Bill Cosby's attorneys say in a new court filing that he is "legally blind" and has registered with a state commission for the blind.

The comedian's eyesight has become an issue in his criminal sexual abuse case because his lawyers contend he won't be able to recognize his accusers.

"No 79-year-old blind man could possibly defend himself against a claim that he sexually assaulted someone he supposedly met once, half a century ago," they wrote in a court document filed Thursday in Pennsylvania.

In a footnote, the lawyers wrote that Cosby is "legally blind" and will provide a doctor's report to the court to prove it at a pretrial hearing that starts Tuesday. In Massachusetts, where Cosby registered for a certificate of blindness, legally blind means vision of 20/200 or less while wearing glasses.

Pennsylvania prosecutors say Cosby's vision doesn't mean he can't assist in his defense. He's charged with drugging and abusing Andrea Constand at his home in 2004, and prosecutors are seeking to put up to 13 other accusers on the witness stand to show a pattern of behavior. Cosby, who says the other women should not be allowed to testify, has denied breaking any laws.