Abstract:
We reported earlier that acetazolamide (ACZ) (an inhibitor of carbonic anhydrase (CA) II & IV) interferes with compensatory axial length and choroidal responses to lens–induced defocus in chicks (ARVO 2004), while benzolamide (BZ), a CA–IV selective inhibitor, does not. This implies that the effects of ACZ on eye growth are not mediated by CA–IV on the RPE. An intraocular pressure (IOP)–based mechanism would be consistent with the IOP lowering action of ACZ. We used our labs’ observation that chicks show normal plus lens responses in constant light (CL) (ARVO 2004) to test this possibility.
1–day old chicks were assigned to either a 12hr light/12 hr dark cycle (DN) or CL. After 10 days, they were fitted with a +15D lens over one eye (T); the contralateral eye served as a control. Chicks received either 70–100mg/day ACZ or vehicle (DMSO) in 2 divided oral doses daily for 5 days. At the start and end of this period, ocular axial dimensions were measured using high frequency A–scan ultrasonography and IOP was measured using a Tonopen. Data were analyzed by ANOVA followed by Tukey–Kramer post–hoc test and are reported below as mean +SEM.
CL chicks had significantly lower IOP than DN chicks at the start of the treatment period (10.4 +0.54, cf. 13.6 +2.45 mmHg, n=12, 9). ACZ did not further lower IOP under CL. Plus lens treated–eyes showed marked choroidal thickening (CT) compared to contralateral eyes under both DN and CL conditions and in both cases, ACZ produced a significant decrease in CT in lens–treated eyes as shown in the table below.
ACZ attenuated the choroidal thickening response to plus lenses in chicks reared in CL as well as DN conditions but did not further lower IOP in CL. Thus these results do not support an IOP–based mechanism and leave unresolved the mechanism for the choroid thinning action of ACZ.
Keywords: emmetropization • intraocular pressure • choroid