Explanation:

• Cataract is a major form of blindness that occurs when the structure of crystallin proteins that make up the lens in human eyes deteriorates.
• Such deterioration causes damaged or disorganised proteins to aggregate and form a milky blue or brown layer, which ultimately affects lens transparency.
• As with aging and under various conditions, the lens protein crystallin aggregates to form opaque structures in the eye lens, which impairs vision and causes cataract.

Hence option 2nd is correct.