Health-related quality of life and related factors among older adults with visual impairments

Abstract

Aim was to explore the health-related quality of life (HRQoL) and related factors among older adults with visual impairment (VI). A total of 39 independently living subjects aged ⩾65 years (83 ± 6.5), referred to the Low Vision Center of the Oulu University Hospital, Finland during one year participated in the study. The participants had low vision or blindness as defined by the World Health Organization (WHO). The 15D, a generic HRQoL instrument, was used to assess the HRQoL, and an ophthalmic examination was performed to assess vision. A population-based control group (n = 1074) was available for comparison. The mean 15D index scores for the participants and the control group were 0.768 (SD = 0.089) and 0.827 (SD = 0.044), respectively, (p < .002). In the dimensions of move (p < .05), see (p < .001), breath (p < .05), usual activities (p < .001), depression (p < .05), and distress (p < .05), the study participants scored statistically significantly lower than the control group. However, the participants had better mental function scores (0.856 vs 0.773, p < .05). Among the participants, there was no difference in the 15D by gender (men 0.755, women 0.774, p > .05), habitation (alone 0.768, with someone 0.770, p > .05), or age (r = –.084), nor did the extent of low vision appear to affect the 15D index in this material. The older adults with VI had poorer 15D index score than Finnish population of equal age, but they scored better in the dimension of mental function. Mental skills may indeed be crucial for independent living despite VI.

Keywords

Introduction

The global population of older adults is predicted to increase rapidly (World Health Organization, [WHO], 2015), and aging is changing the demographics of European countries. People aged 65 or over represent a 19.4% share of the European Union population (Eurostat, 2018). In Finland, the proportion of people over 65 years old is expected to rise from 21% at present to 29% by the year 2060 (Official Statistics of Finland [OSF], 2015). Aging causes slight changes in visual function that reduce visual acuity (VA) (Martinez-Roda et al., 2016). In addition, aging increases the risk of developing a major eye disease (Lee, Feldman, Ostermann, Brown, & Sloan, 2003). However, loss of vision to the extent of visual impairment (VI) as a natural consequence of aging is not inevitable, even though some older adults may assume otherwise.

In this study, VI is defined as a VA of <0.3 (Snellen decimal, equal to 6/20 or logMAR 0.52) in the better eye; this definition encompasses both low vision and blindness (WHO, 2003). VI threatens the survival of those it affects, and its prevalence increases markedly with age and places a particularly heavy burden on women (Bourne et al., 2017). As populations age, more people will be at risk of this condition. In Finnish population, 80%–90% of VI cases occur in people aged 65 and over, and the incidence of VI is increasing most rapidly among people over 85 years old. There are actually in number more people with VI in the 85+ age group than in the 65–84 age group (Ojamo, 2016).

Worldwide VI is unequally distributed: 89% of individuals with VI live in low- or middle-income countries (Bourne et al., 2017; Flaxman et al., 2017). Uncorrected refractive errors and cataracts (Flaxman et al., 2017) are the most frequent causes of mild and moderate VI worldwide, but retinal diseases are becoming increasingly common. In industrialized and developed countries, the most common cause of VI is age-related macular degeneration (AMD) (Flaxman et al., 2017; Mitchell, Liew, Gopinath, & Wong, 2018). Age is a major risk factor and almost all late AMD cases occur in the elderly (Mitchell et al., 2018). In Finland, AMD and other retinal diseases are responsible for 59% of VI in people over 65 years of age; glaucoma is the second most common cause (9%). Blindness (defined by a VA of <0.05 or a visual field radius of <10°) is rare among people over 65 years old and particularly uncommon among people >85 years (Ojamo, 2016).

Previous literature highlights the need to better understand how visual ability affects elderly people (Källstrand-Eriksson, Baigi, Buer, & Hindingh, 2013). Visual loss not to mention VI is associated with functional decline and challenges in performing everyday activities (Pérèz et al., 2017). VI is also associated with depressive symptoms (Bernabei et al., 2011; Brown & Barrett, 2011) and social loneliness (La Grow, Towers, Yeung, Alpass, & Stephens, 2015). Also, wet AMD reduces quality of life, causing symptoms such as vision-related depression, reduced mobility, and a limited capacity to perform routine activities (Varano et al., 2016). Elderly people with low VA reportedly have a worse quality of life (QoL) than their fully sighted peers (Harutyunyan, Giloyan, & Petrosyan, 2017; Källstrand-Eriksson et al., 2013; Renaud et al., 2010).

Health-related quality of life (HRQoL) is a subjective and multidimensional concept with no universally accepted definition (Sintonen, 2001). However, it is widely accepted to have physical, emotional, and social components that may be affected by illness or treatment (Sintonen, 2001). There are both generic and function-specific HRQoL measures available. Previous literature indicates that reduced QoL is associated with lower economic well-being, decreased physical and mental health, functional limitations affecting routine activities and independent mobility, a risk of social isolation, and lower life satisfaction (Brown & Barrett, 2011; La Grow et al., 2015). The 15D HRQoL instrument has been used in population surveys in Finland to investigate the impact of several major chronic conditions on HRQoL. Musculoskeletal disorders such as arthrosis of the hip and knee and back problems followed by psychiatric conditions are associated with the largest losses of HRQoL in Finnish population (Saarni et al., 2006). Previously, it has been noticed that the 15D HRQoL index scores of patients waiting for cataract surgery did not differ from those of their peers (Falck, Kuoppala, Winblad, & Tuulonen, 2008). Similarly, the 15D scores of diabetic patients were not significantly different from those for a control group; significant differences were only observed for patients with severe retinopathy (Schanner, Falck, Keskitalo, & Hautala, 2016). Vision-specific QoL measures have been used to show or quantify the effect of treatments in certain patient groups (e.g., cataract patients). However, unlike more general instruments, function-specific instruments do not permit comparisons with other groups such as stroke or cancer patients. People with macular degeneration have reported the lowest HRQoL scores along with Parkinson’s disease and heart failure on population level (Saarni et al., 2006), but the HRQoL of older adults with VI has not been studied in detail in Finland. A generic HRQoL questionnaire was chosen as it was hypothesized that it could be sensitive enough to detect a decline related to low vision. Should the data support this, it indicates that VI is a major chronic health problem (Haacke et al., 2006; Xie et al., 2006). Mean 15D values for cancer patients have reported to be 0.855 and for stroke 0.801 (Saarni et al., 2006).

The results presented here shed light on the problems and potential strengths of aged people with VI and show that the latter may enable such individuals to maintain a satisfactory QoL despite their VI. As such, our findings may increase understanding of both the close ones and a wide range of health and social care professionals who work with such patients. This study explores HRQoL in detail among older adults with VI and its relationship with factors such as visual function, ophthalmic status, and VI severity, which is highly important in Finland. It is designed to add new knowledge to the international field of disability and VI research by contributing insight into the HRQoL of older adults with VI and the challenges they face in their daily lives by looking at HRQoL on it’s different dimensions.

Methods

In Finland, people are usually referred for vision rehabilitation by an ophthalmologist. During the 12 months over which this study was conducted (May 2016–May 2017), 79 individuals aged 65 or above were referred to Oulu University Hospital Low Vision Center (OLVC). All of them were sent an appointment letter informing about this study and inviting to participate. The study’s inclusion criteria were age >65, living at home, and VI criteria fulfilled (WHO, 2003) both when referred and when examined at the OLVC. Patients who had previously visited OLVC were excluded. Each subject underwent an ophthalmic examination that confirmed their diagnosed VI status.

A total of 24 patients did not participate in the study. A total of 19 gave no reason for refusal, two did not attend their appointment, and three canceled their appointment and informed they did not wish to attend the OLVC. A total of 16 patients were excluded after visiting the OLVC because ophthalmic examination indicated that they did not satisfy the criteria for VI (n = 12), two exhibited advanced memory loss, there was a language barrier in one case, and one had previously visited the OLVC and received vision rehabilitation services. Figure 1 illustrates the participant selection process.

Figure 1.

Flow chart illustrating the study participant selection process.

The final sample included 39 participants who gave written informed consent upon their first visit to the OLVC. An ophthalmologist evaluated each participant’s ophthalmic status during this visit; data on the diagnosis(es) responsible for the VI as well as any other ocular conditions, age, gender, and best corrected distance visual acuity (BCVA), reading acuity, and visual fields (if applicable) were recorded. BCVA for distance was measured by a Snellen decimal chart and the values were converted into logMAR scale (Holladay, 1997, 2004). The same was done for reading acuity, which was measured the patient wearing +3.50D near correction in addition to correction of the refractive error. Each participant was evaluated for VI severity, which was coded on a scale ranging from 1 to 5 based on the WHO classes. Scores of 1 (0.3 > VA ⩾ 0.1 with better eye using the best possible correction) or 2 (0.1 > VA ⩾ 0.05) correspond to low vision. Scores of 3 (0.05 > VA ⩾ 0.02), 4 (VA < 0.02 but patient retains light perception), and 5 (patient has no light perception) all correspond to blindness.

The study was conducted at the onset of the vision rehabilitation process. The participants were compared with a population-based control group of 1074 subjects of equal age and gender examined during a national Health 2011 survey conducted by the National Institute for Health and Welfare (THL) in Finland (Koskinen, Lundqvist, & Ristiluoma, 2012).

HRQoL was assessed using the 15D instrument, which was administered by interview because the participants with VI could not self-administer the questionnaire. The 15D instrument is widely used to assess HRQoL and is known to have high validity and reliability (Sintonen, 2001). It is a generic and comprehensive instrument for measuring HRQoL that follows the WHO’s definition of health. It addresses several distinct dimensions of HRQoL, namely: mobility, vision, hearing, breathing, sleeping, eating, speech, excretion, ability to perform usual activities, mental function, discomfort and symptoms, depression, distress, vitality, and sexual activity. Each dimension is divided into five ordinal levels and the respondent is asked to choose the level best describing their present subjective health status. The responses to a completed questionnaire can be used to establish a profile of the respondent’s current HRQoL and to calculate an index score reflecting their overall HRQoL. The index score ranges from 0 to 1; 0 corresponds to being dead and 1 to the highest possible QoL with no problems on any dimension (Sintonen, 2001).

Research data were stored and analyzed using the IBM SPSS^® program (version 24.0; SPSS Inc., Chicago, IL, USA). It is common that patients do not answer the question of sexual activity. Occasionally, people also leave some other question without an answer. A combined valuation replacement algorithm for the 15D instrument can be used when there are no more than three missing values (Sintonen, 2018), and this is how the data were handled. The respondents’ HRQoL profiles were analyzed to identify dimensions adversely affected by VI. In addition, a total index score (i.e., the 15D score) was produced for each respondent using a set of population-based utility weights and utilities provided for use with the 15D instrument (Sintonen, 2018) to obtain an overall picture of each respondent’s HRQoL based on the guidance for the 15D instrument.

Statistical methods

Statistical analysis of the data consisted of descriptive statistics and comparison of groups. Frequencies and percentages were calculated for the graded variables. For continuous variables, mean and median values, minimum and maximum, and standard deviations were calculated. The relationships of the variables were evaluated by cross-referencing and computing correlation coefficients. The non-parametric Mann–Whitney U test and independent samples t-test were used to examine the differences between variables and to compare the participants and the control group (with p < .05). The effect sizes (Cohen’s d) were calculated to accompany the p-values of the group comparisons to show the magnitude of the presented effects. In interpreting of the effect size measures the standards suggested by Cohen (1988, 1992) were used: small (d = 0.20), medium (d = 0.50), and large (d = 0.80).

The study was approved by the Ethics Committee and the Northern Ostrobothnia Hospital District and followed the good research ethics practices specified by the Finnish Advisory Board on Research Integrity 2012 and the 2017 Helsinki Declaration of the World Medical Association (WMA) (TENK, 2012; WMA, 2017). Participation was voluntary and did not affect the treatment of the elderly subjects with VI. The participants could withdraw or suspend their participation at any stage without giving any reason. The gathered data were processed, analyzed, and stored confidentially so that no individual could be identified.

Results

A total of 39 (63%) of the 62 patients who met the inclusion criteria during the study period participated in the study. A total of 27 (69%) were women. The mean participant age was 83 (SD = 6.5; range: 70–93) years. Most of the participants were 80–89 years old (n = 23). A total of 25 lived alone; the remaining 14 lived with someone – in most cases, their spouse. Retinal diseases were the principal cause of VI in the majority (85%). The disease responsible for the most recent deterioration of vision in the better eye was diagnosed as AMD in 32 cases (wet AMD in 13 cases, dry AMD in 19). The mean reading acuity in the sample was 0.88 logMAR (0.15 on the decimal scale), corresponding to being able to read 20-point text. Most of the patients were moderately visually impaired (class 1, n = 34). The participants lived in cities and sparsely populated areas of northern Finland (Table 1).

Table 1.

Background characteristics of the study participants (n = 39).

Background variable	n (%)
Age (years)
70–74	5 (13)
75–79	5 (13)
80–84	11 (28)
85–89	12 (31)
90+	6 (15)
Gender
Male	12 (31)
Female	27 (69)
Habitation
Living alone	25 (64)
Living with someone	14 (36)
Diagnosis of primary eye disease
Retinal disease^a	33 (84)
Glaucoma	5 (13)
Corneal disease	1 (3)

AMD: age-related macular degeneration.

Including AMD, proliferative diabetic retinopathy, diabetic maculopathy, macular hole, and central retinal venous occlusion.

The mean 15D HRQoL score for the study population was 0.768 (SD = 0.089, range: 0.544–0.945, median: 0.770). The worst 15D mean HRQoL index scores were 0.544, 0.549, and 0.598. The majority scored between 0.717 and 0.797, however. One-fourth scored better than 0.800 and a few even over 0.900. The HRQoL dimensions with the lowest average scores were seeing (M = 0.389, SD = 0.107) and ability to perform usual activities (M = 0.582, SD = 0.245). Dimensions less strongly associated with problems included depression (M = 0.847, SD = 0.170), and distress (M = 0.856, SD = 0.187). A Mann–Whitney U test indicated that neither gender nor living alone had any significant effect on HRQoL (p = .599 and p = .806, respectively). The 15D HRQoL scores did not correlate with age, r(39) = –.084, p = .613. The extent of low vision did not have an effect on HRQoL in this patient population t(37) = 1970, p = .056, d = 1.097. The 15D HRQoL index in relation to the BCVA, reading acuity, and the VI class are collected in Table 2.

Table 2.

The relation of BCVA (logMAR), reading acuity, and VI class (WHO) and the 15D HRQoL index.

Extent of low vision	N (%)	Mean	Mean (15D HRQoL index)	Pearson correlation coefficient (r)
BCVA, right eye	36 (92)	0.9 (±SD 0.514)		−.174
⩽0.99	22 (56)
1.0–1.29	8 (21)
1.3–1.69	6 (15)
⩾1.7	0
BCVA, left eye	32 (82)	1.0 (±SD 0.636)		.220
⩽0.99	20 (51)
1.0–1.29	7 (18)
1.3–1.69	1 (3)
⩾1.7	4 (10)
BCVA, better eye	39 (100)			−.165
>1.0	5 (13)		0.839 (±SD 0.550)
0.79–1.0	8 (21)		0.770 (±SD 0.616)
⩽0.8	26 (66)		0.754 (±SD 0.968)
Reading acuity	38 (97)	0.88 (±SD 0.186)		−.105
>1.0	25 (64)		0.779 (±SD 0.082)
>0.7, ⩽1.0	8 (20)		0.713 (±SD 0.115)
>0.52, ⩽0.7	3 (8)		0.776 (±SD 0.034)
⩽0.52	2 (5)		0.777 (±SD 0.061)
VI class (WHO)	39			.353
Moderate VI	34 (87)		0.758 (±SD 0.089)
Severe	4 (10)		0.825 (±SD 0.052)
Deep VI	1 (3)		0.896
Almost blind or totally blind	0

SD: standard deviation; BCVA: best corrected distance visual acuity; VI: visual impairment; HRQoL: health-related quality of life; WHO: World Health Organization.

One-sample t-test indicated that the mean 15D HRQoL score for older patients with VI was significantly lower (by 0.058 units) than that for the population-based control group t(76) = 3.66, p = .001, d = 0.092. Figure 2 shows the mean 15D HRQoL profiles and scores of the OLVC subjects and the Health 2011 control population.

Figure 2.

Mean 15D profiles accompanied with p-values and Cohen’s d effect size measures of the OLVC participants, and a subsample of the Health 2011 population standardized to match the age and gender distribution of the OLVC sample.

Discussion

This study was carried out to assess the 15D HRQoL and its different dimensions among older adults with VI at the onset at the low vision rehabilitation process. Although the majority of the 70- to 93-year-old study participants reported their overall HRQoL to be at least fair, the differences between individuals were great. Their main challenges related to moving, seeing, breathing, and performing routine activities. Difficulties with mobility can be partly attributed to societal and environmental factors, but VI itself may be a major factor (Schölvinck, Pittens, & Broerse, 2017). Public spaces, poorly marked sidewalks, difficulties reading information about public transportation, and difficulty listening to broadcasts may reduce the ability of visually impaired people to orient themselves, create a fear of losing balance, and increase the time required to make travel preparations (Schölvinck et al., 2017). These results support previous findings that VI reduces perceived HRQoL (Harutyunyan et al., 2017; Källstrand-Eriksson et al., 2013; Renaud et al., 2010).

However, in contrast to previous reports, the participants had few difficulties relating to the dimensions of mental function, depression, or distress. Other studies (Bernabei et al., 2011; Brown & Barrett, 2011; Montejo, Montenegro-Peña, López-Higes, & Montejo, 2016) have found these dimensions to be challenging for people with VI. However, the study participants’ mean score for the mental function dimension was high. Most of the participants (62%) said that they could think clearly and logically, and that their memory functioned well. A third reported some difficulties in thinking clearly and logically or occasional memory loss. Only one participant experienced marked problems with memory.

Our results indicated that age, gender, and living alone had unexpectedly no significant impact on HRQoL, even though two thirds of the participants lived alone. This is contrary to what has been reported before (La Grow et al., 2015). The family status of our sample reflects that of the Finnish VI population, in which 59% of registrants have no immediate family members (Ojamo, 2016). It has previously been reported that older adults with VI exhibit elevated levels of social loneliness and have worse perceived QoL than fully sighted peers (La Grow et al., 2015). Severity of vision loss did not have an impact on the HRQoL, which also was surprising compared with previous studies (Harutyunyan et al., 2017). This may in part be due to the limited number of participants with severe VI; the majority had low vision and the participants of this study were rather homogeneous with the extent of their VI.

There were several statistically significant differences between the study sample and the control group representing the general population. The control group had a higher overall mean 15D HRQoL score, but the study participants had a higher mean mental function score. This suggests that mental skills and memory function may help compensate for visual problems and could be crucial for independent living with VI, an inclusion criterion for the study. Recent studies (Sgaramella, Nota, Carrieri, Soresi, & Sato, 2017) would support this by suggesting that problem solving may play a key role in adapting to the difficulties confronting elderly people with VI when performing routine activities. It was also recently shown (Dormal, Crollen, Baumans, Lepore, & Collignon, 2016) that vision is not required for effective working memory, and that persons with VI rely on non-visual cognitive strategies such as verbal description. In addition to good mental capacity, coping in everyday life and maintaining a good QoL despite VI may also depend on stable general health, resilience, or a supportive spouse. The difference in the mean HRQoL index score between the sample and the population was 0.06 and can be considered both statistically and clinically significant. The smallest clinically relevant (i.e., perceptible by patients) differences between 15D scores are considered to be in the range ⩾0.02–0.03 (Sintonen, 2001), and it has been argued that the most meaningful outcome of a clinical intervention may be a change in the patient’s perception of their own well-being (Renieri, Pitz, Pfeiffer, Beutel, & Zwerenz, 2013). Therefore, even slight differences in mean scores between groups should not be overlooked.

Limitations

In addition to VI, the older participants had also other diseases, disabilities, and medication that were not addressed in this study but do have an effect on perceived HRQoL. Anyhow, both this work and previous studies indicate that VI reduces HRQoL. It is assumed that this negative effect could be mitigated by low-vision rehabilitation and vision rehabilitation counseling. Furthermore, research is needed to assess the effectiveness of such interventions. It will also be necessary to better characterize the impact of multisensory impairment on HRQoL because combined visual and auditory impairment reportedly has a stronger negative effect on HRQoL than either impairment alone (Bernabei et al., 2011; Khil, Wellmann, & Berger, 2015). The study sample includes all subjects living in the hospital district in question who were referred to low vision rehabilitation during one year. Two thirds of the subjects asked to join the study chose to participate. It is not known whether these individuals differed from those who chose not to participate. The study was based on carefully gathered data; the participants’ current ophthalmological status was evaluated at the same time as the interviews were performed. The smallness of the sample examined in this study limits the scope for generalizing its results. However, the sample was representative of the population with VI in Finland. The mean age of newly registered patients with VI in Finland in 2016 (n = 1603) was 84, and 65% of patients in this category were female (Ojamo, 2016); these figures being almost identical to the ones describing the study sample. The gender distribution (69% female, 31% male) of the sample was similar to that of population with VI in Finland and globally. (Bourne et al., 2017). In addition, according to the FVIR, 83% of new registrants have low vision and 15% are blind (Ojamo, 2016). AMD was the leading cause of VI in 74% of new registrants aged 65 + in 2016 in Finland (Ojamo, 2016), which was also the case in the sample.

Conclusion

VI reduces the HRQoL of older adults as compared with the general population. The great majority fared well in terms of HRQoL, showing problems only in the dimensions of vision, moving, and usual activities. However, some participants scored low in practically all dimensions, which may reflect reduced functional capacity due to several health issues. The ability to cope with and maintain a relatively good HRQoL despite VI may relate to individual strengths, such as intact mental capacity. In future research, the possibilities of low vision rehabilitation in restoring the HRQoL await to be evaluated.

Footnotes

Acknowledgements

Harri Sintonen, Jaana Penna, Eila Lukkarila, and Maritta Runtti are warmly acknowledged for their assistance.

Author contribution

H.S. collected data and wrote the manuscript with support and supervision from A.F. and H.K.

Data availability

The material was collected by the first author who can provide access to the data of interest.

Funding

This research was supported by a grant from The Finnish Foundation of Visually Impaired and The Friends of the Blind.

ORCID iD

Heidi J Siira

References

Bernabei

Morini

Moretti

Marchiori

Ferrari

Dalmonte

Atti

A. R.

(2011). Vision and hearing impairments are associated with depressive-anxiety syndrome in Italian elderly. Aging and Mental Health, 15, 467–474.

Bourne

R. R. A.

Flaxman

S. R.

Braithwaite

Cicinelli

M. V.

Das

Jonas

J. B.

Taylor

H. R.

(2017). Magnitude, temporal trends, and projections of the global prevalence of blindness and distance and near vision impairment: A systematic review and meta-analysis. The Lancet Global Health, 5, 888–897.

Brown

R. L.

Barrett

A. E.

(2011). Visual impairment and quality of life among older adults: An examination of explanations for the relationship. The Journals of Gerontology, Series B: Psychological Sciences and Social Sciences, 66, 364–373.

Cohen

(1988). Statistical power analysis for the behavioral sciences. Hillsdale, NJ: Lawrence Erlbaum.

(1992). A power primer. Psychological Bullerin, 112, 155–159.

Dormal

Crollen

Baumans

Lepore

Collignon

(2016). Early but not late blindness leads to enhanced arithmetic and working memory abilities. Cortex, 83, 212–221.

Eurostat. (2018). Population structure and ageing. Retrieved from http://ec.europa.eu/eurostat/statistics-explained/index.php/Population_structure_and_ageing#Further_Eurostat_information

Falck

Kuoppala

Winblad

Tuulonen

(2008). The Pyhäjärvi Cataract Study. 1. Study design, baseline characteristics and the demand for cataract surgery. Acta Ophthalmologica, 86, 648–654.

Finnish Advisory Board on Research Integrity (TENK). (2012). Retrieved from www.tenk.fi/en

10.

Flaxman

S. R.

Bourne

R. R. A.

Resnikoff

Ackland

Braitwaite

Cicinelli

M. V.

Taylor

H. R.

(2017). Global causes of blindness and distance vision impairment 1990–2020: A systematic review and meta-analysis. The Lancet Global Health, 5, 1221–1234.

11.

Haacke

Althaus

Spottke

Siebert

Back

Dodel

(2006). Long-term outcome after stroke: Evaluating health-related quality of life using utility measurements. Stroke, 37, 193–198.

12.

Harutyunyan

Giloyan

Petrosyan

(2017). Factors associated with vision-related quality of life among the adult population living in Nagorno Karabagh. Public Health, 153, 137–146.

13.

Holladay

J. T.

(1997). Proper method for calculating average visual acuity. Journal of Refractive Surgery, 13, 388–391.

14.

Holladay

J. T.

(2004). Visual acuity measurements. Journal of Cataract & Refractive Surgery, 30, 287–290.

15.

Källstrand-Eriksson

Baigi

Buer

Hindingh

(2013). Perceived vision-related quality of life and risk of falling among community living elderly people. Scandinavian Journal of Caring Sciences, 27, 433–439.

16.

Khil

Wellmann

Berger

(2015). Impact of combined sensory impairments on health-related quality of life. Quality of Life Research, 24, 2099–2103.

17.

Koskinen

Lundqvist

Ristiluoma

(Eds.) (2012). Health, functional capacity and welfare in Finland in 2011 (Report 68/2012). Helsinki, Finland: National Institute for Health and Welfare (THL).

18.

La Grow

S. J.

Towers

Yeung

Alpass

Stephens

. (2015). The relationship between loneliness and perceived quality of life among older persons with visual impairments. Journal of Visual Impairment & Blindness, 109, 487–499.

19.

Lee

P. P.

Feldman

Z. W.

Ostermann

Brown

D. S.

Sloan

F. A.

(2003). Longitudinal prevalence of major eye diseases. The Archives of Ophthalmology, 121, 1303–1310.

20.

Martinez-Roda

J. A.

Vilaseca

Ondategui

J. C.

Aguirre

Pujol

(2016). Effects of aging on optical quality and visual function. Clinical and Experimental Optometry, 99, 518–525.

21.

Mitchell

Liew

Gopinath

Wong

T. Y.

(2018). Age-related macular degeneration. The Lancet, 392, 1147–1159.

22.

Montejo

C. P.

Montenegro-Peña

López-Higes

Montejo

R. B.

(2016). Subjective memory complaints in elderly: Relationship with health status, multimorbidity, medications, and use of services in a population-based study. International Psychogeriatrics, 28, 1903–1916.

23.

Official Statistics of Finland. (2015). Population projection. Retrieved from www.stat.fi/tup/suoluk/suoluk_vaesto_en.html#populationprojection

24.

Ojamo

(2016). Annual statistics 2016. The Finnish register of visual impairment. Retrieved from http://nkl.fi/index.php?__file_display_id=12154

25.

Pérèz

Matharan

Daien

Nael

Edjolo

Bourdel-Marchasson

Ritchie

(2017). Visual loss and subsequent activity limitations in the elderly: The French three-city cohort. American Journal of Public Health, 107, 564–569.

26.

Renaud

Levasseur

Gresset

Overbury

Wanet-Defalque

M.-C.

Dubois

M.-R.

. . . Desrosiers

(2010). Health-related and subjective quality of life of older adults with visual impairments. Disability and Rehabilitation, 32, 899–907.

27.

Renieri

Pitz

Pfeiffer

Beutel

M. E.

Zwerenz

(2013). Changes in quality of life in visually impaired patients after low-vision rehabilitation. International Journal of Rehabilitation Research, 36, 48–55.

28.

Saarni

S. I.

Härkänen

Sintonen

Suvisaari

Koskinen

Aromaa

Lönnqvist

(2006). The impact of 29 chronic conditions on health-related quality of life: A general population survey in Finland using 15D and eQ-5D. Quality of Life Research, 15, 1403–1414.

29.

Schanner

Falck

Keskitalo

Hautala

(2016). Health-related quality of life of Finnish patients with diabetes. Scandinavian Journal of Public Health, 44, 765–771.

30.

Schölvinck

A.-F. M.

Pittens

C. A. C. M.

Broerse

J. E. W.

(2017). The research priorities of people with visual impairments in the Netherlands. Journal of Visual Impairment & Blindness, 111, 201–217.

31.

Sgaramella

T. M.

Nota

Carrieri

Soresi

Sato

(2017). Daily functioning, problem solving and satisfaction for quality of life in visually impaired old persons. International Journal of Disability and Human Development, 2, 225–232.

32.

Sintonen

(2001). The 15D Instrument of health-related quality of life: Properties and applications. Annals of Medicine, 33, 328–336.

33.

Sintonen

34.

Varano

Eter

Winyard

Wittrup-Jensen

K. U.

Navarro

Heraghty

(2016). The emotional and physical impact of wet age-related macular degeneration: Findings from the wAMD Patient and Caregiver Survey. Clinical Ophthalmology, 10, 257–267.

35.

World Health Organization. (2003). Prevention of blindness & deafness. Consultation on development of standards for characterization of vision loss and visual. Retrieved from http://apps.who.int/iris/bitstream/handle/10665/68601/WHO_PBL_03.91.pdf?sequence=1&isAllowed=y

36.

World Health Organization. (2015). World report on aging and health. Luxemburg, Europe: Author.

37.

World Medical Association. (2017). Declaration of Helsinki: Ethical principles for medical research involving human subjects. Retrieved from www.wma.net/policies-post/wma-declaration-of-helsinki-ethical-principles-for-medical-research-involving-human-subjects/

38.

Xie

E. Q.

Zheng

Z.-J.

Croft

J. B.

Greenlund

K. J.

Mensah

G. A.

Lebarthe

D. R.

(2006). Impact of stroke on health-related quality of life in the noninstitutionalized population in the United States. Stroke, 37, 2567–2572.