DiagnosticGame visual acuity can be measured by simply covering each eye while viewing the app. To screen for children with myopia or testing presbyopes, these Snap-On Lens/Occluder should be used. A child with myopia at 16 inches will read better without than with the +2.50 lens, however the result with the use of the +2.50 add reflects the subject's vision at 20 feet without glasses, it measures the degree of myopia. For the child with emmetropia or the hyperopia, the near vision with or without the +2.50 will be the same. The Snap-On Lens/Occluder attaches to included magnetic frames.