It is postulated that a lengthy intermission of performing surgery, as happened in the first COVID-19 wave, could induce fading of surgical skills, hence resulting in increased complication rates. However, our results show that the enforced two-month surgical intermission at the peak of the COVID-19 pandemic in 2020 does not increase surgical complication rate when elective cataract operations were resumed.

Contrary to our expectations, a significant decrease in complication rate was observed compared to the period prior to the intermission, which seems to superimpose on the downward trend when benchmarking with previous years. Nevertheless, with the exception of the last two years, we have not taken in account the percentages of risk factors for complications, as well as for factors restricting patients' vision. Both percentages seem higher for the cases of 2019 compared to those in 2020. This can cause selection bias and hence can have had influence on the observed downward trend over the years. Since this latter aspect is beyond the scope of our research, we have not analyzed this any further. The possible decline in complication rates over the years might be partially explained by a better training of ophthalmologists and ophthalmology residents, technological perfection of equipment, and a reduction of infections that could be attributed to an increased use of intracameral antibiotics. The decrease in postoperative complications after the surgical lockdown seems to be mainly on account of the reduction in (corneal and macular) edema.

We hypothesize that the decrease of postoperative complications after surgical lockdown might be more COVID-related. The COVID-19 pandemic has caused changes in capacity management in hospitals, such as a reduction of the number of operations performed daily [7], thereby decreasing time pressure on ophthalmologists. Furthermore, the enforced intermission and consequent restart of surgeries might result in some sort of reset, including extra awareness and cautiousness, when resuming surgery. This is supported by a study of Tzamalis and colleagues who report an increased duration of cataract surgery, presumably due to ophthalmic surgeons being more careful upon the restart of surgery following the COVID-19 induced intermission [8]. Moreover, due to the COVID-19 pandemic hygiene practices were intensified, which could also have contributed to lower complication rates [9].

In accordance with our results, Tzamalis did not find a significant COVID-19-related change in intraoperative complication rates [8], although only the first 160 cases performed by eight consultants after the surgical lockdown were evaluated. Opposite to our findings, a study by Matarazzo and colleagues found an increased complication rate of posterior capsule ruptures (PCR) after the restart of elective cataract surgeries during the COVID-19 pandemic [10]. However, they only evaluated the complication rate of a single center while our research considers the performance of ophthalmologists working in virtually all hospitals in the Netherlands. More importantly, with an intermission period of 19 weeks, their study period of surgical abstinence was twice as long compared to our study. Theodoraki and colleagues in the United Kingdom looked at the incidence of PCR and postoperative cystoid macular edema (PCME) after two months of surgical lockdown in 2020 and evaluated an approximate 7-month period of operations after the lockdown [11]. They did not find a difference in PCR in these seven months, compared to an 11-month period prior to the pandemic. However, after a second surgical lockdown in January 2021, PCR rates were increased. This is in accordance with our results, but in contrast with the findings of Matarazzo [10]. In the study of Theodoraki, opposite to our findings, higher rates of PCME were noted after both surgical lockdowns (Fig. 1A) [11].

Note added in proof: recently, an American group independently obtained similar results [12]. Although there was a higher frequency of complex cataract surgeries performed post-shutdown, intraoperative complication rates before versus after the operation shutdown were not statistically significant. Nevertheless, this study contains a small sample size (306 eyes before and 174 eyes after shutdown were included).

An intermission of two months does not seem to compromise cataract surgical skills, which can be reassuring for both physicians and patients. A practical implication of our study could be that other causes for a leave of absence of two months, such as illness or a sabbatical, most likely will not negatively affect surgical performance. However, for a longer period the opposite may be true [10, 11].

There are some limitations of this study. Registration of complication data can be hampered by incomplete or incorrect data submission into the DCCR database. Cataract surgery combined with corneal, glaucoma or vitreoretinal procedures could not be excluded from the database. Furthermore, the DCCR does not include any information about the surgeon, hence it is not possible to differentiate between residents and ophthalmologists. It seems plausible that the consequences of a long-lasting interruption in surgical activities might have had a greater impact on the former group [5]. Nevertheless, the study of Das and colleagues (although their sample size being small) does not seem to confirm this assumption [12]. A survey enrolled in the United Kingdom found that especially residents reported to have reduced confidence and increased anxiety when restarting surgery after the forced COVID-19 surgical recess [13].

Future research might further investigate complication rates of individual cataract surgery complications to enhance awareness which complications might be more likely to occur after a surgical recess. In addition, it would be interesting to conduct similar research for other, non-ophthalmological elective surgical procedures which were postponed, to evaluate if comparable observations can be made in other surgical fields.