Continuing education CET Part 5 – Binocular sensory status and miscellaneous tests In the latest addition to our occasional series on the assessment and management of binocular vision in practice, Priya Dabasia looks at sensory status and its measurement. Module C16058, one general CET point for optometrists and dispensing opticians

he preceding accounts in ● Confusion – the superimposition this mini series of binocular of two dissimilar images in higher vision (BV) testing have processing, experienced predominantly detailed procedures for on observing complex scenes such as ‘a the (CT), ocular room’. The same patient is more likely motility and heterophoria to report on viewing a small, Tcompensation. The final two articles bright target such as a penlight aim to outline the assessment of ● Retinal rivalry – the observation binocular sensory status, and of alternating percepts or a combined convergence. ‘mosaic’ so that images from each eye Having two frontally positioned eyes are never seen simultaneously. separated by approximately 65mm enhances many aspects of our visual Anomalous retinal correspondence performance – a wide panorama, (ARC) is considered a more efficient higher acuity, and three-dimensional sensory adaptation to heterotropia as perception to a distance of 200 metres, occurs in localised zones provided both eyes are fully functional Figure 1 to the fovea of one eye corresponds to a rather than spanning the binocular and coordinated together. Anomalies Worth 4-Dot point temporal to the fovea in the other field. It facilitates a weaker form of of binocular function have often been test eye. In reality, BSV can still be achieved BSV, relieving diplopia while enabling described as ‘the hidden learning with misaligned visual axes provided a good level of depth perception of up disability’ as they impair academic the disparity occurs within the limits of to 100’’. ARC is believed to develop performance in young children, ‘Panum’s fusional area’; a horizontally from an abnormal enlargement of often resulting in a permanent visual oval group of retinal elements that foveal suppression in the deviated eye impairment when left untreated. increase in size with eccentricity from to encompass the image of the fixation Early detection, using appropriate tests the fovea. When our visual system is object. An alteration in correspondence and exercising proper management is subjected to undue stress such as in takes place so that the fovea of the fixing of paramount importance, but often decompensated heterophoria, the axes eye is now paired with a new parafoveal seen as a challenging aspect of daily may deviate outside Panum’s area, locus of the deviated eye. This change practice. resulting in one of the following: in common visual direction continues Binocular single vision (BSV) ● Diplopia – the perception of two across the retina so that a small area occurs when the image from each eye different, non-fusible images of the nasal to the fovea of the fixing eye now contributes to a single, common percept. object of interest as they stimulate the correlates with elements temporal to the It is considered in three grades: fovea of the fixing eye and parafoveal new extrafoveal point of the deviated ● Sensory – the ability to perceive elements of the deviated eye. Double eye. As a prerequisite to any sensory an image formed with each eye vision is generally experienced in later adaptation, the heterotropia must simultaneously life where the stability of BSV prevents present early, typically under the age of ● Motor – the facility to maintain suppression of one image six years when the binocular system is sensory fusion through a range ● Suppression – sensory adaptation amenable to change. It should also be vergence that develops in early onset conditions small in angle, unilateral and constant ● Stereopsis – the perception of depth up to the age of eight years to avoid in presentation, resulting in a higher based on binocular disparity. undesirable symptoms such as diplopia, prevalence of ARC in . by inhibiting the image of one eye To gain a more in-depth understanding, in favour of the fellow eye during Tests for sensory status it is necessary to appreciate the concept binocular viewing. In heterotropia, The most recognised tests for sensory of retinal correspondence, a function it tends to occur in larger deviations status are Worth 4-Dot, Bagolini of higher processing that takes place misaligned by greater than 40Δ. At the and the Modified OXO tests. Details at the visual cortex. Normal retinal onset, two suppression zones develop of procedures, how to interpret the correspondence is the most favourable at the fovea and fixation point of the results and suggestions of recording the condition in which the fovea of one deviated eye, eventually joining to findings are detailed in turn. eye corresponds with the fovea of span a larger area if left untreated. the other, sharing a common visual Suppression that swaps between the ● Worth 4-Dot test – a dissociative direction during binocular viewing. eyes such as in alternating heterotropia test comprised of four circular lights in This correlation continues for every can also be described as ‘complete’ or a diamond formation viewed against a locus of the retina so that a point nasal ‘total lack of retinal correspondence’ black-grey surround (Figure 1). The test

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Patient response Observation Diagnosis/recording ‘Four lights’ NRC or ARC • One red • Two green • Bottom light – yellow mixture, red or green ‘Five lights’ ‘Five lights’ with Esotropia with • Two red lights on • Three green on heteronymous ‘crossed’ homonymous the left the left diplopia ‘uncrossed’ diplopia • Three green lights on • Two red lights on the right the right

‘Five lights’ L/R with vertical diplopia • Two red lights above • Three green lights below

‘Three green lights’ ‘Two red lights’ Right suppression Left suppression

‘Lights changing between 2 and 3’ Alternating suppression

Figure 2 A summary of patient responses and interpretation of the Worth 4-Dot test it perceives a vertical streak, while the fellow eye observes the spotlight. For can be wall-mounted, arranged over the demonstration purposes, two Bagolini glass plate of a flashlight for near testing lenses have been used to illustrate the or displayed on a computerised chart results in Figure 4. This arrangement such as Test Chart 2000. Red-green is also vital for investigating alternating goggles are used to separate the images heterotropia. of each eye – the right eye observing c) Direct the patient to fixate on a through the red filter perceives the top spotlight held 33cm from the eyes red circle, while the left eye views the d) Ask the patient to report the number two central green circles. The bottom of lines and spots seen, their relative white target provides a fusional stimulus positions and whether any gaps are for binocular viewing as it is common perceived along the streaks to both eyes, perceived either as a yellow e) Repeat for 3m and 6m as required mixture, red/green depending on ocular using a Grade 4 lens at far distance dominance or an alternation of the two to produce a brighter streak for colours in retinal rivalry. easier viewing, reducing the room a) Place the R/G goggles over any near Figure 3 Bagolini lens illumination accordingly. spectacles, taking care that the target is not seen without these filters detecting central suppression and is ● Modified OXO test – a near Mallet b) Turn the room lights off more conducive to natural viewing unit test comprised of two green strips c) Hold the flashlight 40cm from the through minimal dissociation as it is positioned above and below the ‘X’ of an patient’s eyes just below the horizontal performed under ambient illumination. OXO panel (Figure 5). It is essentially midline to mimic the reading position. It is also a perfect illustration of the cost a larger version of the disparity test, Check it is correctly oriented with the efficiency of BV tests – a lens can be as smaller markers are more likely to red and white circles at the top and ‘created’ by smearing the surface of a fall into a central suppression zone, bottom respectively low power trial lens with a finger using rendering it unsuitable for detecting d) Ask the patient to report how many Vaseline or any suitable alternative to ARC and global suppression. dots they see, confirming the colours mimic the Bagolini striations. a) Ask the patient to hold the unit at and relative positions of each. Possible a) Clean a Grade 2 Bagolini lens with their normal reading distance and angle outcomes are illustrated in Figure 2 a microfibre cloth to avoid more than of viewing e) Repeat the test for distance fixation one image being perceived b) Direct the patient to fixate on the with any required spectacle correction. b) Position one lens in front of each Modified OXO target eye with the striations at 45° and c) Position the cross-polarising ● Bagolini test – a lens made up of 135°, either mounted in a lorgnette or visor before the eyes, over any near fine parallel striations that distort placed in a trial frame with refractive correction a spotlight target into a line image correction as required. The test can also d) Ask the patient to report the number perpendicular to their axis (Figure 3). be conducted with the lens oriented of strips perceived and their relative It supersedes the Worth 4-Dot test in horizontally before one eye only so that positions. The responses of patients

16 | Optician | 11.03.11 opticianonline.net Continuing education CET

Patient response Observation Diagnosis/recording ‘One spotlight with two lines’ – lines inter- NRC sect at the middle of the light with no gap

‘One spotlight with two lines’ – lines inter- ARC with central suppression sect at the middle of the light with gap in one line around the central spotlight

‘Two lights with two ‘Two lights with two Exotropia with Esotropia with homonymous lines’ – separated lines’ – separated heteronymous ‘uncrossed’ diplopia horizontally, crossing horizontally, crossing ‘crossed’ diplopia below the central above the central point point

‘Two lights with two lines’ – separated Hypertropia with vertical diplopia vertically crossing at the side

‘One light with one line’ R or L suppression or ‘One streak lighter than the other’

Figure 4 A summary of patient responses and interpretation of the Bagolini test the non-suppressing eye. The depth of of the same object. It is often described absorption is increased incrementally as the ‘thermometer of BV’ since any with heterotropia are summarised in until diplopia is reported or in the reduction is indicative of a recent- Figure 6 case of the Bagolini lens test, a light onset anomaly. Some practitioners also e) Repeat the test for far viewing by streak is perceived by the previously use it as an indirect measure for foveal directing the patient to observe the suppressed eye. suppression as the highest stereoacuity distance FD target at a reduced distance can only be achieved with both central of 1.5 metres. Stereopsis and peripheral fusion. For this reason, Further testing to rule out a smaller Once the basic grades of BSV have it serves as an ideal screening tool for zone of suppression can be evaluated been established, it is now prudent BSV in children as young as six months using the Foveal Suppression Test also for the examiner to evaluate the of age. Rudimentary depth perception found on the near Mallet unit. quality of stereopsis, defined as the can be demonstrated from 3-4 months On detecting suppression using perception of depth based on the although synaptic connections continue any of the three tests described, horizontal disparity of visual axes to optimise up to two years after birth. the level can be quantified using a within Panum’s fusional area, as each As a guide, stereoacuity of 40’’ or neutral density bar held in front of eye receives a slightly dissimilar view better is considered normal, while any

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measure less than 60’’ is suggestive of perception of the ‘hidden’ horizontally inaccurate bifoveal fixation. disparate images. More responsive The range of tests at your perusal children can be asked to name or point varies widely in both design and grading at the objects. levels (Figure 7). The ideal test should be devoid of any monocular cues such ● Frisby test – the only test based on as ‘relative size’ that also contribute to ‘actual depth’ as it employs two Perspex the patient’s perception of depth. Each sheets printed with random patterns of of the tests outlined is undertaken with shapes, separated by 1mm, 3mm and the patient wearing their appropriate 6mm. Each plate is held against a white spectacle correction wherever possible, background at a distance of 40cm, with the target held perpendicular to with the option to evaluate crossed or their line of sight. Any external light uncrossed disparity by reversing the source must be adjusted to ensure even orientation accordingly. Begin with the illumination removing any shadows 6mm plate, asking the patient to identify or glare to facilitate natural binocular the position of the hidden circle from viewing. The Lang and Frisby tests the four boxes. Rotate the plate out of are particularly useful for screening the patient’s view and repeat the test children under the age of four years as Figure 5 Modified OXO test of the near Mallet unit for verification. If the patient responds they do not require goggles to be worn. correctly, use the 3mm and 1mm plates A summary of the five tests is provided of the picture viewed by each eye. The in turn to determine the highest level in Figure 8. Lang II integrates a monocular ‘star’ of stereoacuity. Theoretically, any level to attract the child’s attention when of stereopsis can be evaluated using ● Lang I and Lang II tests – a test viewed at the designated distance of different permutations of plates and card comprised of a series of cylindrical 40cm. The practitioner observes the testing distances. gratings superimposed on a random child carefully for fixation movements dot image that creates two fine strips or ‘grab responses’ that indicate ● Titmus test – also known as a Polaroid Vectograph where crossed polarised filters mounted in goggles are Patient response Observation Diagnosis/recording used to separate the images received by ‘Two markers approximately ARC each eye. The visual task is comprised in a straight line with the of two superimposed patterns polarised central X’ 90° to one another and horizontally Patients may report the marker O X O separated in areas to create crossed and of the deviated eye to be a uncrossed disparities. The Vectograph ‘different size, misaligned or is divided into three sections: dimmer’ relative to the other – ‘Fly’ target: indicates gross stereopsis strip in young children asked to ‘catch its ‘One marker ‘One marker R suppression L suppression wings’ above and in below and in of the of the – Animals: measures three levels of line with the line with the binocular field binocular field O X O O X O crossed disparity by identifying the central X’ central X’ creature that appears to ‘jump out of ‘One marker temporarily Intermittent R or L suppression its box’ in each row disappears’ – ‘Wirt test’: a series of nine targets used to grade finer levels Figure 6 Interpretation of Modified OXO test in a patient with heterotropia using a standard British of stereoacuity by recognising the standard Mallet unit circle in the diamond of four that is perceived in depth.

● TNO test – the only test completely devoid of monocular cues, based on a series of randomly generated red and green dots. Certain aspects are horizontally disparate, thereby perceived in depth when viewed through the appropriate red and green goggles as follows: – Plates 1-3: used for quick screening in which the patient identifies the correct pattern or shape – Plate 4: suppression test consisting of three discs; the central target is seen with both eyes while the outer discs with one eye only – Plates 5-7: designed to grade higher levels of stereoacuity using a series Figure 7 Stereopsis tests: Frisby plates (left) and Titmus fly test of circular targets with a missing

18 | Optician | 11.03.11 opticianonline.net Continuing education CET

Name of test Method of separating images Working distance Level of stereoacuity Other details seen by each eye Lang I • Cylindrical gratings (24 per cm) 40cm Cat - 1200’’ • Monocular cues present if card is superimposed on a series of Star - 600’’ tilted relative to the line of sight random dots Car - 550’’ • Ideal for screening in young children Lang II Moon + Star - 200’’ • No goggles required Car - 400’’ Elephant - 600’’ Frisby • Random patterns of shapes Variable 40cm – 80cm 600’’ - 15’’ • Monocular cues apparent with printed on perspex sheets movement of the patient’s head separated by 6mm, 3mm + 1mm and/or plate, or if held at an oblique angle • No goggles required Titmus • Superimposed images polarised 40cm Fly – 4000’’ • Strong monocular cues with 90 degrees to one another Animals – 400’’-100’’ horizontally separated images Circles – 800’’-40’’ evident without goggles • Cross polarised filter goggles required TNO • Red/green randomly generated 40cm Plates 1-3 – screening • Devoid of monocular cues dots with areas of horizontal Plates 5-7 – 480’’ – 15’’ disparity

• Red/green goggles required

Figure 8 A summary of the main stereopsis tests used in practice

quadrant. The patient is asked to find ‘the missing piece of the pie,’ Multiple-choice questions – take part at opticianonline.net allowing time for a second attempt if an incorrect response is given at the Which of the following statements is On conducting the Bagolini test with a first effort. Each grade is comprised 1TRUE? 4lens positioned before each eye at 45° of two targets so that if one is resolved A Stereopsis is defined as the perception and 135°, the patient reports seeing ‘two inaccurately, the stereoacuity is of depth based on horizontal and vertical lines and two spotlights crossing above the recorded as the previous level where disparity central point’. Which of the following is the both responses were correct. B Sensory status is the ability to maintain most likely diagnosis? The practitioner also has the option fusion through a range of vergence A Exotropia with homonymous diplopia to evaluate lower levels of depth C Stereopsis is the highest indicator for B Esotropia with heteronymous diplopia perception by doubling the testing binocularity C Esotropia with homonymous diplopia distance from 40cm to 80cm so that a D Motor status is the weakest indicator for D Hypertropia with diplopia target of 2,000’’ becomes 1,000’’. binocular function When recording the results, it is Which of the following is NOT an indicator crucial that the name of the test is Which of the following tests for binocular 5of suppression? detailed alongside the stereoacuity in 2sensory status is considered the least A A stereoacuity of 50’’ using the TNO seconds of arc. The sensitivity has been conducive to natural binocular viewing? stereotest found to vary significantly whereby A Bagolini lens B A ‘gap’ in the line image around the central B Modified OXO point in the Bagolini test a 480’’ measure using the TNO test C Frisby C Disappearance of the top nonius marker of equates to 200’’ on the Lang card. If D Worth 4-Dot the fixation disparity test you do not have a stereopsis test at D A ‘jump’ in the vertical line to the left at the your disposal, the Lang 2 pencil test Which of the following statements is break point on measuring NPC using an RAF can be used to establish rudimentary 3FALSE in consideration of ARC? rule depth perception. Patient responses are A The fovea of one eye corresponds to a compared with one eye covered and non-foveal area of the deviated eye Which of the following tests would be both viewing when asked to place a B At the onset a suppression zone develops at 6your ideal choice to assess stereoacuity pencil vertically on top of another held the fovea of the fixing eye in a two-and-a-half-year-old? stationary below. A similar response C It is more likely to present in early-onset A TNO Plates 5-7 indicates suppression and a lack of esotropia B Lang II card stereopsis. D It gives rise to moderate to good stereoacuity C Lang 2 pencil D Wirt Polarised Vectograph ● The final part of this series will look at the measurement and interpretation of convergence.

● Successful participation in this module counts as one credit towards the GOC Priya Dabasia is a clinical optometrist CET scheme administered by Vantage and one towards the Association of at the Fight for Sight Optometry Clinic, City Optometrists Ireland’s scheme. Deadline for responses is April 7 2011 University and Moorfields Eye Hospital

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