The aim of the current study was to investigate the prevalence of age-related eye diseases in a cohort of self-proclaimed healthy elderly, and thus get a very rough estimation of the prevalence of undiagnosed age-related eye conditions in the Belgian population. This study shows that, even in a highly educated, self-conscious elderly cohort without visual complaints, potentially sight threatening ocular pathology is detected and therapeutical interventions are indicated in a significant proportion of individuals. Because of different sample characteristics, these results do not reflect the findings regarding prevalence and causes of visual impairment in a sample of the general population aged over 55, as has been extensively studied in large cohorts (26-35). The outcomes of the current study do not allow to draw population-wide conclusions, but they definitely consolidate the generally accepted and by the AAO formulated recommendation to visit an ophthalmologist every year or two from the age of 65 onwards (10). Although the need for referral was relatively higher among those younger than 65 compared to the 65+ year group in this cohort (41% versus 22%, P > 0.05), all patients that needed an intervention belonged to the 65-74 year subgroup. A possible explanation for this finding is that many of those aged 65 - 74 and willing to participate, already had been diagnosed with, and potentially treated for, an age-related eye disease by their ophthalmologist prior to this study, hence not meeting the inclusion criteria. As such, the latter age group might be considered as a particular target group for early diagnosis and initiation of treatment of age-related ocular pathology. Additionally, one in ten participants were advised to have regular check-ups with their ophthalmologist, bringing the total proportion of participants in whom additional examinations or more frequent follow-up were indicated to 34%. This means that one in three elderly could possibly benefit from regular ophthalmologist visits, which is in accordance with findings documented about 15 years ago by Sloan et al (9). However, the absence of interventions during the 18-month period after study participation among those advised to have a regular follow up of identified changes might indicate that a larger interval between follow-ups suffices in certain conditions. For example, a short interval in cases of asymptomatic pathology that lacks therapeutic implications, such as ERM (with OCT), does not probably fit the cost-effective approach required by current medical care healthcare systems.
The most prevalent causes of blindness and visual impairment are known to vary with age. A review by Finger & Scholl on blindness and visual impairment in high-income countries reported AMD, followed by DRP, as the most frequent causes of blindness and severe visual impairment in those aged 60-79 years. Above this age, AMD remained first, followed by glaucoma (1). According to Klein & Klein, those aged 80 and older represent the heaviest burden of age-related eye disease in the United States, accounting for one-third of all cases of cataract, open-angle glaucoma, and early AMD and two-thirds of late AMD cases (36). Due to its insidious nature, partly related to the centripetal pattern of visual field deterioration, glaucoma is expected to be more prominent in an asymptomatic cohort, such as the one studied here, compared to other prevalent and potentially sight threatening age-related eye conditions such as AMD, often causing symptoms related to centrifugal central vision loss at an earlier disease stage.
Notwithstanding the fact that the majority of participants visited an ophthalmologist less than four years prior to the study, a considerable amount of potentially sight threatening ocular conditions, which participants were not aware of, were uncovered by the comprehensive study protocol. This can be due to little importance attributed to the particular findings by the ophthalmologist, to findings missed by the ophthalmologist, or to the patients’ inability to take in all information given during a consultation. As suggested by Keunen et al., in the Netherlands, more than half of the visually impaired aged 65 and above suffer from an eye disease that could have been treated or prevented, due to a large proportion of the elderly not making use of eye care (26). This was confirmed by Cedrone et al. in Italy (27). Seniors tend to believe that visual impairment is part of the aging process, making them less aware of gradual visual decline. No comparable data exist for the Belgian elders, but the present study concerns a subgroup of seniors with a certain degree of self-consciousness, in view of their willingness to participate to this study.
No high-risk groups for the development of visual impairment could be identified in the study cohort. This can be explained by a selection bias, since patients that were already aware of having eye pathology were excluded. Additionally, the study population of overall healthy and mobile elders has easier access to health care than the average senior, and the majority of the study population paid regular visits to their ophthalmologist, where serious eye diseases had already been diagnosed. Nonetheless, there were several risk factors for visual impairment in this cohort, with aging being the most important one (29, 33, 37, 38). There is no consensus on gender as a potential risk factor, but history of any ocular disease, diabetes mellitus, lower socioeconomic status, unemployment, and institutionalization have been reported as independent risk factors for visual impairment (26, 29, 33, 37, 38). This shows once more that the average study participant had a low-risk profile for the development of visual impairment, except for age. It is striking, however, that even in such a ‘privileged’ group, 26 referrals led to four interventions.
In this asymptomatic cohort, a low prevalence of clinically significant cataract, AMD and DRP was expected. The pseudophakia prevalence of 9% in the current study corresponds well with German findings (39). The single case with significant cataract in the current study was associated with long-term corticosteroid treatment, a well-known risk factor for the development of cataract (40). The prevalence of asymptomatic macular drusen (1.96%) and focal VMT (0.98%) in the study population is in line with previous findings by Jacob et al. in a sample of the Belgian population aged 34-66 years, taking into account the fact that the current study sample had a higher age (41). Belgium has a prevalence of diabetes mellitus of 6.1% among its adults (42). The vast majority of Belgian diabetic patients is older than 65 (43), resulting in a substantially higher prevalence among the elderly. A worldwide meta-analysis by Yau et al. revealed the presence of any form of diabetic retinopathy in 35.36% of diabetic patients (44), in line with the analysis of the National Health and Nutritional Examination Survey (NHANES) data noting a crude prevalence of diabetic retinopathy of 29.5% among patients with diabetes over 65 (45). All this information, coupled with the fact that the current study population had a good general health and a considerably higher socio-economic status, explains the low prevalence of diabetes mellitus and DRP (46).
Glaucomatous pathology is often characterized by a creeping onset and the lack of symptoms until extensive optic nerve damage has occurred. Together with a crude global prevalence of 3.54% in the population aged 40-80 years (47) and a risk that increases with age (15, 36, 47), glaucoma is a model example of an age-related, potentially sight threatening, ocular disease that can be detected in a cohort of asymptomatic elderly. According to a cross-sectional study by Shaikh et al., approximately 78% of US glaucoma cases are undetected and/or untreated, most of them being not even in their sixties (48). This is in agreement with the three interventions related to glaucomatous diagnoses in the current study cohort. Comparable to the findings of Weih et al. (49), the Thessaloniki Eye Study proposed the lack of regular ophthalmologist visits as the main risk factor associated with undiagnosed open angle glaucoma (13). On the contrary, other authors stated that more than half of glaucoma patients identified by population screening had been previously examined by an ophthalmologist or eye care professional, and 17% even by an ophthalmologist in the two years prior to the screening visit (16). In the current study, about half of the referrals and interventions were noted in the subgroup that paid regular visits to their ophthalmologist. All of the interventions and more than half of the referrals for additional examinations took place in participants who, if ever, last visited their ophthalmologist more than one year ago. This highlights the importance of the interval of ophthalmologist visits, but at the same time confirms that the detection threshold in the setting of study screening is different from that in clinical practice. This has been investigated by O’Neill et al., who showed that ophthalmology trainees as well as comprehensive ophthalmologists underestimated glaucoma likelihood in approximately one out of five disc photographs, and that they were twice as likely to underestimate as overestimate glaucoma likelihood, compared to glaucoma specialists (50).
According to the US Preventive Services Task Force and the World Glaucoma Society, current evidence is insufficient accept or reject the idea of routine glaucoma screening, because of a shortage of data, regional economic evaluations, and screening test algorithms with high specificity. The question is raised whether targeted screening could be more effective (20, 21). It will be crucial to determine the ideal window and tools to screen, ideally with a simple, reliable and inexpensive screening test, that can effectively detect disease at a time when intervention can have a significant impact on the patient’s quality of life. This study suggests that screening for glaucoma and other age-related sight threatening conditions could be worthwhile in (subgroups of) the 65-74 years old age group, since all interventions took place in this age group of asymptomatic participants who are likely to have several more decades of living independently and in reasonably good health ahead of them. However, if screening for glaucoma and possibly other age-related ocular diseases such as cataract, AMD and DRP would be cost-effective, a clear strategy regarding referral, follow-up and treatment needs to be defined, since low referral uptake has also been demonstrated in elderly (13, 51).
Limitations of the present study constitute first of all a selection bias, since those who participated may be more health conscious and take better care of themselves. This cohort will probably obtain more regular ophthalmologist visits than less health conscious seniors and those belonging to disadvantaged communities with limited access to health care (52), but less than those with ocular conditions or vision problems and diabetes (53-55). Secondly, some of the data were based on self-report and no clinical measures of visual acuity have been made. A third limitation is the small sample size and, related to this, the small number of incident cases. Study strengths concern the absence of active ocular diagnoses and vision-related symptoms, both typical features of a senior population potentially suited for screening, and the longitudinal component of this study. To our knowledge, this is the first study to assess the prevalence of various age-related ocular pathology in a Belgian cohort of asymptomatic elderly.
Future research focusing on the cost-effectiveness of regular eye examination versus screening programs is warranted. Visual impairment in the elderly is associated with many comorbidities, of which cognitive impairment is a very important one (56-58). With the growing number of seniors in today’s society, the risk of visual decline with aging needs to be effectively reduced to ensure healthy aging with preserved quality of life. This study shows that even in an elderly population with self-proclaimed healthy eyes and good general health, a significant proportion of subjects showed ocular findings that need regular follow up and/or therapeutical intervention. Moreover, the frequency of prior ophthalmological examinations does not seem to be relevant to this proportion, meaning that everyone above 55 years old needs a routine ophthalmological evaluation.