New in Orthoptics

Professor Bruce JW Evans BSc (Hons), PhD, FCOptom, DipCLP, DipOrth, FAAO

Orthoptics special

Everyday optometric orthoptics Top tips and how to specialise rthoptics is defined as, “The study, diagnosis, and non-surgical treatment of anomalies of binocular vision, strabismus, and monocular functional amblyopia”1. Binocular vision (orthoptic) anomalies affect at least 5% of the population and some say that the prevalence is much higher than this. All optometrists will inevitably encounter patients with orthoptic anomalies, and they must be able to recognise these conditions and deal with them appropriately, either by treatment or referral. In other words, orthoptics is not an optional subject for practising optometrists and this is why all optometry training courses and the PQE examinations cover orthoptics/binocular vision anomalies.

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What you need to know about orthoptics Although all optometrists need to have a working knowledge of orthoptics, it is only a minority who choose to specialise in this subject. As with any area of professional practice, optometric skill levels in orthoptics can be considered at three levels: • Minimum level of basic knowledge for safe practice. The most important reason to be ‘safe’ is for the patient’s benefit. A secondary reason in these litigious times is for the practitioner’s safety. In the case of a complaint to the GOC or of civil litigation, you may have to show that there is at least a body of reasonably competent optometrists who would have practised in the way that you did. • Good practice. The College of Optometrists (COptom) guidelines are on the College website at www.collegeoptometrists.org under the heading of ‘Good Optometric Practice’. Although there is no specific section in the

Table 1 Reasons for intervening when an orthoptic anomaly is present 1. If the anomaly is causing symptoms or decreased visual function 2. If the anomaly is likely to worsen if left untreated 3. If the anomaly is likely to be a sign of ocular or systemic pathology

Table 2 Interventions for binocular vision anomalies. The suitability of each intervention will vary according to the details of the case 1. Treat with eye exercises 2. Correct/treat with refractive correction/modification 3. Correct with prisms 4. Treat with patching (occlusion) or penalisation 5. Refer for one of the above treatments by another practitioner 6. Refer for surgery 7. Refer for further investigation

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guidelines on orthoptics, the section on ‘Examining the Younger Child’ is relevant. • Specialist practice. Primary eyecare in the UK is almost synonymous with optometry, and as the optometric profession matures, it is only natural that we are seeing an increasing degree of specialisation within the optometric profession. One of these areas is orthoptics, and indeed the COptom Diploma in Orthoptics2 was the first postgraduate orthoptics qualification in the UK. It is not possible in one article to provide a comprehensive review of orthoptic techniques at any of these three levels. This article provides an overview of the subject, with some ‘top tips’ which it is hoped will be useful for the busy practitioner. Where relevant, the three levels of practice are used to provide a suggested context for some of the procedures that are discussed.

Top tips for everyday optometric orthoptics When do I need to do something about an orthoptic anomaly? As a general rule, there are only three reasons for intervening when a binocular vision anomaly is present3. These are listed in Table 1. It should be noted that not all patients with symptoms are aware of these. This is especially true of children, who may only appreciate that a symptom was present once the condition has been successfully treated. It is only very rarely that binocular vision anomalies are encountered in primary eyecare practice which result from ocular or systemic pathology, but practitioners must always be alert to this possibility (Table 5).

What do I do? When binocular vision anomalies require an intervention, there are several possible options. These are listed in Table 2. These options are not mutually

exclusive. For example, a child with strabismic amblyopia, where the cause of the strabismus is not clear, may be referred for medical investigation, but whilst waiting for the hospital appointment, the optometrist might start patching. As in all healthcare sciences, the diagnosis and management are not fixed entities, but rather are the latest judgements based on the best available evidence at that time. Very often, one treatment is tried in the first instance and if this is not effective, then a second choice treatment will be tried. Practitioners should always try to keep an open mind about their diagnosis and should be prepared to constantly reconsider this in light of their latest findings, and of the patient’s response to treatment.

Detecting and diagnosing incomitant deviations The most commonly used test for detecting incomitant deviations is the ocular motility test. Most optometrists do not perform this on every patient they see4, but it is good practice to perform this test on every new patient, every time a young child is seen, and every time a patient with suspicious symptoms (e.g. diplopia) or signs (e.g. change in cover test results) is seen. A motility test is essential in every case of (suspected) binocular vision anomalies. In the sections of this article on heterophoria and strabismus, it is assumed that the practitioner has ruled out incomitant deviations. Although the motility test sounds simple, it can be very difficult to diagnose an underacting muscle by this test alone. There are really three different motility tests: the objective motility test in which the corneal reflexes of the light target are observed; the cover test in peripheral gaze; and the subjective motility test where the practitioner records changes in diplopia in different positions of gaze. When an incomitancy is detected, it can be confusing to try to interpret these three test results simultaneously, and it can be easier to do them separately. A worksheet for recording the results of these three tests can be found in Appendix 8 of Evans (2002)3. New, or changing, incomitant deviations can be a sign of pathology and require referral; this is mandatory as basic safe practice. The urgency of referral depends on the age, severity, and speed of onset. To take the most extreme example, a sudden onset third nerve palsy requires an emergency referral. Just as in perimetry, good practice would be to evaluate field defects detected with supra-threshold testing using

Orthoptics special

• If the patient has vertical diplopia, then they can view from a distance of 1m, a 70cm horizontal wooden rod (a 50cm or 1m ruler can be used) • If the patient does not have vertical diplopia, then two Maddox rods can be used, placed in a trial frame with axes at 90˚, so that when the patient views a spotlight at a distance of 1-3m, they see two horizontal red lines Question 1: Move the wooden rod (or spotlight) up and down and ask: Where is the vertical diplopia (or separation of the red lines) greatest, in up gaze or down gaze?

• Up gaze: RSR, RIO, LSR, LIO • Down gaze: RIR, RSO, LIR, LSO

Question 2: In the position of maximum diplopia, are the two images parallel or torsional?

• Parallel: RSR, RIR, LSR, LIR • Torsional: RSO, RIO, LSO, LIO

• Right gaze: RSR, RIR Question 3: If parallel, does the separation increase on right or left gaze? • Left gaze: LSR, LIR Question 4: If tilted, does the illusion of • Up gaze: RIO, LIO (unlikely) • Down gaze: RSO, LSO tilt increase in up gaze or down gaze? Question 5: If tilted, then the two rods The arrow will point to the side with the paretic eye will resemble an arrow (< or >), or an X. If • Arrow points to the patient’s right: RSO, RIO they resemble an arrow, which way does • Arrow points to the patient’s left: LSO, LIO the arrow point? Question 6: If crossed, does the tilt angle increase in up gaze or down gaze?

• Up gaze: bilateral IO paresis (very unlikely) • Down gaze: bilateral SO paresis

Table 3 Procedure for Lindblom's method of differentially diagnosing cyclo-vertical incomitancies. The test instructions are given on the left and the paretic muscle indicated by a given answer is on the right full-threshold testing, so good practice with some incomitant deviations detected on motility testing would be to carry out further investigations to precisely quantify the anomaly. One very useful tool for this is the Thomson Software Solutions Hess Screen, which allows any optometrist with a Windows PC to carry out a Hess chart test. The cyclo-vertical incomitancies can be particularly difficult to diagnose, and various algorithmic approaches can be used. The best known of these is the Parks three-step test, but a recent approach5 is simpler and has been found by the author to be very useful (Table 3).

Diagnosing decompensated heterophoria Heterophoria is only a problem if it decompensates, and most cases of decompensated heterophoria are

associated with symptoms (Table 4, first row). Occasionally, heterophoria is encountered which may be decompensating, but the patient may avoid symptoms because they have foveal suppression. This condition is discussed elsewhere in this issue of OT6. These cases of decompensated heterophoria are an example of a condition which may worsen (become a strabismus), if left untreated (Table 1). Figure 1 is a simple model of binocular vision anomalies and is useful for considering what happens when patients develop fusional problems, and the approaches which might be appropriate for treatment. When the eyes are dissociated, most people will exhibit a dissociated deviation. Hopefully, during normal binocular fixation, the person can overcome this dissociated deviation to

Figure 1 A simple model of binocular vision (reproduced with permission from Evans, BJW (2002) Pickwell’s Binocular Vision Anomalies. Fourth edition. Butterworth-Heinemann)

DISSOCIATED DEVIATION

¡

¡

motor fusion

 

fusional reserves

sensory fusion

COMPENSATED HETEROPHORIA OR DECOMPENSATED HETEROPHORIA OR STRABISMUS

fusion lock

render it compensated. Three factors influence how easy it is for a person to overcome their dissociated deviation. First, the size of the dissociated deviation is of some relevance; if it is very large, then it is likely to be harder for the person to overcome. A second factor is the force of motor fusion, which can be measured as the fusional reserves (Figure 1). A person with a heterophoria constantly exerts motor fusion to overcome their heterophoria, so their fusional reserves have to be adequate. Some conditions (e.g. illness, stress, old age) can cause the fusional reserves to deteriorate resulting in a previously compensated heterophoria decompensating. The third factor which influences how well a person can overcome their dissociated deviation is sensory fusion (Figure 1). This relates to the similarity of each eye’s image. For example, a person may have a compensated heterophoria until they develop a degraded image (e.g. from refractive error, cataract or pathology), when each eye’s image becomes less similar. This impairment of sensory fusion can cause heterophoria to decompensate. When a patient presents with a decompensating heterophoria or recent onset strabismus, then a consideration of Figure 1 will usually enable the cause of decompensation to be determined. If the dissociated deviation has changed, then the reason must be determined: a large change in dissociated deviation might be a sign of pathology (Table 5). If a non-pathological reason for decompensation can be found, then the alleviation of this could render a heterophoria compensated. One treatment might be to strengthen motor fusion by training the fusional reserves. In a case of anisometropia (which impairs sensory fusion), a treatment might be to prescribe contact lenses to equalise the retinal image size. The importance of sensory fusion explains why refractive corrections can be so important in the treatment of orthoptic anomalies. This is one reason why a full eye examination is essential for every orthoptic patient. It should include a refraction and all the other components of an eye examination which are appropriate for a patient of that age3. Table 4 has been designed to help with the diagnosis of horizontal decompensated heterophoria. The last two items are designed to detect binocular instability, which is a condition related to decompensated heterophoria3. For vertical heterophoria, if aligning prism of 0.5∆ or more is detected then, after checking trial frame alignment, measure the vertical dissociated phoria. If this is more than the aligning prism and there are symptoms then decompensated vertical heterophoria is a likely diagnosis.

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Orthoptics special

Treating decompensated heterophoria All the interventions listed in Table 2 may be appropriate in some cases of decompensated heterophoria, however, it is very rare for this condition to require referral for surgery. The most suitable treatment for a given case depends on a number of factors, including type of decompensated heterophoria, age, motivation, intelligence, time available and, of course, the treatment preferences of the patient. Decompensated exophoria at near is often associated with convergence insufficiency and both these conditions are usually quite easy to treat with eye exercises (e.g. IFS exercises; Figure 2). But if a patient prefers, then base-in prisms can alleviate symptoms. These might be indicated in an older patient who is quite happy to have base-in prism in their reading spectacles, or in a younger patient who was about to have school examinations and wanted to postpone exercises until after their exams. A careful refraction is important; decompensated exophoria can be caused by the onset of myopia, in which case correction of the myopia might be the only necessary treatment. Even in emmetropic cases, refractive modification can be a very useful treatment for decompensated exophoria. For example, if an emmetropic eight year-old is prescribed -1.00DS, then this will cause accommodative convergence which may render an exophoria compensated. This treatment approach of refractive modification can also be very effective in cases of decompensated exophoria at distance, although these may need bifocals if the negative lenses cause problems at near. Esophoria should always cause the practitioner to suspect latent hypermetropia, and this is one of the indications for a cycloplegic refraction3. Even when no hypermetropia is found, refractive modification is usually very effective at treating near esophoria, where bifocals or varifocals can alleviate the symptoms. In any patient who is being treated by refractive modification, they are monitored every three months or so when, if possible, the refractive modification is reduced. Typically, the patient is prescribed the minimum refractive modification to eliminate any fixation disparity with the Mallett unit and to give good cover test recovery.

Diagnosing and investigating strabismus Strabismus occurs when the visual axes are misaligned and it is usually detected by cover testing. An exception to this is a certain type of microtropia, in which there is a small-angle strabismus and no movement may be seen on cover testing. These cases are difficult to diagnose, but

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Professor Bruce JW Evans BSc (Hons), PhD, FCOptom, DipCLP, DipOrth, FAAO

DISTANCE / NEAR

Score

(delete)

1. Does the patient have one or more of the symptoms of decompensated heterophoria (headache, aching eyes, diplopia, blurred vision, distortions, reduced stereopsis, monocular comfort, If so, score +3 (+2 or +1 if borderline) sore eyes, general irritation)?

Are the symptoms at D K or N K All the following questions apply to D or N, as ticked (if both ticked, complete 2 worksheets) 2. Is the patient orthophoric on cover testing? Yes K or No K If no, score +1 3. Is the cover test recovery rapid and smooth? Yes K or No K If no, score +2 (+1 if borderline) 4. Is the Mallett Hz aligning prism: