Monocular performance of functional amblyopes: another look at the scotoma hypothesis.

The traditional scotoma hypothesis for functional amblyopia is modified to state: whereas the central visual field of a normal visual system and that of an organic amblyope become increasingly scotomatous as light level is decreased from high to low photopic levels, the reverse is true for the central field of a functionally amblyopic visual system. An attempt is made to show how this hypothesis provides a unifying explanation for several seemingly different visual performances observed in functional amblyopes. The paper deals with (1) field inhomogeneities and threshold measures, and (2) threshold changes with light adaptation level. Implications of the modified scotoma hypothesis are discussed for (1) the neutral-density-filter test to distinguish functional from organic amblyopia, (2) the reduced CFF threshold for amblyopic eyes, (3) expectations of stereopsis for amblyopes, and (4) possible mechanisms for amblyopia.