Sun et al. administered a standardized diplopia questionnaire to 195 patients with glaucoma, including 47 patients who had undergone glaucoma drainage device (GDD) surgery, 61 patients who had undergone trabeculectomy, and 87 patients who were treated medically. The medical records of patients with diplopia were retrospectively reviewed to determine whether the diplopia was caused or exacerbated by the glaucoma procedure. Diplopia (monocular or binocular) was reported in 16 (34%) patients in the GDD group, 11 (18%) patients in the trabeculectomy group, and 14 (16%) patients in the medical group. Binocular diplopia was attributed to glaucoma surgery in 11 (23%) patients in the GDD group and 2 (3%) patients in the trabeculectomy group (p = 0.002). The authors conclude that diplopia is more common after GDD implantation compared with trabeculectomy, and it is important to counsel patients on the risk of this complication when contemplating GDD surgery.
Binocular diplopia unrelated to surgery was not uncommon in this study occurring in three (6%) patients in the GDD group, five (8%) patients in the trabeculectomy group, and ten (11%) patients in the medical group. It is noteworthy that the lowest rate of non-surgical diplopia was present in the GDD group and the highest rate was in the medical group. Although these differences were not statistically significant, they raise concern that binocular diplopia may have been more readily attributed to GDD surgery. A prospective evaluation for diplopia preoperatively and postoperatively would be expected to more accurately determine the incidence of diplopia as a complication of glaucoma surgery, and this study design was used by Dobler-Dixon et al. and the Tube Versus Trabeculectomy (TVT) Study.
The present study has other limitations. The lower range of vision in the worse eye was reported as light perception in the GDD and trabeculectomy groups and hand motion in the medical group. The study does not specify how many patients had markedly depressed vision in one eye, but it seems unlikely that these patients would experience binocular diplopia even if a motility disturbance was present. The GDD group was particularly heterogeneous, including implants of several types, unilateral and bilateral implantation, multiple implants in one eye, and prior scleral buckling procedures. Diplopia was evaluated at a single time point, which was variable and could have been as soon as one month postoperatively. It is known that bleb morphology may continue to change for several months after GDD surgery. Despite these limitations, the authors are to be congratulated for providing valuable information about the prevalence of diplopia in glaucoma patients treated both medically and surgically.