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Editors Selection IGR 22-3
Basic Research: Omega-3 depletion and ERG
Comment by Vittorio Porciatti on:
21761 Dietary omega-3 fatty acids and ganglion cell function, Nguyen CT; Vingrys AJ; Bui BV, Investigative Ophthalmology and Visual Science, 2008; 49: 3586-3594
In recent years, the use of nutriceuticals, including omega-3 supplements, has become a billion-dollar industry, and effects have been increasingly debated. The role of polyunsaturated fatty acids (PUFAs), in particular, has been the object of attention since the Western diet is relatively deficient in omega-3 PUFAs compared with omega- 6 PUFAs. Nguyen et al. (1197) from the Department of Optometry and Vision Science of University of Melbourne, Australia, studied the effects of omega-3 depletion on the ERG using a rat model. In their protocol, rats were given either an omega-3-sufficient diet (including flaxseed, safflower and tuna oils) or an omega-3-deficient diet (including safflower only). Treatment started in rat dams five weeks pre-conception and both diets were continued in pups 21 days old through 20 weeks of adult age. This deficient dietary protocol is known to yield an extreme omega-3-deficient depletion. The authors undertook a thorough ERG analysis, which included components believed to originate in the outer retina (a-wave, PIII), middle retina (b-wave, PII) and inner retina (positive Scotopic Threshold Response, pSTR, and negative Scotopic Threshold Response, nSTR). In omega-3-deficient rats, compared to omega-3-sufficient, they found subtle changes in PIII amplitude (-7.5%) and latency (+5.7%), PII amplitude (-8.2%) and latency (+13.6%), pSTR amplitude (-27.4%) and latency (+7.6%), and nSTR amplitude (-7.2%) and latency (+8.3%). The authors concluded that dietary omega-3 has beneficial effects across the retina, with the greatest improvement occurring in ganglion cell function. While the results are consistent with a role of omega-3 in retinal function, these conclusions appear a little too strong. The study does not really show beneficial effects of omega-3. Rather, the study shows that extreme omega- 3 depletion may adversely impact retinal function. Given that the effects are subtle and that dietary deficiencies in omega-3 PUFAs of Western diets are not expected to reach such extremes, the question of whether these effects may be replicated in the human model is still at hand. The second conclusion that omega-3 impacts (improves) retinal ganglion cell function also does not appear to be very solid. Rod outer segments, compared to other retinal elements, contain higher levels of omega-3, and are expected to be the most impacted by depletion. Given that ERG changes are already present in outer- retina ERG components, a downstream effect is expected whereby retinal ganglion cells receive a reduced input, and it is difficult to establish the specific contribution of retinal ganglion cells as the authors acknowledge. In order to establish a beneficial role of omega-3 PUFAs in glaucoma, specific studies are needed (e.g., using glaucoma models receiving omega-3-enriched diets).
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