AIM: To assess foveal cone photoreceptor function in patients with unexplained loss of central visual acuity. METHODS: Testing of foveal cone photoreceptor function was performed using scanning laser densitometry, colour matching (Rayleigh equation), and pattern electroretinography (ERG). Standard tests included full field ERG, electrooculography, visual evoked potentials, static perimetry, and fluorescein angiography. RESULTS: Decreased foveal cone photopigment density and abnormal pattern ERG were found in three patients. Results of colour matching were not unequivocal. CONCLUSION: Testing of foveal cone photoreceptor function using scanning laser densitometry may determine the location of pathological changes in certain patients with unexplained visual loss.