This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous, Subject name: Ophthalmology
[{'content': 'As per Young-Helmholtz theory colour revealing are of_____ types \nSelect and explain. \nA. 2, B. 3, C. 4, D. 5', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. b (3) (Ref. Parsons, Disease of Eye, 19th/131; Khurana, Ophthalmology, 3rd/250; Ganong, Physiology, 21/166)# Normal color vision is trichromatic, the basis of Young-Helmholtz theory of colour vision.YOUNG-HELMHOLTZ THEORY# Cones are photoreceptors tightly packed in fovea centralis where there are no rods and other layers of retina very thin.# The central part of fovea consists of cones and their nuclei largely and all other retinal layers are absent.# The appreciation of colors is function of cones and occurs in photopic vision.# Sensation of any colour is determined by the relative frequency of impulses for cone system.# Normal color vision is trichromatic, the basis of Young-Helmholtz theory of colour vision.# Other theories of color vision are- Hering or Hurvich and James Law (trichromatic signal from cones fed into subsequent neural stage and exhibit spectral opponent and spectral non-opponent property), and- Edwin-Land wavelength theory.', 'role': 'assistant'}]