Computer Vision Syndrome

Monocular Diplopia (Double-vision) and Computer Use

Here's the scenario: you spend a lot of time at a computer screen. After this you notice you have developed an odd type of blurred vision. It is double vision, with a pronounced and sharp ghost image beneath or above the actual image. It is monocular — ie falls into the more unusual type of double vision which is evident even if you cover up one eye. In my case it affected both eyes approximately equally. It would last for many hours, often disappearing only after a night's sleep. And it was bad enough to make driving difficult: lights, signs, and road-markings would all display this intrusive and unpleasant ghosting.

The internet reveals many others complaining about this symptom. Some have been to see ophthalmologists and have been sent for multiple tests before being told there is nothing to find. The commonest theory seems to be that you strain your eyes staring at the screen, your blink-rate goes down, and the double vision results from some corneal drying. So there has been proposed a 20:20:20 rule:

Every 20 minutes do some blinking, then look at something more than 20 feet away for 20 seconds.

The problem in my case was that the double-vision developed over just 5-10 minutes use of a screen. After some experimentation (see below) I concluded that the 20s rule simply treats a general condition of tired, strained, dryish eyes, but does not address this very specific, pronounced and annoying symptom.

A brief search of the medical literature confirms knowledge of this symptom and confirms how common it is (25% of diplopia presentations at Eye Emergency Facilities). It does not reveal the precise cause, why it comes on, nor why it then goes away over 6 hours or so. I spoke to a senior ophthalmic surgeon who is involved in the management of ocular surgical conditions and emergencies and he confessed he was unaware of the condition, and suggested that perhaps I should I get a life away from my computer. Cheers, mate.

Things That Didn't Work

Regular breaks and blinking. I set a timer for 20 minutes. Tried to blink as I worked, and followed the 20s rule. Somewhat to my surprise this made absolutely no difference. But again, I have been using computers extensively for my whole life and have never noticed this symptom before.

I reduced my screen brightness and contrast. It is now down to zero brightness and 15% contrast - for my monitor that still gives a perfectly usable and pleasantly dim screen. This made no difference to the onset time nor the severity of the ghosting. Good grief, what is going on with my eyes?

Eyedrops. These were quite pleasant to use. I put them in before I started, followed the 20s rule, and also put them in at regular intervals during a session. They had no effect on the onset time, severity, nor duration of the diplopia.

Hypromellose, is an artificial tear used to relieve dry eye conditions (eg. conditions associated with the use of VDUs and TVs, infrequent blinking, certain medical treatments, atmospheric pollution and drying atmospheres eg. air-conditioning, central heating, wind and sun). It is also used to moisten hard contact lenses and to lubricate artificial eyes.

At this point I was stuck. I wear varifocals for shortsightedness and the loss of accommodation (focusing-range) typical of a man in his mid-fifties, but all other aspects of my vision were unchanged. Reading a book or newspaper was fine.

What Worked in the End

Currently, after a lot of trying this and that, I am sitting typing this wearing not just my vari-focals, but on top of them a pair of 1.5 dioptre reading glasses. This combination completely, and I really mean completely, prevents the development of the monocular diplopia that was so debilitating. I have stopped using the eyedrops, though still (it's probably a good thing) stop every few minutes and stare out the window into the distance for a while.

So I may think about getting specific computer-glasses. I presume these would have my normal prescription, but be +1.5 dioptres to allow relaxed focus on the screen. They will obviously be blurry for distance.

If you are not a glasses-wearer (either normal eyes or contact lenses) then try some cheap 1.5 dioptre reading glasses. That may be all you need. If you need glasses, then my rather ridiculous stacked glasses is just a temporary solution to establish whether it helps. You can buy reading glasses as flip-up lenses that fit on top of your existing glasses - or you can get prescription computer-glasses specifically made for you.


OK, sort of on the principle that the correct dose of anything is "enough", I tried some +1 dioptre glasses instead of the 1.5. After an hour of working... here it comes. Not so pronounced, but that little ghost was there. Back to the +1.5 glasses.

One of the things that has been puzzling me is exactly what all this reveals about the optical cause of this monocular diplopia. My money is on changes in the lens itself which is having to work to accommodate and focus on an LED screen, and ends up doing so assymetrically causing astigmatism and a double image. This assymetry in the lens persists for many hours after the screen use. This would account for the dramatic improvement seen when comfortable focus is achieved by the additional +1.5 dioptres because the lens can remain relaxed and no longer has to work to accommodate. I suspect my aging lenses are simply more susceptible to this slowly reversible assymetry simply as a side-effect of the age-related loss of elasticity. Given the failure of other therapeutic suggestions above I offer this new theory to the world. Who knows? All just speculation! (Pun intended)

Some Medical Detective Work

First: full eye examination and a retinal photograph compared with 5 years ago. Clean. No early cataracts, normal retina: no exudates, haemorrhages, blood-vessel abnormalities, etc etc.
Refractions: mine have actually improved by about a dioptre in each eye. Yay! So current spectacles slightly over-correct. Minor astigmatism has slightly changed axis in one eye, other eye unchanged. Bottom line nothing that would contribute to this symptom. Updated specs are on the way.

Next: let's see if we can identify the offending structures within the eye's apparatus. So cyclopentolate eye drops to both eyes. These drops reversibly paralyse the ciliary muscles causing a loss of accommodation (ability to alter the focus), and also relaxes the sphincter muscle of the pupil which dilates dramatically. (The photographic equivalent of opening the f-stop up full and throwing away the focus ring on your lens). Right. Done. Now let's see if I can provoke the diplopia now.
OK, after two hours of computer work, which would certainly have produced a very noticable diplopia, I have only the subtlest of diplopia in my right eye and none at all in my left eye. Excellent... we have our culprit!

What does all this mean? Well this confirms that the diplopia mechanism is an uneven refractive error in the lens, and is not due to corneal drying or any retinal or neurological disorder. The trigger is the eye trying to hold focus on the screen, which involves the ciliary muscles distorting the lens. The lens remains misshapen after this process for many hours, but on regaining its shape leaves an eye which passes a detailed eye examination without revealing any abnormality.

If you share this symptom what should you do? Simple. 1) Stop worrying about it. 2) Get some computer glasses (normal prescription + about 1.5 dioptres) that allow you to use a computer without straining to accomodate. 3) Be grateful that the technology exists to investigate and manage symptoms like this. Continue with an annual eye-check by a qualified optician (U.S. = optometrist).

Important Disclaimer

The information on this page is what we medics call "anecdotal" and may not work for others. Please remember that there are specific diseases which may cause monocular diplopia: early cataracts, dry-eyes or corneal distortions may need medical assessment and treatment. However it is always worth trying simple and cheap solutions — if it works then problem solved.

Alan Hope