This is the inital part of the assessment of the refractive error and astimatism (if any). The objective measurement can be taken using an automated machine called an ‘autorefractor’ or manually using an instrument called a ‘retinoscope’.
Retinoscopy is a highy skilled task and requires good co-operation from the patient for the best results. This gives your optometrist an overall guide to the refractive error of your eyes.
If you already have glasses, then your old prescription can serve as a starting point from which the examination can be progressed. Your optometrist is best qualified to decide how he or she carries out your refraction.