Driving ability after pupillary dilatation

The Royal College of Ophthalmologists' guidelines and Driver and Vehicle Licensing Agency (DVLA) recommend that a patient should not drive with dilated pupils based on the rationale that vision may be compromised in acuity and ability to tolerate glare. Arguments exist against these recommendations suggesting that pupillary dilatation does not have any real bearings on driving ability. Aim To determine the effects of pupillary dilatation on the ability to drive.

The study was randomised and prospective. A total of 28 patients had their visual parameters (distance vision, near vision, licence plate reading at 20 m or shorter, and glare) measured and analysed pre- and post-tropicamide 1% dilatation. Paired two-tailed Student's t-test and chi(2)-test were used in the analysis.

At 20 min, following instillation of one drop of tropicamide 1% there is a significant reduction in visual acuity (VA), for distance Snellen and near. There is a significant reduction in the number of people who could read the licence plate at 20 m. Subjective glare assessment changed from 'none' (average score) in the undilated state to 'mild' in the dilated states. The overall patient feedback indicated that a significant 14% believed they would find it difficult to drive postdilatation.

This study demonstrates the rationale behind disallowing driving following pupillary dilatation. The risks to safe driving are proved significant as a result of significant reduction in visual quality and quantity after dilatation.