Outflow mechanisms after deep sclerectomy with two different designs of collagen implant in an animal model

Abstract

Background: To study experimentally two different shapes of collagen implants (CI) used in deep sclerectomy (DS). The ability to promote drainage vessels, outflow mechanisms, success rates, and biodegradability, were studied prospectively in an animal model.

Materials and methods: DS was performed in 20 eyes of ten rabbits. Each rabbit randomly received a cylindrical CI in one eye, while the other eye received a flat CI. Intraocular pressure (IOP) measurement, ultrasound biomicroscopy (UBM) examination of DS site and simultaneous fluorescein and indocyanin green anterior-segment angiography were performed preoperatively, at 1 and 2 weeks, 1, 2, 3, 6 and 9 months for each eye. At the end of the follow-up period, outflow facility (OF) was measured and histological examinations of the filtration site were performed.

Results: In the cylindrical implant group, IOP significantly dropped from a mean pre-operative value of 14.8+/-2.2 mmHg to a mean postoperative values of 10.9+/-3.3, 12.5+/-2.2, 11.8+/-2.6, 11.2+/-2.3, 10.7+/-1.9, 14.0+/- 3.2, 12.6+/-2.4 mmHg at 1, 2 weeks, and 1, 2, 3, 6, and 9 months, respectively. In the flat CI group, IOP significantly dropped from a mean preoperative value of 14.1+/-1.8 mmHg to a mean postoperative values of 10.4+/-2.7, 12.7+/-1.9, 12.5+/-3.2, 11.2+/-1.6, 11.6+/-1.8, 11.5+/-2.3, 11.0+/-2.2 mmHg at 1, 2 weeks, and at 1, 2, 3, 6, and 9 months, respectively. UBM images showed a gradual resorption of both type of CI during the first 3 months, and angiographies showed progressive growth of drainage vessels around the filtration site in both groups. The mean OF 9 months postoperatively for the cylindrical CI was 0.53 (SD +/- 0.23) ml/ min per mmHg and was 0.56 (SD+/-0.17) ml/min per mmHg for the flat CI (P=0.6). Histological examination revealed excellent biocompatibilty and a high density of drainage vessels in the sclera around the operative site in both groups.

Conclusion: Using IOP and OF measurements, UBM, angiography, and histology, we were able to compare two types of CI used as space maintainer in DS. Both CIs showed efficient IOP lowering effect and outflow facility increase, possibly explained by stimulation of drainage vessels growth. Both implants showed excellent biocompatibility. The flat CI showed a slight tendency towards better overall performances.