confusedinthegroove

confusedinthegroove t1_j20k9l5 wrote

Reply to ELI5: When scientists say babies have blurred vision, how do they know? by DreadMCYT

I’m not 100% sure what you’re asking but I’ll try.

If you are asking in gereral; Most babies can focus quite well (like the lens in a camera) on an object but they see it in low resolution. Like they’re recording in 144p instead of HD. Their brains aren’t well developed but the resolution improves as they develop.

They can measure this resolution in a variety of ways. One way is an optokenetic drum, once the baby is a few months old. The eyes will follow a stripey pattern travelling in one direction. If the baby can’t see or resolve the pattern their eyes will not follow it. You can adjust the pattern (bigger or smaller stripes) until the baby can/can’t follow it. With toddlers you can show them two cards, one with a faint picture and one without a picture. Watch where their eyes go and go to the next set of cards.

If you asking how we know a specific baby can’t see, we measure the focusing ability of the babies eye with a special light and lenses. And how well the baby can see with and without glasses with the methods above. If the baby falls significantly outside normal values, we give the glasses and/or eyepatches. If they are slightly outside normal values we might re-examine them in a few months.

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confusedinthegroove t1_j20ede6 wrote

Reply to comment by EdgarsChainsaw in ELI5: When scientists say babies have blurred vision, how do they know? by DreadMCYT

An MRI would never be used to measure focusing properties of the eye in a clinical setting. It would be a very expensive, time consuming and “invasive” (probably not the right word) way to measure the length of the eye but I doubt it could measure the focusing power of the cornea or lens.

Autorefraction or retinoscopy would measure the focusing power of the whole eye. You can derive the power of the lens from biometry (measures the length of the eye and focusing power of the cornea).

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