How are refractive errors detected and measured?

Eye exam: We use an instrument called a phoropter which contains many lenses and can generate many potential pairs of glasses prescriptions. Sometimes the eyes need drops to get a good check for glasses. An ophthalmologist can help you out.

Autorefractors: Retinoscopy, trial frame refractions, phoropter refractions, basically an eye exam at an optometrist or ophthalmologist office, maybe on an iphone in the future.

By eye doctor: An eye doctor will use a phoropter to rapidly change lenses in front of your eyes to determine your refractive error.