Impact of Oncoming Headlight Glare With Cataracts: A Pilot Study

Abstract

Purpose: Oncoming headlight glare (HLG) reduces the visibility of objects on the road and may affect the safety of nighttime driving. With cataracts, the impact of oncoming HLG is expected to be more severe. We used our custom HLG simulator in a driving simulator to measure the impact of HLG on pedestrian detection by normal vision subjects with simulated mild cataracts and by patients with real cataracts. Methods: Five normal vision subjects drove nighttime scenarios under two HLG conditions (with and without HLG: HLGY and HLGN, respectively), and three vision conditions (with plano lens, simulated mild cataract, and optically blurred clip-on). Mild cataract was simulated by applying a 0.8 Bangerter diffusion foil to clip-on plano lenses. The visual acuity with the optically blurred lenses was individually chosen to match the visual acuity with the simulated cataract clip-ons under HLGN. Each nighttime driving scenario contains 24 pedestrian encounters, encompassing four pedestrian types; walking along the left side of the road, walking along the right side of the road, crossing the road from left to right, and crossing the road from right to left. Pedestrian detection performances of five patients with mild real cataracts were measured using the same setup. The cataract patients were tested only in HLGY and HLGN conditions. Participants' visual acuity and contrast sensitivity were also measured in the simulator with and without stationary HLG. Results: For normal vision subjects, both the presence of oncoming HLG and wearing the simulated cataract clip-on reduced pedestrian detection performance. The subjects performed worst in events where the pedestrian crossed from the left, followed by events where the pedestrian crossed from the right. Significant interactions between HLG condition and other factors were also found: (1) the impact of oncoming HLG with the simulated cataract clip-on was larger than with the plano lens clip-on, (2) the impact of oncoming HLG was larger with the optically blurred clip-on than with the plano lens clip-on, but smaller than with the simulated cataract clip-on, and (3) the impact was larger for the pedestrians that crossed from the left than those that crossed from the right, and for the pedestrians walking along the left side of the road than walking along the right side of the road, suggesting that the pedestrian proximity to the glare source contributed to the performance reduction. Under HLGN, almost no pedestrians were missed with the plano lens or the simulated cataract clip-on (0 and 0.5%, respectively), but under HLGY, the rate of pedestrian misses increased to 0.5 and 6%, respectively. With the optically blurred clip-on, the percent of missed pedestrians under HLGN and HLGY did not change much (5% and 6%, respectively). Untimely response rate increased under HLGY with the plano lens and simulated cataract clip-ons, but the increase with the simulated cataract clip-on was significantly larger than with the plano lens clip-on. The contrast sensitivity with the simulated cataract clip-on was significantly degraded under HLGY. The visual acuity with the plano lens clip-on was significantly improved under HLGY, possibly due to pupil myosis. The impact of HLG measured for real cataract patients was similar to the impact on performance of normal vision subjects with simulated cataract clip-ons. Conclusion: Even with mild (simulated or real) cataracts, a substantial negative effect of oncoming HLG was measurable in the detection of crossing and walking-along pedestrians. The lowered pedestrian detection rates and longer response times with HLGY demonstrate a possible risk that oncoming HLG poses to patients driving with cataracts.

Keywords: cataracts; driving simulator; headlight glare; headlight glare simulator; low vision; visual performance.

FIGURE 1

Photo of a pedestrian event (pedestrian walking-along left) with an oncoming car, with (A) the HLG simulator turned off, and (B) the HLG simulator turned on. When an oncoming car appears, a pedestrian appears on either the left or right side of the road, and then walks along or across the road.

FIGURE 2

Timeline schematics of target pedestrian encounters. (A) A pedestrian appears on the left, and then walks along in the same direction as the participant car (Walking along left). (B) A pedestrian appears on the left, and then walks across the road from the left (Crossing from left). (C) A pedestrian appears on the right, and then walks across the road from the right (Crossing from right). (D) A pedestrian appears on the right, and then walks along the right sidewalk (Walking along right). Events are designed based on city driving speed (31 mph ≅ 50 km/h ≅ 14 m/s).

FIGURE 3

Temporal eccentricity changes of pedestrians and oncoming car relative to the participants’ driving direction. For the pedestrian crossing events, Crossing from left and Crossing from right, the pedestrian crosses the line between oncoming headlight and driver (participant) 2 s from the start of the event. For the pedestrian walk along events, Walking along left and Walking along right, pedestrian never crosses the oncoming car-to-participants line of sight during the 4 s event.

FIGURE 4

The impact of HLG on (A) normal vision subjects with three vision conditions, with a plano lens, simulated cataract, and optically blurring clip-ons, and on (B) patients with real cataracts. In both with simulated cataract and optically blurred conditions, oncoming HLG significantly increased response time for the pedestrians. The amount of response time delay with the presence of HLG for real cataract patients was similar to the simulated cataract condition. Significant differences in response time between conditions are marked by an asterisk (^∗). Error bars represent the standard error within each group.

FIGURE 5

Impact of oncoming HLG on response time for various pedestrian types: pedestrian crossing from left and right, and walk along left and right. (A) Normal vision subjects with simulated cataracts. (B) Patients with real cataracts. The main effect of pedestrian types and the interaction between HLG conditions and pedestrian types were found to be significant for normal vision subjects with simulated vision impairments. However, neither was significant for patients with real cataracts. Significant increases in response time are marked by an asterisk (^∗). Error bars represent the standard error within each group.

FIGURE 6

Responses to the questionnaires by normal vision subjects (top row) and patients with real cataracts (bottom row). The questions are shown on the top and scaled responses are shown on the bottom. (A) Perception of real-world HLG during nighttime driving. (B) Comparison of difficulty between the simulated and real-world HLG encounter events. (C) Discomfort level of the simulated HLG during the assessments.

FIGURE 7

Interactions among visual functions, vision conditions, HLG conditions, participant groups, and measurement methods. Note visual acuity and contrast sensitivity were measured with both positive polarity letters (PP: bright letter on dark background) and negative polarity letters (NP: dark letter on bright background). (A) The interaction between visual acuity and HLG condition for vision conditions shows visual acuity improvement under HLGY with the plano lens (presumably due to the positive impact of pupillary myosis), but the effect of myosis disappeared for simulated cataract and real cataracts (presumably due to the negative impact of light scatter by the simulated and real cataracts). (B) The interaction between contrast sensitivity and HLG condition shows a larger negative impact of HLG on contrast sensitivity with simulated cataract and real cataract, compared to the slight negative impact with plano lens. (C) The interaction between visual acuity and measurement method shows that the different polarity of the target letter does not affect the normal vision subjects’ visual acuities, but does affect the real cataract patients (visual acuity decrease with negative polarity). (D) The interaction between contrast sensitivity and measurement method shows that both normal vision subjects and real cataract patients’ contrast sensitivities are affected similarly by the letter polarity (both reduced with positive polarity). The error bars represent the standard errors within each group.