摘要:

Classical color vision theory incorporates the concepts of hard-wired parallel independent processing and of hard-wired opponent-processing. These two powerful concepts can be applied more generally in visual psychophysics. The concept of parallel independent processing can help to understand two extremes of visual performance: disordered vision in patients and the extraordinary visual abilities of athletes and aviators. Three illustrations of this thesis are discussed. First, evidence for dissociations of spatial vision for lowcontrast and high-contrast objects. Second, evidence that a binocular system for motion in depth runs in parallel with the classical disparity-driven binocular system for relative position in depth. Third, evidence that a visual system for motion-defined form parallels the well known system for contrast-defined form. However, in principle these two concepts have limited value because they do not incorporate the possibility that the functional organization of the visual pathway could be modified by descending task-dependent signals.

ISSN:1040-5488    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

Pupillary images recorded by a linear knife-edge photoscreener for infants accommodating more or less within the bounds of chromatic aberration show three smooth offset pupillary irradiance ramps when analyzed with a color video camera and frame-grabbing hardware. Both the shape of the ramps and the lack of a second image in a shadowing experiment support the view that the retina acts as an angularly diffuse partial reflector in photorefraction. We propose a lateral image-spreading characteristic to account for observed color-dependent ramp heights and offsets and consider possible physical mechanisms for lateral spreading.

ISSN:1040-5488    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

We have developed a new test which can rapidly evaluate basic color vision in individual infants. The test consists of a series of large cards constructed with Muncell Hues. It uses a modified preferential looking procedure (FPL) and, to control brightness cues, incorporates a two-phase systematic variation of luminance. First, we evaluate an infant's ability to discriminate 9.5 by 16°achromatic patches of varying luminance from a 26 by 65°achromatic background of midrange luminance. In the second phase the test patch is chromatic and its luminance, relative to the background, is varied over a range of about 1.0 log cd/m2. The number of relative luminances chosen for each infant depends upon his/her performance in phase 1. Seventy 2- and 3-month-olds were tested with 4 broad-band chromatic patches, a red (dominant λ=660 nm), a yellow (dominant λ=580 nm), a green (dominant λ=520 nm), and a blue (dominant λ=475 nm). Results showed that 3- month-olds had little difficulty making any of the chromatic- achromatic discriminations but many 2-month-olds appeared to fail to discriminate the yellow and green from the background at relative luminances close to an adult brightness match. Most importantly, the test shows promise as a relatively simple, time-efficient, and portable tool for the assessment of early color vision.

ISSN:1040-5488    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

An operant preferential looking (OPL) test with random dot stereo targets was used to gather developmental data on stereoacuity thresholds in 180 children between 18 and 65 months of age. Results indicated a steady improvement in stereoacuity with age from 250 sec arc in the youngest children tested to 60 sec arc in the oldest group of children. The greatest improvement in stereoacuity occurs at 30 months of age where mean values improve from 225 to 125 sec arc. This large change in stereo threshold appears to be attributable to the significantly higher variability in responses in the children under 30 months of age vs. the lower variability in responses in children over 30 months of age. The overall steady improvements in stereoacuity appear to be a result of the developmental changes in the variability of responses rather than actual neurophysiological changes within the visual system.

ISSN:1040-5488    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

We evaluated the effects of concentric simultaneous vision bifocal contact lenses on task performance, visual acuity, and stereopsis. Forty extensively screened presbyopes were fitted with CIBA Spectrum centernear bifocal contact lenses (BCL) and with distant contact lenses combined with reading spectacles (DCL) which served as the control. Thirty-two subjects completed the 8-week study. At dispensing and after 8 weeks of regular BCL wear, performance times with BCL were significantly greater than with DCL for all three near tasks. BCL generally resulted in more errors per trial. Visual acuities with BCL were reduced significantly by 0.8 to 1.4 acuity lines compared to DCL. Stereopsis was reduced significantly by 32 to 36 sec arc with BCL compared to DCL at both measurement sessions. It is likely that the decreased task performance with the simultaneous vision BCL is caused by the decreased visual acuity with these lenses. Nonetheless, 27 patients (58.7% of those selected to be fitted; 67.5% of those who were fitted) chose to wear the BCL on a regular basis at the study conclusion. Thus, even though BCL reduced task and visual performance, thoroughly screened and properly fitted presbyopic patients can become satisfied BCL wearers. However, the reduced task and visual performance with BCL should be considered when evaluating prospective BCL candidates.

ISSN:1040-5488    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

The advanced avionic and electro-optical systems installed in Army rotary wing aircraft are becoming increasingly incompatible with spectacle wear. Therefore, the prevalence of spectacle wear among Army aviators is an important consideration in the development of future systems. A review of spectacle prevalence data from the Aviation Epidemiology Data Register (AEDR) for the years 1986, 1987, 1988, and 1989 was performed. Data were consistent across all 4 years, with mean prevalence of spectacle wear being 22% for active component forces. Reserve and National Guard components displayed mean spectacle wear prevalences of 27% and 32%, respectively. These prevalence rates are higher than those previously obtained in 1985 by a similar, but slightly different paradigm. Spectacle-wearing aviators exist in greater numbers than previously documented and represent a segment of the aviation population that will have increasing compatibility problems with advanced flight systems. Therefore, system planners will need to address these incompatibilities in future hardware developments.

ISSN:1040-5488    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

Contact lenses were soaked in hydrogen peroxide (H2O2) solutions of 1 to 20 mM (34 to 680 ppm) and placed on isolated rabbit corneas to determine whether H2O2 could penetrate across the tissue into the artificial aqueous humor used to perfuse the endothelial surface. Corneas with intact epithelium allowed no H2O2 to cross into the perfusing fluid even with the lenses containing the highest (20 mM) concentration of peroxide. If the epithelium was removed a transient pulse of H2O2 appeared in the perfusing fluid only from lenses with 10 or 20 mM H2O2. The cornea metabolized H2O2 rapidly (the rate varying with the concentration) and thus the small quantities of H2O2 in the contact lenses (less than 400 nmol at 20 mM) are destroyed before diffusing across the entire thickness of the cornea. When the contact lens was replaced by a 0.8 ml saline containing H2O2, and renewed every 15 min, H2O2 crossed the intact cornea to the perfusing fluid when its concentration at the epithelium was between 3 and 4 mM. Should such larger quantities be presented to the epithelium (for example, in eye drops) the concentration, volume, and duration of exposure will determine whether H2O2 enters the anterior chamber. It is concluded that in the clinical situation of typical contact lens use in an eye with intact epithelium neither the corneal endothelium nor other intraocular tissues will be damaged by residual concentrations of H2O2 up to 680 ppm, whether in single or daily events.

ISSN:1040-5488    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

The results of a previous experiment have shown that stereothreshold varies as a function of the luminance difference between a target and its background. When the luminance of the target is the same as that of the background (isoluminance) the stereothreshold was elevated by a factor of 3 as compared with a situation where there was maximum luminance difference between the target and the background. Generally, if the target and the background have the same color, stereothreshold at a particular luminance difference level was lower (stereoacuity better) than if the target and the background have different colors. This indicates a possible effect of chromatic aberration on stereothreshold which could be responsible for the 3-fold increase in threshold at isoluminance. This possibility has been investigated in this experiment. The results show that even though stereothresholds are sensitive to chromatic aberration this factor cannot explain the elevated stereothreshold at isoluminance.

ISSN:1040-5488    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

The measurement of contrast sensitivity at varying grating frequencies is used increasingly to study visual and neural disorders. It provides more information than conventional acuity measures. Refractive errors initially affect high spatial frequencies, whereas lower spatial frequencies are affected only when these errors are pronounced. Neurophysiological alterations are reflected by depressed sensitivity to coarse gratings. Visual dysfunction has been associated with workplace exposures to a wide range of organic solvents. In microelectronics assembly where large quantities of organic solvents are used in many aspects of the work processes, visual deficits have been observed. The objective of the present study was to compare contrast sensitivity among former microelectronics assembly workers, with normal far and near visual acuity, and a reference group from the same region, with similar acuity. No significant differences were observed between scores at the two ends of the contrast sensitivity curves; however, at the intermediate spatial frequencies, the former microelectronics workers' scores were significantly lower (Student's t-test; p<0.05). For the microelectronics workers, no relation was observed between age and contrast sensitivity at any spatial frequency, whereas for the reference group, contrast sensitivity scores were progressively lower with age at spatial frequencies >6.0 cpd (r2=0.15 at 6 cpd to r2=0.45 at 18.0 cpd), suggesting that for the former there is some form of interference with the expected contrast sensitivity loss with age. Lower contrast sensitivity scores in intermediate spatial frequencies, observed among the former microelectronics workers, possibly reflect neural alterations, which may have resulted from exposure to neurotoxic substances. These findings suggest the need for further studies on visual functions in microelectronics workers.

ISSN:1040-5488    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

A retrospective clinical case study was conducted to determine which therapeutic modality was considered most efficacious in treatment of vernal keratoconjunctivitis (VKC). Therapeutic modalities included: (1) antihistamine- vasoconstrictor preparations; (2) disodium cromoglycate (DSCG); and (3) steroids. Eighteen clinical patients were evaluated based on signs and symptoms. Treatment and management were based on prior experience of the attending clinician. Randomization was not used in forming the patient base for this study, because all patients were part of a private health care facility. Results indicated corticosteroids were the single most effective agents in treating VKC, yet DSCG induced less iatrogenic risk with only a slight decrease in effectiveness when the original inflammation has abated. Antihistamine-vasoconstrictor preparations had only limited success in effective treatment of VKC. The study showed that concurrent use of a steroid and DSCG provided the most efficacious treatment modality for VKC.

ISSN:1040-5488    

出版商:OVID    

年代:1991

数据来源: OVID