CET Continuing education Part 4 – Compensation assessment In the latest in our series looking at binocular vision assessment in practice, Priya Dabasia describes the assessment and management of compensation and decompensation. Module C15357, one general CET point for optometrists and dispensing opticians

he first part in this binocular vision to present in daily between the in which the fovea mini-series detailed the practice. ‘Compensation’ refers to the of one corresponds with a small detection and measurement control of a : foveal area of the fellow eye in higher of heterophoria using the ● ‘Well compensated’ – fully controlled cortical processing. This horizontally (CT). This article with no symptoms in the absence of oval group of retinal elements is aims to provide an overview suppression known as Panum’s area, and occurs for ofT the assessment of heterophoria ● ‘Decompensating’ – poor control every point of the , increasing in compensation and management of poorly with symptoms, or where a practitioner size with eccentricity from the fovea controlled deviations. Heterophoria deems that lack of treatment is where it measures 5-10 minutes of occurs when both visual axes are likely to result in a deterioration of arc (Figure 1). For fusion to take place directed toward the point but binocularity between the eyes, images must either deviate on dissociation. In the absence ● ‘Full decompensation’ – complete fall exactly on the same points, or of a visual stimulus such as under the failure of the system resulting slightly disparate elements provided closed lid at rest, our eyes have a natural in a breakdown of a heterophoria to a they are located within Panum’s area. tendency to revert to their resting states heterotropia. This is highly probable in This misalignment of one or both visual by deviating upwards and outwards. childhood as a result of the instability axes is called (FD) or During CT, this translates on average of binocular vision, with associated retinal slip, and is evaluated clinically as a small at distance and foveal suppression and gradual loss of to provide a measure for the degree at near fixation. A summary depth perception. of compensation in heterophoria. of the basic types of heterophoria is When the is subjected to shown in Table 1. Panum’s fusional area such undue stress, the axes slip closer Decompensated heterophoria is one For normal binocular single vision, to the limit of Panum’s area – if the of the most common anomalies of there is a point to point correlation misalignment is large enough to fall

Table 1 A summary of heterophoria types, features and causes

Type Details Causes Esophoria Convergence excess Greater at near than distance • Anatomical (narrow PD) Eye moves nasally under • Refractive (high hypermetropia) Divergence weakness Greater at distance than near cover • High AC/A ratio Non-specific Similar angle at near and distance • Weak divergent (negative) fusional reserves Exophoria Convergence weakness Greater at near, often but • Anatomical (wide PD) Eye moves temporally under not always with convergence • Refractive (, ) cover insufficiency • Weak convergent (positive) fusional reserves Divergence excess Greater at distance than near • Age Non-specific Similar angle at near and distance

Vertical phoria Hyper/hypo One eye rotates upwards and the • Refractive (high myopia) Eye moves up or down other downwards under cover under cover Alternating hyper/hypo Either eye moves upwards/ • Weak vertical fusional reserves downwards under cover • Anatomical (abnormal ) • Incomitancy – extraocular muscle anomaly (see Part 2) Cyclophoria either eye Incyclophoria Upper end of vertical axis is nasal • Oblique ‘wheel rotates’ under cover Excyclophoria Upper end of vertical axis is • Incomitancy temporal

26 | Optician | 17.12.10 opticianonline.net Continuing education CET

from adapting to a decompensating Fixation point heterophoria through suppression, making it increasingly likely that they present with symptoms of: ● Headaches – horizontal heterophoria is associated mostly with a bilateral frontal ache while hyperphoria results in occipital pain Fusion ● Asthenopia – eye ache, dull pain behind the eyes and/or general soreness ● Blurring of print and difficulty changing focus to distance following a period of near work – the focusing capability of the eye is affected by the accommodative-vergence induced to control a heterophoria Figure 1 Panum’s fusional area ● Intermittent diplopia usually following a period of intense work beyond, the patient will appreciate , arising primarily as ● Intermittent ‘confusion’ or distorted physiological double vision (diplopia) a consequence of the relationship vision – instability in binocular in the absence of suppression. between and alignment results in the perception of accommodative-convergence. A young letters or words moving, flickering or Causes of decompensation hyperopic patient without spectacle jumping so that words/ lines of text The size of a heterophoria does not correction must accommodate to are missed or patients may even report relate directly with the likelihood of overcome refractive blur; the resulting shapes or patterns on the page a patient becoming symptomatic – a accommodative-convergence effort ● Less commonly patients describe 2 dioptre hyperphoria can give rise induces an esophoric deviation that difficulties in depth perception, to a multitude of symptoms while is greater at near. Similarly, a myopic particularly during sport a patient can be oblivious to an 8 patient reading unaided lacks the ● Adaptation to binocular discomfort dioptre exophoria. The causes of accommodative-convergence to by closing one eye to read, or adopting decompensation can be attributed to control a near exophoria. The other an abnormal head posture to prevent one or more of the following: contributory factor that cannot be double vision by using the nose to block ● Reduction in fusional reserves – the corrected is age – as the amplitude of the image of one eye. convergence, divergence and vertical accommodation reduces over time, the Typically, these symptoms will be range between the eyes that maintains average heterophoria at near has been absent on waking, arising later in binocular single vision found to increase up to 6Δ at the age the day with increased visual activity. ● Disruption in fusion of monocular of 65 years. Patients may report that symptoms images of each eye alleviate with breaks from work. ● Exceptionally large amplitude Symptoms of decompensation heterophoria The difficulty in making a diagnosis Tests for assessing From a clinical perspective, the based on symptoms alone is that they can compensation practical manifestations of these factors be non-specific ranging from general Compensation is evaluated using are listed in Table 2. irritation to vertigo/ nausea. Unlike in tests conducted during the course of The main optical cause of childhood, the increasing stability of the a routine , with the decompensation is uncorrected binocular system prevents young adults addition of a few readily available

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Table 2 A summary of the causes of decompensation of heterophoria Optical Medical Environmental Uncorrected refractive error Poor health, fatigue, worry and anxiety Increase in ocular activity • Esophoria decompensated by uncorrected • Reduces fusional reserves • Change in occupation hyperopia • Reduces amplitudes of accommoda- • Extended period of work at a particular • Exophoria decompensated by uncorrected tion and subsequent accommodative- distance (eg prolonged VDU viewing) myopia convergence Over/under corrected refractive error Traumatic injuries Poor working environment • Reduces the acuity and dissociates the eyes • Head trauma can result in temporary or • Reading at too close a distance for long periods • More pronounced where one eye is affected permanent reduction in fusion • Poor illumination or contrast of visual task more than the other Poorly fitted spectacles Adverse effects of drugs Playing games • Particularly with high refractive errors that • Certain antihypertensive and antidepres- • Video games that involve rapid, repeated can induce unwanted prismatic effects sant agents can reduce accommodation pursuit fixation movements • Alcohol has been found to reduce • ‘Magic Eye’ 3D autostereograms that dissociate horizontal fusional reserves and disrupt accommodation and convergence Short period of occlusion Night driving • Difference in image size between the eyes • Patch worn over one eye following a • Reduced visual information prevents binocular () makes fusion difficult corneal injury functioning between the eyes • Patch worn in childhood for the treat-

ment of Extensive visual field loss Extensive monocular viewing • reduces binocular matching • Jewellers between the eyes • Watch makers • Advanced AMD in one eye supplementary assessments. ● Frequency of deviation – whether it is constant or intermittent, presenting 1) History and symptoms – it is with fatigue or at a particular fixation essential for the practitioner to acquire distance full details of the presenting symptoms ● Speed of recovery to binocular suggestive of decompensation including fixation – a ‘smooth and rapid’ onset, frequency, alleviating factors, motion indicates good control with associations in addition to ascertaining strong fusional reserves, while a the following: ‘slow and jerky’ movement warns ● General health – whether the the examiner of imminent symptoms patient has had any recent periods of if not present already. A grading illness or changes to medications scale can be used from 1-5 where 1 ● Visual requirements – any increase represents full control and 5 describes in ocular activity with changes in a heterophoria readily breaking down occupation, new leisure activities to a heterotropia etc. ● Presence of ‘Hering’s movement’ ● Previous ocular history – any – observed in large angle phorias history of binocular vision anomalies on removal of the cover in which including prismatic corrections or both the uncovered and covered eye orthoptic exercises. Figure 2 Set-up for the measurement of fusional reserves exhibit a versional movement, half with automated the amplitude of the total deviation. 2) Measurement of monocular Take care not to dissociate the deviation vs binocular visual acuity. – in and without spectacle correction at fully with repeated cyclic occlusion of decompensation, binocular acuity can the patient’s reading distance, VDU the alternate CT before FD tests for be worse or only slightly better than the distance, 6m and 6m+ to obtain compensation have been performed. For monocular acuity in each eye. This can maximal information. Ask the patient this reason, if you wish to measure the be evaluated by directing the patient to to report any appreciation of blur and/ angle of heterophoria for monitoring, fixate on the best line of acuity while or diplopia during the course of the it is advised that you leave the prism occluding one eye. On removal of the CT. On detecting a heterophoria, your CT till later. occluder, the patient is asked to report notes should include details of: if the line is perceived ‘better, worse ● Direction of deviation – it can be 4) Refraction – can help to establish or the same’. When a heterophoria is purely horizontal, vertical, torsional the cause of heterophoria as well as poorly controlled, it is common for (cyclo) or a combination providing options for management. A patients to hesitate, blink repeatedly or ● Angle of deviation – graded as cyclopegic agent is indicated for use report diplopia. ‘minimal’ (less than 10Δ), ‘moderate’ in testing young children, particularly (25-35Δ) or ‘marked’ (greater than on detecting an esophoria likely to be 3) Cover test (CT) – performed with 40Δ) attributed to high hypermetropia.

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Table 3 Typical amplitudes of fusional reserves at near and distance with prism orientations required for assessment Base direction Fusional reserve (Δ) Near fixation (30cm) Distance fixation (6m) Out (convergent) 30-35 20-25 In (divergent) 12-14 6-8 Up (infravergence) 2-4 2-4 Down (supravergence) 2-4 2-4

Figure 3 Near Mallet unit

5) Fusional reserves – represents the power until the patient reports horizontal vergence and vertical range persistent diplopia recording this as required to overcome a heterophoria. the break point It is measured using a rotating prism or ● Now reduce the prism power prism bar as follows: until a clear single image is regained ● Ask the patient to hold a budgie to ascertain the ‘Recovery’ stick target at a distance of 30cm, ● Repeat the steps above with fixating on the smallest line of letters the prism orientated in the three discernable by the weaker eye remaining base directions in turn. ● Introduce a prism of low power The test can also be performed for in front of one eye (Figure 2) with distance fixation using a suitable line the base in the appropriate direction on a letter chart for fixation. If a patient to the fusional reserve under is unable to appreciate diplopia, an investigation. This may easily be done objective measure can be obtained by using an automated phoropter unit. observing the position of the eye under It is advisable to begin by measuring the prism. Normal values for distance the opposing reserve responsible for and near fusional reserves are shown in controlling the heterophoria – for Table 3. exophoria you must investigate the convergent reserves and vice versa 6) Fixation disparity (FD) – ● Increase the prism power in small evaluated clinically by determining the increments giving the patient a few prismatic or spherical power required seconds between adjustments to to reduce FD to zero, otherwise ensure the letters are perceived single known as the ‘aligning prism/sphere’ and clear or ‘retinal slip’. In general, symptoms ● Ask the patient to report when they worsen as the amount of aligning are unable to overcome the image prism increases. The most recognised blur and record the corresponding test used since the 1960s can be prism power as the blur point. This found on the Mallet unit (Figure 3), a provides a measure of the positive/ handheld device incorporating an array negative relative convergence of near vision tests and assessments ● Continue to increase the prism for binocular function (see later for opticianonline.net 17.12.10 | Optician | 29 CET Continuing education

procedure). Alternative tests for FD 4) Ask the patient if they still see two are commercially available, but tend strips: to differ in the presence and degree ● If both strips are perceived, of visual information identical to each proceed to Step 5 eye (binocular lock) generating variable ● If one strip disappears, it is likely results. that the image of one eye is being suppressed at the cortical processing 7) Foveal suppression – young stage, rendering the test unsuitable children have the ability to adapt to foe continued use? The test cannot a large untreated heterophoria by be continued and you are advised to suppressing the foveal image of one eye, annotate your records accordingly while the remainder of the binocular eg R suppression field remains normal. This test is ● Temporary disappearance or particularly indicated where a large ‘flashing’ of the strips could deviation is present without any of the be attributed to intermittent expected symptoms of decompensation, suppression or a cortical or subjective appreciation of FD. Such phenomenon known as ‘retinal a test is integrated in the Mallet unit rivalry’ or ‘binocular instability’. comprised of five rows of letters arranged in vertical bars so that the Figure 4 FD target on the near Mallet unit NB When both strips are seen, do not central letters are perceived binocularly (with surrounding text) assume that suppression is not present as and the letters to either side by one it can occur over a smaller area detected eye only when viewed through cross use a single panel with four radiating using the foveal suppression test. polarised filters at a distance of 35cm. strips. The markers and central panel A small suppression area is indicated are illuminated internally, while the 5) Direct the patient to read 2-3 lines when the patient fails to read the letters surrounding text requires an external of the text surrounding the FD target to one side of the binocular lock. The light source set at a distance of 10 inches. to stabilize binocular viewing. This step size of the zone can be recorded from This also stimulates paramacular and is frequently missed wasting invaluable 20 to five minutes of arc. peripheral fusion in normal binocular time attempting to align a disparity that viewing by adjusting for the reduction in is not strictly present. 8) Near point of convergence (NPC) – illuminance through the Polaroid visor. convergence insufficiency is indicated Before you begin, ensure that the 6) Again ask the patient if the 2 strips with a reading of more than 10cm, patient is adjusted for near viewing with are in a straight line above and below often presenting with convergence the appropriate spectacle correction and the X. If the strips temporarily disappear weakness exophoria. reading addition as required. Familiarise such as in intermittent suppression, yourself with the polarisation of the visor ascertain whether they align at the 9) Amplitude of acccommodation so that you recognise which eye views moment when both strips are present. and AC/A ratio – provides useful each strip. It is inadvisable to confirm If both strips are aligned, repeat steps information for management given the this by relying on the patient’s subjective 2-6 using the horizontal markers to association between accommodation response on occlusion of each eye, as it evaluate vertical slip. and convergence. risks dissociating binocularity potentially breaking a heterophoria down to a 7) Misalignment can be monocular or 10) – reduced depth perception heterotropia. In standard British units binocular in which one or both strips (typically less than 100 seconds or arc) the top and right strips are seen by the move out of line respectively. The can provide an indirect measure of foveal left eye and vice versa. Then follow the former is an excellent indicator for suppression. steps below: as it identifies the non-dominant eye for management. You Fixation disparity (Mallet unit) 1) Ask the patient to hold the unit at can now use prisms to correct the slip as The Mallet unit FD test is comprised of their normal reading distance and angle follows: two small markers in the form of green of viewing; this can be measured using ● Crossed FD – the top strip seen by strips, located above and below the ‘X’ the retractable tape incorporated within the left eye is perceived to the right of an ‘OXO’ target. Coloured strips are the housing. of the X and vice versa associated easier for the patient to differentiate with an exophoria corrected with from the OXO panel which provides the 2) Direct the patient to fixate on the Base in prisms binocular fusion lock required to mimic OXO panel and vertically illuminated ● Uncrossed FD – the top strip seen natural viewing; the choice of green markers, and ask them to report whether by the left eye is seen to the left means they are less easily suppressed the two strips appear in a straight line of the X and vice versa associated (Figure 4). The presence or absence of FD above and below the X. Rarely, patients with an esophoria corrected with is indicated by the subjective appreciation can report a true misalignment but in the Base out prisms of the relative positions of these strips, majority of cases this identifies unreliable ● Vertical FD – if the left strip viewed through cross polarised filters to patients, or improves the appreciation of is seen by the right eye and is ensure that only one strip is perceived by the smallest misalignment by comparing reported higher than the X, it is each eye. Vertical nonius strips are used their position when viewed through the associated with uncompensated to detect horizontal FD, while horizontal visor. left hyperphoria corrected with markers evaluate vertical FD. Older Base up prisms before the right versions of the unit have two separate 3) Position the cross-polarising visor eye and Base down in front of the targets accordingly while newer models before the eyes. left, and vice versa

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● Cyclo FD – indicated by ‘sloping’ Figure 5 Observation Diagnosis of one or both strips, frequently Possible presenting secondary to a vertical results of the deviation. Any residual cyclo slip FD test and O X O No horizontal FD/slip is assessed by rotating the target so their that the strips are perpendicular to interpretation their original orientation. If a vertical disparity coexists with horizontal slip, it is advisable to begin by correcting the latter as in practice a vertical deviation is often the secondary O X O Deep central suppression R presentation. Possible outcomes of the FD test and the interpretation of results using a standard British unit is tabulated in Figure 5. Begin with a low powered prism Left ‘crossed’ slip with O X O of 0.5Δ and increase incrementally uncompensated exophoria as required, taking care to stabilize binocular viewing between adjustments by asking the patient to read the surrounding text. Record the weakest prism power required for precise Right and Left ‘uncrossed’ slip alignment (eg Near FD – 2Δ base in R/ O X O no vertical slip) with uncompensated esophoria In younger patients with ample accommodation, spherical lenses can be used to align horizontal slip and control the heterophoria by manipulating O L vertical slip with uncompensated the accommodation-convergence X R hyperphoria relationship: O ● Exophoria with crossed FD – ᑔᑘᑤᑡᑀᑨᑘᑢᑠᑀᑣᑦᑰᑱᑩrequires negative ᑥᑠᑦᑱᑰᑀᑘᑙᑒᑕᑘ!ᑧ spheres ᑱᑀᑃᑀᑀᑄᑄᑁᑂᑑᑁᑄᑂᑃᑂᑀᑀᑃᑅᑒᑇᑇᑀᑀᑗᑘᑢᑠᑀᑃto induce ᑔᑧ∃!ᑀᑨᑙ8/ᑀᑠᑩ.#!/0ᑀᑦ1,,(%!.ᑀ+∀ᑀᑣ,0%ᑱᑩ(ᑀᑖ−1%,)!∗0.%+0ᑀᑦ%(2!.ᑀᑤ(1/ᑀ7 &1/0ᑀ5ᑄᑄᑁᑇᑐᑈ ᑦ%),(%∀4%∗#ᑀ0∃!ᑀ(!∗/ᑀ! #%∗#ᑀ,.+ᑱ!//

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accommodative-convergence ● Esophoria with uncrossed FD – requires positive spheres and/ or extra bifocal addition to relax accommodative-convergence.

8) Repeat steps 2-7 for distance viewing stabilising binocular viewing using an appropriate line on the letter chart.

Management of decompensated heterophoria The presence of FD does not always warrant treatment but is indicated Figure 6 Test Chart 2000 FD test and new Test Chart 2000 XPert target when a heterophoria is symptomatic, asymptomatic with foveal suppression that fully comprehend the reason for fixation on removal of the cover. or likely to decompensate and degrade treatment which is usually administered binocularity in due course. When over an intense period of 2-3 weeks. 5) Surgery – usually involves weakening left untreated in young children, The principle is to improve oculomotor one muscle and strengthening another suppression can deepen developing control and re-establish accurate muscle to reduce the angle of heterophoria. into amblyopia. The first stage of coordination rather than to solely increase It is often the only feasible option management is to remove the cause of fusional reserves. Their use is limited in in cyclophoria, vertical phorias or decompensation such as environmental vertical deviations and larger horizontal unusually large horizontal phorias. factors that are unfavourable to such as esophoria and comfortable binocular viewing. Advise exophoria greater than 10Δ and 15-20Δ 6) Botulinum Toxin A – can be used reading at a greater distance, regular respectively. in the management of large horizontal breaks with VDU work or adjustments ● Esophoria – requires improvement heterophoria by temporarily reducing to the contrast and/or lighting of visual of negative relative convergence the angle of deviation. It does however tasks accordingly. You may also need to with stereograms, bar reading and require repeated injections to maintain address any general health issues by fusional reserve exercises with comfortable control. referring the patient to their GP. Next, base in prisms consider options to provide two similar ● Exophoria – requires improvement Computerised tests for images for fusion, increase fusional of positive relative convergence compensation reserves and/or reduce the size of a and binocular convergence with The Test Chart 2000 and Near Chart deviation as follows: stereograms, fusional exercises 2000 were originally developed by and base out prisms. Professor Thomson of City University 1) Correct the refractive error – required in the mid 90s. Newer additions to the to create two clear, equally sized images 4) Prisms – effectively reduce the product range include Vision Screener for binocular fusion. Even small angle of heterophoria remaining for programs for schools and more recently corrections otherwise deemed clinically the patient to control, with particular the iChart 2000 designed for use with insignificant can improve control. usefulness in vertical deviations. They iPhone and iPod touch devices. All In significant anisometropia, contact also provide an option when exercises these applications integrate a FD test lenses may provide a better alternative fail or are simply impractical given to assess heterophoria compensation to reduce the aniseikonia and facilitate the patient’s age or poor health, and based on the original Mallet unit design, fusion accordingly. temporary relief for eg students with thereby following a similar procedure. imminent exams. There is no hard and Research indicates a good correlation 2) Modification of refractive error – fast rule when it comes to deciding on between the tests, largely attributed alters the accommodative-convergence prismatic correction, but you may find to the choice of binocular lock highly by applying a negative add in exophoria the following guidelines useful: conducive to natural binocular viewing. and positive add in esophoria as ● Issue half the angle of deviation in The monocular markers are viewed follows: dioptres to allow fusional reserves with each eye using a visor comprised ● Hyperopic esophoria – full to develop of red and green filters in front of the correction with extra +0.25DS ● Use the weakest prism to align right and left eyes respectively (Figure and bifocal addition as required markers of the FD test 6). For practitioners who do not feel ● Hyperopic exophoria – under- ● In strong ocular dominance with as comfortable using coloured filters, correction as required monocular slip, prism should be the revised Test Chart 2000 XPert ● Myopic esophoria – under- issued for this non-dominant eye. uses cross-polarised filters with an correction by 0.50DS Larger prisms may be divided additional target of red markers around ● Myopic exophoria – overcorrection between the eyes but distributed a central white cross. The software also if ample accommodation by no unequally with the weaker power includes the following supplementary more than -3.00DS, gradually before the dominant eye. tests: reducing this power over months Before the final prescription is issued, ● Associated phoria test – provides to allow fusional reserves to be confirm subjective appreciation of a measure of the actual size of FD exercised accordingly. comfortable control using the near/ rather than the prism/ spherical power distance letter chart and repeat the CT required to overcome it 3) Orthoptic exercises – only a feasible with this prismatic correction to observe ● Suppression tests – including option with cooperative patients the rapid, smooth recovery to binocular ‘Worths 4 dot’ test, ‘Traffic lights

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suppression’ test and the ‘Binocularity’ test (iChart 2000) comprised of lines of Multiple-choice questions – take part at opticianonline.net five letters of reducing size following a similar procedure to the Mallet unit What is the size of Panum’s fusional area Which of the following is NOT a test foveal suppression test 1at the fovea? 4used specifically for the assessment of ● Stereopsis – random dot stereogram A 5-10 seconds of arc compensation? test consisting of red and green dots B 5-10 minutes of arc A Associated phoria viewed monocularly through red/ C 1-5 seconds of arc B Stereopsis green filters in which the illusion D 1-5 minutes of arc C Foveal suppression of depth is created by a disparity in D Jump convergence certain areas. Fixation disparity can otherwise be 2known as which of the following? In the measurement of fusional reserves, It is clear from this article that A Aligning sphere 5in which order do you record your results? B Cortical slip A Recovery point/break point/blur point the evaluation of heterophoria C Dissociated phoria B Blur point/break point/recovery point compensation is based not on a single D Manifest deviation C Break point/blur point/recovery point measure but a caveat of tests yielding D Break point/recovery point/blur point significant information of binocular Which of the following scenarios is most functioning and indeed a patient’s 3likely to result in decompensation of a On using the standard British Mallet unit general health. The tests are simple heterophoria? 6FD test, your patient reports a movement but effective diagnostic tools which A Poorly fitting spectacles of -1.00DS power of the bottom strip to the left. Which of the are relatively easy to learn, but must be B A contact wearer with R -3.25DS and L following options can be used to overcome used regularly to maximise practitioner -4.25DS correction the slip? skill and confidence. It is therefore C A patient suffering with allergic rhinitis over A Base in prisms and/or negative spherical important that clinical staff familiarise the past week lenses themselves with the battery of tests D Painting miniatures at a working distance of B Base in prisms and/or positive spherical at their disposal, and know how to 20cm under an energy saving lamp lenses interpret the results in order to best C Base out prisms and/or negative spherical serve the interests of the patient. lenses D Base up prisms and/or negative spherical ● The final article in this series considers lenses tests for retinal correspondence and other useful measures of binocularity recommended for daily practice. Successful participation in this module counts as one credit towards the GOC CET scheme administered by Vantage and one towards the Association of Optometrists Ireland’s scheme. Deadline for responses is January 13 2011 References 1 Evans BJW. Pickwell’s Binocular Vision Anomalies, p 8 (Fourth edition), Butterworth 4 Evans BJW. Pickwell’s Binocular Vision 7 Evans BJW. Pickwell’s Binocular Vision Heinemann, Oxford, 2002. Anomalies, p 69 (Fourth edition), Butterworth Anomalies, p 112 (Fourth edition), Butterworth 2 Evans BJW. Pickwell’s Binocular Vision Heinemann, Oxford, 2002. Heinemann, Oxford, 2002. Anomalies, p 7 (Fourth edition), Butterworth 5 Evans BJW. Pickwell’s Binocular Vision www.thomson-software-solutions.com Heinemann, Oxford, 2002. Anomalies, p 68 (Fourth edition), Butterworth 3 Evans BJW. Pickwell’s Binocular Vision Heinemann, Oxford, 2002. ● Priya Dabasia is a clinical optometrist Anomalies, p 65 (Fourth edition), Butterworth 6 Evans BJW. Binocular Vision Anomalies: Part, at the Fight for Sight Clinic, City Heinemann, Oxford, 2002. OT, 38, 2007. University and Moorfields Eye Hospital

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