How can you check that DVLA field of vision machine is OK.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Paul Rhodes on 25/04/2021 22:48:21:

Michael,

I do not wish to be unduly provocative but you don’t explain what you mean by ergonomics in this matter. […]

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Ergonomics … ‘Man in his working environment’

The working environment in this case being driving a motor vehicle … a physical one on the road.

A visual acuity test at 6metres, with the subject wearing his actual prescription glasses, is more relevant than a test at 3metres.

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Paul Rhodes on 25/04/2021 22:48:21:

[…]

I am sorry but I still find it unconvincing that Mark’ varifocals should give a sharp image at 3m when the object came from 6 via a mirror, but be difficult/ impossible when reading at exactly the same 3m when reading the half sized image.. This is not to doubt the honesty of Mark’s assertions but rather to question the science that both you and he accept.

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That aspect is very simple …

The object distance is 6metres when you are viewing the reflection : you don’t focus on the mirror surface; the mirror simply folds the light path.

MichaelG.

[Nick Clarke 3Participant @nickclarke3]

Posted by Michael Gilligan on 25/04/2021 21:11:33:

”Our DVLA eye test chart is a 3m Snellen style eye chart. The chart is made of plastic and perfect for hanging on a wall. Our direct eye test chart conforms to DVLA standards. It includes the 7.5 test line as introduced by the DVLA and must be viewed from 6m away.”

Carrying out functional vision assessments is part of the day job, including visual acuity tests using both Snellen and Logmar test charts.

The Snellen test is a standard test that can only be carried out at 6m or 20ft. All reduced Snellen charts are 'Snellen style' as in the quote above. The Snellen chart does not include a line for 6/7.5 so the DVLA chart has this added – whether the 'viewed from 6m away' is a typo, or whether it is a separate line that is meant to be viewed from 6m, I don't know – but I suspect the former. The reason for this extra line is that by the nature of the test interpolation between the lines is not possible – although I have seen an ophthalmic surgeon with many years of experience estimate between lines accurately.

Moving out of my professional experience to my personal experience wearing varifocals all varifocals can operate at any strength between the distance setting and the close up setting (used to be 14" – probably now 35-40cm) – and usually a little beyond both of these. The only difference is in the rate of change between the two and this can mean more of the lens is available in the area most used for driving or computer use so less searching for the 'sweet spot' is needed for these tasks – but they will all match the prescribed distance and close up powers somewhere. (and everything in between)

[Michael GilliganParticipant @michaelgilligan61133]

Thanks for the comments, Nick

MichaelG.

[MacolmParticipant @macolm]

The design of varifocal lenses is always a compromise between the desired gradation of optical power, and the inevitable distortions that result. The latter are the reason for the "swimming" effects, which for those lucky enough are completely corrected in the brain, and which for a minority are never tolerated. Designs have improved greatly over the years, but often minimised distortion results in perceived peripheral soft focus.

Most of the more expensive makes give some form of money back guarantee on the lenses, though mounting costs will probably not be covered.

[Ian Skeldon 2Participant @ianskeldon2]

I have some experience in the field of opthalmology and have seen many reasons for both slow and sudden unset of reduced peripheral vision, some factors that can help are life style, smoking is terrible for good eye care, good diet is beneficial especially some of the supplements like Lutein, Bilberry, and Zeaxanthin but sadly age is something that you can't do anything about.

Your ability to see at any or all distances with your central vision is not an indication that your peripheral vision is ok. Opticians and technicians are not able to tell a person when to press or when to expect to see a light as that rather defeats the object and would create false positives no doubt. Conditions such as AMD, Glaucoma or high intra ocular pressure can certainly damage peripheral vision, along with things like poor vascular activity, arthritis and rheumatic conditions also seem to be common with vision problems. It is also possible to have variation when being tested, some days you may have poor sight and on another occasion not so bad.

[paul oldfieldParticipant @pauloldfield44733]

Just in case this is of interest to PVF deficient readers . Mine was discovered in 2016 , following a routine eye test at my optician . Since then it was referred to the DVLA , and further tests carried out at specsavers , it was also referred to my GP and brain scans completed at my local hospital . Old occipital and cerebellar strokes were found , the GP thought lifestyle , I thought Trauma ( 3 major concussions ). To apply for a reinstatement of your license the DVLA require it to be a non progressive condition . In 2017 , I applied to the DVLA to be treated as a ' special case ' and eventually managed to get an appointment at Anglia driveability for an assessment . The 'inside ' practical exam was hard (to put it mildly ) and lasted 45 mins to an hour . The driving assessment lasted an hour , with two examiners in the car . When they said I had driven ' flawlessly ' , I replied that I should do after a million miles driving . So reinstated . I had historically probably four Visual Field tests on machines , Goldman , Esterman etc plus one with flashing lights and a brake pedal . The machine tests all confirmed upper left PVF deficits , but my eyes had compensated for those deficits . I had my annual test last week at my optician – Rt eye = 3 misses (as per previous year ) Left eye = Perfect (previous year 3 misses ) and no false +ves . Optician put the left eye improvement down to cataract op (rt eye had been done ) . So there is hope for us all .

[vic neweyParticipant @vicnewey60017]

I have Ocular Hypertension, sometimes as high as 35 but eye drops help keep it lower, rarely below 21. The clinic is amazed that it's not caused any damage to my optic nerve so far.

However, in early May I filled in my new over 70's licence application for my birth date 25th June and ticked I had an eye problem, weeks later a reply came asking for details and I ticked ocular hypertension giving name of my consultant etc who can confirm I do not have Glaucoma etc.

Weeks go by again and then a letter arrives telling me to select one of the few special Specsaver branches for the two tests. Clearly a medical consultants confirmation of my eyesight is not good enough for them.

The only option at Specsavers was 8-45AM for any of these appointments, the DVLA specify that their customer must be the first to use it each day to avoid contamination etc.

First was reading the eye test letters on a weird square monitor, alternate eyes without my glasses then repeated with them on, I can easily get to the bottom two letters on a normal opticians one but struggled on this as it made my vision feel weird with the glare.

Then the field of view test, so much better doing both eyes together as covering one eye up with an elastic pirate patch or more recently cotton wool held on with tape so you have to screw your eye up while looking through the other one and then swap for the eye you just screwed up closed for two minutes.

He showed me the printout of the test, he wasn't allowed to actually tell me but it looked 100% to me, no little crosses missing, then he checked for any I had missed and then said very good and got out a phone for me to sign with the end of my finger and he pressed send.

Today my licence arrived at last after 5 months, no mention of of anything to do with those tests etc

Edited By vic newey on 29/09/2022 17:10:27

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