Retrobulbar Diversion of Aqueous Humor: Laboratory Studies

Introduction: This laboratory-based surgical and histopathologic study evaluates the efficacy and explores the mechanism of action of a new form of glaucoma tube shunt for glaucoma. Existing polymeric implants frequently become encapsulated between the sclera and tenons capsule and become impervious to aqueous humor. This pilot study analyzes histologic and tonometric changes after retrobulbar diversion of aqueous directly from anterior chamber (AC) into the retrobulbar space (RS) versus standard subtenons scleral reservoir diversion. Materials and Methods: This was an IACUC-approved 6-month masked comparative animal study. Front-to-back 1-piece (AC-to-RS) shunts (n = 4) and standard Ahmed FP8 shunts (n = 3) were implanted unilaterally in a total of 7 rabbits. Operative eyes were serially monitored throughout the trial period and underwent postmortem histologic assessment 24 hours after in vivo intracameral India ink dye injection to discern the pathway for retrobulbar aqueous reuptake. Results: Sustained intraocular pressure reduction occurred in these normotensive rabbits with AC-RS shunts, from preoperative mean 13.5 +/- 0.3 to mean 10.6 +/- 0.3 mm Hg through 6 months, significantly lower than with the standard FP8 (P < 0.001). Qualitative histologic analysis revealed lacunar distribution of India ink throughout the RS, demonstrating successful diffuse posterior diversion and reuptake of aqueous humor. Conclusions: Retrobulbar shunts can divert aqueous from the AC into the RS, potentially overcoming plate encapsulation associated with standard subtenons scleral reservoir placement. Elimination of the bleb from the periequatorial globe may substantially simplify surgery and obviate the risks of bleb leak.