Double Vision

Most times when we have someone complaining of double vision, it turns out to be blurred, or ghosting that they are actually seeing. They generally do not complain about double vision, until we ask about it, which we always do.

I had a patient in last week who had been suffering double vision for the past six months. His complaints were quite specific and he particularly complained that when trying to pick something up off the floor, it was not in the position he thought it was. Double Vision (Diplopia) is usually a disturbing thing to have, I thought it unlikely that this client genuinely was seeing two of things- why wait this long to complain??  Using a combination of Cover Testing, where we look at where the eyes are pointing, and ocular motility, where we check the functions of the eye muscles, it became obvious that this man had an incommitant squint.

Concommitant squints are the same size in every direction of gaze, and are by far the most common type. Many concommitant squints can be helped in practice using prisms to eliminate the doubling,  or sometimes eye exercises (depending on the cause) but usually do not require referral for specialist investigation.

Incommitant squints on the other hand are due to one or more muscles which move the eye around failing. Each eye has six extraocular muscles, each of which need to work in close harmony with the other 5 on the same side and the other six around the other eye to ensure single vision in every direction of viewing. If one or more muscles becomes weak, or fails, almost always double vision will be the result. The incommitance is that, for example, if the muscle that moves the left eye outward (to the left) fails, vision will be double on looking left, but because that muscle is not required to look right, vision would most likely be single to the right. therefore the angle of the squint varies with the position of gaze.

A failed eye muscle arises either because the muscle has been directly damaged, or the blood supply or the nerve supply to it has been compromised. You can imagine that nerve failure or blood vessel failure in the head is always potentially a serious thing, and requires urgent investigation to try to find a cause. Many thorough investigations often result in no cause being found, which is probably the best result possible, given that some other causes could be strokes, tumours and Multiple Sclerosis.

I don’t know how this client has managed for the past 6 months, but he seemed to have acquired a tilt of his head towards his right shoulder- patients often develop a head position that puts the eyes in the direction where vision is single. He should have been seen 6 months ago and referred urgently then.

All cases of double vision should be investigated, those that are only in a certain direction more promptly! I am amazed how many web surfers arrive at our site searching the term “double vision”.

If you or a family member has double vision, get it checked out ASAP.

Local eyecare for all the family

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