Prevalence of Pseudophakia: A U.S. Population-Based Study

Abstract

Purpose:

To determine current prevalence and trends of pseudophakia in a well-defined U.S. population, calculating values for Olmsted County, Minnesota from 1988 through 2018.

Setting:

Mayo Clinic, Rochester, Minnesota.

Design:

Population-Based Cohort Study.

Methods:

Rochester Epidemiology Project (REP) databases were used to identify all cases of pseudophakia in Olmsted County, Minnesota, between January 1, 1988, and December 31, 2018. Age- and sex-specific prevalence rates were calculated in 1988, 1998, 2008, and 2018 using REP census population estimates and mortality counts. Poisson regression analysis was used to assess changes in prevalence over time. Mortality rates were estimated by Kaplan-Meier analysis.

Results:

In 2018, 10,024 county residents were pseudophakic in at least one eye, for a total population prevalence of 6.5%. Prevalence increased 67% in the last 10 years and 590% in the last 30 years (P<0.001). By 2018, 51% of residents aged 75 years and 88% of residents aged 85 years and older were pseudophakic in at least one eye, 53% of pseudophakic residents 65 years and older were bilaterally pseudophakic, and 29% of pseudophakic residents had lived with pseudophakia for more than 10 years. Prevalence was higher among women than men and increased with age (P<0.001). Overall, pseudophakia had a lower all-cause mortality compared to the general Minnesota population (P<0.001).

Conclusion:

In 2018, the majority of residents aged 75 years and older were pseudophakic in at least one eye. These numbers underscore the changing visual status of older adults and the large number of adults who benefit from cataract surgery.

INTRODUCTION

Cataract surgery rates have increased worldwide over the last decades.^1–4 In the United States, an estimated 3.8 million cataract surgeries are performed annually.⁵ Increasing cataract surgery rates coupled with improvements in surgical techniques and outcomes, and a growing demand for improved vision have led to a large pool of Americans living with pseudophakia.

Prevalence of pseudophakia describes the proportion of individuals living with pseudophakia on a certain date regardless of how long ago the cataract surgery was performed. Current data on the prevalence of pseudophakia is important as it allows assessment of the impact of pseudophakia on a population and its health-care system, as well as assessing changes in the visual status of older Americans. To date, population-based studies providing a descriptive epidemiology of pseudophakia among population groups relevant to the United States are now well over a decade old.^{3, 6–13}

While individuals living with pseudophakia have improved vision and an improved quality of life,^14–15 an increase in the prevalence of pseudophakia also creates a need to effectively manage the long-term eye care requirements of this growing population and to address the burden of subsequent procedures (i.e. YAG capsulotomy) and complications, such as retinal tears or detachments.

Because recent U.S. population-based estimates of pseudophakia prevalence are few, we sought to determine the current prevalence and historical trends of pseudophakia in a well-defined United States population, by calculating values for Olmsted County, Minnesota over the 30-year period of 1988 through 2018.

METHODS

This study complied with the Health Insurance Portability and Accountability Act and was approved by the Institutional Review Boards of Mayo Clinic and Olmsted Medical Center; data was only included from subjects who had provided authorization to review their medical records for research.

Data Sources

Data was obtained by using the resources of the Rochester Epidemiology Project (REP), a medical records linkage system that has linked and archived the medical records, diagnoses, surgical interventions, and demographics of virtually all persons residing in Olmsted County, Minnesota for over 50 years.^16–17 The REP takes advantage of the fact that more than 95% of Olmsted County residents receive their healthcare from two institutions: the Mayo Clinic (plus its 2 affiliated hospitals) and the Olmsted Medical Center (plus its affiliated hospital).¹⁷ Medical records generated by all healthcare providers are linked and recorded in a central diagnostic index. Thus, the REP provides a data retrieval system of essentially all patient-physician interactions in Olmsted County, a relatively isolated, semi-urban community (2020 population 160,228).^16–18 Only a small proportion of residents (approximately 2%) do not allow any of their medical records to be used for research.¹⁸

The characteristics of the population are very similar to the populations of Minnesota and the Upper Midwest and are comparable to the entire US population regarding age, sex, and mortality rates. However, Olmsted County is less ethnically diverse (83.6% vs. 72.4% white) and more educated (91.1% vs. 80.4% high school graduates) than the rest of the United States.¹⁸

Pseudophakia Cohort

We used REP databases to identify all county residents diagnosed with pseudophakia in at least one eye between January 1, 1988 and December 31, 2018 to estimate pseudophakia prevalence rates and to assess historical trends within the defined population of Olmsted County. Primary cataract surgeries and pseudophakia were retrospectively identified by using the International Classification of Diseases, 9^th Revision, ICD 9–10 diagnosis codes and Current Procedural Terminology, CPT Procedure codes as described previously.^4,12 Included were cataract extractions performed by phacoemulsification, extracapsular cataract extraction, intracapsular cataract extraction, lens aspiration, and pars plana lensectomy as a primary procedure or as a combined procedure with penetrating keratoplasty, trabeculectomy, or glaucoma shunt procedure. Excluded were pars plana lensectomy when combined with a vitreoretinal procedure to improve surgical visualization, cataract extraction in the surgical management of ocular trauma, and aphakia. The usefulness of the REP in providing a complete description of all diagnoses and surgeries within the Olmsted County population is well established.¹⁷ Case over-ascertainment has been identified as less than 1% in prior REP reviews.¹⁹

Data Collection and Analysis

REP resources provided sex, age, and duration of time since initial or second eye cataract surgery for every identified case. Contralateral eye surgery is common, and REP data allowed us to longitudinally follow all residents after their initial surgery to capture all second eye surgeries in order to avoid double counting cases.

The age- and sex-adjusted prevalence of pseudophakia was calculated for each time period by dividing the number of pseudophakia cases by REP census population estimates. REP census data provide a validated, virtually complete enumeration of County populations at any point in time.^17–18 Prevalence rates were described as percentages. Poisson regression test was used to analyze changes in prevalence over time and between genders. Error of distribution was utilized to calculate 95% confidence intervals. Kaplan-Meier survival analysis was used to determine all-cause 10-year mortality rates within the cohort. A one-sample log-rank test was used to compare the observed mortality within the cohort to the expected mortality rate in the general Minnesota population. Expected mortality within the general Minnesota population was constructed using age- and sex-specific death rates obtained by using resources of the Minnesota State Demographers Office. All statistical analyses were performed with Statistical Analysis System 9.4 (SAS, Cary, North Carolina, USA).

RESULTS

The pseudophakia study cohort included 10,204 individuals (4,099 men, 6,089 women) in 2018 of which 85.5% were white, 5.5% Asian, 4.8% black, and 4.2% Hispanic, as well as 5,488 individuals (2,138 men, 3,350 women) in 2008; 2,690 individuals (915 men, 1,775 women) in 1998; and 1,181 individuals (372 men, 809 women) in 1988. The mean age at initial cataract surgery was 76 years ±11 in 1988, 76 years ± 10 in 1998, 74 years ± 10 in 2008, and 73 years ± 10 in 2018.

The 2018 prevalence of pseudophakia in at least one eye among the total Olmsted County population was 6.5% (5.4% men, 7.6% women), and among adults 50 years of age and older was 20.4% (17.6% men, 22.9% women). Pseudophakia prevalence increased significantly with age (Figure 1, Table 1, P<0.001), and was higher among women than men (P<0.001). In 2018, pseudophakia replaced bilateral phakia as the predominant visual status for all residents aged 75 years and older, reaching 51% in residents aged 75–79 years, 67% in residents aged 80–84 years, and 88% in residents aged 85 years or more. (Figure 1). Pseudophakia in at least one eye surpassed 50% prevalence at an earlier age in women than in men (74 years and 79 years, respectively; P<0.001).

Figure 1.

Age-specific 2018 prevalence of pseudophakia in at least one eye among the total population of Olmsted County, MN. Insert shows age-specific prevalence of pseudophakia among living residents by year in the 8^th decade of life. Error bars represent 95% confidence intervals.

Table 1.

Prevalence of Pseudophakia by age and gender from 1988–2018 in Olmsted County, MN, USA

	Pseudophakia per 100 residents
	1988			1998			2008			2018
	Prevalence *	% prevalent cases bilateral+		Prevalence *	% prevalent cases bilateral+		Prevalence *	% prevalent cases bilateral+		Prevalence *	% prevalent cases bilateral+
All Ages	1.1 (1.0–1.2)	22.3		2.2 (2.1–2.3)	35.7		3.9 (3.8–4.0)	44.4		6.5 (6.4–6.7)	59.5
Aged ≥ 50 years	5.1 (4.9–5.5)	22.3		8.8 (8.5–9.2)	36.1		12.6 (12.3–12.9)	44.8		20.4 (20.0–20.8)	60.2
Gender
Women	1.5 (1.4–1.6)	22.6		2.9 (2.8–3.0)	36.8		4.7 (4.5–4.8)	45.9		7.6 (7.5–7.8)	61.7
Men	0.7 (0.6–0.8)	21.5		1.6 (1.4–1.7)	33.4		3.1 (3.0–3.2)	41.9		5.4 (5.2–5.5)	56.3
Age Groups (years)
0–49	.02 (.01–.03)	22.2		.09 (.07–.11)	22.9		.14 (.12–.17)	27.7		.18 (.15–.20)	23.9
50–54	0.5 (0.4–0.8)	19.2		0.7 (0.6–1.0)	29.4		1.1 (1.0–1.4)	31.1		1.2 (1.0–1.3)	41.9
55–59	1.1 (0.8–1.4)	20.9		1.4 (1.1–1.7)	29.0		2.8 (2.5–3.2)	32.4		3.7 (3.3–4.1)	45.2
60–64	2.1 (1.7–2.7)	27.8		3.2 (2.7–3.8)	37.1		5.6 (5.0–6.2)	34.6		8.5 (7.9–9.2)	46.6
65–69	3.8 (3.2–4.5)	28.3		6.7 (5.9–7.6)	32.3		10.2 (9.4–11.1)	36.5		17.8 (16.8–18.8)	52.7
70–74	6.6 (5.7–7.7)	19.9		12.4 (11.3–13.7)	36.7		18.4 (17.2–19.7)	40.0		33.6 (32.2–35.0)	56.5
75–79	12.3 (10.9–13.8)	19.8		18.8 (17.3–20.3)	35.8		30.9 (29.3–32.6)	46.8		52.7 (51.1–54.4)	62.8
80–84	15.8 (13.9–18.0)	21.8		26.1 (23.9–28.5)	36.3		44.0 (41.4–46.7)	51.4		67.0 (64.0–70.1)	65.4
85+	20.1 (17.9–22.6)	22.8		40.0 (37.3–43.0)	37.9		51.8 (49.0–54.5)	50.0		87.7 (83.9–90.6)	66.3

^*Values shown as the percentage, 95% confidence interval (CI) shown in parenthesis. CI’s calculated using Poisson distribution

⁺% prevalent cases with both eyes pseudophakic

Historical trends in age-specific prevalence of pseudophakia from 1988 through 2018 are shown in Figure 2 and Table 1. Pseudophakia prevalence among the total County population was 1.1% in 1988, 2.2% in 1998, 3.9% in 2008, and 6.5% in 2018. Overall prevalence increased 67% over the last 10 years and increased 590% over the last 30 years. The temporal increase in pseudophakia prevalence was significant in all age groups (P< 0.001) but was most notable in older ages. In all study periods, pseudophakia was more prevalent among women than men (P<0.001). Among all pseudophakic residents, bilateral pseudophakia increased from 22% in 1988 to 60% in 2018 (Table 1, P<0.001). In residents with pseudophakia, bilateral pseudophakia surpassed unilateral pseudophakia among residents aged 65 years or older in 2018 (Figure 3, Table 1). In residents with bilateral pseudophakia, the median time between first and second eye surgery decreased over time, steadily dropping from 517 days in 1988 to 116 days in 2018.

Figure 2.

Age-specific prevalence of pseudophakia in at least one eye over 30-year period from 1988 through 2018 among total population of Olmsted County, MN. Error bars represent 95% confidence intervals.

Figure 3.

Age-specific 2018 prevalence of unilateral and bilateral pseudophakia among total Olmsted County population.

Figure 4 shows age-specific 2018 prevalence of pseudophakia in at least one eye according to duration of time since the initial cataract surgery. In 2018, 37% of pseudophakic individuals had their initial cataract surgery within the previous 5 years, 34% had their initial surgery within the previous 5–10 years, 23% had their initial cataract surgery within the previous 10–20 years, 5% had their initial surgery within the previous 20–30 years, and 1% had their initial surgery 30 or more years prior. Among very elderly residents (aged 85 years or more) in 2018, 41% had lived with their pseudophakia for more than 10 years. There was a significant shift in prevalence of pseudophakia to younger ages over time, as illustrated by the prominent leftward shift of the pseudophakia prevalence curves between 1988 and 2018 as shown in Supplementary Figure 1.

Figure 4.

Age-specific 2018 prevalence of pseudophakia in at least one eye among the total Olmsted County population according to duration of time since initial cataract surgery.

Overall, county residents with pseudophakia had a significantly lower all-cause mortality when compared to age-and sex-matched expected death rates within the Minnesota general population as shown in a Kaplan-Meier plot (expected number of death 8,732 vs observed number of deaths 8,001, P<0.001, Figure 5). When stratifying by gender, women demonstrated a stronger protective association between pseudophakia and mortality than men (P<0.001 versus P=0.01, respectively). When stratifying by age, a protective association between pseudophakia and mortality was only present in age groups 70 to 79 years (P=0.003) and 80 years and older (P<0.001).

Figure 5.

10-year Kaplan-Meier survival analysis for all Olmsted County residents with pseudophakia in at least one eye during the 30-year study period compared to the age- and sex-adjusted general Minnesota population.

DISCUSSION

This population-based descriptive epidemiologic study found that by 2018 the prevalence of pseudophakia in as least one eye had increased 67% compared to 10 years prior and 590% compared to 30 years prior. While 6.5% of the total population was pseudophakic in at least one eye in 2018, the prevalence of pseudophakia had increased to 51% in residents aged 75–79 years, 67% in residents aged 80–84 years, and 88% in residents aged 85 years or more. Consequently, pseudophakia in at least one eye replaced bilateral phakia as the predominant visual status in adults aged 75 years and older in our defined population by 2018. Additionally, most pseudophakic residents were bilaterally pseudophakic, and 29% had been living with pseudophakia for more than 10 years in 2018. Clearly, living with pseudophakia is a remarkably common condition in our county and underscores the impact cataract surgery and pseudophakia have had in changing the visual status of older Americans.

The large increase in pseudophakia prevalence over the past 3 decades can be explained primarily by a similar increase in incident cataract surgery in Olmsted County during the same time.^4,12 However, our study also found a statistically significant shift toward surgery at a younger age and an improved life expectancy in individuals with pseudophakia. As might be expected, all 3 factors likely play a role in the large increase in prevalence of pseudophakia since 1988.

Population-based estimates of pseudophakia prevalence within the U.S. are limited,^{3, 6–11, 13} and most are over a decade old.^{6–8, 10–11} These studies estimated U.S. pseudophakia prevalence rates at 4.8% to 9.9%. The diversity of these estimates is due, in part, to different study periods as well as different geographic and ethnicity distributions. U.S. population-based pseudophakia prevalence estimates among various ethnic population groups range from 9.9% in Chinese-Americans,¹³ 8.2% in Hispanic-Americans,¹⁰ 5.6% in Caucasians,⁸ and 4.8% in African-Americans.¹¹ Congdon and coworkers⁶ coalesced previous population-based age-, gender-, and ethnicity-adjusted prevalence rates from the U.S. and worldwide to estimate pseudophakia prevalence in the U.S. population as a whole and found a prevalence of 5.1% in 2000, and predicted prevalence would reach 8.6% by 2020, a 60% increase.

Our 2018 population-based pseudophakia prevalence of 6.5% among the total population and 20% in adults older than 50 years provides an updated prevalence estimate among a population that has accessible health care and is predominantly Caucasian (Olmsted County: 83.6% non-Hispanic white). Our 20% pseudophakia prevalence in residents 50 years and older is considerably higher than Congdon’s 2020 8.6% estimate for the total U.S. population over 40 years of age. However, it must be remembered that REP estimates are not a truly representative sample of all population groups in the U.S.^17–18 and any generalization should be limited to the U.S. white population.

Population-based estimates of pseudophakia prevalence are more numerous from other countries and estimates range from 1.4% to 17.7%.^{3, 14, 20–25} A prevalence of 17.7%, which is similar to our results, was reported by Navarro and coworkers,²⁰ using a cross-sectional 2003–2004 analysis of 1155 Spaniards 65 years of age and older. However, Schuster and coworkers,¹⁴ using 2007–2011 Gutenburg Health Study data from a younger, predominantly white population aged 35–74 years, found the prevalence of pseudophakia to be 4.63%.

Compared to unilateral pseudophakia, bilateral pseudophakia is associated with improved patient-reported physical and social health, improved visual acuity, and increase quality-adjusted life years.^14–15 Among our pseudophakic population, bilateral pseudophakia increased from 22% in 1988 to 60% in 2018, showing that bilateral pseudophakia has now become the predominant visual status of our residents.

While cataracts have been linked to increased mortality rates, previous cataract surgery has been associated with decreased mortality rates.^26–27 Tseng and coworkers,²⁶ using a 5% sample of Medicare beneficiaries, found that all-cause mortality per 100 person-years was 2.98 in beneficiaries with cataract and 2.78 in beneficiaries with cataract surgery (P<0.001), and the strongest associations between cataract surgery and mortality were in women and in patients 80–84 years of age. Similarly, our study showed decreased mortality in the overall REP pseudophakic population compared to the general Minnesota population, and this protective association was also strongest for women and only found in residents aged 70 years and older. Like Tseng and coworkers,²⁶ we hypothesize that pseudophakia is protective primarily in older residents through an improvement in vision that results in a decreased risk of falls and accidents, an increased ability to remain active in social and physical activities, and an increased ability to receive routine medical care and medications.

There are few estimates of how long individuals live with their pseudophakia, and these studies are limited primarily to the very elderly (aged 85 years or more).^28–30 Owing to the infrastructure of the REP, we can longitudinally follow all residents after their initial cataract surgery. Our residents appear to be able to enjoy the benefits of cataract surgery for a relatively long time. In 2018, 71% of residents had lived with their pseudophakia for less than 10 years, 23% had lived with their pseudophakia for 10–20 years, and 6% had been pseudophakic for more than 20 years. Of our very elderly residents (85 years of age or more), 41% have been living with their pseudophakia for more than 10 years. Additionally, long-term IOL complications such as IOL dislocation or IOL exchange rates have remained stable or decreased.^31,32

The prevalence of cataracts in the 2000 U.S. population was estimated at 49.9% in those aged 75–79 years and 68.3% in those aged 80 years and older, while the prevalence of pseudophakia was much lower at 13.5% in those aged 75–79 years and 29.6% in those aged 80 years and older.⁶ Similar to the 2000 U.S. general population, the prevalence of pseudophakia in our 1998 REP cohort for residents aged 75–79 years and 80–84 years was 18.3% and 26.1%, respectively. Twenty years later, the prevalence of pseudophakia in the same age groups in the 2018 REP cohort had increased to 52.7% and 67.0%, respectively. While our study cannot determine the optimal prevalence of pseudophakia, our results suggest progress in addressing County resident’s cataract surgical needs over the past two decades.

Strengths of the REP include the ability to perform long-term population-based studies on patients of all ages within a stable well-defined geographic area for which the REP has complete data capture. Less than 2% of residents decline to participate in the REP. Thus, the REP captures health care information on virtually the entire Olmsted County population.¹⁶The frequency of follow-up is very high with >90% of60+ year olds seen a least once per year at an REP site.¹⁷ The REP has supported >2000 peer-reviewed publications since 1966 with studies of prevalence and temporal trends in incidence being hallmarks of the REP.¹⁸ The REP avoids patient inclusion bias and recall bias, which are common confounders in studies that are not population-based. Finally, REP databases are inclusive of all ages groups and, unlike Medicare databases, are not limited to enrollees 65 years and older nor does it exclude enrollees in Medicare health maintenance organizations.^16,17

These strengths notwithstanding, our study has limitations regarding diversity and geography. First, our findings can only be extrapolated to semi-urban U.S. white populations. The study, however, does provide up-to-date population-based prevalence information from a predominantly white population that can be used in comparing pseudophakia prevalence to other ethnic population groups relevant to the U.S. It should be remembered that no single community in the U.S. is completely representative of the entire U.S. and no specific geographic unit can claim a superior level of representativeness.¹⁷ Second, the number lens extractions due to refractive lens exchange or the number of immediate sequential bilateral cataract extraction within our database is unknown. Although both procedures are likely very low in number, their influence on our results is unknown. Third, potentially relevant information, such as visual acuity, is not in our database. Fourth, mortality assessment could be affected by confounding by indication where pseudophakic residents are inherently different from residents not undergoing cataract surgery or residual confounding from lack of availability of certain covariates. Finally, our estimates are prior to the COVID pandemic and its effect on pseudophakia prevalence within our population over time is unknown.

In conclusion, residents living with pseudophakia have increased substantially over the past 3 decades. Drivers of the higher prevalence rates include increasing incident cataract surgery, surgery performed at younger ages, and improved life expectancy in pseudophakic individuals. Living with pseudophakia is a remarkably common condition in our population, with pseudophakia in at least one eye becoming the predominant visual status of individuals aged 75 years and older in 2018. Additionally, residents are enjoying the benefits of their cataract surgery for an extended time, as 29% of current residents have lived with their pseudophakia for >10 years, with the majority of residents now bilaterally pseudophakic.

Supplementary Material

Supplementary Figure 1

Supplemental Figure 1. Temporal changes in the prevalence of pseudophakia in at least one eye in the total Olmsted County population between 1988 and 2018. There is a shift in prevalence to younger ages over time as illustrated by the leftward shift of prevalence curves.

WHAT WAS KNOWN:

• Cataract surgery rates have increased globally during the past decades.

• Estimates of pseudophakia in the U.S. are limited, with the majority of studies being over a decade old.

WHAT THIS PAPER ADDS:

• The prevalence of pseudophakia increased by 67% during the past 10 years and by 590% during the past 30 years in this defined U.S. population

• In 2018, pseudophakia in at least one eye replaced bilateral phakia as the predominant visual status in residents 75 years and older, with the majority being bilaterally pseudophakic.

• Drivers of increasing pseudophakia prevalence are rising incident cataract surgery rates, surgery performed at a younger age, and pseudophakic individuals living longer with their pseudophakia.