Sympathetic Nervous System Plays a Role in Postnatal Eyeball Enlargement in the Rabbit

PURPOSE. To examine the role of ocular sympathetic activity in the enlargement of the rabbit eyeball during postnatal growth. METHODS. Fourteen New Zealand albino rabbits aged 5 weeks underwent unilateral surgical transection of the cervical sympathetic trunk caudal to the superior cervical ganglion. Postoperative enlargement of both eyeballs was monitored by measuring the axial length and corneal diameters every 2 weeks for 22 weeks (7‐27 weeks of age). Rabbits were housed under a 12-hour light/12hour dark cycle, and the measurements were made in the middle of the light period. At a final age of 30 to 31 weeks, the refractive state of the whole eye was determined on both sides by measurement through the central cornea with a refractometer. Rabbits were then killed, eyeballs enucleated, and their ocular volumes determined. RESULTS. From 9 weeks of age the axial length and corneal diameters were significantly shorter (P , 0.05) in the decentralized eye (surgical side) compared with the intact eye. This reduction remained statistically significant 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 significantly alter the refractive state of the eye when measured in young adulthood. (Invest Ophthalmol Vis Sci. 2000;41:2684 ‐2688)