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EpidemiologyThe prevalence of strabismus and amblyopia in seven-year-olds has been reported to be 2.3% and 3.6% respectively.1 In comparison, whilst the prevalence of symptomatic manifest deviations is reduced in adults because of sensory adaptations, there is a corresponding rise in BV anomalies as visual tasks become more challenging. In a cohort of individuals performing demanding near vision tasks, the prevalence of non-strabismic BV dysfunction has been found to be as high as 32.3%.2 Similar results have also been reported where 22.3% of symptomatic adults presenting to a general optometric clinic had some degree of binocular or accommodative dysfunction.3 In the

MOdulE 14 PaRT 6: BINOCulaR VISION COuRSE COdE: C-15084 O

lynne Weddell BSc (Hons) FCOptomBinocular vision (BV) anomalies are commonly encountered in optometric

practice. As a result the optometrist needs to be able to recognise binocular

dysfunction and investigate it appropriately. This can be done simply and

with inexpensive equipment in a primary eye care practice. It is the author’s

opinion that many binocular disorders can be managed optometrically

and therefore do not require referral unless it lies beyond the expertise of

the examining practitioner or underlying ocular or systemic pathologies

are suspected. This article, therefore, discusses how to effectively

investigate BV anomalies to aid appropriate detection and management.

elderly population accommodative dysfunction is the norm but systemic disorders such as cerebral vascular accidents may affect binocular function.4, 5

History and symptomsEach and every optometric examination should begin with a thorough symptoms and history interview regardless of the BV status. A recently acquired incomitant deviation is likely to be symptomatic presenting with diplopia and blurred vision and possibly symptoms of any associated systemic condition. By contrast, the symptoms associated with a latent deviation may either be absent or non-specific, thus creating a diagnostic dilemma.

Headaches and asthenopia are

likely to present frequently to the optometrist. It has been reported that the lifetime prevalence of headaches in men and women aged 25-64 years was 93% and 99% respectively and the prevalence at one point in time was 11% in men and 22% in women.6

The International Headache Society is currently responsible for the classification of headache disorders into distinct groups.7 There are three major groups: “primary”, “secondary and cranial neuralgias”, and “facial pain and other headaches”. These groups are further sub-divided into 14 types, 91 subtypes and additional sub-forms. Of these 91 subtypes, one is attributed to disorders of the eyes, of which there are four sub-forms. One of these sub-forms includes “headaches attributed to heterophoria or heterotropia (latent or manifest squint)” and another to “uncorrected refractive error”. It is commonly assumed that a headache may be related to an eye disorder but it is clear that it is a widespread problem with

Investigative techniques in binocular vision

Figure 1 Kay Crowded LogMAR chart for assessing visual acuity in children from the age of 36 months (courtesy of Kay Pictures)


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Vision / Visual acuityIt is recommended that vision and/or visual acuity (VA) is the first test conducted in any optometric examination. This is advisable for many reasons including the establishment of base-line data and protection against litigation. The vision (unaided) or VA (ideally with optimal refractive correction) is traditionally measured using a Snellen chart in the UK. However, this is not without its limitations, which are well documented:• Non-linear reduction in size of letters.• Randomised spacing between letters.• Varying number of letters per line.

VA can be reduced by the arrangement of additional contours in the field of vision in normal eyes and this is exaggerated in the amblyopic eye. Such crowded optoptypes are more realistic of the visual world around us. A chart that utilises a logarithmic progression, such as the logMAR chart, will provide consistent task difficulty and the net result is a more accurate measurement of VA. This is important because the presence of reduced VA in the absence of any pathology will alert the practitioner to the possibility of amblyopia. For example an individual with a vague history, and the findings of a unilateral strabismus, with associated amblyopia, could imply the deviation is long-standing.

With children, measurement of VA using the same charts is unlikely. Instead there are other specialist tests available such as the Kay Crowded LogMAR chart (Kay Pictures) (Figure 1) suitable from age 36 months onwards,

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and for the slightly older child the LogMAR Crowded Test (Keeler Ophthalmic Instruments) (Figure 2).

assessment of Binocular VisionThe College of Optometrists10 provides guidelines for good optometric practice, advising that during a full eye examination there should be “an assessment of habitual ocular muscle balance.” As such, assessment of BV is a fundamental requirement of all sight examinations. Many of the following tests are not specialist orthoptic tests and therefore their use should not be restricted to individuals suspected of BV dysfunction alone.

BV tests are divided into two groups, motor tests in which part of the visual system is in motion, and sensory tests in which the ability of the two eyes to integrate visual information is investigated. It is assumed that during all the tests the patient is sitting with their head upright. Examples are listed in Table 1.

Motor TestsCover TestThe cover test is an objective test used to determine the presence of latent and manifest deviations. It is the foundation for all BV examinations and it should be used routinely in all optometric examinations. To conduct this test the patient should be directed towards appropriate targets at 6m (distance) and the patient’s habitual near working distance. In divergent deviations it may also be repeated for distances greater than 6m. A target requiring precise accommodation and fixation should be selected, such as a letter on the line of (or one line larger than) the VA of the weaker eye. At near, an appropriate letter on a “budgie stick” or an element of a picture should be selected. The cover test should then also be repeated with a spotlight as a fixation target, especially for convergent deviations, to assess the effect of accommodation on the angle of the deviation. Cover test should also be repeated with and

a wide variety of diverse and possibly multi-factorial aetiologies. This is borne out by epidemiological studies which find benign primary headaches are the most common type.6,8,9

Reports of blurred vision may relate to a BV dysfunction but other causes such as pathology and uncorrected refractive error must be excluded first

Other important considerations relate to general health and medications. For instance, a recent debilitating illness may result in a latent deviation decompensating or diabetes mellitus may result in acquired cranial nerve palsy. In children additional information should also be sought regarding their birth and family history, ocular history with respect to childhood refractive error and anomalies of BV (including trauma), as these disorders influence the development of binocularity.

Finally, during the interview, the patient can be observed in their habitual position and any abnormal head posture (AHP), manifest deviation, ptosis and/or broad epicanthal folds noted.

Figure 2 LogMAR Crowded test for assessing visual acuity in children aged 36 months and above

Motor Tests Sensory Tests

Cover test Bagolini lenses

Motility Worth’s Four Dots

Measurement of accommodation Fixation disparity

Near point of convergence Stereopsis

Table 1 Examples of motor and sensory tests used in the investigation of binocular vision

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without the refractive correction in place to observe the effect on the angle of the deviation. Similarly it should be measured with and without an AHP if relevant, to observe the effect of the AHP.

The cover test should first be done to determine the presence of a manifest deviation (cover/uncover test) and then to determine the presence of a latent deviation (alternating cover test). When recording results, it should be noted whether the deviation is manifest or latent as well as the direction of the deviation (eso- vs. exo-) and an estimation of the size of the deviation; Table 2 shows a standardised description of deviation sizes.12 For accurate assessment of the size of a deviation, a prism cover test should be performed (see later). For latent

deviations, it is also important to assess the speed of the movement of the eye when taking up fixation, and to record whether it is rapid, moderate, slow, or to a blink. A rapid movement suggests that the deviation is controlled by adequate fusional reserves whereas a delayed recovery or recovery to a blink suggests that the fusional reserves are inadequate.

In most instances a matt black occluder is used to conduct a cover test. Spielman11 described a semi-translucent occluder, which permits visualisation of the eye behind the cover and blurs the target sufficiently to prevent fusion (Figure 3). It is useful when assessing dissociated vertical deviations (DVD) and nystagmus.

Prism Cover Test (PCT)This is an objective test to measure the angle of deviation in horizontal and vertical deviations. The patient should be directed to fixate on a suitable target at either 6m (distance PCT) or at 33cm (near PCT); the patient’s habitual working distance is not used, to ensure

that subsequent measurements can be compared consistently. Initially an alternating cover test is performed so that the angle and direction of deviation can be estimated. A prism bar or loose prisms are placed before either eye when assessing a latent deviation or before the deviated eye when assessing a manifest deviation. The direction of the prism base is selected depending upon the direction of the deviation (Table 3). The prism power is gradually increased during the alternating cover test until all of the remaining eye movement is neutralised; the practitioner should ensure that the eyes are not allowed to fuse during changes of the occluder (Figure 4).

The prism power should be noted when there is no movement observed, as the angle of the deviation is now neutralised.

Figure 3 A Spielman occluder, which allows visualisation of the eye behind the cover

Figure 4 Measurement of the angle of deviation using prism cover test

Classification deviation in prism dioptres (∆)

Minimal <10

Small 10 - 20

Moderate 20 – 40

Large > 40

Table 2 Classification of the size of deviation according to the estimated size of the angle. Modified from Ansons and Davis12

deviation Prism direction

Convergent (Eso) Base-Out

Divergent (Exo) Base-In

Right hyper Base-down right or base-up left

Left hyper Base-up right or base-down left

Table 3 Direction of prism direction to neutralise ocular deviations

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However, to confirm this point, the prism should be increased by one more power step to check that the eye movement is reversed. In manifest deviations this procedure measures the full angle of deviation. To measure the habitual angle, the same technique should be used but using a cover/uncover test.

Problems may arise when the deviation has both horizontal and vertical elements. In this instance the largest deviation should be measured first and a second prism bar used before the same eye, to measure the second deviation. Practical problems arise from this in placing one prism bar over another and also when combinations of large prisms are used the resultant prism power cannot be calculated by simple arithmetic.

Torsional deviations cannot be measured objectively and the simplest subjective technique that can be used in a community optometric practice utilises two different coloured Maddox rods inserted into a trial frame or phoropter; this test is referred to as the Double Maddox Rod Test.

double Maddox Rod TestA Maddox rod is a lens consisting of a series of high-powered cylinders that blur a spot of light into a streak. It has limited use for the measurement of latent deviations but for the measurement of cyclodeviations, two different coloured Maddox rods are placed with their cylinder axes vertical, one in front of each eye. The patient views a spot of light at either 6m or 33cm and in torsional deviations they should report two non-parallel horizontal lines. The orientation of one of the Maddox rods should be adjusted until both lines are perceived as being parallel. The amount that the Maddox rod has been rotated in degrees gives the size of the torsional deviation.

Hirschberg testIn young children, uncooperative patients, or patients with markedly reduced VA, the angle of deviation can be estimated by observing corneal reflections.13 The patient fixates on a pen torch held at 33cm and the practitioner observes the reflections on the patient’s


cornea (first Purkinje image) and notes any asymmetry between the eyes (Figure 5). The reflection will be displaced temporally in the deviated eye with an esotropia and nasally in the deviated eye with an exotropia. However, the practitioner should first note the position of the corneal reflection in the “straight” fixating eye, as it is not always central; for most individuals, as the fovea is located temporally to the posterior pole, the reflections should lie nasally to the corneal apex (Figure 5a).

A 1mm displacement of the corneal reflection corresponds to a 22∆ deviation14, 15 (Figures 5b and 5c). Obviously this method of estimating the size of a deviation is only suitable with moderate to large manifest deviations. It can be further refined by the Krimsky technique16 in which a prism is placed before the fixating eye and the prismatic power increased until the corneal reflections are symmetrical. The Krimsky and Hirschberg tests are significantly less accurate than the PCT even when estimated by an experienced practitioner.17

assessment of Comitancy MotilityThe motility test is used to assess the function of each muscle pairing of the eyes across the motor field. The patient is instructed to view a pen torch at no closer than 33cm; any closer than this and the medial recti have an exaggerated effect on the results. The torch is moved from the primary position to the eight cardinal positions of gaze in a star-like fashion. The patient is directed to report any diplopia or discomfort at any point. The practitioner should also observe the reflexes until one of the reflexes disappears from one eye, as the nose obscures it (indicating movement into the single visual field of one eye). An alternating cover test should be performed in all directions of gaze, as some individuals may not notice diplopia; thus objective assessment of any ocular misalignment can be made.

Figure 5 (a) Positive angle kappa fovea lies 30 temporal to the posterior pole and angle kappa is 1mm. (b) Right eye fixating, left eye deviated positive angle kappa of 1mm. (c) Right eye fixating, left eye deviated negative angle kappa of 1mm

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Many optometric practitioners encounter difficulty in isolating the paretic muscle when an incomitant deviation is discovered, though of course it is possible that more than one muscle could be affected. A knowledge of the actions of the extraocular muscles assists with this (Table 4) and whilst a Hess Screen or Lees Plot will identify a paretic muscle with ease, these are rarely found in primary eye care practices. As such, it is important to determine the paretic muscle by performing a cover test in each direction of gaze although an easier approach might be to adopt the Park-Helveston test instead.

Park-Helveston Three Step TestThis test, originally described by Park18 but modified by Helveston,19 uses three steps to determine which muscle is affected in a vertical incomitant deviation. As the name suggests, three separate tests and observations are conducted during the ocular motility test, the answers to which isolate the likely affected muscle (Table 5).

Fusional ReservesMotor fusion is the ability to align the two eyes so that sensory fusion and hence binocular single vision (BSV) can occur. Fusional reserves are the amount of vergence that can be undertaken before diplopia occurs. They can be measured at distance or near, with loose prisms, prism bars or rotary prisms in a phoropter. The technique can be used in latent and manifest deviations, the latter providing that the angle of the deviation is corrected using prisms; the test can also be modified in children to provide an objective assessment.

The patient should wear their optimal refractive correction for the fixation distance being tested (ie distance refractive correction worn for distance fusional reserves and near refractive correction, including a near addition for presbyopes, for near fusional reserves). The patient should then fixate a target requiring precise fixation and accommodation, such as a Snellen letter at distance or a letter on

a reading chart or a “budgie stick” at near. Prisms are then placed before one eye and the prismatic power increased slowly, so that the patient has the chance to adapt to the change in vergence, until diplopia is reported. The prism power value just before that at which diplopia occurred is the “break” point or the limit of fusional vergence. The prism is held in position and the power slowly reduced until single vision is re-established. The point at which this occurs is the “recovery” point. It is advisable also to observe the eye movements behind the prism, particularly if subjective responses are poor.

When measuring base-out (convergent) fusional reserves, the patient may report blurring of the image prior to diplopia as the prism power is increased. This is the “blur” point and represents the limit of the convergence/accommodation relationship. As the convergent prism is increased, the individual has to

increase their convergence but as the target distance is kept constant, accommodation should remain static. When the target blurs it is because convergence can no longer be increased while accommodation is relaxed. Various authors have produced tables of normative values for fusional reserves20, 21 but Table 6 is easiest to memorise.

The measurement of prism fusion ranges should be compared to the norms and to the opposing fusion range to the deviation. It should be used as part of a battery of tests to determine whether a latent deviation is decompensating.

Prism Reflex Test - 20ΔThis test can be used as an objective assessment in children aged over six months to demonstrate BSV and the presence of motor fusion. The patient’s attention is directed towards an accommodative near target. The

Muscle Primary action Secondary action Tertiary action

Superior Oblique Intorsion Depression Abduction

Inferior Oblique Extorsion Elevation Abduction

Superior Rectus Elevation Intorsion Adduction

Inferior Rectus Depression Extorsion Adduction

Lateral Rectus Abduction

Medial Rectus Adduction

Table 4 Actions of the extraocular muscles

Step Outcome Possible affected Muscle

1. Is the deviation a right or a left hyper-

deviation?

Right RSO, RIR, LIO, LSR

Left RIO, RSR, LSO, LIR

2. Is the hyper-deviation greater in right or left gaze?

Right RSR, RIR, LIO, LSO

Left LSR, LIR, RIO, RSO

3. Is the hyper-deviation greater with head tilt to the right or to the left?

Right RSO, RSR, LIO, LSO

Left RIO, RIR, LSO, LSR

Table 5 Identifying the paretic muscle in ocular motility using the Park-Helveston Three Step Test

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prism is held base-out before each eye in turn. The prism held before one eye shifts the image of the object and therefore the eye must move to maintain fixation of the object by the fovea; due to Herring’s law, the other eye will also move, initially abducting and then adducting, to maintain the image on the fovea of this eye (Figure 6). The opposite sequence of movements should be seen as the prism is removed. The prism should then be placed before the other eye and the same observations noted. A prism of 20∆ Δwill induce large eye movements that will be easy to observe. If a 20∆ Δ prism is not overcome, smaller prisms can be used eg 15 ∆ Δ and then 10 ∆..

Convergence & accommodationThe near point of convergence (NPC) and amplitude of accommodation (AoA) can be measured subjectively using an RAF rule or appropriate target, which is advanced slowly towards the patient from at least 30cm until the patient reports diplopia and blurring, respectively. Some individuals do not notice diplopia for NPC testing and so objective observation of one eye diverging may be needed. Average values of the NPC should be 6 to 10cm but this test does not assess the ability of an individual to change convergence in everyday situations. For this, the jump convergence should be

tested instead, whereby the patient is directed to look at a distant target and then to transfer their gaze immediately to a small near target. A failure of this test is the inability of one or both eyes to make a convergent movement, or slow or hesitant convergence.

Objective assessment of accommodation assesses the accuracy of accommodative response, and is typically conducted by dynamic retinoscopy. In the monocular estimation method (MEM), the patient fixates on an accommodative target in the plane of the retinoscope while the full refractive correction is worn. The light from the retinoscope is then quickly swept across the pupil in one direction only and the reflex assessed. A fast “with” movement should be observed, as the accommodation response should be slightly less than (therefore behind) the accommodative stimulus (the target on the retinoscope); this is the accommodative lag. Positive lenses of increasing power are then very briefly placed before one eye to neutralise the “with” movement. Normal values are between zero and +0.75DS, when assessed at the preferred working distance, for children22 and pre-presbyopes.23 Where an “against” movement is observed, this indicates over-accommodation (accommodative lead), which will need to be neutralised with negative lenses. This indicates a BV problem and is likely to be associated with over-convergence, thus warranting further investigation (see later).

In MEM, it is assumed that placing lenses in front of the eye does not alter the accommodative demand. However, this is not at all certain and therefore the alternative Nott method24,25 can be used, whereby the practitioner moves forward if there is an accommodative lead or backwards if there is a lag, until the reflex on retinoscopy is neutralised; the fixation target remains at a fixed distance. The dioptric distance between the target and the position of neutralisation gives the accommodative lag or lead. A greater lag may be found

with MEM than the Nott method and the latter is more accurate in young adults.26

accommodative/convergence ratiosAccommodation and convergence do not occur in isolation and as a result it is often preferable to evaluate the link between the two. Accommodative convergence (AC) is the convergence arising as a result of accommodation (A). Therefore, by altering the amount of accommodation a practitioner can measure the change in convergence. By comparison, convergence accommodation (CA) is the amount of convergence (C) arising as a result of accommodation and therefore as an alternative the practitioner can alter the amount of vergence while the accommodative state is maintained. These are termed the AC/A and CA/C ratios, respectively. aC/a RatioFor each dioptre of accommodation exerted the eyes should converge by 3-5∆.27 This is inborn and remains relatively unchanged from childhood to early presbyopia.28 In certain conditions such as convergence excess, there may be an associated high AC/A ratio. In contrast, in simulated distance exotropia a high AC/A ratio masks the large exo deviation that is present at near, so that the condition appears to be a large exo deviation at distance only. The AC/A


distance Break Point (∆)

Base-in 6 metres 10

Base-out 6 metres 20

Base-in 40 cm 20

Base-out 40 cm 40

Base-down R 3

Base-up R 3

Table 6 Average fusional reserves

Figure 6 Movement of the eyes during the 20∆ base-out prism test

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ratio may be measured by two techniques in primary optometric practice:• Gradient method• Heterophoria method

Gradient methodThe deviation is measured at near using a PCT with and without a binocular addition of +3.00DS lenses. This is then repeated for distance fixation with and without a binocular addition of -3.00DS lenses. These results are then used to calculate the AC/A ratio using the following formula:29

AC/A = PCT with accn. – PCT without accn.

Amount of accommodation exerted

Heterophoria methodIn this method a PCT is performed at distance and near and the total change in convergence between the two viewing distances is divided by the dioptric change in accommodation; the method also takes account of the inter-pupillary distance (IPD). The formula is as follows:

AC/A ratio = IPD (cm) + near PCT – distance PCT

Accommodation (D)

In general the heterophoria method gives higher AC/A ratios as it takes account of proximal convergence.21

Sensory StatusAn individual with a manifest deviation will either have diplopia with normal retinal correspondence (NRC) or, rarely, unharmonious retinal correspondence (UHRC). The two conditions can be differentiated by the use of prisms. In NRC the amount of prism that relieves the diplopia will also eliminate the strabismus. In UHRC the amount of prism that eliminates diplopia will be different to the amount of prism that eliminates the manifest deviation.

If the deviation occurred at an early enough age, suppression or abnormal retinal correspondence (ARC) will have developed and thus diplopia will be absent. Suppression is more likely to occur in the presence of large angle strabismus, especially if intermittent, alternating and if beginning later in life. By comparison, ARC is more likely to occur with early onset, small angle, and constant unilateral deviations.

Worth’s Four dot TestWorth’s four dot test30 is used to investigate the presence of global suppression, but has been criticised as dissociation may occur with the red/green glasses employed.31 It has also been suggested that it can be used to detect a central suppression scotoma32 as well as the presence of diplopia. It consists of four coloured spot lights arranged in a diamond pattern. The patient wears red/green spectacles over their optimal refractive correction, with the red lens conventionally placed in front of the right eye. The patient views the coloured dots and reports one red light, two green lights, and one light as a mixture of red/green (due to retinal rivalry) if they have BSV. If diplopia is present, the patient will report seeing five lights, and either two or three lights only if suppression is present (Figure 7).

Bagolini lensesBagolini lenses are used in clinical practice to investigate retinal correspondence.33 They are plano lenses with fine striations designed so as not to affect accommodation and to produce minimal interference with VA and binocularity. They are available as loose lenses, which are usually placed at 45o and 135o in a trial frame, or more conveniently as a lorgnette. The lenses are placed in front of the patient’s refractive correction and a spotlight is viewed at eye level at either 33cm or 6m in a well-illuminated room. In the presence of bifoveal fusion the patient sees an “X” pattern but if central suppression is present a break will be reported in one of the lines; when global suppression is present, only one line will be observed (Figure 8).

4∆ base out testThis test can be used to demonstrate the presence of bifoveal fixation but should not be used in isolation to detect the presence of a central scotoma associated with ARC. In this technique, first described by Worth30 using a 12∆ prism, the patient is directed towards a fixation target at either 6m or 33cm but in young children a near target is essential. A prism of 4∆ is introduced before the right eye with base out and the bi-phasic movements as described when a 20∆ prism base out test is used (see earlier), should be observed, although the movements are smaller. If the prism is placed before an eye with a central scotoma, the image of the fixation target will fall within the suppression scotoma and so no movement of either eye will be observed.

Fixation disparityAny point on the retina of one eye corresponds with a small area on the retina in the other eye; this area is termed Panum’s area. If a misalignment of the visual axis occurs, and the image of an object does not fall within Panum’s area, diplopia will be reported.

Figure 7 Figure 7. Worth Lights and the possible responses

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However, if the deviation is small, as long as the image falls within Panum’s area, diplopia will be avoided. This small deviation from a corresponding area is termed fixation disparity. Mallett34 argued that fixation disparity is a sign of stress on the BV system. However, Schor35 stated that fixation disparity is used to control vergences. Despite these arguments fixation disparity is frequently assessed in optometric practice using the Mallett unit.

The Mallett unit was originally designed for assessing fixation disparity at near in optometric practice36 and was subsequently modified for distance.37

Modified versions are used commonly today,38 although in either case, it is truly an assessment of the “aligning prism”. The patient views a target common to both eyes; the word OXO as well as two nonius lines either side of the X. Dissociation of the nonius lines occurs with polarised visors and any misalignment of the lines, due to a fixation disparity, is noted. Prisms, or less commonly binocular spheres, can then be used to realign the markers; this is considered to be the associated phoria. Mallett39 originally advocated that the full amount of aligning prism should be prescribed to relieve the symptoms of the decompensating heterophoria. However, it was later suggested that 1∆ in pre-presbyopes and 2∆ in presbyopes was unlikely to be symptomatic.40 In addition, previous aligning prisms that have been measured in a patient, at a time when symptoms were not present, should also be considered, so as not to prescribe more prism than is necessary. Results from the Mallett unit should be used in conjunction with other tests to aid diagnosis and management.

StereopsisThere are a number of stereopsis tests available for use in optometric practice and they allow a practitioner to establish whether BSV is present and also the quality. Stereopsis tests can be divided into two groups: global (random dot) and

local (contoured), with the exception being the Randot Stereo Test, which incorporates both. Local tests such as the Titmus Fly use simple contoured targets that are displaced to give a disparity of depth but suffer from monocular clues which have been reported with the Titmus circles,42 and Random Dot E stereotest.43 Global tests, such as the TNO random dot stereograms and Lang, rely on larger more complex patterns of random dots, which are displaced in relation to each other. Being truly binocular tests, global stereopsis tests are more affected by amblyopia and strabismus,41 thus identifying such conditions more accurately.

ConclusionAll patients undergoing an eye examination, regardless of their

presenting symptoms, should receive an assessment of binocular vision. Cover test and ocular motility should be conducted to determine the presence of either a manifest or latent deviation and to explore the possibility of an incomitant deviation. Incomitant deviations are likely to present with sudden onset symptoms, requiring prompt investigation, or possibly long-standing problems with symptoms that have arisen recently because the deviation has decompensated. Concomitant manifest deviations in adults are likely to be asymptomatic due to the development of either suppression or ARC and several tests may need to be conducted to confirm this.

about the authorLynne Weddell is senior lecturer at City University, London. She is joint Module co-ordinator for Binocular Vision and Paediatric Optometry as well as the paediatric clinic manager. Previously she was senior lecturer at the Institute of Optometry and she has also worked within the hospital eye service in paediatric and visual impairment clinics.

ReferencesSee www.optometry.co.uk and search ‘references’.

MSc in Clinical OptometryCITY UNIVERSITY and OT have joined forces to allow readers to achieve CET points through to a full Masters in Clinical Optometry. MSc courses running at City University include: Principles of Therapeutics (apply anytime – web-based), Independent Prescribing (September 2011), Glaucoma (July 2011), Principles of Prescribing (February 13 – 15 2011)and Binocular Vision (November 14-16 2010). For further information please contact Dr Michelle L Hennelly by emailing [email protected] or call 0207 040 8352.

Figure 8 Possible responses with the Bagolini lens test. (a) Image seen by right eye, (b) Image seen by left eye, (c) Bifoveal fixation or manifest deviation with anomalous retinal correspondence (ARC), (d) Central suppression in left eye, (e) Global suppression, (f) Manifest deviation with unharmonious retinal correspondence (UHRC) or NRC

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1. Which of the following statements is FalSE?a) The cover test enables a practitioner to differentiate between latent andmanifest deviationsb) Base in prism is used to neutralise a divergent deviation on prism cover testc) A common cause of a headache is an anomaly of binocular visiond) Measuring fixation disparity is a test of sensory status

2) Which of the following techniques can be used to measure the angle of deviation in a blind eye?a) Prism cover testb) Maddox rodc) Hirschberg testd) Double Maddox rod

3) during the Hirschberg test it is noted that the reflection is central in the right eye but is 1mm nasal in the left eye. What is the most likely estimate of the angle of deviation?a) 20∆ right esotropia or 20∆ left esotropiab) 20∆ right exotropia or 20∆ left exotropiac) 20∆ right exotropia or 20∆ left esotropiad) 20∆ right esotropia or 20∆ left exotropia

4) a patient has a right hypertropia, which is greater on left gaze and decreases when the head is tilted to the left shoulder. Which extraocular muscle is most likely to be affected? a) Right superior obliqueb) Right inferior rectusc) Left superior obliqued) Left superior rectus

5) Which of the following tests will be MOST accurate in measuring the angle of a latent deviation in a five-year-old child?a) Prism cover testb) Krimsky testc) Maddox rodd) Hirshberg test

6) Which of the following statements about prism fusion ranges is TRuE?a) They are larger at distance rather than at nearb) The vertical range is increased with a long-standing IVth verve paresisc) The convergent range is greater at distance than at neard) Blur is often reported when the divergent range is measured

7) Which of the following tests does NOT assess global stereopsis?a) TNO stereotestb) Titmus Fly Wirt Circlesc) Randot stereo testd) Lang

8) Which of the following statements regarding the aC/a ratio is FalSE?a) The normal ratio is 3 – 5∆b) It remains static from childhood to presbyopiac) It might be significantly increased in convergence excess esotropiad) It is higher when measured by the gradient than heterophoria method

9) Which of the following statements about the assessment of accommodation is TRuE?a) In the Nott method, if a “with” movement is noted the practitioner should move closer to the patient to neutralise itb) A greater lag of accommodation will be found with the Nott method than with the MEM techniquec) The MEM method is more accurate in young adultsd) Accommodative lead may be associated with binocular dysfunction

10) Which of the following is TRuE about the 20∆ base out test?a) It is better to use at distance with young childrenb) Failure of one eye to make a compensatory movement may indicate suppressionc) When placed in front of the right eye, the right eye should abduct then adductd) When placed in front of the right eye, the right eye should adduct then abduct

11) a near prism cover test reveals 8∆ esophoria. With + 2.00 lenses, the measurement changes to 2∆ exophoria. What is the aC/a ratio?a) 10 dioptresb) 8 dioptresc) 5 dioptresd) 3 dioptres

12) a child views a near target at 25cm, and the reflex on retinoscopy is neutralised at 40cm. What information does this give you about the accuracy of accommodation?a) 1.50D lagb) 1.50D leadc) 2.50D lagd) 2.50D lead

Module questions Course code: C-15084 O

PlEaSE NOTE There is only one correct answer. all CET is now FREE. Enter online. Please complete online by midnight on december 15 2010 - You will be unable to submit exams after this date – answers to the module will be published on www.optometry.co.uk

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