How are babies fitted with glasses?

July 12, 2015 12:21 PM

After watching this precious video, I wondered, how are babies fitted with glasses? Optometrist visits in my experience have been highly interactive: tell me what line you can read, what looks better this or this, etc. How do they do this for babies who don't have language skills yet? How do they know they have the right prescription?
posted by cecic to Health & Fitness (15 answers total)

i wondered this too. i know that the (a?) standard way of measuring the interest of a baby is the length of an attentive gaze - they stare at something for longer if it's "interesting". this is where reports of babies "doing maths" come from - they take three sweeties (or whatever), cover them up, possibly remove one, and then uncover them. the baby pays attention for longer if a sweetie was removed. hence the argument they can "count" (in some limited sense).

so my best guess is that they use something similar with different lenses. but it sounds hopelessly inefficient.

and a little googling suggests that's basically it - using cards with squares on. the other method mentioned there is that they can try to measure the curvature of the eye directly, and so determine what the shape (and so strength) of the lens is.
posted by andrewcooke at 12:30 PM on July 12, 2015 [3 favorites]

Best answer: When I go in, they sometimes first use an instrument to estimate my prescription, and then they do the interactive stuff to tweak it and get it perfect. It may be that they use the same instrument to measure the shape of the baby's eyeball, and they just can't do the tweaking-to-get-it-perfect until the kid is old enough to respond to language.
posted by ArbitraryAndCapricious at 12:31 PM on July 12, 2015 [7 favorites]

Best answer: I'm pretty sure that what they do is dilate the baby's pupils extremely widely, then shine a "picture" (I think a plus sign? but I don't know why I think that) through the baby's pupil and onto the retina, then swap out lenses until the picture comes into focus on the retina. I have a friend who had an extremely premature baby, and that's how she described the process to me when her daughter got glasses at 10 months old.
posted by KathrynT at 1:01 PM on July 12, 2015 [8 favorites]

KathrynT's description of how they do the measuring is better than mine (the "other" way in my answer). i wish you could edit or delete posts here.
posted by andrewcooke at 1:12 PM on July 12, 2015

I used to work on a research study of babies and toddlers where we measured visual acuity. So, not an optometrist, but until one comes along to tell you how they do it - for clinical research purposes, we used either the Teller cards linked above or something very similar. It's been a few years so I don't remember if they looked exactly like the ones pictured there.

Optometrists probably have something fancier, but as a general rule, with a little training working with kids, and some patience, we could get a pretty decent starter measurement with the cards.
posted by Stacey at 1:13 PM on July 12, 2015 [1 favorite]

Best answer: The last time I had an eye exam they scanned my eyes and got all the info they needed. They did the "better 1" thing once as more of a formality. The machine was right.
posted by O9scar at 2:31 PM on July 12, 2015 [1 favorite]

Best answer: Refraction is not the same as visual acuity (screening using charts and fixed distances). Using a scope and lenses, a non-verbal patient can be refracted to determine lens prescription. If a more precise reading is needed, the eyes can be dilated or cyclopleged. There are other observations and tests pediatric optometrists/ophthalmologists perform to determine issues such as developmentally appropriate eye teaming or eye turn which may lead to corrective lenses as well. Her little frames are a one piece moulded plastic/zyl that are comfortable and safe. A professional can do a refraction with the lenses on to check correction, but her eyes relaxing and finding focus is a pretty good indication too.
posted by lawliet at 3:10 PM on July 12, 2015 [2 favorites]

An interesting point about the scanning machines optometrists use is that they are pretty much dead-on for accuracy (as O9scar mentions above).

But vision is a subjective thing, which is why they still go through the "bette one, better two" process. People tend to tweak their preference for what is familiar to them, usually biased towards their previous vision situation.

This based on one of my research studies with clients, optometrists, and ophthalmologist in both the US and EU.
posted by qwip at 5:31 PM on July 12, 2015

Interesting, qwip! Does that mean that I'm better off just going with the original reading and figuring that my eyes will adjust?
posted by ArbitraryAndCapricious at 6:03 PM on July 12, 2015

It means people try to guess what is right and instead of deciphering precise focus they often use perception to try to make their focus precise. An infant does not have these biases but it is still possible to correct vision or vision issues to help them navigate perception.
posted by lawliet at 6:35 PM on July 12, 2015

Dumb question here: how do they know the image on the retina is in focus? I mean, they have to look through the lens, right? Which is not focusing properly. So their view of the retina will be out of focus, no?
posted by mpark at 11:31 PM on July 12, 2015

@mpark - i guess this is what that thing on a stick with a light that they (opticians) peer through when they stare into your eye does - presumably it's an extra lens so that they can focus on the back of the eye. (as far as i know - i was a physicist way back in the day - there's no real reason why that wouldn't work. basically you just need a lens that's the "opposite" of the eye's lens). using that i guess they see projected brightness and shadows on the back of the eye, much like a camera obscura.
posted by andrewcooke at 5:48 AM on July 13, 2015

Thanks andrewcooke. That seems to be begging the question though: sure you can have the "opposite" lens to the eye's, if you know what the eye's lens is--and if you know that, why bother with the retina projection?

Anyway, this has fallen way down the list of asks, so I hardly expect anyone to read this, much less reply.
posted by mpark at 3:11 PM on July 13, 2015

Here's an article on automated refraction techniques that shows some optical diagrams with discussion.
posted by doctord at 9:55 AM on July 14, 2015

@mpark - i guess they are very similar (and i vaguely remember opticians having to twiddle a dial to get the thing to work, so i guess they were focussing something). the main difference would be that when an optician uses the stick thing they are adjusting the focus until they can see the back of the eye correctly, while a machine that is measuring your prescription would need to be be a little bit cleverer and do the equivalent for a distant optician ("at infinity"), and find additional "non-spherical" parameters (to get a complete prescription).

in practice, looking at the link from doctord, it looks like (although i am not completely sure) that's how early machines did work (the section "image quality analysis"). but later machines have more sophisticated ways of knowing when thing are "in focus".
posted by andrewcooke at 10:24 AM on July 14, 2015