Changes in the nerve fiber layer thickness following a reduction of intraocular pressure after trabeculectomy.

PURPOSE: To assess changes in the nerve fiber layer thickness after trabeculectomy using scanning laser polarimetry.

METHODS

The authors prospectively enrolled 46 eyes from 46 patients with primary open-angle glaucoma in whom intraocular pressure had been reduced by more than 30% after trabeculectomy without significant ophthalmic complications and from whom good quality images were obtained by a scanning laser polarimetry preoperatively and at 3 to 6 months after trabeculectomy. In each enrolled eye, changes in the nerve fiber layer thickness after surgery in the defined ring (1.8 disc diameters) around the optic disc were calculated in 10 degrees intervals (36 sectors in total) and in the following 4 quadrants (the sum of 9 10 degrees sectors): superior, nasal, inferior, and temporal.

RESULTS

The mean intraocular pressure was 22.6 +/- 6.9 mm Hg preoperatively and 10.2 +/- 3.7 mm Hg postoperatively (P < 0.01). According to the analyses in every 10 degrees, the postoperative nerve fiber layer thickness was significantly greater than the preoperative nerve fiber layer thickness in the superotemporal region (10-50 degrees) and inferotemporal region (290-340 degrees) of the optic disc (P < 0.05). A stepwise multiple regression analysis showed that only the preoperative mean deviation in the Humphrey visual fields was a significant independent factor associated with changes in the nerve fiber layer thickness in the nasal and inferior quadrants.

CONCLUSIONS

The thickness of the nerve fiber layer, as measured by scanning laser polarimetry, may increase after trabeculectomy, especially in the superotemporal and inferotemporal regions, and can be expected in cases in the early stage of glaucoma that have a better mean deviation.