exclusive. For example, a child withstrabismic amblyopia, where the cause ofthe strabismus is not clear, may be referredfor medical investigation, but whilstwaiting for the hospital appointment, theoptometrist might start patching. As in allhealthcare sciences, the diagnosis andmanagement are not fixed entities, butrather are the latest judgements based onthe best available evidence at that time.Very often, one treatment is tried in thefirst instance and if this is not effective,then a second choice treatment will betried. Practitioners should always try tokeep an open mind about their diagnosisand should be prepared to constantlyreconsider this in light of their latestfindings, and of the patient’s response totreatment.

Detecting and diagnosingincomitant deviationsThe most commonly used test fordetecting incomitant deviations is theocular motility test. Most optometrists donot perform this on every patient they see4,but it is good practice to perform this teston every new patient, every time a youngchild is seen, and every time a patient withsuspicious symptoms (e.g. diplopia) orsigns (e.g. change in cover test results) isseen. A motility test is essential in everycase of (suspected) binocular visionanomalies. In the sections of this article onheterophoria and strabismus, it is assumedthat the practitioner has ruled outincomitant deviations.

Although the motility test soundssimple, it can be very difficult to diagnosean underacting muscle by this test alone.There are really three different motilitytests: the objective motility test in whichthe corneal reflexes of the light target areobserved; the cover test in peripheral gaze;and the subjective motility test where thepractitioner records changes in diplopia indifferent positions of gaze. When anincomitancy is detected, it can beconfusing to try to interpret these three testresults simultaneously, and it can be easierto do them separately. A worksheet forrecording the results of these three testscan be found in Appendix 8 of Evans(2002)3.

New, or changing, incomitantdeviations can be a sign of pathology andrequire referral; this is mandatory as basicsafe practice. The urgency of referraldepends on the age, severity, and speed ofonset. To take the most extreme example, asudden onset third nerve palsy requires anemergency referral.

Just as in perimetry, good practicewould be to evaluate field defects detectedwith supra-threshold testing using

Everyday optometric orthopticsTop tips and how to specialise

Orthoptics special

guidelines on orthoptics, the section on‘Examining the Younger Child’ isrelevant.

• Specialist practice. Primary eyecare inthe UK is almost synonymous withoptometry, and as the optometricprofession matures, it is only naturalthat we are seeing an increasing degreeof specialisation within the optometricprofession. One of these areas isorthoptics, and indeed the COptomDiploma in Orthoptics2 was the firstpostgraduate orthoptics qualification inthe UK.

It is not possible in one article to providea comprehensive review of orthoptictechniques at any of these three levels. Thisarticle provides an overview of the subject,with some ‘top tips’ which it is hoped willbe useful for the busy practitioner. Whererelevant, the three levels of practice areused to provide a suggested context forsome of the procedures that are discussed.

Top tips for everydayoptometric orthoptics

When do I need to do somethingabout an orthoptic anomaly?As a general rule, there are only threereasons for intervening when a binocularvision anomaly is present3. These are listedin Table 1. It should be noted that not allpatients with symptoms are aware of these.This is especially true of children, whomay only appreciate that a symptom waspresent once the condition has beensuccessfully treated.

It is only very rarely that binocularvision anomalies are encountered inprimary eyecare practice which result fromocular or systemic pathology, butpractitioners must always be alert to thispossibility (Table 5).

What do I do?When binocular vision anomalies requirean intervention, there are several possibleoptions. These are listed in Table 2.

These options are not mutually

Orthoptics is defined as, “The study, diagnosis, andnon-surgical treatment of anomalies of binocular vision,strabismus, and monocular functional amblyopia”1. Binocular

vision (orthoptic) anomalies affect at least 5% of the populationand some say that the prevalence is much higher than this. Alloptometrists will inevitably encounter patients with orthopticanomalies, and they must be able to recognise these conditions anddeal with them appropriately, either by treatment or referral. Inother words, orthoptics is not an optional subject for practisingoptometrists and this is why all optometry training courses and thePQE examinations cover orthoptics/binocular vision anomalies.

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

28 | January 14 | 2005 OT

What you need toknow about orthopticsAlthough all optometrists need to have aworking knowledge of orthoptics, it is onlya minority who choose to specialise in thissubject. As with any area of professionalpractice, optometric skill levels inorthoptics can be considered at threelevels:• Minimum level of basic knowledge

for safe practice. The most importantreason to be ‘safe’ is for the patient’sbenefit. A secondary reason in theselitigious times is for the practitioner’ssafety. In the case of a complaint to theGOC or of civil litigation, you mayhave to show that there is at least abody of reasonably competentoptometrists who would have practisedin the way that you did.

• Good practice. The College ofOptometrists (COptom) guidelines areon the College website at www.college-optometrists.org under the heading of‘Good Optometric Practice’. Althoughthere is no specific section in the

1. If the anomaly is causing symptoms ordecreased visual function

2. If the anomaly is likely to worsenif left untreated

3. If the anomaly is likely to be a sign ofocular or systemic pathology

Table 1Reasons for intervening when an orthoptic

anomaly is present

1. Treat with eye exercises2. Correct/treat with refractive

correction/modification3. Correct with prisms4. Treat with patching (occlusion) or

penalisation5. Refer for one of the above treatments

by another practitioner6. Refer for surgery7. Refer for further investigation

Table 2Interventions for binocular vision anomalies.The suitability of each intervention will vary

according to the details of the case

Orthoptics special

29 | January 14 | 2005 OT

full-threshold testing, so good practicewith some incomitant deviations detectedon motility testing would be to carry outfurther investigations to precisely quantifythe anomaly. One very useful tool for thisis the Thomson Software Solutions HessScreen, which allows any optometrist witha Windows PC to carry out a Hess charttest. The cyclo-vertical incomitancies canbe particularly difficult to diagnose, andvarious algorithmic approaches can beused. The best known of these is the Parksthree-step test, but a recent approach5 issimpler and has been found by the authorto be very useful (Table 3).

Diagnosing decompensatedheterophoriaHeterophoria is only a problem if itdecompensates, and most cases ofdecompensated heterophoria are

associated with symptoms (Table 4, firstrow). Occasionally, heterophoria isencountered which may bedecompensating, but the patient mayavoid symptoms because they have fovealsuppression. This condition is discussedelsewhere in this issue of OT6. These casesof decompensated heterophoria are anexample of a condition which may worsen(become a strabismus), if left untreated(Table 1).

Figure 1 is a simple model of binocularvision anomalies and is useful forconsidering what happens when patientsdevelop fusional problems, and theapproaches which might be appropriatefor treatment. When the eyes aredissociated, most people will exhibit adissociated deviation. Hopefully, duringnormal binocular fixation, the person canovercome this dissociated deviation to

render it compensated. Three factorsinfluence how easy it is for a person toovercome their dissociated deviation.First, the size of the dissociated deviationis of some relevance; if it is very large,then it is likely to be harder for theperson to overcome. A second factor isthe force of motor fusion, which can bemeasured as the fusional reserves(Figure 1). A person with a heterophoriaconstantly exerts motor fusion toovercome their heterophoria, so theirfusional reserves have to be adequate.Some conditions (e.g. illness, stress, oldage) can cause the fusional reserves todeteriorate resulting in a previouslycompensated heterophoriadecompensating.

The third factor which influences howwell a person can overcome theirdissociated deviation is sensory fusion(Figure 1). This relates to the similarity ofeach eye’s image. For example, a personmay have a compensated heterophoriauntil they develop a degraded image(e.g. from refractive error, cataract orpathology), when each eye’s imagebecomes less similar. This impairment ofsensory fusion can cause heterophoria todecompensate.

When a patient presents with adecompensating heterophoria or recentonset strabismus, then a consideration ofFigure 1 will usually enable the cause ofdecompensation to be determined. If thedissociated deviation has changed, thenthe reason must be determined: a largechange in dissociated deviation might bea sign of pathology (Table 5).

If a non-pathological reason fordecompensation can be found, then thealleviation of this could render aheterophoria compensated. Onetreatment might be to strengthen motorfusion by training the fusional reserves. Ina case of anisometropia (which impairssensory fusion), a treatment might be toprescribe contact lenses to equalise theretinal image size. The importance ofsensory fusion explains why refractivecorrections can be so important in thetreatment of orthoptic anomalies. This isone reason why a full eye examination isessential for every orthoptic patient. Itshould include a refraction and all theother components of an eye examinationwhich are appropriate for a patient of thatage3.

Table 4 has been designed to helpwith the diagnosis of horizontaldecompensated heterophoria. The lasttwo items are designed to detectbinocular instability, which is a conditionrelated to decompensated heterophoria3.For vertical heterophoria, if aligningprism of 0.5∆ or more is detected then,after checking trial frame alignment,measure the vertical dissociated phoria. Ifthis is more than the aligning prism andthere are symptoms then decompensatedvertical heterophoria is a likely diagnosis.

Figure 1A simple model of binocular vision (reproduced with permission from Evans, BJW (2002) Pickwell’s

Binocular Vision Anomalies. Fourth edition. Butterworth-Heinemann)

DISSOCIATED DEVIATION

COMPENSATED HETEROPHORIAOR DECOMPENSATED HETEROPHORIA

OR STRABISMUS

��motorfusion

sensoryfusion

fusionalreserves

fusionlock

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

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

• Right gaze: RSR, RIR• Left gaze: LSR, LIR

• Up gaze: RIO, LIO (unlikely)• Down gaze: RSO, LSO

The arrow will point to the side with the paretic eye• Arrow points to the patient’s right: RSO, RIO• Arrow points to the patient’s left: LSO, LIO

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

• If the patient has vertical diplopia, then they can view from a distance of 1m, a 70cmhorizontal 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, placedin a trial frame with axes at 90˚, so that when the patient views a spotlight at a distanceof 1-3m, they see two horizontal red lines

Question 1: Move the wooden rod (orspotlight) up and down and ask:Where is the vertical diplopia (orseparation of the red lines) greatest, inup gaze or down gaze?

Question 2: In the position of maximumdiplopia, are the two images parallel ortorsional?

Question 3: If parallel, does theseparation increase on right or left gaze?

Question 4: If tilted, does the illusion oftilt increase in up gaze or down gaze?

Question 5: If tilted, then the two rodswill resemble an arrow (< or >), or an X. Ifthey resemble an arrow, which way doesthe arrow point?

Question 6: If crossed, does the tiltangle increase in up gaze or down gaze?

Table 3Procedure for Lindblom's method of differentially diagnosing cyclo-vertical

incomitancies. The test instructions are given on the left and the pareticmuscle indicated by a given answer is on the right

30 | January 14 | 2005 OT

Treating decompensatedheterophoriaAll the interventions listed in Table 2 maybe appropriate in some cases ofdecompensated heterophoria, however, itis very rare for this condition to requirereferral for surgery. The most suitabletreatment for a given case depends on anumber of factors, including type ofdecompensated heterophoria, age,motivation, intelligence, time availableand, of course, the treatment preferencesof the patient.

Decompensated exophoria at near isoften associated with convergenceinsufficiency and both these conditions areusually quite easy to treat with eyeexercises (e.g. IFS exercises; Figure 2). Butif a patient prefers, then base-in prisms canalleviate symptoms. These might beindicated in an older patient who is quitehappy to have base-in prism in theirreading spectacles, or in a younger patientwho was about to have schoolexaminations and wanted to postponeexercises until after their exams. A carefulrefraction is important; decompensatedexophoria can be caused by the onset ofmyopia, in which case correction of themyopia might be the only necessarytreatment. Even in emmetropic cases,refractive modification can be a very usefultreatment for decompensated exophoria.For example, if an emmetropic eightyear-old is prescribed -1.00DS, then thiswill cause accommodative convergencewhich may render an exophoriacompensated.

This treatment approach of refractivemodification can also be very effective incases of decompensated exophoria atdistance, although these may need bifocalsif the negative lenses cause problems atnear.

Esophoria should always cause thepractitioner to suspect latenthypermetropia, and this is one of theindications for a cycloplegic refraction3.Even when no hypermetropia is found,refractive modification is usually veryeffective at treating near esophoria, wherebifocals or varifocals can alleviate thesymptoms. In any patient who is beingtreated by refractive modification, they aremonitored every three months or so when,if possible, the refractive modification isreduced. Typically, the patient is prescribedthe minimum refractive modification toeliminate any fixation disparity with theMallett unit and to give good cover testrecovery.

Diagnosing and investigatingstrabismusStrabismus occurs when the visual axes aremisaligned and it is usually detected bycover testing. An exception to this is acertain type of microtropia, in which thereis a small-angle strabismus and nomovement may be seen on cover testing.These cases are difficult to diagnose, but

the practitioner’s suspicions should bearoused by poor acuity in one eye fromstrabismic amblyopia. A checklistapproach to the diagnosis of microtropiais provided in Chapter 16 of Evans (2002)3

and in Evans (2005)7.The first goal in the investigation of

strabismus is to find its cause, and this iscrucial in recent onset strabismus. Bothcomitant and incomitant deviations canresult from pathology, so it is important tolook for suspicious signs (Table 5).

Three different aspects of strabismusrequire investigation. First, the motordeviation should be estimated (from thecover test movement) or ideally measured(e.g. by prism cover test or dissociationtest). Second, the binocular sensoryadaptation needs to be assessed. The mostbasic level of practice would be to recordwhether the patient has diplopia. If there

Table 4Scoring system illustrating the diagnosis of horizontal decompensated heterophoria and

binocular instability (reproduced with permission from Evans BJW (2002) Pickwell’s BinocularVision Anomalies. Fourth edition, Butterworth-Heinemann)

Figure 2Institute Free-space Stereogram (IFS)

exercises (reproduced with permission

from IOO Sales)

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

DDIISSTTAANNCCEE // NNEEAARR ((ddeelleettee))

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,

sore eyes, general irritation)? IIff ssoo,, ssccoorree ++33 ((++22 oorr ++11 iiff bboorrddeerrlliinnee))

Are the symptoms at D � or N �

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 � or No � IIff nnoo,, ssccoorree ++11

3. Is the cover test recovery rapid and smooth?

Yes � or No � IIff nnoo,, ssccoorree ++22 ((++11 iiff bboorrddeerrlliinnee))

4. Is the Mallett Hz aligning prism: <1∆ for patients under 40, or <2∆ for pxs over 40?

Yes � or No � IIff nnoo,, ssccoorree ++22

If a vertical aligning prism of 0.5∆ or more is detected, see note at bottom of page.

AALLLL TTHHEE FFOOLLLLOOWWIINNGG QQUUEESSTTIIOONNSS AAPPPPLLYY TTOO HHOORRIIZZOONNTTAALL RREESSUULLTTSS

5. Is the Mallett aligning prism stable (Nonius strips stationary with any required prism)?

Yes � or No � IIff nnoo,, ssccoorree ++11

6. Using the polarised letters binocular status test, is any foveal suppression < 4’?

Yes � or No � IIff nnoo,, ssccoorree ++22

AAdddd uupp ssccoorree ssoo ffaarr aanndd eenntteerr iinn rriigghhtt hhaanndd ccoolluummnn

iiff ssccoorree:: << 44 ddiiaaggnnoossee nnoorrmmaall,, >>55 ttrreeaatt,, 44--55 ccoonnttiinnuuee ddoowwnn ttaabbllee aaddddiinngg ttoo ssccoorree ssoo ffaarr

7. Sheard’s criterion:

(a) measure the dissociated phoria (e.g., Maddox wing, prism cover test); record size &

stability

(b) measure the fusional reserve opposing the heterophoria (i.e., convergent, or base out, in

exophoria). Record as blur/break/recovery in ∆.

Is the blur point, or if no blur point the break point, [in (b)]

at least twice the phoria [in (a)]? Yes � or No � IIff nnoo,, ssccoorree ++22

8. Percival’s criterion: measure the other fusional reserve and compare the two break points.

Is the larger break point less than twice the smaller break point?

Yes � or No � IIff nnoo,, ssccoorree ++11

9. When you measured the dissociated heterophoria, was the result stable, or unstable

(varying over a range of ±2∆ or more). (e.g., during Maddox wing test, if the Hz phoria was

4∆ XOP and the arrow was moving from 2 to 6, then result unstable)

Stable � or Unstable � IIff uunnssttaabbllee,, ssccoorree ++11

10. Using the fusional reserve measurements, add the divergent break point to the convergent

break point. Is the total (=fusional amplitude) at least 20∆?

Yes � or No � IIff nnoo,, ssccoorree ++11

AAdddd uupp ttoottaall ssccoorree ((ffrroomm bbootthh sseeccttiioonnss ooff ttaabbllee)) aanndd eenntteerr iinn rriigghhtt hhaanndd ccoolluummnn.. IIff ttoottaall ssccoorree::

<<66 tthheenn ddiiaaggnnoossee ccoommppeennssaatteedd hheetteerroopphhoorriiaa,, iiff >>55 ddiiaaggnnoossee ddeeccoommppeennssaatteedd hheetteerroopphhoorriiaa..

SSccoorree

31 | January 14 | 2005 OT

Orthoptics special

neither have a great deal of experience ofthese cases, nor the required visual acuitytests, most of them tend to be treated byhospital orthoptists or optometric practiceswhich specialise in paediatrics. Childrenaged between five and seven years arecommonly treated either in communityoptometric practices or in hospital eyedepartments. Whoever carries out thetreatment will need to give the patientclear instructions about occlusion, monitorthem closely, and carry out regularrefractions to ensure that any spectacles areup to date. Full-time occlusion is usuallybest, so that a child who does not improve(e.g. after four to six weeks) can be referredfor further investigations.

Cases of amblyopia which are purelyanisometropic (where no strabismusincluding microtropia is present) can betreated at older ages, certainly into their teenyears and probably beyond3. These casesoften improve with refractive correctionalone, and contact lenses are ideal. Somecases also require patching. The main skillsneeded in the management of these patientsare visual acuity measurement, accuraterefractions, spectacle dispensing, contactlenses, and general optometric checks (e.g.ophthalmoscopy and visual fields) to ruleout pathology. This means these patientscan usually be cared for in primary eyecare(optometric) practices.

is a strabismus and no diplopia, then thepatient has a binocular sensoryadaptation. Good practice would be todetermine what this adaptation is, andexpert practice might involve measuringthe depth of adaptation3.

The third aspect of strabismus to beinvestigated is amblyopia. An attemptshould always be made to measuremonocular acuities, and ‘crowded’ acuitytests should be used at the earliest possibleage. It would also be good practice todetect eccentric fixation by directophthalmoscopy.

Treating strabismusThe first two factors which need to beconsidered in the investigation ofstrabismus are the ages of the patient nowand when the strabismus developed.Infrequently, the optometrist might see achild when strabismus has only recentlydeveloped. Typically, these will beesotropes of school age where there wasan intermittent esotropia, which hasrecently become a constant esotropia.Whenever an esotropia is encountered,hypermetropia must always be suspectedas the cause and in young children this isone of the indications for a cycloplegicrefraction. If uncorrected hypermetropia iscausing an esotropia, then thehypermetropia should be corrected.

If a child is found to have anintermittent strabismus, then earlyintervention is required to try to preventthe deviation from becoming constant.Similar investigations and treatments tothose outlined in the section onheterophoria are warranted.

People with constant strabismus whodo not have diplopia must have one of thetwo diplopia avoiding mechanisms(sensory adaptations) – suppression orHARC. Orthoptic exercises are usuallycontra-indicated in these cases, because totreat either the sensory adaptation or themotor angle in isolation could causeintractable diplopia.

One feature which does requiretreatment, if the patient is of the right age,is amblyopia. Strabismic amblyopiashould not be treated over the age ofabout seven to 12 years. Between theseages, it should be treated very carefully,with regular monitoring of binocularstatus, because there is a slight risk ofcausing intractable diplopia. Generallyspeaking, patients should be treated asyoung as possible. Pre-school children aremore difficult to treat and it is best forthese cases to be managed by practitionerswho have the appropriate expertise,experience, and equipment. Thesepractitioners may be optometrists, butsince many community optometrists

SStteepp

Detect incomitancy

Look for orbitalpathology

Detect any ocularpathology

Look for neurologicalproblems

Look for obviouscauses of thestrabismus

Monitor the size ofthe deviation

Is the strabismusresponding totreatment?

RRaattiioonnaallee

Any new or changing incomitancyrequires prompt referral to ahospital ophthalmology unit

Orbital pathology can causestrabismus, although this is rare

Pathology which destroys ordiminishes the vision in asignificant part of the visualfield of one eye can dissociatethe eyes and cause strabismus

Pathology in the brain can causecomitant, as well as incomitant,deviations

There is usually only one reasonwhy a patient develops astrabismus. If you find anon-pathological cause, thenthe likelihood of there beingpathology is greatly reduced

If the deviation is increasingthen there must be a reason

If you think that you aretreating the cause of thestrabismus (e.g. hypermetropia),then the situation shouldimprove

WWhhaatt ttoo ddoo

• Carry out a careful motility test, including questions about diplopia• If the results are unclear, then carry out a cover test in peripheral gaze or ideally a

Hess screen test• If there is a new or changing incomitancy, then refer

• Is proptosis present?• Are the eye movements restricted?• Is there pain on eye movements?

• Check pupil reactions, particularly looking for an afferent pupillary defect• Carry out careful ophthalmoscopy. In younger children, dilated fundoscopy might be

necessary to obtain a good view, commonly after cycloplegic refraction. Keepchecking ophthalmoscopy at regular intervals

• As soon as the child is old enough, check visual fields

• Carefully check pupil reactions and visual fields• Assess and record the optic disc appearance in both eyes• Monitor reports of general health (see text)

• If a child has an esotropia, then look for hypermetropia• If an older patient is developing an exotropia, then have they always had an

exophoria which is gradually decompensating with worsening cataract?• In every case, still look for pathology. But if you have found an obvious cause, then

it is probably the cause

• If you cannot find the reason why a deviation is increasing (e.g. child withaccommodative esotropia starting to read more), then refer for a second opinion

• If a strabismus does not respond to treatment (e.g. giving plus for hypermetropia),then review your diagnosis (e.g. accommodative esotropia)

• Failure to respond to treatment might indicate a pathological cause, so refer for asecond opinion

Table 5Summary of some steps in determining if pathology is present in strabismus

(reproduced with permission from Eye Essentials: Binocular Vision, Evans, 2005)

Orthoptics special

32 | January 14 | 2005 OT

How to specialisein orthopticsOrthoptic investigation is a corecomponent of every optometrist’s work,and all optometrists should be able to givebasic orthoptic treatment (e.g. exercises fora convergence insufficiency or spectaclesfor a patient with an accommodativeeso-deviation resulting simply fromuncorrected hypermetropia). Practitionerswho wish to increase their orthopticexpertise will find it easiest to take onestep at a time. For example, explore thetreatment of convergence insufficiencywith exercises other than simple push-up(e.g. Figure 2). Then look for a case ofdecompensated exophoria at near and trythese exercises on this patient. If patientsare not suitable for exercises, then tryrefractive modification.

Near eso-deviations which cannot becorrected by the full plus revealed by acycloplegic may respond well tomultifocals. Eye exercises foreso-deviations are harder work than forexo-deviations, but can also be effectivewith a suitably motivated patient.

The treatment of non-strabismicanisometropic amblyopia isstraightforward, as described earlier. Aspractitioners gain experience, increasinglychallenging cases of strabismic amblyopiacan be treated. If an amblyopic patientwhose age makes them suitable for

treatment is seen by a practitioner whodoes not wish to treat them, then they willneed to refer the patient to anotherpractitioner.

Orthoptics is an exciting area andoptometrists who specialise find this bothinteresting and rewarding. Many CETcourses on orthoptics (binocular visionanomalies) are available, and the COptomDiploma in Orthoptics provides astructured framework within whichpractitioners can increase their knowledgeand skills in this field.

About the authorBruce Evans is Director of Research at theInstitute of Optometry and is VisitingProfessor to City University in London. Hespends most of his working week seeingpatients in a community optometricpractice in Brentwood, Essex. He haswritten over 130 publications, includingfour textbooks on binocular visionanomalies.

The exercises illustrated in Figure 2can be obtained from IOO Sales(Telephone: 020-7378 0330 or visitwww.ioosales.co.uk). This company existsto raise funds for the Institute ofOptometry and pays a small ‘Award toinventors’ to the author based on sales ofthe exercises.

References

1. Millodot M (2000) Dictionary ofOptometry. Fifth edition.Butterworth-Heinemann, Oxford.

2. Evans BJW (2004) The Diploma inOrthoptics. Part 1: A ‘how to’ guide.Optician 226; 5934: 26-27.

3. Evans BJW (2002) Pickwell’sBinocular Vision Anomalies. Fourthedition. Butterworth-Heinemann,Oxford.

4. Stevenson R (1999) Clinical practicesurvey 1998. College of OptometristsNewsletter 69: 7-10.

5. Lindblom B, Westheimer G and HoytWF (1997) Torsional diplopia andits perceptual consequences: a‘user-friendly’ test for oblique eyemuscle palsies. Neuro-Ophthalmology18: 105-110.

6. Tang STW and Evans BJW (2005) TheNear Mallett Unit Foveal SuppressionTest. OT (Optometry Today/Optics Today)45:1.

7. Evans BJW (2005) Eye Essentials:Binocular Vision. ButterworthHeinemann Health, Oxford.

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