Choroidal and retinal thickness in normal and autonomic denervated eyes: preliminary OCT-data in adult chicken

Abstract

Purpose : For small eyes, high frequency ultrasound is the method of choice to measure changes in the various layers of the chicken posterior eye. Here we ask if optical coherence tomography (OCT) represents an alternative method for the larger adult eye, and if these measurements are also feasible in awake animals. Further, we compare data of normal eyes with autonomic denervated eyes, in which sympathetic and parasympathetic innervation is surgically removed.

Methods : In 8 mature chickens (1200 gr body weight), transection of the two parasympathetic pathways (ciliary ganglion, pterygopalatine ganglion) and sympathetic pathway (superior cervical ganglion) was performed unilaterally. The contralateral unlesioned eye served as a control. Seven days post surgery, choroidal thickness was measured in alert, hand-held animals with OCT (Spectralis, Heidelberg Engineering). Choroidal and retinal thickness was measured at 3 to 5 spots on at least 3 OCT-scans per eye, and data compared using a paired Student`s t-test. Additionally, interocular pressure (IOP) was measured using a rebound tonometer.

Results : Repetitive OCT-measurements are feasible in the awake animals. Choroids in lesioned sites were significantly thinner compared to contralateral controls (177 ± 9 µm on the lesioned side vs. 207 ± 10 µm in the contralateral control; paired t-test, p = 0.04) while retinal thickness was unaffected (195 ± 6 µm on the lesioned side vs. 189 ± 5 µm on the contralateral control side; paired t-test, p = 0.33). IOP in the lesioned side at the end of the experiments (day 6 post surgery) was significantly higher (lesioned eye versus control eye: 14 ± 3 mm Hg versus 38 ± 5 mm, p = <0.001).

Conclusions : OCT-measurements are a valuable tool to detect thickness changes in posterior layers of adult and awake animals, and repetitive measurements under various experimental manipulations are possible, including off-axis measurements in future applications. The observed reduced IOP in lesioned sides might contribute to the observed choroidal thinning. If this is a consequence of reduced blood flow, reduced aqueous humor production or reduced filling of the choroidal lacunae remains to be elucidated.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.