This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous System, Subject name: Physiology
True about Fovea is 
Select and explain. 
A. Contains only rods, B. Contains only cones, C. Situated above optic disc, D. Contains both rodes & cons
B: Contains only cones
Answer: B: Contains only cones 
Explanation: Ans: b (Contains only cones)Ref: Ganong, 21rd edi., Pg. 152Fovea contains only cones. Cones play a very important role in color vision and rods in nightvision (dim light) Cones are the visual receptors which imparts to the eye, the ability for color visionThere are 3 types of cone pigments: -Cyanolabe -Erythrolabe -Chlorolabe The other visual receptor -rods is mainly for night vision.The pigment present in rods is rhodopsin.Dark adaptationIt is the adjustment of visual mechanism from bright light vision to dim light vision (i.e. switching from cone vision to rod vision)Visual areas in brainPrimary visual cortex area - 17Visual association area - 18,19Frontal eye field - 8Note: Lateral geniculate body is concerned with vision.Medial geniculate body is concerned with hearing.(Remember- L for light and M for music)