Reliability of Snellen charts for testing visual acuity for driving: prospective study and postal questionnaire.
OBJECTIVE
To assess the ability of patients with binocular 6/9 or 6/12 vision on the Snellen chart (Snellen acuity) to read a number plate at 20.5 m (the required standard for driving) and to determine how health professionals advise such patients about driving.


METHODS
Prospective study of patients and postal questionnaire to healthcare professionals.


METHODS
50 patients with 6/9 vision and 50 with 6/12 vision and 100 general practitioners, 100 optometrists or opticians, and 100 ophthalmologists.


METHODS
Ophthalmology outpatient clinics in Sheffield.


METHODS
Ability to read a number plate at 20.5 m and health professionals' advice about driving on the basis of visual acuity.


RESULTS
26% of patients with 6/9 vision failed the number plate test, and 34% with 6/12 vision passed it. Of the general practitioners advising patients with 6/9 vision, 76% said the patients could drive, 13% said they should not drive, and 11% were unsure. Of the general practitioners advising patients with 6/12 vision, 21% said the patients could drive, 54% said they should not drive, and 25% were unsure. The level of acuity at which optometrists, opticians, and ophthalmologists would advise drivers against driving ranged from 6/9(-2) (ability to read all except two letters on the 6/9 line of the Snellen chart) to less than 6/18.


CONCLUSIONS
Snellen acuity is a poor predictor of an individual's ability to meet the required visual standard for driving. Patients with 6/9 vision or less should be warned that they may fail to meet this standard, but those with 6/12 vision should not be assumed to be below the standard.
Currie
Z
Z
Ophthalmology Department, Royal Hallamshire Hospital, Sheffield S10 2JF. zanna@zcurrie.freeserve.co.uk
Bhan
A
A
Pepper
I
I
D001334:Automobile Driving / Q000331:legislation & jurisprudence*; D005194:Family Practice; D006266:Health Education; D006801:Humans; D009885:Ophthalmology; D009907:Optometry; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D011795:Surveys and Questionnaires; D014787:Vision Tests / Q000592:standards*; D014792:Visual Acuity