Step 1: Understanding the Kriyas.
- (A) Sheetali: Sheetali is a breathing technique that cools the body but does not specifically improve eyesight.
- (B) Neti: Neti is a nasal cleansing technique, which clears the sinuses, but does not directly affect eyesight.
- (C) Kapalbhati: Kapalbhati is a breathing exercise that benefits the respiratory system but is not primarily focused on improving eyesight.
- (D) Trataka: Trataka is a meditation technique that involves focusing on a single point, typically a flame, to improve concentration and strengthen the visual mechanism. It is well-known for its benefits in improving eyesight and calming the mind.
Step 2: Conclusion.
Thus, the correct answer is (D) Trataka, as it specifically improves eyesight and tones up the visual mechanism.
Final Answer: (D) Trataka.