Alex R. Bowers

On-road driving with moderate visual field loss

Purpose: We examined the relationship between visual field extent and driving performance in an open, on-road environment using a detailed scoring method that assessed the quality of specific skills for a range of maneuvers. The purpose was to determine which maneuvers and skills should be included in future, larger scale investigations of the effect of peripheral field loss on driving performance. Methods: Twenty-eight current drivers (67 ± 14 years) with restricted peripheral visual fields participated. Binocular visual field extent was quantified using Goldmann perimetry (V4e target). The useful field of view (UFOV®) and Pelli-Robson letter contrast sensitivity tests were administered. Driving performance was assessed along a 14-mile route on roads in the city of Birmingham, Alabama. The course included a representative variety of general driving maneuvers, as well as maneuvers expected to be difficult for people with restricted fields. Results: Drivers with more restricted horizontal and vertical binocular field extents showed significantly (p ≤ 0.05) poorer skills in speed matching when changing lanes, in maintaining lane position and keeping to the path of the curve when driving around curves, and received significantly (p ≤ 0.05) poorer ratings for anticipatory skills. Deficits in UFOV performance and poorer contrast sensitivity scores were significantly (p ≤ 0.05) correlated with overall driving performance as well as specific maneuver/skill combinations. Conclusions: In a small sample of drivers, mild to moderate peripheral visual field restrictions were adversely associated with specific driving skills involved in maneuvers for which a wide field of vision is likely to be important (however most were regarded as safe drivers). Further studies using similar assessment methods with drivers with more restricted fields are necessary to determine the minimum field extent for safe driving.

Driving With Hemianopia, I: Detection Performance in a Driving Simulator

PURPOSE This study was designed to examine the effect of homonymous hemianopia (HH) on detection of pedestrian figures in multiple realistic and hazardous situations within the controlled environment of a driving simulator. METHODS Twelve people with complete HH and without visual neglect or cognitive decline and 12 matched (age, sex, and years of driving experience) normally sighted (NV) drivers participated. They drove predetermined city and rural highway routes (total, 120 minutes) during which pedestrian figures appeared at random intervals along the roadway (R-Peds; n = 144) and at intersections (I-Peds; n = 10). Detection rates and response times were derived from participant horn presses. RESULTS Drivers with HH exhibited significantly (P < 0.001) lower R-Ped detection rates on the blind side than did NV drivers (range, 6%-100%). Detection of I-Peds on the blind side was also poor (8%-55%). Age and blind-side detection rates correlated negatively (Spearman r = -0.71, P = 0.009). Although blind-side response times of drivers with HH were significantly (P < 0.001) longer than those of NV drivers, most were within a commonly used 2.5-second guideline. CONCLUSIONS Most participants with HH had blind-side detection rates that seem incompatible with safe driving; however, the relationship of our simulator detection performance measures to on-road performance has yet to be established. In determining fitness to drive for people with HH, the results underscore the importance of individualized assessments including evaluations of blind-side hazard detection.

Community-Based Trial of a Peripheral Prism Visual Field Expansion Device for Hemianopia

OBJECTIVE To determine the functional utility for general mobility of peripheral prism glasses, a novel visual field expansion device for hemianopia, in a large-scale, community-based, multicenter study with long-term follow-up. METHODS Forty-three participants with homonymous hemianopia were fitted with temporary press-on Fresnel peripheral prism segments of 40 prism diopters. Follow-up questionnaires evaluating functional benefits for mobility were administered in the office at week 6. Participants who continued wearing the prisms were interviewed again by telephone after a median of 12 months. Primary outcome measures included clinical success (a clinical decision to continue wear) and 5-point ratings of prism helpfulness for obstacle avoidance when walking. RESULTS Thirty-two participants (74%) continued prism wear at week 6, and 20 (47%) were still wearing the prisms after 12 months (median time, 8 hours per day). These participants rated the prism glasses as very helpful for obstacle avoidance and reported significant benefits for obstacle avoidance in a variety of mobility situations. Success rates varied among clinic groups (27%-81%), with higher rates at the clinics that fitted more patients. CONCLUSION Our results demonstrate the functional utility of peripheral prism glasses as a general mobility aid for patients with hemianopia.

Illumination and reading performance in age‐related macular degeneration

Background:Previous studies have compared low vision reading performance at optimal task illuminance and consulting room illuminance (500 to 600 lux). However, it is uncertain the extent to which low vision reading performance can be improved when task illumination is increased from levels more representative of those found in the typical living room (50 lux) to levels likely to maximise performance.

Oral and silent reading performance with macular degeneration.

Previous studies have shown that reading rate for very large print (6 degrees, 1.86 logMAR character size) is a strong predictor of oral reading rate with low vision devices (LVDs). We investigated whether this would apply using large print sizes more readily available in clinical situations (e.g. 2 degrees, 1.4 logMAR), for subjects with macular degeneration. We assessed rauding rates--reading for understanding. A combination of near word visual acuity and large print reading rate (without LVDs) provided the best prediction of oral rauding rates (with LVDs). However, near word visual acuity alone was almost as good. Similarly, silent rauding rate was predicted best by near word visual acuity alone. We give near visual acuity limits as a clinical guide to expected oral and silent reading performance with LVDs for patients with macular degeneration.

Driving with Hemianopia, II: Lane Position and Steering in a Driving Simulator

PURPOSE The hypothesis that drivers with homonymous hemianopia (HH) would take a lane position that increased the safety margin on their blind side was tested with a driving simulator. METHODS Twelve participants with HH (six right HH and six left; nine men; mean age, 50 years; range 31-72), and 12 matched current drivers with normal vision (NV) each completed approximately 120 minutes of simulator driving. Lane position and steering stability were evaluated for specific road segment types (straight segments, curves, and turns) in city and rural undivided highway driving. RESULTS The drivers with right HH held a lane position significantly (P = 0.001) to the left of NV drivers on the straight road segments and to a lesser extent on the curves. The drivers with left HH had a lane position similar to that of the NV drivers on straights and curves, but followed a significantly (P = 0.005) more rightward path on the left turns. CONCLUSIONS The results support the hypothesis that drivers with HH take a lane position that increases the safety margin on their blind side; however, absolute lane position varies as the steering maneuver and location of the risk from oncoming traffic change with road segment type.

Driving with central field loss I: effect of central scotomas on responses to hazards.

OBJECTIVES To determine how central field loss (CFL) affects reaction time to pedestrians and to test the hypothesis that scotomas lateral to the preferred retinal locus will delay detection of hazards approaching from that side. METHODS Participants with binocular CFL (scotoma diameter, 7°-25°; visual acuity, 0.3-1.0 logMAR) using lateral preferred retinal fixation loci and matched controls with normal vision drove in a simulator for approximately 1½ hours per session for 2 sessions a week apart. Participants responded to frequent virtual pedestrians who appeared on either the left or right sides and approached the participants lane on a collision trajectory that, therefore, caused them to remain in approximately the same area of the visual field. RESULTS The study included 11 individuals with CFL and 11 controls with normal vision. The CFL participants had more detection failures for pedestrians who appeared in areas of visual field loss than did controls in corresponding areas (6.4% vs 0.2%). Furthermore, the CFL participants reacted more slowly to pedestrians in blind than nonscotomatous areas (4.28 vs 2.43 seconds, P < .001) and overall had more late and missed responses than controls (29% vs 3%, P < .001). Scotoma size and contrast sensitivity predicted outcomes in blind and seeing areas, respectively. Visual acuity was not correlated with response measures. CONCLUSIONS In addition to causing visual acuity and contrast sensitivity loss, the central scotoma per se delayed hazard detection even though small eye movements could potentially compensate for the loss. Responses in nonscotomatous areas were also delayed, although to a lesser extent, possibly because of the eccentricity of fixation. Our findings will help practitioners advise patients with CFL about specific difficulties they may face when driving.

Randomized Crossover Clinical Trial of Real and Sham Peripheral Prism Glasses for Hemianopia

IMPORTANCE There is a major lack of randomized controlled clinical trials evaluating the efficacy of prismatic treatments for hemianopia. Evidence for their effectiveness is mostly based on anecdotal case reports and open-label evaluations without a control condition. OBJECTIVE To evaluate the efficacy of real relative to sham peripheral prism glasses for patients with complete homonymous hemianopia. DESIGN, SETTING, AND PARTICIPANTS Double-masked, randomized crossover trial at 13 study sites, including the Peli laboratory at Schepens Eye Research Institute, 11 vision rehabilitation clinics in the United States, and 1 in the United Kingdom. Patients were 18 years or older with complete homonymous hemianopia for at least 3 months and without visual neglect or significant cognitive decline. INTERVENTION Patients were allocated by minimization into 2 groups. One group received real (57-prism diopter) oblique and sham (<5-prism diopter) horizontal prisms; the other received real horizontal and sham oblique, in counterbalanced order. Each crossover period was 4 weeks. MAIN OUTCOMES AND MEASURES The primary outcome was the overall difference, across the 2 periods of the crossover, between the proportion of participants who wanted to continue with (said yes to) real prisms and the proportion who said yes to sham prisms. The secondary outcome was the difference in perceived mobility improvement between real and sham prisms. RESULTS Of 73 patients randomized, 61 completed the crossover. A significantly higher proportion said yes to real than sham prisms (64% vs 36%; odds ratio, 5.3; 95% CI, 1.8-21.0). Participants who continued wear after 6 months reported greater improvement in mobility with real than sham prisms at crossover end (P = .002); participants who discontinued wear reported no difference. CONCLUSIONS AND RELEVANCE Real peripheral prism glasses were more helpful for obstacle avoidance when walking than sham glasses, with no differences between the horizontal and oblique designs. Peripheral prism glasses provide a simple and inexpensive mobility rehabilitation intervention for hemianopia. TRIAL REGISTRATION clinicaltrials.gov Identifier: NCT00494676.

Can we improve clinical prediction of at-risk older drivers?

OBJECTIVES To conduct a pilot study to evaluate the predictive value of the Montreal Cognitive Assessment test (MoCA) and a brief test of multiple object tracking (MOT) relative to other tests of cognition and attention in identifying at-risk older drivers, and to determine which combination of tests provided the best overall prediction. METHODS Forty-seven currently licensed drivers (58-95 years), primarily from a clinical driving evaluation program, participated. Their performance was measured on: (1) a screening test battery, comprising MoCA, MOT, Mini-Mental State Examination (MMSE), Trail-Making Test, visual acuity, contrast sensitivity, and Useful Field of View (UFOV) and (2) a standardized road test. RESULTS Eighteen participants were rated at-risk on the road test. UFOV subtest 2 was the best single predictor with an area under the curve (AUC) of .84. Neither MoCA nor MOT was a better predictor of the at-risk outcome than either MMSE or UFOV, respectively. The best four-test combination (MMSE, UFOV subtest 2, visual acuity and contrast sensitivity) was able to identify at-risk drivers with 95% specificity and 80% sensitivity (.91 AUC). CONCLUSIONS Although the best four-test combination was much better than a single test in identifying at-risk drivers, there is still much work to do in this field to establish test batteries that have both high sensitivity and specificity.

Eye movements and reading with simulated visual impairment

The purpose of this study was to investigate the effects of simulated visual impairment on the reading speed and reading eye movements of young, normally‐sighted observers. Afocal diffusing filters (Ryser occlusion foils) were used to create three levels of impairment and eye movements were recorded using a spectacle‐mounted, infra‐red limbal reflection system. Reading speed decreased significantly (P<0.01) as the level of impairment increased. Eye movement analysis revealed the main contributory factors to be increased fixation durations, shorter sac‐cades (resulting in increased numbers of forward saccades per line) and, to a lesser extent, increased time required for page navigation. The results suggest that in order to achieve optimal reading speeds, print size should be at least four times the acuity threshold and that print contrast should be at least twenty times contrast threshold.