TRANSSCLERAL FLOW OF AQUEOUS-HUMOR - AN IN-VITRO EXPERIMENT

BACKGROUND AND OBJECTIVE: The minimal scleral flap thickness to ensure transscleral flow following a trabeculectomy has never been determine d. The present study was designed to determine, in vitro, the critical scleral flap thickness that allows transscleral flow. MATERIALS AND M ETHODS: The apparatus consisted of two horizontal glass chambers (A an d B) connected to each other by a customized scleral disc holder. High -pressure chamber A (at 25 mm Hg) was filled with sodium pertechnetate (Tc-99m) labeled normal saline and low-pressure chamber B (at 5 mm Hg ) with normal saline. Transscleral flow of labeled normal saline from high-pressure chamber A via varying thickness scleral discs to low-pre ssure chamber B was observed over 16 hours using a gamma camera. Compu ter analysis was performed on the obtained images. RESULTS: Transscler al flow of labeled saline was observed only with scleral discs 0.5 mm thick or less. CONCLUSIONS: If the findings hold true for the in vivo situation, aqueous humor may reach the subconjunctival space following trabeculectomy via the transscleral route, provided scleral flap thic kness is less than 0.5 mm. In addition, normal uveoscleral aqueous out flow may occur across sclera less than 0.5 mm thick, e.g., posterior t o extraocular muscle insertions.