Inhibitory effect of atropine on myopia development in the chick: mode of application and unilateral versus bilateral lens wear.

Abstract

Abstract: : Purpose: Atropine has been shown to be effective at inhibiting myopia development in humans and in the chick model of myopia. We sought to test the magnitude of the contralateral drug effect using intravitreal and topical dosing and unilateral and bilateral negative lens treatment. Methods: 7–day–old Rhode Island Red – Rhode Island White cross chickens (n = 7–9 per group) were fitted with –15 D lenses either monocularly or binocularly. Atropine sulphate or dH₂O were given to lens wearing eyes using a single intravitreal injection (10µl), or topical application (totalling 60µl). After 4.5 days of lens wear and drug treatment, refractive errors (RE) and axial length (AL) were measured using retinoscopy and A–scan ultrasonography (mean±SD). All techniques (except topical application) were performed under isoflurane (2% in oxygen) anaesthesia. Results:–15 D lenses (with dH₂O intravitreal injections) resulted in –12.31±3.48 D of myopia and increased the AL by 0.47±0.14 mm compared to untreated contralateral eyes. Nearly 80% of the myopia was inhibited (DIFF RE –2.20±2.23 D, AL 0.08±0.13 mm, p<0.001) when atropine (1.48 µmoles) was given by intravitreal injection to the negative lens–wearing eye. When lenses were worn bilaterally and atropine given to one eye, myopia reduced in both eyes (control –9.72±3.89 D, ATR 2.21±3.50 D, p<0.01, contralateral dH₂O –0.89±3.65 D, p<0.05). Topical application was less effective than intravitreal application; a 6 times higher dose (8.86 µmoles) inhibited only 60% of the myopia produced with unilateral negative lens wear (DIFF –5.66±5.11 D, p=0.016). Animals treated with bilateral –15 D lenses and topical water to one eye developed high myopia in both eyes (dH₂O –15.03±1.04 D, contralateral –13.94±1.52 D). When negative lenses were worn bilaterally and atropine applied topically to only one eye myopia reduced in both eyes, even when the dose was only 1.77 µmoles (ATR –6.94±2.29 D, p<0.001, contralateral –7.00±1.95 D p<0.001). Conclusion: To inhibit myopia higher doses of atropine are required topically compared to intravitreally. A contralateral drug effect with bilateral negative lenses was observed with both application modes. Further, in topical dosing the contralateral effect increased such that it was equal to the dosed eye. In the unilateral model the emmetropic eye appears to mask the contralateral effect.

Keywords: myopia • refractive error development • pharmacology