The purpose o f this clinical study was to develop and conduct a low vision training programme using the SLO. The most important part was to identify the retinal locations patients used for viewing and to characterise their performance. Other potential retinal locations with similar or better visual ability were also investigated. The aim was to use professional training methods to enhance the reading ability of these areas.
example, fixation (Timberlake et al, 1986; Schuchard and Raasch, 1992) and search tasks (Schuchard, 1991), but in the current thesis new and improved techniques for assessment of visual function have been achieved. The results show that accurate and repeatable measurements in patients with age-related macular disease can be accomplished.
In order to determine the effectiveness of a low vision training programme the visual performances in the following areas were evaluated throughout the study as summarised below:
A. Standard clinical examination of i) distance VA,
ii) near VA with patient’s magnifying device and iii) words read per minute with magnifying device. B. SLO assessments of
iv) fixation stability,
v) time for search and identification of a target, vi) percentage of letters read correctly and vii) maximum speed of recognition.
During the course of the programme, performance improved significantly in all tasks except iii), i.e. reading speed. In general, these results would appear to agree with previous claims of benefits with training (Backman and Inde, 1979; Nilsson and Nilsson, 1994a, 1994b), even though the methods utilised for eccentric viewing and assessment were different. However, more specifically, it does not endorse claims o f improved reading speed (Collins, 1987).
Reasons for such "success" in the present study must be examined carefully. At least three possible explanations could account for the observed results. First, skill acquisition through practise could have improved patient’s results. Second,
psychological factors could have enhanced patients’ wellbeing and in turn affected their performance. Third, true visual improvement could have taken place due to patients’ learnt use of a retinal area that had better performance than the PRL.
As discussed earlier, the impact of learning and practise on performance is well known (Overington, 1976). The visual tests in this study, although not difficult, represented unfamiliar tasks for the patients. Elderly patients with visual deficits may take longer to adjust to unusual tasks, particularly in a highly technical environment. Even young partially sighted patients have been shown to improve their visual performance with continued practise (Overbury and Bross, 1978).
Concentration and attention are other important aspects that may influence such assessments. In normal observers, peripheral acuity (Low, 1943; Saugstad and Lie,
1964), general perceptual ability (Bruce and Low, 1951) and motion detection (Johnson and Leibowitz, 1974) can be enhanced by training. Such achievements may be related to the ability to learn to shift attention from a central part o f the field to the periphery. Our patients had longstanding loss of central vision, hence the need to shift attention had been long present. The learning effect in attention may be an important element in low vision training, but relative to normal observers this effect may be diminished. Conversely, a reduction in the size of useful field o f view occurs with age but this may be recovered partially with practise (Ball et al, 1988). Patients with ARMD are relatively elderly and since they need to obtain information at some distance from the fovea, they may indeed benefit from training.
Psychological support almost certainly has an substantial role in low vision training (Goodrich and Mehr, 1986). Increased levels of achievement may been obtained if individuals are in a suitable psychological state. In any clinical trail placebo effects are well known, they are often psychological in origin but may manifest in measurable effects. A phenomenon known as the Hawthorne Effect exists where individuals perform better if given attention (Mayo, 1945). In the present study the significance of the psychological aspect can not be isolated from other influences. In order to do this, a further study would be required involving a larger patient base, a trained group and two control groups. In the first control, patients would receive psychological support but no vision training, in the second.
patients would receive no "treatment". All subjects would undergo full visual assessment using SLO technology. In this manner, the relative influence of psychological and training elements would be determined.
The present study has been directed particularly towards investigation o f the potential benefits o f eccentric viewing. The patients’ choice o f PRL is of great consequence because if the "optimal" retinal area is selected then training to reposition the angle of view is unnecessary. This is the first time that a study has endeavoured to address this issue. In order to determine the suitability of patients’ choice of PRLs it was necessary to compare the performances o f various retinal locations. The data show that, for the group as a whole, ARLs did not achieve significantly better results than the PRLs in any of the tasks assessed. More
specifically, no difference in performance for the PRLs and ARLs was found for the visual tasks of acuity measured with the SLO and fixation stability. In the three other tasks assessed (search and identification of a target, percentage o f letters read correctly and maximum identification speed) PRLs demonstrated significantly better performances. This suggests that training patients to change their angle of view is futile and superfluous. Even when the PRL was situated in the horizontal meridian and the patient was attempting to read into a scotoma, training to reposition the angle of view did not allow faster reading speed.
The finding that PRLs performed at least as well if not better than the ARLs is highly relevant to eccentric viewing training. Even in the present study, with the benefit o f sophisticated equipment, it was not possible to locate retinal areas that performed better than the PRLs. Studies which have less information on patients’ visual status would presumably have less opportunity for successfully identifying more optimal retinal areas. In all previous clinical training programmes advocating eccentric viewing techniques, two severe limitations are present: First, limited information is available when locating the viewing position. For example, an Amsler grid has been advocated as "a useful aid for refining and identifying the exact angle of best view" (Collins, 1987). Relative to SLO technology this is an
extremely crude technique. Second, the trainer is unaware of the exact retinal location utilised by a patient during any given task. This is further complicated by the fact that some patients appear to have directional referencing to their PRL, making them unable to report accurately on their true eye position.
That ARLs do not produce significantly better performance than PRLs is apparent when the results are analysed for the whole group. However, individual cases can be cited where response to the ARLs seemed to be positive. For example, with patient JD the PRL was positioned at the fovea. Prior to entering the study she had investigated the possibility of eccentric viewing and found that her vision seemed to improve. This was confirmed by the SLO acuity test where acuity was found to be better at ARLs than the PRL (see Table 20, pl37). Similarly, fixation stability and percentage of letters read correctly was slightly better at an ARL. Further, when the patient used her PRL for reading a scotoma was projected to the right of fixation on the visual field. Logically the ARL was better placed for reading and therefore it might be expected that her reading speed would improve - but this was not found to be the case on reading normal text. It cannot be discounted that, when attempting a task where her fixation position could nolonger be monitored, this patient returned to using her PRL. Other commitments on the SLO did not allow this aspect to be pursued in detail.
Low vision training techniques:
The term "training" covers many techniques all aimed at successful rehabilitation. Programmes may involve nothing more technical than basic instructions relating to dealing with the limitations of low vision and magnifying devices (Mehr and Fried, 1975; Faye, 1976; Kelleher, 1976). Such rehabilitation methods have obvious value. This practical advice also offers psychological support. In the current study these aspects were not under review, although our patients’ responses to the questionnaires indicate how much this form of rehabilitation would be appreciated by patients in the UK.
conception in the early 1970s the approach has been to direct the damaged fovea towards an area above or below the text to be read (Backman and Inde, 1979). Also, it has been somewhat dogmatically promulgated that "few patients can learn eccentric viewing effectively by themselves" (Nilsson and Nilsson, 1986). Recent more objective findings, both in the present thesis and other studies, have
demonstrated that many patients self-acquire eccentric viewing and often have a strong preference for a single retinal location (Timberlake et al, 1986; Guez et al, 1993). In addition, some appear to have directional referencing to the PRL (White and Bedell, 1990). As discussed earlier, although overall the effect o f training was to improve visual performance, this benefit was not derived from changing the patient’s viewing angle.
The criteria defining whether or not an individual patient would benefit from training have not yet been identified. In some studies a number o f patients are assigned to undergo no eccentric viewing training (Nilsson and Nilsson, 1986; Ighe,
1994), but unfortunately the reason for retaining centric viewing even though severe visual loss has occurred is not discussed. As Faye (1976) remarked with regard to basic instruction on handling a magnifier, not every patient needs a training
programme to learn to use his aids. The same may be true in eccentric viewing, not all patients can be trained, or indeed, need to be.
Extremes are easily identified, for example, benefit can not be derived from training of patients with Alzheimer’s disease or individuals with good central vision. Outside those extremes the definition of boundary conditions become more
difficult. A reasonable IQ to facilitate comprehension and a suitable level of
manual dexterity are helpful. Whilst, from first principles, the size and the position of a field defect may seem important, this must have a relatively low priority since many patients choose to read into a scotoma.
In this study, benefits were evident from training as a result of multi-factorial elements. These included the acquisition and perfection of new visual techniques and improvement in patients’ well-being. The timing of intervention with training
may be important since changes in the visual system and psychological status may occur over a period of time. System changes may also occur, e.g. cortical
adaptation. White and Bedell (1990) have suggested that training in SES may be unhelpful for patients with recent loss of vision since visual acuity correlates with saccadic rather than fixational eye movements and suppression of saccadic eye movements may prolong adaptation to the new visual status. The psychological status o f the patient has a significant role since hope and expectation for recovery may affect motivation. The rate of loss of vision has influence since patients are shocked by a rapid decrease but may adapt to the situation if progression is slow (Schulz, 1977). Hence, there may be a critical period where training may be most beneficial.
The successful use of the SLO for assessment of residual vision in patients with macular disease and for low vision training has been demonstrated by this study. Detailed evaluation of central visual function and the identification o f specific retinal areas would not be possible without the SLO. The major part of this thesis was concerned with the development and standardisation of techniques and
software required to provide useful data in the assessment of clinical problems. Specific software has been developed and tested and the results have been promulgated within the scientific community (Culham et al, 1992; Culham et al,
1993; see Appendices VI and VII). Following this study, large numbers of patients need to be assessed and from that boundary conditions for training can be defined. Advanced training procedures can be developed and those patients who may benefit could be identified.