We review Antoni van Leeuwenhoek's (1632 - 1723) microscopic studies of comparative ocular anatomy in humans, mammals, birds, and fish. His contributions in anatomical microscopy to ocular biology has been overshadowed by his prolific work and first observations of protists and bacteria, spermatozoa, red blood cells, and dental plaque. Leeuwenhoek's Delftian optical and artisanal heritage more than compensated for any lack of formal scientific training and, in keeping with his Royal Society ethos, shone light onto the "fabric of the eye" in order to better understand its function, which he had extended with his microscopes. He has provided the earliest known microscopic descriptions of the tear film, eyelids, cornea, aqueous, crystalline lens, vitreous, retina, optic nerve, and photoreceptor--as well as the first descriptions of cataract, vitreous floaters, and corneal pathology. His description of the aquatic mammal Cetacean eye foreshadowed an understanding of the optical complexities of aerial and submarine vision of whales. His observations challenged classical teaching at that time, particularly in relation to the optic nerve.