The Auckland Cataract Study: Assessing Preoperative Risk Stratification Systems for Phacoemulsification Surgery in a Teaching Hospital


To evaluate 2 preoperative risk stratification systems for assessing the risk of complications in phacoemulsification cataract surgery, performed by residents, fellows, and attending physicians in a public teaching hospital.


Cohort study.


One observer assessed the clinical data of 500 consecutive cases, prior to phacoemulsification cataract surgery performed between April and June 2015 at Greenlane Clinical Centre, Auckland, New Zealand. Preoperatively 2 risk scores were calculated for each case using the Muhtaseb and Buckinghamshire risk stratification systems. Complications, intraoperative and postoperative, and visual outcomes were analyzed in relation to these risk scores.


Intraoperative complication rates increased with higher risk scores using the Muhtaseb or Buckinghamshire stratification system ( P = .001 and P = .003, respectively, n = 500). The odds ratios for residents and fellows were not significantly different from attending physicians after case-mix adjustment according to risk scores ( P > .05). Postoperative complication rates increased with higher Buckinghamshire risk scores but not with Muhtaseb scores ( P = .014 and P = .094, respectively, n = 476). Postoperative corrected-distance visual acuity was poorer with higher risk scores ( P < .001 for both, n = 476).


This study confirms that the risk of intraoperative complications increases with higher preoperative risk scores. Furthermore, higher risk scores correlate with poorer postoperative visual acuity and the Buckinghamshire risk score also correlates with postoperative complications. Therefore, preoperative assessment using such risk stratification systems could assist individual informed consent, preoperative surgical planning, safe allocation of cases to trainees, and more meaningful analyses of outcomes for individual surgeons and institutions.

There is growing international interest in objective preoperative risk stratification systems aimed at minimizing surgical complications and improving outcomes across all surgical specialties. With an exponential growth in demand for, and delivery of, cataract surgery worldwide there are associated increased expectations regarding outcomes. Therefore, identifying and stratifying patient risk factors is increasingly important.

Muhtaseb and associates devised a preoperative risk stratification system for phacoemulsification cataract surgery after reviewing the literature to identify the most consistently reported patient risk factors associated with intraoperative complications. They observed that the risk score, which was calculated by adding the scores for each risk factor present, was predictive of intraoperative complications. This system was subsequently validated in independent studies. The Buckinghamshire Healthcare NHS Trust uses a similar risk stratification system based on work by Butler and Narendran and associates applying the concept of cumulative risk from individual risk factors. The Buckinghamshire and Butler system has been used with trainees and consultants (Benjamin L, written communication, December 15, 2014).

The purpose of this study was to (1) confirm the validity of the Muhtaseb system in a teaching hospital setting in New Zealand, and (2) concurrently evaluate the Buckinghamshire system in the same setting. If validated, we anticipate that clinical application of such preoperative risk stratification systems may enable a reduction in intraoperative complications associated with phacoemulsification cataract surgery.


A cohort study was conducted of 500 consecutive cases of phacoemulsification cataract surgery performed between April 9, 2015 and June 12, 2015. All surgeries were performed at Greenlane Clinical Centre (GLCC), Auckland District Health Board (ADHB), Auckland, New Zealand—the largest ophthalmic center in New Zealand that serves over 23% of the population. The study protocol was approved by the ADHB research committee and the study adhered to the tenets of the Declaration of Helsinki.

Preoperatively, 1 investigator (B.K.) reviewed the clinical notes for each case to calculate 2 separate risk scores—an “M-score” using a risk stratification system devised by Muhtaseb and associates and a “B-score” using a system from the Buckinghamshire Healthcare NHS Trust. Each system allocates points to each risk factor according to its potential risk for an intraoperative complication. The investigator added up the points for all risk factors that were documented in the preoperative consultation notes to give a final M- and B-score for each case ( Table 1 ).

Table 1

Preoperative Risk Factors as per the Muhtaseb and Buckinghamshire Risk Stratification Systems for Cataract Surgery

Risk Factor M-Score a B-Score b
Age (y) >88 years 1 80–90 years 1
90+ years 2
Ametropia (>6 diopters of myopia or hyperopia) 1
Axial length <21.5 mm 2
>26 mm 1
>30 mm 2
Brunescent/white/dense/total cataract/no fundus view 3 3
Corneal scarring 1
Diabetic retinopathy 1
Fuchs endothelial dystrophy 1
Only eye 1
Oral alpha-receptor antagonist Doxazosin 1
Tamsulosin or similar 2
Phacodonesis 3 3
Pseudoexfoliation 3
Posterior capsule plaque 1
Posterior polar cataract 1
Previous vitrectomy 1 1
Shallow anterior chamber (<2.5 mm) 1 1
Small pupil <3 mm 1 2
Miscellaneous risks assessed by the surgeon (eg, poor position/cooperation) 1 2
Maximum score 18 22

a M score: risk score for intraoperative complications in cataract surgery using the Muhtaseb risk stratification system.

b B score: risk score for intraoperative complications in cataract surgery using the Buckinghamshire risk stratification system.

All surgeons were masked to the risk scores and perioperative management was provided as per routine protocol at GLCC. All study data were entered into a password-protected computerized database. Ethnicity was recorded as self-identified by the patients. In New Zealand, “Asians” are commonly defined as peoples from East, South, and Southeast Asia.

Following surgery and the routine 4- to 6-week postoperative follow-up, the investigator (B.K.) reviewed all clinical/surgical notes to collect data on surgeon level (resident/registrar, fellow, attending physician/senior medical officer), any intraoperative complications (capsular tear, zonular dialysis, iris prolapse, iris trauma, vitreous loss, dropped nucleus, choroidal hemorrhage, wound complication, other), postoperative complications (cystoid macular edema, corneal edema, uveitis, endophthalmitis, retinal detachment, elevated intraocular pressure over 21, other) and corrected-distance visual acuity (CDVA).

Statistical advice was sought from professional biostatisticians. Statistical analyses were performed using SPSS version 22 (Statistical Package for the Social Sciences GmbH Software, Munich, Germany). Logistic regression analyses were conducted to identify trends in complication rates with regard to risk scores and surgeon groups. The validated Muhtaseb system was used to calculate case-mix adjusted odds ratios between surgeon groups. Z-tests were performed for comparison of proportions. P values <.05 were considered statistically significant.


Phacoemulsification cataract surgery was performed on 498 of the 500 consecutive cases (496 patients). The mean age was 72.3 ± 11.9 years (range 15–96 years) and 57% were female. New Zealand European/European ethnicity made up 55.6% of the study population. Two cases could not proceed to phacoemulsification owing to complications and had to return for combined surgery—1 case with an M-score of 7 and B-score of 7 was abandoned owing to severe iris prolapse prior to phacoemulsification and returned for a phacovitrectomy; a second case with high myopia and keratoconus that had an M-score of 7 and B-score of 8 was abandoned after corneal incisions because of severe zonular weakness and returned for intracapsular cataract extraction (ICCE) and penetrating keratoplasty. Both cases were planned for and performed by attending physicians.

The median M-score was 0 and over 90% of cases scored M < 4 (n = 463, 92.6%). The median B-score was 1 and 469 cases (93.8%) scored B < 5. The complication rates increased with an increasing M-score ( P = .001) or B-score ( P = .003) ( Figure 1 ). The baseline intraoperative complication rate for a case with no significant risk factors (M-score of 0) was 7.2% (95% confidence interval [CI] 4.2%–10.3%). The complication rate increased significantly compared to baseline with an M-score >3 ( P = .021). With the Buckinghamshire system, the baseline intraoperative complication rate for a case with no significant risk factors (B-score of 0) was 9.2% (95% CI 4.9–13.6). The complication rate increased significantly compared with baseline with a B-score >6 ( P = .001).

Figure 1

Intraoperative complication rates (with 95% confidence interval) for each risk score based on the Muhtaseb and Buckinghamshire preoperative risk stratification systems for cataract surgery (N = 500). M-score: risk score using the Muhtaseb risk stratification system. B-score: risk score using the Buckinghamshire risk stratification system. Results were not graphed if there were fewer than 2 cases with the same risk score to avoid obscuring possible trends.

Surgery was performed by 1 of 36 surgeons—8 residents, 6 fellows, 22 attending physicians—with or without assistance from a second surgeon. Residents performed 93 cases (18.6%), fellows 109 (21.8%), and attending physicians 298 (59.6%), with various mixtures of risk scores ( Figure 2 ).

Figure 2

Proportion of phacoemulsification cases performed by residents, fellows, and attending physicians, per risk score, using the Muhtaseb risk stratification system (N = 500). Data labels indicate number of cases performed.

There were 42 cases (8.4%) that had an intraoperative complication. In comparison to attending physicians, residents or fellows did not have a significantly higher or lower odds ratio before and after case-mix adjustment using the preoperative M-scores ( Table 2 ).

Table 2

Unadjusted and Adjusted Odds Ratios per Surgeon Grade for an Intraoperative Complication in Phacoemulsification Cataract Surgery (95% Confidence Interval)

Surgeon Grade Unadjusted OR P Value Adjusted OR a P Value
Attending 1.00 .55 1.00 .40
Fellow 0.75 (0.31–1.79) .52 0.72 (0.30–1.73) .46
Resident 1.32 (0.61–2.85) .49 1.45 (0.66–3.18) .36

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Jan 5, 2017 | Posted by in OPHTHALMOLOGY | Comments Off on The Auckland Cataract Study: Assessing Preoperative Risk Stratification Systems for Phacoemulsification Surgery in a Teaching Hospital

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