The moving Dynamic Random Dot Stereosize test: development, age norms, and comparison with the Frisby, Randot, and Stereo Smile tests.

PURPOSE: To determine the response of infants and children to the Moving Dynamic Random Dot Stereosize (MDRS) test and to collect cross-sectional age-related data. METHODS: Sixty visually normal individuals were divided into four age groups: 0.5-<2, 2-<5, 5-<8, and 8-<20 years. Stereopsis was measured with the MDRS test on two occasions, plus the Frisby, Randot, or Stereo Smile tests, as was age appropriate. RESULTS: All children aged >2 years and 80% of the children between ages 6 months and 2 years were able to perform the MDRS test on at least one occasion. Sixty percent of the 6-month to 2-year-old children were able to perform the Stereo Smile test on both occasions. Performance on the MDRS test improved with age up to 9 years. Improvement on the Frisby and Randot tests was seen in children aged up to 7 years. Mean and 95% confidence interval ranges for each test are given. CONCLUSION: This study gives evidence that aspects of the visual system are not fully mature until age 7-9 years. The MDRS test is a visually demanding but cognitively simple test that shows potential for detecting visual anomalies in young children.

What is low vision? A re-evaluation of definitions.

PURPOSE: To re-evaluate definitions of low vision, visual impairment, and disability. METHODS: We review current definitions of legal blindness and low vision and how these definitions are variably based on disability or impairment. We argue for a definite distinction being made between criteria for visual impairment and visual disability, low vision being defined as the presence of a visual impairment that results in a disability. Visual impairment is defined according to population norms and a statistical cut-off is used. Visual disability is defined by consideration of the level of visual measures which result in measurable or reportable disability. We consider the evidence that contrast sensitivity should be a criterion for visual disability in addition to visual acuity and visual field. CONCLUSIONS: According to the current information, we define visual impairment as best monocular or binocular visual acuity <(worse than) 6/7.5, total horizontal visual field <146 degrees (Goldmann III-4e) or <109 degrees (III-3e), and contrast sensitivity <1.5 (PelliRobson); we define visual disability as best monocular or binocular visual acuity <6/12 or contrast sensitivity <1.05.

Crowding in central and eccentric vision: the effects of contour interaction and attention.

PURPOSE: To quantify the crowding effect with eccentric stimuli and to determine the relative contribution of neural interaction and attention to crowding in central and eccentric vision. METHODS: Monocular visual acuity was measured with computer-generated tumbling E and Landolt C targets presented centrally or at 2 degrees in the right visual field. Crowding distractors were designed to cause increasing contour interaction or increasing need for focused attention. A four-alternative forced-choice method of constant stimuli was used. In experiment 2 the distance between the target and the distractors was varied. RESULTS: Data are presented in terms of normalized visual acuity. Crowding in central vision was minimal, mainly caused by contour interaction, and did not occur with distractors more than four stroke widths distant. Crowding in eccentric vision was far greater in magnitude and extent (occurring for distractors as far as 16 stroke widths distant) and was caused by contour interaction and attentional factors. CONCLUSIONS: The results indicate that eccentric vision differs quantitatively and qualitatively from central vision. The extent of contour interaction effects are consistent with the proposed size of cortical processing zones. The results are discussed with reference to current theories of preattentive and attentive tasks and with reference to subjects with low vision due to central scotoma who use an eccentric retinal locus for fixation.

Evaluating the value of low-vision services.

BACKGROUND: Low-vision care is a widely accepted and valued service provided by many optometrists. As in other areas of health care, evaluation of the outcome of low-vision care is increasingly necessary so it can be properly positioned in the health care delivery system. METHODS: This article reviews the literature relating to the prevalence of low vision, its impact on affected individuals, and how low-vision intervention affects those with visual impairments. This review considers the ways in which the impact of low-vision care has been evaluated. RESULTS: The existing literature demonstrates that low-vision intervention can be highly valued by low-vision patients and can have a significant impact on an individual's daily life and activities. Evaluating this impact is a significant challenge-particularly if the goal is to gauge the outcome of low vision care as broadly as possible. CONCLUSIONS: Evaluation of health-related quality of life is a desirable option for evaluation of outcomes, and the application of quality of life instruments to the visually impaired population is necessary. There remain unresolved issues of optometric research that need to be addressed.

The validity of current clinical tests of contrast sensitivity and their ability to predict reading speed in low vision.

PURPOSE: Contrast sensitivity (CS) testing using chart tests of CS is becoming increasingly common in low vision assessment. Yet we know little about the validity of these charts, i.e. which region of the spatial frequency spectrum is being measured. In this study we aimed to determine the validity of currently available CS charts by comparison against oscilloscope-based CS. We also determined their relative ability to predict reading speed. METHODS: CS was measured with five commercially available charts and the contrast sensitivity function was determined with sinusoidal gratings presented on a Joyce screen using a two-alternative forced choice staircase technique in 36 observers with low vision and 3 with normal vision. Reading rate was also measured with the subject reading with his or her own optical low vision aid. RESULTS: The results show that the Pelli-Robson chart and the Cambridge gratings are good measures of medium to low spatial frequencies, as would be predicted from their design, while the Regan and UW charts correlated with medium to high frequencies. The Vistech chart was a good predictor of CS at each spatial frequency. CONCLUSIONS: The best chart test of CS depends on which region of the CS curve is of interest. All the charts were good predictors of reading rate.

Accommodative response in children and young adults using dynamic retinoscopy.

Accommodation in children and non-verbal adults can be difficult to assess using standard subjective techniques and hence is often not evaluated. By using a modification of Nott dynamic retinoscopy, rapid objective evaluation of accommodative function is possible. In this study, accommodative response to a range of accommodative demands was measured in 55 normally sighted children and young adults using dynamic retinoscopy. The data were found to fall into four age groupings: 3-10-year-olds' mean accommodation was accurate to within 0.5 D, although 3-5-year-olds over-accommodated slightly, while 6-10-year-olds under-accommodated. Subjects over 10 years of age showed under-accommodation which increased with accommodative demand. These norms are presented for clinical use against which measurements on an individual paediatric or non-verbal patient can be compared. Future studies will determine whether specific patient populations, e.g. patients with cerebral palsy or low vision, demonstrate normal or reduced accommodation.

Reduced accommodation in children with cerebral palsy.

Accommodation in 43 subjects with cerebral palsy was measured objectively using a dynamic retinoscopy technique, which has already been shown to be reliable and repeatable. The subject's ages ranged from 3 to 35 years. Of these, 42% were found to have an accommodative response pattern which was different from the normal control group for his/her age. Nearly 29% had an estimated amplitude of accommodation of 4 D or less. The presence of reduced accommodation was found to be associated with reduced visual acuity, but was not associated with cognitive or communication ability, refractive error or age. The prevalence of other ocular disorders in this group is also high. These findings have developmental and educational implications.

Outcome of low vision aid provision: the effectiveness of a low vision clinic.

PURPOSE: Although there is an increasing need for primary low vision (LV) care, few studies have considered the success rates of optometric LV rehabilitation. We considered the objective success and perceived benefit obtained by 57 elderly LV patients. METHOD: Tests of reading speed and questionnaires were administered in the patient's home after initial and follow-up visits to a LV clinic. Additional information was taken from the patient's clinic record. RESULTS: Benefits from attending the clinic were reported by 89.5% of patients and 81% of patients were regularly using low vision aids (LVA's). There was a discrepancy between ability to read 1M print in the clinic (75% of patients) and the reported ability to read regular-sized print at home (35%). Perceived benefit from visiting the clinic was strongly associated with the ability to perform daily living tasks and to read 2M print. There was some association between perceived benefit and frequency of using the LVA's, but not with duration of use. CONCLUSION: The results encourage a change in emphasis during LV assessments from sustained reading to the ability to perform daily living activities.

Reduced accommodation in children with Down syndrome.

PURPOSE: To examine the accommodative accuracy and amplitude in children with Down syndrome. Accommodation is usually assumed to be good in children and is rarely measured. METHODS: A dynamic retinoscopy technique was developed that allows rapid and reliable measures of accuracy and amplitude of accommodation in infants and children. RESULTS: Use of the dynamic technique with a small sample of schoolchildren with Down syndrome shows that 80% have reduced amplitude of accommodation, in comparison to a control group of developmentally normal children. CONCLUSIONS: Optometric management of children with Down syndrome should include consideration of accommodation.

Reading performance with low vision aids: relationship with contrast sensitivity.

Reading performance and contrast sensitivity were measured in 30 subjects with low vision due to a variety of pathologies. The Pepper test was used to quantify reading rate and accuracy with the subject's own prescribed optical reading low vision aid. It was found that both reading rate and accuracy were repeatable measures. Reading rates were found to be correlated with contrast sensitivity at 0.5 c/deg (r = 0.62). Multiple regression analysis also showed that the best predictor of reading rate was contrast sensitivity at 0.5 c/deg and that no other components of the contrast sensitivity function helped to explain more of the variance. This indicates that primarily low spatial frequencies are necessary for reading with optical low vision aids, as has been found previously for reading with a close circuit TV system.

Vision assessment and rehabilitation in low vision.

This subjective review of the year's literature on low vision, with particular emphasis on rehabilitation, attempts to search out and discuss what is new and innovative rather than to cover the year's publications with equal weight. The review covers areas of testing and assessment of children and the multiply impaired with low vision, vision stimulation, low vision aids and devices, approaches in congenital and acquired nystagmus, potential advances in high-technology applied to low vision, and psychological and educational aspects including lighting requirements for the elderly.

Modulation transfer functions of low-vision AIDS: comparison with spatial-frequency requirements in low vision.

Modulation transfer functions (MTF's) of 26 low-vision aids (LVA's) were measured by using the EROS solid-state system. The object and image distances of the LVA's were as in normal usage by a patient. The contrast thresholds of patients who use LVA's were also measured. All LVA's measured have more than adequate contrast transmission at the low frequencies that are important for these subjects, but many have wasted transmission at medium and high frequencies. LVA's with poorer high-frequency MTF can be used successfully by low-vision patients. It is suggested that in future design high resolution should be sacrificed for a greater lens diameter while maintaining a high MTF at low spatial frequencies.

Use and non-use of low vision aids by visually impaired children.

The results of this study indicated that children do use and benefit from low vision aids and that the child's need for near low vision aids can be predicted from their age, unmagnified reading performance, and visual field characteristics. The use of distance monoculars is less easily predicted. However, many visually impaired children both in mainstream special units and in schools for the blind are not being supplied appropriate low vision aids (LVAs). Many have not had an LVA assessment within 1 year and others are experiencing difficulties with LVAs that could be eliminated or reduced.

Do long wavelength pass filters improve low vision performance?

It has been suggested that the wearing of band-pass tints may improve the contrast performance in certain ocular conditions. We examined this by measuring grating visual acuity (VA) for targets of various contrasts. The benefits of Corning CPF 511, 527 and 550 lenses, and neutral density (ND) filters were examined with and without the presence of glare. Generally, patients with anterior sector conditions showed improved performance with band-pass filters (not with ND filters). It is suggested that the filter reduces the scatter within the ocular media. People with retinitis pigmentosa or diabetic retinopathy rarely benefited. The CPF 511 most frequently improved VA followed by CPF 527 and 550 respectively. We suggest that a condition of glare is incorporated when assessing suitability with tints.

The experience of a university-based low vision clinic.

An open low vision clinic has been in operation at University of Wales College of Cardiff, Department of Optometry for 5 years. This paper describes the demography and visual characteristics of 218 consecutively presenting patients. A detailed survey of the aids prescribed is conducted. A significant proportion of low vision patients required only simple aids (56.8%) and low magnification (71.6%). It is suggested that these patients could be assisted in an optometric practice. In addition, visual acuity, distance or near is not a good indicator of eventual visual performance with an LVA. Therefore, it was concluded that all patients having measurable form vision should receive a low vision assessment.

Rivalry with continuous and flashed stimuli as a measure of ocular dominance across the visual field.

Two measures of sensory ocular dominance were compared. Both involved dichoptic presentation of orthogonal gratings--a situation which results in binocular rivalry. The gratings were presently briefly in experiment 1 and continuously in experiment 2 and by the predominance of one grating over the other a quantitative estimation of ocular dominance was obtained in both cases. Comparison of the results showed that (a) binocular rivalry suppression was present for exposures of 250 ms and (b) the briefly presented gratings were a more sensitive test for ocular dominance than conventional continuously presented stimuli. The variation of dominance over the horizontal meridian of the visual field was considered. For many subjects a consistent different in the ocular dominance in the two halves of the visual field, and therefore of the cortex, was found. Some showed dominance of the ipsilateral eye in each hemisphere while others showed dominance of the contralateral eye. It was found that there is, in fact, a continuum of types of dominance pattern amongst individuals.