Visual standards for driving Flashcards
How important is it to notify DVLA when you notice an eye condition that could put you in danger:
*“It is a criminal offence for a driving license holder or applicant to fail to notify the Drivers Medical Branch, Driver and Vehicle Licensing Centre, Swansea, immediately they become aware of any eyesight condition which is likely to cause them to be a source of danger to the public when driving.”
*Failure to notify can also have serious motor insurance implications.
*Let dvla know as soon as you think something is wrong with your vision
When should you notify DVLA if you notice an eye condition that could put you in danger:
As soon as the person has knowledge that a danger exists and this includes when they have received professional advice that their condition represents an immediate or potential danger when driving
What are drivers asked in terms of vision:
Whether they meet the standard for driving and if need to wear corrective glasses or contact lenses to achieve this standard
What is shown on drivers licence in terms of vision:
*Drivers who have a refractive correction have it indicated on back of driving licence
*This means the person needs to wear glasses for driving
What is the standard for group 1 drivers:
- Read in good daylight with the aid of glasses or contact lenses, if worn a registration mark fixed to a motor vehicle and containing characters 79mm high and 50mm wide from 20 metres (just under 66 feet )
AND - The visual acuity (with the aid of glasses or contact lenses if worn) must be at least 6/12 (0.5 decimal) with both eyes open, or in the only eye if monocular.”
What does group 1 consist of:
Ordinary family cars and light vans
How reliable is number plate test found on test charts:
- There is no precise Snellen equivalent to the number plate standard
- In terms of visual angle it is equivalent to 6/15 BUT…
- Drasdo and Haggerty found that applying a standard of 6/9-2 (6/10) resulted in a mathematical equivalent to this (i.e. this standard failed the same proportion of people, but not necessarily the same individuals).
- The normal number plate test found on many test charts is NOT equivalent and should not be relied upon.”
- SO Just because someone can read the number from 20m, doesn’t mean they can read 6/12 and vice versa
Advice to patients on whether they can pass the number plate test based on Snellen VA
- Latham et al(2014) found that with a binocular VA of 6/12 not all participants could pass the number plate test
- And some participants passed the number plate test but had VA below 6/12 (approx. 14-15%)
They suggest the following
To best predict drivers’ ability to read a number-plate, vision should be assessed using a logMAR letter chart or a Snellen chart scored by full line
Drivers with 6/7.5 or better vision can be advised that they meet the driving standard. If no 6/7.5 line on the chart then driver should be able to read 6/6.
Drivers with acuity between 6/9 and 6/12 should be advised to check their ability to read a number-plate, as some may not be able to.
Whats different about using number plate test and driving:
Conditions in test room are different – artificial lighting in room compared to outside lighting and weather conditions different
How should optometrists respond if a patient asks if they are fit to drive:
- Optoms should not provide certificates of ability to pass the “number plate test” based on consulting room tests
- It is unwise to pass “number plate test” based on Snellen VA alone
If it is only based on acuity (i.e. not fields or diplopia etc) it is best to advise the patient to satisfy themselves that they can pass the “number plate test” - If in doubt the patient should report to the Licensing Centre who will arrange for the test to be accurately carried out at a Driving Test Centre
Rule for driving and vision:
Drivers should prove that their vision meets standard for driving every 10 years
Example of whether px is fit to drive:
Hyperopic Presbyope:
- Unaided Vision R 6/24 L 6/24 Binoc 6/24 +1
- Wears N/V specs only
- Rx: R+2.00DS6/5L+2.00DS6/5
- Add +2.00D R & L = N5
- Without distance glasses, this patient would probably not pass the Number Plate Test and does not achieve 6/12
- Advise the patient of the legal requirements for driving
What does group 2 (Class 2) drivers involve:
- LGV = large goods vehicles (lorries) AND
- PCV = passenger carrying vehicles (buses)
Criteria for group 2 drives:
- Must pass the number plate test
- Must achieve at least 6/7.5 VA in the better eye [was 6/9 previously]
- Must achieve at least 6/60 VA in the worse eye [was 6/12 previously]
- “Must have a corrective power of < or = +8.00D” There’s no specific limit for the corrective power of contact lenses.
Do the new standards for Group 2 help optometrists – why:
- No!
The difference in VA between 6/7.5 and 6/9 is very small
Not every Snellen chart has a 6/7.5 line
Test chart must be positioned accurately at 6m
Charts at shorter distances than 6m and scaled to 6m must be accurately scaled
+8.00D refraction limit does not specify whether it is the mean sphere power or “highest powered meridian”
Hyperopes often become more hyperopic as they get older, so may start off less than +8.00D before crossing the +8.00D boundary
Calling px back on different day under same conditions could result in up to a line difference in va from what they read day before = va very variable
Rule of visual fields and driving:
- There is no statutory requirement in UK legislation for fields of vision for Group 1 drivers but the Second EC Directive applies.
*So difficult to tell if px is okay to drive or not
*Doesn’t say if with the correction or without
*How the EC directive requirements are interpreted are country dependent – most say with standard or habitual rx
Criteria for driving and visual fields:
The following standard is usually applied when there is evidence that a defect exists.
-The minimum field of vision for safe driving is defined as a field of vision of at least 120 degrees on the horizontal measured by the Goldmann perimeter using the III4e settings (or equivalent perimetry).
-And there should be no significant defect in the binocular field which encroaches within 20 degrees of fixation above or below the meridian = circle of radius 20 degrees
Which visual field defects are not accepted as safe for driving:
Homonymous or bitemporal defects which come close to fixation, whether hemaniopic or quadrantopic,
What is the estermann test and procedure of it:
- Esterman test presents a bright stimulus (10dB) at each of 120 locations within the visual field
- If more than 20% false positives then the test is invalid
- Test carried out at 1/3rd metre
- 4 to 5 minutes for the test
Disadvantages of estermann test:
-Stimuli arranged in a pattern that was designed to predict a person’s mobility (walking) performance…..
oThe density of targets is higher within the central 20 degrees and in the lower hemifield. Therefore the sensitivity to detect paracentral scotomata is lowest in the upper visual field. Unfortunately, this area is particularly relevant when driving!
-Number of locations tested within the most functionally-relevant area of a driver’s visual field is very limited,
-Only 34 locations tested within the central ±20°, no locations within the central ±7.5°, and a predominance of these central locations falling in the lower half of the visual field (22 versus 12)
-Can only detect the densest of scotoma(ta)
-Fusion difficulties
-Only about 25% of the Esterman points tested fall within the key parts of the field for driving.
DVLA guidance for esterman tests with defects affecting central 20° only:
For GROUP 1 licensing purposes, pending the following are generally regarded as acceptable central loss:
Scattered single missed points
A single cluster of up to 3 contiguous points
DVLA guidance for esterman tests with defects affecting central 20° wholly or partly:
For GROUP 1 licensing purposes the following are generally regarded as unacceptable (i.e. significant) central loss:
A cluster of 4 or more continuous points that is either wholly or partly within the central 20 degree area
- Unacceptable central loss:
Loss consisting of both a single cluster of 3 contiguous missed points up to and including 20° from fixation, and any additional separate missed point(s) within the central 20° area
Central loss of any size that is an extension of a hemianopia or quadrantanopia
Example of esterman fail:
A cluster of more than 3 contiguous missed points in the central 20 degrees.
Exceptional cases for issuing a licence to drivers who previously have held a licence which was lost by failing the visual field rules:
- They can reapply for a licence if the defect:
- Has been present for at least 12 months
- Is caused by an isolated event or a non-progressive condition
and there is no other progressive condition that is likely to affect the visual fields
- And there must be clinical confirmation of full functional adaptation
- If the re-application is accepted then the applicant must carry out a satisfactory practical driving assessment
