<prompt> The average distance of the fovea from the temporal margin of the optic disc is -1 disc diameter2 disc diameter3 disc diameter4 disc diameter  <response>: 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 