First things first, what in the world is the eye doctor doing when they ask this annoying question?
The procedure itself is called refraction. If you jump back to your physics days, remember that refraction is the bending of light as it passes through different mediums (ie air to glass). It’s this property that we use with spectacles (or contacts) to make light focus directly on the retina, rather than in front, such as in near-sighted cases, or behind, as in far-sighted cases.
I hate that test… I never know what the right answer is!
This is something that I hear all the time when talking to friends, family, random strangers – almost everyone!
A lot of people put themselves under a lot of pressure during refraction, because they’re afraid that if they give the “wrong answer”, they’ll end up with crappy glasses.
But guess what?
There is no wrong answer! This is a completely subjective test, meaning it’s all about what you think looks best! As the doctor, I can’t see through your eyes to know which one looks better to you – only you do that. Yes, I can have an idea based on clinical experience, but at the end of the day, this is a part of the eye exam where you get to have a say.
And if they look the same?
Tell me! This is honestly an important description, and I’d rather you tell me that they look the same than trying to figure out which one may be a hair clearer.
Do the numbers matter?
I feel like there are two ways that this question could be taken, so to clarify: yes, the answer that you give me 100% determines the next lens that I show you.
But my choice of numbers? That’s completely arbitrary.
I personally really like just using one and two, which more commonly becomes “here’s the first lens, and here’s the second” – it seems simpler, and from my experience it works really well.
That said, there’s no problem with the doctors that get all the way up to 10 with their numbers. Or always keep the same number with the same lens. Or use letters.
None of that really matters.
*As a fun aside, when I told my older brother about this sometime during optometry school, he begged me to do a refraction using chicken and egg instead of one and two. I’ve been tempted on mulitple occasions, but so far haven’t pulled the trigger on trying this technique 🙂
How do you know where to begin?
Getting the numbers for a starting point for refraction depends on a number of factors:
- If you’re a new or established patient
- If you’re already wearing glasses
- What technology the doctor has available
- Your unique needs as a patient
In the case of an established patient, or a new patient who’s already wearing glasses, it’s pretty easy to either pull up the prescription for your last visit, or read the prescription in your current glasses, and use those numbers as a starting point.
With completely new patients, especially those who have never worn glasses, the options depend more on what technology the doc has available. Most practices at this point have a device called an auto-refractor – which is exactly what it sounds like: a machine that automatically determines an estimate of the prescription of your eyes.
If this isn’t available or doesn’t seem to be providing reliable results, the doctor may also perform retinoscopy, where they shine a light towards your eye, which then creates a reflex that will move in response to movement of the light. As lenses are added, the reflex changes, until there is very little movement, corresponding with the approximate power of your glasses prescription!
Retinoscopy is actually one of my favorite techniques, and is my preferred method of determining a preliminary glasses prescription, as it doesn’t require a machine, can be done literally anywhere, and shows me valuable information about the state of your eye and focusing system! For these reasons, it is perfectly suited to my preferred patient populations – children, special needs, and those who have suffered brain injuries.
Wait.. so if there are machines, what’s the point of refraction at all?!
The short answer is that machines aren’t perfect. Yes, they can provide a good estimate, but that’s all it is – an estimate! When we ask “which is better, one or two”, that estimate is refined to specifically fit your preferences.
Because you are much more than just a set of numbers.
If you have any comments or questions, please contact me – I’d love to hear from you! If you enjoyed this post, please subscribe, or like my page on Facebook!