Abstract
Purpose::
Vasopressin is a naturally occurring anti-diuretic hormone which acts both in the CNS and periphery to control osmolarity and body fluid volume via the regulation of vasoconstriction, free water absorption and alterations in aquaporin expression. It has also been implicated in the regulation of intraocular pressure (IOP) (Gondim et al., 2001). As our previous research suggests that alterations in fluid dynamics in the retina are closely associated with refractive development (Liang et al., 2004) we investigated the dose related effect of vasopressin on refractive compensation and ocular growth in response to lens-induced defocus in the chick model.
Methods::
Chicks were raised from days 5-10 post-hatching under a 12 hr day/night cycle at 31°C following a monocular intravitreal injection of 5µl of either PBS, 1 × 10-6 mg or 5 × 10-6 mg of vasopressin in PBS (fellow eyes received 5µl of PBS), and fitting with ±10D lenses or no lens. Biometry including retinoscopy and A-scan ultrasonography was performed and eyes were prepared for histological and immunological analysis.
Results::
Injection of 1 × 10-6 mg of Vasopressin resulted in a 3D myopic shift beyond the refraction of PBS control, while 5 × 10-6 mg of vasopressin reduced compensation to +10D lenses, leading to a significant Lens × Drug interaction effect (p = .003) for Refractive State. Similar changes were seen in measures of Axial Length, with the majority of growth begin observed in the Vitreous Chamber. Growth patterns were comparable between groups for Anterior Chamber measure, with the greatest depth, although non-significant, being observed in the 1 × 10-6 mg Vasopressin condition. Little change was observed in the no lens groups.
Conclusions::
Increased refractive compensation and axial elongation in the presence of negative defocus and vasopressin, a natural anti-diuretic hormone, supports Crewther 2000’s hypothesis that modulation of retinal fluid dynamics plays a role in the process of refractive compensation.
Keywords: myopia • retina: neurochemistry • intraocular pressure