#T4TD Driving at night

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Did you know that more than half of people with established multiple sclerosis (pwMS) have had an episode of optic neuritis (an MS lesion in the optic nerve)? Not all episodes of optic neuritis cause symptoms and can be subclinical. We detect the latter using visual evoked potentials that show slowed conduction in a particular optic nerve. 

When optic neuritis recovers the conduction speed of nerve impulses travelling through the recovered nerve rarely gets back to normal and is slower than the conduction speed in the unaffected eye. In addition, the conduction speed can change depending on fatigue or ambient temperature changes. The conduction in the affected, by remyelinated, nerves can even fail and this is can result in intermittent blurring or loss of vision called Uhthoff’s phenomenon. 

The brain is usually quite good at compensating for the signals coming from the eyes at different speeds, but the one thing it is poor at doing is adjusting for depth perception. The reason we have two eyes with overlapping visual fields or binocular vision is for depth perception. This is why pwMS with previous optic neuritis may have poor depth perception, which affects their ability to judge where for example a cup or glass is on the table and as a result of this they often spill drinks. PwMS will also have difficulty playing ball sports such as tennis, table tennis or any sport that requires accurate depth perception. 

One function that seems to very sensitive to this phenomenon is judging distances whilst driving at night; for example, estimating how far you are from the traffic intersection or a stop sign. Many of my patients don’t like driving at night because of this. Why? Well, the brain uses a process called parallax to compensate for the loss of depth perception; i.e. the brain uses the relative size of familiar objects to help make a judgment on how far something is away from you in the distance. By using parallax somebody who is blind in one eye can judge depth and distance relatively well. However, at night in the dark when images are not well illuminated and use of colour vision drops judgement by parallax fails and depth perception deteriorates. 

I would be interested to know if any of you have any of these problems with depth perception and driving at night. If you do the chances are that you have had optic neuritis in the past. 

Unfortunately, there is little we can do to treat this phenomenon, but knowing about and understanding why it occurs may help you compensate for this impairment, disability or handicap. 

Parallax: Have you ever wondered why the setting-sun and full-moon on the horizon look so big compared to it being smaller when it above us in the sky? It is actually not bigger; simply having a reference on the horizon (trees, mountains, buildings, the sea, etc.) makes your brain perceive it as being larger, i.e. closer. This is how parallax affects how the brain works and judges distance from you to an object in the distance. 

#T4TD = Thought for the Day

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About the author

Prof G

Professor of Neurology, Barts & The London. MS & Preventive Neurology thinker, blogger, runner, vegetable gardener, husband, father, cook and wine & food lover.

22 comments

  • Thats really interesting to know. Is it always visible on the optic nerve in the normal eye test opticians/neuros do and scans if you’ve actually had ON?

    I ask because I’ve had loads of problems with my eyes that started just before an MS relapse (pain, light sentitivity and aching) and am under Moorfields Eye Hospital for it. Recently an optometrist said the continuous eye aching I experience could be due to the corneal nerves ‘misfiring’ and experiencing more pain from dry eyes (which I have, but its under control now and the state of my eye surface no way near reflects the pain I get!). I’m still waiting to see the external eye disease consultant. I have no visible ON nerve damage that Moorfierds as of yet/Neurologists has seen. This has been the most frustrating issue, and worse than any of the other ‘MS’ symptoms.

  • I started with optic neuritis, about 15 years ago, over the last 12 months I have noticed a blurring of vision that comes and goes, depth perception isn’t as good, I’m always hitting the frame of a tennis tennis raquet I used to be a good tennis player too!

  • Hi Prof G

    I’m just asking about the comment u stated about u having a cure. I’m just asking if that’s correct and what on earth is it?

    Regards, Janet B

  • “Unfortunately, there is little we can do to treat this phenomenon“. Doesn’t this apply to pretty much all MS symptoms / deficits? Double vision – put a patch over one of the lenses in your glasses; weak leg – use a cane; bladder problems – wear a nappy; cognitive problems – write things down…. It’s all sticking plaster low tec solutions. We are in the 21st Century with fantastic technological advances, but Charcot could have prescribed most of the ‘solutions’ to MS symptoms / defects which neuros today are prescribing c. 200 years after his birth! I hate MS with a vengeance, but second on my hate list is the lack of any progress to stop worsening disability or to encourage partial recovery of some lost functions / deficits. When you started in the MS field c.30 years ago could you have imagined that in 2020 MS would still be so intractable?

    • There is a remyelination therapy called opicinumab that may help this symptom. If it is shown to be effective not all is lost.

      • Is Biogen still working on it? There are no fresh news about it on the internet since the last trial. Maybe they are working on a way to properly get it into the CNS? I have read that there are some companies that set up ways to engineer proteins to increase their concentration into the brain… still on mice I think :/

  • Hanging the first item of washing on a line is hilarious. I flail around like a horror movie teen trapped in a giant spider web.

  • My goodness, this explains a lot. I am sure I have had optic neuritis – I have had episodes of eye pain and Photopsia but have always been told that my optic nerve appears normal.

    I have also known for a while that my depth perception while driving was off – in the day as well as the night – but thought this was a general MS symptom and didn’t realize it was associated with optic neuritis. I avoid night driving as I find it really hard.

    I have had several minor car accidents in the last few years and am now thinking that I should maybe stop driving – would you recommend this? My consultant has currently approved a three year license for me.

  • I think my depth perception was a little affected when I had Optic Neuritis. The episode lasted about four weeks in total, but it was only the first week or so that I was totally blind. It was my second relapse, following a week of diplopia six months earlier. I was never worried I wouldn’t get better. In the first week it affected my running a little – mostly my ability to run in a straight line! But it was at Christmas time and some lovely new running kit arrived in the post. A planned trip to Barcelona was cancelled, not because of my health but because Gatwick flooded, so I spent my break running and drinking Buck’s Fizz. I discovered that a run is not only a good hangover cure but also eases symptoms during a relapse.

    A few years and more relapses later and two months before I was due to be diagnosed (seriously, it was a “come in and we’ll diagnose you on that day” sort of appointment) I had nystagmus. It lasted for weeks and affected my depth perception much more. I’d rather be half blind forever than go through that again.

    Lately, and especially since working from home, I have noticed some difficulty with my vision. Possibly more in the eye that had ON. I don’t know if it’s the increased hours of screen time (no more in person meetings, no more walking around a big office or walking to my other office). Or could it just be that after 39 year of not needing glasses, something as ordinary as middle age is the cause?

  • No, circa 20 years PPMS, but very grateful for excellent vision, including night vision. But I don’t drive at night as I am more likely to be fatigued then.

  • I had optic neuritis in last relapse and partially recovered from it. I am still not sure if it is optic neuritis because the optic nerve at the retina seems normal, OCT is normal as well as the visual field.
    I have bad vision after waking up then it gets worse and improves a couple of times during the day. In the evening it finally gets better so, at night, I see better than during the day. The whole story is strange according to my Neuro and to several opticians/optometrist/eye specialists. I have myopia also and I had difficulties at sunset. I need to test evoked visual potentials.

    • Hi all

      I’ve never had the eye pain (thank God) but I’ve got persistent double vision. I have varifocals with prisms which help a lot xxx I’ve had RRMS since December 2017 and I used to be a ward sister on a cancer surgery unit till MS appeared! Nice to meet u all xxx

  • Great post!! Thanks!

    I have had optic neuritis – which eventually led to my MS diagnosis about 6 years ago.

    I used to have a very long commute to work. The very first and biggest difficulty I had while driving was when I would begin to change lanes. I could not judge how far or close the vehicle behind me in the next lane was while looking at the side/rear view mirror. Here’s the kicker – this was during broad daylight. The problem went away after a few months.

    But because of optic neuritis, the problem that I have even today is – climbing down the stairs. It is very difficult for me to perceive the depth as I climb down from stair to stair, so I slow down quite a bit and take my time. However, I have no major issues going up the stairs.

  • ON in both eyes. Right in 2008 and the left in 2010. Both went to complete blindness in a few hours. I am now very careful about driving at night and some times prefer not to. I’m an old lady now so I use that as my excuse. I have found that contrast has been another big issue. I cannot differentiate very similar colors in low light. Two dark socks on a dark floor in low light and they might as well not be there.

  • This is interesting! My vision spins out a lot, not when driving. Mostly when I’m sitting have a conversation with somebody.

    As it is, i try to avoid driving at night, especially on unfamiliar roads because of what you described. Hills and bends seem to come out of nowhere! It’s terrifying, my boyfriend simply things I’m a bad driver. As far as I’m aware none of my scans have shown up optic neuritis.

  • Night driving and depth perception were an issue when I drove, now the problem is working with colour in artificial light. I use a daylight lamp and increasingly a magnifier too.

  • Driving at night is definitely difficult
    It’s especially difficult when I’m blinded by the glare of oncoming vehicles. Is that related to MS too?

  • That was so helpful, thanks for posting. I experienced optic neuritis as my first symptom 5 years before MS diagnosis. I do have difficulty driving at night. I tend to find it difficult to recognise where I am and turn down the wrong roads. I get more anxious driving at night too and feel stupid when I don’t recognise a road that is familiar in daylight.

  • Such a well explained article on something I struggle with and didn’t understand why. Night driving and regularly knocking drinks over. Dropping them too as though they fall through my hand yet my hand has grip
    My symptoms on diagnosis was ON and balance problems. I also get intermittent disturbed vision. I’ve been told it’s migraine by origin. But it’s not same as my head aches.

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