Porterfield and Wells on the motions of our eyes

William Porterfield (ca 1969-1771) and William Charles Wells (1757-1817) conducted experimental investigations on eye movements related to accommodation, binocular vision, and vertigo. Porterfield gave a correct interpretation of Scheiner's experiment and invented an optometer to measure the near and far points of distinct vision. He also demonstrated the involvement of the crystalline lens in accommodation by examining vision in an aphakic person. Wells devised an alternative means of measuring the limits of vision and noted his own deterioration of sight with age; he studied the effects of belladonna on pupil size and accommodation. Their analyses of binocular visual direction contrasted Porterfield's view that perceived location was innately determined with Well's argument that visual direction was innate whereas visual distance was learned. Both Porterfield and Wells investigated the involvement of eye movements in binocular vision and in postrotary visual motion. Porterfield maintained that the eyes did not move following body rotation, whereas Wells, using an afterimage as stabilised retinal image, described the characteristics of postrotary nystagmus and their dependence on head orientation. Despite the neglect of Well's work, he should be considered as laying the foundations for the study of vestibular-visual interaction, even though the function of the vestibular system was not known at that time.