Coz they still need us to confirm if we can read or not with different lenses.
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They have the letters calibrated for distance and size in a way that 20-20 vision can reliably read ‘this’ line. So they have you read the best line you can and that corresponds to a certain level of vision and then they use a series of lenses to find the prescription that will get you back to 20-20, or what is considered normal.
Your eye’s health is examined with an ophthalmoscope and different types of light for viewing the retina and fundus.
This is a separate instrument than the photoropter, where you are asked which of the lens choices improves the test chart, and there is no “looking in your eyes”, only operating the machine.
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