the role of the optometrist in dyslexia

8/14/2019 The Role of the Optometrist in Dyslexia

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The role of the optometrist in dyslexia

Part 3 Coloured filters

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Continuing Professional Development

the USA, the UK and Australia, to detect andtreat Irlen syndrome or scotopic sensitivitysyndrome. The latter term is probablyinappropriate and, in view of the firstdetailed description of the syndrome byMeares, Meares-Irlen syndrome seems to bethe most appropriate term.

The condition is characterised bysymptoms of eyestrain and visual perceptualdistortions when reading. The eyestrain issaid to occur predominantly with reading andis typified by sore, tired eyes, visualdiscomfort and headaches. The visualperceptual distortions include blurring,doubling, fading, shimmering, movement of

words or letters, and seeing patterns andshapes on the page.

Meares-Irlen syndrome is treated withcoloured filters, either coloured sheets(overlays) placed on the page or colouredlenses. An additional approach, for computerusers, is to change the colour of the screen

background and/or text. Another method,changing the colour of the illuminating light,is a possibility for people who consistently

work under the same lighting conditions.Irlen claimed that the required colour

differed from person to person and was veryspecific: if a person was given colouredspectacles of a similar colour, but slightlydifferent to their required colour, then they

would receive much less benefit than with theappropriate colour2. Proponents of the Irlensystem claim that up to 60% of people with areading problem, and 10% of good readers,suffer from this disorder.

Intuitive Colorimeterand Wilkins/MRC systemOne of the first scientists in the UK to takethis subject seriously was Professor Arnold

Wilkins, who was at the time based at theMedical Research Council (MRC) AppliedPsychology Unit in Cambridge. He developedthe Intuitive Colorimeter (Figure 1), anoptometric instrument to systematicallysample colour space. Hue, saturation, andluminance are independently varied whilstthe patient views text. A unique feature of theinstrument is that, because colours arechanged gradually, people adapt to thecolours so they are unaware of the precise

colour that they are viewing.The development of the Wilkins Intuitive

Colorimeter meant that a double-masked,randomised placebo-controlled trial ofMeares-Irlen syndrome became possible3.

About the authorProfessor Bruce Evans is Director

of Research at the Institute ofOptometry and is Visiting

Professor to City University inLondon. He is also a shareholder

of Optometric Educators and hasan independent practice in

Brentwood, Essex.

This is the final article in a series of three papers to updateeyecare practitioners on their role in dyslexia. The series is basedon a recent book by the author1.

Bruce Evans BSc, PhD, FCOptom, DipCLP, DipOrth, FAAO

Module 1 Part 3Dyslexia and vision

Part 1 (OT, 30/01/04) provided an overviewof specific learning difficulties, diagnosis ofdyslexia, terminology, aetiology of dyslexia,types of dyslexia, non-specific learningdifficulties, the role of visual symptoms andthe evidence-based approach. Part 2 (OT,27/02/04) concentrated on the diagnosis and

treatment of two fairly common optometricfindings in dyslexia binocular instabilityand accommodative insufficiency. It alsodiscussed other optometric factors (e.g.refractive errors and visual fields), themagnocellular deficit, the Dunlop test,behavioural optometry, and version eyemovements and tracking.

This final part covers coloured filtertreatments including syntonic phototherapy,Meares-Irlen syndrome, the IntuitiveColorimeter, mechanisms for the benefitfrom colour, clinical protocols, and acomparison of available systems. Finally,some conclusions are drawn on the role of

the optometrist in dyslexia.

Syntonic phototherapySyntonic phototherapy is sometimes thoughtof as a sub-discipline of behaviouraloptometry. One of its key componentsinvolves the patient staring at a coloured lightsource. This is usually prescribed together

with vision therapy and/or yoked prisms. It isargued that this treatment alters theautonomic nervous system, which in turnbrings about a wide range of benefits,including a change in visual fields(see Part 2). There seems to be few believersin this approach these days, but there are a

few followers in the UK. There also does notappear to be any randomised controlled trialsof this intervention1.

Meares-Irlen syndrome:initial claimsIn 1980, Olive Meares suggested that somechildrens perception of text and certain casesof reading disabilities were influenced byprint characteristics. She found that in somecases, the white gaps between the words andlines masked the print and caused visualperceptual anomalies, such as words blurring,doubling and jumping. She noted that this

was helped by reducing the size of the print,

using coloured paper, reducing contrast, orusing white print on black paper.

Following these early reports, Helen Irlenestablished a proprietary system, based onIrlen Institutes, in several countries including

ABDO has awarded this article

2 CET credits (GD).

The College of Optometrists has

awarded this article 2 CET credits.

There are 12 MCQs with

a pass mark of 60%.

The Association of Optometrists Irelandhas awarded 1 CET credit.


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Continuing Professional Development Bruce Evans BSc, PhD, FCOptom, DipCLP, DipOrth, FAAO

30 | March 26 | 2004 OT

This trial demonstrated that individually

prescribed filters could alleviate thesymptoms of Meares-Irlen syndrome, andthe benefit could not be solely attributed toa placebo effect. A second independent,double-masked randomised controlledtrial, over a longer time period and usingthe Irlen system, showed that individuallyand precisely prescribed coloured filtersimproved performance at conventionalmeasures of reading performance4. A thirddouble-masked, randomised controlledtrial supported the use of individuallyprescribed coloured filters for people with

visually-precipitated migraine5.There are now about 250 colorimeters

in use worldwide and the patent is ownedby the MRC in the UK. They are used inconjunction with Professor Wilkins systemof precision tinted lenses (PTLs) to makeup lenses to match a given colorimetersetting. The tints are evenly spaced, basedon the CIE UCS chromaticity diagram. Ageometric progression is used, so that triallenses can be stacked to obtain over100,000 colours. They are combined in alogical way, like trial lens spheres, toreproduce and check tints.

A range of coloured overlays (Figure 2a) Intuitive Overlays has also beendeveloped for screening, and a reading test

(Figure 2b) the Wilkins Rate of ReadingTest investigates the effect of colouredfilters on reading. This new type of readingtest was necessary because conventionalreading tests were designed to measure

reading skills and to be relativelyunaffected by visual factors (e.g. they usedlarge text and widely-spaced lines). Toassess visual factors, a new type of test wasrequired with the opposite characteristics,i.e. greatly affected by visual factors butrelatively unaffected by reading skills. The

Wilkins Rate of Reading Test is just such atest and takes about five minutes to run.

In recent years, a great deal of researchhas been carried out with the the WilkinsIntuitive Overlays and the Wilkins Rate ofReading Test, which has been reviewed inthe literature1,6. Controlled trials show thatindividually prescribed coloured filters notonly reduce symptoms of asthenopia, butalso improve reading performance.

Meares-Irlen syndrome probably existson a continuum, with many people beingaffected to a mild degree and fewer to asevere degree. Inevitably, estimates of the

prevalence will vary depending on theseverity of the condition one is seeking todetect. About 5% of all schoolchildren havea very marked degree of Meares-Irlensyndrome and will perform 25% faster atthe Wilkins Rate of Reading Test with anoverlay than without. The relationship withdyslexia is often overstated. Recent researchsuggests that Meares-Irlen syndrome is onlya little more common in dyslexia than ingood readers. But when Meares-Irlensyndrome co-exists with dyslexia, it will, ofcourse, represent an added burden topeople who already find reading difficult.Other studies have shown that Meares-Irlen

syndrome affects adults almost ascommonly as children1.

Mechanism for thebenefit from colourSeveral potential mechanisms have beenproposed to explain the benefit fromcoloured filters in Meares-Irlen syndrome.Some are based on a hypothetical linkbetween the benefit from colour and other

visual correlates of reading disability(e.g. binocular vision anomalies or themagnocellular deficit). However, until nowthese hypotheses have not been able toaccount for the high degree of specificity of

the required colour, which has beenstressed by Irlen and substantiated bydouble-masked, randomisedplacebo-controlled trials1.

An alternative mechanism, initiallyproposed by Wilkins, is based on patternglare7. Striped patterns can be unpleasantto look at and some people experienceeyestrain and visual perceptual distortions

when viewing them. In fact, thesesymptoms are remarkably similar to thosereported by patients with Meares-Irlensyndrome. The mechanism for thesesymptoms is likely to be a hyperexcitabilityof the visual cortex, which can also occur in

some cases of migraine and epilepsy. Linesof print on a page form a striped pattern,

which can have the spatial properties of apattern which may cause pattern glare. Itseems likely that this mechanism is

responsible for at least some patientssymptoms of visual stress with reading.

Wilkins theory is that people whobenefit from precision tinted lenses have a

visual cortex that is hyperexcitable8. Insome, this hyperexcitability may lead toepilepsy and, more commonly, it may leadto migraine. In other people, thehyperexcitability may never result in eitherof these conditions, but may cause visualperceptual distortions and visualdiscomfort sometimes described as visualstress. Some of the neurones in the visualcortex are sensitive to specific colours, andso varying the colour of the illuminatinglight may change the pattern of excitation

within the cortex. This could account forthe benefit from specific coloured filters6.

This theory has been further developed,linking it with the magnocellular deficit indyslexia1. There is considerable (but not

unequivocal) evidence for a magnocellulardeficit in many people with dyslexia (seePart 2). It would make sense if this deficit

was related to the benefit from colouredfilters, but there has been one majorproblem with making such a connection.

This is that the magno system is notsensitive to specific colours, yet bothdouble-masked randomised controlledtrials of coloured filter treatments forreading difficulties show that the colourneeds to be individually and preciselydetermined.

One theory, through a consideration ofvisual attention, links the visual stress

theory of Wilkins and the magno deficittheory1. Visual attention is a form ofselective attention, which can be thoughtof as a spotlight focussing our attentionduring reading on the word or group ofsmall words around fixation. This spotlightof visual attention is believed to bemediated predominantly via the magnosystem, and there is evidence to suggestthat the spotlight can be weakened indyslexia. This would be expected to causethe person to experience more peripheraldistractions on the page.

Text forms a striped pattern and stripedpatterns cause pattern glare, or visual stress.

It is hypothesised that a weakenedspotlight of visual attention will cause(a) the striped pattern from text to be morenoticeable, causing more pattern glare and(b) the peripheral distortions resultingfrom pattern glare to be much morenoticeable1. Some of the symptomsreported by people with Meares-Irlensyndrome (e.g. seeing patterns on the pageformed by the gaps between words) canalso be observed (if they are looked for) bygood readers who do not suffer from visualstress. An additional reason why people

with reading difficulties might be morelikely to notice these symptoms could

simply be that they have trouble gatheringmeaning from the text, and are thereforemore likely to be distracted by irrelevantpatterns.

Recent research suggests that

Figures 2a and 2b(a) Wilkins Intuitive Overlays and

(b) Wilkins Rate of Reading Test(reproduced with permission from IOO Sales)

Figure 1The Intuitive Colorimeter (reproduced withpermission from Cerium Visual Technologies)

a b


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coloured filters. With children,overlays are tried first andcoloured lenses are onlyprescribed once a definitebenefit from the overlays hasbeen demonstrated.

A definite benefit fromcoloured overlays can bedemonstrated in one of two

ways. First, the patient may bedispensed a coloured overlayof their preferred colour touse on a trial basis for up toone school term. If itgenuinely reduces symptomsof eyestrain and headache,then the child is likely tocontinue to use it. Parents andteachers can look for animprovement in the readingfluency. The second method

of detecting a genuine benefitfrom an overlay is toinvestigate the effect of theoverlay on performance at the

Wilkins Rate of Reading Testor using the DevelopmentalEye Movement (DEM) Test9. Itshould be noted that althoughthe DEM test is claimedto be a measure of eyemovements, this has not beendemonstrated experimentally1.

The test requires subjects torapidly identify randomlyspaced numbers, and it is

therefore not surprising thatperformance is improved bycoloured filters whichimprove visual perception.

Data from the first 20,000pairs of precision tintsprescribed showed that thechoice of colour was highlyidiosyncratic almost everyconceivable colour was chosenby some people. This meansthat clinicians who wish toprescribe coloured lenses topeople with readingdifficulties need to test using a

very large range of colours(like the Wilkins/MRC systemor the Irlen system) to findthe optimal colour. Testing

with a small range of colouredfilters is unlikely to find theoptimal tint for every patient.

If only a small range oftints is used, the situation isanalogous to carrying out arefraction using, for example,only nine different power triallenses. The practitioner mightbe able to find a trial lens

which helps the patient, but it

will not necessarily be the bestprescription for them.Precision tinted lenses need tobe prescribed individually insome cases with considerable

31 | March 26 | 2004 OT


individually prescribedcoloured filters can also helppeople with visuallyprecipitated epilepsy. Onerandomised controlled trialhas also suggested that theycan help reduce the frequencyof headaches in people with

visually precipitatedmigraine5. Clearly, precisiontinted lenses are not atreatment for forms ofmigraine which do not have a

visual trigger (e.g. thosetriggered by hormonal ordietary factors). But they canbe an effective treatment forcases where there is a visualtrigger (e.g. flickering lightthrough trees, text, fluorescentlighting, computers). Migraine

is common, affecting 8% ofthe UK population. So,migraine has become animportant new use of theIntuitive Colorimeter andprecision tinted lenses.

In summary, the term visualstress is nowadays proving tobe more useful than Meares-Irlen syndrome. Visual stresscan be defined as symptoms ofeyestrain, headaches and visualperceptual distortions whichoccur when viewing repetitive

visual stimuli, including text,

and which are alleviated byindividually prescribedcoloured filters. The conditionis believed to result fromhyperexcitability of the visualcortex and is particularlyprevalent in people withreading difficulties, migraineand photosensitive epilepsy.

The diagnosis is one ofexclusion; conventionaloptometric factors (e.g.refractive errors, orthopticanomalies) need to beexcluded first.

Clinical protocolA clinical system is currentlyin operation where teachers,optometrists andpsychologists screen children

with coloured overlays.Children who show asustained benefit from anoverlay are then referred to anoptometrist or hospitaldepartment which has a

Wilkins Intuitive Colorimeter.Optometrists should firstdetect any pathology, which is

very rare in these cases. Next,optometrists detect and treatany refractive and orthopticproblems, and theninvestigate the effect of

An instrument designed by the Medical

Research Council for selecting the optimum

colour

for the relief of Visual Stress in

Lease for as

little as 117

+ vat per month

The Intuitive

Colorimeter

Mk2

For further information contact:

Cerium Visual Technologies LtdCerium Technology Park,

Appledore Road,Tenterden,Kent TN30 7DE

Tel: 01580-765211

Fax: 01580-765573Email: [email protected]

www.ceriumvistech.co.uk

Cerium

OverlayTesting Set

Overlays are ideally used for initialscreening of patients who exhibitsymptoms of visual stress. Patientswho gain benefit from a specificoverlay should receive a full eyeexamination prior to assessmentusing the Intuitive Colorimeter.Research has shown that thesepatients will almost always obtaingreater benefit from PrecisionTinted Lenses than from the over-lay, and that the colour of the tint-ed lens will almost always be dif-ferent from the colour of the over-

The IntuitiveColorimeter allows a

logical and sequential

exploration of colourspace and is the only

instrument whoseresulting lenses are

validated by peerreviewed evidence


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32 | March 26 | 2004 OT

less, or even occasionally can do withoutthem. There are several possibleexplanations for this. It is possible thatcortical hyperexcitability might change overthe years and the optical media of the eyecertainly transmit less light with age.

Additionally, people often become moreable to change their environment. Forexample, they may be able to change thetype of lighting, use a flat screen computerdisplay, change to dictation software, orchange the typographic features of text onthe computer or on print-outs.

Can overlay colourpredict tinted lens colour?

The optimal colour of tinted lens for apatient is usually different to their optimaloverlay colour, and this has been explainedby reference to colour adaptation. When apatient looks through coloured lenses (or

into the Intuitive Colorimeter) they fullyadapt to the colour, but when they look ata coloured sheet on the page they onlypartially adapt to the colour. This issue hasbeen investigated in a controlledexperiment which showed that tintedlenses should not be made up to match apreferred overlay colour for a person11. Inother words, to find the best colour foroverlay, patients need to be tested withoverlays, and to find the best colour forspectacles they need to be tested withlenses and/or with the Wilkins IntuitiveColorimeter.

Comparison of systemsThere are now various proprietary systemsavailable in the UK to prescribe colouredfilters for people with reading difficulties.In addition to the Irlen and Wilkinssystems, the Chromagen system has alsobeen marketed for this purpose.Chromagen is a tinted contact lens systemoriginally developed for use by people withcolour vision defects. This use of theChromagen system for correcting colour

vision defects has attracted considerablecontroversy, as have claims it can be usedto treat people with dyslexia.

With the Chromagen system, patients

are sometimes prescribed different coloursfor each eye. Some Chromagenpractitioners say that patients commonlyneed different colours for each eye; others

who use this system argue that almost alldyslexic users end up with the same colourfor each eye. Unfortunately, this issueremains unresolved and there appears to be

no research to investigate whether patientsdo better with different tints or with thesame tints in each eye. Indeed, since acortical mechanism is believed to accountfor the benefit from coloured filters, it

would be more logical to hypothesise thatdifferent colours are required for eachhemifield rather than each eye. Althoughthis would seem impractical from aprescribing point of view, it would beanother interesting area to research.

The three systems available in the UK,which have been validated12withrandomised controlled trials published inpeer-reviewed journals are compared in

Table 1. D-M RCT is double-maskedrandomised placebo controlled trial. Thereis a masked controlled trial for the Irlensystem and another for the Chromagensystem, but it is unclear whether these werefully double-masked.

Three other approaches are also availablein the UK, but these have not beeninvestigated in published randomisedcontrolled trials and so they are still bestconsidered as experimental. The first issyntonic phototherapy. A differentapproach, TintaVision, uses a computermonitor to select overlays. Another method,Orthoscopics, involves instruments calledthe Read-Eye and the Optopraxometer. The

TintaVision and Orthoscopics systems mayboth be confounded by the effects of colouradaptation and there appears to be norandomised controlled trials, or even fulldescriptions of these systems in the

peer-reviewed literature (as evidenced byPubMed search using key words identifiedfrom manufacturers websites, March 2004).

ConclusionsPeople with reading difficulties need to bemanaged by a multi-disciplinary team, in

which optometrists play an important part.It is helpful if practitioners write reportsabout all the children they see who havedifficulties at school. These reports can besent to parents, class teachers, special needsteachers and educational psychologists.

They should include information on anyinterventions which are needed, but are just

as important when no abnormalities aredetected. In addition to helping thechildren by improving communication,these reports will also help the practitioner.

Teachers often report difficulties in findingeyecare practitioners who specialise in thisfield. The regular use of reports will helpteachers to know where to send their

precision. So, it is safest to use a validatedsystem like the Wilkins IntuitiveColorimeter, or to refer to a colleague whohas the appropriate equipment.

The effect of ambient lighting also needsto be considered. If a patients tints need tobe precisely defined, then the requiredcolour will vary under different types oflighting. This effect (metamerism) isminimised if the dyes used to tint thelenses have smooth transmission curves,

which is the case for Wilkins PTLs. This isone reason why commercial systems forproviding PTLs should be fully described inthe refereed scientific literature.

The final precision tinted lensspecification can be checked under lighting

which is similar to that where the patientusually works, if this is known. This isespecially important for patients whose tintis light and who are found on clinical

testing to be particularly precise in theirchoice of colour (like all clinical testing, thedegree of precision varies from one patientto another). A freeware computerspreadsheet (available free of charge from

www.essex.ac.uk/psychology/overlays/lens.htm) allows practitioners using the WilkinsIntuitive Colorimeter and PTLs toinvestigate the effect of different types ofambient lighting. This computer programalso allows practitioners to check whetherthe tints protect the eyes adequately for usein sunlight, and to predict whether the tintsare likely to influence the perception oftraffic signals. This information is not

usually required for children with dyslexiawho are told to wear the tints only indoors,but the information is relevant for adults

with visually precipitated migraine.A clinical audit showed that, one year

after being prescribed PTLs, 80% of patientswere still using them daily10. This comparedfavourably with the continued use ofconventional (untinted) spectacles in thesame audit.

The colour which is required cangradually change over time, so it is usual tocheck the colorimetry result about once a

year for children. Two years seems to be anappropriate interval for many adults, who

usually recognise when their symptoms arereturning. It seems that people whoexperience the symptoms of Meares-Irlensyndrome as children typically continue toexperience some of these symptomsthroughout life. In some cases, thesymptoms reduce a little over the years andpeople may need their coloured spectacles

Bruce Evans BSc, PhD, FCOptom, DipCLP, DipOrth, FAAO

Table 1

ScreeningTesting: ability to find optimal tintValidationEstablished

Design minimises metamerismAvailability of contact lensesPractised by eyecare professionalsResearch

IrlenOverlays

Very large range of coloursIDPS (unpublished proprietary system)

1983

Probably notYesNo

Many papers, one M RCT

Wilkins/MRCOverlays

Very large range of coloursWilkins Rate of Reading Test

1993

YesYesYes

Many papers, two D-M RCTs

ChromagenNone

Nine coloursWilkins Rate of Reading Test

c. 1997 for dyslexia

Probably notYesYes

Two papers, one M RCT


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children with specific learning difficulties.Dyslexia is common, so clinicians

should actively look for it. It is advisable toenquire about the reading and spelling ofall patients who are of school age. Whenoptometrists examine people with specificlearning difficulties, it is helpful to take adetailed symptoms and history (see Table 1,Part 1). When examining people with(suspected) dyslexia, a very carefulbinocular and accommodative work-up isessential (see Part 2). Orthoptic exercises,

where appropriate, can be helpful,although these are not likely to be requiredfor the majority of people with dyslexia.

It is also appropriate to investigate theeffect of coloured filters. Coloured overlaysare a useful screening tool, but a rangeshould be used which samples colours in asystematic and representative way (e.g. theIntuitive Overlays). Children who show a

significant benefit from an overlay (eithersustained use or a significant improvementin performance) are likely to benefit morefrom coloured lenses. Since these are wornon a more sustained basis, they should beprescribed with more precision, and theIntuitive Colorimeter is the only

instrument so far which has been validatedfor this purpose. The colour of the requiredlens is usually different to the colour of theoptimal overlay and it is not appropriate toprescribe one from the other.

Dyslexic children require a specialist eyeexamination which, in addition to the testsin a routine (e.g. GOS) eye examination,should also include more detailedassessment of symptoms, binocularco-ordination, accommodative functionand the effect of coloured filters. Typically,this testing takes about 45 minutes to onehour and most optometrists charge anadditional fee, as outlined in the AOPdocument Sight tests and eyeexaminations: Scope and charging13.

Dyslexia is primarily an educationalproblem and optometrists do not diagnosedyslexia, but they can detect visualproblems which may co-exist and which

may contribute to the patients overalldifficulties. Optometric treatment will notremove the need for extra teaching.

Although we may alleviate visual factorswhich can contribute to reading difficulties,we should not expect to be able to cure ortreat dyslexia.

Ethical statementand acknowledgment

The author does not have a financialinterest in any of the investigative tools,diagnostic instruments or coloured filtertreatments described in this article. An

earlier, shorter version of this manuscriptwas published by Optometric Educators asa distance learning article.

References

For a full set of references, [email protected]

1. Which one of the followingstatements about Meares-Irlensyndrome is true?

a. Different people need differentcolours, but a selection of nine coloursis adequate

b. Once chosen, the colour which aperson needs will stay the samethroughout life

c. It can be helped by coloured filters,adjusting the set-up of computerscreens, and changing the typographicfeatures of text

d. People only need coloured filters for a

short period and can then usually dowithout them

2. Which one of the followingstatements best describes the keysymptoms of Meares-Irlen syndrome?

a. Visual perceptual distortions, soreeyes, tired eyes, visual discomfort,headaches

b. Visual perceptual distortions, nausea,tired eyes, visual discomfort,headaches

MCQs

The role of the optometrist in dyslexiaPart 3 Coloured filters

Please note there is only ONE correct answer

Module 1 Part 3 of the Dyslexia and vision series

c. Floaters, sore eyes, tired eyes, visualdiscomfort, headaches

d. Diplopia, sore eyes, tired eyes, visualdiscomfort, headaches

3. Which one of the following termshas been used to describeMeares-Irlen syndrome?

a. Irlen syndromeb. Scotopic sensitivity syndromec. Photopic sensitivity syndromed. (a) and (b)

4. Which one of the following

statements is true about theWilkins Rate of Reading Test?

a. It is greatly influenced by readingskills, less so by visual factors

b. It is greatly influenced byvisual factors, less so by readingskills

c. It is greatly influenced by readingcomprehension, less so by readingspeed

d. It takes about 15 to 20 minutes toadminister

5. Which one of the followingstatements about the influence ofdifferent types of ambient lightingon the effect of coloured filters ismost accurate?

a. Ambient lighting is irrelevant to theprescribing of coloured lenses, but isrelevant for overlays

b. Ambient lighting is irrelevant to theprescribing of coloured overlays, but isrelevant for coloured lenses

c. The influence is greater for saturatedtints and less significant for lightertints

d. The influence is minimised withCerium precision tinted lenses becausethey have smooth transmission curves

6. Which one of the followingstatements is not true about

visual attention?a. It is a form of selective attentionb. It can result in a sort of attentional

spotlightc. It is mediated predominantly by the

magno systemd. It explains why green, but not blue,

coloured filters help

7. Which one of the followingstatements is true?

a. All dyslexic children who needcoloured filters also need fusionalreserve eye exercises

b. All dyslexic children who need eye

exercises also need coloured filters

An answer return form is included in this issue. It should be completed and returned to:

CPD initiatives (c4767c), OT, Victoria House, 178-180 Fleet Road, Fleet, Hampshire,

GU51 4DA by April 21, 2004.Under no circumstances will forms received after this date be marked the answers tothe module will have appeared in our April 23 issue and scores sent electronically to theaccrediting bodies. Continued overleaf

When you get yourCPD results, please retain

them as you will need themlater in the year for

self certification purposes.

Keep all yourCPD results ...


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34 | March 26 | 2004 OT

Continuing Professional Development Bruce Evans BSc, PhD, FCOptom, DipCLP, DipOrth, FAAO

1. What are the best two tests fordetecting clinically significantbinocular instability?

a. Cover test and stereo-acuityb. Cover test and fusional reservesc. Stereo-acuity and fusional reservesd. Fusional reserves and Mallett unit

OXO test

d is correctBinocular instability is characterised bylow fusional reserves and vergenceinstability. The vergence instability ismuch more likely to be clinicallysignificant if it occurs under fusedconditions, such as with the Mallett OXOtest which simulates normal readingconditions.

2. Which one of the followingstatements is most important?

When carrying out the Mallett OXOtest:

a. the patient should be asked if thelines are perfectly aligned and if oneor both ever move

b. the patient should be asked if thelines are perfectly aligned and if theyappear flat on the page

c. the patient should be asked if thelines are perfectly aligned and if theyare the same size

d. the patient should be asked if thelines are perfectly aligned and if theyappear the same colour

a is correct

It is probably not enough just to askwhether the Nonius markers (green strips)are lined up. Many of the patients, who

would answer Yes to this question, wouldalso answer Yes to a supplementaryquestion: Do one or both of the lines evermove? This latter question is the best wayof identifying patients who are likely tohave symptoms (Karania and Evans, inpreparation). If one of the Nonius markersmoves, then the direction of movement isidentified and the aligning prism or sphereis determined. This is the prism (base-in foran exo-slip) or sphere (negative for anexo-slip) which eliminates movement ofthe strip.

3. Which one of the followingstatements is most accurate? Theamplitude of accommodation:

a. is always low in dyslexiab. is more likely to be low in a poor than

in a good readerc. if poor, should be treated by prescribing

negative lenses in spectacles tostimulate accommodation

d. can be treated by training convergentfusional reserves with free-spacestereograms

b is correctThe amplitude of accommodation is not

always low in dyslexia, but in matchedgroup studies it has been found to be loweron average in children who are dyslexicthan in good readers. A low amplitude ofaccommodation is not usually treated by

prescribing negative lenses or by fusionalreserve exercises.

4. Which one of the followingstatements is true? MEM retinoscopy:

a. stands for minimum eye retinoscopyb. diagnoses dyslexiac. is carried out whilst the patient fixes

with both eyesd. is carried out whilst the patient

wears the subjective refractivefindings

c is correctThe accommodative lag can be measuredby retinoscopy using the monocularestimate method (MEM). The subjectbinocularly fixates a detailed target on theretinoscope and is asked to keep this clear.Retinoscopy is carried out along thehorizontal meridian and lenses are verybriefly held in front of each eye toneutralise the retinoscope reflex. Each lensshould only be present for a split secondso as not to disrupt the status of thepatients accommodative and binocularresponse. As far as possible, the testsimulates normal viewing conditions sothe patient typically only wears a refractivecorrection if they would usually do so toread.

5. Which one of the followingstatements is true? Binocularinstability is:

a. more common in poor thanin good readers

b. a major cause of dyslexia

c. cured by prescribing tinted lensesd. an exophoria at near combined withan esophoria at distance

a is correct

c. All dyslexic children who usecoloured overlays need assessmentof binocular function

d. Dyslexic children who have acoloured filter will not needeye exercises

8. Which one of the followingstatements is most accurate?Syntonic phototherapy is:

a. a controversial treatment usingindividually prescribed colouredlenses

b. a controversial treatment wherepatients view a coloured light source,that is claimed to be effective throughan influence on their reflexes

c. a controversial treatment wherepatients view a coloured light source,that is claimed to be effective through

an influence on their cortical visualprocessingd. a controversial treatment where

MCQsModule 1 Part 3 of the Dyslexia and vision series (continued)

patients view a coloured light source,that is claimed to be effective throughan influence on their autonomicnervous system

9. In Meares-Irlen syndrome, thesymptoms were first describedin detail by whom?

a. Arnold Wilkinsb. Helen Mearesc. Helen Irlend. Olive Meares

10. Which one of the followingstatements is true?

a. 80% of people prescribed with precisiontinted lenses still use them after one year

b. Astigmatic corrections cure Meares-Irlensyndrome

c. Tinted lens colour can be predicted from

overlay colourd. Overlay colour can be predicted fromtinted lens colour

11. Which one of the followingstatements about pattern glare ismost accurate?

a. It is particularly prevalent in dyslexiab. It is particularly prevalent in migraine

and photosensitive epilepsyc. It is explained by cortical

hyperexcitabilityd. All of the above

12. Which of the following groups ofsystems has been supported byrandomised controlled trials?

a. Intuitive Colorimeter, Orthoscopics,Irlen

b. Chromagen, Irlen, IntuitiveColorimeter

c. TintaVision, Intuitive Colorimeter,

Irlend. Syntonic phototherapy, TintaVision,Orthoscopics

The role of the optometrist in dyslexiaPart 2 Optometric correlates in dyslexia

Here are the correct answers to Module 1, Part 2which appeared in our February 27, 2004 issue.


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the role of the optometrist in dyslexia

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