe United States. It is projected that by 2070, the Asian population willreach 11% of the total population of the United States. Virtually all of thepopulation-based data relating to ophthalmologic disorders in Asians havebeen performed in Asia. The reported relative proportion of PACG versusPOAG, however, among some Asian populations and of normal-tensionglaucoma versus high-tension glaucoma among the Japanese seems to applyto the United States Asian population. This assertion is based onwidespread clinical impression and analysis of Medicare claims data [56]. Understanding the differences is important for optimal treatment of theseminority populations as the proportion of Asians in the United Statescontinues to grow. The common denominator in all of these diseases is the role of thephysician and patient. Educational programs aimed at the physician tofacilitate cultural competence and at the patient to increase level of knowledgeabout their disease are appropriate and enthusiastically endorsed.

Eye Diseases↗
PubMed2004

Evidence of basal temporo-occipital cortex involvement in stereoscopic vision in humans: a study with subdural electrode recordings.

Stereoscopic vision is based on small differences in both retinal images known as retinal disparities. We investigated the cortical responses to retinal disparities in a patient suffering from occipital epilepsy by recording evoked potentials to random dot stereograms (RDS) from subdural electrodes placed in the parieto-occipito-temporal junction, medial surface of the occipital lobe (pericalcarine cortex) and basal surface of the occipital and temporal lobes (fusiform gyrus). Clear responses to disparity present in RDS were found in the fusiform cortex. We observed that the fusiform responses discriminate the onset from the offset of the stimulus, correlation from uncorrelation, and they show a longer latency than responses found in the pericalcarine cortex. Our findings indicate that the fusiform area is involved in the processing of the stereoscopic information and shows responses that suggest a high level of stereoscopic processing.

Brain Mapping↗
PubMed2002

The Müller-Lyer illusion in touch and vision: implications for multisensory processes.

In six experiments, we used the Müller-Lyer illusion to investigate factors in the integration of touch, movement, and spatial cues in haptic shape perception, and in the similarity with the visual illusion. Latencies provided evidence against the hypothesis that scanning times explain the haptic illusion. Distinctive fin effects supported the hypothesis that cue distinctiveness contributes to the illusion, but showed also that it depends on modality-specific conditions, and is not the main factor. Allocentric cues from scanning an external frame (EF) did not reduce the haptic illusion. Scanning elicited downward movements and more negative errors for horizontal convergent figures and more positive errors for vertical divergent figures, suggesting a modality-specific movement effect. But the Müller-Lyer illusion was highly significant for both vertical and horizontal figures. By contrast, instructions to use body-centered reference and to ignore the fins reduced the haptic illusion for vertical figures in touch from 12.60% to 1.7%. In vision, without explicit egocentric reference, instructions to ignore fins did not reduce the illusion to near floor level, though external cues were present. But the visual illusion was reduced to the same level as in touch with instructions that included the use of body-centered cues. The new evidence shows that the same instructions reduced the Müller-Lyer illusion almost to zero in both vision and touch. It suggests that the similarity of the illusions is not fortuitous. The results on touch supported the hypothesis that body-centered spatial reference is involved in integrating inputs from touch and movement for accurate haptic shape perception. The finding that explicit egocentric reference had the same effect on vision suggests that it may be a common factor in the integration of disparate inputs from multisensory sources.

Adolescent↗
PubMed2001

Perceptual aspects of two-dimensional and stereoscopic display techniques in endoscopic surgery: review and current problems.

The aim of this review is to analyze the perceptual aspects of endoscopic imaging systems. After discussing depth perception in natural settings, the problems of perceiving depth in 2-dimensional representations are investigated. We discuss the impact of stereoscopic video systems on the cerebral perceptual system, emphasising the fact that despite the addition of binocular disparity information, existing stereoscopic video systems are still different from normal 3-dimensional vision. Both 2-dimensional and stereoscopic video systems require a rescaling of visual information to guide motor behavior. A review of the growing number of papers comparing 2-dimensional and stereoscopic video systems shows that only about 50% of investigators found a significant benefit for stereoscopic systems. It is unlikely that image display technology for endoscopic surgery can ever progress to the stage where it is equivalent to normal vision. Within this limitation, progress will result from a multidisciplinary approach, involving technological advances in the quality of the displayed image together with psychovisuomotor and ergonomics research, which facilitates the cerebral rescaling and perception process by the endoscopic surgeon.

Data Display↗
PubMedDate not supplied

Lamellar keratoplasty with the Barraquer microkeratome.

Lamellar keratoplasty was performed in 17 eyes: 6 with corneal opacities following epidemic keratoconjunctivitis, 3 with herpes keratitis, 2 with anterior corneal dystrophies, and 6 others. The Barraquer microkeratome was used for the resection in both the host and the donor. A technique is described to correct major disparities in diameter between the bed and the donor disc. In eyes with vision limited only by corneal diseases (11), the best postoperative spectacle corrected visual acuity was 20/25; the mean postoperative spectacle corrected visual acuity for the 11 eyes was 20/40.

Adolescent↗
PubMed1998

Linear and nonlinear transparencies in binocular vision.

When the product of a vertical square-wave grating (contrast envelope) and a horizontal sinusoidal grating (carrier) are viewed binocularly with different disparity cues they can be perceived transparently at different depths. We found, however, that the transparency was asymmetric; it only occurred when the envelope was perceived to be the overlaying surface. When the same two signals were added, the percept of transparency was symmetrical; either signal could be seen in front of or behind the other at different depths. Differences between these multiplicative and additive signal combinations were examined in two experiments. In one, we measured disparity thresholds for transparency as a function of the spatial frequency of the envelope. In the other, we measured disparity discrimination thresholds. In both experiments the thresholds for the multiplicative condition, unlike the additive condition, showed distinct minima at low envelope frequencies. The different sensitivity curves found for multiplicative and additive signal combinations suggest that different processes mediated the disparity signal. The data are consistent with a two-channel model of binocular matching, with multiple depth cues represented at single retinal locations.

Depth Perception↗
PubMed1997

Comparison of Snellen acuity and objective assessment using the spatial frequency sweep PVER.

BACKGROUND: We compared the vision objectively assessed by spatial frequency sweep pattern-reversal visual-evoked response (SPVER) with the Snellen acuity in patients. METHODS: SPVER acuity and Snellen acuity were measured in 100 patients with various ocular pathologies, including macular diseases, diffuse retinal degeneration, optic nerve diseases, glaucoma, and high myopia. For SPVER, 10 sinusoidally modulated vertical gratings were presented as stimuli. The responses were averaged and displayed through the discrete Fourier transform on the monitor display. The PVER acuity was determined by extrapolating the SPVER amplitude-spatial frequency function to baseline. RESULTS: Vision ranged from 20/15 to 20/400 with Snellen acuity, and from 20/25 to 20/190 with SPVER. The overall correlation between the two acuities was r = 0.666. The correlation varied from r = 0.895 in eyes with glaucoma to r = 0.436 in eyes with optic nerve disease. Seventy-seven eyes (77%) had a visual acuity agreement of within 1.0 octave between the two measurements. CONCLUSION: The SPVER acuity and the Snellen acuity correlated to a certain degree. Discrepancies were found in certain diseases, with the highest disparity in patients with optic nerve disease. We conclude that the SPVER is effective in estimating vision objectively, particularly in patients in whom the standard Snellen test is impossible to perform or yields unreliable results.

Adolescent↗
PubMed1988

Accommodative adaptation induced by sustained disparity-vergence.

Pre- and post-task measures of dark focus (DF) were used to assess the response of the accommodative system to within-task disparity-vergence in 10 late-onset myopes (LOM's) and 10 emmetropes. Disparity was induced by 3 and 6 delta base-out prisms imposed during a 3 D near-vision task undertaken for 3- and 10-min periods. Accommodation was measured after the task at 1-s intervals over a 90-s period using an objective infrared optometer to determine post-task regression of DF toward pretask values. After the 3-min task both groups show a reduction in DF adaptation with increasing disparity-vergence. After the 10-min task, disparity continues to have a significant effect on accommodative adaptation in LOM's but not in emmetropes, suggesting diminished prism adaptation in LOM's. The implications of these findings are discussed with regard to both current models of accommodation-vergence interaction and the etiology of late-onset myopia.

Accommodation, Ocular↗
PubMed2000

Ocular contributions to age-related loss in coarse stereopsis.

PURPOSE: To determine the basis for the dramatic decline in coarse stereopsis that occurs with age. METHODS: The Frisby test was used to assess stereopsis in a large sample of randomly selected persons over the age of 58 years. A number of other vision functions were also assessed in the same persons. The data were used to address the question of whether the decline in stereopsis reflects age-related alterations in cortical stereopsis mechanisms themselves (e.g., disparity detectors) or a degradation of the signal reaching the cortex as a result of alterations in earlier visual components. Two of three vision measures were binocular and thus reflect predominantly the function of the better eye. RESULTS: We find, as many others have reported, that even very coarse stereopsis declines dramatically with age. Despite not having separately assessed each eye, we find that among those selected to have good ocular function there was no significant decline in coarse stereopsis with age. CONCLUSION: These findings suggest that the enormous decline in coarse stereopsis with age can be accounted for by alterations in early stages of vision processing.

Aged↗
PubMed2005

Gaze-contingent soft tissue deformation tracking for minimally invasive robotic surgery.

The introduction of surgical robots in Minimally Invasive Surgery (MIS) has allowed enhanced manual dexterity through the use of microprocessor controlled mechanical wrists. Although fully autonomous robots are attractive, both ethical and legal barriers can prohibit their practical use in surgery. The purpose of this paper is to demonstrate that it is possible to use real-time binocular eye tracking for empowering robots with human vision by using knowledge acquired in situ. By utilizing the close relationship between the horizontal disparity and the depth perception varying with the viewing distance, it is possible to use ocular vergence for recovering 3D motion and deformation of the soft tissue during MIS procedures. Both phantom and in vivo experiments were carried out to assess the potential frequency limit of the system and its intrinsic depth recovery accuracy. The potential applications of the technique include motion stabilization and intra-operative planning in the presence of large tissue deformation.

Artificial Intelligence↗
PubMed1985

[Stereovision in random dot pattern VECP: normal findings and clinical use].

Cortical potentials evoked by dynamic random dot stereograms were recorded in 15 normal subjects and 19 patients with impaired stereoscopic vision. The potentials obtained were compaired with those evoked by similarly arranged checkerboard contrast stimuli, binocularly presented. The two modes of stimulation yielded potentials of similar component latencies but the stereoscopically evoked component amplitudes were significantly lower. In nine-channel recordings the stereoscopically evoked potentials were found to be located farther anterior topographically, suggesting a different neural generating mechanism. Patients with impaired stereoscopic vision had lower amplitudes and longer peak latencies than normal subjects. In addition, larger disparities had to be used to elicit a response in these patients. There was a high degree of correlation between the disparity thresholds determined by evoked cortical potentials and those obtained by sensory measurements.

Depth Perception↗
PubMed1986

Binocular vs. monocular task performance.

Functional advantages of binocularity were investigated by having 13 subjects perform a group of occupational-type tasks under monocular and binocular conditions. Significant binocular advantages ranging from 29.5% (pointers in straws) to 3.7% (reading speed) were measured. Tasks with many disparity cues showed the greatest binocular advantage. This shows that patients with normal binocular vision use binocular cues, most likely stereopsis, to enhance performance. In a second experiment, three subjects with normal binocular vision underwent monocular occlusion for 5 days to investigate whether monocular skills improved to compensate for the loss of binocular vision. During that period binocular performance was consistently better than monocular performance, and both monocular and binocular performance improved, even though the subjects were only gaining monocular experience. Although the 5 day occlusion period does not simulate the long-term denial of normal binocularity that strabismics or monocular patients experience, it shows that binocular superiority remains after short-term loss of binocularity.

Functional Laterality↗
PubMed2002

Adaptive control of vergence in humans.

Vergence eye alignment minimizes horizontal, vertical, and cyclodisparities to optimize stereo-depth perception. Only the horizontal component of vergence is under voluntary control. Couplings with voluntary version and horizontal vergence guide vertical vergence and cyclovergence. Can these couplings be modified in response to sensory demands on binocular vision? We have modified vertical vergence and cyclovergence in response to optical changes in disparity. Vertical vergence was stimulated with aniseikonic lenses that exaggerated vertical disparity in tertiary gaze. Vertical vergence adapted in an hour to produce nonconcomitant changes in vertical phoria that varied with vertical eye position in tertiary gaze. Cyclovergence was stimulated with cyclodisparities that varied with gaze elevation and convergence angle. Cyclovergence adapted within 2 hours to produce nonconcomitant changes in cyclophoria that varied with gaze elevation and convergence. The adaptive couplings for vertical vergence and cyclovergence are modeled as a combination of passive orbital mechanics and active gain control of the vertical recti and obliques. Vergence adaptation is a calibration process that adjusts the innervation for horizontal, vertical, and torsion components of vergence to the physical constraints set by the extraocular muscles and orbital connective tissues. Passive orbital mechanics simplify the neural control for precise vertical vergence and cyclovergence that are needed to achieve binocular alignment under open-loop conditions in response to perceived spatial location.

Adaptation, Physiological↗