Simply put, the refraction is the part of the eye exam in which we determine your eyeglass prescription. AKA the better-one-or-two part. Traditionally, we actually perform two refractions . . . objective and subjective.
The objective refraction can be done manually with a hand-held instrument or by machine . . . automated is what we like to call that . . . performed by a technician during pre-testing. Either way, you don’t have to say a word as we measure what it takes to focus distant light rays onto the retina – the length of your eyeball(s). Why is this done? One, it gives the doctor a starting point – a ballpark measurement – from which to perform the subjective refraction. Two, assessing the light reflecting off your retina is one way to check for cataracts; and three . . . , well this is now sounding like a boring board exam review, so two reasons are all you need. Trust me!
The subjective refraction is where you get involved, and it’s really cool, because what the doctor is measuring is NOT your eyeball but actually how your BRAIN “sees” the chart . . . ewwwwwww . . . is right. This is the which-one-is-better-one-or-two part that some people either love or hate. Love because dang that chart is clear! Hate because dang I think I failed! And it is true . . . you could zig, when you should have zagged. But remember, it’s you and the eye doctor that are doing this together. SO, an astute eye doctor will take the time to double or even triple-check that you’re not straying into refraction no-man’s land, and keep you on the straight and narrow towards your best spectacle prescription.
Ask any eye doctor, and they’ll tell you that performing a refraction, determining your visual correction, is an art form. Heck, one of the must reads of any optometry student or ophthalmology resident is The Fine Art of Prescribing Eyeglasses Without Making a Spectacle of Yourself by Milder and Rubin. It’s been around forever. Check out the cover, you’ll see what I mean.