THE ORGANOPHOSPHATE PESTICIDE CHLORPYRIFOS AFFECTS FORM DEPRIVATION MYOPIA

PURPOSE. The effects of the anti-cholinesterase organophosphate pestic ide chlorpyrifos (CPF) on the refractive development of the eye were e xamined. Form deprivation was used to induce eye growth to address the previously reported relationship between organophosphate pesticide us e and the incidence of myopia. METHODS. Chickens, a well-established a nimal model for experimental myopia and organophosphate neurotoxicity, were dosed with chlorpyrifos (3 mg/kg per day,, orally, from day 2 to day 9 after hatching) or corn oil vehicle (VEH) with or without monoc ular form deprivation (MFD) over the same period. The set of dependent measures included the refractive state of each eye measured using ret inoscopy, axial dimensions determined with A-scan ultrasound, and intr aocular pressure. RESULTS. Dosing with CPF yielded an inhibition of 35 % butyrlrylcholinesterase in plasma and 45% acetylcholinesterase in br ain. MFD resulted in a significant degree of myopia in form-deprived e yes resulting from significant lengthening of the vitreal chamber of t he eye. CPF significantly reduced the effect of MFD, resulting in less myopic eyes (mean refraction: VEH-MFD = -16.2 +/- 2.3 diopters; CPF-M FD = -11.1 +/- 1.8 diopters) with significantly shorter vitreal chambe rs, Nonoccluded eyes were, on average, slightly hyperopic. Treatment w ith CPF for 1 week in the absence of MFD led to no significant change in ocular dimensions or refraction relative to controls. CONCLUSIONS. The use of form deprivation as a challenge suggests that CPF treatment interferes with the visual regulation of eye growth.