Abstract
Purpose :
The dopaminergic system plays a central role in the development of myopia across all animal models investigated, including non-human primates. However, the question remains whether the dopaminergic system also plays a role in human myopia. Recently, a small pilot study reported that children being administered the dopamine reuptake inhibitor methylphenidate (Ritalin) for the treatment of attention deficit hyperactivity disorder (ADHD) showed slower rates of myopia progression. This may suggest that, as observed in animal models, elevated dopamine levels can retard myopia development in humans. To better understand whether Ritalin treatment can modulate eye growth, this study used the chicken model of experimental myopia to investigate its effects without the contributing factor of an ADHD diagnosis.
Methods :
Chicks were fitted with translucent diffusers for a period of seven days (n=6 per group) with Ritalin administered either systemically (ingestion) or through direct intravitreal injection at a dose of 0.05 mg per day. A dose response curve was also generated for intravitreal injections (0.05 mg, 0.005 mg, and 0.0005 mg per day). The degree of myopia induced was assessed by measuring refraction (automated infrared photoretinoscopy) and axial length (A-scan ultrasonography) before the commencement and at the end of the experimental period. Retinal tissue was also extracted and analysed for changes in dopamine levels using liquid chromatography tandem mass spectrometry (LC-MS-MS).
Results :
Although no dose-dependent effect was observed, the development of experimental myopia was inhibited by roughly 50% in response to daily intravitreal administration of Ritalin over a seven day period (ANOVA (F(3, 21)=7.55, p<0.05). Protection was also observed in response to daily Ritalin ingestion, although the effect was smaller (ANOVA (F(1, 11)=7.35, p<0.05). Both systemic and intravitreal administration of Ritalin lead to elevated retinal dopamine levels in myopic (ANOVA (F(2, 19)=13.93, p<0.05) or otherwise untreated eyes (ANOVA (F(2, 19)=14.62, p<0.05).
Conclusions :
This study reports that Ritalin treatment can inhibit the development of experimental myopia, although to a lesser extent than observed for direct pharmacological stimulation of dopamine receptors. Together with observational studies in humans, this would suggest that the dopaminergic system may play a role in human myopia.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.