Glaucoma Surgery “Failure” Ill-Defined, Varies Widely in Studies

IOP-based classifications are poor surrogates for postoperative VF progression rates. Long-term VF rates provide a more relevant outcome measure and may be incorporated into composite success criteria. Photo: Brian D. Fisher, OD. Click image to enlarge. Using visual field (VF) stabilization as a research study endpoint in trials of glaucoma surgery is resource-intensive, requiring large sample sizes, extended follow-ups and frequent testing. But it’s more reflective of the success or failure of surgery than intraocular pressure (IOP), which is most often used as a surrogate marker, researchers argue in a recent paper for American Journal of Ophthalmology. While IOP is simpler to measure and provides an assessment of the immediate effect of surgery, its correlation with VF progression is variable. Some patients may continue to experience VF deterioration despite maintaining low IOP levels, while others with elevated IOP may exhibit no progression. Although the thresholds defining failure are fairly standardized with regard to the specific IOP cutoff, guidelines on their practical application remain somewhat ambiguous, with numerous minor variations in the definition of success. The researchers reviewed IOP thresholds used as failure criteria in glaucoma surgical outcome studies, evaluated their impact on success rates and examined the relationship between surgical success criteria and VF progression rates. Their findings underscored that even the most effective IOP-based criteria are poor surrogate outcomes for long-term visual field preservation.“Our results suggest that defining success based on IOP thresholds may be weak because minor variations in failure criteria can significantly alter estimated success rates, with results ranging from poor to outstanding depending on the specific set of criteria used,” the study authors wrote in their paper. “Therefore, the results from studies using slightly different criteria should be interpreted with caution and cannot be directly compared. This may be problematic when pooling the results from different studies.”From 2,503 initial studies, the team included 277, identifying 144 using high IOP failure criteria. The 21mm Hg criterion variations showed success rates at five years ranging from 8.7% to 74.0% for trabeculectomy and 22.1% to 89.9% for deep sclerectomy. The median Cohen’s kappa for 21mm Hg criteria indicated fair agreement (0.39 for trabeculectomy, 0.42 for deep sclerectomy). A subset of 199 trabeculectomy eyes were eligible for the VF analysis. Overall, the median postoperative progression rate was -0.36dB/year. Distributions of progression rates greatly overlapped between failure and success groups as defined by the various criteria.When looking at the relationship between VF rates and IOP-based criteria, patterns emerged. Criteria that required the presence of IOP above predefined cutoffs in more than one visit or for an extended period, and after a time window from the original surgery, performed better overall than those based on a single IOP measurement above the threshold at any point after surgery. The researchers did not find this surprising, as early postoperative IOP values may not reflect the long-term IOP control of a successful operation.“We believe that such a composite criterion better reflects the goal of surgery, which is to reduce IOP sufficiently to preserve visual function while avoiding vision-threatening complications,” the study concluded. “Our hope is that future guidelines will prioritize defining success and failure based on clinically meaningful criteria rather than arbitrary thresholds.”Click here for the journal source. Rabiolo A, Triolo G, Servillo A, et al. Evaluating high intraocular pressure criteria for failure in glaucoma surgery: impact on estimated success and visual field rates. Am J Ophthalmol. July 3, 2025. [Epub ahead of print].