Experimental Evaluation of Ab–Externo Laser Sclerostomy as an Alternative to Current Filtering Procedures

Abstract

Abstract: : Purpose: To evaluate the efficacy and safety of the ultrashort pulsed carbon dioxide (CO₂) laser sclerostomy on intraocular pressure (IOP). Methods:Twenty adult rabbit eyes underwent ab–externo limbal sclerostomies (three 0.5 – 0.8 mm openings) using a CO₂ laser (10.600 nm wavelength, 10 mJ energy, 2 msec pulse duration, 2 Hz repetition rate). The laser surgery was performed unilaterally, under anesthesia (ketamine and xylazine i.m.), in ten eyes under a scleral flap and ten eyes under the conjunctiva. The aqueous humor coming out was the indication for the interruption of the laser application. At the end of the procedure, the conjunctiva and the scleral flap were sutured with a 10/0 suture and an antibiotic–corticosteroid ointment was applied, as well as drops for the first postsurgical month. IOP was evaluated by Tono–Pen tonometer regularly as well as the draining efficacy of the sclerostomies in the third month by the injection of fluorescein in the anterior chamber. Histological examination was performed at the end of the follow–up period (3 months). Results:Mean preoperative IOP was reduced in the first week postoperatively. Thereafter, marked regression was noted and at the end of follow–up period lower IOP (3.2 – 4.0 mm Hg) was preserved in only eight eyes (40%). Filtration was retained in only five eyes with sclerostomies under scleral flap and in three beneath the conjunctiva. The light and electron microscopic findings coincided with the clinical results. Strong fibroid response was observed with augmented fibroblastic activity in conjunction with productive widening of the endoplasmic reticulum and its sisternae and several capillaries with some hemorrhagic phenomena, which gradually prevented the draining effect of the fistula. Conclusions: Based on these findings, laser CO₂ sclerostomy proved to be less effective than conventional trabeculectomy in IOP reduction. The ultra short pulses prevent the excessive thermal effect on the targeted tissue. However, it seems that the reconstructive response of the tissues is still a strong threat to the preservation of the aqueous draining.

Keywords: microscopy: electron microscopy • pathology: experimental • wound healing