Optometrists may find it unusual to consider the concept of ‘success’ in relation to one of their prescribing strategies, because the supply of spectacles for the correction of refractive error is almost invariably successful. It has always been clear, however, from a large number of surveys carried out in several countries over many years, that one cannot expect to achieve 100% success in the prescription of low vision aids (LVAs). Whilst surveys of whole populations are very useful to determine the effectiveness of low vision care, it is helpful for the practitioner to consider how this relates to an individual patient they are assessing. Why are some patients unsuccessful, and could this have been predicted (and even prevented) if the assessment or prescribing routines had been modified?
Prognostic Factors for the Successful Use of Low Vision AIDS
It is very difficult to generalise which patients will do particularly well with low vision rehabilitation and which will struggle. Although each patient should be treated as an individual, clinical experience suggests that some groups of people are more likely to respond well to LVAs ( Table 21.1 ).
| Factor | Likely to Respond Better to LVAs | Likely to Respond Less Well to LVAs |
|---|---|---|
| Visual acuity | 0.5–1.3 logMAR |
|
| Contrast sensitivity | Better than 1.05 log units | Poorer than 1.00 log units |
| Visual field | Well defined, small scotoma |
|
| Stability | Stable condition | Progressive or fluctuating condition |
| Current treatment | No ophthalmological treatment | Undergoing medical or surgical treatment |
| Employment situation |
|
|
| Comorbidity | No comorbidity |
|
| Acceptance | Accepting of sight loss |
|
Those patients with a moderate visual acuity (VA) loss are most likely to benefit from magnification. In severe vision loss, the choice of LVAs is more limited and they are more difficult to use (they usually have high magnification, associated with short working distance and small field-of-view). Those with vision better than about 0.4 logMAR are also often difficult to help as they are more likely to assume that spectacles can completely ‘cure’ their vision loss. When asked what tasks they have difficulty with, they often identify an extensive list: it is not that their vision is insufficient to perform any of these tasks, but that it is not as good as the patient believes it could (or should) be.
Low contrast sensitivity (CS) has a severe effect on functional performance, and optical aids do not enhance contrast. Poor CS (such that contrast reserve is less than 3:1) makes using any optical device for reading difficult. A contrast reserve greater than 10:1 means that magnification and lighting are often very effective. People with CS of better than 1.05 log units read more fluently with magnifiers ( ).
It is much more difficult to prescribe LVAs to aid peripheral field loss than it is to prescribe magnifying devices: and if a magnifying aid is required by a patient with extensive field loss, there must be sufficient field remaining to appreciate the magnified image. With an annular or ring scotoma, there may be good acuity for single letters but a very small visual field, which makes reading words almost impossible: it is very difficult for these patients to use eccentric viewing. The patient is more likely to quickly adapt to viewing eccentrically if an absolute central scotoma is present.
Rapidly changing vision makes rehabilitation challenging, whether in a progressive condition, like retinitis pigmentosa, or a condition where the vision fluctuates, like diabetic retinopathy. If the condition is stable, the LVA will not require frequent changing and the patient will have the opportunity to become proficient in its use. If there are rapid changes in vision, major changes in the type of aid may need to be made at every visit in order to provide the increasing magnification required. One of the advantages of electronic vision enhancement systems (EVES) in such cases is the ability to deliver increasing magnification without the need for a change in the device or the way it is used. If the condition is active, the patient may be seeking or receiving medical or surgical treatment, which may cause their vision to fluctuate and make the patient uninterested in LVAs whilst there is the prospect of a ‘cure’.
As a general rule, people with lifelong, stable levels of low vision are better candidates for help, as they have not previously relied on good vision to perform a task. On the other hand, they might have little visual experience and have become experienced with tactile and auditory methods. A patient with an acquired loss of long duration must be questioned carefully to find out why they have never sought help before: they could also have well-developed nonvisual strategies which they will not abandon, or simply have become accustomed to not performing particular tasks. There may be a very good reason for their action, however, such as the recent death of a spouse who had previously performed many visual tasks for them.
Having specific and realistic aims is important. Fortunately, the most common requirement identified by people attending a low vision clinic is difficulty with reading and writing ( ). asked patients who were attending a low vision service for the first time, ‘What are your chief complaints about your vision?’ Two-thirds of the patients responded that reading was their major concern. However, more than a quarter responded ‘driving’—something which low vision clinics are not generally able to help with (apart from those areas where driving with bioptic telescopes is permitted). It is interesting that 11% of patients in this study identified no complaints: it is not uncommon to find that a patient cannot name any specific task when asked ‘what would you like to be able to improve’. This patient, who is perhaps looking for a general improvement in their vision, is much more difficult to manage than the patient who brings in a written list of specific requests.
The patient must be willing to accept the restrictions on the performance of the task imposed by the use of an LVA, which may be physical (such as the close working distance) or optical (such as aberrations when viewing through the lens periphery). The choice of which aid will be most appropriate for them often depends on which they perceive to create the least restriction.
The level of psychological adjustment to, and acceptance of, vision loss is probably the single most important factor in successfully using LVAs. Someone who accepts their vision loss is likely to present to the low vision clinic, to engage with suggestions which are made, and to be comfortable using LVAs in public. Interestingly, the best predictor of adjustment is personality type and not visual ability, severity of visual impairment or duration of sight loss ( ). This study showed that people with high levels of conscientiousness (the desire to carry out tasks carefully and diligently) and lower levels of neuroticism (less likely to experience anxiety, or to be overwhelmed by minor frustrations) were most likely to be successful.
Even if the prognosis does not seem to be encouraging, much can be achieved if the patient is sufficiently motivated and the practitioner adjusts their own and the patient’s expectations. If the patient is only motivated to do something which cannot be assisted with aids, however, then no further action can be taken. For these patients, then, aids are simply not appropriate and it is perhaps misleading to call them ‘unsuccessful’. Even if a magnifier is not prescribed, it is unlikely that the assessment was a waste of time. It is difficult to tell someone that they will not be able to perform some tasks, such as driving, but this awareness can help the patient adjust to their eye condition. They may be willing to accept further low vision help in the future and an open invitation to reattend the clinic should be offered.
Defining Success
One of the major difficulties in conducting evaluations to determine ‘success’ is in deciding exactly what this is. If considering the success of a treatment, or intervention, it is important to have a clear idea exactly what it was intended to achieve, such that it is clear whether that aim has been achieved. Often, in a medical field, a treatment is evaluated initially under very closely controlled conditions, with carefully selected participants who have no other health conditions (comorbidities) which might influence how well the treatment works. This gives a measure of efficacy: if and how it works under ideal conditions. In more normal clinical circumstances, these ideal conditions may not be met. The individuals being treated may present with mitigating factors that make the treatment less likely to succeed, or they may not comply with the instructions for optimum use of the device, or they may prefer alternative means to carry out the activity. Measuring what happens as a result of the treatment under these conditions tells us about its effectiveness. To put this in the context of low vision, efficacy may be measured by asking the patient to use a magnifier to read standard texts with optimum lighting in a clinic, but effectiveness is how well the patient can use the device in their everyday life.
A major complication when considering low vision rehabilitation is that it is a so-called ‘complex intervention’. This means that it consists of many overlapping and complementary aspects, each of which may have both direct and indirect influences in many areas of daily life. This means that the true effect may not be captured by a single ‘outcome measure’: for example, if providing a magnifier allows the patient to remain in employment, it is unlikely that a measure of reading speed is enough to represent the full effect on that patient’s life. If an attempt is made to single out one element of the intervention to study in isolation, the effect may be very small, and be judged to be insignificant.
In fact, identified 47 different outcome measures in their systematic review of the effectiveness of low vision rehabilitation. Unfortunately, if each intervention is evaluated using a different outcome measure, it is not possible to compare the effectiveness of competing methods of rehabilitation ( ).
As the use of magnifying devices is at the forefront of much provision, improvement in acuity is one possible outcome measure. This is not as helpful as it seems, however, because this is much more a function of the device than of the user: it is relatively straightforward to improve single letter acuity by altering the magnification selected. Even extending this to word reading acuity is not sufficient: just because a patient can ‘see to read’ (i.e. they can recognise words of newsprint size) this does not necessarily mean that they will regularly read the newspaper for pleasure ( ). This was demonstrated by , who found that whilst 75% of the patients surveyed could read 1 M (approximately newsprint size) print in the clinic, only 35% admitted to reading normal print at home.
It may be that this difference is related to the reading speed achieved. It is suggested that to read for education, work or leisure over an extended period requires a fluent speed of at least 80 words per minute (wpm), whereas a much slower speed (40 wpm) could support survival reading (see Chapter 3 for further details). This important distinction has led to reading speed being considered an important outcome measure for rehabilitation using magnifiers. A much broader definition of success could be used, such as that of who suggested that low-vision care is successful when more independence is gained, when more understanding of the eye condition and the way it affects daily life is gained, and when the patient feels that all possible avenues have been explored, whether or not increased independence is possible. Considering the use of magnifiers specifically, used a more functional definition of success, asking the patient if they could read newspaper text and see TV pictures and subtitles. Various studies ( ) have emphasised the fact that relatively modest gains in ability may be useful for some individuals. Leat et al. found that 79% of patients used an aid for ‘reading-related tasks’ but 23% could only read for 1 minute or less. Nonetheless, 81% used their aid at least 1× daily, and 86% kept it with them constantly, or within easy reach. They conclude that
‘short frequent bursts of activity can be useful, and patient expectations modified accordingly … Extended reading should be considered a bonus’
presumably suggesting that for many patients, ‘survival’ reading is a useful endpoint. The Manchester Low Vision Questionnaire (MLVQ) is an attempt to quantify the usefulness of devices for that particular individual in a structured way, in terms of how much they are used (if ever), for how many tasks, and with what degree of difficulty ( ).
To try to capture potential improvements in everyday functioning as a result of vision rehabilitation, in a quantitative method, various patient-reported outcome measures (PROMs) have been suggested for use. These include both vision-related (VR) and health-related (HR) quality of life (QoL) instruments (see Chapter 4 ), which describe the individual’s ability to perform everyday tasks: the so-called Activities of Daily Living (ADLs) or Instrumental Activities of Daily Living (IADLs). ADLs are fundamental abilities, regardless of the person’s circumstances, and include the ability to eat and maintain personal hygiene. IADLs are not so necessary for life, but they are important for living independently and functioning well within society. They include, for example, preparing meals, managing finances and using transport. VRQoL often concentrates heavily on these IADLs, so many of which rely on the ability to read. They are therefore likely to be more sensitive to the intervention as they relate specifically to vision. The HRQoL questionnaires are more general and often relate to ADLs and so are less relevant to vision impairment (VI). However, they do allow vision rehabilitation to be compared to interventions and treatments in other healthcare specialties. The most common method used to make these comparisons at the present time is the EQ-5D instrument ( ). The currency for such comparisons is Quality Adjusted Life Years (QALYs), which is a product of the length of time an individual lives with the condition, and their QoL during that time ( ). To establish whether a treatment offers ‘value for money’ the QALYs gained can be judged against the cost. This will include the direct cost of equipment, staff time and healthcare resources (e.g. clinic visits). The time contributed by informal carers (family members and friends), which might be reduced if the patient becomes more independent, is also accounted for. This will allow an incremental cost-effectiveness ratio (ICER) to be calculated: this is a measure of the extra cost for the extra QALY. Such health economic evaluations are rare in vision rehabilitation studies ( ) but evaluated the ICER for portable EVES magnifiers being provided in addition to optical aids in a hospital clinic. If a new intervention is both better and cheaper, it will obviously be adopted, but if it is more expensive, then such economic evaluations can be used by healthcare providers in deciding whether to allocate limited resources to it.
Improvements in functioning and independence are likely to increase feelings of well-being and decrease depression in patients, and these characteristics have also been the subject of questionnaires used to evaluate the success of rehabilitation.
A further consideration is the timing of any measurement taken to judge success. It should be far enough removed from the initial consultation that the patient has had the opportunity to obtain full benefit from it but is also over the initial positive effect from the contact itself. It would be hoped that any effect measured would be sustained over a prolonged period, but for many patients, their condition is advancing in addition to their age, which could mitigate this to some extent.
A further problem with studying the effectiveness of low vision rehabilitation is an ethical one: having a control group with no access to low vision services is unfair to those randomised to this group. This means that many published studies are case series, which are confounded by many other effects (such as increased contact time, natural adaptation to vision loss and practice in living with low vision). Some of these concerns can be overcome with waiting list control studies, but these can only take place in centres where there is a long delay before appointments can be offered.
Evidence for the Success of Low Vision Rehabilitation
As noted previously, the methods of evaluation are varied but can be summarised as performance-based (e.g. reading speed) or patient-reported (using validated PROMs) ( ). If the rehabilitation involves provision of devices (e.g. magnifiers), then an additional measure would be usage of the devices.
A very traditional approach is that reported by , who found significant improvement in reading speed after provision of magnifiers (from a mean of 20 to 72 wpm for the whole group). A total of 94% of patients were able to read newsprint-sized text with aids, compared to only 16% without. However, this observational study design is considered as low-quality evidence, because there is no comparison of alternative types of magnifiers, or even of no intervention. A systematic review of optical and electronic aids ( ) found that there was modest evidence that reading with stand-mounted EVES was faster than with optical devices. Electronic aids also support longer duration reading but are less versatile (tend to be used for fewer tasks) than optical aids, as evidenced by use of the MLVQ ( ).
In a telephone survey of 88 patients from different clinics who had been prescribed with various types of magnifiers approximately 1 year previously, 71% of the aids had been used during the previous week, but 19% had not been used in the past 3 months ( ). The most common reasons for abandonment included worsening vision, the aid no longer being effective, and use of an alternative device for the task: there was no association with patient age, acuity level or type of magnifier. reported 85.4% of devices still in use between 1 and 2 years after supply, in their telephone survey of users. They found that continued use was associated with the presence of a supportive helper at home: in fact, in their rehabilitation setting, many spouses had received education on the importance of family support. All the patients had also received extensive training (median >20 hours) in the use of devices.
Although low vision rehabilitation differs substantially in its scope (the range of services incorporated) and its organisation (‘one-stop-shop’ multidisciplinary vs multiagency), the primary aim is to improve overall functioning and independence for patients. It is therefore necessary to measure this directly in order to assess effectiveness of an intervention. LOVIT (The Veterans Affairs Low Vision Intervention Trial) was an evaluation of a comprehensive outpatient rehabilitation programme for individuals with macular disease causing moderate to severe loss of vision (worse than 6/30; 0.7 logMAR) ( ). The comprehensive intervention included optical and electronic magnifiers, training and homework using aids (five 2-hour in-practice sessions, each followed by 5 hours homework exercises) and advice on environmental modification. Outcomes were measured with the Visual Functioning Questionnaire-48 (VFQ-48), which asked participants to describe their activity limitations in reading, mobility, visual information processing and visually guided movement. Importantly the study had a control group who received no care: individuals were randomly assigned to a ‘waiting list’ or to immediate intervention. This study provided the first robust evidence of a significant benefit of rehabilitation in all the activity domains, but particularly on reading ability. In contrast, the waiting list group showed small losses in functioning, suggesting that it is beneficial to begin rehabilitation as soon as possible. Despite the strengths of this research, it should not be assumed that its results will be replicated by every low vision clinic: it is an evaluation of a particular protocol, in a specific group of patients. An evaluation of the Welsh Low Vision Service, which is a much less intensive intervention, and delivered on a multi-agency basis, also found very significant improvements in functioning and high usage of aids reported by patients immediately ( ) and 18 months later ( ). There have been a number of recent studies which have suggested that the finding of a significant improvement in vision-related functioning (VRQoL) as a result of vision rehabilitation can be replicated in several settings ( ). There is not, however, any consistent evidence of an improvement in HRQoL ( ; ). To tackle the issue of improving psychological well-being, the use of self-management programmes has been advocated. Such a programme is intended to provide the patient with the skills to manage their condition more effectively, by teaching problem-solving skills and goal setting. It is often delivered over a 6- to 8-week period involving weekly meetings and targets ( ). However, these programs have not been found to offer any additional benefit when combined with a standard rehabilitation intervention ( ).
A specific component of UK low vision rehabilitation is an assessment of need by a rehabilitation officer from the local council’s sensory team or a charity, followed up by a number of visits to deliver targeted training and support. This might involve, for example, lighting advice, household tasks, emotional support and long cane training. In a study by , participants who were also accessing optometric low vision assessments were randomised to receive this home visit intervention or to a waiting list control. There was a significantly greater increase in visual function (based on the VFQ-48) in those who received home visits compared with those who did not. The participants also reported their satisfaction with the help received, with only 2/34 participants reporting it as unhelpful. There was, however, no effect on depression, well-being or loneliness, which have been suggested to be improved by the enhancement in visual functioning ( )
Does Training Work?
In the UK, low vision care was initially concentrated on the supply of optical aids from hospital-based clinics, and these did not always achieve success. A survey at Glasgow Eye Infirmary ( ) found that 33% of patients never used their LVA. found that of 72% of patients who were provided with a spectacle-mounted LVA, only 23% found it useful at home. These findings were contrasted with surveys from outside the UK ( ) which showed much higher success rates. As these non-UK clinics routinely provided a training programme in the use of the aids, it could be suggested that this training is generating the enhanced success. In fact, repeated the ‘patient satisfaction’ questionnaire in a low vision clinic where training was an integral part of the service. On this occasion, 92% of patients stated that the service was sufficient to meet their needs, which compares favourably to the 55% of patients in the original survey who had expressed satisfaction when asked the same question. Training obviously requires a major commitment of the service in time and personnel, but with a lower wastage rate of LVAs the overall cost of the service is not excessive: the increased benefit to the patient is more difficult to quantify.
There are few studies which have isolated the effects of training from other aspects of their service. monitored the reading speed and duration of 12 patients over a period of 10 consecutive days as they underwent training in using the aids. Improvement occurred throughout the period, and it appeared that it had not reached a final plateau at the conclusion of the study; it was suggested that 15 to 20 days would be needed to achieve that. There is the possibility, however, that the same improvement would have occurred with practice alone and that the training was not a significant factor. This obviously needs to be evaluated with a randomised controlled trial, such as that reported by and . In this study, patients received a new EVES and were randomised to either receive only the instructions provided by the manufacturer, or to receive weekly training in their home with a series of exercises involving realistic tasks performed with the EVES. Although the use of the EVES increased reading performance and decreased patient-reported difficulty on a VRQoL measure, in both groups, there was no evidence for an additional benefit of training.
A positive benefit for the effect of training in the use of optical aids was reported by . A population of 40 consecutive elderly patients, all with age-related maculopathy and acuity less than 6/60, were randomly assigned to two experimental groups—‘trained’ and ‘untrained’. The results are given in Table 21.2 .
