On left, the patient’s left eye has no cataract and all structures are visible. On right, retinal image from fundus camera confirms the presence of a cataract. (From Choi, Hjelmstad, Taibl, and Sayegh, SPIE Proc. 85671Y , 2013) Article by guest blogger Roger S. Reiss , SPIE Fellow and recipient of the 2000 SPIE President's Award. Reiss was the original Ad Hoc Chair of SPIE Optomechanical Working Group. He manages the LinkedIn Group “ Photonic Engineering and Photonic Instruments .” The human eye and its interface with the human brain fit the definition of an "instrument system." The human eye by itself is also an instrument by definition. After the invention of the microscope and the telescope, the human eye was the first and only detector for hundreds of years, only to be supplemented and in most cases supplanted by an electro-optical detector of various configurations. The evolution of the eye has been and still is a mystery. In National Geogr...