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S. Crewther, H. Liang, B.M. Junghans, D.P. Crewther; Form Deprived Myopia Is Associated With Hyperosmolarity and Increased Potassium in the Outer Retinal Area . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2284.
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Purpose: Whilst high relative Na+ and Cl– abundance exists in the retina and choroid of the eye of the myopic chick immediately after form deprivation (FD) (Liang et al 2004), reports by Oakley & Steinberg & colleagues in the 1970s and 80s led Crewther (2000) to suggest that prolonged occlusion should also lead to a significant change in K+ abundance in the subretinal space. We tested this hypothesis using X–Ray elemental microanalysis (XREM) in chicks recovering from FD. Methods: Thirty–two chickens were raised from 2–16 days with the right eye occluded with a translucent goggle and then given up to 120 hours visual experience prior to sacrifice and preparation of areas of central retina for scanning electron microscopy and XREM of freeze dried and bulk frozen tissue. Results: Comparison of the deprived (Rx=–22D) and fellow retinae (Rx=+1.1D) at T=0 showed a greater abundance of K+ in the area of the subretinal space at T=0. The relative K+ abundance fell to levels signficantly lower than normal within 24 hours. This level was evident for the next few days. Much higher levels of Na+ and Cl– ions were seen in the choroid, retinal pigment epithelium (RPE)/photoreceptor area with smaller but significant increases in the inner retina at occluder removal. These levels decreased over the next few days in the freeze dried samples. Significantly higher concentrations of NaCl only appeared in the bulk frozen choroidal material after 48 hours of visual experience and extensive dilation of the choroidal lymphatics. Conclusions: As predicted FDM is associated with an increase in abundance of K+ in the region of the subretinal space and recovery between 24 and120 hours is associated with lower levels than normal. On the other hand the high levels of Na+ and Cl– ions occur across the entire retina and choroid and although gradually decreasing to normal levels persist through the period of choroidal swelling suggesting that both abundance the hyperosmolarity and reduced K+ ion in combination play a central role in the rapid and dramatic change in choroidal and retinal thickness. Relative ion abundances had all returned to stable levels by the time of refractive and morphological recovery in these chicks at T=120 hours.
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