The degree of adjustment the patent uses on the handheld optical device to accomplish these tasks becomes a measure of visual acuity which can then be translated into an eyeglass prescription.The binocular auto-refractor measures sphere, cylinder, axis and pupillary distance.
The 6/6 terminology is more commonly used in Europe and Australia, and represents the distance in metres.
The eye care professional will change lenses and other settings while asking the patient for feedback on which set of lenses give the best vision.
Researchers at the MIT Media Laboratory have proposed an eyepiece and software for use with a smartphone as a cheaper alternative to traditional subjective refraction equipment.
The system is called NETRA ("near-eye tool for refractive assessment").
A patent was filed for the system in 2010, and the primary audience for the device was projected to be the developing world where access to eye care professionals is limited.