Coz they still need us to confirm if we can read or not with different lenses.
In: 3
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.
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.