American Academy of Ophthalmology (2007).
Refractive Errors and Refractive Surgery (Preferred Practice Pattern). San Francisco: American Academy of Ophthalmology. Also
U.S. Preventive Services Task Force (2009). Screening for Impaired Visual Acuity in Older Adults. Rockville, MD: Agency for Healthcare Research and Quality. Available online: http://www.uspreventiveservicestaskforce.org/uspstf/uspsviseld.htm.