Which eye do you use?
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Did you know that most people have a dominant eye just like they have a dominant hand? It’s true. It’s known as ocular dominance. Yes, there is a small percentage of the population where neither eye is dominant, but this is more of the rare exception rather than the rule.
The first thing most people think is that I’m right handed, so I must be right eye dominant! It’s true that right-handedness (90% of individuals) and right eye dominant (65% of individuals) is far more common, but there appears to be no direct correlation between the two. Trust us. Countless studies have looked into it.
Right Handed People are Not Necessarily Right Eye Domiant
So can you figure out which eye is your dominant eye? Let’s review two at home tests for checking your ocular dominance.
- The Dolman Method: This involves holding a small card up in front yourself that has a hole in the centre of it and fixating on a target in the distance. It’s important to hold the card with both hands to prevent bias. Slowly pull the card back towards your face and your dominant eye will be revealed.
- The Miles Test: The miles test is very similar to the Dolman test, but it doesn’t involve the use of a card, it only requires you to hold your arms out directly in front of you and trying to sight a distance image. Once again, slowly pull your arms back towards your face and your dominant eye will be revealed.
These tests work extremely well for quickly determining ocular dominance, but their limitations are that they are forced choice tests, you can only ever choose one eye. The vast majority of the time though these tests are more than adequate. But your eye doctor may also perform additional tests to determine subjectively how high your ocular dominance is.
One test that we like to use in our eye clinic is a technique called lens fogging. Lens fogging involves changing the prescription in front of one eye (usually adding plus lens power) and determining how it affects your distance and near acuity.
The benefit of lens fogging is that it gives us a bit of subjective response on your ocular dominance and how closely linked the two eyes are. Some people can tolerate vast vision changes in front of their non-dominant eye with little change in visual perception, while other patients notice even the slightest adjustments.
So why does all this matter, how does ocular dominance help your eye doctor?
Knowing ocular dominance can help your eye doctor better understand visual symptoms you are experiencing, or why you might be having problems with particular work or sporting activities. It’s also used to balance eyeglass prescriptions to ensure that your eyes feel like they’re working as a team.
Ocular dominance more often than not only starts to factor into eye exams as patients get into their 40's and start noticing near vision problems. If you're nearsighted you'll know your close to needing reading glasses when you start taking your glasses off to read and you start saying things like, "it's just more comfortable to read without my glasses on".
Your optometrist can use ocular dominance alongside a technique known as monovision to help some patients see clearly in both the distance and up close.
Monovision can be done in eyeglasses,
but is more commonly used in contact lens fittings,
laser eye surgery and cataract surgery.
Monovision is a proven eye care technique where one eye (usually the dominant eye) is corrected to favour distance acuity while the other eye (the non-dominant eye) is favoured towards near acuity. It is usually first tried in contact lenses because of the ease of adjusting prescription parameters, but it’s also sometimes tried in low nearsighted patients looking at getting laser eye surgery or cataract surgery, where only one eye is initially treated.
Case Example: Meet Jenna, a 43-year-old system analyst who is starting to notice problems with her near vision. She loves her contact lenses and in fact wears them almost exclusively.
She’s a dream patient though and wears her glasses at home every morning and evening just to give her eyes a break. She’s terrified about the thought of needing progressive lenses because she doesn’t want to give up wearing contact lenses because she's very active.
Our examination did reveal early signs of presbyopia (age-related near vision loss), and she did, in fact, need reading glasses to see 20/20 vision up close. Her reading power was still small, only +1.00 reading glasses, but she was still devastated.
We discussed her options which included:
Giving up her contact lenses and just wearing eyeglasses (that didn’t go over well),
Reading glasses over top of her contact lenses (she didn’t love this idea but was pleased to know it was an option and that she wasn't going to hurt her eyes),
Multi-focal contact lenses (she didn’t want to give up her current lenses, but didn't even know that bifocal/multi-focal contact lenses were an option)
Monovision.
She loved her current contact lenses and was having no problems with distance acuity, dryness or comfort so we elected to try monovision. It was the easiest first option to try and if it didn't work we still had other options. She showed right eye dominance using the Dolman Test and lens fogging allowed us to add ¾ of her reading power (+0.75 diopters) before it started to affect her distance acuity. As she was early into the presbyopia process, this amount was more than adequate to return her functional vision back to normal. We refit her with new monovision contact lenses, and she was thrilled to have both her distance and near vision back and not have to give up wearing her current contact lenses.
So what are the limitations of monovision?
Monovision is not the greatest thing since sliced bread. It does have it's limitations, and not everyone is a considered a good candidate for monovision contact lenses, monovision laser eye surgery or even monovision cataract surgery.
The point of the article is to highlight one option your eye doctor may explore with you in trying to achieve your visual goals. For some patients, we might use a subtle monovision just in their contact lenses (like Jenna) to help with sports or make it slightly easier to read on the computer screen at work.
Monovision vision may result in the loss of perfect depth perception though. By uncoupling the two eyes and forcing them to work somewhat independently, you are reducing that binocular stimulus. Going to a 3D movie is less fun, judging distances may be slightly harder, threading a needle may take a couple of extra tries and night driving glare can increase. Higher reading powers require more ocular disparity which can start to affect distance acuity adversely. You doctor must check your distance vision to ensure that you still meet legal driving requirements.
As such, most patients that choose monovision still need driving and reading glasses to maximize their binocularity and vision in these critical activities. But they know that monovision is more about lifestyle and not always needing eyeglasses to get by.
