Colour vision loss may be an early sign of disability
Visual symptoms, such as flashes of light or eye pain, are common in multiple sclerosis and are caused by inflammation of the optic nerve (optic neuritis). But one symptom that’s often not discussed is an impairment of colour vision. These impairment take the form of problems seeing certain colours or difficulties distinguishing between different colours (such as red vs. dark pink).
Different wavelengths of light are detected by specialized cells (called rods and cones) in the retina of the eye. Rod cells detect low light and have little in involvement in colour vision. The three types of cone cells found in humans are most sensitive to three wavelengths of light that roughly correspond with three colours: long wavelength (red), medium (green) and short (blue). Another way of describing it is that we see colours in an opposing way: either red or green (hence traffic lights); either blue or yellow; and either black or white. When cones are stimulated by light, the retina and optic nerve process this information into a colour and relay this to the brain. The ability to see colours varies from species to species (dogs have difficulty distinguishing orange from red), and from person to person. My blue may be your mauve.
People with hereditary colour blindness typically have a genetic defect in their ability to produce the proteins needed to detect colour. This gene is found on the X chromosome, so colour blindness is more common in men (who have only one copy of the X chromosome) than in women (who have two copies of X). Colour blindness affects about 8% of men and less than 1% of women of European descent.
However, the impaired colour vision in MS isn’t true colour-blindness and isn’t related to a genetic defect. Rather, it’s caused by the same inflammatory process that causes MRI lesions in the brain. What’s affected is the optic nerve. This nerve lies outside of the central nervous system, but is actually an extension of the CNS (rather than being a peripheral nerve). This means that optic nerve is the most accessible part of the CNS available for scrutiny, and provides some indication of what’s going on in the brain. MS inflammation causes damage to the optic nerve, just as lesions in the CNS cause damage to nerve fibres in the CNS.
A new study has found that about 1 in 5 people with MS have some degree of impairment in their colour vision (Martinez-Lapiscina and colleagues. Mult Scler 2014; epublished January 7, 2014). Impairments mostly appear to affect the perception and contrast of reds and greens (Gregori and colleagues. J Neurol Sci 2011;300:130-134; Flanagan & Zele. Ophthalmic Physiol Opt 2004;24:225-233).
Colour-vision impairment is more common during a bout of optic neuritis (Serbecis and colleagues. PLoS One 2010;5:e13877), but difficulty distinguishing between colours can occur even if there is no optic neuritis or other eye symptoms. In the study mentioned above, an important finding was that changes in colour vision were associated with greater physical and mental impairment (Martinez-Lapiscina 2014), indicating that the extent of damage to the optic nerve was related to the amount of damage to the brain. People with impaired colour vision were more likely to have greater physical disability one year later than those with normal colour vision.
Other studies have also reported that the optic nerve damage is an early sign that MS is progressing (Garcia-Martin and colleagues. Neurology 2013;81:76-83). Optic nerve damage has traditionally been viewed as optic neuritis, which is characterized by difficulty seeing or reading small text, flashes of light, and other symptoms . What these new studies have found is that impairments of colour vision appear to be a more sensitive way of detecting optic nerve damage (Villoslada and colleagues. Mult Scler 2012;18:991-999; Gundogan and colleagues. Indian J Ophthalmol 2013;61:100-103). In fact, colour-vision changes can be detected in people who have never had optic neuritis or other eye symptoms during their MS (Moura and colleagues. Vis Neurosci 2008;25:463-468).
These studies suggest that changes in colour vision are important so they need to be reported to your neurologist. Colour-perception changes may be an early warning sign that you are experiencing more severe disease and, by implication, that your MS treatment isn’t doing a good enough job.
As a final note, if your colour vision is impaired, you may be concerned that you will no longer be able to drive a car. One study found that among people with MS who had changes in their colour perception, their vision was still sharp enough to drive and they didn’t appear to be at risk of an accident or barrelling through a red light (Shultheis and colleagues. Arch Phys Med Rehabil 2010;91:315-317). But extra caution is needed when driving if you have any MS-related vision problems.
Answer all questions as if you were wearing glasses or contacts (if you need them).
Adapted from the National Eye Institute Visual Functioning Questionnaire 25 (VFQ-25), July 1996, developed at RAND under the sponsorship of the National Eye Institute.
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