Retinax Five (also known as Retinax 5 or simply Retinax) was a 23rd century drug used to correct various visual impairments. Daniel Latham had trouble reading computer screens, even with his Retinax treatments. Because of that, he preferred to read and write with old-fashioned books. (TOS novel: The Case of the Colonist's Corpse) James T. Kirk was particularly sensitive to Retinax. Because of this sensitivity, which Kirk considered an "allergy," Leonard McCoy gave him a pair of eyeglasses for his 52nd birthday. (TOS movie & novelization: The Wrath of Khan; TOS novel: In the Name of Honor)