Measuring Pedestrian Collision Detection With Peripheral Field Loss and the Impact of Peripheral Prisms

Purpose Peripheral field loss (PFL) due to retinitis pigmentosa, choroideremia, or glaucoma often results in a highly constricted residual central field, which makes it difficult for patients to avoid collision with approaching pedestrians. We developed a virtual environment to evaluate the ability of patients to detect pedestrians and judge potential collisions. We validated the system with both PFL patients and normally sighted subjects with simulated PFL. We also tested whether properly placed high-power prisms may improve pedestrian detection. Methods A virtual park-like open space was rendered using a driving simulator (configured for walking speeds), and pedestrians in testing scenarios appeared within and outside the residual central field. Nine normally sighted subjects and eight PFL patients performed the pedestrian detection and collision judgment tasks. The performance of the subjects with simulated PFL was further evaluated with field of view expanding prisms. Results The virtual system for testing pedestrian detection and collision judgment was validated. The performance of PFL patients and normally sighted subjects with simulated PFL were similar. The prisms for simulated PFL improved detection rates, reduced detection response times, and supported reasonable collision judgments in the prism-expanded field; detections and collision judgments in the residual central field were not influenced negatively by the prisms. Conclusions The scenarios in a virtual environment are suitable for evaluating PFL and the impact of field of view expanding devices. Translational Relevance This study validated an objective means to evaluate field expansion devices in reproducible near-real-life settings.

should be minimized, especially with PFL patients.
With the prism placed in the fronto-parallel plane (Fig. A1a), the angle of incidence is same as the visual eccentricity and the TIR starts at 5º visual eccentricity on the base side as the prism power increases with the visual eccentricity toward the base side. However, the face-form tilt 49 can reduce (base-out, Fig. A1b) or increase (base-in, Fig. A1c) the magnitude of the angle of incidence toward the base side even at the same visual eccentricity. When the peripheral prisms are placed on the spectacles in a base-out configuration, the face-form tilt of the frame 49 reduces the absolute angle of incidence on the base side and consequently moves the TIR transition point farther peripherally (Fig. A1b). On the other hand, in base-in configuration, the face-form tilt increases the absolute angle of incidence on the base side, which results in moving the TIR transition point centrally (Fig. A1c). Figure A1. Effect of face-form tilt in various prism base configurations. (a) Top, view from above of the ray diagram when the prisms are placed in fronto-parallel plane with view at primary gaze (black arrow). The angle of incidence in red indicates the critical angle of incidence where TIR first occurs. Blue arrows indicate the residual central field in the patient with PFL. In left HH, the left side of the primary gaze (black arrow) is blind. The graph below shows the shifted field as a function of visual eccentricity with 57Δ base-out prism. Due to the TIR at about -5°, eccentricities farther than that cannot be seen in the shifted field. The residual central field is indicated in blue highlighted area and left of the vertical dashed line is the blind side of the patient with left HH. When the total face-form tilt is 10° (5° on each side), ray diagrams and the graphs for (b) base-out and (c) base-in prism are shown. Due to the decreased magnitude of angle of incidence in the base-out configuration by the face-form tilt, TIR is moved farther to larger visual eccentricity and does not impede visibility within the residual central field of the patient with PFL in primary position of gaze (also providing for wider eye scanning range in HH). However, in base-in configuration, TIR blocks vision for almost half of the residual central field and provides no eye scanning range in HH. In addition, the base-out configuration in (b) shows much farther field expansion in the blind side than the other two configurations.
For a HH patient with the eyes at the primary position of gaze, that range of ineffective expansion is usually in the blind field area, and does not affect the functionality of the prisms.
The only impact occurs when the patient scans toward the blind side, where for eye movements larger than 5º the fovea direction is pointed into TIR range (though below it). As a result, the peripheral field expansion does not increase beyond the expansion achieved with 5º scanning. 25 However, in PFL with its residual field around the fovea, the TIR area is likely to fall within the residual central field even in primary position of gaze and limit the field expansion effect of the high-power prisms, as shown in Fig 5b. In addition, image compression is higher near the TIR transition and thus visibility is lower due to the minification. Therefore, the transition to the TIR region should be pushed towards the blind field as much as possible. Since the field loss For high-power prisms, the prism power is not constant and varies with angle of incidence. 25 The prism placed on the goggles has a combination of effect of oblique tilt, angle of incidence, and perceived prism shift from the long back vertex distance. Since oblique prisms were used on the goggles, the angle of incidence is also affected by the oblique tilt angle.
Since prism power at -4.7° and 8.3° angle of incidence are 40. 3° and 22.8° respectively, 25 the reduced lateral shift in oblique design is 38.5° and 21.8°, respectively. Therefore, the prism shows in the spectacles the island from 13° (=21.8 -8.7) to 43° (=38.5 + 4.9) which results in the perceived lateral shift from 11° to 39° due to the long vertex distance in the goggles.

Closest distance between the participant and pedestrian
We calculated the closest distance between two people while they are approaching to determine whether such distance is larger than their body width so they could pass without contact. As (A1) Figure A2. The distance between the participant and the pedestrian at time t is specified, and the closest distance between them while approaching is then calculated.