Effects of direct intravitreal dopamine injections on the development of lid-suture induced myopia in rabbits

Background: Dopamine (DA) storage and release are reduced in form deprivation myopia (FDM) in a wide range of species, from chicks to primates. FDM can be prevented by treatment with DA agonists such as apomorphine, and paradoxically by the dopamine neurotoxin 6-hydroxydopamine. In this study, we increased the DA levels by direct intravitreal DA injections to learn if FDM can be suppressed in a rabbit model. Methods: Seven-day-old rabbits were deprived of pattern vision by the suturing the right eyelids after natural eye opening. In the first group (FD, n=20), the right eye received form deprivation (FD) alone. In the second group (DA-FD, n=16), the deprived eye of 7-day-old rabbits received four intravitreal injections of 20 mu g dopamine every 5 days. In the third group (saline-FD, n=16), the deprived eye received saline injections with the same schedule. The contralateral eye remained untreated as a control. At the end of the 8-week deprivation period, the effects of DA on refractive error, corneal curvature and ocular dimensions were assessed by streak retinoscopy, keratometry and A-scan ultrasonography, respectively. Results: Eight weeks of FDM induced a myopic shift of -2.70 +/- 0.87 D (n=20) in treated eyes compared with contralateral eyes. The major structural correlate of the myopia appeared to be elongation of the vitreous chamber (0.7 +/- 0.3 mm, n=20) and axial elongation (0.9 +/- 0.3 mm, n=20), respectively. Repeated intravitreal injections of DA fully prevented the myopic shift (-0.06 +/- 0.37 D), elongation of the vitreous chamber (0.1 +/- 0.3 mm, n=16) and axial elongation (0.3 +/- 0.2 mm, n=16) due to lid suture, whereas saline injections had slight effect. Conclusions: FD by suturing eyelids is an effective technique to induce a significant myopic shift, vitreous chamber and axial elongation in rabbits as a model of myopia development. These changes associated with FD were retarded by intravitreal injections of DA.