Lipids account for approximately 3% of the wet weight of the RPE; about half are phospholipids. Phosphatidylcholine and phosphatidylethanolamine make up more than 80% of the total phospholipid content. In general, levels of saturated fatty acids are higher in the RPE than in the adjacent outer segments. The saturated fatty acids palmitic acid and stearic acid are used for retinol esterification and for energy metabolism by the RPE mitochondria. The level of polyunsaturated fatty acids, such as docosahexaenoic acid (22:6, n–3), is much lower in the RPE than in the outer segments, although the level of arachidonic acid is relatively high. A number of studies have suggested that the retina may be spared the effects of essential fatty acid deficiency because the RPE efficiently sequesters fatty acids from the blood. The RPE actively conserves and efficiently reuses fatty acids, thus preventing their loss as waste products.
Excerpted from BCSC 2020-2021 series: Section 2 - Fundamentals and Principles of Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.