Routine Eye Examination

CET Continuing education Routine eye examination Part 3 – Binocular assessment In the third part of our series on the eye examination, Andrew Franklin and Bill Harvey look at the assessment and interpretation of binocular status. Module C8290, one general CET point, suitable for optometrists and DOs

he assessment of binocular previous question. Leading questions function is often one of the should be avoided, especially when weaker areas of a routine, dealing with children. If they are out if observation of candidates of line ask the patient ‘Which one is out in the professional qualifica- of line with the X?’ Ttions examination is any guide. Tests are You should know before you start the done for no clearly logical reason, often test which line is seen by which eye. because they always have been, and in If you cannot remember it from last an order which defeats the object of the time, simply look at the target through testing. Binocular vision seems to be one the visor yourself (Figure 1). Even if of those areas that practitioners shy away you think you can remember, check from, and students often take an instant anyway, as it is possible for the polarisa- dislike to. Many retests and subsequent tion of the visor not to match that of the remakes of spectacles are the result of a Mallett Unit at distance or near or both, practitioner overlooking the effects of a Figure 1 A distance fixation disparity target especially if the visor is a replacement. change of prescription on the binocular If both eyes can see both bars, nobody status of the patient. before the assessment of fixation dispar- will have a fixation disparity. Under no It would be useful to define what it ity. This is particularly important if the circumstances cover one of the patient’s is we are trying to determine: patient has been dissociated recently, as eyes and ask ‘Which line can you see ● Does the patient have a squint or a they always will be during an examina- now?’ This is dissociation. phoria? tion. Taking monocular acuities, retin- Following this, ask ‘Is it to the left ● If they have a phoria, is it oscopy, ophthalmoscopy and so on will or to the right?’ or ‘Is it towards me compensated? all disrupt the binocular status. It should or away from me?’ With children, the ● If they have a binocular problem, is it be remembered that the polarised visor latter question may be more sensible, going to need referral or management? used significantly reduces light levels as they tend to confuse their lefts and Tests of motor function can be and illumination should be adjusted rights on occasion. divided into ‘binocular’ tests which accordingly. The minimum prism (to the nearest maintain fusion (for example, fixation Before applying the visor, the patient ½∆) or alteration in the spherical disparity) and those which dissociate should be asked: ‘Are the two red (green) element of the Rx which aligns the the eyes (such as cover test and the lines exactly in line with each other or polarised lines should be noted. Maddox rod). As a general principle, are they out of line?’ It is surprising how When assessing fixation dispar- binocular tests should always precede often a patient will report displacement ity for near, don’t be restricted to one dissociation tests. In practice, this is of the lines even without the visor. Are target position. Many patients read or often reversed and frequently patients they trustworthy observers? Do you look at computer screens in a variety of are tested for fixation disparity having want to prescribe on their subjective positions. Many patients have ‘A’ and ‘V’ been thoroughly dissociated before, and response? patterns and it doesn’t take long to check in some cases, during the test. The odd Having established that the patient is if the patient is still compensated when false positive might be expected in these not likely to lead you astray, repeat the the eyes are elevated or depressed. cases. Until you have done a cover test, you won’t necessarily know what the Fixation disparity Product list fixation disparity findings mean. No slip Method These are some of the UK suppliers of found on a patient with a phoria would The fixation disparity test is often instruments needed for binocular assessment indicate that the phoria is compensated, performed in such a way as to render at least for the moment, but the same it worthless. Even the wording of the ● Haag Streit (Clement Clarke) finding on a strabismic subject would instructions and questions to the patient ● Birmingham Optical Group (Nidek) indicate harmonious anomalous retinal can affect the chances of finding a ● Buchmann UK correspondence. Small degrees of slip fixation disparity, particularly in ● Grafton Optical usually point towards an uncompen- children and the more literal minded ● Institute of Optometry sated phoria, especially if there are adult. This test should ideally precede ● Keeler symptoms, but a larger slip may be any dissociation test. ● Norville associated with microtropia. Binocular vision should be stabilised, ● Sussex Vision Sometimes the slip seems to vary at by reading a line of letters or words random, and the markers may oscillate

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across the neutral point. This is indicative of binocular instability. The condi- tion is associated with uncompensated heterophoria and the fusional reserves tend to be low. In general, if you keep adding small amounts of prism or sphere the slip will stabilise.

Cover test The cover test is essential, being the only way to tell squints and phorias apart. It can also be used to estimate or measure the direction and size of the deviation and to indicate whether a phoria is compensated or not. Figure 2a Looking behind an opaque Figure 2b Transparent occluders help visualise eye There is a certain amount of confu- occulder is useful movements behind the cover sion about the cover test, partly arising because it tends to be taught in a module 6/18, a spotlight may be used. Note that Multiple positions of fixation may be labelled ‘binocular vision’ and often this is a non-accommodative target. The useful to investigate incomitancy. based on orthoptic practice rather than reason for using it is that the angular When examining myopic patients the needs of a routine eye examination. subtense of letters larger than 6/18 is without their spectacles it should be While there is considerable overlap, the large enough to significantly distort remembered that unaided distance two have different goals and require- the results, particularly when looking vision below 6/60 does not mean that ments. In a routine eye examination at small vertical elements. However, a non-accommodative target should be we are screening a normal population many practitioners find there is still used at near. Many myopes habitually for those individuals whose motor or more eso-deviation when a letter target read without spectacles at a non-stand- sensory status requires intervention. In is used. If in doubt, use both. ard distance, and most will be able to the hospital eye service, there is a greater The position of the target is impor- fixate an accommodative target for the need to classify and quantify so that the tant, particularly at near. The cover test near cover test. This applies to myopic effects of treatment may be recorded. should be performed with fixation at a presbyopes too. As this is an article about routine eye distance and position which is relevant examination, the approach will be to the patient and their habitual visual Occluder biased towards that. environment. There is occasionally a The occluder may be opaque or translu- tendency to perform the near cover test cent. Opaque occluders should be wide Target with the eyes level, in the same position enough to allow them to be angled so as The target should be accommodative that they were in when fixating a to allow observation of the eye under the (small enough for the hypermetrope distant target. This is fine if you want cover, while maintaining proper disso- to employ enough accommodation to to compare distance and near deviations ciation (Figure 2a). The latter allows us overcome their ametropia and hence while removing any variability that an to observe eye movements behind the reveal any eso-movement), so use a A or V pattern would induce. In other cover (Figure 2b) and is particularly letter slightly larger than the acuity of words, if you are trying to classify the helpful when trying to see dissociated the worst eye. If the target is too small, deviation accurately. However, we are vertical deviations. the maintenance of accurate fixation generally trying to find out what is The use of fingers, thumbs, hands is difficult. The patient may narrow happening while the patient goes about and so on should be avoided as adequate the palpebral fissure to see better, their daily business. dissociation may not be achieved. A making observation of the eyes diffi- When performing the near cover translucent or white occluder is an asset, cult. Occasionally ciliary spasm might test, it is a good idea to quickly check causing fewer pupil reactions which be triggered. if there are any significant variations can be distracting when looking at small If the acuity of the worst eye is below with elevation and depression of gaze. deviations.

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correction that the patient is currently wearing is allowing the patient comfortable vision, so checking both fixation disparity and cover test at any fixation distance relevant to the patient (includ- ing computer distance in many cases) would seem a good idea. You may also need to know what happens without the correction. It is usually worth checking for A and V patterns when you have the patient fixating a near target. If you change the prescription significantly during the routine, you should check if the change Figure 3 The RAF rule is lowered to aid convergence Figure 4 Motility has affected the binocular status. Remember that even small changes Occluders should ideally have no add nothing that you don’t already in refraction can affect ocular motor sharp corners. In most respects other know. If you are finding a different balance significantly, so even increasing than this a frame rule makes a good deviation with the alternate cover test, a reading addition by half a dioptre can occluder, but there is an outside chance you are not dissociating for long enough induce an uncompensated exophoria if of catching a lively patient in the eye. on the cover/uncover test. care is not taken. The subjective alternate cover (‘phi’) Technique test is a different matter. This can detect Maddox rod and wing The cover should be held over the eye deviations that are too small to be seen Maddox rod for five seconds, which is rather longer by the practitioner (typically less than This may be used to measure the devia- than initially feels right. Less may result 1Δ). One of the recurrent myths in tion either using prisms or a tangent in incomplete dissociation and an under- optometry is the one that says that devia- scale. Correlation with cover test results estimation of the deviation. It should be tions below 4Δ cannot be detected by is poor, probably due to the abnormal remembered that repeated testing may the human eye. visual environment generated by the increase the deviation through fatigue. This is nonsense, and the easiest way Maddox rod. The cover should be held close to the eye to prove this is to observe a subject It should also be remembered that the or dissociation may be incomplete. successively fixating test chart letters test uses a non-accommodative target. Cover the right eye and observe the of known separation. These are rarely It is said to measure the ‘total phoria’ left. If it moves to take up fixation there of much significance if horizontal, but though as long as the patient is alive is a squint. If it doesn’t move there is small vertical deviations are surpris- this is not so. It also generates numbers either no squint or a microtropia with ingly common and may be a pointer without requiring any observation identity. Uncover the right eye, still towards incomitancy. skills. It is useful to identify and measure watching the left. If it moves now, two To do this, alternate the cover between small deviations (particularly vertical things are possible. If it moved to take the two eyes, and ask the patient if the ones) and to investigate incomitancies. up fixation when you covered the right target is moving at all. If it is, determine In routine refraction its use is rarely eye, it is a squint and it is now moving whether it moves in the same direction justified since it adds no new informa- back into its customary position. If there as the cover, which indicates exophoria, tion to that found with the cover test was no movement of the left eye when or in the opposite direction, as it would and it usually seems to constitute a box- you covered the right, you are seeing a with an esophoric patient. If there is a filling exercise. ‘Hering movement’ and the patient has vertical movement, it is time to use the central suppression in the left eye. Maddox rod. Maddox wing If no movement is seen in the left eye, This is a convenient test for measure- cover the right eye again but watch the Measurement ment of the deviation, but correlation right eye under the cover this time. If it This may be achieved with loose prisms with cover test results is poor and corre- moves out, the patient has an exophoria. or a prism bar, but this is rarely neces- lation of either with symptoms as bad. If it moves in, they have an esophoria. sary in routine examination. Estimation As the cover test is always done it is If it goes down, they have a hypophoria. is accurate enough with practice unless questionable whether this test yields Should it go up, they may have a hyper- surgery is contemplated (unlikely in any essential information most of the phoria or a dissociated vertical devia- routine practice). To practise, a tangent time. tion, or both. If it is a right hyperphoria screen is useful, but not essential if The target is set at 30cms which is too the left eye will move down when it is you are able observe a subject fixat- short for anyone over 5 foot tall, and the covered, and back up again when it is ing successively two targets of known scale is a poor accommodative target. uncovered. Uncover the right eye, and angular separation. At 6m, separation watch it. It should be seen to move back of 12cm corresponds to 2Δ (this is about ‘Flash’ Maddox test to fixation. If it doesn’t, the patient may the width of the 6/9 line on a standard This is basically a cover test which uses have dissociated and broken down to a Snellen chart), 24cm corresponding to the tangent scales of the Maddox rod squint. Repeat the above, covering the 4Δ and so on. or wing to measure the deviation, as an left eye. alternative to prism measurement. The The objective alternate cover test is How many fixation disparity eye fixating the streak, or the arrow of often employed to investigate phorias. If tests/cover tests should I do? the wing test, is covered. The patient is you are dissociating the patient properly It depends what you need to know. instructed to tell you which number the during the cover/uncover test, it will In general, you want to know if any streak or arrow is pointing to immedi-

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Positions of gaze

RSR RIO LIO LSR RLR RMR LMR LLR

RIO RSO LSO LIR

R = Right LR = Lateral rectus L = Left MR = Medial rectus SR = Superior rectus SO = Superior oblique IO = Inferior oblique IR = Inferior rectus

Figure 5 A ‘star’ pattern and the muscles acting in each direction Figure 6 Titmus (Wirt) ately after you remove the cover. This pia when dissociated, this should also is probably the most useful way to use You should always write something be noted. Maddox tests and it has been used in down in the records. research. ● If there is no anomaly write FULL Jump convergence AND NORMAL Jump convergence is useful, especially Convergence ● If an anomaly is present, record in those who need to change fixation The RAF rule is the usual tool, but which eye is affected, and in which frequently. The patient is asked to fixate any thin vertical line will do, as will a position(s) of gaze in turn on distant and near targets and to single letter on a budgie stick. The end ● If you can, work out which muscle is report any diplopia. Voluntary conver- of the instrument nearest to the eyes palsied, and write it down gence is almost exclusively activated by should be supported by the patient to this test. ensure that it cannot slip and catch the eye. Care should be taken that often more remote in tall patients or Accommodation the rule is angled slightly downwards those with long working distances. This will be discussed in a later article on rather than perpendicular to the face or This test activates both voluntary and near corrections, though it is frequently higher as the eyes usually look slightly reflex convergence. investigated along with near point of down when converging, and most The practitioner should watch the convergence. patients find convergence easier with eyes, rather than relying on the patient some depression of the eyes (Figure to report diplopia. Sometimes conver- Motility 3). However, there are exceptions to gence breaks but the patient does not Target both of these statements. Computer report diplopia. This may simply be The ideal target is a pen-torch, used operators may need to converge with down to wandering attention, but it unfocused, and preferably not too bright, their eyes level or elevated, and those could also indicate suppression. The held as demonstrated in Figure 4. Too with A patterns may be happier in this eye doesn’t necessarily always deviate bright a torch may cause spontaneous position. The target is moved slowly outwards. Patients with esophoria and dissociation, especially in exophores, towards the patient and the patient is a high AC/A ration will over-converge. and avoidable discomfort. asked to report when the target goes The near point of convergence should Paradoxically, cheaper pen-torches double (normally 8-10cms). The target be recorded in centimetres, along with obtainable from market traders are often is then withdrawn until recovery which eye deviated and in which direc- the best, and they are cheap enough occurs (10-15cms). The near point is tion. If the patient does not report diplo- to be lost without pain. The pen-torch

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allows us to see a reflex on the cornea Titmus (Wirt) (Figure 6) The pictures go from 1,200 seconds to which may help to decide if both eyes This is supposed to be performed at 550 seconds of arc on the Lang I card, and are fixating the target. This is particu- 40cms but the actual testing distance from 600 seconds to 200 seconds on the larly useful when the visual axis of one depends on the length of the patient’s Lang II. Failure indicates the presence of of the eyes is intercepted by the patient’s arms. The patient wears polarising a clinically significant anomaly which nose. Under such circumstances we are spectacles. It can measure stereoscopic should be followed up. effectively performing a cover test and acuity up to 40 seconds of arc. It also the patient’s phoria will be expressed. features grosser tests for children (The Frisby Unless we know that one of the eyes animals go down to 100 seconds) but This consists of random-dot patterns cannot see the target, it is possible that many quite young children can be tested on plastic slabs of varying thicknesses, we might misinterpret the deviation with the main rings. Those new to the which should be viewed against (and as being due to an incomitancy, rather test seem to work their way through the not too close to) a blank surface. Parallax than the relationship between accom- fly and animals just because they have clues are a problem unless the patients modation and convergence. a child sitting in their chair. The gross head is stationary and the test is difficult Some practitioners, however, do tests are not compulsory, if the patient to explain to under-fives. seem to carry this to extremes, turning can do the rings. It is important not to off the main room lights in order to see let the patient see the targets without Mallet unit the reflex better. It’s true you can see the the polarising visor as monocular cues This should be used in near darkness reflex very well, but little else is discern- are rather obvious on the first two rings and relies on a degree of patient under- ible. Keep the lights on, you are less and the animals. standing and compliance often not likely to miss something important. possible. For this reason, it is probably TNO only worth using if no other stereo test Method This is used at approximately 40cms is available, as patients tend to dissociate Instruct the patient to follow the target with the patient wearing red and green while using it. ● and report any diplopia or pain. The goggles. It can measure stereoscopic practitioner should rely on observa- acuity up to 15 seconds (but more ● This series is adapted from Eye tion of the patient’s eyes rather than usually 30 seconds) of arc. There are Essentials; Routine Eye Examination by patient reports, as the patient might also some gross tests for children. Andrew Franklin and William Harvey. be suppressing. The pattern used is of Elsevier Science. little consequence provided that it is Lang methodical. This is a grosser test, designed to be a ● Andrew Franklin works in private A ‘star’ pattern is typically used screening device for young children. practice (Figure 5) but the ‘H’ pattern or its variants are equally effective. Move the target slowly or you will not be able to Multiple-choice questions – take part at opticianonline.net interpret the movement of the eyes. If you think there might be an incom- Which of the following is not a What is a suitable time to occlude during itancy present but it isn’t an obvious 1dissociating test? 4the cover test? one, base your diagnosis on the cover A Cover test A As little as possible to minimise the test in different positions of gaze rather B Maddox rod dissociation than simple observation of the moving C Fixation disparity measurement B 1 second eyes. D Monocular acuity measurement C 5 seconds All eight diagnostic positions of gaze D As long as it takes to completely break down should be investigated, the straight up What might oscillating markers on the the binocular lock and down positions being used to look 2mallett unit indicate? for A and V syndromes rather than any A Lack of stereopsis If the eye move from one target to a specific muscle anomaly. B Uncompensated heterophoria 5second 12 cm apart, both at a 6 metre The eyelids should also be observed C Microtropia viewing distance, what eye movement will be as a narrowing of the palpebral fissure D Anomalous retinal correspondence required? may indicate the presence of Duane’s A 0.5 syndrome.Voluntary movements (as The eye behind the translucent cover B 1 opposed to the pursuit movements 3shoots up, both right and left. What C 2 used in motility) may be checked during might this indicate? D 5 ophthalmoscopy. It is possible for one to A Dissociated vertical deviation be normal and the other not. B Right hyperphoria What might be the expect distance at C Right hypertropia 6which a target moving towards the face Stereoscopic acuity D Microtropia becomes double? This is an indication of binocular- A 0cm ity. Where visual acuities are good B 5cm and equal, stereoscopic acuity should C 8-10cm be good, even in pre-school children D 10-15cm (although with these patients it may be more difficult to demonstrate). Poor To take part in this module go to opticianonline.net and click on the Continuing Education stereoscopic acuity in patients with section. Successful participation in each module of this series counts as one credit towards good visual acuity is indicative of poorly the GOC CET scheme administered by Vantage and one towards the Association of compensated ocular motor balance. Optometrists Ireland’s scheme. The deadline for responses is February 14 Useful tests include:

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