Dopamine and Myopia Control
Dopamine is a major neurotransmitter in the retina involved in signal transmission in the visual system. Studies in animal eyes suggest that dopamine participates in visually guided eye growth regulation (Pendrak K, Nguyen T, Lin T, Capehart C, Zhu X, Stone RA. Retinal dopamine in the recovery from experimental myopia. Curr Eye Res. 1997 Feb;16(2):152-7)
Dopamine, a major metabolite of levodopa, releases in response to light. Past Treatments with Dopamine: L-Dopa has been used as the gold-standard drug in the treatment of Parkinson’s disease and low-dose administration of the drug has been the most effective treatment of Parkinson’s. Possible treatments involving dopamine in preventing a decrease in visual acuity have shown to be successful in the past. L-dopa treatment in children with amblyopia showed an improvement in visual acuity. (Leguire LE, Komaromy KL, Nairus TM, Rogers GL. Long-term follow-up of L-dopa treatment in children with amblyopia. J Pediatr Ophthalmol Strabismus. 2002 Nov–Dec;39(6):326-30; quiz 345-6) In rabbits, injections of dopamine prevented the myopic shift and vitreous chamber and axial elongation typically associated with FDM. (Gao Q, Liu Q, Ma P, Zhong X, Wu J, Ge J. Effects of direct intravitreal dopamine injections on the development of lid-suture induced myopia in rabbits. Graefes Arch Clin Exp Ophthalmol. 2006 Oct;244(10):1329–35. Epub 2006 Mar 21) In guinea pigs, systemic L-dopa has shown to inhibit the myopic shift associated with FDM and has compensated to the drop in retinal dopamine levels. (Mao J, Liu S, Qin W, Li F, Wu X, Tan Q. Levodopa inhibits the development of form-deprivation myopia in guinea pigs. Optom Vis Sci. 2010 Jan;87(1):53–60) These experiments show promise in treating myopia in humans.
Possible Side Effects of Dopamine Treatment: Unfortunately, several side effects of L-Dopa have been experimentally determined. L-Dopa and some of its metabolites have been shown to have pro-oxidant properties, and oxidative stress has been shown to increase the pathogenesis of Parkinson’s disease. This promotion of free-radical formation by L-Dopa does seem to directly effect its possible future treatment of myopia due to the fact that free-radicals could further cause damage to those proteins responsible for controlling structural proteins in the eye. It has also been shown that levodopa and some of its metabolites such as dopa/dopamine quinone are toxic for nigral neurons. This toxic effect must be analyzed before treatment of levodopa for myopia to prevent damaging effects to these neurons.
Optom Vis Sci. 2010 Jan;87(1):53-60.
Levodopa inhibits the development of form-deprivation myopia in guinea pigs.
Mao J, Liu S, Qin W, Li F, Wu X, Tan Q.
Department of Ophthalmology, Xiang-Ya Hospital, Central South University, Changsha, Hunan, China. email@example.com
It has been shown that visual deprivation leads to a myopic refractive error and also reduces the retinal concentration of dopamine. Exogenously 3,4-dihydroxy-L-phenylalanine (levodopa, L-DOPA) can be converted into dopamine in vivo, which safely and effectively treats Parkinson disease. Moreover, L-DOPA was also used in the treatment of amblyopia in clinical studies. However, the effect of L-DOPA on the development of myopia has not been studied. The aim of this study was to investigate whether intraperitoneal injection of L-DOPA could inhibit form-deprivation myopia in guinea pigs and to explore a new strategy for drug treatment of myopia.
Ten days of eye occlusion caused the form-deprived eyes to elongate and become myopic, and retinal dopamine content to decrease, but the corneal radius of curvature was not affected. Repeated intraperitoneal injection of L-DOPA could inhibit the myopic shift (from -3.62 +/- 0.98 D to -1.50 +/- 0.38 D; p < 0.001) due to goggles occluding and compensate retinal dopamine (from 0.65 +/- 0.10 ng to 1.33 +/- 0.23 ng; p < 0.001). Administration of L-DOPA to the unoccluded animals had no effect on its ocular refraction. There was no effect of intraperitoneal saline on the ocular refractive state and retinal dopamine. CONCLUSIONS: Systemic L-DOPA was partly effective in this guinea pig model and, therefore, is worth testing for effectiveness in progressing human myopes.