This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Ophthalmology
Macula lutea of the retina lies from the optic disc at a distance of: 
Select and explain. 
A. 1 mm, B. 2 mm, C. 3 mm, D. 4 mm
C: 3 mm
Answer: C: 3 mm 
Explanation: The macula lutea is an area of the retina approximately 5.5 mm in diameter that is rich in cones, situated about 2 disc diameters (DD) temporal to the optic disc (1 DD= 1.5 mm). That is totally 3mm. The central 1.5 mm of the macula is termed the fovea, which has a small central depression approximately 0.35 mm in diameter called the foveola. The vision is most acute at the foveola, where only cones are found; each cone directly relays to a single ganglion cell. Ref: Parsons' Diseases of the Eye By Ramanjit Sihota & Radhika Tandon, 21st edition, Page 302.