Introduction

The impact of amblyopia on health-related quality of life (HRQoL) has not been adequately explored. Amblyopia is an important condition that can affect up to 5% of the general population.1 Despite an increasing body of evidence describing the effectiveness of amblyopia treatment, little robust evidence regarding HRQoL implications of the condition and/or its treatment is emerging. Within the allocation of health-care resources, there is increasing demand for evidence regarding not only treatment effectiveness but also the implication of the condition and/or the effect its treatment has on the patient in both the immediate and the long term. The use of patient-reported outcomes, such as HRQoL questionnaires, can be useful in determining the impact a condition has on an individual.

Screening programmes currently exist within the United Kingdom to identify children who have or those who are at risk of developing amblyopia. A recent report examined the clinical importance and cost-effectiveness of pre-school vision screening for children aged up to 5 years.1 It concluded that the cost-effectiveness of screening for amblyopia is dependent on the long-term utility (or HRQoL) effects of unilateral vision loss. However, the authors noted that the evidence of the impact of amblyopia and/or its treatment on HRQoL was limited. The purpose of this study is to undertake a systematic literature review to examine the HRQoL implications of amblyopia and/or its treatment, and to evaluate the measures identified in the reported studies.

Materials and methods

Literature search

A systematic literature search was undertaken during the period of 7–14 May 2010. The electronic databases searched are detailed in Appendix 1. Specific search strategies were used for each database. Search strategies were performed to identify literature pertaining to amblyopia terms, amblyopia treatment terms, children terms, and QoL terms. No date or language restrictions were applied. Details of the literature search terms and database search strategies are shown Appendix 1.

A total of 1876 articles were identified through the database searches. An additional 10 articles were identified through a recent HTA publication1 and two systematic reviews on amblyopia screening and treatment.2, 3 These articles were not identified because the publication was in a journal that was not included in the search engines used (ie, articles were published in journals not found on Medline). After the removal of duplicates, a total of 632 articles were applicable for this review. Every article identified was checked by one reviewer (JC) and subjected to a pre-determine inclusion/exclusion criteria. Articles were rejected at title if they were not related to the subject area (n=479), and rejected at abstract if they were in a non-English publication or not pertinent to the research question (n=111). Letters, reviews, and editorials describing other studies reporting HRQoL implications of amblyopia were excluded. Where abstracts were ambiguous, the article was obtained. A further seven articles were rejected at full paper stage. These were found to be review papers, summaries of other studies, or contained no data to inform the research question.

A total of 35 articles were included in the review. The PRISMA flow diagram of study identification is shown in Figure 1. Details of the included papers are shown in Table 1.

Figure 1
figure 1

PRISMA flow diagram of study identification.

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Table 1 Articles included in the review and their source
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Data extraction and synthesis

Data were extracted by one reviewer (JC). Papers were assessed and data extracted using a data extraction form (see Appendix 2). Papers were examined in terms of the instruments used in the study. Newly developed HRQoL instruments identified were assessed in terms of reliability, validity, and responsiveness (see Table 2). Studies were also examined to determine whether the study respondents were children, parents, or adults who had undergone amblyopia treatment as a child. Finally, the HRQoL implications of amblyopia were extracted.

Table 2 Assessment of HRQoL measures
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Results

The majority of the studies reported HRQoL from a parental perspective (n=22).4, 5, 6, 7, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 28, 29, 31, 32, 34, 36, 37 Some studies reported results from adults who had amblyopia as a child (n=9).8, 9, 10, 11, 24, 26, 27, 30, 33 One study involved questioning both parents and children (n=1).25 Only three studies reported results solely from the child's perspective (n=3).12, 35, 38

Study methodology: instruments used

From the 35 papers identified, 5 used an existing measure in their study methodology to determine the impact of amblyopia on HRQoL. Three studies used the Children's Visual Function Questionnaire (CVFQ).4, 7, 23 One study used the Self-Perception Profile for Children (SPPC),12 and one study used the Visual Function Index (VF-14).8

The CVFQ

The CVFQ is a vision-specific instrument designed for use in children up to 7 years of age. Two versions are available for younger (<3 years of age, which contains 34 items) and older children (3–7 years, which contains 39 items). The instrument consists of four dimensions: competence, personality, family impact, and treatment difficulty, and has undergone testing of reliability and validity.41

The SPPC

Webber et al12 used the SPPC to explore the effect amblyopia has on a child's self-esteem. This measure has been assessed for reliability and validity42 and has been used in other ophthalmological studies to determine the impact of myopia on a child's well-being.43, 44 The measure consists of 36 items, which form 6 domains (namely scholastic competence, social acceptance, athletic competence, physical appearance, behavioural conduct, and global self-worth). Each domain contains six questions, which are answered on a four-part scale.

The VF-14

The VF-14 is a well-recognised measure of vision-related functional status that has been used in many areas of ophthalmology research, particularly cataract.45 The measure consists of 14 items relating to activities of daily living, which are answered on a 4-part scale.45

Developed measures

Five studies were identified that developed their own instruments, and described the psychometric properties of these measures. These include the Amblyopia Treatment Index (ATI),13 the Amblyopia and Strabismus Questionnaire (A&SQ),30 the Psychological Impact Questionnaire,8 the Protection Motivation Theory (PMT) Questionnaire,28 and the Patching Success Questionnaire (PSQ).16 These are summarised in Table 3.

Table 3 Summary of developed HRQoL instruments used in studies
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The ATI has undergone further testing of validity.6 The literature search identified that this instrument has been used in subsequent studies to investigate the impact of amblyopia and/or its treatment.5, 21, 22 The A&SQ has undergone additional testing of validity and reliability.9, 10, 11 An English version has also been developed and tested.24

Sabri et al8 developed a Psychological Impact Questionnaire and administered this in conjunction with the VF-14 to assess the construct validity of their questionnaire. The measure was developed through a literature search, clinician input, and discussion groups with amblyopic subjects. It consists of eight questions, which are answered on a five-part Likert scale.

Searle et al28 produced a questionnaire, based on the application of PMT applied to the results of interviews of parents of amblyopic children.29 The questionnaire contains seven domains and the questions are asked using a five-point Likert-type scale, although the exact number of questions is not clear from the study methodology.

Loudon et al19 developed a PSQ, a questionnaire based on the PMT. Additional questions were included to incorporate experiences of clinicians treating patients with amblyopia. The PSQ has been used in subsequent studies to explore the impact of amblyopia and/or its treatment.16, 17, 18

A number of papers (n=7) developed their own questionnaires (Table 4).15, 20, 26, 31, 32, 36, 37 The psychometric properties of these instruments were not disclosed.

Table 4 Summary of studies that developed their own questionnaires
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Six studies used qualitative methods to report the HRQoL implications of amblyopia and/or its treatment (n=6).14, 25, 29, 34, 35, 38 The majority used semi-structured interviews (n=4);14, 25, 29, 34 two studies used a structured interview approach (n=2).35, 38 Two studies used proxy methods (such as educational attainment) to report the impact of amblyopia on HRQoL (n=2).27, 33

Study methodologies

The identified studies can be summarised both in terms of their study methodologies (ie, the respondent) and the HRQoL implications identified. The identified studies may be summarised into the following broad categories.

Questioning parents about the impact of amblyopia treatment on the child's HRQoL

A total of 22 articles explored the impact of amblyopia treatment on the child's HRQoL from the parental perspective (n=22).4, 5, 6, 7, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 28, 29, 31, 32, 34, 36, 37

Some of these articles specifically examined the issue of treatment compliance. Compliance might reflect the presence of QoL implications in amblyopia treatment. However, treatment compliance may also relate to parental non-concordance. Parental choice of treatment modalities and timing of treatment can affect concordance. Parental understanding of the condition was noted to impact treatment compliance.14, 16, 17, 19, 20, 28, 29, 37

Questioning children about the impact of amblyopia treatment on their HRQoL

Four papers examined the impact of amblyopia and/or its treatment on a child's HRQoL from the child's perspective (n=4).12, 25, 35, 38 One used a combination of both parental and child reporting (n=1).25 Three studies used qualitative interviews in their methodology (n=3).25, 35, 38 It should be noted that two of the identified papers reported findings from the same cohort (part of the ALSPAC (Avon Longitudinal Study of Parents and Children)).

The impact of amblyopia treatment on adults when they undertook amblyopia treatment as a child

Nine papers were identified that reported the HRQoL implications of amblyopia and/or its treatment on adults who had undergone amblyopia treatment as a child (n=9).8, 9, 10, 11, 24, 26, 27, 30, 33

The impact of amblyopia in later life: the use of proxy measures

Two papers were identified, which explored the impact of amblyopia on adults using proxy measures of HRQoL (n=2).27, 33 The consequences of amblyopia on educational attainment, occupational status, risk of developing long-term vision loss, behaviour, and social functioning were examined. No association was found between amblyopia and educational achievement in one study,27 whereas the other reported a borderline significant effect of amblyopia on the completion of a university degree qualification.33 No statistically significant association between amblyopia and occupational classification was found.27, 33 The risk of developing long-term vision loss in the better-seeing eye was reported to be greater in amblyopes.33 Amblyopia was not found to be associated with significant behavioural problems or bullying.27

HRQoL implications of amblyopia and/or its treatment

The HRQoL implications of amblyopia and/or its treatment could be considered to fall into four broad categories: impact on family life, social interactions, undertaking daily activities, as well as feelings and behaviour. These can be examined as to whether they occur as a result of amblyopia itself and/or its treatment (see Table 5).

Table 5 Summary of quality-of-life implications of amblyopia and/or its treatment identified in the literature search
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Impact on family life

Amblyopia treatment was reported to impact family life. This resulted in increased stress and anxiety for the parent/guardian facilitating the treatment, and negatively impacted carer–child relationships.5, 6, 13, 15, 21, 22, 31, 34 Other relationships within the family were also affected.5, 6, 13, 15, 21, 22 Siblings teased or bullied the child who undertook amblyopia treatment. The increased parental attention that treatment is associated with may also be an issue. Compliance with treatment is intrinsically linked to HRQoL. Often the negative aspects of amblyopia treatment are reported, yet treatment may not always be a negative experience. If compliance is good, praise and attention may be given to the child thereby improving the parent–child relationship.

Social interactions

Bullying15, 25, 26, 34, 35, 38 and interactions with peers5, 6, 8, 9, 10, 11, 13, 15, 21, 22, 24, 25, 30, 38 were reported to occur as a result of amblyopia and/or its treatment. Noticeable differences in the change in appearance (by nature of wearing glasses and/or patch) meant that treatment was obvious to others. The age at which emergence of negative opinions towards others has not been adequately explored. Feelings of isolation and noting differences between others were also documented.5, 6, 8, 13, 21, 22, 25

Activities

One of the frequently reported HRQoL implications of amblyopia was the impact the condition had on career choice and educational attainment.5, 6, 9, 10, 11, 13, 15, 21, 22, 24, 26, 27, 30, 34 This could be in the immediate (such as if the treatment was undertaken during school hours) or in the long term (the implication of amblyopia in adulthood). The impact that amblyopia and treatment had on daily living activities was well documented.5, 6, 8, 9, 10, 11, 13, 21, 22, 24, 26, 27, 28, 29, 30, 34

Feelings and behaviour

Feelings of low self-esteem and negative self-image were reported as a result of amblyopia and/or its treatment.12, 20, 25, 26, 28, 29, 31, 32, 34, 37 Other psychosocial implications included feelings of depression, frustration, and embarrassment.8, 15, 25, 27, 28, 29, 36 Literature that explored the understanding of amblyopia and its implications was identified,8, 9, 10, 11, 20, 24, 26, 28, 29, 30, 33, 37 with attempts made to understand why compliance to treatment may be poor in some cases. Other studies explored feelings associated with the treatment of amblyopia, specifically the sensation of patch/drops/glasses.5, 6, 13, 21, 22

Discussion

The concept of QoL can be considered in terms of four domains: symptoms of the disease and side effects of treatment, physical and functional status, emotional status, and social functioning.46 It seems that the main HRQoL implications of amblyopia appear to be related to treatment of the condition rather than to the condition itself.

The search strategy used for the literature review incorporated standard terms used in HRQoL studies. However, it is possible that by extending the search strategy to include terms specifically relating to the four domains of QoL, additional studies may have been identified. The functional ability of subjects with amblyopia is an area of increasing interest, with impaired fine motor skills and slower reading speed being reported.47, 48

Some of the identified studies included subjects who had a diagnosis of strabismus and a diagnosis of amblyopia; and some of the HRQoL instruments used included questions specifically relating to strabismus. Large-angled strabismus has been documented to negatively impact QoL.49, 50 It is possible that the studies identified in the literature review which reported lower HRQoL may actually be detecting HRQoL implications of strabismus rather than those of amblyopia. Only two of the studies identified in the literature review reported HRQoL in subjects with ‘straight-eyed’ amblyopia (anisometropic or small-angled strabismus measuring <10 prism dioptres).15, 26

The adult's vs the child's perspective

Some HRQoL instruments used in the identified studies were derived from consultations with ophthalmic professionals and/or parents of children with amblyopia. Therefore, the items included in the instrument design are deemed to be of importance from an adult's perspective. The included items may be of importance to adults, but not necessarily to the child. For example, a parent may feel that educational attainment and the ability to see well at school is of great importance; however, this view may not be shared by the child. In some of the studies identified, the reported findings are taken from a parental perspective. It is not possible to state that the impact of amblyopia treatment felt by the child is the same as that perceived by adults on how, or what the child should feel or experience. Some of the questions asked included how well the child could see while undertaking treatment. The parent/guardian cannot directly assess this; they can only make a judgement on how they perceive the child is able to see while on treatment. Their judgement could be influenced by how important they judge the activity to be (such as school work or interacting with friends).

Measuring HRQoL in a young age group is challenging; however, this has been achieved in conditions such as childhood cancers, asthma, and dermatitis.50, 51, 52, 53, 54 Some of the difficulties involved include the burden of the task (ie, how difficult it is for the child to complete the questionnaire). This corresponds to the number of items (or questions) included, the scales used to answer the questions (yes/no or Likert-type scales), and the time taken to complete the task. Development of an instrument specifically designed to assess self-reported HRQoL in subjects with amblyopia is currently being undertaken by the author.55

Some studies reported HRQoL on adults who had undertaken amblyopia treatment as a child. It is possible that the recollections of adults in terms of amblyopia impacting childhood experiences could be tainted by subsequent events in adulthood. The responses are given from an adult's perspective, despite respondents being asked to recall childhood experiences and events. Recall bias is a recognised challenge in patient-reported outcomes and HRQoL research.56

Determining QoL by treatment compliance

Treatment compliance in amblyopia therapy is influenced by both the child and the parent/guardian. Although the child may object to the wearing of glasses or a patch on a personal level, a parent's perspectives can influence the success of such treatment. This may incorporate their own experiences or impressions of patching/wearing glasses, or their understanding of the condition and the importance of treatment. Although these factors have been explored in the literature, to use compliance as a measure of HRQoL is questionable. Parental understanding of the condition and belief in the prescribed treatment are key components for good treatment compliance. However, parents can be well-informed and positive, yet compliance may still be poor. Another argument against using treatment compliance as a measure of HRQoL is that a child may consent to wearing the patch, but their daily activities and social interactions may still be affected. In this instance, using treatment compliance would not truly represent any HRQoL implications of amblyopia and/or its treatment.

Use of proxy measures to determine QoL

Some of the identified studies used proxy measures to determine the impact of amblyopia and/or treatment on HRQoL. These included educational attainment, occupation, long-term vision loss, and social functioning (as measured by self-reported depression of psychological distress in adult life). Such outcomes are influenced by many factors. The presence of amblyopia cannot be solely used to either explain episodes of psychological distress in adulthood or educational attainment. These studies highlight the importance of making the distinction between HRQoL and functional status or ability. Functional status and health status use measures that determine an individual's ability to perform or carry out an activity. HRQoL incorporates both the ability and an ‘evaluation of the subjective experience of being able to complete a given activity’.57 Some of the identified studies fail to address this issue and report functional status alone.

Changing trends in glasses and patches

The manner by which people who wear glasses are perceived is changing. Glasses are becoming increasingly popular, and the social acceptance of this has much improved. With traditional ‘NHS style’ glasses being a thing of the past, it could be argued that the reported HRQoL findings from some of the earlier literature may not truly reflect on how things are in modern day practice. Similarly, the choice and style of patches have also changed, with a movement towards coloured patches, and patches that fit over glasses, to improve comfort and appearance. This has started to be explored in recent studies.23

It is clear that there are HRQoL implications associated with amblyopia; however, these are related to amblyopia treatment rather than to the condition itself. Despite differing study methodologies, four key components of HRQoL were identified: those of physical ability (undertaking daily tasks), emotional status (feelings and behaviour), social interactions, and impact on family life. Very few of the studies identified assessed HRQoL from the child's perspective. Current recommendations from the Department of Health encourage the participation of children respondents in the assessment of their own health and treatment,58 and future studies in this area need to address this issue.

The HRQoL measures used in the identified studies failed to report the psychometric properties of the measures themselves (ie, reliability and validity), with the exception of the ATI, A&SQ, and Psychological Impact Questionnaire. Although their reported findings may be of clinical importance, their use in economic evaluations and subsequent policy-making decisions are limited. Further research is required to assess the immediate and long-term utility effects of amblyopia and/or its treatment, using more robust methods of HRQoL assessment.