Complex cataract extraction, characterized by poor pupillary dilation with or without poor capsular visualization, intuitively requires a higher level of technical skill compared to more routine procedures. There are varying reports on residents’ learning curve in phacoemulsification in terms of the rates of intraoperative and postoperative complications with increasing training experiences. Some studies [7, 8] found no difference, while others [9,10,11,12,13,14] reported that complication rates decline with increasing surgical experience. Aaronson et al. [10] reviewing 14,520 cataract surgeries reported that complication rates (posterior capsule rupture and/or loss of capsular bag support) decline with increasing surgical experience, also among residents over time. Randlewood et al. [15] found that residents continue to improve their surgical competency (complication rates and phacoemulsification efficiency) significantly well beyond the first 80 resident phacoemulsification cases.

Our resident cohort had no prior experience performing cataract extraction before their training. Resident-performed cases are attended by experienced surgeons who teach the procedure by providing graduated autonomy and real-time assistance and guidance on a step-by-step basis. As it is not possible to retroactively assess the relative involvement of the attending surgeon from the medical record alone, a longitudinal assessment of resident complications throughout their training was not a focus of this analysis.

Our analysis demonstrated an overall vitrectomy rate for resident surgeons of 5.5% (range 4.24–12.35%), similar to prior reports in the literature (range 4.04–15%) [9, 16, 17]. Furthermore, we found the rates of a major complication requiring an unplanned vitrectomy to be higher for complex cases requiring pupil expansion, independent of other potential anatomical factors. There were no statistically significant differences in axial length (P=0.144), anterior chamber depth (P=0.203), main cataract types or severity (P=0.015 for type, P=0.118 for NSC severity, P=0.627 for CC severity, P=0.614 for PSC severity) between the “Vitrectomy” and “No-Vitrectomy” groups. In the multivariate analysis, patients with mainly posterior subcapsular and white/mature cataracts had higher odds of surgical complications compared to patients with mainly nuclear sclerotic cataracts, consistent with several other studies [4, 9, 18].

There are additionally varying reports in the literature on the rate of intraoperative complications in patients with limited pupillary dilation [4, 9, 18,19,20]. The largest study reviewing 55,567 cases performed by 406 surgeons (of all experience levels) in the UK reported an adjusted odds ratio of 1.45 (95% CI 1.10–1.91; P=0.0231) for complications in patients with small pupils compared to those with medium and large pupils [4]. Our data similarly demonstrated an increased odds of a major complication, namely, vitreous loss, when a pupil expansion device was used; cases requiring a PED had a higher odd (OR=4.64, P=0.01) of requiring an unplanned PPVx compared to routine cases. It is important to note that these complications occurred despite the usage of PED, as our analysis was designed to analyze the association and not necessarily causation. Although the use of PED improves visualization and limits iris prolapse, these eyes may have additional factors (e.g., case duration, anterior chamber stability, and anesthesia considerations) that increase the likelihood of complication beyond the additional technical skills required for placement and removal.

Pseudoexfoliation syndrome is known to complicate cataract surgeries due to poor mydriasis, weak zonular support, and high intraocular pressure [21, 22]. Interestingly, many recent studies have found lack of significant association of pseudoexfoliation syndrome and vitreous complications [18, 23, 24]. This indicates that not all patients with pseudoexfoliation syndromes are at a high risk, and further preoperative evaluation of these patients may be warranted for assessment of their operative risk; one such suggestion is a new clinical classification for predicting the zonular strength based on the maximum pupillary dilation [25].

Our findings are echoed by Williams et al. [26], which reviewed 5,772 eyes that underwent phacoemulsification (including 4,905 non-complex, 500 complex without iris manipulation, and 367 complex with manipulation). Williams et al. [26] found that the incidence of any intraoperative complication in complex cases, regardless of iris manipulation, is significantly higher than in the non-complex phacoemulsification (P<0.0001). However, when comparing intraoperative complications in complex cases with and without iris manipulation, there were no statistically significant differences in rates of posterior capsule rupture, vitreous loss, retained lens, and zonular dialysis (P=0.623, 0.692, 0.622, and 0.457, respectively). In addition, the authors found that only complex cases with iris manipulation led to increased rates of postoperative inflammation (OR=2.3; P=0.005) and IOP spikes of more than 10 mmHg (P=0.001); they suggest that direct iris manipulation, as opposed to just the case complexity, is associated with postoperative inflammation and IOP spikes [26].

Additional vitrectomy rates were not statistically different between the two types of PED analyzed (Malyugin rings and iris hooks); this finding is supported by Nderitu and Ursell [20] who found that despite longer operating time, iris hooks are as safe and effective as Malyugin rings with similar intraoperative complications. However, they also reported there was a significantly increased risk of postoperative complication (anterior uveitis, corneal edema, etc.) with the use of the Malyugin ring (6.7%) compared to routine cases (2.6%), or cases utilizing iris hooks (1.1%) [20].

There is a great deal of variability in the criteria for use of capsular dye, as many contributing factors can dictate the use of these devices (supervising attending preferences, microscope parameters, resident experience levels, etc.). It is indeed the case that even highly trained surgeons utilize capsular dye to improve visualization in routine cases, and the use of dye should not necessarily be interpreted as an absolute indicator of case complexity. When we compared “Routine” cases to “Dye-only,” there were no significant differences in the odds of an AVx and/or a PPVx, indicating that the use of dye did not have an impact on complication rate. When comparing “PED-only” cases to both the “Routine’ and “Dye-only” groups, there were significantly higher odds of vitreous loss requiring a PPVx (OR=4.64, P=0.01 and OR=6.48, P=0.005, respectively). The higher odds ratio noted here when comparing the “PED-only” to the “Dye-only” group suggests that the use of a PED without capsular dye purports a higher risk of a complication; however, when we analyzed complication rates for the “PED-only” and “Both” groups, there were no statistically significant differences in vitrectomy rates. These results demonstrate that the routine use of capsular dye does not have a definitive impact on complication rate, and surgeons (of all levels of expertise) should use capsular dye based on individual case requirements and preferences. We can furthermore infer that the complications associated with the use of a PED were not related to diminished anterior capsule visualization and were secondary to any number of the other potential complicating factors (Tables 1, 2, 4, and 5) that limit anterior chamber stability and visualization. Regardless, resident-performed cases where pupil expansion was required had significantly higher odds of complication, and it is critical for supervising attendings and perioperative services to be appropriately prepared for potential complications given the magnitude of this association.

A major limitation of this study is related to the retrospective nature of the chart review. However, we believe operative reports consistently describe when major complications such as vitreous loss and lens subluxation occur, and the rates of complications reported are representative of actual surgical events. Regardless, the details of why and how a complication occurred are variably described, and it is important not to ascribe causality from an association without a carefully designed prospective analysis to evaluate that specific question. Higher complication rates due to capsular compromise and zonular instability occur in cases where PEDs are utilized, but not necessarily as a direct result of their use. An additional limitation results from variable levels of resident participation in surgery, which is often not recorded in the operative report. A more comprehensive analysis with a larger sample is warranted to further assess the impact of the various factors that increase case complexity to help further minimize vision-threatening complications.