Here's an excuse that's sure to become popular in classrooms throughout the city: "I didn't do my homework because I don't want to go blind."

Pediatric ophthalmologist Mark Steele told the Post that elementary students at the city's most-esteemed private schools are at a greater risk of myopia than their public school peers. "There's a correlation between private schools and nearsightedness," said Dr. Steele. "The kids in private school do more reading, and that puts them at increased risk. Youngsters doing a lot of reading tend to become nearsighted. The bulk of students get it between the ages of nine and 14."

The difference in vision can be so pronounced that Dr. Steel said he often diagnoses students from first to sixth grades as "private school" or "selective magnet school." He added: "These schools screen for intelligent kids, who probably would have read more no matter what." While parents and tutors say that assigned reading and homework is excessive at some of the city's most competitive schools (allegedly up to four hours per night at Riverdale Country School in the Bronx), Victoria Goldman — author of "The Manhattan Guide to Private Schools" — says nearsightedness can be blamed on other after-school activities. "These kids have BlackBerries and [iPods] and computer games and video games," said Goldman. "The eye strain is from all of those things. It isn't just the homework."