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High-volume surgery, fewer complications

Swedish study finds lower complication rates may be due to lower case mix.

Howard Larkin

Posted: Wednesday, July 29, 2020

Lower capsule complication rates often seen among the high-volume cataract surgeons, as well as for most surgeons in recent years, may be due to more favourable case mixes, according to a Swedish National Cataract Register study.
Speaking at the 37th Congress of the ESCRS in Paris, Madeleine Zetterberg MD, PhD, reviewed a study based on data from more than 118,000 cataract surgeries performed in Sweden from 2007 through 2016. It found that surgeons doing fewer than 1,000 procedures annually had higher mean posterior capsule rupture rates than those doing 1,000 or more – 2.15% for those doing 10 to 99 cases, 1.32% for 100 to 499 cases and 0.59% for 500 to 999 cases, compared with 0.48 and 0.47% for 1,000 to 1,499 and 1,500+ cases respectively.
However, the study also found that high-volume surgeons had significantly lower mean case mix risk scores – 1.34 for those doing 10 to 99 cases, 1.49 for 100 to 499 cases, and 1.28 for 500 to 999 cases, compared with 1.15 and 1.14 for 1,000 to 1,499 and 1,500+ cases respectively.
High-volume cataract surgeons have a slightly lower-case mix, which may explain their lower rate of capsule complications, said Professor Zetterberg, of the University of Gothenburg, and Sahlgrenska University Hospital, Mölndal, Sweden.
“The difference was not all that great, though. The high-volume surgeons are still doing a lot of complicated cases.”
Similarly, the study found that case mix risk scores declined slightly from 2007 through 2016. This suggests that improving case mix may also be a factor in improvements in capsule complication rates seen over the period, Dr Zetterberg added.
>Developing a risk score
To perform the analysis, Professor Zetterberg and colleagues first developed a risk score for assessing case mix difficulty. Logistic regression analysis of data on a range of demographic, clinical and operative difficulty parameters found several that were significantly linked with increased posterior capsule rupture.
These were preoperative best correct visual acuity of less than 0.1, or 20/200; pseudoexfoliations; sight-threatening ocular comorbidity; use of trypan blue, which is a marker for dense cataracts; mechanical pupil dilation, which is a marker for small pupils; and iris hooks at the rhexis margin, which represent zonular dehiscence.
“These were all very highly associated with increased capsule complications,” Dr Zetterberg noted.
A composite risk score was created based on these parameters by multiplying out the odds ratio for each parameter. A score was assigned for each cataract case. Individual risk scores were averaged for each surgeon and for each volume group.
For surgeons with 100-499 cases, per surgeon mean risk scores ranged from 1.01 to 5.19, with individual risk scores for patients in this group ranging from 1.00 to 62.90. For surgeons with 500-999 cases, per surgeon mean risk scores ranged from 1.00 to 2.02 with individual patient risk scores from 1.00 to 62.90. Surgeons with 1,000 to 1,499 cases saw per surgeon risk scores of 1.01 to 1.27 with individual patient case scores of 1.00 to 46.59. Surgeons operating more than 1,500 cases had per surgeon mean scores of 1.06 to 1.26 with individual patient scores of 1.00 to 46.59.
Among the study’s other findings were that ocular comorbidity increased from about 30% of cases in 2007 to 37% in 2016, while cases with BCVA ≤ 0.1 decreased from 20% of cases to about 10%.
In addition to the case mix and complication correlations, the study found that the proportion of cases performed by surgeons doing 1,000 to 1,499 and 1,500+ cases increased significantly in recent years, to about 21% and 12% of total volume respectively in 2016.
Those doing 500-999 cases increased slightly and accounted for the biggest slice of volume at about 35% in 2016. This mid-volume group edged out in 2014 those doing 100-499 cases, which declined from a 60% market share in 2007 to about 30% in 2016.

Madeleine Zetterberg: madeleine.zetterberg@gu.se