Field Expansion with Multiplexing Prism Glasses Improves Pedestrian Detection for Acquired Monocular Vision

Abstract

Purpose: Patients with acquired monocular vision (AMV) lose vision in the temporal crescent on the side of the blind eye. This visual field loss affects patients' ability to detect potential hazards in the blind field. Mounting a base-in multiplexing prism (MxP) on the nasal side of the seeing eye can provide true field expansion and enable detection of potential collision hazards. We evaluated the efficacy of the MxP glasses in a virtual reality walking environment.

Methods: A three-dimensional printed clip-on MxP holder that can be adjusted for an individual user's facial parameters was developed. Virtual reality walking scenarios were designed to evaluate the effect of MxP field expansion on the detection of a pedestrian approaching from different initial bearing angles and courses. The pedestrian detection rates and response times of 10 participants with simulated AMV (normally sighted participants with one eye patched) and three patients with AMV were measured.

Results: The MxP provided true field expansion of about 25°. Participants performed significantly better with the MxP than without the MxP in the pedestrian detection task on their blind field, while their seeing field performance was not significantly different.

Conclusions: The MxP glasses for patients with AMV improved the detection of potential collision hazards in the blind field.

Translational relevance: The MxP with an adjustable clip-on holder may help patients with AMV to decrease the risk of collision with other pedestrians.

Keywords: 3D printing; collision; field expansion; monocular vision; prism; simulator; vision multiplexing.

Figure 1.

Design of the 3D-printed clip-on MxP holder. The holder is designed to fit the top rim of the spectacles frame and is mounted using clips and brackets. The MxP segment is attached to one of the two arms depending on the side of vision loss.

Figure 2.

Mounting MxP segment. Hooks (solid red) on the MxP segment are inserted in the slots (green area) in the arm. The hooks rest on the blue stubs in the slot. The MxP segment is produced in a rectangular shape (dashed red) and then trimmed to accommodate the nose on one side and to eliminate possible diplopia on the other.

Figure 3.

Top view (left) and side view (right) of the flexible mechanism used to adjust the tilt angle of the MxP. (A) A moveable wedge is placed in the grooves between the body and arm. The grooves have lips on the top and bottom, restricting the wedge from popping out of the grooves. (B) Each successive step of the wedge in the grooves rotates the arm (MxP) by 1° with respect to the spectacles frame within the range of 0° to 17°. The wedge is glued in place after the fitting.

Figure 4.

Spectacles with the 3D printed clip-on MxP holder fit on a participant with left AMV. (A) The MxP segment is trimmed to match the contour of the nose of the individual. The MxP extends over the nose bridge to allow the scanning of the seeing eye (left eye here) toward the blind field (toward the blind eye) outside the frame. (B) The wedge is placed in the grooves to rotate the arm to the required negative face-form tilt angle.

Figure 5.

VR walking scenario in the driving simulator. The blue dashed line at 0° marks the center of the front monitor. (A) Panoramic view of the walking scenario as seen from a participant with normal vision as a pedestrian approaches the participant on the right at 80° bearing. (B) Panoramic view with 3D printed clip-on MxP holder for a patient with left AMV. The MxP (white dashed line) shows the same pedestrian in the shifted view as the field expansion, superimposed over the see-through view of the buildings at 55°. Note the prism distortion of the right display bezel in the shifted view through the MxP.

Figure 6.

Pedestrians on center-to-center collision courses with left AMV. The gray area marks the blind field of a patient with left AMV. (A) A 45° bearing pedestrian (see Supplementary Movie B1A), (B) a 65° bearing pedestrian (see Supplementary Movie B1B), and (C) an 80° bearing pedestrian (see Supplementary Movie B1C). The solid black circle represents the collision point. These colliding pedestrians would stay at a fixed bearing angle with respect to the participant (red) for the entire event. The 65° and 80° bearing pedestrians would stay in the blind field and are not detectable by patients with AMV without scanning into the blind field. See Supplementary Material, Appendix B1 for details of movies.

Figure 7.

Pedestrians (initially appear at 65° as an example) on (A and B) near-collision and (C) noncollision courses defined by path crossing distance (d_pc). The solid red line marks the participant's path, and the solid black circle represents the participant's location after walking for six seconds. A pedestrian who crosses (A) 2 m in front of (d_pc= +2 m) (see Supplementary Movie B2A) or (B) 2 m behind (d_pc = –2 m) (see Supplementary Movie B2B) the collision point is defined as a near-collision. (C) A noncollision course pedestrian crosses 12 m in front of the participant (d_pc= +12 m) (see Supplementary Movie B2C). The violet line and the open circle mark the pedestrian's path and locations after six seconds (solid line for the actual course and dashed line for center-to-center collision course). See Supplementary Material, Appendix B2 for details of movies.

Figure 8.

Detection rate of pedestrians with and without MxP glasses. (A) Average detection rate with normal vision, simulated AMV, and AMV+MxP. MxP improved the detection rate in the blind field (65° and 80°) and did not significantly affect the detection rate of the 45° pedestrians. **P < 0.01. (B) Average detection rates of the three patients with AMV in both viewing conditions. Statistical analyses were not applied for the three patients with AMV. Error bars are standard errors.

Figure 9.

Pedestrian response times with and without MxP glasses. (A) Response times for individual participants with normal vision, simulated AMV, and AMV+MxP. In the blind field, participants responded significantly faster in AMV+MxP than AMV to pedestrians appearing at 65° and 80°. Response times to the 45° pedestrians on the seeing nasal field were not different across conditions. **P < 0.01. (B) Response times of the three patients (R1, R2, and R3) with AMV and AMV+MxP. Statistical analyses were not applied for the 3 patients with AMV.

Figure 10.

Detection rate and response time for pedestrians initially appearing at a 65° bearing angle with different courses across the viewing conditions. (A) Bearing span as a function of time for pedestrians initially appearing at 65° and walking on four different courses. When the patient is looking straight, the bearing angle of the pedestrian is the same as visual eccentricity. The vertical width in the colored shaded area indicates the horizontal angular size of the pedestrian throughout the event. Colored symbol markers indicate when the pedestrians on different courses enter the seeing field of AMV (red plus, blue cross, and green circle for d_pc = +12 m, +2 m, and 0, respectively). All pedestrians were visible upon their initial appearance in the AMV+MxP condition (marked with grey vertical gratings). (B) Detection rate and (C) response time to the 65° pedestrians across viewing conditions. In the center-to-center collision course (d_pc = 0), delayed entering of the pedestrian into the seeing field in AMV resulted in longer response times and lower detection rate. Pedestrians that crossed behind the participant (d_pc = –2 m) did not enter the seeing field of AMV. In AMV+MxP, the detection rate and response time for pedestrians on all courses were improved. Error bars are standard errors. *, ^#P < 0.01 for AMV+MxP vs. AMV and AMV+MxP vs. NV, respectively.

Figure 11.

Detection rate and response time for pedestrians initially appearing at 80° bearing with different courses across viewing conditions. (A) Bearing spans as a function of time of 80° pedestrians on different courses. Colored symbols indicate when the pedestrians entered the seeing field of AMV (red plus, blue cross, and green circle for d_pc = +12 m, +2 m, and 0, respectively). (B) Detection rate and (C) response time of different pedestrian types across viewing conditions. The late entry of the pedestrian into the seeing field resulted in slower response times and reduced detection rates of center-to-center collisions. Pedestrians that passed behind (d_pc = –2 m) did not appear in the seeing field of AMV. In AMV+MxP, the detection rates and response times of pedestrians on all courses were improved. Error bars are standard errors. *, ^# P < 0.01 for AMV+MxP vs. AMV and AMV+MxP vs. NV, respectively.

Figure 12.

Detection rate and response time for pedestrians that initially appeared at 45° bearing with different courses across viewing conditions. (A) Bearing span of 45° pedestrians on different courses as a function of time. (B) Detection rate and (C) response time of 45° pedestrians on different courses across the viewing conditions. There was no difference in pedestrian detection performance across viewing conditions and courses, which suggests that the MxP did not negatively affect the detection of pedestrians in the see-through view. Error bars are standard errors.

Figure 13.

Collision judgment of (A) 45°, (B) 65°, and (C) 80° pedestrians on different courses across viewing conditions. MxP did not significantly affect the collision judgment compared with NV and simulated AMV conditions. Error bars are standard errors.

Figure 14.

Collision judgment of participants with normal vision for pedestrians approaching on different courses (initial bearing angle and path crossing distance, d_pc) based on Qiu et al. (IOVS. 2017;58:ARVO E-Abstract 3287) and the current work. (A) Collision judgment of the pedestrians with the same path crossing distance (d_pc = +2 m and –2 m) as a function of initial bearing angles. (B) Path crossing distance for 50% collision judgment for pedestrians as a function of initial bearing angles. Pedestrians from more central initial bearing angles that crossed in front of the participant were more often judged as a collision. There is no such effect for those crossing behinds.