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    Diplopia in glaucoma patients is more prevalent than previously thought, occurring in 1 and 5 patients whether they are treated medically or surgically. The condition was most common following glaucoma drainage device surgery, especially the Baerveldt 350.

    Diplopia is a known complication of glaucoma treatment, but it has not been rigorously studied across the spectrum of medically and surgically treated patients with glaucoma, and it has never been assessed prospectively with an instrument specifically designed to assess diplopia.

    The authors of this prospective study used the Diplopia Questionnaire, a patient-reported outcome measure designed to assess symptoms of diplopia in specific gaze positions, to assess the incidence of diplopia in 195 adults who were either treated medically or had undergone glaucoma drainage device surgery (Baerveldt 350, Baerveldt 250 or Ahmed FP7) or trabeculectomy.

    Patients who responded “sometimes,” “often” or “always” in distance straight ahead or reading positions on the Diplopia Questionnaire were deemed to have diplopia. A chart review was performed jointly by a strabismus specialist and a glaucoma subspecialist to characterize the type and cause of the diplopia.

    The overall incidence of diplopia was 21%. Binocular diplopia was significantly more common after filtering surgery compared with trabeculectomy (23% vs. 3%, P=0.002), especially among patients who received a Baerveldt 350. The most common type of strabismus associated with binocular diplopia following glaucoma surgery was hypertropia (10/11 filtering surgeries, 2/2 trabeculectomies). Diplopia was also more common in patients with multiple and bilateral drainage devices.

    Monocular diplopia was found in a similar proportion of patients treated medically, post-trabeculectomy and post-filtering surgery (5%, 7% and 4 %, respectively). Binocular diplopia not due to surgery was found in similar proportions after filtering surgery, trabeculectomy and medically treatment (11%, 6% and 8%, respectively).

    One drawback of this study was the inability to standardize for the location of implants and trabeculectomy. Regardless, it does appear that diplopia is very common and we need to thoroughly evaluated patients after glaucoma surgery. The authors suggest that it may be helpful for patients undergoing glaucoma surgery to have a standardized assessment of diplopia and strabismus both before and after surgery.