Glaucoma Drainage Device Size May Contribute to Diplopia

A glaucoma drainage device (GDD) with larger surface area or higher profile is thought to have the advantage of greater outflow. But there may also be disadvantages associated with its size or height, explains a controlled study published in the Journal of Glaucoma. Previous investigations have demonstrated that diplopia can occur in patients with a GDD, and this new analysis uses a patient-reported outcome measure (PROM) tool — the standardized, verified diplopia questionnaire (DQ) — to compare risk related to 3 implants.

Researchers at the Mayo Clinic in Rochester, Minnesota led this study, conducted from August 2017 to July 2019. Individuals at least 18 years of age were recruited at routine glaucoma appointments. Patients receiving either the Ahmed^® Glaucoma Valve Model FP7 (New World Medical, Inc.), Baerveldt^® 250 (B250), or Baerveldt 350 (Abbott Medical Optics Inc.) were compared with a medically treated control group of patients. Of 228 enrolled, 35 received the Ahmed valve, 32 obtained B250, 62 had B350 implants, and 99 individuals were included in the medically controlled group. Surgical patients completed the DQ at least 30 days postoperatively, and medically-controlled patients completed the PROM shortly after enrolling. 

Diplopia was defined as symptoms that occurred in reading or at primary distance gaze; “always,” “often,” or “sometimes,” during the week prior to taking the questionnaire. Of total participants, 23 in the GDD groups developed diplopia, while 5 control individuals reported symptoms (P =.001). Of the 23 with symptoms, 8 were FP7 recipients, 2 were in the B250 group, and 13 had B350 implants.

A pair of specialist reviewers evaluated whether each case of diplopia resulted from a GDD, based on when symptoms began, new or more severe misalignment than documented at the preoperative exam, and relevant clinical data. They determined 2 in the FP7 group had diplopia attributable to GDDs. The B250 group had zero and the B350 had 4 patients with diplopia attributable to GDDs. Patients who developed diplopia received a thorough orthoptic evaluation. Misalignment resolved in 3 GDD patients: 1 with FP7 and 2 in the B350 group.

Compared with control individuals, DQ scores were significantly higher for those in the FP7 group (P =.002), and for B350 recipients (P =.001). Because there was a greater incidence of diplopia in these 2 groups — and 5 of 6 patients with attributable symptoms exhibited ipsilateral hypertropia — the study speculates that “increased height or plate area may contribute” to diplopia by confining extraocular muscles or impeding eye movement with greater implant size, including scar tissue.

Some participants were not prescreened for strabismus or diplopia prior to surgery, due to the time frame. Limitations of this research include an uneven spread of GDD types among 12 surgeons who were internal or external to the clinic, as well as no preoperative DQ for individuals who enrolled postoperatively. Also, the low number of diplopia cases attributed to GDDs may have indicated an insufficient sample to detect significant difference between groups. A strength of the investigation is DQ’s proven test-retest reliability.

“Our findings indicate that when considering a GDD placement, patients should be counseled about the risk of developing diplopia, especially if they have pre-existing strabismus or reduced fusion range,” the study adds.

Reference

Kilgore KP, Wang F, Stern NC, et al. Rates of diplopia in Ahmed FP7, Baerveldt 250 and 350 patients compared to medical controls. J Glaucoma. Published online May 27, 2021. doi:10.1097/IJG.0000000000001886