Abstract
Abstract: :
Purpose: Emmetropization can be demonstrated experimentally using defocusing lenses; chick eyes show compensatory changes in both the choroid and sclera (axial length), opposite for positive and negative lenses. We investigated whether acetazolamide (ACZ), a nonselective carbonic anhydrase inhibitor, could inhibit one or more of these changes. These changes are mediated largely locally by the retina, with the retinal pigment epithelium (RPE) playing a critical role in signaling between retina and choroid/sclera. Carbonic anhydrase is involved in the regulation of pH gradients and fluid transport, influencing both IOP (via the ciliary epithelium, CA–II) and retina–choroid signaling (RPE; CA–IV). Methods: Ten day–old chicks were fitted with either +15D or –15D lenses over one eye (T); the contralateral eye served as the control (C). Chicks received either 100mg/day ACZ or vehicle (dimethyl sulfoxide, DMSO) in two divided doses orally for 5 days. Treatment effects were measured at baseline and after 5 days of treatment using high frequency A–scan ultrasonography. Lens treatment effects were assessed in terms of interocular differences. Intraocular pressure (IOP) was measured using a Tonopen, day 5 measurements were made 3 hours after the last ACZ/DMSO dose. Data were analyzed by ANOVA followed by Tukey–Kramer post–hoc test and are reported below as Mean + SEM Results: Lens–induced changes in internal axial length (IAL) and choroidal changes were significantly altered by ACZ (see table). ACZ treated–birds showed a significantly larger fall in IOP (baseline–day5) compared to DMSO–treated birds.
Conclusions: ACZ interferes with the compensatory axial length and choroidal responses to lens–induced defocus. To distinguish between a RPE and ciliary epithelium location for these effects, further studies are underway using a CA–IV selective inhibitor.
Keywords: emmetropization • enzymes/enzyme inhibitors • intraocular pressure