Visual acuity testing. From the laboratory to the clinic

AbstractThe need for precision in visual acuity assessment for low vision research led to the design of the Bailey–Lovie letter chart. This paper describes the decisions behind the design principles used and how the logarithmic progression of sizes led to the development of the logMAR designation of visual acuity and the improved sensitivity gained from letter-by-letter scoring. While the principles have since been adopted by most major clinical research studies and for use in most low vision clinics, use of charts of this design and application of letter-by-letter scoring are also important for the accurate assessment of visual acuity in any clinical setting. We discuss the test protocols that should be applied to visual acuity testing and the use of other tests for assessing profound low vision when the limits of visual acuity measurement by letter charts are reached

Auditory-visual speech perception: The effect of visual acuity in older people

"Article Copyright 2004 The Authors." "Published edition Copyright 2004 Australian Academic Press. Published version of the paper reproduced here with permission from the publisher."This study aimed to investigate the benefit gained by older people in auditory-visual speech perception compared to auditory-only perception and to investigate the correlation between visual acuity and benefit gained. A total of 77 community-based older people participated in the study. Pure-tone audiometry showed that 36% had normal hearing, 40% had a mild hearing loss and the remainder (23%) had a moderate or greater loss. Objective easurements of corrected distance and near visual acuities were obtained using the Bailey-Lovie logMAR distance and near visual acuity tests. According to the criteria used in the present study, 34% had some distance vision impairment and 9% had some near vision impairment. The benefit gained in auditory-visual speech perception was determined by comparing auditory-only and auditory-visual performance on the Bamford-Kowal-Bench Australian Version Speech reading Test. An average visual benefit of 28.8% was achieved by the participants, and, for the vast majority of participants (86%), the benefit gained was statistically significant. A significant correlation was not found between either distance or near visual acuity and benefit gained in auditory-visual speech perception. The implications of these findings are that it is important for audiologists to recommend the use of lipreading to older clients, irrespective of their visual impairment, as the majority will gain significant benefit from the use of visual cues

Problem Based Learning in Optometry

Problem based learning in Optometr

Problem based learning in Optometry

Problem based learning in Optometr

Hearing and vision impairments affect the everyday lives of healthy older Australians

Letter to the edito

Low vision services in Australia

A survey of the low vision clinics in Australia was conducted to allow comparison of methods of service provision among clinics. This paper reports the findings with respect to the patient characteristics and the planning, organization, personnel, and services provided by low vision clinics in Australia. The major change that has occurred in recent years is services in country regions through satellite clinics or private optometric practices. Recommendations for improvements are given

High contrast and low contrast visual acuity in age related macular degeneration

Low contrast Bailey-Lovie visual acuity (LCBL) and high contrast Bailey-Lovie visual acuity (HCBL) were measured in subjects with age-related macular degeneration (ARM) and subjects with normal visual function. Low and high contrast visual acuities and the difference between low and high contrast acuities were significantly different for the ARM group compared with the normals, confirming previous findings of disruption to contrast discrimination in ARM. The high contrast Bailey-Lovie chart was found to be a useful screening device for macular degeneration using a pass/fail criterion of 6/7.5. Pre-ARM (PARM) subjects can be defined as those with drusen and/or pigmentary disturbance and high contrast acuity of better than 6/7.5. However, the low contrast chart used at normal clinical illuminances is of no additional diagnostic value in ARM

Reading performance of adults with low vision

Many factors, related to the reading task, the low vision device and the patient, affect the reading performance and eventual reading rehabilitation of a patient with low vision. Reading performance can be defined in terms of near visual acuity and reading rate - both need to be adequate for reading to be functionally useful. Near visual acuity can be simply and accurately measured with standardised test charts, but the patient's potential reading rate cannot be so easily determined. In this study, reading performance of adults with low vision was examined, firstly with respect to current clinical practice by a survey of low vision clinic records and interviews with patients, and secondly, in an experimental investigation. Data on the ophthalmic characteristics of an adult low vision population were collected retrospectively from the records of a low vision clinic, with emphasis on the powers and types of near low vision devices prescribed and the patients' performances, frequency of use and satisfaction with these devices. Subjects with age related macular degeneration (ARMD) who had previously attended the low vision clinic were interviewed, to investigate their use of near optical low vision devices. In the experimental investigation, the visual functions of subjects with normal and low vision were assessed and reading rate for scrolled printed text was measured at different character sizes and with different window sizes (number of characters in the reading field). The results confirmed that many patient variables significantly affect reading performance. However, the experimental study showed for the first time, that a high proportion of the variance in maximum reading rate for a group of subjects with normal and low vision can be predicted from standard clinically-applicable measures of visual performance. This has not previously been possible because of the use of limited sets of clinical measures. Stepwise multiple regression analysis indicated that for low vision subjects, near word visual acuity, age and right visual field size (degrees) were the strongest predictors of maximum reading rate, accounting for 80% of the variance. This study used a one-line, forced scrolled method to measure maximum oral reading rates, so further research is needed to confirm these findings for everyday reading. The experimental results found that for most patients to read at maximum or near maximum reading rate, character size needs to be 2112 times threshold print size (0.4 log acuity reserve). However, for the first time, it was clearly identified that there is an interaction between required acuity reserve and window size. Maximum reading rate can be achieved with low acuity reserve and large window sizes or high acuity reserve and small window sizes, but the latter is easier to obtain with stand or hand-held magnifiers. Thus, higher magnifications should be prescribed than those calculated from simple geometric principles. This study showed that reading performance of adults will be equivalent when magnification is supplied by either large print or optical magnifiers, provided optimum acuity reserve is provided. While the survey of patient records and the interviews of ARMD subjects indicated that patients continue to use near low vision devices, satisfaction rates decrease over time. This may be due to progressive vision loss together with poor reading illuminances, but the factors determining satisfaction with near low vision devices were unable to be identified by this study. Low vision patients are more likely to be assisted with reading by the prescription of a near low vision device if they are referred to low vision services earlier in the course of their ocular disease, when visual acuity is relatively good. Individual program plans should be used by vision rehabilitation services to assist patients to set specific, realistic goals. The interviews with the ARMD subjects indicated the need for more follow-up care for some patients - those whose vision loss progresses and/or whose functional needs change. This, together with earlier referral of patients, has repercussions for the cost-effectiveness of low vision service delivery. Recommendations are given on the methods of measuring visual acuity, letter contrast sensitivity and central visual fields and the use of the results for reading rehabilitation. Based on the assessment of these visual functions, predictions about the usefulness of a low vision patient's potential reading rate after prescription of, and training with, a near low vision device can be made. Further research is planned to improve reading and visual field assessment methods and to establish vision requirements for everyday reading of stationary text, which will improve the selection of appropriate reading rehabilitation programs for adults with low vision

Temporal summation in age-related maculopathy

We measured temporal summation in subjects with atrophic age-related maculopathy (ARM) and age-matched control subjects at photopic and scotopic luminance levels. Although the ARM subjects did show longer critical durations in each case these differences were not statistically significant. This result, in conjunction with our earlier work on temporal discrimination, indicates that the processes which are responsible for temporal summation of the eye (presumably located at the receptors) are more resistant to the degenerative processes of ARM than are those responsible for temporal discrimination. This may be because the simple threshold procedure used here does not sufficiently stress the temporal response system to show a deficit

Repeated visual acuity measurement: Establishing the patient's own criterion for change

We measured visual acuity in 10 young subjects, 10 times each over a period of approximately 3 weeks, using Bailey-Lovie charts. We used a consistent end-point criterion and scored each letter read on the chart. We derived the mean and standard deviation of visual acuity measures for each subject, and for the group. The standard deviation for the group was about 3 times that of the individuals in the group. We calculated the criterion for reduction of visual acuity for the group, as group mean plus 1.96 group standard deviations; use of this criterion would consistently fail to detect patients with clinically significant reductions in visual acuity. We recommend that visual acuity be measured to threshold for every patient. Measuring visual acuity between three and five times provides an estimate of the patient’s variability and allows a criterion for reduction of visual acuity to be established for the individual patient. Use of this criterion will enhance the sensitivity of visual acuity measurement as a diagnostic tool