The effect of conjunctival flap type in primary trabeculectomy on surgical site oxygen metabolism and the hypotensive effect of the operation

PURPOSE: To study the effect of conjunctival incision type in primary trabeculectomy on surgical site oxygen metabolism, complication rate and the hypotensive effect of the operation.
METHODS: 162 patients (200 eyes) with moderate and advanced primary open-angle glaucoma were randomized into two groups, 100 eyes each. All patients underwent primary trabeculectomy, Group 1 — with a fornix-based conjunctival flap, Group 2 — with a limbus-based conjunctival flap. Hemoglobin oxygen saturation (SO2), bleb hyperemia (H) and tonometry (IOP) were monitored on 1 day, 1 week, 1, 3, 6 and 12 months after the surgery. IOP compensation was assessed according to the Glaucoma guidelines average values: 17 mmHg for moderate glaucoma and 14 mmHg for advanced glaucoma.
RESULTS: Assessment of SO2 rates in conjunctival veins in the bleb zone on day 1 after the surgery showed a significant 17-18% decrease of oxygen saturation with no statistically significant difference between the groups. One week after trabeculectomy patients in both groups exhibited a tendency toward normalization of venous blood saturation rates with a statistically significant advantage of the first group: 46.1±3.4% and 36.8±3.6%. The tendency remains throughout the early postoperative period, reaching preoperative rates by 6 month after trabeculectomy: 55.6±2.2% and 54.8±2.3%. Difference between hyperemia rates was insignificant with ∆Н=-2.2%. 1 week after the surgery hyperemia in the fornixbased conjunctival flap group decreased by 3.6%, while limbus-based conjunctival flap showed a decrease of only 0.8% (statistically significant difference). This index gradually lowered to normal values up to 3-6 months after trabeculectomy in both groups; however a difference of 2-3% remained until the 3d month.
There was no significant difference in preoperative IOP rates: 28.4±5.6 and 28.7±5.8 mmHg. On day 1 after surgery IOP lowered to 9.2±1.9 и 8.4±2.3 mmHg correspondingly. Similar values were noted on 1 week timepoint (insignificant difference). 1 month after the operation IOP rate in Group 2 exceeded those in Group 1 by 1.5 mmHg with no evident reason. This tendency continued up till 1 year, reaching a statistically significant difference at 3 months and 1 year after trabeculectomy (3.6, 1.5 and 4 mmHg at 3, 6, 12 months correspondingly).
At the end of the follow-up period absolute surgical success equaled 69 and 54% in Groups I and II correspondingly (insignificant difference). Bleb needling was required in 26 and 37% of cases, postoperative hypotensive therapy — in 18 and 25%. Relative surgical success showed a moderate difference, equaling 95 and 91%.
No conjunctival perforation during fornix-based conjunctival flap incision was noted. In limbus-based conjunctival flap group there were 4 cases of perforations in the paralimbal zone. Shallow anterior chamber was noted intraoperatively in 18 and 23% of cases. Fornix-based conjunctival flap required additional sutures in 9% of cases. No such necessity was noted in the limbus-based conjunctival flap group. Postoperative hyphema was registered in 7 and 11% of cases, disadaptation of the edges of the conjunctival incision was visualized in 14 and 2% of cases, external filtration — in 8 and 2%. Choroidal detachment developed in 7 and 11% of cases, with 4 and 5% requiring surgical treatment.
CONCLUSION: Trabeculectomy with both fornix-based and limbus-based conjunctival flap incision leads to a substantial metabolic disturbance at the operation site, leading to a significant increase in oxygen consumption and surgical site hyperemia — with a significant advantage on the part of the fornix-based conjunctival flap. It is a less traumatic method of forming a conjunctival flap, associated with lower perforation and choroidal detachment incidence.
Limbus-based conjunctival flap showed better results in terms of conjunctival incision disadaptation and additional suture necessity. Both methods showed comparable qualified surgical success rates with a significant difference in postoperative hypotensive measures.

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