Monthly Archive for: ‘October, 2014’

A simulation of horizontal diplopia (double vision)

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.

An photo of a red eye

The problem of taking risks

We had a contact lens patient’s mother in today to order her son more contact lenses. She was concerned that he was on occasions sleeping in them, despite being clearly instructed by us not to.

Statistically, sleeping in contact lenses is the number one risk of eye infections in contact lens wear – every one of our new contact lens patients has had this explained to them, and the reasons why it is a bad idea.

I recently had a young girl woman in Kingscourt on a Saturday afternoon for a routine contact lens check. When questioned, she denied ever sleeping in them, and told me that she had put them in at 9.00am that morning. After looking at her eyes with the slit lamp, there were clearly signs suggestive that she was not being “entirely truthful”. She wore daily disposable contact lenses which are unsuitable for overnight wear, at all, ever.

I asked her “When was the last time you slept with the lenses in?”.

She replied “last night”.

“So how long have you had them in for?”.

“I put them in on Wednesday”!

The problem is that, when you are told you should not do something, and you do it (perhaps accidentally) it is maybe not unreasonable to think “They said I shouldn’t do that, BUT I CAN, I was OK”. That is the way we perceive risk- by our individual experience. Statistically, young men are the worst for not heeding advise about what they should and should not do with contact lenses, and statistically they are the group most likely to present with Microbial Keratitis.

Statistics are they way we should assess risk, not by our own experience. Drink drivers are more likely to crash cars than sober people – FACT, most people would agree with that, but many who do drink drive think that they are OK, because they have “done it for years and never had an accident”.

I advised a lady once that she should not spit on her contact lenses before putting them in, she should use contact lens conditioning solution, to which she told me that she had been doing that since I was in nappies! That might be true, but as I advised her, that doesn’t make it a good idea, though it was obvious she was never going to listen.

No-one would ever think that playing Russian Roulette with one bullet in six chambers is a good idea, nor would they argue that “I did it, I’m OK, I can do it” Everyone knows there is a 1 in 6 chance of being wrong, and also that eventually you would blow your head off- it probably will not take too many turns to achieve it. Very few people would ever consider playing that game. The risks of contact lens infections are much, much less than blowing a hole in your head playing Russian Roulette, but do not think “I’m OK I can do it”- sight is precious, you only get two eyes, and they need to last you a lifetime.

And like silly games with guns, you could have a problem the very first time! Though it is true that infections increase with every consecutive night of sleeping with them in, and overwearers are more likely to fall prey to infection, there is a chance it could be you, first time, next time…

Estimates are that approximately 15-20 in every 100000 soft contact lens wearers per year will suffer a microbial keratitis, and there are probably a lot more than 15-20 in every 100 thousand lens wearers who are complete lunatics, doing everything wrong and mostly getting away with it, but don’t take the chance.

There is a refresher “Contact Lens Dos and Don’ts” here. If you are a contact lens wearer it will take 2 minutes to read it.


The Hazard of Blue Light

In the past few years there has been increasing worry among vision scientists and eye care providers over the “Blue Light Hazard” –  High Energy Visible (HEV) Light which can be emitted by flourescent lights and the illumination systems of modern monitors.

If you sit at a screen 7 to 8 hours per day, it would be worth having a look at the settings of the monitor to try to at least minimise HEV Light exposure.

Unfortunately, most phones and tablets do not come with any way to adjust the output of the screen, which means there is no way to reduce the blue output- which is why many spectacle lens manufacturers are now offering “Blue Control” Antireflective coatings.

With children and teenagers spending hours staring at laptops, tablets and phones, it may be advisable to consider a protective coating for them.

You can read more about the hazard of HEV light here.

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