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PubMed2003

Binocular vision and prehension in middle childhood.

Binocular cues have been shown previously to make an important contribution to the control of natural prehensile movements in adults [Visual Cognition 4 (1997) 113, Vision Research 32 (1992) 1513, Neuropsychologia 38 (2000) 1473]. The present study examined the role of binocular vision in the control of prehension in middle childhood. Fourteen children aged 5-6 years, and 16 children aged 10-11 years reached out and grasped different sized objects at different distances, in either binocular or monocular viewing conditions. In contrast to adult data, many of the principal kinematic indices of the children's reaches were unaffected by the removal of binocular information. The older children, like adults, spent an increased amount of time in the final approach to the object when only monocular information was available. However, both peak wrist velocities and peak grip apertures were unaffected by the removal of binocular information and continued to scale with object properties in the normal way. These results suggest that the use of binocular cues to control prehensile movements is not yet mature at the age of 10-11 years.

Child↗
PubMed2002

The role of the cyclopean eye in vision: sometimes inappropriate, always irrelevant.

During binocular fixation, the eyes usually point in different directions, and yet, each object is judged to lie in a single direction. It is commonly believed that a particular location in the head serves as the origin for such directional judgments. This location is known as the cyclopean eye. We argue here that observers can judge visually perceived directions from angular information alone, and do not require positional information supplied by a cyclopean eye. We show that experimental findings reported as evidence for the cyclopean concept can also be explained solely by angular information without the need for a cyclopean eye. Recent findings concerning binocular shape perception and the cyclopean illusion demonstrate that binocular perception is incompatible with vision from a single vantage point. The concept of the cyclopean eye is sometimes inappropriate and always irrelevant as far as vision is concerned.

Depth Perception↗
PubMed2003

Simulation of artificial vision: I. Eccentric reading of isolated words, and perceptual learning.

Simulations of artificial vision were performed to assess "minimum requirements for useful artificial vision". Retinal prostheses will be implanted at a fixed (and probably eccentric) location of the retina. To mimic this condition on normal observers, we projected stimuli of various sizes and content on a defined stabilised area of the visual field. In experiment 1, we asked subjects to read isolated 4-letter words presented at various degrees of pixelisation and at various eccentricities. Reading performance dropped abruptly when the number of pixels was reduced below a certain threshold. For central reading, a viewing area containing about 300 pixels was necessary for close to perfect reading (>90% correctly read words). At eccentricities beyond 10 degrees, close to perfect reading was never achieved even if more than 300 pixels were used. A control experiment using isolated letter recognition in the same conditions suggested that lower reading performance at high eccentricity was in part due to the "crowding effect". In experiment 2, we investigated whether the task of eccentric reading under such specific conditions could be improved by training. Two subjects, naive to this task, were trained to read pixelised 4-letter words presented at 15 degrees eccentricity. Reading performance of both subjects increased impressively throughout the experiment. Low initial reading scores (range 6%-23% correct) improved impressively (range 64%-85% correct) after about one month of training (about 1 h/day). Control tests demonstrated that the learning process consisted essentially in an adaptation to use an eccentric area of the retina for reading. These results indicate that functional retinal implants consisting of more than 300 stimulation contacts will be needed. They might successfully restore some reading abilities in blind patients, even if they have to be placed outside the foveal area. Reaching optimal performance may, however, require a significant adaptation process.

Adult↗
PubMed2003

Early binocular vision in human infants: limitations on the generality of the Superposition Hypothesis.

The Superposition Hypothesis states that the binocular vision of newborn infants blends together the monocular visual responses of the two eyes, even when the visual stimulus evokes binocular rivalry in adults. According to the Superposition Hypothesis, this blending is replaced by binocular rivalry after the emergence of stereopsis [Neonate Cognition: Beyond the Blooming, Buzzing Confusion, Erlbaum, Hillsdale, NJ, 1985, p. 37; Early Visual Development Normal and Abnormal, Oxford University Press, New York, 1993, p. 201]. The main evidence for the Superposition Hypothesis is a preferential looking experiment [Vision Res., 26 (3) (1986) 501], in which 8-12-week-old infants fixated a rivalrous (for adults) dichoptic plaid, in preference over a fusible grating of parallel lines. This report describes our attempt to repeat that important experiment. Infant stereopsis emerged at 8.6 weeks under our conditions, but infants did not preferentially fixate the dichoptic plaid at any age between age 5 and 16 weeks. Control experiments showed that our result was not due to technical differences between their experiment and ours (red/green vs. polarizing glasses, the use of a fixation point, or the infant observation apparatus). Therefore, blending of the visual responses to rivalrous (for adults) stimuli is not a general feature of the pre-stereoptic infant visual system.

Analysis of Variance↗
PubMed1997

Capture of visual direction: an unexpected phenomenon in binocular vision.

Binocular perception of visual direction is based on laws which were formulated more than 100 years ago. These laws govern the directions in which human beings perceive objects visible to both eyes (binocular objects) and objects visible to only one eye (monocular objects). We report here that the laws do not hold for monocular objects adjacent to binocular objects. The perceived directions of these monocular objects are captured by those of nearby binocular objects. Capture of binocular visual direction is an unexpected phenomenon because it refutes the generally accepted notion that a particular retinal location gives rise to a particular subjective visual direction. The practical consequence is that the subjective techniques for measuring eye position which are widely used in fundamental research and clinical practice are unreliable if they are used in densely structured stimuli. We suggest that capture results from a mechanism of lateral interaction between adjacent visual directions. This mechanism ensures that, despite eye movements, objects have the same spatial order in monocular and binocular vision. This conservation of spatial order also explains why retinal blind spots are not manifest in binocular vision.

Convergence, Ocular↗
PubMed1991

Measurement of low vision in children and infants.

The authors evaluated a preferential looking technique (Teller acuity cards) and a set of gross behavioral indicators (visual function battery) for the ability to rank visually impaired children and infants on the basis of their visual function. Fourteen older children with a diagnosis of cicatricial retinopathy of prematurity who were capable of giving Snellen acuities and a group of 31 preverbal infants with decreased vision due to a variety of causes were tested. Teller acuity card and visual function battery findings were highly correlated with each other (and with Snellen acuities in the older group); however, the Teller acuity cards provided better discrimination in the moderately visually impaired range, whereas the visual function battery was better in the severely impaired range. It is concluded that, in children and infants, visual function over the entire spectrum of low vision can be characterized by using a combination of the Teller acuity cards and the visual function battery.

Adolescent↗
PubMed2004

Binocular vision impairment after refractive surgery.

PURPOSE: To illustrate the need for an accurate preoperative orthoptic examination to prevent postoperative changes in binocular vision. SETTING: Department of Ophthalmology, University Hospital Antwerp, Edegem, Belgium. METHODS: Five patients presenting major subjective complaints after refractive surgery were analyzed. RESULTS: In 1 patient, a latent N IV palsy decompensated after laser in situ keratomileusis (LASIK) in the more myopic eye to achieve monovision. A second patient, operated on for N IV palsy 10 years earlier, presented a recurrence of the palsy after bilateral LASIK for myopia. The third patient complained of discomfort in binocular vision caused by aggravation of a preexisting intermittent esotropia that worsened after LASIK for hyperopia. The fourth patient complained of diplopia after LASIK in the highly anisometropic and exotropic eye. The fifth patient experienced a decrease in fusion and stereopsis at the time he became anisometropic after bilateral LASIK. CONCLUSIONS: Special care should be taken of patients who have a preoperative history of strabismus surgery, an overcorrection or undercorrection in 1 or both eyes, or anisometropia and of those who are unhappy with contact lenses. An orthoptic examination should be done with and without spectacle correction to detect underlying vertical phorias. Intended monovision should be examined initially using contact lenses.

Adult↗
PubMed1992

Functional binocular vision is not dependent on visual experience in the praying mantis.

In vertebrates, it has been shown that binocular visual experience is necessary to develop normal spatial vision. We have investigated whether this is also true for an invertebrate, the praying mantis. The praying mantis is a predatory insect in which prey localization involves the use of binocular disparities. We raised mantids which had one eye occluded throughout development and tested monocular visual fixation and binocular distance estimation in the adult animals. The results revealed that both fixation and prey catching behavior were normally functional in the monocularly reared animals. Thus we conclude that, in mantids, binocular vision is based on a fixed mode of development.

Animals↗
PubMed2004

Do routine eye exams improve vision?

We use a longitudinal national sample of Medicare claims linked to the National Long-Term Care Survey (NLTCS) to assess the productivity of routine eye examinations. Although such exams are widely recommended by professional organizations for certain populations, there is limited empirical evidence on the productivity of such care. We measure two outcomes, the ability to continue reading, and no onset of blindness or low vision, accounting for potential endogeneity of frequency of eye exams. Using instrumental variables, we find a statistically significant and beneficial effect of routine eye exams for both outcomes. Marginal effects for reading ability are large, but decline in the number of years with eye exams. Effects for blindness/low vision are smaller for the general elderly population, but larger for persons with diabetes. Instrumental variables provide a useful approach for assessing the productivity of particular interventions, particularly in situations in which randomized controlled trials are expensive or perhaps unethical and difficult to conduct over a lengthy time period.

Cost-Benefit Analysis↗
PubMed2001

The influence of level and polarity of figure-ground contrast on vision.

PURPOSE: To document the effect upon human foveal vision of changes in the level and polarity of figure-ground contrast under photopic controlled test conditions, with particular emphasis on performance at low contrast levels. METHODS: Using a forced-choice psychophysical paradigm, threshold acuity estimates were derived at 9 discrete levels over a near-3 octave contrast range for Landolt ring-type stimuli of either positive or negative polarity. Data were obtained under binocular conditions from 10 young adults, each wearing their optimum low myopic spectacle correction. RESULTS: Visual acuity declined linearly with reducing stimulus contrast, the deterioration increasing substantially at <10% figure-ground contrast regardless of stimulus polarity. Performance was slightly (but not statistically significantly) better for positive contrast stimuli. CONCLUSION: Irrespective of contrast polarity, a reduction in stimulus figure-ground contrast <10% produces an accelerated decrement in photopic foveal vision compared to the performance at levels >10%. Some clinical and practical implications of this outcome are considered with regard to the examination of patients with normal and compromised visual function.

Adult↗
PubMed2000

The effect of pupil dilation with tropicamide on vision and driving simulator performance.

PURPOSE: To assess the effect of pupil dilation on vision and driving ability. METHODS: A series of tests on various parameters of visual function and driving simulator performance were performed on 12 healthy drivers, before and after pupil dilation using guttae tropicamide 1%. A driving simulator (Transport Research Laboratory) was used to measure reaction time (RT), speed maintenance and steering accuracy. Tests of basic visual function included high- and low-contrast visual acuity (HCVA and LCVA), Pelli-Robson contrast threshold (CT) and Goldmann perimetry (FIELDS). Useful Field of View (UFOV--a test of visual attention) was also undertaken. The mean differences in the pre- and post-dilatation measurements were tested for statistical significance at the 95% level using one-tail paired t-tests. RESULTS: Pupillary dilation resulted in a statistically significant deterioration in CT and HCVA only. Five of 12 drivers also exhibited deterioration in LCVA, CT and RT. Little evidence emerged for deterioration in FIELDS and UFOV. Also, 7 of 12 drivers appeared to adjust their driving behaviour by reducing their speed on the driving simulator, leading to improved steering accuracy. CONCLUSIONS: Pupillary dilation may lead to a decrease in vision and daylight driving performance in young people. A larger study, including a broader spectrum of subjects, is warranted before guidelines can be recommended.

Adult↗
PubMedDate not supplied

Unemployment and under-employment in adults with vision impairment: The RVIB Employment Survey.

PURPOSE: The purpose of this study was to describe the labour force status in Victorian adults with vision impairment and any factors associated with unemployment and under-employment. METHODS: Participants were recruited in 1997. A telephone interview was conducted by trained interviewers. RESULTS: A total of 250 people participated. They ranged in age from 19 to 59 years (mean 40.7 years) and 119 (48%) were male. Thirty-nine (16%) people regarded themselves to be totally blind. Nearly everyone (n=241, 96%) had been employed at some time during their lifetime; however, only 149 (60%) were currently employed. The current rate of participation in the labour force was 73.3% (95% CL, 67.8%, 78.8%) and the current unemployment rate was 18.2% (95% CL, 12.6%, 23.9%). The current rate of under-employment was 16.0% (95% CL, 10.7%, 21.4%). A total of 126 (50%) people had used services that help with employment at some stage; this was not significantly associated with current employment status (P > 0.10). The factors significantly associated with unemployment in multivariate analyses were a self-report of eyesight limiting time available for work or other activities (OR=3.02; 95% CL, 1.56, 5.85) and currently looking for work (OR=5.92; 95% CL, 2.94, 11.9); never having worked was of borderline significance (OR=5.26; 95% CL, 0.85, 32.7) as a result of the small numbers of people surveyed. The only factor significantly associated with under-employment was self-employment (OR=5.46; 95% CL, 1.95, 15.3). DISCUSSION: Results from this study reveal that visual function is not a predictor of labour force status. The relatively low use of specialty employment services and the rather high rate of discouraged job seekers suggest that the employment outcomes of people who use these services should be investigated further, and that attention should be directed at improving retention of employment in people with vision impairment.

Adolescent↗
PubMed2000

Functional implications of vision impairment.

This study investigated the functional implications of vision impairment. A total of 508 participants in the Visual Impairment Project completed the VF-14 questionnaire, vision-related functional tasks, an interview, and the ophthalmic examination. Participants with less than 6/12 presenting acuity were more likely to report a moderate to high degree of difficulty performing VF-14 items (odds ratios from 6 to 44). They were also more likely to be unable to recognize a 10 cent coin (OR; 7.0, 95% CL; 2.6, 19.3) or correctly read a telephone number (OR; 10.1, 95% CI; 5.6, 18.1). As demonstrated by the VF-14 and the functional tasks administered in this study, visual impairment affects the ability of people to conduct a variety of common daily tasks.

Aged↗
PubMed1999

Paediatric community vision screening--a new model.

The purpose of this study was to establish if a community based model using a Hospital Optometrist and Community Orthoptist can provide a practical secondary vision screening service for children. These professionals working in an Inner London Health Centre, assessed children who had failed primary vision screening. In total 483 new patients were seen between April 1994 and March 1996 with the largest referral source being the school nurse screening programme. The majority were managed by the team with a total onward referral rate to the Hospital Eye Service of 14%. In 78% of these cases the consultant's diagnosis agreed with the reason for referral. Where the consultant's diagnosis differed the children were identified as normal or a variant of normal. This model of care provides a 'one stop service' where a child identified as having a potential visual problem at primary screening can be assessed, refracted and provided with spectacles in a local setting without hospital referral. Referrals to the Hospital Eye Service are considerably reduced and a convenient service is provided for parents and children.

Age Distribution↗
PubMed2004

Effect of light filters on reading speed in normal and low vision due to age-related macular degeneration.

PURPOSE: To investigate the effects of light filters on reading speed in normal and low vision due to age-related macular degeneration (AMD). METHODS: Reading speed was determined for 12 subjects with normal vision and 12 subjects with non-exudative AMD using stationary lowercase nonsensical print in Times Roman font and four light filters; a yellow Corning Photochromic Filter (CPF) 450, a grey neural density (ND) filter, an individual filter obtained using the Intuitive Colorimeter and a clear filter. RESULTS: There was no statistically significant light filter effect on reading speed for the normal subjects. The AMD group demonstrated a statistically significant 5% average improvement in reading speed with the CPF450 compared with the other filters although some AMD subjects had improvements of 10-15%. CONCLUSIONS: Light filters obtained using the Intuitive Colorimeter(R) performed poorly when compared with the CPF450, ND and clear filters for both the study groups. For the AMD group, average reading speed was statistically greater with the CPF450 than the other filters, however it is questionable whether the improvement (5%) would be clinically significant. As some of the subjects with AMD had greater improvements with the CPF450 we advocate clinical assessment of light filters using existing protocols on an individual basis.

Aged↗
PubMed2004

[Central vision].

The clinical assessment of vision by means of optotypes does by no means test just two-point resolution, since a correct naming of the letters or digits requires a preceding visual object recognition. Cortical lesions can massively deteriorate vision up to a "Seelenblindheit" in spite of intact optics and retina. There are different processing levels involved in the analysis which can be individually defective, leading to disorders from visual indiscrimination to agnosia or anomia.

Agnosia↗
PubMed2004

[Color vision and the diagnosis of reduced visual acuity].

Unexplained visual acuity loss requires a systematic approach to gather as many findings of diagnostic value as possible. Most retinal or optic nerve diseases are accompanied by color vision disorders. The type and severity of color vision disorders may provide additional diagnostic or guiding information or may uncover aggravating or simulating factors.

Adult↗
PubMed1989

[Monocular and binocular vision following lens implantation in traumatic cataract].

Lens implantation after surgery for traumatic cataract is a major help in rehabilitating the patient. Most such patients are still at work. Surgical problems result from injuries to the cornea, iris, lens, and vitreous body. If possible a posterior chamber lens should be implanted in the bag. In 35 patients, 24 posterior chamber lenses and 11 anterior chamber lenses were implanted. In 27 cases the traumatic cataract had been caused by perforating injury and in eight by contusion. In 28 patients there was a significant improvement in visual acuity by the day they were discharged. At short focus more than one-half of the patients had simultaneous vision with striated glasses, and two-fifths at long focus. Two-fifths of all patients attained stereoscopic vision at both short and long focus. The binocular functions were worse in most of the cases where the visual acuity of the injured eye was 0.4 or less.

Adult↗

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