Evaluation of Melbourne Edge Test contrast sensitivity measures in the visually impaired

An optometrist's guide to the top candidate inherited retinal diseases for gene therapy

This review presents the phenotypic and genotypic profiles of a select group of inherited retinal diseases (IRDs) that are currently the focus of retinal gene therapy trials globally. Research progress in IRD treatment trials may soon lead to their availability in Australia and New Zealand, as either approved treatment or a clinical trial. The salient clinical characteristics of retinitis pigmentosa-the largest IRD category-are highlighted, with specific reference to RPE65-associated Leber congenital amaurosis, followed by other specific IRDs, namely choroideremia and ABCA4-associated Stargardt disease. These IRDs are selected based on their candidacy for gene therapy. Guidance on the clinical diagnostic tests that support each of these diagnoses will be presented. More broadly, the most useful structure and function measures to monitor IRD progression is discussed, along with the key assessments that offer differential diagnostic insight. This review is intended to be a clinical guide for optometrists, to assist in assessment and management of individuals who may be eligible for current and future gene therapies. A companion article in this issue will provide an overview of the basic principles of gene therapy and its development as a new treatment for inherited retinal diseases.

Comparing the Shape of Contrast Sensitivity Functions for Normal and Low Vision

Purpose

The contrast sensitivity function (CSF) provides a detailed description of an individual's spatial-pattern detection capability. We tested the hypothesis that the CSFs of people with low vision differ from a “normal” CSF only in their horizontal and vertical positions along the spatial frequency (SF) and contrast sensitivity (CS) axes.

Methods

Contrast sensitivity for detecting horizontal sinewave gratings was measured with a two temporal-interval forced-choice staircase procedure, for a range of SFs spanning 5 to 6 octaves, for 20 low-vision observers and five adults with normal vision. An asymmetric parabolic function was used to fit the aggregate data of the normal-vision observers, yielding the “normal template.” Each of the 20 low-vision CSFs was fit in two ways, by using a shape-invariant version of the normal template (with the width parameters fixed) that was shifted along the log-SF and log-CS axes, and by an unconstrained asymmetric parabolic function (“free-fit”).

Results

The two fitting methods yielded values of the peak CS, the SF corresponding to peak CS, and the high cut-off SF that were highly correlated and in good agreement with each other. In addition, the width parameters of the low-vision CSFs were comparable with those of the normal template, implying that low-vision CSFs are similar in shape to the normal CSF.

Conclusions

The excellent agreement of parameters estimated by the two fitting methods suggests that low-vision CSFs can be approximated by a normal CSF shifted along the log-SF and log-CS axes to account for the impaired acuity and contrast sensitivity.

Balance and Gait Impairment in Transient Ischemic Attack and Minor Stroke

BACKGROUND

There has been little research into gait and balance impairment in transient ischemic attack (TIA) and minor stroke, despite these conditions affecting large numbers of people and the potential impact on function. The aim of this study was to determine the impact of TIA and minor stroke on gait and balance.

METHODS

Twelve people with TIA or minor stroke without previous gait/balance problems and 12 age- and sex-matched controls were recruited. Participants (mean age 67 years) underwent a comprehensive assessment including physiological, balance, and gait measures (clinical and computerized [NeuroCom/GAITRite]). Matched-pairs analysis was undertaken.

RESULTS

Groups were similar in body mass index, vision, leg proprioception/strength, and reaction time. Cognition was worse in the TIA/minor stroke group: mean Montreal Cognitive Assessment score 22.2 versus 26.6, P = .001. People with TIA/minor stroke were significantly worse on all but one clinical test. Median scores for TIA/minor stroke versus control were as follows: Timed Up and Go (TUG), 9.4 versus 7.6 seconds, P = .019; TUG dual task, 12.3 versus 8.5 seconds, P = .012; Four Square Step Test, 10.9 versus 7.2 seconds, P = .006. Mean Step Test score for TIA/minor stroke versus control was 14.1 versus 17.7, P = .021. The TIA/minor stroke group also had significantly worse performance on computerized tests: increased turn time/sway, increased step length, slower comfortable/fast gait speeds, and greater proportion of gait cycle spent in double support.

CONCLUSIONS

This study found that people with TIA/minor stroke have gait and balance dysfunction despite having no obvious physiological impairments. Intervention studies aimed at improving balance and gait in this population are needed.

A Preliminary Study of the Effectiveness of an Otolaryngology-based Multidisciplinary Falls Prevention Clinic

Because the cause of falls is often multifactorial, efforts to identify risk factors and promote prevention would benefit from a multidisciplinary approach in which the contributions of a broad range of body systems are considered. We describe the practices and procedures followed at the otolaryngology-based multidisciplinary Falls Prevention Clinic at Henry Ford Hospital in Detroit. Our team is made up of an otolaryngologist, an audiologist, an internist, and a physical therapist. Our multidisciplinary approach involves evaluations of vestibular and balance function, cardiovascular function, and visual function; lower-extremity strength and sensation; cognition and mood; and medication use. We also assess a number of nonmedical risk factors. Evaluations are made over the course of two clinic visits. To assess the effectiveness of our approach, we conducted a preliminary study based on chart reviews and telephone interviews of 52 patients who had been referred to our clinic for evaluation and counseling. The basis of our study was a comparison of the number of falls that patients had experienced during the 6 months prior to their first visit to our clinic and the number of falls they experienced during the 6 months after their second visit. We found that among “true fallers” (i.e., those who had actually experienced a fall at some point during the study), 64.7% reported that they had experienced fewer falls after their clinic visits than before (p < 0.001). Also, 59.1% of patients who had been “frequent fallers” prior to their clinic evaluation (i.e., ≥3 falls during the previous 6 mo) reported that they had not fallen at all during the 6 months following their last visit. Finally, our evaluations identified a substantial number of risk factors in individual patients that had been missed previously, including many nonvestibular factors that might not have been detected without a multidisciplinary approach. We conclude that the results of this preliminary study demonstrate the potential that a comprehensive falls prevention clinic can have in reducing the number of falls among outpatients at risk, and we believe that further study is warranted.

Retinitis pigmentosa: visual function and multidisciplinary management

Retinitis pigmentosa (RP) is a leading cause of blindness and visual disability in younger people. Optometrists have a major role in detecting RP and in reducing the visual disability associated with RP. This review summarises the literature relating to visual function in people with RP, with particular attention given to night-blindness, visual acuity decrease and visual field contraction. The range of low vision aids available for people with RP is reviewed and suggestions given on aids that have been found to be most successful. Most importantly, this review overviews the range of services available to people with RP and emphasises how optometrists need to work with a network of professionals to ensure the best possible visual outcomes for people with RP. Particular mention is made of current findings relating to orientation and mobility training, driving, sensory substitution and adaptive technology. The modern optometrist needs to be aware of the multiple needs of people with RP and have the ability to link them with the professionals best able to help them.