When the eyes are exposed to the environment, they are easily affected by strong light stimulation and harmful substances. At the same time, prolonged use of the eyes or incorrect eye habits can cause visual fatigue, which mainly manifests as eye dryness, soreness, blurred vision, and various discomforts. The main reason for this is a decline in the function of the eye, especially the cornea and retina on the surface of the eye, which have the greatest impact on the normal function of the eye. Research has found that supplementation with appropriate foods or nutrients can effectively strengthen the eye against external and internal stimuli, thereby alleviating or avoiding visual fatigue. Among these, supplementation with polyunsaturated fatty acids has been found to be effective at protecting eye health and relieving visual fatigue. This article summarizes the sources of polyunsaturated fatty acids (including the main dietary sources and internal synthesis), the mechanisms of digestion and absorption of polyunsaturated fatty acids in the body and the safety of polyunsaturated fatty acid applications. It also reviews the mechanism of action of polyunsaturated fatty acids in aiding the relief of visual fatigue based on the mechanism of impaired function or structure of the ocular surface and fundus in the hope of providing some reference and insight into the development and application of polyunsaturated fatty acids in functional foods for the relief of visual fatigue.