Some factors producing individual differences in dark adaptation
Since Aubert’s (1864) original work, many attempts have been made to describe or to classify individual variations in dark adaptation. Piper (1903) and later Wöllflin (1905) distinguished two main classes, one showing a rapid initial rise in sensitivity, with a high final maximum, and the other a slower increase, with a lower final value. Lohmann (1907) showed that dark-adaptation curves obtained with the homatropinized and eseriniced eye were very different and suggested that pupil diameter was the underlying factor. Best (1917) found two main types, one with a rapid initial increase in sensitivity, and the others with a slower increase, both reaching approximately the same final values. He nevertheless states that the final thresholds of normal observers differ by as much as12:1 Cobb (1919) found threshold differences of 7·4 : 1 after 30 min. In the dark. Flugel (1921) also mentions two classes characterized by unusually slow, or unusually rapid, initial rises in sensitivity. Wynn Jones (1921) found considerable differences in observers (25 :1 after 16 min. In the dark), dividing them into those whose dark adaption was ( a ) poor at the end beginning and at the end, ( b ) poor at the beginning and good at the end, ( c ) good at the beginning and good at the end, ( d ) good at the beginning and poor at the end. Matthey (1932) also grouped individuals into the same four types. Gross deficiency in vitamin A undoubtedly produces marked differences in dark adaption (see for instance Tansley 1939). Convincing data on this subject have been advanced by Fridericia and Holm (1924), Tansley (1931) and by Guilbert and Hart (1935), in animals. Recently Edumund and Clemmesen (1936) and others have claimed that a small deficiency even in apparently healthy individuals will produce some slowing in the logical factor is generally held to be responsible for individual variations in dark adaption, nor is any real division into types recognized.