The effect of pupil dilation on driving vision in Canada.

BACKGROUND To determine whether there is a clinically significant reduction in visual acuity (VA) or contrast sensitivity (CS), with and without glare, following examination with pupil dilation in patients currently driving. METHODS From November 1, 2004, to February 28, 2005, 105 consecutive patients were assessed in our institution. The better eye was assessed pre- and post-dilation with and without glare administered through the Brightness Acuity Tester. VA was assessed using the Early Treatment in Diabetic Retinopathy Study (ETDRS) and Snellen charts. CS was measured using the Vistech VCTS 6500 Chart. RESULTS With no glare, there was a mean reduction of 4.8 letters read from the ETDRS chart following dilation (p < 0.001). With glare, there was a mean reduction of 7.1 letters (p < 0.001). Compared with patients with initial VA of 20/20, patients presenting with a Snellen VA of 20/25 to 20/40 had a 9.75 relative risk of postdilation VA worse than 20/40, whereas patients with initial VA of 20/40 had a 19.8 relative risk of postdilation VA worse than 20/40. With the addition of glare, these relative risks increased to 13.9 and 28.8, respectively. Without glare, there was a significant reduction in CS after dilation at spatial frequencies of 2.0, 4.0, and 6.0 cycles/degree (p = 0.014, p < 0.001, and p < 0.001, respectively). With glare, there was a greater reduction in CS at these 3 spatial frequencies (p < 0.001 for all). INTERPRETATION There is a significant reduction in VA and CS after dilation that is further confounded by the effect of glare. This reduction may limit some patients from driving after dilation.