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Abstract
With no prior information of either spherical or cylindrical components, objective (evoked potential) refraction can be performed up to 100 times faster than by comparable averaging procedures. The new procedure is to directly obtain the required graph of evoked potential (EP) amplitude vs. some stimulus parameter rather than to make separate measurements of each point on the graph. Fourier-analyzed EP's provide the clinician with an immediate indication of the result of altering refractive correction, so that this EP procedure is analogous to conventional subjective refraction. While the subject views the pattern through a rotating stenopeic slit, a 10-second plot of EP amplitude vs. slit angle can indicate the axes of astigmatism to within 10°. The slit is then set parallel first to one axis of astigmatism and is then turned through 90° while the subject views the pattern through a lens whose power is continuously oscillated. Each of these two graphs of EP ajnplitude vs. lens power can be obtained in 10 to 20 seconds; these data give a complete description of the required refractive correction to within 0.5 D. The use of checks rather than stripes gives a faster procedure.