Intravitreal Injections for Myopia Control

Intravitreal injections were performed using a 0.5-mL insulin syringe (30-gauge needle, BD Medical, Le Pont deClaix, France). They consisted of atropine sulfate monohydrate (250 µg/360 nMol, > 97%, Sigma-Aldrich, Deisenhofen, Germany) in 25 µL saline, or spiperone (500 µMol, Sigma-Aldrich, Deisenhofen, Germany) in 25 µL ascorbic acid (1 mg/mL, pH 7.4), or a combination of both atropine and spiperone in 25 µL ascorbic acid, while the fellow eye received 25 µL saline or 25 µL ascorbic acid, respectively. Alternatively, both eyes received 25 µL saline. The atropine dose was selected based on previous experiments [21 (link)], where daily injections completely blocked myopia induced by wearing − 7D lenses. The dose of spiperone was also selected based on previous experiments. Thomson et al. [17 (link)] had shown that daily injections of 500 µMol of spiperone suppressed the protective effects of dopamine or a dopamine agonist against the development of both deprivation myopia and lens-induced myopia. Ashby and Schaeffel [23 (link)] had found that 500 µMol spiperone blocked the protective effect of bright light on deprivation myopia in chickens. All injections were performed under mild ether anesthesia. The intravitreal injection procedure in the chicken is well established (e.g., [11 (link), 24 (link)–26 (link)]) and, as in previous studies, we never observed ocular inflammations.