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Optometry & Vision Science:
doi: 10.1097/OPX.0b013e318255da45
Original Articles

A Cross-Sectional Analysis of U.S. Contact Lens User Demographics

Swanson, Mark W.*

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Article Outline
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Author Information

*OD, MSPH, FAAO

Department of Optometry, University of Alabama at Birmingham, Birmingham, Alabama.

Received September 6, 2011; accepted February 9, 2012.

Mark W. Swanson Department of Optometry University of Alabama at Birmingham 1716 University Blvd. Birmingham, Alabama 35294-0010 e-mail: mswanson@uab.edu

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Abstract

Purpose. Large population studies carried out in the United States, while addressing refractive error prevalence, have published little addressing the modes of refractive correction. As such, there are little data in the biomedical literature concerning the characteristics of the contact lens wearing population in the United States. The purpose of this project was to develop estimates of the demographic characteristics of a cross section of contact lens wearers in the United States based on those who wore contact lenses on the day of their National Health and Nutrition Examination Survey (NHANES) examination.

Methods. The NHANES is a nationally representative sample of the U.S. population. As part of NHANES, the type of refractive correction used is collected during a mobile medical clinic examination along with demographic variables. Data files from the 2005–2006 and 2007–2008 NHANES were obtained from the National Center for Health Statistics. Demographic characteristics of the U.S. population using contacts during the medical clinic examination were derived. Associations between demographic variables and contact lens use were explored in age-stratified univariate and multivariate analyses taking into account the complex sampling frame.

Results. In univariate analysis, age (p < 0.001) and the availability of health insurance (p = 0.007) have negative associations with contact lens use, while female gender (p < 0.001), higher socioeconomic status (p < 0.001), and higher educational attainment (p < 0.001) are associated with increased contact lens use. In multivariate analysis, age (p < 0.001), socioeconomic status (p < 0.001), the interaction of age with gender (p < 0.001), and the interaction of socioeconomic status with education (p = 0.002) are associated with contact lens use.

Conclusions. Four demographic variables, age, socioeconomic status, age-gender interaction, and socioeconomic status-education interaction, defined those likely to be using contact lens on any given day in the United States. Together, these four variables identify almost 9 of 10 contact lens users.

Estimates of the size of the contact lens population in both the United States and worldwide vary substantially with worldwide estimates ranging from 125 million in 2004 to 100 million in 2009 to 140 million in 2010.13 Sources largely from industry placed the size of the U.S. contact lens population in 2004 at between 28 to 39 million persons, with estimates in 2009 of 38 to 39 million.1,2 Large population studies carried out in the United States while addressing refractive error prevalence have published little addressing the modes of refractive correction. As such, there are little data in the biomedical literature concerning the characteristics of the contact lens wearing population in the United States. Most data on contact lens demographics are supplied by the contact lens industry with little information on how the data were collected or supplying precision of the estimates.

The National Health and Nutrition Examination Survey (NHANES) is one of the major data collection instruments used in the United States to track health trends for children and adults. The NHANES has been administered since the 1960s by the National Center for Health Statistics (NCHS) under the direction of the Centers for Disease Control and Prevention. The NHANES is a nationally representative sample of the U.S. population and each year enrolls about 5000 people. There are two main components of the NHANES: an interview and a medical examination. The interviews are conducted by trained health care interviewers in participant's homes and includes socioeconomic, demographic, and health risk factor information. The medical examination is conducted in mobile clinics by physicians and other trained health personnel which travel to sites throughout the country. The examination component consists of medical, dental, and physiological measurements as well as laboratory tests.4 NHANES data have been used previously to estimate the prevalence of refractive error and undercorrection of refractive error in the United States.46 The purpose of this project was to develop estimates on the demographic characteristics of contact lens users based on NHANES data.

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METHODS

NHANES Methods

In each NHANES cycle, a subsample of participants aged 12 years and older is selected for examination within the mobile medical clinics. As part of the mobile clinic examination, distance visual acuity (Snellen) is measured for all participants while near acuity is measured only for participants older than 50 years. Before any visual acuity testing, participants are asked whether they use glasses or contacts for distance vision activities such as watching television (Fig. 1). If the subject answers yes to using glasses or contacts for distance tasks, a composite response of using corrective lenses is noted. Participants are then asked whether the corrective lenses were available at the clinic visit. If yes, it is noted whether the correction is contacts, glasses, or whether both together are used for acuity testing. For all participants having spectacles with them, the spectacles are measured by automated lensometry. Similar methods are applied for near acuity. Each participant regardless of whether corrective lenses are reportedly used has distance refractive correction estimated by autorefraction.

Figure 1
Figure 1
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Statistical Methods and Variable Definitions

The NHANES is a probability sample intended to be representative of the U.S. population with a complex sampling scheme using stratification, clustering, and oversampling of some demographic groups. Data from the 2005–2006 and 2007–2008 NHANES were obtained from the National Center for Health Statistics. These 2-year cycles are the most current publicly available NHANES data and were merged into a single file. Merging cycles allows a larger absolute sample size and tighter confidence interval (CI) calculations of the weighted sample. After merging, 4-year sample weights were then generated for the entire data set using the method suggested by NCHS.6 This produced an actual sample size of 13,074 with a 4-year weighted U.S. population aged 12 years and older of 232,830,156. Interview and medical examination data have different sample weights and in keeping with the methods suggested by NCHS medical examination sample weights were used for all calculations. An age-stratified cross-sectional study was carried out. All statistical analyses were carried out on the appropriate 4-year weighted sample accounting for the complex design (SAS survey) using SAS version 9.2 (SAS Institute, Cary, NC). Chi-squared and logistic regression methods were used to evaluate associations between the demographic and measured variables. Variance estimations and 95% CI were calculated using the Taylor linearization method. Rao-Scott χ2 values are given where reported. In multivariate association analyses, each individual demographic variable and age interaction terms were entered into regression equations. Due to the well-known associations of ethnicity with income and education with income, both were added as potential interaction terms. Stepwise reductions of variables not approaching statistical significance (p ≥ 0.1) were done until the most parsimonious model with highest concordance was achieved.

Subjects were considered to be contact lens wearers if they used contact lenses for the entering distance visual acuity task. This included individuals who used a combination of spectacles and contacts for acuity testing. A convenient categorical variable for age was created with four levels: 12 to 18 years, >18 to ≤40 years, >40 to <50 years, and 50 years and older. The age categories represent a combination of common clinical divisions and collected data categories. Although the NHANES sample is extremely large, contact lens wear becomes infrequent in older adults necessitating categorical grouping, further NHANES truncates age at 85 and true linear analysis is not possible. The developed age categories were used in univariate and multivariate analyses except as noted for descriptive statistics. NHANES classifies race into five categories: Mexican, other Hispanic, white, African-American, and other race including those of mixed race. White race and other race were used as the reference categories for comparative analyses unless otherwise noted. The variable poverty to income ratio (PIR) was used as the measure of socioeconomic status. PIR is a continuous measure used by the U.S. government to assess poverty status and takes into account income, expenses, and family size. Those with PIR <1.0 have income below the federal poverty level for families, while those with PIR >4 are considered high income. A five-level categorical variable of PIR was created based on criteria used in reporting data from the Medical Expenditure Panel Survey.8 High income was used as the reference for analyses except as noted. Educational attainment was categorized into five categories <9th grade, 9th to 11th grade, high school graduate or General Educational Development equivalent, some college or associate degree, and college graduate or above. NHANES collects data on whether each subject is covered by health insurance as a dichotomous response. This dichotomous response to having insurance was used in univariate and multivariate tests. For those having health insurance, subjects are asked a series of questions to determine whether they are covered by Medicare, Medicaid, private insurance, or military- and state-sponsored plans. The type of insurance was only evaluated in univariate analysis with contact lens wear for general demographic information. An age-limited analysis of those younger than 65 years was carried out to evaluate the impact of Medicare.

Use of contact lenses during the near acuity task was considered separately to develop estimates of type and use of presbyopic contacts in the United States. Near-contact use was divided into three broad categories: those who used a combination of glasses and contacts, those who used only contacts (presumed multifocals), and those who used contacts that were likely prescribed as monovision. Estimates of presumed multifocal contact lens wear were derived by calculating those who used only contact lenses for the distance and near acuity testing and did not use glasses with the contacts for either task or have monovision correction coded. A specific coding comment is found in NHANES data denoting whether subjects were wearing monovision in either spectacles or contact lenses. As a part of NHANES protocol, this comment should be queried for each subject. The coding of both the distance and near acuity included an option for subjects using both glasses and contacts together during testing. If the subject used glasses with contacts for either task, they were classified as using both.

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RESULTS

For the U.S. population older than 12 years in the aggregate years 2005–2008, an estimated 47.6% (95% CI 45.8–49.4) of the population reported using either glasses or contact lenses for distance vision. Of those reported using distance vision correction, a population estimate of 89.8% had verifiable corrective lenses with them at the time of the NHANES mobile health clinic examination. Characteristics of those with corrective lenses are found in Table 1. Those who did not have corrective lenses with them were more likely to be younger, be of non-white race, have lower educational attainment, and have lower socioeconomic status.

Table 1
Table 1
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The current data provide a cross-sectional assessment of lens wear in the United States. Based on estimates from those having a verifiable lens correction, at least 8.4% (95% CI 7.4–9.4) of the total U.S. population older than 12 years used contact lenses on any given day during the years 2005–2008 (Table 2). Within the U.S. population using corrective lenses, 18.7% (95% CI 16.5–19.3) used contacts lenses for distance vision. There were at least 18.6 million contact lenses wearers (95% CI 17.4–20.8) on an average day during this period (Table 2).

Table 2
Table 2
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Age

Corrective lens use for distance vision in the U.S. population differs by a number of demographic factors but varies most dramatically with age increasing from approximately one-third among those aged 12 to 18 years (33.9%, 95% CI 31.4–36.5) to almost two-thirds for those aged 50 years and older (63.6%, 95% CI 61.4–65.8). As the percentage of the U.S. population using distance corrective lenses increased, contact lens use decreased. Contact lens wear peaked in the U.S. population in the age group >18 to ≤40 years at 12.6% (95% CI 10.9–14.0) and prevalence decreased to <4% of the U.S. population (3.6%, 95% CI 2.6–4.6) for those aged 50 years and older. Of those using corrective lenses, the age groups 12 to 18 years and >18 to ≤40 years had similar rates of contact lens usage at 39.0% (95% CI 31.9–46.0) and 37.1% (95% CI 33.3–41.0), respectively. The highest use of contact lenses was found in the 10-year period between ages 15 to 25 years with almost half of refractive correction in the group aged 15 to 20 years by contacts (46.3%, 95% CI 39.3–53.3). Decline in the use of contact lenses began in the late twenties with the median age of contact lens wearers in the United States being 31.4 years (95% CI 29.7–33.1). There were no NHANES participants older than 80 years using contact lenses. Univariately, increasing age is inversely associated with contact lens wear. Each five-year increase in age over age 20 years resulted in a 30% [odds ratio (OR) 0.70, 95% CI 0.67–0.73] reduced odds of using contact lenses.

More than 86% of the U.S. population older than 50 years reported using corrective lenses for near vision (86.5%, 95% CI 85.2–87.8). Based on data obtained at both the distance and near testing, slightly <3 million people older than 50 years in the United States used contact lenses daily in this period. The breakdown of lens wear at near was 31.8% spectacles and contact lens combination (95% CI 21.2–42.4), 17.3% monovision (95% CI 9.0–25.5), and 51% (95% CI 44.1–57.7) multifocal lenses.

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Gender

Gender was associated with contact wear with women 40% more likely to use contacts than men (OR 1.40, 95% CI 1.18–1.66). Women made up about two-thirds of all contact lens wearers during the 2005–2008 time period (64.7%, 95% CI 61.4–68.0) (Table 3). On closer examination however, gender differences in contact lens use are age-dependent. The median age of women contact lens wearers was about 3 years older than men at 32.7 years (29.7–35.7 years) and 29.6 years (26.4–32.9 years). For both the age groups 12 to 18 years (χ2 = 1.14, p = 0.28) and >18 to ≤40 years (χ2 = 0.02, p = 0.87), gender differences were not statistically significant in age-stratified univariate analysis. Over the age of 40 years, gender differences in contact lens use became marked. The gender ratio of women to men contact lens wearers increased from 1.5:1 in the age group <18 years to 3:1 for those 50 years and older. Women comprised 68.3% (95% CI 58.8–77.9) of all contact users aged >40 to <50 years and 74.3% (95% CI 63.9–84.6) in those aged 50 years and older. In each of the older age cohorts, gender differences in contact lens use were statistically significant (χ2 = 6.71, p = 0.01, and χ2 = 9.03, p = 0.005, respectively).

Table 3
Table 3
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Ethnicity

Whites are the largest ethnic demographic group in the United States and comprised 70.1% (95% CI 65.5–74.6) of the U.S. population aged 12 years and older during 2005–2008. Whites made up a slightly larger percentage of all contact lens wearers (77.5%, 95% CI 71.9–83.2) compared with their population prevalence (Table 3). Non-whites, however, made up almost one-third of contact lens users (29.4%, 95% CI 21.9–36.6) in the demographic >18 to ≤40 age group. As a group (OR 1.04, 95% CI 0.81–1.35), non-whites were not less likely to use contact lenses than whites. While whites make up the bulk of total contact lens users, they did not have the highest prevalence of contact lens use by ethnicity. The NHANES ethnic group “other” had the highest usage of contact lenses (23.7%, 95% CI 16.1–31.1) with Mexican Americans having the second highest prevalence. The ethnic group “other” is a heterogeneous group, but it presumably has a large constituency of those with Asian descent. African-Americans and non-Mexican Hispanics had the lowest use of contact lenses among the NHANES ethnic groups but were no less likely to use contact lenses than whites. African-Americans (OR 0.62, 95% CI 0.39–0.96) and non-Mexican Hispanics (OR 0.62, 95% CI 0.38–0.99) did have reduced odds of using contact lenses when the reference group is “other race.” Contact lens use among ethnic minorities decreased relative to population in the age group >40 to <50 years, and this trend continued with age so much so that contact lenses users aged 50 years and older were almost exclusively white (92.3%, 95% CI 87.4–96.9). This is partially accounted for by population demographics. Whites are proportionally a larger percentage of the U.S. population older than 50 years (78.5%, 95% CI 73.9–83.1) and represent an even higher percentage of the U.S. population using corrective lenses for distance (82.5%, 95% CI 77.8–87.2) in this age group.

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Socioeconomic Status

Socioeconomic status was associated with contact lens use (χ2 = 60.4, p < 0.001). More than 60% of the U.S. population was found in the middle and high income PIR groups (Table 4). Among those reported using corrective lenses for distance, 72% had middle or high income with >80% of all contact lens users in these two socioeconomic groups. All socioeconomic groups had reduced odds of using contact lenses compared with those with high income. The trend was however not strictly linear. A small increase in the prevalence of contact lens use was found among those whose socioeconomic status is at the poverty level. In fact, compared with those in the middle income demographic, those meeting the poverty definition were no less likely to use contact lenses (OR 0.77, 95% CI 0.54–1.11). Older contact lens users had higher socioeconomic status than younger users. In both the age groups, >40 to <50 years (92.8%, 95% CI 86.5–99.2) and 50 years and older (93.6%, 95% CI 88.7–98.5), >90% of contact lens users were in the middle or high socioeconomic groups. In both these age groups, almost two-thirds of contact lens users were in the high-income demographic.

Table 4
Table 4
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Education

In the U.S. population during the study period, about 55% (55.4%, 95% CI 52.3–58.5) of adults older than 18 years had some college or were college graduates and beyond (Table 5). As education level increased, so did the percentage of the population who used refractive correction. Among the population older than 18 years, those with at least some college education accounted for >60% of all refractive correction users (61.2%, 95% CI 57.9–64.6) and almost 80% of contact lens users (78.6%, 95% CI 73.2–84.0). Higher educational attainment was associated with contact lens use (χ2 = 73.1, p < 0.001). Contact lens use among those using refractive correction increased from 2.5% (95% CI 0.0–5.6) among those with less than a 9th grade education to >20% among those with college degrees (23.4%, 95% CI 19.5–27.2). Compared with those with college degrees, persons with all other levels of educational attainment had lower odds of contact lens use. The differences in the prevalence of contact lens use among those with some college and college degrees approached statistical significance (OR 0.82, 95% CI 0.66–1.02), while those with all lower levels of educational attainment had a statistically significant 60 to 90% reduced odds of contact lens use. Similar to other demographic characteristics, changes in contact use and educational attainment were seen with aging. Approximately 80% of all contact lens users in the age groups >18 to ≤40 years (79.3%, 95% CI 73.2–85.5) and >40 to <50 years (85.3%, 95% CI 76.4–94.1) had at least some college. The percentage of persons aged 50 years and older with some college education decreased (69.2%, 95% CI 55.7–82.8) with a larger share of contact lens wearers among those with high school and 9th to 11th grade education.

Table 5
Table 5
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Health Insurance

Approximately 17% of the U.S. population did not have health insurance during the years 2005–2008. Health insurance coverage during this period followed a U-shaped distribution decreasing from 87% among adolescents aged 12 to 18 years to 70% among those >18 to ≤40 years before increasing to near-universal coverage for seniors 65 years and older (98.4%, 95% CI 98.0–98.8). Those with health insurance had higher overall use of refractive error correction (51% vs. 39%) but lower use of contact lenses among those using refractive correction than Americans without health insurance (18% vs. 24%, χ2 = 8.3, p = 0.007). While this was true, overall, about 85% of contact lenses wearers did have some form of health insurance (84.9%, 95% CI 81.9–87.8). The difference in contact lens use among those with and without health insurance was largely accounted for by the near-universal coverage of seniors who were also much less likely to use contact lenses. For the population younger than 65 years, contact lens use is nearly equivalent (p = 0.68) between those with (24.6%, 95% CI 19.8–29.4) and without health insurance (23.6%, 95% CI 20.9–26.4). As might be expected, those with private insurance had a higher rate of contact lens use than did those with the major federal low-income health insurance plan Medicaid (Table 6).

Table 6
Table 6
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Multivariate Associations

After model reduction, four demographic variables, two main effects, age and PIR, and two interactions terms, age by gender and educational attainment by PIR, show association with contact lens use (Table 7). These association models hold true for the population aged 18 years and older and for those aged 31 years and older in whom contact lens use begins to decline in the U.S. population. As in univariate models, increasing age was independently and inversely associated with contact lens use. As would be predicted from age-stratified univariate analysis, gender only becomes important in association with contact lens use with aging as older women are far more likely to use contacts than older men. While higher socioeconomic status is globally associated with contact lens use, particularly interesting is the interaction between education and socioeconomic status. Among adults with income at the poverty level, as education level increased contact lens use concomitantly increased (Table 8). In contrast to adults with high income, contact lens use increased with lower levels of educational attainment.

Table 7
Table 7
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Table 8
Table 8
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DISCUSSION

Data from the NHANES provides a cross-sectional view of the U.S. contact lens population. The estimated size of the U.S. population using contact lenses from the NHANES data is far smaller than that reported from other sources.13 These smaller estimates are likely related to a number of design and implementation factors in both the NHANES and industry data. Most data from the contact lens industry appear to be from practitioner surveys, random telephone surveys, and sales data extrapolated to the U.S. population. Practitioner surveys and sales data are inherently biased. In recent years, the validity of the traditional random digit dialed telephone survey has been questioned as more Americans screen calls with caller identification and the transition away from landline to cell phone-only households.9

NHANES has a complex sampling frame explicitly intended to be representative of the U.S. population; however, as with any administrative data set, there are limitations and advantages. The NHANES data used represents an amalgamation of the U.S. population from 2005 to 2008 and as such is based on a smaller overall size U.S. population than comparable 2008 estimates from industry sources. Mobile medical clinic participation, where contact lens data is generated, was limited to those aged 12 years and older as part of the NHANES design. While the population younger than 12 years using contacts is likely relatively small, it will lead to some underestimation error. The NHANES question sequence does not ask each interviewee or medical clinic participant directly whether they wear contacts lenses. The lead question to participants (Fig. 1) only records whether refractive correction is used and not the specific type. Correction type is recorded only if participants have their corrective lenses at the time of the medical evaluation. Due to this question sequence, about 10% of the weighted U.S. population who reported using refractive correction was not classified as to the type of correction. It would be anticipated that at least some of this segment of the population would be contact lens users. Those who did not have correction with them were younger, more likely an ethnic minority than white, and had lower education level and lower socioeconomic status. Younger Americans are more likely to use contacts which would contribute to a larger total contact lens wearing population, but this is balanced by the lower prevalence of use among those with lower socioeconomic status and lower education levels.

The total contact lens wearing population in the United States comprised those who wear lens every day and those who wear lenses on a less than a daily basis. On any given day, a part-time wearer may choose to use spectacles or no correction at all rather than contacts. Less than every day wear is common and known to vary with lens type.10 The NHANES medical examination itself is relatively innocuous and subjects are not dilated. As such, participants would not necessarily be biased against contact lens wear anticipating dilating drops. Given the question sequence, NHANES likely captures all every day wearers and a random probability sample of those part-time wearers likely to use contact lenses on any single given day. This would lead to some degree of underestimation of the number of part-time wearers.

Using the NHANES data does have merits. Both the actual and weighted sample sizes are extremely large eliminating many potential sources of selection bias. With the highly defined sampling frame, CIs can be calculated around the estimates, something that is not reported in data from industry sources. The NHANES relies on actual lens wear rather than self-report and as such is not subject to reporting bias. Self-report data that does not specify time periods (e.g., “have you worn contacts in the last week, six months, etc.”) could be subject to significant individual variation in those identifying themselves as a contact lens user given the high rate of contact lens discontinuation. The NHANES is now administered on continuous 2-year cycles opening the possibility of long-term monitoring. Overall, it is likely that while the NHANES data underestimates the size of the U.S. contact lens population, it likely does give an accurate picture of its composition.

As expected, age had an inverse association with contact lens use. The pattern of age-related decline in contact lens use does follow that seen from other data sources,13 with the decline in contact lens use appearing well before presbyopia. Estimates from NHANES for both the percentage of the U.S. population using refractive correction and those using contact lenses were smaller across each age demographic group than is generally reported from industry data. One of the additional limitations of NHANES is the lack of data on near vision correction use in the early presbyopic age group >40 to <50 years. This appears to be a period when the prevalence of contact use declines significantly at least for distance vision wear. Unfortunately, how this relates to near vision cannot be evaluated due to the lack of near acuity testing for this group. It is unfortunate that these data are unavailable as it would allow not only calculation of contact lens use but also exploration of factors related to the onset of presbyopia. Among those aged 50 years and older, the breakdown of the use of spectacle and contacts combination, multifocal and monovision lens appears to generally follow the pattern reported by Morgan et al.11 from a recent international prescribing survey. Some caution should be used with interpretation of the modality of contact use at near. The data are highly dependent on the accurate coding of the number of monovision users at the time of the NHANES examination. Also, CIs around the modality type are large. Aside from the direct association with contact lens use, the impact of age was seen across all the other demographic variables.

Most reports indicate that women are far more likely to use contacts than men.1,2 Although this is true, it gives an incomplete picture as gender differences in contact lens use are largely dependent on age. Assuming that most contact lens users began lens wear in adolescence and early adulthood, NHANES data suggest that men leave contact lens wear much younger and at a faster rate than do women. Dropout among contact lens users is an important issue for practitioners. Most studies of lens dropouts have concentrated on lens-patient interaction factors such as dryness and comfort. While these factors are undoubtedly important, demographic data suggest that gender-specific differences leading to lens discontinuance may exist. Further research is needed to clarify what these differences may be.

Although almost all adults older than 50 years who use contact lenses are white, after accounting for other factors ethnicity appears to play little role in contact lens use. Non-whites appear at least as likely as whites to use contact lenses. This bodes well for the future given the changing demographics of the U.S. population. Some caution should be exercised in interpreting the ethnicity data. Despite the large sample size and oversampling of some ethnic groups, precision of the estimates in some subgroups (age by ethnicity, “other”) is poor. The U.S. population is more diverse than the five NHANES ethnic groups. Most data presented on ethnicity related to contact lens wear list the Hispanic population as a single group. Based on the current data, Mexican Americans were more likely to use contacts than non-Mexican Hispanics. While these differences appear to be related to factors beyond ethnicity, it suggests that the Hispanic population is not homogenous related to refractive correction use. The Hispanic population in the United States is in fact composed of 28 subgroups for census purposes based on the country of origin.12 Given the rapid growth of this population, future studies may need to be planned to account for differences within those of Hispanic ethnicity. Obviously, it would be incorrect to assume the group “other ethnicity” represents a single entity. The NHANES coding guide describes the “other race” category to include Asians, Pacific Islanders, Native Americans, and those who have multiracial heritage. Based on census data, Asian Americans would be the largest constituent of this group. The high use of contact lenses in this group is likely driven by the high prevalence of myopia in those of Asian descent.13 It should also be considered that almost 15% of all marriages in the United States are currently between persons of different ethnicity, and the multiethnic population is growing rapidly.14 Little is known about refractive error in those of multiethnic descent.

Having health insurance has been associated with higher rates of use of eye examination and better vision outcomes.15 Knowing this, the inverse association of contact use and health insurance might seem puzzling. The association of health insurance and contact lens wear is distorted in the U.S. population by the near-universal coverage of older adults by Medicare. After taking into account the large impact of Medicare, by evaluating adults younger than 65 years, no association with having health insurance and contact lens use was found. The absence of an association is likely due to the relatively high percentage of younger adults in the age group >18 to ≤40 years who do not have health insurance compared with teens and older adults. Also, vision insurance or vision discount plans likely have a more direct association with contact lens wear. Census data estimate that about 21% of working age adults have vision insurance.16 Data on ancillary insurance such as dental and vision are not collected as part of NHANES.

Perhaps the most interesting associations with contact lens use in the U.S. population were those with socioeconomic status and the interaction of education and socioeconomic status. Higher socioeconomic status being associated with contact lens use makes intuitive sense given that a large percentage of contact lens-related expenses are out of pocket. While education level was associated with contact lens use in univariate analysis, it is not surprising it was not significant in multivariate analyses. Socioeconomic status and education level are known to co-vary with each other.17 Particularly curious is the increase in contact lens use by those whose income is at the poverty level. A number of possible explanations might account for why those in poverty have increased contact lens use including higher use of medically necessary contacts, coverage of contact lenses by state or federal indigent insurance plans, or a higher cost-benefit valuation in this group for contact lenses. Education level clearly plays a role in contact lens use among this group. Low-income persons with higher education might logically represent college students or young professionals beginning careers; however, the mean age of this group is well past the typical college years. Equally curious is the increased use of contacts seen among those with high socioeconomic status but low educational attainment compared with those in the same socioeconomic class but with higher education level. Older contact lens users do generally show higher income with lower education level which could explain this relationship. However, when age is looked at across the spectrum of education level among those with high socioeconomic status, no dramatic age affects are seen. The reasons why those with high PIR and low lower education have higher contact lens use are unclear.

Within the limitations of the data, the NHANES provides an unbiased source of demographic information on cross-sectional contact lens use within the United States. From the data, a number of broad conclusions can be drawn. Contact lens use in the United States is associated with four demographic variables: age, socioeconomic status, age-gender interaction, and socioeconomic status-education interaction. Together these four variables identify almost 9 of 10 contact lens users. The U.S. population shows no ethnic bias in contact lens use. Socioeconomic status and educational level should be looked at in conjunction with each other relative to contact lens use. Gender differences in contact lens use may be due to differential dropout of lens wear by men.

Mark W. Swanson

Department of Optometry

University of Alabama at Birmingham

1716 University Blvd.

Birmingham, Alabama 35294-0010

e-mail: mswanson@uab.edu

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ACKNOWLEDGMENTS

This work was supported by Centers for Disease Control and Prevention (CDC), National Center for Health Statistics (NCHS), National Health and Nutrition Examination Survey, and U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, Hyattsville, MD. Data years 2005–2006 and 2007–2008.

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REFERENCES

1. Barr JT. 2004 Annual Report. Cont Lens Spectrum 2005;20:26–32. Available at: http://www.clspectrum.com/article.aspx?article=12733. Accessed August 11, 2011.

2. Weisbarth R. State of the Industry. Lecture given at the Ciba Educators Meeting, Scottsdale, Arizona, March 25, 2011.

3. Cavanagh HD, Robertson DM, Petroll WM, Jester JV. Castroviejo Lecture 2009: 40 years in search of the perfect contact lens. Cornea 2010;29:1075–85.

4. Centers for Disease Control and Prevention. National Center for Health Statistics. National Health and Nutrition Examination Survey. Available at: http://www.cdc.gov/nchs/nhanes.htm. Accessed March 13, 2012.

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12. United States Census Bureau. 2010 Census Briefs: Overview of Race and Hispanic Origin: 2010. Available at: http://www.census.gov/prod/cen2010/briefs/c2010br-02.pdf. Accessed August 1, 2011.

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15. Centers for Disease Control and Prevention (CDC). Reasons for not seeking eye care among adults aged >/=40 years with moderate-to-severe visual impairment—21 States, 2006–2009. MMWR Morb Mortal Wkly Rep 2011;60:610–3.

16. United States Census Bureau. People Without Health Insurance for the Entire Year by Selected Characteristics: 2008 and 2009. Available at: http://www.census.gov/compendia/statab/2011/tables/11s0153.pdf. Accessed August 1, 2011.

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contact lens; prevalence; NHANES; demographic

© 2012 American Academy of Optometry

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