This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Special Senses, Subject name: Physiology
[{'content': 'For detection of light, minimum amount of light (quanta) reaching retina should be: \nSelect and explain. \nA. 1, B. 6-May, C. 54, D. More than 500', 'role': 'user'}, {'content': 'Answer: B \nExplanation: "Visual threshold" is the minimum amount of light detected by retina. Threshold for a single rod is 1 quantum of light. To distinguish light from this discharge, at least 5-6 rods should be excited synchronously. Hence, about 5-6 quanta of light is the \'visual threshold\' for retina. For 5-6 rods to be excited, about 100 quanta of light should reach the eye (cornea). Many of the quanta are absorbed, reflected, or refracted in the intervening ocular media.', 'role': 'assistant'}]