Epidemiology of cataract operations performed in public hospitals and private hospitals/ clinics in Denmark between 2004 and 2012

Transcription

1 Epidemiology of cataract operations performed in public hospitals and private hospitals/ clinics in Denmark between 2004 and 2012 Søren Solborg Bjerrum, 1 Kim Lyngby Mikkelsen 2 and Morten la Cour 1 1 Department of Ophthalmology, Glostrup Hospital, Copenhagen, Denmark 2 The Patient Compensation Association, Copenhagen, Denmark ABSTRACT. Purpose: To study the epidemiology and mortality in patients who had cataract surgery in public hospitals and private hospitals/clinics in Denmark between 2004 and 2012 and to assess the validity of the Danish cataract registries. Methods: Register- and chart-based study. Results: A total of cataract operations were performed in patients. Patients who had cataract surgery in public hospitals had an overall statistically significantly 62% higher mortality compared to patients who had cataract surgery in private hospitals/clinics. The decrease in mean age at first eye cataract surgery in private hospitals/clinics was statistically significantly greater compared to the decrease in mean age at first eye cataract surgery in public hospitals (p < 0.001). The median time interval between first and second eye cataract surgery decreased statistically significantly during the study period (p < 0.001) and was statistically significantly shorter in all calendar years for patients operated in private hospitals/clinics compared to patients operated in public hospitals (p < 0.001). In all, 46% of the cataract operations performed in private hospitals/clinics that led to cases of postoperative endophthalmitis were not registered in any registry. Conclusion: In general, patients who had cataract surgery in private hospitals/ clinics were healthier, had first eye cataract surgery at an increasingly younger age and had a reduced time interval between cataract surgeries in the two eyes compared to patients who had cataract surgery in public hospitals. The lack of registration of cataract surgery by the private hospitals/clinics limits the quality of the registries. Key words: cataract epidemiology mortality private public Acta Ophthalmol. 2015: 93: ª 2014 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd doi: /aos Introduction Like many other European countries, Denmark does not have one single national cataract registry (Behndig et al. 2013). Since 1995, it has been mandatory for all public eye departments in Denmark to register cataract surgery to the Danish National Patient Registry (NPR). In 2004, registration of cataract surgery to the NPR was also made compulsory for private hospitals/ clinics (Ministrial order no ). However, there are two exceptions to NPR registration. Ophthalmologists in private practice can have agreements with local public health providers that allow them to perform a certain number of operations without referral. These operations are performed outside the hospital system and are registered in the National Health Insurance Service Registry (NHI). The second exception is private hospitals/clinics that have made agreements with the organization of public health providers (Danish Regions) to perform cataract surgery under the waiting list guarantee. These private hospitals/clinics can register their operations in the Registry of Danish patients treated in hospitals in other countries, and activities in private specialist practice that are not settled by the health insurance agreement (DUSAS) or the NPR. Hence, all cataract surgery performed after 2004 is mandated by law to be registered in either the NPR, the NHI or DUSAS. Unlike Sweden, which has a very detailed national cataract registry (Behndig et al. 2011), the Danish registries do not contain information on, for example visual acuity, astigmatism and postoperative complications such as postoperative endophthalmitis after cataract surgery (PE). In addition, many cataract operations performed in private hospitals/clinics are not registered in the NPR (Solborg Bjerrum et al. 2013) and therefore the exact number of cataract operations in Denmark is unknown. The purpose of this paper was to study the epidemiology of cataract surgery in Denmark in the calendar 16

2 period by obtaining information on cataract surgery from the three Danish cataract registries. We wanted to compare the epidemiology of cataract operations performed in public hospitals and private hospitals/ clinics and to assess if there was a difference in the mortality of patients who had cataract surgery in public hospitals compared to patients who had cataract surgery in private hospitals/clinics. Finally, we wanted to study the validity of the registration of cataract surgery in the registries. Materials and Methods The study was approved by the Danish Data Protection Agency (journal number: ) and by the local ethics committee (journal number: H ). Data sources The Danish Statens Serum Institut is responsible for the three registries that were used as primary data sources in this study: The NPR, the NHI and DUSAS. All Danish citizens have a unique civil registration number (CRN) which is kept in the CRN Registry. We used the CRN of each individual to identify cataract operations in the three registries, to identify if more than one surgical procedure was registered in the same individual and to link cataract operations in the three registries together. The NPR was accessed on April 9, 2013, and the NHI and DUSAS were accessed on June 21, The CRN registry was accessed to determine whether the individuals found in the registries were alive on December 31, 2012, and if not, the date of death. The registries The NPR contains information on discharge summaries created after surgical procedures performed in Denmark on persons with a permanent address in Denmark. It provides information on the date of surgery, which eye that had surgery, the CRN of the patient and the WHO ICD diagnosis (WHO ICD-10 Diagnosis) associated with the treatment via the so-called SKS coding system (SKS værktøjerne). The NPR also contains information about the Nordic Medico-Statistical Committee Codes (Nomesco codes) associated with the treatment. The NHI contains information about public healthcare services such as cataract surgery between the Danish Regions and service providers such as ophthalmologists in private practise. Only operations performed in private hospitals/clinics are reported to this registry. The NHI provides information about which week of the year the operation was billed and the CRN of patient. It does not register whether left or right eye surgery was performed, and it does not use the SKS coding system. Instead, the NHI uses so-called specialty numbers and service codes. As the NHI does not provide the exact date of surgery, we defined Thursday as the day of surgery for each individual. DUSAS contains information about cataract operations that are financed by private insurances and cataract operations that are performed by so-called aftalesygehuse which are private hospitals/clinics that have made special agreements with the Danish Regions. These operations are neither reported to the NPR or to the NHI. DUSAS also holds information about patients who have cataract surgery in hospitals outside Denmark and uses the same coding system as the NPR. Like the NHI, DUSAS does not contain information on which eye that had surgery, but provides the date of surgery. Validation of the registries Cases of PE are only treated in public eye departments and these cases are in the NPR. The proportion of nonregistered cataract operations that lead to PE can thus be used as a proxy measure of the completeness of the registration of cataract surgery in the registries. We have previously conducted a study on PE (Solborg Bjerrum et al. 2013). In this study, we used the same search criteria in the NPR as previously described (Solborg Bjerrum et al. 2013) to find all PE cases that had cataract surgery on the Island of Zealand or small surroundings islands (Denmark). To validate the registries, we studied all PE cases that had cataract surgery in the calendar period January 1, 2004 June 30, The months from July 1, 2012 and forward were omitted from this analysis to ensure completeness of the data by taking into account possible registration delay. The charts of the PE cases were reviewed to confirm the diagnosis of PE and record where the cataract operation was performed. We then investigated how many of the PE cases that were preceded by a cataract operation that was registered in the NPR, the NHI or DUSAS. Inclusion criteria Patients were included if they were registered with cataract surgery in the study period January 1, 2004 December 31, Cataract surgery was divided into two groups: (1) Regular cataract surgery which is ordinary phacoemulsification cataract surgery. (2) Irregular cataract surgery which is all other cataract operations and where the cataract might be secondary to prior ocular surgery. This was performed to minimize the potential bias in the mortality analyses because some cataract operations such as combined cataract surgery with pars plana vitrectomy are only performed in public hospitals. The NPR was used to identify patients where the cataract could be secondary to prior ocular surgery in the calendar period January 1, 1996 December 31, Prior ocular surgery was defined as: surgery involving vitrectomies with the surgical codes KCKC and KCKD except KCKD60 (anterior vitrectomy), reconstructions of the cornea or sclera with the surgical code KCGG or trauma surgery on the eye with the surgical codes KCDB, KCDC or KCGF. If a patient was registered with prior ocular surgery, the cataract operation was classified as irregular cataract surgery. Patients, in which information on which eye that had surgery was missing, were also classified as having irregular cataract surgery if they were registered with prior ocular surgery. Therefore, we might have classified some cataract operations as irregular that were in fact regular if the patient underwent prior ocular surgery on the noncataract operated eye. Table 1 shows how many patients that were classified as having irregular cataract surgery because they were registered with prior ocular surgery. In the NPR, regular cataract surgery was defined as surgery 17

3 Table 1. The number of patients who had prior ocular surgery. Patients who had cataract surgery in public hospitals Patients who had cataract surgery in private hospitals/clinics Number involving the diagnosis code for age-related cataract (DH25), and the surgical code for phacoemulsification cataract surgery (KCJE20) that did not involve the surgical codes for prior ocular surgery or the diagnosis code for tumour in the eye or eye surroundings (DC69). Irregular cataract surgery was defined in the NPR as intracapsular, extracapsular or extracapsular cataract surgery with phacoemulsification involving the surgical codes KCJC, KCJD or KCJE. In DUSAS, the information on cataract surgery was not as detailed as in the NPR. Therefore, regular cataract surgery was defined as surgery with the surgical code for phacoemulsification (KCJE20), and other cataract operations were defined as irregular cataract surgery. In the NHI, the service codes did not reveal which kind of cataract operation that was performed. We therefore classified all patients as having regular cataract surgery unless they were registered with prior ocular surgery in the NPR. The following service codes were used to define cataract surgery: 5003, 5008, 5012, 5014, 5016, 5070, 5075, 5103, 5108, 5120, 5301, 6400, 6401, 6410, 6411, 6412, 6413, 6414, 6415, 6439 and Exclusions Three hundred and five patients (0.1%) were excluded because of an invalid CRN. Seventy operations in 66 patients (0.03%) with the service code 5003 were excluded from the NHI because the payment fees were too small to represent cataract surgery. A total of 1002 operations in 501 patients (0.2%) were excluded from the NHI because the operations were registered twice. MP 12.1, College Station, TX, USA. Multivariable linear regression was used to calculate the association between mean age at first eye cataract surgery and calendar year and place of surgery (public hospitals or private hospitals/clinics). Median regression was used to calculate the association between the time between cataract surgery on the first and second eye and calendar year and place of surgery (public hospitals or private hospitals/clinics), using the calendar year when the second eye had surgery. Median regression is less sensitive to outliers and minimizes the bias of the varying maximal follow-up time introduced by the study design. For example, patients who had first eye cataract surgery in the beginning of the study period were more likely to have a longer follow-up period until second eye cataract surgery than patients who had first eye cataract surgery in the end of the study period. We only included patients in this analysis who had bilateral surgery and at least 1 year of follow-up. To further minimize bias from varying follow-up time due to the study design, patients were only included if they had a maximum of 1 year between the two cataract operations. A total of patients were excluded from this analysis because the time between the two operations was more than 1 year. Another patients were excluded from this analysis because they had <1 year of follow-up. In the calculation of the standardized mortality ratio (SMR), patients were followed from the day of cataract surgery on the first eye until date of emigration, date of death or the last study date on December 31, In the SMR analyses, we used official Danish life tables from the years (Statistikbanken) to compare the mortality in our cohort of cataract-operated patients with the mortality in the background Danish population. In the SMR analyses in different calendar periods (Fig. 6), we used official Danish life tables from the years , and (Statistikbanken), to study the three calendar periods , and , respectively. Patients were only included in the SMR calculations if they were older than 50 years. Poisson regression was used to directly compare the mortality in patients who had cataract surgery in public hospitals and patients who had cataract surgery in private hospitals/clinics. All estimates were controlled for sex and age. Differences in the mortality between cataractoperated patients in public hospitals and private hospitals/clinics are reported as incidence rate ratios (IRRs). Logistic regression was used to compare odds of registered and non-registered cataract operations in the different calendar periods. A p-value <0.05 was considered statistically significant. Results A total of cataract operations were identified in patients. Regular cataract surgery was performed in 82% of the cases. In all, 85% of the operations in our study were registered in the NPR, 11.6% of the operations were registered in the NHI and the remaining 3.4% of the operations were registered in DUSAS. Statistics The data were entered into a database (Access 2010; Microsoft Corporation, Redmond, WA, USA). Statistical analyses were conducted using Stata Fig. 1. The number of registered cataract operations in the three registries throughout the study period. 18

4 The number of registered cataract operations throughout the study period is shown in Figure 1. In 2012, the number of registered cataract operations in Denmark had increased by 40.2% compared to The sex ratio of the cataract-operated patients changed during the study period. The proportion of first eye cataract-operated patients who were female decreased statistically significantly by 4.3% from 62.5% in 2004 to 58.2% in 2012 (95% CI: %, p < 0.001, linear regression). A similar trend occurred for second eye cataractoperated patients who were female. Figure 2 shows the number of registered cataract operations in public hospitals and private hospitals/clinics during the study period. Figure 2 shows that the number of registered cataract operations in public hospitals increased by 21.8% during the study period, while the number of registered cataract operations in private hospitals/clinics increased by 91.7%. Overall, 65.6% of all registered cataract operations were performed in public hospitals during the study period. The development of the median time interval between first and second eye cataract surgery during the study period is shown in Fig. 3. Figure 3 shows that the median time interval between first and second eye cataract surgery was statistically significantly higher in each calendar year for patients who had cataract surgery in public hospitals compared to patients who had cataract surgery in private hospitals/clinics (p < for each calendar year, median regression). The linear decrease in the median time interval for the entire calendar period , which did not differ statistically significantly for patients who had cataract surgery in public hospitals or private hospitals/clinics, was 2.8 days per year (95% CI: 2.73 Fig. 2. The number of registered cataract operations in public hospitals and private hospitals/ clinics during the study period. Fig. 3. The median time interval (days) between first and second eye cataract surgery during the study period. 2.87, p < 0.001). On average, the median time interval was 7 days shorter for patients who had cataract surgery in private hospitals/clinics compared to patients who had cataract surgery in public hospitals (95% CI: , p < 0.001). Validation of bilateral cataract surgery In 15.9% of the cataract operations (n = ), it was not registered which eye that had surgery. Of these, 16.9% of the operations (n = ) were in patients that were registered with one operation, 81.2% of the operations (n = ) were in patients that were registered with two operations. The remaining 1.9% of the operations (n = 1237) were in patients that were registered with three, four or five cataract operations. To include patients, in which it was unknown which eye that had surgery, we made the assumption that all patients that were registered with two operations had bilateral surgery. Two validations were carried out to validate this assumption. (1) In the NPR, we looked at all patients who were registered with two operations and where information on which eye that had surgery was available. Of these patients, only 3.3% (n = 4774) were registered with two cataract operations on the same eye. Therefore, 96.7% of the patients that were registered with two cataract operations had bilateral surgery. (2) We reviewed a total of 100 charts from public eye departments and private hospitals/clinics in patients that were registered with two cataract operations but where there was no information on which eye that had surgery. All 100 patients had bilateral cataract surgery. The number of cataract surgeries per patient is shown in Fig. 4. Figure 4 shows that 0.5% of the patients were registered with more than two cataract operations. If these patients were defined as having bilateral cataract surgery, 68% of all patients had bilateral cataract surgery during the study period. The development in the mean age at first eye cataract surgery during the study period is shown in Fig. 5. In 2004, the mean age at first eye cataract surgery in private hospitals/ clinics was statistically significantly 19

5 Fig. 4. The number of cataract surgeries per patient. Fig. 5. The mean age at first eye cataract surgery during the study period years higher compared to the mean age at first eye cataract surgery in public hospitals (95% CI: , p < 0.001, multiple linear regression). The mean age at first eye cataract surgery in private hospitals/clinics remained statistically significantly higher compared to the mean age at first eye cataract surgery in public hospitals in each year until 2008 when the difference was no longer statistically significant (p = 0.15). In the calendar period , the mean age at first eye cataract surgery in private hospitals/clinics was statistically significantly lower compared to the mean age at first eye cataract surgery in public hospitals in each year. In 2012, the mean age at first eye cataract surgery in private hospitals/clinics was 0.61 years lower compared to the mean age at first eye cataract surgery in public hospitals (95% CI: , p < 0.001). Looking at the entire study period, the mean age at first eye cataract surgery decreased statistically significantly 0.29 years per year for the cataract-operated patients in private hospitals/clinics (95% CI: , p < 0.001) and statistitically significantly 0.07 years per year for the cataract-operated patients in public hospitals (95% CI: , p < 0.001). The decrease in the mean age at first eye cataract surgery for the cataract-operated patients in private hospitals/clinics was statistically significantly greater from the decrease in the mean age at first eye cataract surgery for the cataract-operated patients in public hospitals (p < 0.001). Table 2 shows the SMR for patients in different age groups who had regular cataract surgery performed in public hospitals (n = ) or private hospitals/clinics (n = ). Patients who had cataract surgery in public hospitals had a 21% higher overall SMR compared to patients who had cataract surgery in private hospitals/clinics. In all age groups, except for the age group years who had cataract surgery in private hospitals/clinics, cataract-operated men had a statistically significantly higher SMR compared to cataract-operated women. For irregular cataract surgery, the overall SMR for patients who had cataract surgery in public hospitals (n = ) was 1.28 (95% CI: ), and the SMR for patients who had cataract surgery in private hospitals/clinics (n = 9430) was 1.02 (95% CI: ). We divided the study period into three-3-year calendar periods to analyse the development of the SMR for patients who had regular cataract surgery, see Fig. 6. The overall mortality in patients who had regular cataract surgery in public hospitals was 62% (IRR: 1.62, 95% CI: , p < 0.001, poisson regression) higher compared to patients who had cataract surgery in private hospitals/clinics. The mortality rate ratio between patients who had cataract surgery in public hospitals and private hospitals/clinics increased during the study period, being 44% higher in 2004 (IRR = 1.44, 95% CI: , p < 0.001) and 93% higher in 2012 (IRR = 1.93, 95% CI: , p < 0.001). This increase in mortality inequality between patients who had cataract surgery in public hospitals and patients who had cataract surgery in private hospitals/clinics was highly statistically significant (IRR = 1.93/ 1.44 = 1.35, 95% CI: , p < 0.001). Validation of the registration of cataract surgery In a previous study, we showed that only 27 of 72 cataract operations (38%) in private hospitals/clinics that led to PE were registered in the NPR in the calendar period (Solborg Bjerrum et al. 2013). We wanted to investigate how many of these nonregistered cataract operations that were registered in the other two registries. In DUSAS, we did not find any of the cataract operations that led to PE. In the calendar period , seven of the cataract operations that led to PE were found in the NHI. In the calendar period , three of the cataract operations that led to PE were found in the NHI. We did not find any 20

6 Table 2. The standardized mortality ratio (SMR) for patients who had regular cataract surgery in public hospitals or private hospitals/clinics for different age groups and sexes. of the cataract operations that led to PE in the NHI in the calendar period 2010-June 30, In all, 39 of 72 cataract operations (54.2%) performed in private hospitals/clinics that led to PE were registered in any of the three registries, see Fig. 7. The odds of reporting of cataract surgery by the private hospitals/ clinics were similar for the three Person-years Observed deaths Expected deaths SMR (95% CI) Patients who had cataract surgery in public hospitals Men years ( ) Men years ( ) Men years ( ) Men years ( ) Men years ( ) Total men ( ) Women years ( ) Women years ( ) Women years ( ) Women years ( ) Women years ( ) Total women ( ) Overall ( ) Patients who had cataract surgery in private hospitals/clinics Men years ( ) Men years ( ) Men years ( ) Men years ( ) Men years ( ) Total men ( ) Women years ( ) Women years ( ) Women years ( ) Women years ( ) Women years ( ) Total women ( ) Overall ( ) CI = confidence interval. Fig. 6. The development of the standardized mortality ratio (SMR) during the study period for patients who had regular cataract surgery. calendar periods (p = 0.45, test for homogeneity). Discussion The study shows that the number of registered cataract operations in Denmark increased by 40.2% in Denmark from 2004 to 2012 and that there were noticeable differences in the epidemiology of cataract surgery performed in public hospitals and private hospitals/clinics. First, patients who had cataract surgery in public hospitals had a statistically significantly higher mortality compared to patients who had cataract surgery in private hospitals/clinics during the entire period. The excess mortality in patients who had cataract surgery in public hospitals increased statistically significantly during the study period. Second, the mean age at first eye cataract surgery decreased statistically significantly during the study period, but statistically significantly more so in patients operated in private hospitals/clinics than patients operated in public hospitals. Third, the median time interval between first and second eye cataract surgery decreased significantly during the study period and to a similar extend in private hospitals/clinics and public hospitals. However, the median time interval between first and second eye cataract surgery was constantly statistically significantly shorter in private hospitals/ clinics compared to public hospitals during the entire study period. The increase in the number of registered cataract operations during the study period was primarily caused by an increase in the number of registered cataract operations in private hospitals/clinics which almost doubled between 2004 and 2012 (Fig. 2). In 2008, there was a nationwide strike among nurses at public hospitals in Denmark. This explains why there was a decrease in the overall number of registered cataract operations that year (Fig. 1), a subsequent increase in the number of registered cataract operations in private hospitals/clinics (Fig. 2) and an increase in the median time interval between first and second eye cataract surgery in public hospitals that year (Fig. 3). After 2010, the number of cataract operations in private hospitals/clinics declined. This decline in private hospital/clinic activity was most likely part of a general structural change in the Danish healthcare system, where the private market share has declined substantially within recent years. In line with a previous study (Behndig et al. 2011), we found a decrease in the proportion of cataractoperated patients who were female during the study period. In this study, we integrated data on cataract operations from all three 21

7 Fig. 7. The percentage of cataract operations in private hospitals/clinics that led to cases of PE that were registered in any registry. The numbers to the left of the stacked bars refer to the number of cataract operations that led to cases of PE. One cataract operation that was registered in the National Patient Registry (NPR) in 2005 was included in this figure as registered even though the operation was registered on the wrong eye. Danish cataract registries including some of the NPR data on cataract surgery which has been published previously (Solborg Bjerrum et al. 2013). This was performed to calculate the proportion of PE-complicated cataract operations performed in private hospitals/clinics that were registered in any registry, see Fig. 7. We found that the true number of cataract operations in private hospitals/clinics might be almost twice the number of cataract operations that are registered. Furthermore, the registration of cataract surgery by the private hospitals/clinics did not improve during the study period. In a previous study (Solborg Bjerrum et al. 2013), we have showed that an unproportionally large number of PE cases after non-registered cataract surgery were performed in a few private hospitals/clinics which performed a large number of registered cataract operations. There were major differences in the mortality of the patients who had cataract surgery in public hospitals and private hospitals/clinics. The overall mortality of the patients who had cataract surgery in private hospitals/ clinics did not differ statistically significantly from the mortality in the Danish background population, whereas the patients who had cataract surgery in public hospitals had a statistically significantly higher mortality compared to the mortality in the Danish background population. This finding is very different from the SMR results in a previous Danish study of 6352 cataract-operated eyes that had surgery at a single public eye department between 1996 and 1998 (Boberg-Ans et al. 2006). In that study, a total SMR of 1.04 was found that did not differ statistically significantly from the mortality in the Danish background population. Our study included a much larger number of eyes and reflects the mortality of Danish patients who had cataract surgery in public hospitals in the entire country, which might explain the difference. The results of the mortality analyses indicate that patients who had cataract surgery in public hospitals were not as healthy as patients who had cataract surgery in private hospitals/clinics. Overall, patients who had cataract surgery in public hospitals had a mortality that was statistically significantly 62% higher than patients who had cataract surgery in private hospitals/clinics. Furthermore, we found an increase in the mortality inequality between patients who had cataract surgery in public hospitals, and patients who had cataract surgery in private hospitals/clinics during the study period. Looking across age groups, men had a statistically significantly higher mortality compared to women in all age groups, in both public hospitals and private hospitals/clinics. Also, younger age was statistically significantly associated with higher mortality. Previous studies have documented that patients with lens changes or surgically demanding cataract have a shorter life expectancy than people of the same age and sex without lens changes or surgically demanding cataract (Podgor et al. 1985; Benson et al. 1988; Street & Javitt 1992; Klein et al. 1995; Ninn-Pedersen & Stenevi 1995; Boberg-Ans et al. 2006). One hypothesis is that when a cataract is so dense that vision is impaired, it reflects the presence of systemic factors such as diabetes that increase the mortality of the patient (Ninn-Pedersen & Stenevi 1995). Interestingly, women above 80 years in our study who had cataract surgery in either public hospitals or private hospitals/clinics had a SMR that was statistically significantly below one. This shows that it is the healthiest women who have cataract surgery at this age. One problem with the SMR calculations in this study is that the mortality of the cataract-operated patients is compared with the mortality in the background population and not to the mortality of patients without cataract. Therefore, we might underestimate the true difference in the mortality between individuals who have surgically demanding cataract and those that do not. Patients who had cataract surgery in public hospitals in the calendar period had a statistically significantly lower mean age at first eye cataract surgery compared to patients who had cataract surgery in private hospitals/clinics. The reason for this difference could be that there were waiting lists for cataract surgery in public hospitals during this calendar period, and patients that were still working or patients that needed to have their driving licence renewed were prioritized first. Looking at the entire study period, the mean age at first eye cataract surgery decreased statistically significantly both for patients who had cataract surgery in public hospitals and for patients who had cataract surgery in private hospitals/clinics, but statistically significantly more so in patients operated in private hospitals/clinics than patients operated in public hospitals. This indicates that there was a possible change in the indications for performing cataract surgery during the study period, so private hospitals/clinics performed cataract surgery in patients that were increas- 22

8 ingly younger compared to patients who had cataract surgery in public hospitals. We cannot exclude that some of the increase in the number of cataract operations by private hospitals/clinics in younger patients was also motivated by the desire to correct a refractive error. The majority of cataract operations in private hospitals/clinics are registered in the NPR where we only included cases that had a cataract diagnosis code and a surgical code for phacoemulsification cataract surgery. Here, we observed the same trend (results not shown). In the other two registries, the diagnoses are either absent or inconsistently coded, and thus, cataract surgery cannot be clearly distinguished from refractive lens surgery as the surgical code (KCJE20) is the same. We found a statistically significantly linear decrease in the median time interval between first and second eye cataract surgery during the study period which did not differ statistically significantly between patients who had cataract surgery in public hospitals and patients who had cataract surgery in private hospitals/clinics. The median time interval was statistically significantly higher in each calendar year for patients who had cataract surgery in public hospitals compared to patients who had cataract surgery in private hospitals/clinics. This shows that both public hospitals and private hospitals/clinics progressively reduced the time interval between cataract surgeries in the two eyes during the study period. There are several problems with the Danish registries. First, the lack of registration by the private hospitals/ clinics makes the registries incomplete. This is a problem in most European countries in which there is a general lack of systematic reporting of cataract surgery (Behndig et al. 2013). If we want to use the risk of postoperative complications such as PE as quality indicators of cataract surgery in Denmark, this can only be performed for registered surgery. Second, the coding procedures in the registries are not uniform, and some of the registries are incomplete. Third, there are possible errors in the registries as a few patients in this study were registered with as many as five operations. However, as only 0.5% of the patients were registered with more than two cataract operations, this is deemed to be a minor error. The NPR is the registry with the most registered operations, and the information in the NPR is much more comprehensive compared to the other registries. We hope that legislation can be adjusted so that all cataract surgery will be registered in the NPR in the future. If the registration of cataract surgery by the private hospitals/clinics becomes more complete, the Danish cataract registries can be excellent and cheap tools to monitor the epidemiology and the quality of cataract surgery in Denmark. References Behndig A, Montan P, Stenevi U, Kugelberg M & Lundstrom M (2011): One million cataract surgeries: Swedish National Cataract Register J Cataract Refract Surg 37: Behndig A, Cochener B, Guell JL et al. (2013): Endophthalmitis prophylaxis in cataract surgery: overview of current practice patterns in 9 European countries. J Cataract Refract Surg 39: Benson WH, Farber ME & Caplan RJ (1988): Increased mortality rates after cataract surgery. A statistical analysis. Ophthalmology 95: Boberg-Ans G, Henning V, Villumsen J & la Cour M (2006): Longterm incidence of rhegmatogenous retinal detachment and survival in a defined population undergoing standardized phacoemulsification surgery. Acta Ophthalmol Scand 84: Klein R, Klein BE & Moss SE (1995): Agerelated eye disease and survival. The Beaver Dam Eye Study. Arch Ophthalmol 113: Ministrial order no. 986 (2003): formation.dk. Accessed May 28, Ninn-Pedersen K & Stenevi U (1995): Cataract patients in a defined Swedish population : VII inpatient and outpatient standardised mortality ratios. Br J Ophthalmol 79: Nomesco codes (2009): Publikationer/~/media/Projekt%20sites/Nowbase/Publikationer/NCSP/NCSP%201_14. ashx. Accessed May 28. Podgor MJ, Cassel GH & Kannel WB (1985): Lens changes and survival in a population-based study. N Engl J Med 313: SKS værktøjerne (2014): Accessed May 28, Solborg Bjerrum S, Kiilgaard JF, Mikkelsen KL & la Cour M (2013): Outsourced cataract surgery and postoperative endophthalmitis. Acta Ophthalmol 91: Statistikbanken (2014): dk. Accessed May 28, Street DA & Javitt JC (1992): National five-year mortality after inpatient cataract extraction. AmJOphthalmol113: WHO ICD-10 Diagnosis (2010): classifications/icd/en/. Accessed May 28, Received on June 19th, Accepted on September 24th, Correspondence: Søren Solborg Bjerrum, MD Department of Ophthalmology Glostrup Hospital Nordre Ringvej Glostrup, Denmark Tel: Fax: sorensolborg@gmail.com Grant support has been given to Søren Solborg Bjerrum from Fight For Sight Denmark, the Synoptik Foundation, the Svend Hansen Scholarship, the Danielsen Foundation, the Foundation of the advancement of Medical Science (the A.P. Møller Foundation), the Wedell Erichsen Scholarship, the Civil Engineer Lars Andersen Scholarship and the Einar Willumsen Schorlarship. No conflicting relationship exists for any author. 23