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D.P. Crewther, S. Crewther, H. Liang, B. Junghans; Evidence for Ionic Control of Refractive Compensation . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2809.
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Purpose: A recent model (Crewther, 2000) based on control of fluid across the retinal pigment epithelium (RPE) reproduces most of the features of choroidal change during recovery from form deprivation myopia. The vitreous chamber and choroid appear to act as reservoirs, with the RPE controlling movement of fluid between them. Furthermore, our data from X-ray scattering electron microscopy shows concurrent ionic concentration shifts (mainly [K], [Na], [Cl]) occurring across the RPE and subretinal space suggesting a close association between the ionic changes and the fluid movement. Thus to test such a model unselective blockade of K+ channels by BaSO4, was investigated. Methods: 65 chicks were raised from days 5-10 post-hatching with monocular +10D, 0D, -10D lenses. On day 5, 33 chicks were administered an intravitreal injection.of BaSO4 (target concentration of 5.0 mM) and 32 control chicks were injected with a similar volume saline before lens application. Results: K channel blockade produced an immediate and striking reduction in compensation to either +ve or –ve lenses. Mean refractions (SAL+10D: +8.23; SAL+0D: +0.40D; SAL-10D: -8.6; Ba+10D: +2.8; Ba0D: -2.3; Ba–10D: -2.9). ANOVA showed a strong main effect for treatment (F(1,21) = 11.7, p = 0.003, while simple t-tests, comparing Ba and SAL chicks for the same lens power, demonstrated significant reductions in compensation for both +10D and –10D lenses. Conclusions: This data supports the hypothesis that potassium currents play a role in the processes responsible for compensation to imposed optical defocus. Crewther DP (2000) Prog Ret and Eye Res, 19: 421-457
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