Cataracts, the clouding of the lens, cause half of the world's blindness. Most cataracts are age-related and arise when crystallin proteins in the lens become oxidized and aggregate over time. Surgery is currently the only recognized treatment to effectively cure cataracts, but this method is expensive and invasive. Therefore, we formulated a natural and non-invasive alternative. In the eye, a natural antioxidant glutathione (GSH)—produced by the enzyme glutathione reductase (GSR)—exists to combat oxidation, but GSH levels decrease with age. Studies have also suggested that another enzyme—25-hydroxylase (CH25H)—can convert cholesterol in the eye into 25-hydroxycholesterol (25HC), which reverses crystallin aggregation. We expressed and purified GSR and CH25H for the prevention and treatment of cataracts, respectively. To deliver these proteins through the cornea and into the lens, we engineered biodegradable chitosan nanoparticles, thus creating a natural and non-invasive alternative to surgery.