#T4TD colour vision

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When your neurologist looks in your eyes with an ophthalmoscope he/she is looking for the telltale signs of previous damage to the optic nerve. The sign we look for is optic disc pallor. The optic disc is made up of nerve fibres from the retina, which then pass out of the back of the eye to form the optic nerve. If you have had optic neuritis in the past and have lost nerve fibres this can be detected with an ophthalmoscope, OCT (optical coherence tomography) or with retinal photography. Nerve fibre loss from optic neuritis makes the optic disc look pale (see figure below).

The optic disc receives its blood supply from small arteries from the back of the eye; the amount of blood is proportional to the number of nerve fibres in the optic disc. The lower the number of nerve fibres the fewer blood vessels there are the paler the disc looks. Please remember red blood cells are red and give a health optic disc a pinkish colour (see top images above).

Did you know that with a typical attack of optic neuritis you lose about 20% of the nerve fibres in the eye? If you lose so many nerve fibres why isn’t your vision so badly affected in that eye? That is simply because your visual system is able to compensate for the damage; it has spare capacity. Despite this most pwMS who have optic neuritis will know that although their visual acuity, or gross vision, may have recovered they have subtle deficits that we don’t routinely test for. For example, colour vision is often abnormal; colours appear washed out. Contrast sensitivity is abnormal; you may have difficulty distinguishing between shades of grey. Depth perception is all over the place; you need binocular (both eyes) vision for accurate depth perception. If you have poor depth perception you may see things in 3D when they should be in 2D and you may have difficulty judging distances. You may also find that you are hypersensitive to bright lights or lights with certain wavelengths; I find a lot of pwMS become intolerant of fluorescent lights after an attack of optic neuritis. 

The problem with the COVID-19 induced changes in our MS service is that with remote consultations I can do this aspect of the neurological examination. Is it important? Yes, firstly it allows one to determine what neuronal systems have been affected by MS, which is required for diagnosis, i.e. dissemination of disease in space, and secondly for assessing your EDSS or Expanded Disability Status Scale. 

I am telling you all this as we developed a web-EDSS that requires you to know if your neurological examination is normal or abnormal. Having optic disc pallor is one clinical sign that may affect the EDSS. If you can’t get this information from your neurologist you can get a reasonable idea if your optic nerve has been affected by MS by downloading and using one of the many colour vision applications on your smartphone; we recommend using ‘eye handbook’ as it is free. So before completing your webEDSS you will need to know if you have abnormal colour vision in your left or right eye; this could be used as a proxy for optic nerve involvement. Please note if you have congenital colour blindness, which is more common in males, you can’t use this sign as a proxy for optic nerve involvement.

#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.

2 comments

  • This answers my absolute discomfort for florescent lights. I’ve asked to move consulting rooms, I had an hours cognitive assessment and the lighting impacted on my concentration. My ON is historic but still getting fading, perception and hazy vision that alters through the day.

    I also found answering the EDDS questions difficult. In doors I sometimes use stick but use walls, furniture, or bash into things. I’ve always got bruised legs. It’s not that I can’t walk but I can’t walk that safely I suppose. Out and about I’ll use wheels as I find everything seems to rush at me. As if my brain is over whelmed as opposed to indoors where I know the lay out. Is this usual in MS ?

  • I got diagnosed on the basis of one bout of ON picked up by an ophthalmologist (and associated MRI damage/clinical history). I’ve continued seeing that ophthalmologist over the years and apparently my optic nerve looks great, they’ve subjected it to all kinds of imaging (eg nerve fibre thickness) and visual field tests. Apparently you can’t tell anything has happened, all the tests are normal. But I know my vision is not the same. I used to have excellent hand eye coordination and was great at ball sports, but not anymore. At first my 3D vision was terrible and I couldn’t hit a ball at all. Over time my eyes have adapted a bit, but it’s just not ‘right’. I really miss what I used to have!

    Otherwise it’s ok and I just have this weird thing at night where circles of bright red lights stay in my vision just a microsecond longer than everything else. Means they kind of “hang” in the air if I look away and look back quickly.”, it only happens with red LED lights arranged in a circle so obviously there’s a very particular type of damage that’s persisted.

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