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Sally A McFadden; The Effect of Atropine on Lens Induced Myopia in the Guinea Pig. Invest. Ophthalmol. Vis. Sci. 2017;58(8):5467.
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Atropine has long been proposed as a treatment for myopia: early studies show that atropine can slow myopia progression in children. However, rebound occurs and unacceptable side effects include blurred vision and photophobia (Tong et al, 2009). These side effects are not observed with lower doses of atropine (0.5% and 0.1%) which still inhibit myopic progression, although with reduced treatment impact (Chia et al, 2012). We studied the effect of atropine eye drops on eye growth and on the initial response to lens-induced myopia in young guinea pigs to determine if atropine can inhibit defocus-induced myopia.
To induce myopia, guinea pigs wore a -6D lens on one eye from 7-14 days of age. Simultaneously, animals received either Atropine (0.1%, N=19) or PBS (1mM, N=16) on the lens-wearing eye. To test the effect on normal growth, another group (N=7) that did not wear lenses, received 1% Atropine on one eye and PBS on the fellow eye from 9-24 days of age. Drugs were topically applied to the cornea twice/day. After 1 week of eye drops (at 15 or 17 days of age), both eyes were cyclopleged and refractive error measured. Animals were anaesthetised with isoflurane and axial length measured with high frequency ultrasound. Intraocular pressure was measured in the normal growth animals after 2 weeks of eye drops. The difference between the two eyes (diff) was assessed with matched-pair t-tests.
Both groups wearing a lens and treated with either saline or 0.1% atropine developed significant relative myopia (diff: -2.6±0.7D, p=.014 and -2.7±0.8D, p=.013 respectively) and ocular expansion (30 ± 13µm, p=.032; 34±16µm, p=.047 respectively). The degree of myopia and ocular increase was similar in both groups (p=.93 and p=.85). However, atropine treated eyes developed a thinner crystalline lens than saline-treated animals (-16µm Vs. +4µm) and increased anterior chamber depths (+29µm Vs +1µm). Similarly, 6/7 animals not wearing a lens but treated with 1% atropine also had thinner lenses (mean diff to saline eye: -27±7µm, p=.01). However, 1% atropine did not change normal refractive development over 1 week (diff of .99D, p=.4) or intraocular pressure after 2 weeks.
Low dose Atropine fails to inhibit the early induction of myopia and ocular elongation from minus lens wear in young guinea pigs, and instead affects the anterior of the eye, suggesting it does not directly target myopia initiation from defocus signals.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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