The preceding chapters on various heterophoric anomalies have described the general outlines for the management of these conditions. This chapter gives details of particular exercises which may be fitted into the aims outlined. For example, the treatment of central suppression is appropriate to several different anomalies. The details of exercises for the treatment of suppression are given later rather than repeating them in each of the previous chapters.
The general principles of eye exercises and the factors to be considered in the selection of patients are described in Chapter 6 . A distinction can be made between exercises that provide a smooth, gradual, stimulus (ramp) and those that employ a sudden, step-like, stimulus ( Fig. 10.1 ). An example of the former is push-up, ‘pen-to-nose’ near point of convergence exercises. Ramp exercises are exemplified by flipper exercises where the patient rapidly alternates accommodation between plus and minus lenses. Although a few studies support the argument that one of these types is more effective than another, most authors nowadays accept that eye exercises are more likely to be effective if they employ a variety of approaches.
Exercises in this chapter will be considered under three main headings: (1) development of fusional reserves and relative accommodation; (2) exercises that train accommodation and convergence in their usual relationship; (3) exercises for the treatment of central suppression. The treatment of central suppression has been left until last because, in many cases, this does not require treatment. Sensory adaptations to heterophoria often spontaneously resolve when motor factors have been treated.
A study, somewhat limited by excluding participants with binocular vision anomalies, found that methods that exercise convergence and accommodation independently are most effective ( Horwood & Toor, 2014 ). The study found that an enthusiastic therapist and the patient trying harder was a major factor on the outcome. Fusional reserves can be used to assess the outcome, but the reserves to blur point were so inconsistent they were unusable ( Horwood & Toor, 2014 ).
Development of Fusional Reserves and Relative Accommodation
The aim of the exercise appropriate to each kind of anomaly has been described in the previous chapters, but the general principles can be summarised as follows:
In esophoric conditions: develop divergent reserves and/or positive relative accommodation.
In exophoric conditions: develop convergent reserves and/or negative relative accommodation.
In general, the object of this type of exercise is to exert the fusional reserve while keeping the accommodation unchanged: or, the other way round, induce changes in the accommodation while maintaining fixed vergence. Some methods exercise both, but one function is changed in excess of the other. The intention is to strengthen and increase the function which opposes the troublesome heterophoria, and to extend the range, or to ‘loosen up’ the accommodation-convergence relationship.
Are Fusional Reserve Exercises Effective?
Exercises to increase the fusional reserves are essentially visual feedback-based neuro-motor conditioning or enhancement therapies. On a very simple level, repeating a vergence task results in an improvement in performance, assessed by objective eye movement recording ( Jainta, Bucci, Wiener-Vacher, & Kapoula, 2011 ), although this study was not a randomised controlled trial (RCT). Indeed, most research in this field has significant limitations, but four thorough RCTs have been carried out and provide mixed results.
The first two RCTs, of 46 adults ( Scheiman, Mitchell, Cotter, Kulp et al., 2005 ) and 221 children ( CITT, 2008 ) with convergence insufficiency exophoria (CIES; p. 118) produced similar results, replicating a smaller pilot study of children ( Scheiman, Mitchell, Cotter, Cooper et al., 2005 ). Intensive exercises were found to be more effective at treating CIES than simple pen-to-nose exercises. Indeed, the pen-to-nose exercises, which have been criticised as very basic ( Kushner, 2005 ), were not found to be effective at improving the near point of convergence and convergent fusional reserves. This is perhaps not surprising because the participants were selected as having the syndrome of CIES. As they had low convergent fusional reserves in addition to a remote near point of convergence, it is not surprising that push-up exercises were ineffective because these would only be expected to address the near point of convergence. Second, the treatment dose in each group was not matched. The intensive vision therapy group and placebo therapy group received a 60 minute clinic session weekly, in addition to 15 minutes a day home therapy, whereas the push-up group received only 15 minutes a day ( CITT, 2008 ). So, the placebo therapy group received more hours of treatment and are likely to have received a greater placebo effect than the push-up group.
Using the Convergence Insufficiency Symptom Survey (CISS) questionnaire, in children symptoms improved most in the group receiving intensive exercises ( CITT, 2008 ). With adults, symptoms improved significantly in all groups and the groups receiving push-up exercises or more intensive exercises did not improve symptomatically better than the group receiving placebo exercises ( Scheiman, Mitchell, Cotter, Kulp et al., 2005 ). It is interesting that in the group that received the most intensive vision therapy, at the end of the trial 56% of children and 58% of adults were still symptomatic (see pp. 64–65).
A smaller RCT in 2018 compared three approaches for treating CIES: simple home push-up exercises; office-based vision therapy with a synoptophore (120 min/week) and additional home exercises; and augmented office-based vision therapy involving synoptophore and near vision tasks through minus lenses and base-out prism (120 min/week). There were 28 participants in each group, aged 15–35 years, and the study was single-masked ( Aletaha, Daneshvar, Mosallaei, Bagheri, & Khalili, 2018 ). The convergent fusional reserves, near point of convergence, near exophoria, and CISS symptoms improved significantly, most markedly in the two groups receiving office-based therapies. The authors did not consider whether the results could be explained by a simple dose effect.
A later study by the Convergence Insufficiency Treatment Trial (CITT) group in children aged 9–14 years improved the matching of active and placebo vision therapy, in that the therapist contact time and treatment time was matched in both groups ( Scheiman et al., 2019 ). This research showed an improvement in convergent fusional reserves and near point of convergence in the experimental group, but no significant improvement in symptoms ( CITT-ART Investigator Group, 2019 ) or reading performance compared with the control group ( Scheiman et al., 2019 ). The lack of a significant improvement in symptoms could be explained by inadequacies of the CISS tool for measuring symptoms ( Horwood et al., 2014 ; Horan, Ticho, Khammar, Allen, & Shah, 2015 ), and it is noted that the CISS questionnaire is not well-suited to the digital age ( CITT-ART Investigator Group, 2019 ). An alternative explanation is that much of the positive effect of eye exercises on symptoms is attributable to placebo effects or response bias, as active and control treatments were better matched in the CITT-Attention & Reading Trial (ART) study than in previous research by this group.
Overall, these studies support the conclusion that patients with CIES experience an improvement in convergent fusional reserves and near point of convergence following intensive vision therapy. Some evidence indicates that this can be associated with an improvement in symptoms, but this finding is equivocal.
There is some evidence from objective recordings of eye movements and functional magnetic resonance imaging (fMRI) that these parameters improve when CIES is treated. As well as improving the appropriate fusional reserve, the exercises train proximal vergence ( Hokoda & Ciuffreda, 1983 ) and may ( Bobier & McRae, 1996 ; Singh, Mani, & Hussaindeen, 2017 ), or may not ( Hung, Ciuffreda, & Semmlow, 1986 ; Brautaset & Jennings, 2006a ) increase the AC/A ratio.
Most research relates to horizontal fusional reserves, particularly convergent reserves which most often require treatment. There is a suggestion, from a noncontrolled trial, that vertical fusional reserves could possibly be improved ( Luu et al., 2000 ), although the evidence base is weak for vision therapy to train any motor function other than convergent fusional reserves and near point of convergence.
What are the Essential Features of Successful Exercises?
The evidence reviewed earlier, provides some support for eye exercises to train convergent fusional reserves, especially in patients whose exophoria is at risk of breaking down to a strabismus. This raises the question of how best to provide this vision training.
Fusional reserve exercises can employ a variety of methods of dissociating the eyes, including red/green filters (anaglyph), polarisation (vectograms), and haploscopic devices (e.g., stereoscopes). An alternative method used since 1940 ( Revell, 1971 ) is to employ free-space fusion. This has several advantages, including that no specialist equipment is needed. Additionally, research indicates that vergence latencies are much shorter, equivalent to saccades, under free-space conditions, but not when viewing through artificial instruments ( Hung, 1998 ). This may support the clinical observation that when exercises are carried out under more natural free-space conditions, improvements in visual function are more likely to translate into everyday life.
Notwithstanding the method of dissociation, there appear to be two schools of thought regarding the most effective type of exercise. One viewpoint, typified by Vaegan (1979) , is that the details of the exercises are relatively unimportant, and the key feature is to maintain an overconverged posture for as long as possible. If this hypothesis is correct, the benefit some clinicians report from combining varied approaches may simply be that they keep the patient interested during potentially boring periods of overconvergence.
An alternative viewpoint is that the use of more than one technique may help the effect transfer into everyday vision ( Cooper et al., 1983 ), as may the use of different stimulus parameters ( Feldman, Cooper, & Eichler, 1993 ). Stimulus parameters can be varied, for example, by using different target types and sizes. Another important factor may be whether the vergence is changed gradually (ramp) or in jumps (step). Some studies have found that steps of disparity yield greater improvements than ramps, although another study found slow stimulus changes to be optimal ( Daum, Rutstein, & Eskridge, 1978 ). It may be ideal to use both step and ramp stimuli ( Ciuffreda & Tannen, 1995 ). A range of different instruments for eye exercises are available from the American company, Bernell ( Appendix 12 ).
In the CITT study, the group that benefitted most from treatment had a longer duration of treatment and included procedures ( Table 10.2 ) designed to target fusional vergence and others aimed at overall convergence, with the therapist able to freely manipulate vergence and accommodative demand using multiple procedures ( Scheiman et al., 2010 ). These authors found that 4 weeks is an appropriate time for a progress evaluation.
Virtual Reality Systems
An exciting development in this field is the use of three-dimensional (3-D) displays for eye exercises. In particular, the immersive nature of virtual reality headsets has great potential for creating a game environment, to engage patients in vision therapy. One device that is currently available has been described in the literature ( Backus, Dornbos, Tran, Blaha, & Gupta, 2018 ; Fortenbacher, Bartolini, Dornbos, & Tran, 2018 ), but it is likely that other devices will be available in due course.
Polarised Vectogram and Anaglyph Techniques
With polarised vectograms ( Fig. 10.2 ) the eyes are dissociated by means of cross polarisation. The targets are transparent plastic sheets with a picture on each sheet of the same scene but taken from slightly different angles. The sheets are polarised in different directions and the patient wears appropriately polarised glasses. The sheets are back-illuminated by a uniform source and are placed so that the two pictures are directly on top of one another. A nonstrabismic patient should report seeing one picture, in 3-D relief. To treat an esophoric condition, the sheet that the right eye sees is slowly moved to the right of the left eye’s sheet. If the patient continues to perceive a stereoscopic image, the right eye must have moved to the right to follow the target, i.e., divergence has occurred. The sheet is moved further until the patient reports blur, diplopia, or suppression (loss of stereopsis) when the sheet is moved back until binocularity is restored. The procedure is repeated, encouraging the patient to try and maintain binocularity for as long as possible. To train convergence (to overcome an exophoria) the right eye’s image would be crossed over to the left of the left eye’s image.
A similar technique can be used with anaglyphs, where the eyes are dissociated by means of red and green targets and goggles instead of polarisation. Because wearing different coloured lenses in front of each eye is unnatural, anaglyph techniques are more ‘artificial’ than polarised vectogram methods. However, dissociation by red/green lenses allows the targets to be generated on television or basic computer screens ( Cooper, 1988a ). This type of eye exercise is available on the internet in a system called Orthoweb ( Field, 2002 ).
Variable Prism Stereoscopes
A variable prism device, such as a rotary prism, prism bar, or variable prism stereoscope, is used in the same way as described for the measurement of fusional reserves in Chapter 4 . The patient looks at targets small enough to require precise convergence and accommodation while the power of the prism is gradually increased to change vergence in the direction opposing the phoria. The patient is asked to maintain clear single vision as long as possible, but when blurring or doubling occurs, the prism power is reduced, and the patient asked to recover clear single vision as soon as possible. The procedure is repeated for periods of about 5 minutes. The exercise is carried out for near vision, distance vision, or both, as the patient’s difficulties suggest is appropriate.
If a variable prism stereoscope is used for distance vision, the card holder is removed, and the patient looks across the room. For near vision, this instrument can be used either with a single line of letters in the card holder and the septum removed or using a stereoscope card with separate right and left eye pictures and with the septum in place. In the latter case, 9Δ base-out in each eye will be required. The stereoscope cards appropriate for this should have most of the picture common to both eyes, so ‘fusion’ can take place, but have small parts of each eye’s picture presented to only one eye to act as ‘monocular markers’. In those cases where suppression is particularly marked, this type of card should be used in the early stages of treatment. Note that in all cases the patient should be asked to report that doubling has been observed, in the sense that the target is seen to break into two and the images drift apart. In some cases, double vision may not occur until one of the images has moved outside a fairly large suppression area. In these cases, the target is not seen to double, but a second peripheral image suddenly appears; this is most likely in divergence excess exophoria.
A simple variable prism method is to use a prism bar with a target placed at the appropriate distance. This can be loaned to the patient to use at home.
Lens (Holmes) Stereoscope
It will be seen from Fig. 10.3 that a lens (Holmes) stereoscope can be considered to have two ‘orthophoria lines’ from the focal point of each of the lenses to a point mid-way between the lenses themselves. In most stereoscopes, these are purely imaginary lines, but are useful in deciding which exercise is appropriate to esophoria or to exophoria. If the two pictures on the stereoscope card are of such a separation and at such a distance that they fall one on each of these orthophoria lines, their images will coincide with each other on the mid-line of the instrument. This will mean that, ignoring any proximal convergence, the eyes will have to converge and accommodate according to the normal accommodation-convergence relationship for the distance of the images. To use a card with a greater picture separation, but at the same card distance, would require the eyes to diverge in order to ‘fuse’, and a card with less picture separation would induce convergence. No change in accommodation would be required.
The diagram in Fig. 10.3 also shows that if the card distance is increased without changing the separation of the pictures, i.e., the card holder is drawn away from the patient’s eyes, the picture separation will now be narrow for the new card distance and therefore convergence will be required to maintain ‘fusion’. In this new position, the card’s picture will lie inside the orthophoria lines. At the same time, the image distance will have increased, so that less accommodation is required. This means that when the card distance is increased, convergence and negative relative accommodation will be exercised which will help patients with exophoric conditions. In summary, when using the Holmes stereoscope:
In esophoric conditions: use cards of increasing picture separation and/or move the card holder towards the patient’s eyes.
In exophoric conditions: use cards of decreasing picture separation and/or move the card holder away from the patient’s eyes.
Other Stereoscopic Devices
There are many different designs of stereoscope. A well-known one is the Brewster stereoscope, which is fairly similar to the Holmes design. A currently available Brewster stereoscope is the Bernell-O-Scope ( Appendix 12 ).
A slightly different approach is to use apertures rather than lenses to achieve dissociation, as in the Bernell Aperture Rule ( Fig. 10.4 ). A single aperture is used to train relative convergence and two apertures are used to train relative divergence.
Mirrors can also be used to dissociate the eyes, as in the single mirror haploscope, which is consulting-room equipment. A new version of the Pigeon-Cantonnet stereoscope, which is a portable instrument employing mirrors, is available as the Bernell Mirror Stereoscope ( Appendix 12 ).
Exercises of the fusional reserve type can also be carried out with a major haploscope (synoptophore) using ‘fusion slides’. The restricted field, stimulation of proximal convergence and other disadvantages of this type of instrument do not seem to affect its use for training fusional reserves. However, this major instrument is hardly necessary for heterophoria problems.
Free-space techniques do not require a stereoscope but involve the fusion of two stereo-pairs by overconverging or underconverging in ‘free-space’.
One feature of free-space techniques is the use of physiological diplopia and it will be seen that there are many ways in which physiological diplopia can be useful in the treatment of heterophoria. The first step with any of these exercises is to demonstrate physiological diplopia and the easiest method is to use two fairly large and obvious objects as targets, for example, two pencils. These objects are held on the median line against a plain background ( Fig. 10.5 ). The demonstration should include the patient fixating the nearer pencil and noticing the far pencil in uncrossed physiological diplopia, and then fixating the far pencil and being aware of the near one in crossed diplopia. Difficulty in seeing both the diplopic images indicates a gross degree of suppression, which is usually overcome quite quickly in heterophoria. Patients may have difficulty in alternating between uncrossed and crossed diplopia. In these cases, it is useful to ask the patient to practise doing this alternation as an exercise (p. 147). Once the patient has mastered the principle of physiological diplopia with pencils, then they can progress to other free-space techniques, such as the ‘three cats’ exercise.
‘Three Cats’ Exercise
The equipment for this exercise is simply a piece of card with two line drawings of cats, side by side and separated by about 5 cm from centre to centre. Each cat is incomplete in some way: an ear, an eye, or the tail is missing, so only when the two are fused is a complete cat formed ( Fig. 10.6 ). This method does not require a stereoscope and is particularly useful for exophoric conditions, using the procedure in Table 10.1 . The process of converging to achieve fusion of two laterally separated targets, such that the right eye fixates the left target and the left eye the right target, is sometimes called chiastopic fusion ( Goss, 1995 ).