Cod liver oil and lutein provide nutrients to the eyes from different perspectives, so they are both helpful in keeping the eyes healthy. Cod liver oil is mainly extracted from the livers of marine fish and is rich in vitamin A and vitamin D. Vitamin A, also known as retinol, is a component of the photoreceptors in the cells that make up the optic cones, which is important for maintaining dark vision, and a deficiency of retinol can lead to night blindness and even serious illnesses such as corneal perforation. Lutein is a carotenoid found in fruits and vegetables, and is beneficial to the eyes by promoting the regeneration of violet red matter in retinal cells, preventing oxidation of the macula, and relieving visual fatigue. Cod liver oil and lutein nourish our eyes from different perspectives, but it is not difficult to obtain both vitamin A and lutein in cod liver oil from natural foods. If you eat a well-balanced diet, the average person will not be deficient in vitamin A and lutein. Therefore, it is still recommended to use cod liver oil and lutein under the supervision of a doctor.