In an unusually candid interview yesterday, the greatest late night talk show host of our time - David Letterman - says he may retire after his current contract at CBS ends two years from now. Letterman, speaking to "CBS This Morning" co-anchor Charlie Rose, also said he has taken medications to treat depression beginning in 2003, after he was forced to take a brief leave from "Late Show" because of a painful bout with shingles. Yesterday’s pre-taped interview was tied to next Wednesday's telecast of the 35th Annual Kennedy Centers Honors - Letterman is one of the honorees - and, incidentally, scoops Oprah Winfrey's Letterman interview on OWN scheduled for early January. Show business's most famous recluse, Letterman rarely speaks in public - and almost never about his private life - which makes the Rose encounter so unusual. He said of his 30-plus-year career that "I wish I hadn't been so gosh darn single minded because when your focus is that tight, you miss a lot of what's going on around you." Depression, he said, set in after he ended a regimen of drugs to treat the shingles that had caused inflammation around his eyes, and "that's when I said to [his doctor, Louis Aronne] I'll try anything just to get rid of this..." Asked about leaving “Late Show,” he said that he was aware his idol and mentor Johnny Carson had also missed leaving "The Tonight Show" in 1992 after his legendary 30-year run. "And I know I would miss it," he said. "But I'd find other things to do."