This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Lens, Subject name: Ophthalmology
In senile nuclear cataract, type of myopia seen is 
Select and explain. 
A. Curvature myopia, B. Index myopia, C. Axial myopia, D. Positional myopia
B: Index myopia
Answer: B: Index myopia 
Explanation: Index myopia results from an increase in the refractive index of the crystalline lens associated with nuclear sclerosisVisual deterioration due to senile cataract has some typical features. It is painless and gradually progressive in nature. Patients with central opacities (e.g., cupuliform cataract) have early loss of vision. These patients see better when the pupil is dilated due to dim light in the evening (day blindness). In patients with peripheral opacities (e.g. cuneiform cataract) visual loss is delayed and the vision is improved in bright light when the pupil is contracted. In patients with nuclear sclerosis, distant vision deteriorates due to progressive index myopia. Such patients may be able to read without presbyopic glasses. This improvement in near vision is referred to as 'second sight&;. As opacification progresses, vision steadily diminishes, until the only perception of light and accurate projection of rays remains in the stage of mature cataract.Ref: Khurana comprehensive ophthalmology 4th ed; Pg179