It is useful to measure Snellen acuity under lighted and darkened examination conditions. While visual acuity testing in the ophthalmologist’s office is commonly performed in a darkened room, diminished Snellen acuity from a symptomatic cataract may sometimes be demonstrated only in a lighted room. Distance and near visual acuity must be tested and a careful refraction performed so that best-corrected visual acuity can be determined. In some patients, pinhole visual acuity is better than acuity obtained with refractive correction. Visual acuity may improve after pupillary dilation, especially in patients with PSCs.