Disclosed is the use of a synthetic retinal derivative in the manufacture of a medicament for improving visual function in a subject having a deficiency in endogenously produced 11-cis retinal, wherein the medicament is administered to the subject according to the following dosing schedule: (a) administering a first therapeutic dose of a synthetic retinal derivative to a subject in need thereof, wherein the first therapeutic dose is administered as a divided dose over a period of from about 2 to about 7 days (b) providing a resting period of from about 7 to about 28 days and (c) administering a second therapeutic dose of the synthetic retinal derivative to said subject following the end of the resting period, wherein said subject demonstrates a decline in visual function prior to administration of the second therapeutic dose, and wherein the synthetic retinal derivative is a 9-cis-retinyl ester or a 11-cis-retinyl ester which is selected respectively from 9-cis-retinyl acetate or 9-cis-retinyl succinate or from 11-cis-retinyl acetate, 11-cis-retinyl succinate, 11-cis-retinyl citrate, 11-cis-retinyl ketoglutarate, 11-cis-retinyl fumarate, 11-cis-retinyl malate or 11-cis-retinyl oxaloacetate, or the synthetic retinal derivative may be selected from 9-cis retinal, 11-cis-retinal, 9-cis-retinol, or 11-cis-retinol.
