Influence of peripheral iridectomy on intravitreous penetration of topical nipradilol

Penetration of drug from the anterior chamber to the vitreous is substantial in aphakic eyes, but negligible in normal phakic eyes. The purpose of this study is to investigate the effect of the presence of peripheral iridectomy (PI) which bypasses iris-lens diaphragm on the drug penetration from the anterior chamber to the vitreous.

Twelve Japanese White rabbits underwent PI in a randomly chosen eye and the same procedures except removal of the peripheral iris in the contralateral eye. Nine weeks after the procedure, topical instillation of 20 microl of 1% nipradilol into the both eyes was repeated three times at five-minute intervals, and two hours later the animals were sacrificed and the both eyes were enucleated. Concentrations of nipradilol in the aqueous and vitreous were determined using a high-performance liquid chromatography.

The concentrations of nipradilol were significantly greater in the eyes with PI than those in the contralateral control eyes in the aqueous (5636 +/- 1688 vs 2835 +/- 663 ng/g, mean +/- standard error, n = 12, p = 0.0028) and in the anterior vitreous (11.9 +/- 2.5 vs 5.6 +/- 1.0 ng/g, p = 0.0047), while not in the posterior vitreous or in the posterior retina-choroid. The ratios of the nipradilol concentrations in the anterior or posterior vitreous to that in the aqueous were not significantly different between the both eyes.

The presence of PI had little effect on the penetration of topically instilled nipradilol from the anterior chamber to vitreous.