Lecture 2: visual fields and vision standards Flashcards
What happens if you don’t inform DVLA once you become aware of an eye condition which is likely to be a source of danger to the public when driving?
-criminal offense
-serious motor insurance implications
How can you tell from somone’s driving licence that they need glasses for driving?
01 code on back of driving licence
What are the visual standards for group 1 drivers?
-be able to read a registration plate in good daylight with glasses or CL if required
-characters 79mm high and 50mm wide from 20 meters
-VA must be at least 6/12 with both eyes or only one eye is monocular with aids of glasses to CL if required
Is the number plate test reliable?
*There is no precise Snellen equivalent to the number plate standard
*If you look at the visual angle, the number plate test is equivalent to 6/15
Latham et al (2014) found:
-people with binocular VA 6/12 could not all pass the number plate test
-some people passed the number plate test but had a VA below 6/12
-different lighting in test room
-weather affects number plate test
What can be done according to Latham et al (2014) to ensure people can read the number plate?
-to predict a drivers abiltiy to read the number plate, vision should be assessed using logMAR letter chart or a snellen chart scored by full line
-drivers with 6/7.5 or 6/6 (if there is no 6/7.5 line) or better vision can be advised that they meet the driving standard.
-drivers with VA between 6/9-6/12 should be advised to check their ability to read a nuber-plate as they might not be able to
How should optometrists respond to a patient who asks if their fit to drive?
AOP advice: dont provide certificates of ability to pass number plate tests based on consulting room tests
-advise px to statify themselves that they can pass the number plate test alone (at 20m in different weather conditions)
-px can report to licsecing centre who will arrange for the test to be accurately carried out at a driving test centre
When are drivers required to prove their vision meets the standards?
every 10 years more frequently as they age
What type of drivers does group 2 include?
What are the visual standards for group 2 drivers?
LGV: large good vehicles (lorries)
PCV: passenger carrying vehicles (buses)
-at least 6/7.5 VA in the better eye
-at least 6/60 VA in the worse eye
-Must have a corrective power of less than or equal to +8.00D. No limit for corrective power of contact lenses.
Why are the standards for gorup 2 drivers challenging for optometrists?
-not every snellen chart has a 6/7.5 line
-test chart needs to positioned accurately at 6m
-charts at shorter distances but be accurately scaled
-+8.00 refraction limit doesn’t specify if its mean sphere power or highest powered meridian
-hyperopes become more hyperopic as they get older. may start of less than +8.00
What correction should be used when testing fields for driving requirements?
habituial correction
binocular telescope in netherlands
What are the visual field requirements for driving?
standards are applied when there is evidence that a defect exists:
-minimum field of vision is 120 degrees horizontally
-there should be no significant defect in the binocular field which encroaches within 20 degrees of fixation above or below the meridian
-homonymous or bitemporal defects which come close to fixation are not accepted
What type of visual field testing is used to assess visual requirements?
estermen test (supratherehold testing)
-carried out on HFA
-presents a bright stimulus 10dB) at each of the 120 locations
-more than 20% false positives means test is invalid
-carried out at 1/3rd metre
-4 to 5 minutes for the test
What are the disadvantages of esterman?
-limited locations of points in the functionally-relevant area of a drivers visual field
-only 34 locations tested in central 20 degrees
-no locations in central 7.5 degrees
-predomiance of central locations are in the lower half of vf (22 vs 12)
-a lot of test points fall on the dashboard (lower vf)
-sensitivity to detect paracentral scotomata is lowest in the upper visual field. This area is particularly relevant when driving
-can only detect the densest scotoma
-fusion difficulties
What defects affecting the central 20 degrees are acceptable for group 1 drivers?
What defects affecting the central 20 degrees are unacceptable for group 1 drivers?
-scattered single missed points
-a single cluster of up to 3 contiguous points
-a cluster of 4 or more contiguous points that are either wholly or party within the central 20 degrees area
-loss consisting of a single cluster of 3 contiguous missed points up to and including the 20 degrees fixation area and any additional separate missed points within the central 20 degrees area
-central loss of any size that is an extension of hemianopia or quadrantopia
When can a person reapply for a licence who previously lost it due to failing the visual field rules?
-defect has been present for atleast 12 months
-defect was caused by an isolated event or non-progressive condition
-there is no other progressive condition that affects visual fields
-must be a clinical confirmation of full functional adaptation
-if re-application is accepted, applicant must carry out a satidafactory practical driving assessment
When can a driving licence be issued for someone who has a static field defect?
-a 3 year provisional licence will be issues if:
-condition is non-progressive
-apllicant has fully adapted to fied defect
-no other relevant medical conditions
-instructor completes a on-road assessment to make sure driver is competent
-if assessment is favorable, a unrestricted provisional licence is issued in the normal way
What is disregarded on an estermen test for peripheral defects?
-a cluster of up to 3 missed points lying on or across the horizontal meridian
-a vertical defect of only a single point width but of any length which touches or cuts through horizontal meridian
What are the visual field requirements for group 2 drivers?
-horizontal visual field of atleast 160 degrees
-extension should be at least 70 degrees left and right and 30 degrees up or down
-no defects should be present within a radium of central 30 degrees
What are the requirements about diplopia for group 1 drivers?
what are the requirements about diplopia for group 2 drivers?
-cease driving on diagnosis
-resume driving on confirmation to the licescing authority that the diplopia is controlled by glasses or by a patch
-exceptionally a stable corrected diplopia of 6 months duration or more may be compatible with driving if there is consultant support indication adaptation
-permanent refusal or revocation if insuperable diplopia
-patching is not acceptable
What are the requirments of colour vision for group 1 and group 2 drivers?
defective colour vision is no bar to driving
What are the conditions for monocular group 1 drivers ?
-must inform DVLA if complete loss of an eye
-driving can be resumed after adaptation (driver can satisfy VA, number plstr and vf requirements in remaining eye)
What are the requiremnts for monocular group 2 drivers?
-complete loss of vision in one eye or corrected acuity of less than 3/60 in one eye means applicants are barred from holding group 2 licence
What lighting requirements can lead to stopping a person being issued a driving licence?
-px with cataract or refractive surgery may be unable to meet required standards of poor light or glare
-inabilty to see effectively when driving at night with headlights or due to night vision defect (RP)
How can blepharospasm affect driving requirements for group 1 and group 2 drivers?
-must not drive and inform DVLA
-consultant opinion required. if mild, drivib can be allowed
-control of mild blepharosopasm with Botulinium toxin may be acceptable (no side effects like diplopia)
-DVLA should be informed of any changes or deterioration in condition
-driving not permitted if condition is severe
What advice should be given about driving during frames and lenses selection?
-limitations of high powered lenses
-danger of wearing tints at dusk or at night
-dangers of transition lenses when entering tunnels and roads shaded by trees
-px with borderline VA should be advised not to drive vehicles with tinted winscreens or tinted lenses
How can diabetic retinopathy affect visual field requirements for driving?
-pan retinal photocoagulation can cause reduced visual fields
-DVLA will investigate if laser treatment is carried out on both eyes
