Changes in Ocular Dimensions following Trabeculectomy and Glaucoma Drainage Device Surgery

Abstract

Abstract: : Purpose: This prospective, interventional study examines the changes in axial length (AL) after trabeculectomy and glaucoma drainage device (GDD) surgery. We then created a correlation equation to predict the AL change after filtering surgery. Methods: 39 patients undergoing trabeculectomy and 22 undergoing Baerveldt 350 tube shunt implantation for uncontrolled glaucoma had AL measurements at 1 week, 1 month and >3 months after surgery. AL was measured by partial coherence interferometry. This non-contact method eliminates false low axial length readings induced by probe pressure on the eye. IOP was categorized as hypotonous (0-4 mmHg), low (5-9), normal (10-17) and high (18 or greater). Results: There was a significant difference in AL after surgery compared to pre-operatively at all time points (p<0.001), with a mean reduction of -0.17 ± 0.02mm (1 week), -0.15 ± 0.02mm (1 month), and -0.16 ± 0.02mm (3 months). There was a significant difference between trabeculectomy and tube groups at 1mo (p<0.05) with mean reduction of -0.18 in trabeculectomy and -0.01 in GDD group, but no difference was found at 1 week or 3mo (p>0.05). At 3mo or later, the AL reduction is related to post-operative IOP and IOP reduction (p<0.05, Stepwise multiple regression). However, it is not related to age, gender, type of surgery and lens status (P>0.1). 6.6% (4/61) of trabeculectomy patients had hypotony after 3 months, with a mean AL reduction (-0.39 ± 0.11) that was significantly lower (p<0.01) than the other trabeculectomy eyes (-0.14 ± 0.15). There were no eyes with hypotony at 3 months following GDD. Conclusions: There is a significant, but small decrease in AL after both trabeculectomy and GDD surgery. This effect is greater in eyes that are hypotonous after surgery. Prior studies may have over-estimated AL changes after trabeculectomy because of probe pressure-induced artifact. We calculated that AL reduction can be predicted after 3mo by the formula: AL reduction (mm)=-0.199+0.0059x IOP reduction+0.0083x target IOP.

Keywords: clinical (human) or epidemiologic studies: out • intraocular pressure • anatomy