The goal of this clinical trial is to analyze the protective effects of oral ascorbic acid on the corneal endothelial layer undergoing oxidative stress due to phacoemulsification in patients with hard cataracts. The main questions it aims to answer are: 1. Will oral vitamin C administration provide better protection to the corneal endothelium in hard cataract phacoemulsification by comparing preoperative and postoperative administration, preoperative only, and no administration? 2. How does oxidative stress (MDA levels) in the aqueous humour increase after oral vitamin C administration compared to no administration? 3. Will there any changes in MDA levels in the aqueous humour and blood after oral vitamin C administration compared to no administration? 4. Does MDA levels in the aqueous humour correlate with MDA levels in the blood? Researchers will compare vitamin C to a placebo to see if vitamin C as an antioxidant works in preventing corneal endothelial damage due to phacoemulsification. Participants will: * Take 500 mg of oral vitamin C or placebo three times a day for seven days prior to phacoemulsification * Undergo phacoemulsification * Take vitamin C or placebo three times a day for 28 days after phacoemulsification * Visit the ophthalmology clinic 1, 7, 28, and 42 days post-operative for checkups * Keep a logbook to record the drug they take and to write symptoms of possible side effect of the drug