<prompt> Which of the following represent the average distance of the fovea from the temporal margin of the optic disc?1 disc diameter2 disc diameter3 disc diameter4 disc diameter  <response>: Fovea centralis is the central depressed pa of the macula. It is situated about 2 disc diameters 3mm away from the temporal margin of the disc. It is about 1.5mm in diameter and is the most sensitive pa of the retina. It is tightly packed with cones and there are no rods. Ref: Comprehensive Ophthalmology By A K Khurana, 4th Edition, Pages 249, 251. 