Glaucoma and Driving Risk under Simulated Fog Conditions

Purpose: We evaluate driving risk under simulated fog conditions in glaucoma and healthy subjects. Methods: This cross-sectional study included 41 glaucoma patients and 25 age-atched healthy subjects who underwent driving simulation. Tests consisted of curve negotiation without and with fog preview at 30 m of distance and two controlled speeds (slow and fast). Inverse time-to-line crossing (invTLC) was used as metric to quantify risk; higher invTLC values indicating higher risk, as less time is available to avoid drifting out of the road. Piecewise regression models were used to investigate the relationship between differences in invTLC in fog and nonfog conditions and visual field loss. Results: Glaucoma patients had greater increase in driving risk under fog compared to controls, as indicated by invTLC differences (0.490 +/- 0.578 s(-1) and 0.208 +/- 0.106 s(-1), respectively; P = 0.002). Mean deviation (MD) of the better eye was significantly associated with driving risk under fog, with a breakpoint of -9 dB identified by piecewise regression. For values below the breakpoint, each 1 dB lower MD of better eye was associated with 0.117 s(-1) higher invTLC under fast speed (adjusted R-2 = 57.9%; P < 0.001). Conclusions: Glaucoma patients have a steeper increase in driving risk under fog conditions when compared to healthy subjects, especially when the severity of visual field damage falls below -9 dB of MD in the better eye.