Prevalence of major eye diseases and causes of visual impairment in the adult Finnish population: a nationwide population-based survey

Self-reported chronic eye diseases and visual function

The home interview included the following questions on eye diseases: ‘Has a doctor diagnosed one of the following diseases: cataract, glaucoma, degenerative fundus changes, or other visual defect or injury?’ and ‘Have changes caused by diabetes been diagnosed in the fundus of your eye?’. During the survey examination, the presence of cataract and glaucoma were specifically asked by the field physician. Self-reported visual disturbances were assessed by asking questions on difficulties with reading normal newspaper text, and text and subtitles on television, and whether eyesight restricted the respondent’s ability to move about.

Ophthalmic data from registers and case records

To identify people with chronic eye diseases, we also gathered information concerning the entire sample from the National Hospital Discharge Register, the National Medication Reimbursement Register and the National Prescription Register (Fig. 1). The last two registers mentioned included information on glaucoma only. The diagnosis codes for the major eye diseases in the 8th, 9th and 10th versions of the International Classification of Diseases (ICD) are shown in Table 1. For 1243 persons, information on chronic eye diseases before 2002 was also traced from case records at public central hospitals and the offices of private ophthalmologists. These included 360 persons with or without self-reported eye diseases who had reduced VA (< 0.5) assessed in survey examination, 317 persons who had reported eye diseases or difficulties in vision but whose VA was unknown, and 566 non-participants (Fig. 1). Case records were obtained from 55%, 39% and 14%, respectively. The presence of chronic eye diseases was assessed based on diagnosis (ICD codes, Table 1) or remarks on case records. Eye diseases were considered clinically relevant if there was any information on their existence that also indicated a need for previous eye care services.

VA measurement

As part of the survey health examination, distance VA was measured binocularly at 4 m using a modification of the logMAR letter chart published by Precision Vision (Ferris et al. 1982). Participants used their current spectacles if they had any. The illumination was optimized to 350 lux or more on distance vision charts. VA values were presented as a decimal (Snellen) equivalent. In this study, VA of < 0.5 was defined as reduced VA and VA of ≤ 0.25 was defined as visual impairment. Low vision was defined as VA of ≤ 0.25 but not < 0.1. VA of < 0.1 means blindness.

Statistical analysis

The sampling design was accounted for using sudaan software (version 9.0.1 and 10.0; RTI, Research Triangle Park, NC, USA) for the Statistical Analysis System (version 9.1; SAS Institute, Cary, North Carolina, USA). The sampling probabilities for people aged 80 years and older were twice as high as for the younger people. The values of the sample weights were therefore half for the older people of those of the younger people. Weighted averages of the sample thus estimate the population averages correctly. The sample weights were further calibrated by post-stratification defined by age, gender, area and native language to account for non-response and missing data.

The prevalence of cataract, ARM and glaucoma was estimated as a percentage of all the participants (i.e. participated in a home interview, an abbreviated home interview, a phone interview or a final questionnaire; n = 7413). Because self-reported DR was assessed only in the home interview, the prevalence of DR was assessed among the participants in this study phase (n = 6986). DR could not be assessed for 187 persons who reported diabetes mellitus (DM) but had not had a retinal examination or photography or were unable to answer the question on DR. Those who had not reported chronic eye diseases and/or for whom there was no information on chronic eye diseases based on register data, case records or the survey examination were presumed to have no chronic eye diseases. Gender- and/or age-adjusted prevalences of eye diseases in the study population were determined with logistic regression analysis and the predictive margins approach (Lee 1981; Graubard & Korn 1999).

The agreement between self-reported and documented chronic eye diseases was assessed using the overall kappa value (Fleiss 1981) in persons with VA < 0.5 (n = 360). The overall kappa statistic, which is a weighted average of stratum-specific kappa values, was used because the standard kappa statistic can be sensitive to confounding factors. In this case, age is associated strongly with eye diseases, and the stratification was therefore based on age groups. The sensitivity of self-reported data was defined as the proportion of persons with a positive diagnosis in documented data matched by correct positive reports in the interview (i.e. weighted number of positive in both / weighted number of positive in documented data × 100) and the specificity of self-reported data as the proportion of persons without a particular eye disease in documented data matched by correct negative reports in the interview (i.e. weighted number of negative in both/ weighted number of negative in documented data × 100).

Agreement between self-reported and documented chronic eye diseases

Based on the survey examination, 360 persons had reduced VA (< 0.5) at the time of the Health 2000 survey. In 219 of 360 cases, diagnoses of one or more chronic eye diseases (i.e. operated or unoperated cataract, glaucoma, ARM, DR or other chronic eye diseases) could be assessed based on the national registers and/or case records. When self-reported eye diseases were included, 249 of 360 persons had one or more chronic eye diseases. The agreement between self-reported and documented diagnoses was fair to good for all four chronic eye diseases (overall kappa values 0.30–0.78; Table 2). The agreement was excellent for glaucoma in particular. The sensitivity of self-reported cataract, glaucoma, ARM and DR was good to moderate (55–72%; Table 2), and the specificity of self-reported cataract, glaucoma, ARM and DR was very high (88–100%; Table 2).

Estimated total prevalence of chronic eye diseases

The most common chronic eye disease in the study population was cataract (including operated cases), with a prevalence of 9.5% [95% confidence interval (CI) 8.9–10.2%] (Table 3). About half (53%) of the persons with cataract had had cataract surgery in one or both eyes. The prevalence of cataract increased significantly with age (p < 0.001), from 2% in persons under 65 to 67% in those aged 85 or older. The prevalence of glaucoma was 4.5% (95% CI 4.0–5.0%), increasing from 2% in people aged 30–64 to 20% in the oldest age group (p < 0.001). ARM was almost as common as glaucoma, with a prevalence of 3.8% (95% CI 3.4–4.3%). The prevalence of ARM increased from 1% in those aged 30–64 to 27% in the oldest age group (p < 0.001). Only 1% of the population had DR (95% CI 0.7–1.2%), ranging from 0.6% to 2.4% in the different age groups. In our study, 16% of persons with known DM, and 23% of those taking medication for DM, reported having DR.

Cataract, glaucoma and ARM seemed to be more common in women than in men, but this gender difference was statistically significant only for total cataract and glaucoma [odds ratio (OR) 1.55, 95% CI 1.26–1.91; OR 1.57, 95% CI 1.24–1.98, respectively]. Unoperated cataract was more common in women than in men (OR 1.66, 95% CI 1.28–2.15), but there was no gender difference in operated cataract (OR 1.19, 95% CI 0.93–1.55). Gender difference in glaucoma was observed only in persons under 75 years of age.

Population prevalence of reduced VA associated with chronic eye diseases

The population prevalences of reduced VA (< 0.5) related to chronic eye diseases were 1.1% for unoperated cataract, 1.0% for ARM, 0.6% for glaucoma and 0.1% for DR (Table 4). The prevalences increased significantly with age (p < 0.01) for all these diseases and seemed to be more common in women than in men, although the gender differences were not statistically significant (p > 0.05). In persons aged 65 or older the prevalences of reduced VA related to unoperated cataract, ARM, glaucoma and DR were 4.2%, 3.7%, 2.3% and 0.4%, respectively.

Reduced VA related to unoperated cataract became noticeable after 65, while the prevalences of glaucoma and ARM with reduced VA started to increase a decade later, after 75. In people aged 65–74, reduced VA was related most commonly to unoperated cataract (2.2%) and in people aged 85 or older to ARM (14.5%). In those aged 75–84, unoperated cataract and ARM with reduced VA were almost equally common (5.2% and 4.4%, respectively). Of all those with ARM, almost a third (30%) had VA < 0.5; among those with unoperated cataract the corresponding proportion was nearly as high (28%). A far lower proportion of persons with glaucoma (16%) and DR (15%) had reduced VA.

Prevalence of chronic eye diseases in persons with reduced VA

The prevalence of chronic eye diseases in persons with reduced VA (VA < 0.5), low vision (VA 0.1–0.25) and blindness (VA < 0.1) is presented in Table 5. The most common chronic eye disease in the 360 persons with reduced VA was unoperated cataract alone or combined with some other chronic eye disease, with a prevalence of 29%. The prevalence of ARM, glaucoma, DR and other chronic eye diseases were 26%, 16%, 3% and 23%, respectively. The cause of reduced VA could not be assessed in 132 persons. Of the 228 participants with reduced VA and some chronic eye disease (i.e. unoperated cataract, glaucoma, ARM, DR or another chronic eye disease), 53% had a single eye disease, 35% had two eye diseases and 12% had three or more eye diseases. Of those with VA < 0.5 but no documented or self-reported chronic eye diseases (132 persons), 73% had VA 0.3–0.4 and only a quarter reported using spectacles for distant viewing, 61% had not had a vision examination during the past 5 years and 35% had never had any kind of vision examination as a result of reduced VA.

The existence of chronic eye diseases could be assessed in 71 of the 101 persons with low vision and in 37 of the 46 blind persons. In those with low vision (VA 0.1–0.25), the most common eye diseases were unoperated cataract (31%), ARM (26%), glaucoma (19%) and DR (8%). In 16%, the only known cause of the low vision was unoperated cataract, in 7% ARM, in 5% glaucoma and in 1% DR. In blind persons (VA < 0.1), ARM (62%) and glaucoma (28%) were the most prevalent eye diseases, whereas the prevalences of unoperated cataract and DR alone or with other eye diseases were only 18% and 5%, respectively. In 4% unoperated cataract and in 12% ARM were considered to be the only cause of blindness. Glaucoma and DR were associated with blindness only in combination with other eye diseases. Of those with low vision but no documented or self-reported chronic eye diseases (30 persons), 54% had not had any kind of vision examination, 75% had a dementia and 25% were living in an institution. Of those with blindness but without known eye diseases (nine persons), only 8% had not had any kind of vision examination, 89% had a dementia and 26% were living in an institution.

Prevalence of chronic eye diseases

As expected, the prevalences of cataract (2%), glaucoma (2%) and ARM (1%) were low in persons aged 30–64. In those aged 65 or older, the prevalences of cataract including previous cataract surgery (38% for women, 28% for men) were in agreement with those reported in the Swedish community Skövde, in a population aged 70–84 (42% for women and 27% for men). In that study, the Lens Opacities Classification System III (LOCS III) was used for grading and the criteria corresponded to clinically significant cataract [i.e. posterior subcapsular cataract (PSC) > 1, cortical cataract (CC) > 3 and nuclear opalescence (NO) ≥ 4] (Östberg et al. 2006). Other previously reported prevalence rates are much higher, because of the different definitions of cataract. In Finland, for example, Häkkinen (1984) reported a prevalence of 48% in persons aged 65 and older when cataract was defined as opacities in the retinoscopic reflex, and Hirvelä et al. (1995) reported a prevalence of 64% in persons aged 70 and older based on LOCS II grading with milder criteria (grade > 0 for PSC, grade > 1 for CC and NO). The lower prevalence rates found for cataract in the present study reflect the degree of visual inconvenience caused by cataract in practice.

For comparisons between studies, the prevalence of previous cataract surgery is more unequivocal, although the greater amount of cataract surgery performed in recent years makes comparisons difficult. Both in our whole study population (5%) and in persons aged 65 and older (19%) the prevalence of operated cataract was higher than reported earlier: 4% in persons aged 40 and older (McCarty et al. 2000), 6% in persons aged over 48 (Mitchell et al. 1997), 5% in those aged 50 and older (Sasaki et al. 2000), 10% in those aged 65 and older (Reidy et al. 1998) and 11% in those aged 70 and older (Hirvelä et al. 1995).

The prevalence of glaucoma in the Finnish population aged 30 and older was 4.5%, which is higher than in many earlier reports. The prevalence increased with age from 2% in those aged 30–64 to 20% at the age of 85 or older. In most studies, the prevalence of open-angle glaucoma (OAG) varies from 1% to 3% in middle-aged or older persons (Tielsch et al. 1991; Dielemans et al. 1994; Mitchell et al. 1996; Wolfs et al. 2000; Weih et al. 2001), and the overall prevalence of all types of glaucoma is 2–3% (Bonomi et al. 1998; Nizankowska & Kaczmarek 2005). However, substantial geographic variation was noted. This may be because of the differences in the occurrence of the pseudoexfoliation syndrome and subsequent capsular glaucoma, which are common in Finland and the other Nordic countries (Krause et al. 1988; Ringvold et al. 1988; Arnarsson et al. 2007; Åström & Linden 2007; Åström et al. 2007). Correspondingly, the prevalence rates reported in the Nordic countries are fairly similar to our findings: the prevalence of OAG was 2–5% in middle-aged or older persons and capsular glaucoma explained 30–85% of the prevalence of OAG (Jonasson & Thordarson 1987; Ringvold et al. 1991; Hirvelä et al. 1994; Ekström 1996; Jonasson et al. 2003; Åström et al. 2007; Tarkkanen et al. 2008).

The total prevalence of ARM was fairly low (3.8%) because of its infrequent existence (1.2%) in persons aged 30–64. In those aged 65 and older, the prevalence of reported ARM increased gradually from 8% (between 65 and 74) to 27% (85 and older). The high prevalence of ARM in people aged 75 and older is consistent with most previous studies reporting prevalence rates for both all and late ARM (Klein et al. 1992c; Mitchell et al. 1995; Vingerling et al. 1995). In accordance with our results, Mitchell (1993) found that 19% of persons aged 75–84 and 26% of those aged 85 and older had ARM, based on case records. In other previous studies, the prevalence of all ARM was considerably higher because early macular changes assessed with ophthalmoscopy or fundus photographs were included. In Finland, for example, 25% of persons aged 65 or older (Häkkinen 1984) and 41% of persons aged 70 or older (Laatikainen & Hirvelä 1995) had at least early age-related macular changes. It is probable that those reporting ARM in the present study had either advanced early ARM or late ARM. In previous studies, the prevalence of late ARM varied between 4–5% in persons aged 75–84 (compared with 15% of all ARM in the present study) and between 11% and 35% in persons aged 85 or older (compared with 27% of all ARM in the present study) (Laatikainen & Hirvelä 1995; Mitchell et al. 1995; Vingerling et al. 1995). It is obvious that persons with late ARM are more aware of their eye disease, although a previous study showed that 67% of patients with late ARM were unaware of it (Topouzis et al. 2006). On the other hand, even late ARM may remain unnoticed because 40–60% of late ARM is found only in one eye, when binocular VA remains unaffected (Vinding 1989; Laatikainen & Hirvelä 1995; Topouzis et al. 2006).

DR is the most common ocular complication of DM, with potentially devastating effects on vision. According to information from the National Prescribing Register, 3% of the Finnish population was using medication for DM at the time of the Health 2000 survey (National Agency for Medicines and Social Insurance Institution 2002). The prevalence of 1% found for DR in our study may indicate that about one third of people with diabetes have retinopathy. In our study population, 23% of those reporting taking medication for DM had DR. However, the prevalence of DR in all those with DM was lower (16%), suggesting that retinal changes are more infrequent in those with DM only treated dietarily, which is in accordance with an earlier report (Mitchell et al. 1998). As expected, the prevalence of DR in studies using ophthalmoscopy or fundus photographs to assess DR has been found to be higher than in our study. In Australian middle-aged or older persons, the prevalence of DR was 1.5–2.3% in the general population and 29–32% in those with DM (Mitchell et al. 1998; McKay et al. 2000). Hirvelä & Laatikainen (1997) observed that 5% of the whole population and 21% of the people with diabetes aged 70 and older had DR. They also found that in the majority of cases the retinal changes were mild, and preproliferative or proliferative changes were present in only 3.5% of persons with DM. This may at least partly explain the lower prevalence of DR among people with diabetes in the present study. It is unlikely that all people with diabetes are aware of their retinal lesions, especially in the early stages. We are still concerned that 41% of persons with DM reported not having had diabetes-related retinal photography or a fundus examination at all, although a quarter of these persons reported having seen an ophthalmologist earlier. Thus it is possible that they were merely unaware that a fundus examination had been performed on that occasion. However, McKay et al. (2000) also reported that almost one third of their Australian patients with DM had never seen an ophthalmologist, and only about half of them had had a retinal examination in the previous 2 years.

In this study, women had cataract and glaucoma more often than men. Most previous studies have shown that lens opacities and cataract are more common in women than in men (Leibowitz et al. 1980; Häkkinen 1984; Gibson et al. 1985; Jonasson & Thordarson 1987; Klein et al. 1992a; Hirvelä et al. 1995; Reidy et al. 1998; Östberg et al. 2006), but the age-adjusted gender difference was statistically significant in only a few studies (Jonasson & Thordarson 1987; Klein et al. 1992a; Reidy et al. 1998; Östberg et al. 2006). Contrary to our findings, previous studies have reported that glaucoma is more prevalent in men than in women (Leibowitz et al. 1980; Jonasson & Thordarson 1987; Dielemans et al. 1994; Ekström 1996; Bonomi et al. 1998; Reidy et al. 1998; Wolfs et al. 2000) or that there is no gender difference (Martinez et al. 1982; Gibson et al. 1985; Ringvold et al. 1991; Klein et al. 1992b; Hirvelä et al. 1994; Weih et al. 2001; Jonasson et al. 2003; Nizankowska & Kaczmarek 2005). The gender differences found in our study may be caused by earlier manifestation of these eye diseases in women and/or differences in seeking treatment; this is supported by the fact that there was no gender difference in the prevalences of major eye diseases in persons with VA < 0.5. Also, the prevalence of operated cataract was similar in both men and women.

Prevalence of reduced VA associated with major eye diseases in the population

In persons aged 30–64, the prevalence of reduced VA caused by major eye diseases was very low. In this age group only 18 of the 5434 persons (0.3%) had reduced VA (< 0.5) associated with these diseases. In persons aged 65 or older, the prevalence of reduced VA associated with unoperated cataract, ARM, glaucoma and DR was 4.2%, 3.7%, 2.3% and 0.4%, respectively. The high prevalence of reduced VA in elderly people highlights the need to screen for these diseases more thoroughly among them.

Prevalence of chronic eye diseases in persons with visual impairment

In this study, the most common eye diseases in persons with visual impairment (VA ≤ 0.25) were ARM (37%), unoperated cataract (27%), glaucoma (22%) and DR (7%) with other eye diseases or alone. According to the Finnish Register of Visual Impairment, 40% of visual impairment at the time of the Health 2000 survey was associated with ARM, 8% with glaucoma and 9% with DR (Ojamo 2001). The figures concerning the prevalence of ARM and DR are similar to our results. However, the prevalence of glaucoma in persons with visual impairment was higher in our study. Unlike the Finnish Register of Visual Impairment, we were unable to assess the main reason for visual impairment, and our results merely report the total prevalence of major eye diseases in persons with visual impairment. In our study, too, glaucoma had seldom been the only cause of low vision (5%) and blindness (0%). The Finnish Register of Visual Impairment does not contain any information on cataract, because permanent visual impairment can usually be prevented with surgery.

Methodological considerations

Participation is an important factor contributing to the estimated prevalence rates in population studies. Although our study had a high response rate, it is likely that selective participation nevertheless caused some bias in the results. Based on the national registers and the case records obtained, non-participants were more likely to have ARM (p < 0.01), but with other diseases the differences were not significant (cataract p = 0.24, glaucoma p = 0.13 and DR p = 0.18). There are various potential reasons for non-participation. In addition to eye diseases, cognitive impairment and other chronic conditions prevent persons from attending a population survey (Livingston et al. 1997; Munoz et al. 1999). On the other hand, those with a known eye disease requiring regular follow-up and medication may be particularly willing to participate in a health examination survey. In our study, however, the bias was probably smaller than usual because of the exceptionally high response rate and the nationwide sampling design.

To improve the reliability of our results, we supplemented our information on self-reported eye diseases with data from the national registers. Also, case records were gathered for non-participants and persons with VA < 0.5 or reporting difficulties in vision or eye diseases without assessed VA. Even so, it is likely that the reported prevalences of cataract, ARM and DR are underestimations of the true rates in the Finnish population. Previous studies in the US have shown that only 18% of persons with verified ARM, 33% of those with DR and 46% of those with cataract reported having these eye diseases, possibly because of recall error or uncertainty of the diagnosis (Klein et al. 1986; Linton et al. 1991). Mild changes, in particular, were more unlikely to be reported. Our result concerning the correlation between register-based and self-reported eye diseases agreed with earlier studies, although we got higher sensitivity rates. The poor correlation between self-reported and specialist-assessed ARM in persons aged 30–74 may be because of the low prevalence of ARM and the higher prevalence of other degenerative fundus changes in this age group. It was possible to determine persons with glaucoma more comprehensively thanks to the National Medication Reimbursement Register and the National Prescription Register; glaucoma patients seemed more likely to participate in the survey. However, even the prevalence of glaucoma may be an underestimate because 10–50% of glaucoma patients may not be aware of their disease (Tielsch et al. 1991; Wang et al. 1994).

There seems to be many persons with reduced VA who do not know that they have an eye disease; the presence of eye disease could not be verified from case records or the national register, either. Based on the previous studies, eye symptoms have been found to be one major reason to contact eye services (Orr et al. 1999; Wang et al. 1999; Keeffe et al. 2002). This is in accordance with our finding that the number of persons without known eye diseases is higher in the categories of better VA. Some of the decreased VA may also be explained by uncorrected or under-corrected refractive errors. In persons with visual impairment, especially among blind persons, dementia explained most of the missing information on eye diseases.

In conclusion, this article provides the first nationwide population-based prevalence estimates of clinically relevant major eye diseases in the Finnish adult population. The high prevalence and the important role of these mainly age-related eye diseases as the cause of visual impairment, together with the growing number of elderly people, mean that continuous efforts are needed to discover and treat eye diseases in order to maintain the quality of life of patients and to alleviate the social and economic burden of serious eye diseases.