Alan W. Johnston

Mobility of People with Retinitis Pigmentosa as a Function of Vision and Psychological Variables

We investigated the mobility performance of subjects with retinitis pigmentosa (RP) as a function of clinical measures of residual vision and psychological variables. We found a highly significant correlation between clinical measures of residual vision and mobility. Pelli-Robson contrast sensitivity and residual visual field together explained 64% of the variance in mobility performance in an indoor shopping mall. We suggest a simple new clinical method of scoring the visual field for predicting mobility performance, the RP Concentric Field Rating. The RP Concentric Field Rating alone explained 60% of the variance in mobility performance. In spite of expectations derived from reading the recent literature, we did not find a significant correlation between psychological variables and mobility performance in a group of subjects with RP.

Relationship between vision impairment and ability to perform activities of daily living

Purpose: To determine the relationship between clinical measures of vision impairment and the ability to perform activities of daily living (ADLs).

Visual characteristics of low vision children.

A retrospective survey of pediatric clinical files from the Kooyong Low Vision Clinic (LVC) showed that the major causes of low vision were congenital or inherited conditions and most children had 6/60 (20/200) or better distance acuities. A classroom evaluation of these children showed that overall, the clinically determined visual acuity corresponded with classroom performance. A high rate of use of prescribed low vision aids was found, and a reading evaluation on a standardized test showed poor performance with respect to reading speed and comprehension, but almost all the children had adequate reading accuracy. Considering the importance of reading in education, greater emphasis on reading evaluations in routine low vision examinations is recommended.

Comparison of functional mobility performance with clinical vision measures in simulated retinitis pigmentosa

Simulations of retinitis pigmentosa (RP) under various conditions of retinal illuminance were designed and investigated in order that they might be used in the mobility training of clients with early RP. Goggles incorporating a 2.5 neutral density (ND) filter with a 0.5-mm diameter pinhole were found to be a potentially useful simulation device for this purpose. This investigation also compared mobility performance with clinical vision measures under photopic, mesopic, and scotopic conditions of retinal illuminance. Although none of the clinical vision measures we used was entirely predictive of mobility performance, some measures were better predictors than others. For a severe constriction of the visual field and decreasing retinal illuminance, both edge contrast sensitivity and visual acuity, measured outdoors, accounted for a greater proportion of the variance in mobility performance than did low contrast visual acuity measured under the same circumstances. The same clinical vision measures, taken in-doors, were of no value in predicting outdoor mobility performance.

A Weighted version of the Melbourne Low-Vision ADL index : A measure of disability impact

Objective. To develop a version of the Melbourne Low-Vision ADL Index that measures the personal impact of disability in activities of daily living (ADL’s). Also, to determine the relationship between clinical measures of vision impairment and disability impact. Methods. The Melbourne Low-Vision ADL Index (MLVAI) is a desk-based clinical assessment of disability in ADL’s. Ability to perform each item is rated on a five-level descriptive scale from zero to four. In this study, the original version of the MLVAI was modified to measure disability impact. The simple modification involved weighting each item by the importance of that item to the person being tested. Importance was also rated on a five-level scale from zero to four. The validity and reliability of the Weighted Melbourne Low-Vision ADL Index (MLVAIW) was determined for 97 vision-impaired subjects in a cross-sectional study. Results. Cronbach’s alpha coefficient indicated an internal reliability of 0.94, and an intraclass correlation coefficient indicated an overall reliability of 0.88. The standard error of measurement was 24.7 points (out of a possible score of 400). There was a statistically significant difference in test scores between normal subjects and vision-impaired subjects. All vision measures had a high, statistically significant correlation with MLVAIW score. Near-word acuity had the strongest correlation (rs = 0.78, p < 0.001), followed by Melbourne Edge Test contrast sensitivity (rs = −0.72, p < 0.001). Visual field had the weakest correlation (rs = −0.52, p < 0.001). The best predictive model of MLVAIW score incorporated the variables age, near-word acuity, and visual field. Together, these variables accounted for 65.1% of the variance in MLVAIW score. Conclusions. The MLVAI is highly valid and reliable when weighted by a scale that reflects the personal importance of ADL’s. The MLVAIW can provide information over and above that obtained with the usual clinical vision measures and may be used to assess low-vision patients and to measure low-vision rehabilitation outcomes. It is suggested that the assessment of disability using the original MLVAI and the assessment of the impact of disability using the MLVAIW should be kept separate to facilitate the clear interpretation of the outcomes of low-vision rehabilitation.

Preliminary investigation of the responsiveness of the Melbourne low vision ADL index to low-vision rehabilitation

Purpose. To conduct a preliminary investigation on the ability of the Melbourne Low Vision ADL Index to detect changes in functional ability as a result of low-vision rehabilitation. Methods. Twenty two subjects with age-related macular degeneration (ARMD) who were newly referred to the Kooyong Low Vision Clinic were recruited. The Melbourne Low Vision ADL Index was administered prerehabilitation and postrehabilitation. Changes in scores and effect size statistics were analyzed. Results. The median total score for the subjects prerehabilitation was 67, and the median total score postrehabilitation was 76. The difference in prerehabilitation and postrehabilitation scores was statistically significant (Wilcoxon signed rank test = 248.5, p < 0.001). The mean change score for the total Melbourne Low Vision ADL Index was 9.3 (SD, 5.6). Thus the overall effect size statistic (mean change score divided by SD of prerehabilitation score) was 0.78. Conclusions. This preliminary investigation indicates that the Melbourne Low Vision ADL Index is responsive to a rehabilitation program for patients with ARMD. It has potential to be used as a measure of low-vision rehabilitation outcomes.

The Importance of the Test Parameters in the Clinical Assessment of Accommodative Facility

Normative data for accommodative facility have recently become available. This study investigates the effect of varying the test parameters of lens power, target size, test distance, and test duration on binocular accommodative facility. Binocular accommodative facility decreased as a function of increasing lens power and decreasing target size. Differences in response times to the plus and minus phases of the flip test were not evident under any of the conditions. Interesting effects of proximity occurred at the nearer test distance. The results show the importance of strict control of testing procedures to achieve meaningful data.

Optometric manpower in Australia

Surveys of optometric manpower in Australia were conducted by the Australian Optometrical Association (AOA) in 1982, 1984 and 1987. The primary aim of these surveys was to establish a data base on current levels of optometric manpower in Australia. Information on the characteristics of registered optometrists residing in Australia was collected by the State Divisions of the AOA and through a survey of Australian optometrists.

Color vision characteristics of visually impaired children.

A classroom assessment of color vision characteristics of children with low vision was conducted using a battery of tests. The results showed 75% of the children failed one or more tests, although only 24% had a moderate or severe color vision defect. Comparisons with the low vision clinic color vision assessment showed that many of the children were not identified as being color vision defective. Considering the use of color-coded information in education, greater emphasis on color vision evaluations in routine low vision examinations is recommended.

Visibility of Traffic Control Devices: Catering for the Real Observer

Despite continuing review of design rules for traffic control devices and occasional reviews of visual standards for operators of vehicles, there is still a gulf between what the design engineer expects users to be able to see and the actual visual performance of the user population under practical conditions This paper reviews the visual characteristics of the ‘ real ’ observer using both conventional methods of assessment and an information theory approach. Recent research by the authors and their colleagues on the acquisition of information by observers with normal and degraded vision shows that present scales for specifying visual performance do not adequately represent the visual requirements of many practical tasks These studies also suggest that there should be a. more systematic approach to the development of design rules based on visual performance characteristics of the whole user population rather than only that proportion of the population which has normal vision. Equally there should be a mor...