The average distance of the fovea from the temporal margin of the optic disc is -

Fovea centralis is the central depressed pa of the macula. It is about 1.5 mm in diameter and is the most sensitive pa of the retina. In its centre is a shining pit called foveola (0.35-mm diameter) which is situated about 2 disc diameters (3 mm) away from the temporal margin of the disc and about 1 mm below the horizontal meridian. Ref:comprehensive ophthalmology AK KHURANA page no :250