Modulation of constant light effects on the eye by ciliary ganglionectomy and optic nerve section

Our previous studies have shown that an environment of constant light (CL) can lead to development of high degree of hyperopia in newborn chicks by in ducing severe corneal flattening, and compensatory growth of the vitreous c hamber. We wish to know whether the abnormal eye growth and progressive hyp eropia under CL conditions is accomplished by a mechanism that uses the vis ual processing pathways of the central nervous system (CNS) or by a mechani sm located in the eye. Thirty white leghorn chicks (Cornell K-strain) were raised under 12 h light/12 h dark (12L/12D) for either optic nerve section (ONS) or ciliary ganglion section (CGS). Another 30 chicks were raised unde r CL for ONS or CGS. Refractive states and corneal curvatures were measured by infrared (IR) photoretinoscopy and IR keratometry, respectively. The ax ial lengths of the ocular components were measured by A-scan ultrasonograph y. Both ONS and CGS surgery produced dilated pupils and accommodative paral ysis. Four weeks after surgery, CGS eyes exhibited a hyperopic defocus, fla tter cornea, and shorter vitreous chamber depth under both CL and normal co nditions, whereas ONS eyes showed a smaller radius of corneal curvature and shallow vitreous chamber only in the normal light cycle group. CGS eyes of CL chicks showed significantly deeper vitreous chambers than did fellow co ntrol eyes. Our results indicate that optic nerve section does not seem to influence CL effects. Thus, local mechanisms may play a major role in the o cular development of chicks. The ciliary nerve is necessary for the normal corneal and anterior chamber growth, and pr-events CL effects. The progress ively increasing vitreous chamber depth under CL may be influenced by both local and central mechanisms. (C) 2000 Elsevier Science Ltd. All rights res erved.