600498 Disclosed is the use of a synthetic retinal derivative for the preparation of a medicament for the treatment or prevention of an impairment in rod-mediated dark adaptation after light exposure, an impairment in night vision, or an impairment in contrast sensitivity in a subject, wherein said medicament is for administration to said subject intermittently with a period between doses of less than once a month over a period of at least three months, wherein said synthetic retinal derivative is a 9-cis-retinyl ester of formula (l) or an 11-cis-retinyl ester of formula (II), wherein A in each formula is CH2OR and R forms said retinyl ester, and the ester substituent of said synthetic retinal derivative comprises a carboxylate radical of a C1-C10 monocarboxylic acid or a C2-C22 polycarboxylic acid.
