This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Optics and refraction, Subject name: Ophthalmology
[{'content': 'Presbyopia occurs as a result of the following \nSelect and explain. \nA. Shoening of eye ball, B. Hardening of lens, C. Thinning of the lens, D. Lengthening of eye ball', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Presbyopia (eyesight of old age) is not an error of refraction but a condition of physiological insufficiency of accommodation leading to a progressive fall in near vision. The cause of presbyopia is believed to be due to thickening and loss of flexibility of the lens in the eye. Reference: AK khurana 7th edition', 'role': 'assistant'}]