Meeting the UK visual standards with reduced contrast sensitivity

Purpose The visual standard to hold aUK driver's license since 2012 includesvisual acuity (VA) measured indoorsand the ability to read a car numberplateoutdoors. Individuals with reduced contrastsensitivity may have greater visualdifficulties outdoors. The agreement betweenthe two tests in the presence of combinedreduction in contrast sensitivity and VA wasinvestigated.Methods Simulation glasses (‘sim-specs’)were used to reduce both high-contrast VAand contrast sensitivity (CS). Followingevaluation of the influence of sim-specson VA and CS, levels 2 to 4 were chosen togive a range of VAs on either side of thedriving standard of 6/12. Sixty-twoparticipants wearing sim-specs then had VAtested with Snellen and ETDRS chartsindoors, and ability to read a numberplateassessed outdoors as per DVLAregulations.Results Sim-specs reduced VA and CS by~ 0.10 logMAR VA per 0.10 logCS. Thesensitivity of test chart VA o6/12 to correctlypredict failure on the numberplate was 61%for Snellen and 56% for ETDRS.Conclusion False-negative and -positiverates were higher than in a previous studywith uncorrected refractive error only.Reduced CS increased the lack of agreementbetween the two driving vision standards,which likely occurs as the VA test isperformed indoors and the numberplatetest outdoors. The increased likelihood offailing the numberplate test even thoughVA is 6/12 or better needs to be consideredwhen advising patients on fitness todrive who have ocular disease such ascataract.