A pilot evaluation of on-road detection performance by drivers with hemianopia using oblique peripheral prisms

Abstract

Aims. Homonymous hemianopia (HH), a severe visual consequence of stroke, causes difficulties in detecting obstacles on the nonseeing (blind) side. We conducted a pilot study to evaluate the effects of oblique peripheral prisms, a novel development in optical treatments for HH, on detection of unexpected hazards when driving. Methods. Twelve people with complete HH (median 49 years, range 29-68) completed road tests with sham oblique prism glasses (SP) and real oblique prism glasses (RP). A masked evaluator rated driving performance along the 25 km routes on busy streets in Ghent, Belgium. Results. The proportion of satisfactory responses to unexpected hazards on the blind side was higher in the RP than the SP drive (80% versus 30%; P = 0.001), but similar for unexpected hazards on the seeing side. Conclusions. These pilot data suggest that oblique peripheral prisms may improve responses of people with HH to blindside hazards when driving and provide the basis for a future, larger-sample clinical trial. Testing responses to unexpected hazards in areas of heavy vehicle and pedestrian traffic appears promising as a real-world outcome measure for future evaluations of HH rehabilitation interventions aimed at improving detection when driving.

Figure 1

(a) Press-on 40Δ Fresnel peripheral prism segments in the oblique configuration on the left spectacle lens as fitted for the study to a patient with left HH. The upper prism is base out and base down, and the lower prism is base out and base up, shown with 9 mm interprism separation, providing expansion in the central area of the visual field used when driving (Figure 2(b)). The effect of the lower prism is notable by the apparent shift of the centrally located lower lid margin, iris, and sclera (imaged by the prism segment). The wearer has an uninterrupted binocular view through the central prism-free area of the lens. (b) Higher-power, 57Δ permanent prism glasses in the oblique configuration with 12 mm interprism separation (not used in this study, but now available from Chadwick Optical Inc., White River Junction, VT, USA).

Figure 2

Binocular visual field (Goldmann V4e) of a patient with left HH (a) without peripheral prisms, (b) with 40Δ oblique peripheral prisms as fitted for this study with no vertical separation between the expansion areas (9 mm interprism separation and 30° angle of tilt), and (c) with the original horizontal design of 40Δ peripheral prisms for walking [21] (12 mm interprism separation). The oblique design provides about 20° of lateral expansion into central areas of the blind hemifield in the region used when looking through a car windshield (rectangle represents the field of view through a typical car windshield for driving on the right [22]); the horizontal design does not provide expansion within this area. Small black squares are the individual points mapped during the perimetry.

Figure 3

Number (median and interquartile range) of interventions in each drive for individual participants. Noncurrent drivers had fewer interventions in the real prism (RP) than the sham prism (SP) drives, and more interventions than current drivers in the SP but not the RP drives. The thick horizontal line within each box is the median; the vertical extent of the box is the interquartile range (IQR); vertical lines at box ends represent the largest nonoutlier data points within 1.5x IQR. Open triangle is a far outlier (>3x IQR).

Figure 4

Total numbers of unsatisfactory and satisfactory responses to hazardous events on the seeing and blind sides for the 12 participants. The proportion of satisfactory responses to blindside hazards was significantly higher with real prisms (RP) than sham prisms (SP).

Figure 5

Percent of satisfactory responses to unexpected hazardous events on the blind side in the sham prism (SP) and real prism (RP) drives for the eight participants with blindside events in both drives. The diagonal line represents identical performance in the two drives. Six drivers (three current and three noncurrent) had a higher proportion of satisfactory responses in the RP than the SP drive (data points above the diagonal; P = 0.03).

Figure 6

Percent of satisfactory responses to unexpected blindside hazards for current and noncurrent drivers. Both current and noncurrent drivers had better responses in the real prism (RP) than the sham prism (SP) condition, suggesting that the use of the peripheral prisms improved detection of blindside hazards for current drivers as well as noncurrent drivers. Numbers under each bar are the total number of hazards in each condition. Error bars represent 95% confidence limits.