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Frank Schaeffel, Ute Mathis; Inhibition Of Lens-induced Myopia In Chicks With A Plant Extract: Black-currant. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6304.
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A major obstacle in current attempts to inhibit myopia progression by drugs is that side effects may limit long-term application. Furthermore, drugs may loose their effects over time. It is therefore tempting to look into natural plant extracts that are regularly found in food. Iida et al (Ophthalmic Research 44, 242-250, 2010) tested a commercially available black currant extract (BC, Currantex, "Just the Berries") and found dose-dependent inhibition of negative lens-induced axial eye growth in white leghorn chicks. We have repeated a similar experiment in two strains of black and white chicks.
Three batches of 12 chicks were used in 3 experiments. Six chicks of each batch wore a -7D lens in one eye, the fellow eye remained untreated, and were fed daily, by gavage into the crop using feeding needles, with BC extract (obtained from German representative of Currantex, Hamburg) from day 7 to 11, while the other 6 chicks received only lens treatment and regular food. Refractions and ocular biometry were measured before and after the treatment period. Doses were 400 mg BC/kg body weight (one batch) and 600 mg BC/kg body weight (two batches).
Normally fed animals developed amounts of myopia in the lens-treated eyes which were appropriate to compensate for the power of the negative lenses. BC-fed animals showed slightly less myopia. However, the difference did not achieve significance (df=34, T=-1.80, p< 0.08, t-test) despite the large number of chicks. Furthermore, there was no trend of a difference in axial lengths between BC-fed and normally fed chicks (mean difference in axial length between lens-treated and open fellow eyes: normal food 0.623mm+-0.23, BC 0.657mm+-0.24). Also, no effect was detected of BC feeding on refractive development and eye growth in the fellow eyes with normal vision.
Different from a previous study we did not observe an effect of BC extract on lens induced myopia in black and white chickens. There are several options to reconcile the results (1) different sensitivity of different chicken strains to BC, (2) different time courses of the inhibitory effects so that all chicks reached full compensation of the lenses before the final measurements took place, (3) a very small effect of BC that would need large sample size for statistical confirmation, (4) different potency of the BC extracts from different lots.
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