1. http://www.nei.nih.gov/eyedata/pdf/VPUS.pdf
2. http://www.nei.nih/eyedata/pbd_tables.asp
3. Surveillance for sensory impairment, activity limitation, and health-related quality of life among older adults. Surveillance for selected public health indicators affecting older adultsâUnited States, 1993â97;Campbell;MMWR CDC Surveill Summ,1999
4. Transmission of light through cataracts;Sadun;Am J Ophthalmol,1990