Ординатура / Офтальмология / Английские материалы / Binocular Vision and Orthoptics Investigation and Management_Doshi, Evans_2001

Figure 6.8

IFS Card 2. The actual card is A4 size, larger than that shown

Card 3

To maintain patient interest, Card 3 employs a different approach. It uses an autostereogram, which has been specially created for the exercises (Figure 6.10). Autostereograms are pictures based on random dot stereograms, and the principle and history of the development ofthese has been summarized by Thimbleby and Neesham (1993). These images have been very fashionable, and readily hold a fascination for people of all ages.

The images can be viewed by over-con- verging or by diverging, so great care is taken in the IFS instructions to ensure that only over-convergence is used by patients during the exercises. The images that are used in the IFS Cards 3 and 4 have been specially designed by a company called Altered States, which is a leading European manufacturer of customdesigned autostereogram images. When patients over-converge appropriately, they see a series of steps leading up towards them. As their eyes 'walk up each step', they over-converge by increasing degrees.

follows a similar principle to that used in Card 3. These last two cards do not require very high degrees of over-convergence. since this would make it too difficult to achieve fusion in the slightly unusual world of virtual, autostcrcograrn, reality. Nonetheless, exploring this fascinating perceptual experience does manage to keep the patient in an over-converged state for quite long periods of time, helping to consolidate the effect of the exercises.

Follow-up

Very rarely do patients telephone in to report a problem with the exercises. The problems they might report and solutions to these are given in the practitioner instructions that come with the IPS exercises.

At the follow-up appointment, after 3-4 weeks, the practitioner should enquire about how easy or difficult the exercises have been. how often they have been done, and for how long on average each day. Patients should be asked about any change in their initial symptoms and whether any new symptoms have occurred.

The relevant clinical tests should be repeated and the results compared with those obtained before giving the exercises (see third case study in Chapter 16). If the symptoms and clinical signs have improved, then the exercises can be stopped. Occasionally the exercises need to be continued for a little longer. If there has been no or very little improvement, then alternative approaches need to be considered, as discussed in Chapters 3 and 4, and in Evans (1997). If the exercises have been successful then the patient is asked to keep them and it is explained that a further 'topup' session with the exercises is occasionally required. Most older patients recognize the return of their symptoms and initiate a further session of exercises themselves. Younger patients may need to be reexamined, perhaps in 3 months. to check the clinical signs. Patients can be reassured that top-up exercises are usually much easier and need to be carried out for a shorter period than first time around.

Conclusions

The IPS exercises are not a panacea but. for some patients, represent a fairly straightforward and cost-effective method of treating certain common orthoptic anomalies. This generic type of exercise has been

validated with randomized controlled trials. and the IFS exercises have been designed to contain the features that the literature suggests are the most important parameters for this type of intervention. It is hoped that a randomized controlled trial with the exercises will be possible soon. A preliminary open trial of over 20 consecutive patients has produced encouraging results (Evans. 2000).

Acknowledgements and ethical declaration

Several people have made helpful comments on earlier versions of the IFS exercises and their help is gratefully acknowledged. especially: Mr Paul Adler. Dr Alison Finlay. Dr Adrian Jennings. Mrs Anita Lightstone. Mr John O'Donnell and Mr David Stidwill.

The exercises can be obtained from 100 Marketing Ltd (telephone 02D7 378 033D). 100 Marketing Ltd is a company that exists to raise funds for the Institute of Optometry. which is a charity. 100 Marketing Ltd pays a small 'award to inventors' to the author. based on sales of the exercises.

The help of Altered States. the company which created Cards 3 and 4. is gratefully acknowledged. Altered States (telephone 0207350 1200j is a leading European developer of custom-designed autostereogram images.

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pathology. and requires urgent referral unless there is an obvious cause that responds to treatment. For example. an obvious cause of esotropia is uncorrected hypermetropia, in which case refractive correction should eliminate the strabismus. In another example, if an optometrist has been monitoring a large exophoria for a number of years and this starts to decompensate with increasing schoolwork. causing diplopia, then the optometrist may choose to correct this by refractive management or with orthoptic exercises (see Chapters 3 and 6).

Monocular diplopia or binocular triplopia can occur through a rather similar mechanism to paradoxical diplopia: because of a persistence of the sensory state preceding a surgical intervention. The strabismic eye sees two images of a fixation point as a result of competition between the innate normal retinal correspondence and long-standing anomalous retinal correspondence that existed before surgery. When both eyes are open, the normal retinal correspondence in the dominant eye can cause triplopia (von Noorden, 1996, pp. 269-70).

Most cases of strabismus do not have diplopia but have developed binocular sensory adaptations. These adaptations are either harmonious anomalous retinal correspondence (HARC) or suppression, and these topics are discussed in Chapters 8 and 9. Intractable diplopia (see below) suggests that either patients were unable to develop sensory adaptations (e.g. they were too old when the strabismus occurred) or that there has been a change in their sensory or motor status.

Rarely, binocular diplopia can result from a change in fixation preference, when a previously dominant eye becomes the more myopic, causing a change in ocular dominance. Such cases are resolved by correction ofthe myopia.

A particularly troublesome form of binocular sensory diplopia occurs in nonstrabismic patients who have developed a macula or retinal lesion causing metamorphopsia. Bifoveal fusion may be impossible, yet peripheral fusion is likely to be normal.

It is possible that sensory diplopia might also occur as one of the anomalous visual effects accompanying migraine or epilepsy. One theory is that these anomalous visual effects result from hyperexcitability of the visual cortex (Wilkins, 1995, p. 157).

52 Binocular Vision and Orthoptics

Covering one eye halves the sensory input to the visual cortex, and thus reduces the probability of such anomalous visual effects (Wilkins, 1995, pp. 21-3). Hence, sensory diplopia from this source could conceivably present as binocular diplopia that resolves on covering one eye, although the patient does not have a strabismus.

Can the patient achieve binocular single vision?

It is noted in Chapter 14 that the complaint of binocular diplopia strongly suggests that there is the potential for binocular single vision, especially if the patient can consciously control the diplopia by adopting a compensatory head posture. Exceptions are the intractable cases described later in this chapter. In every case, it is important to establish whether the diplopia can be eliminated. This should be investigated with prisms before surgery is considered.

Loose prisms, rotary prisms (e.g. in a refractor head) or prism bars can be used. It should be noted that errors can occur when prisms are stacked (e.g. several loose prisms placed in a trial frame; Firth and Whittle, 1(94).

The effect of prisms on diplopia from comitant strabismus can be investigated using the Mallett OXO test (Figure 7.4; available from 1.0.0. Marketing Ltd. Tel.

Figure 7.4

Diagram sholVing the use of a Mallett unit to investigate the effectof prisms on diplopia

0207 3780330). Even incomitant cases, if the incomitancy is subtle, sometimes benefit from the prism suggested by testing with the Mallett unit in the primary position (see Chapter 16). An advantage of the Mallett OXO test is that it does not dissociate the patient. but instead preserves normal viewing conditions. For patients with good visual acuity, the usual small OXOcan be used. Patients with poor acuity can use the large OXO. which is included on modern near Mallett Units (the usual use for the large OXO is for assessing sensory factors in strabismus; Chapter 9).

If a diplopic patient views the appropriate test whilst wearing the polarized visors. then he or she should report seeing two OXOs, one with a line above the X and another with a line below the X (Figure 7.4a). The position of the OXOsreveals the' type of diplopia (e.g. horizontal in Figure 7.4). Prisms are introduced and adjusted to bring the OXOs closer together (Figure 7.4b). It should be determined whether the patient can fuse the diplopic OXOs (as in Figure 7.4c). If this is not possible, then there may be sensory fusion disruption syndrome or horror [usionis, as described below. If the patient can fuse the OXOs, then the prism should be refined to eliminate any fixation disparity (Figure 7.4d). If there is no significant incomitancy, then the patient should be able to move the head and, when viewing through the appropriate prisms, maintain binocular single vision. In patients with horizontal diplopia and with adequate accommodation. spheres (minus for exotropia, or plus at near for esotropia) can be used to try and eliminate the diplopia by altering the accommodative convergence.

If a prismatic or spherical correction eliminates the diplopia. then this can be prescribed. Some patients adapt to the correction and require a stronger prescription, but this is not usually the case. This is because patients with binocular vision anomalies do not usually adapt to prisms (North and Henson, 1981), unlike patients with normal binocular vision (North and Henson, 1992; Rosenfield, 1997). With larger angles that may require surgical intervention a prism adaptation test or a trial with botulinum toxin is advisable before surgery, as described in Chapter 14.

A postoperative diplopia test can be used to investigate the presence of diplopia or suppression in patients without the potential for binocular single vision. The post-

operative diplopia test is also described in Chapter 14. Patients with diplopia or suppression should have this test carried out before surgery, to assess the risk or inducing intractable diplopia after surgery.

It can be difficult to investigate the effect of prisms in patients with very large deviations. The management of these patients is discussed in Chapter 14.

Overview of commonplace treatments for diplopia

Many cases of diplopia can be treated by optical or surgical means (for example, see the first case study in Chapter 16). Table 7.1 gives examples of typical treatmen ts for some of the causes of diplopia that are listed in Figure 7.3. Occasionally diplopia does not respond to standard treatment. or other considerations mean that the usual treatment (e.g. surgery) is contraindicated. These cases are described as intractable diplopia.

Causes of intractable diplopia

The word intractable means 'not easily dealt with'. Intractable diplopia can be very distressing for patients, sometimes greatly impairing their ability to live a full and happy life. Some cases can be managed surgically, and an ophthalmologist will be able to advise on this. Other cases cannot be managed surgically, and these patients may turn to the optometrist to treat the diplopia through optical or other means.

The author sees cases of intractable diplopia that are referred for hypnosis, and the main causes of intractable diplopia in these cases include;

•Secondary deviation from unsuccessful surgery; in some cases a surgeon advises against further surgery

•Late onset strabismus, which may in some cases be inoperable (e.g. for medical reasons)

•Acquired anisometropia (e.g. iatrogenic to complicated cataract or refractive surgery); some cases may not be suitable for contact lenses

•Retinal distortion following detachment or macula lesion

•Sensory fusion disruption syndrome (see below)

•Horrorfusionis (see below).

54 Binocular Vision and Orthoptics

are a long way apart so that surgery might make the symptoms worse through reducing the angle of the deviation. However. each patient is different, and it should not be concluded that patients will necessarily be helped by increasing the separation of the two images (see Case Study 2). It seems safer to conclude that, if the diplopia cannot be eliminated, it is generally best to avoid changing the angle of the diplopia from that to which the patient has become accustomed, unless testing has suggested that the patient may be more comfortable with a new angle or equally tolerant of a cosmetically improved angle of deviation.

Management of intractable diplopia

The management options for intractable diplopia are limited, and include occlusion and hypnosis.

Occlusion

Occlusion is the simplest method to treat intractable diplopia. As long as the diplopia is of the binocular type (Figure 7,3), then occlusion can eliminate the diplopia. There are various forms of occlusion, which differ in the type of optical appliance and in the depth of occlusion. These are summarized in Figure 7.5.

Tarsorraphy and botulinum toxin are invasive, associated with a higher risk than other methods, and achieve a very

Figure 7,5

Typesof occlusion

poor cosmetic outcome. They are therefore best considered as a last resort.

A simple eye patch is perhaps the oldest form of occlusion. If the patch fits well, then this method is virtually guaranteed to achieve a satisfactory outcome, in terms of completely blocking out the image from the unwanted eye. There are a few cases so sensitive to any visual input from their non-preferred eye that they can be bothered by the peripheral visual image that can be experienced in the occluded eye of occluding spectacles or even contact lenses. For these rare cases, an eye patch may be the preferred approach. However, the method is unsightly and for most cases is best thought of as a temporary measure.

Similarly, the use of a blackened spectacle lens achieves a poor cosmetic outcome and is best thought of as a temporary measure. However, this approach should not be ignored. For example, elderly patients with diplopia from a recent onset deviation who are waiting to see an ophthalmologist can be helped considerably by either providing an eye patch or, for spectacle wearers, covering the spectacle lens of the non-preferred eye with masking tape. Patients who have undergone a cataract operation in one eye and who have induced anisometropia whilst awaiting the operation in the other eye can also be helped in this way.

In the days when glass lenses were in common usage, Chavasse lenses were used. These have an irregular surface to depress the visual acuity whilst permitting

the eye to be seen from the front. Similarly, frosted lenses are translucent and are cosmetically better than black lenses. CR39 lenses can be frosted, and plastic materials are much preferred for reasons of safety. An inexpensive translucent occluder can be made with Favlon or with sticky tape stuck onto a normal spectacle lens. A few diplopic patients who are particularly sensitive to any image in their non-preferred eye can still be bothered by the image from a frosted or Chavasse lens.

Bangerter foils (available from Spectacles Direct, Tamworth) are an interesting form of translucent occlusion. These are 'presson' films that are adhered to a lens, in a similar way to Fresnel lenses. Bangerter foils are not prismatic, but instead are frosted with a series of differing degrees of opacification. The foils were originally developed for amblyopia therapy, and are graded according to the typical level of decimal visual acuity obtained through the foil. McIntyre and Fells (1996) described the use of these filters to treat patients with intractable diplopia. Their open trial included 14 patients with strabismus onset in childhood and 10 with strabismus onset in adult life, including two with metamorphopsia from retinal dysfunction. Unsurprisingly, they found that the filters were much more likely to be successful for children. The ultimate goal of gradually reducing the density of the required filter until the patient was asymptomatic with no filter or with an almost clear filter was achieved in four of the childhood onset patients. None of the adult onset group achieved this, but one-third of these ended up with good and one-third with fair 'foil cosmesis', and one-third with an unsatisfactory outcome.

Spectacle lenses of a high and/or inappropriate power can be used to blur, or 'fog', the non-preferred eye and this may make it easier for the patient to suppress a diplopic image. This approach is particularly suitable for cases where the non-pre- ferred eye already has a high refractive error. However, not all cases are able to suppress a blurred image, and occasionally a patient may be encountered who prefers clear diplopic images at a 'familiar' degree of separation to diplopia where one of the images is unclear (see Case Study 2).

Wildsoet et al. (1998) investigated the effect of different types of occluders (opaque, frosted, +1.50D blur) on visual function of the non-occluded eye in 20

the 'mystique' surrounding hypnosis) help to create a very strong placebo effect that convinces them that they are in a special state. It is no surprise that suggestions that are made to the patient about how they wiIl change as a result of the hypnosis often have the desired effect. since placebo effects can be very powerful. To the current author. it is this second, 'placebo'. explanation that makes most sense. There is a vast amount of research demonstrating that the placebo effect is pervasive and extremely powerful (Evans, 1997b). Indeed, up to one-third of drugs prescribed in the USA may in essence be placebos (Ross and Olsen, 1982).

Whichever explanation about the mechanism for hypnosis is found to be correct. this procedure can be an extremely useful tool for clinicians from a variety of disciplines. One of the classic experiments in hypnosis is to tell a good hypnotic subject that he or she is temporarily blind. Some subjects wiIl then open their eyes and will believe and. in many respects, behave as if they were blind. If hypnosis can be used to create this effect. then it is very likely that it could also be used to create other, more positive, visual impressions, including the suppression of a diplopic image.

Hypnosis has been used to treat very many conditions, ranging from stuttering (Moss and Oakley, 1997) to providing pain relief during child birth (DiIlenburger and Keenan. 1996) and dental and other surgical procedures (Karle and Boys. 1998). There is some evidence that hypnotic suggestions do not just make patients 'feel better' about a condition. but might actually create a physiological change (Evans and Richardson. 1988). Medd (1997) used hypnosis to treat dystonia, and noted that 'hypnosis may not achieve its effects simply by alleviating anxiety or depression. but may have influence also by acting upon the neurological substratum of the condition by allowing the natural inhibition of unwanted efferent impulses to take place'. Gruzelier (1998) found undeniable evidence of neurophysiological changes in susceptible patients who had received hypnotic suggestions.

The most common reason for the current author using hypnosis in optometric practice is for intractable diplopia. Typically, adults with acquired diplopia following trauma or unsuccessful strabismus

56 ill Binocular Vision and Orthoptics

successfully to suppress the strabismic eye, causing relief of their diplopia, This subject was reviewed by Evans et al. (1996).

There are many myths about hypnosis. and patients need to be reassured that the clinical use of hypnosis is very different from the 'stage hypnosis' that they might have seen on television. Patients do not need to be weak-willed, since the hypnosis does not involve them losing control. Indeed, they need to be willing to be hypnotized, and their co-operation is essential. Surprisingly, patients who anticipate that it will not be possible for them to be hypnotized often turn out to be good hypnotic subjects, responding very well to the suggestions that are made. Patients are told that they will remember everything when they 'wake up', and are never asked to do anything foolish or anything that is uncomfortable or painful. After the hypnosis patients invariably feel relaxed and refreshed. They do not usually enter a 'deep trance' that is completely unlike anything that they have ever experienced. A useful analogy is to liken the hypnotic state with the situation when a person is quietly reading a very gripping novel. or is in a cinema and is engrossed in a film. In these situations, people might temporarily lose an immediate awareness of where they are, or of the time of day. but they are still conscious and, on occasions, fully aware of where they are and what they are doing. The situation with clinical hypnosis is very similar.

In a clinical setting, hypnosis typically involves three stages. First, hypnosis is induced, usually by a combination of techniques. During the second stage, the patient is given post-hypnotic suggestions. For example, such a suggestion might be that the patient will suppress the unwanted second image in diplopia. Various elaborations of this suggestion are made. Finally, the patient is de-induced - 'woken up' - typically by counting down from 1() to one.

Usually, patients need about three to four 30-minute sessions of hypnosis (see Case Study 3). A few cases report a more or less complete elimination of the diplopia; most cases report that the diplopia is less bothersome, although still present on some occasions. Occasionally, the hypnosis has no appreciable effect. The cases that are most difficult to treat seem to be those where the diplopic image is moving, as often happens in sensory fusion disruption syndrome.