How do optometrists determine what strength prescription a toddler needs with such limited communication skills?
In: 7
For most people who are just near or far sighted, it’s just an issue of the shape of your eye, and the lens not being able to focus the light exactly onto the retina. For this, you can take measurements and they can get fairly close to required prescription. For those who use corrective lenses, you’re probably familiar with the machine that shows either a barn or balloons or something fairly simple, and it goes in and out of focus, usually ending in focus. This machine can take some measurements and get pretty darn close to your required Rx. You’ll notice that when you later go into the exam room and the doctor starts the “which is better, 1 or 2” part of the exam to get your exact measurements, the starting point isn’t just some random setting, it’s fairly close, say about within 95% of your actual needed correction. They got to this point with those prior measurements.
For a young child who isn’t reading yet, getting 95% of the way there will be such a big improvement that the 5% difference won’t be significant.
When I was really young I remember they used to have a machine and you looked into it and everything was blurry and then all of a sudden a desert scene with a road and a cactus would come into focus and then go blurry again. This would spit out your approximate prescription. You would then go see the doctor and they would refine everything.
The trick is that in most cases you can estimate the prescription fairly decently by looking into the eye with an adjustable lens and illumination. Your eye sees things sharp when the optical system in it can focus light onto your retina accurately. However, it is two-way: your retina can only be *seen* sharply from the front if the focus is good. You can [shine a light into the patient’s eye through lenses and observe the reflection from inside the eyeball](https://www.youtube.com/watch?v=kAreDffuVCQ) to check if the lens you are trying causes the retina to be illuminated just right. The [autorefractor](https://en.wikipedia.org/wiki/Autorefractor) is a more modern machine that performs this measurement automatically and more accurately than using the manual method – it basically pans through focus settings while you try to look at an image shown to you until it finds a correction that lets its internal camera see certain stuff inside your eye in sharp contrast. This is the machine /u/Michelledelhuman is talking about.
Others have made good explanations but you’ve just reminded me of using Cardiff acuity cards in a previous A&E job.
They let you know if a young child was managing to see and roughly how well if we had concerns (part of neurology exam). They were aimed at about 12-30 months.
It’s a set of A4 grey cards with simple line drawings in white on them (house, duck etc). The white lines on the pictures got progressively thinner of the cards so it got more and more difficult to see gi at the grey. You sat child on parents lap and you sat either 50cm or 1m away with the cards stacked in order and go through them relatively quickly while watching the kids eyes. They’d flick up and down depending on if the picture was at the top or bottom of the card. Really effective in a calm child and always made me smile doing it since I though it was such a clever test, and the kids usually smiled at the pictures. Thanks for the memory
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