Sympathetic nervous system plays a role in postnatal eyeball enlargement in the rabbit

PURPOSE. To examine the role of ocular sympathetic activity in the enlargem ent of the rabbit eyeball during postnatal growth. METHODS. Fourteen New Zealand albino rabbits aged 5 weeks underwent unilate ral surgical transection of the cervical sympathetic trunk caudal to the su perior cervical ganglion. Postoperative enlargement of both eyeballs was mo nitored by measuring the axial length and corneal diameters every 2 weeks f or 22 weeks (7-27 weeks of age). Rabbits were housed under a 12-hour light/ 12-hour dark cycle, and the measurements were made in the middle of the lig ht period. At a final age of 30 to 31 weeks, the refractive state of the wh ole eye was determined on both sides by measurement through the central cor nea with a refractometer. Rabbits were then killed, eyeballs enucleated, an d their ocular volumes determined. RESULTS. From 9 weeks of age the axial length and corneal diameters were si gnificantly shorter (P < 0.05) in the decentralized eye (surgical side) com pared with the intact eye. This reduction remained statistically significan t throughout the study period. However, the final refractive states of the two eyes were found not to be different. The mean ocular volume determined after postmortem enucleation was 4.5% less in the decentralized eye than in the intact eye (P < 0.05). CONCLUSIONS. Sympathetic nervous system activity is involved in the normal enlargement of the rabbit eyeball during postnatal growth. However, removal of the ocular sympathetic tone at the age of 5 weeks does not significantl y alter the refractive state of the rye when measured in young adulthood.