Meeting the uk driving vision standards with reduced contrast sensitivity

ABSTRACT PURPOSE The visual standard to hold a UK driver's license since 2012 includes visual acuity (VA) measured indoors and the ability to read a car numberplate outdoors.

Individuals with reduced contrast sensitivity may have greater visual difficulties outdoors. The agreement between the two tests in the presence of combined reduction in contrast sensitivity

and VA was investigated. METHODS Simulation glasses (‘sim-specs’) were used to reduce both high-contrast VA and contrast sensitivity (CS). Following evaluation of the influence of sim-specs

on VA and CS, levels 2 to 4 were chosen to give a range of VAs on either side of the driving standard of 6/12. Sixty-two participants wearing sim-specs then had VA tested with Snellen and

ETDRS charts indoors, and ability to read a numberplate assessed outdoors as per DVLA regulations. RESULTS Sim-specs reduced VA and CS by ~0.10 logMAR VA per 0.10 logCS. The sensitivity of

test chart VA <6/12 to correctly predict failure on the numberplate was 61% for Snellen and 56% for ETDRS. CONCLUSION False-negative and -positive rates were higher than in a previous

study with uncorrected refractive error only. Reduced CS increased the lack of agreement between the two driving vision standards, which likely occurs as the VA test is performed indoors and

the numberplate test outdoors. The increased likelihood of failing the numberplate test even though VA is 6/12 or better needs to be considered when advising patients on fitness to drive

who have ocular disease such as cataract. SIMILAR CONTENT BEING VIEWED BY OTHERS MESOPIC CONDITIONS OPTIMISE THE DETECTION OF VISUAL FUNCTION LOSS IN DRIVERS WITH SIMULATED MEDIA OPACITY

Article Open access 01 August 2022 DISCREPANCY AND AGREEMENT BETWEEN SUBJECTIVE SYMPTOMS AND VISUAL FIELD IMPAIRMENT IN GLAUCOMA PATIENTS AT A DRIVING ASSESSMENT CLINIC Article Open access

02 January 2025 NEAR VISION DATA AND NEAR CORRECTION REQUIREMENTS FROM COMMUNITY EYE HEALTH PROGRAMMES IN NINE COUNTRIES Article Open access 22 January 2024 INTRODUCTION To hold a valid

driver’s license in the UK motorists currently have to meet two different visual acuity (VA) standards: correctly read a post-2001 style car registration plate (‘numberplate’) in outdoor

conditions and achieve 6/12 Snellen on a test chart.1 The latter standard was introduced in May 2012 to bring the UK into line with an EU directive on driving licensure.2 The directive gives

guidance on the licensing of motorists so that the requirements to hold a license are consistent across Europe. The interpretation of the directive and its application in law is at the

discretion of each country. The DVLA in the UK gives no guidance on the measurement of ‘6/12 Snellen’ in terms of test chart type and scoring, whereas the methods for assessing the

numberplate test are more detailed, in terms of the test conditions, viewing distance and that all figures have to be correctly read for the numberplate to be ‘passed’. The addition of the

second standard complicates advising motorists of their suitability to drive. Where two visual tasks are different, perfect agreement between the two measures would not be expected and we

have previously found this to be the case for people with uncorrected refractive error.3 The agreement between the standards is complicated by one test being performed indoors in the clinic

environment with consistent light levels, and the other outdoors where light intensity will be higher and more variable depending on environmental conditions, with an increased likelihood of

glare sources. Disability glare increases with opacification of the ocular media such as with cataract, resulting from light scatter,4 which casts a veiling luminance and reduces light

sensitivity at the retina. The effects of glare in outdoors conditions does not relate consistently to visual performance indoors.5 Contrast sensitivity (CS) testing has been proposed as an

additional method for assessing visual function relating to ‘real world’ activities with particular applications in patients with ocular disease.6 For example, with conditions affecting the

clarity of the ocular media such as cataract, reductions in high-contrast VA and CS are usually found in combination,7 thus a patient with borderline vision for driving due to the presence

of ocular disease (rather than just uncorrected refractive error) is likely to also suffer from a loss of CS. CS testing is not required for the UK driving regulations but is mentioned in

the EU directive, which states that where there is doubt as to the ability to achieve the driving standards, that a person should be examined by a ‘competent medical authority’ with

consideration to glare and CS, amongst other tests. This study investigated how the ability to achieve both driving vision standards—seeing 6/12 on an indoor test chart and correctly reading

a car numberplate outdoors—is affected in the presence of both reduced VA and CS. High-contrast VA was reduced to around the pass–fail point for driving where there is uncertainty as to

whether both visual standards for driving will be achieved using simulation glasses, which also reduce CS. The likelihood of passing one but not both standards in the presence of reduced CS

was quantified. MATERIALS AND METHODS NORMATIVE DATA Cambridge simulation glasses8 (‘sim-specs’) were used to reduce high-contrast VA and CS in combination. These have been developed to aid

inclusive design for individuals with visual impairment. The sim-specs create light scatter and multiple pairs can be worn to create varying levels of visual impairment. A normative study

was first conducted to determine the level of sim-specs to be used to reduce VA to levels on either side of the driving standard of 6/12. A previous study3 has shown uncertainty in the

ability to achieve a numberplate pass with Snellen VAs in the range of 6/9 to 6/36. 30 participants (mean age 34.9±12.7, 16 males, 14 females) took part in the normative study. Each had

high-contrast VA measured with an ETDRS logMAR chart9 at 3 m scored on a letter by letter basis10 and CS was assessed with the Pelli Robson chart at 1 m, scored in logCS on a letter by

letter basis.11 With logMAR VA scoring, a lower number indicates better VA and with logCS scoring, a lower score represents poorer CS. For both charts, participants wore any refractive

correction required and were measured with no sim-specs and then sim-specs in each of levels 2, 3, and 4. This allowed sim-specs to be chosen for the main study which would reduce VA to a

target range on either side of the driving standard of 6/12 where there is likely to be lack of agreement between the two driving vision standards. DRIVING VISION TESTS The ability to meet

both the driving vision standards was then assessed in 62 participants (mean age 25.3±11.2, 26 males, 36 females) with sim-specs in levels 2 to 4 to give a range of visual performance. For

38 participants, measurements were made with one level of sim-specs and for 24 participants two different levels were used. High-contrast VA was measured indoors in a well-lit clinical

examination room with an ETDRS style logMAR chart and a Snellen layout chart, both viewed at 6 m via a mirror (Thomson Test Chart 2000 XPert software, version 11.09; Thomson Software

Solutions, Hatfield, Herts, UK). The ETDRS chart presents 5 × 5 proportioned Sloan letters12 with five letters on each row and consistent spacing. The Snellen chart presents 5 × 4 British

letters13 with a variable number of letters per line, from one letter at 6/60 to eight at 6/5. The 6/12 line had five letters. ETDRS VA was scored on a letter by letter basis10 and Snellen

as the last whole line correctly read. The Snellen chart is still commonly found in clinic settings and GP and optometric practices and is traditionally scored on a ‘whole line’ basis. The

ETDRS chart is increasingly used in research and clinic settings where more precise measures of VA are required which can be obtained by the letter by letter scoring method. The numberplate

test was conducted outdoors at 20 m in accordance with DVLA regulations1 and scored as a ‘pass’ if all the figures on one plate were correctly read. Three attempts were given for plates with

a yellow background with different letter and number combinations, as per the regulations. All participants gave written informed consent to participate and ethical approval for the study

was obtained from Anglia Ruskin University. The study adhered to the tenets of the Declaration of Helsinki. We certify that all applicable institutional and governmental regulations

concerning the ethical use of human volunteers were followed during this research. RESULTS NORMATIVE SIM-SPEC DATA The normative data for the reduction in VA and CS from baseline levels with

sim-spec in levels 2 to 4 shown in Table 1. LogMAR and logCS reductions are given in relation to the ‘no sim-spec’ condition. There was a consistent reduction in both VA and CS with

increasing levels of sim-specs. The relationship between sim-spec level and VA is given by the regression equation VA=(0.19 × sim-spec level) −0.34 with an _R_2 of 0.99, and between sim-spec

level and CS (CS) by the equation CS=(−0.28 × sim-spec level)+2.01, also with an _R_2 of 0.99. There was a significant correlation between the reduction in VA and CS (Pearson correlation:

_r_=−0.751; _P_<0.001) with ~0.10 logMAR reduction in VA for each 0.10 logCS reduction in CS. DRIVING VISION TESTS To compare the two driving standards, sensitivity and specificity were

calculated, as there was a continuum of VA scores but a pass/fail on the numberplate. A true positive was taken as VA worse than 6/12 or +0.30 logMAR correctly predicting a numberplate fail.

A false positive indicated not achieving 6/12 or +0.30 logMAR but passing the numberplate, whereas a false negative occurred where 6/12 or +0.30 logMAR is achieved, yet the numberplate test

was failed. A true negative indicated a pass on both tests. An ‘overlap zone’ was defined as the range of acuities within which there was uncertainty as to whether both driving standards

would be met or both failed, that is, the range of acuities where there were false positives or false negatives. Acuities better than the lower limit of the overlap zone predict a pass on

the numberplate and at those worse than the upper limit of the zone a fail is predicted. This approach was chosen as where there is uncertainty that the driving requirements will be met, VA

in the clinic setting is more often taken as an indicator as to whether the numberplate test would be passed. SNELLEN CHART The overlap-zone encompassing the range of VA where some

participants passed one, but failed the other test extended from 6/12 to 6/24 and included 62 measurements (Figure 1). Sensitivity for the Snellen VA correctly predicting a numberplate fail

was 61% and specificity 62%. Figure 1a shows those participants who would achieve the test chart driving standard when tested using a Snellen style chart but who may or may not meet the

numberplate standard (false-negative rate of 15%). Figure 1b shows those participants who failed to achieve the test chart driving standard for the Snellen chart but who may or may not meet

the numberplate standard (false-positive rate of 24%). ETDRS STYLE CHART The overlap zone for the ETDRS style chart is shown in Figure 2. The zone extended from +0.08 to +0.54 logMAR

(Snellen equivalent 6/7.2 to 6/20.7), with a sensitivity of 56% and specificity of 81% (Table 2). Figure 2a shows those participants who would achieve the test chart driving standard when

tested using an ETDRS chart but who may or may not meet the numberplate standard (false-negative rate of 13%). Figure 2b shows those participants who failed to achieve the test chart driving

standard for the ETDRS chart but who may or may not meet the numberplate standard (false-positive rate of 13%). DISCUSSION The ability to hold a driver's license is important for

mobility and maintaining independence. Reduced CS has been shown to be associated with crash involvement in some studies.14 In patients with cataract, reduced CS has been shown to be

associated with self regulation of driving and depressive symptoms.15 When advising patients on their ability to meet the driving vision standards, the likelihood that CS is reduced along

with VA needs to be considered. The sim-specs provided a useful tool to study the effects of both reduced high-contrast VA and reduced CS as they allow for controlled reduction of VA and CS

to desired levels. For this study, levels 2 to 4 yielded acuities in the target range on either side of the driving test chart standard of 6/12, from 6/7.5 to 6/24 for the Snellen chart and

0.00 to +0.68 logMAR for the ETDRS chart. Levels 3 and 4 (Table 1) gave a reduction in VA to levels comparable to ‘mild visual impairment’ in the International Statistical Classification of

Diseases.16 There was a consistent relationship between sim-spec level and change in VA and CS so that higher levels of sim-specs could be used to simulate more severe degrees of visual

impairment. The relationship between the amount of reduction of VA and CS of approximately 0.10 logMAR VA to 0.10 logCS is similar to that found in mild and moderate cataracts.17, 18 We have

previously investigated the agreement between the two driving vision standards3 in participants with uncorrected refractive error which reduces VA without significantly affecting CS.19 Our

previous study identified zones of overlap between the results of the two driving vision standards, extending from 6/9 to 6/36 for the Snellen chart and between +0.12 and +0.84 logMAR for an

ETDRS style chart. The extent of the overlap zones in the present study with the additional reduction in CS were similar (Figures 1 and 2) although the number of participants within the

overlap zone between the two standards was higher when CS was reduced. Good sensitivity of a clinical test is desirable such as where a clinic room test chart is used to predict numberplate

performance. This measure is dependent on the false-negative rate, which represents those people who may be able to achieve the 6/12 or +0.30 logMAR standard in the clinic room, yet would be

unable to pass the outdoor numberplate test (Figures 1 and 2a). Thus they could be incorrectly advised that they would meet the driving vision requirements on the basis of their test chart

acuity. In this study, sensitivity was reduced for both charts compared with our previous study,3 from 97 to 61% for the Snellen and from 91 to 56% for the ETDRS chart. The most notable

finding of the present study is that the addition of reduced CS along with reduced VA increases the false-negative rate from 2 to 15% for the Snellen chart and from 6 to 14% for the ETDRS

chart. Thus, a greater proportion of individuals with reduced CS could be potentially incorrectly advised as to their visual fitness to drive. The false-positive rate was similar to our

previous study3 for the ETDRS chart but increased from 15 to 24% for the Snellen chart. Individuals classified as false positives (Figures 1 and 2b) would have been able to meet the older UK

driving standard of seeing the numberplate alone but now fail to meet the complete standard since the introduction of the additional 6/12 criteria in 2012 in line with the EU directive.2

The differences in false-positive rate between the ETDRS and Snellen charts may relate to the difference in layouts with the Snellen chart having variable numbers of letters per line and the

lowest whole correct line being used for scoring. The letter by letter scoring adopted for the ETDRS chart gives credit for partially completed lines, which may increase VA from a bare fail

to a bare pass, therefore it is preferable for measuring driver’s VA as the false-positive rate is lower. The increase in false-positive and -negative rates with reduced CS highlights the

importance of environmental conditions when tests are performed outdoors in the presence of reduced CS, as would often be found in those patients with cataract. An interesting consideration

is that when the practical driving test is taken, it is the outdoor numberplate that is used to assess driver’s vision with a reliance on self report of Snellen acuity below 6/12. Average

age when taking the driving test in the UK is around 23 years.20 At this age, uncorrected refractive error is more likely to be reducing vision than ocular disease. License renewal is then

only required after age 70, or where referral for medical opinion on visual fitness to drive has been made by the DVLA such as when drivers report that they suffer from an ocular disease. In

this case it is more likely for visual acuities to be tested in an indoors clinic environment. Older drivers and those with ocular disease are much more likely to have reduced CS21, 22 and

so would have an increased chance of being false negatives who would actually fail the numberplate when tested outdoors. SUMMARY AND CONCLUSIONS The EU directive on driver’s licensing2 aimed

to standardise visual requirements to drive across Europe. The retention of the existing UK outdoor numberplate test (to facilitate testing by driving test examiners and police) along with

the additional test chart 6/12 requirement and the lack of perfect agreement between these two measures, means that some driver's are able to meet only one or other of the standards.

This study shows that the likelihood of this increases in the presence of reduced CS. Care needs to be exercised when giving an opinion on visual fitness to drive based only on test chart

visual acuities, especially with older patients and those with ocular disease such as cataract that are known to reduce CS. Some patients may not meet the criterion to access NHS funded

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Google Scholar  Download references ACKNOWLEDGEMENTS This research received no specific grant from any funding agency in the public, commercial or not-for-profit sector. The authors would

like to thank Agatha Jaworski and Jessica Massey for assistance with data collection. AUTHOR INFORMATION AUTHORS AND AFFILIATIONS * Department of Vision and Hearing Sciences, Visual Function

and Physiology Research Group, Anglia Ruskin University, Cambridge, UK S Rae, K Latham & M F Katsou * Vision and Eye Research Unit, Anglia Ruskin University, Cambridge, UK S Rae & K

Latham Authors * S Rae View author publications You can also search for this author inPubMed Google Scholar * K Latham View author publications You can also search for this author inPubMed 

Google Scholar * M F Katsou View author publications You can also search for this author inPubMed Google Scholar CORRESPONDING AUTHOR Correspondence to S Rae. ETHICS DECLARATIONS COMPETING

INTERESTS The authors declare no conflict of interest. RIGHTS AND PERMISSIONS Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Rae, S., Latham, K. & Katsou, M. Meeting the

UK driving vision standards with reduced contrast sensitivity. _Eye_ 30, 89–94 (2016). https://doi.org/10.1038/eye.2015.188 Download citation * Received: 13 April 2015 * Accepted: 27 August

2015 * Published: 16 October 2015 * Issue Date: January 2016 * DOI: https://doi.org/10.1038/eye.2015.188 SHARE THIS ARTICLE Anyone you share the following link with will be able to read this

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