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Seeing double: managing patients with diplopia: This article discusses the options for managing patients presenting with diplopia in routing practice.

Optometrists [??]

Dispensing opticians [??]


Managing patients suffering from diplopia can be challenging. Once active neurological or ocular diseases have been ruled out, optometric management can be started, which may include correcting the underlying refractive error, prescribing prisms, providing occlusion, or performing vision therapy (VT).

The first stage of management is to establish and remove the cause of diplopia, referring the patient to an ophthalmologist or neurologist where indicated. Following this, optometric treatment should be performed as soon as possible to improve the outcome for the patient

Refractive error

The goal of optical correction is to improve the quality of the retinal image by correcting the underlying refractive error in order to increase binocular fusion ranges. It is usually the first step in managing patients affected by diplopia. Even small refractive corrections can improve binocular control. (1) Correcting hyperopia or myopia can help to compensate for esophoria and exophoria, respectively. In patients with diplopia as a result of anisometropia, contact lenses can reduce the impact of aniseikonia and differential prismatic effects, helping to enable fusion.

Refractive errors can be also modified to alter the accommodative-convergence link. In hyperopic patients with decompensated esophoria, the maximum plus should be prescribed to compensate for the esophoria. Furthermore, a positive addition may be considered for near tasks in the form of bifocal or multifocal lenses where there is poor control of deviation at near. VT should also be considered as the power of these lenses is gradually reduced while the patient improves their control of the deviation. When the patient is myopic and exophoric, correction of myopia usually restores the normal accommodative-convergence link. However, in cases where an exophoria remains decompensated with full correction, a myopic overcorrection can be considered if the patient has adequate accommodative amplitude (see Figure 1). A negative addition of up to -3.00D can be prescribed and gradually reduced as control improves with the help of VT. (1)


Prisms are usually recommended for treating symptomatic binocular diplopia. They alleviate diplopia by altering the path of light rays and aligning the image on the fovea of the deviating eye. (2,3) The aim should be to provide the minimum prism that results in measurable improvement in binocular function on clinical tests of fusion; thus, the minimum amount of prism for stable fusion in free space at far and near. (4) The practitioner must consider the potential negative effects of prism adaptation as the patient may 'eat up' the initial amount of prescribed prism and require even greater amounts to manage their symptoms. (5) In patients suffering from diplopia due to ocular motor disorders, some suggest prescribing unequal amounts of prism with more given to the affected eye. (6) In patients with decompensated heterophoria at near, the Mallett unit fixation disparity test can be useful to determine the minimum prism correction required. Ideally, patients should try the prism in the practice with a Halberg clip, using Fresnel prisms from trial sets; these are available with or without handles in the power range from 2 to 40A.

Using the trial prism in the practice, the patient should be involved in activities for at least 20-30 minutes, after which the practitioner can check if the prism amount and direction is stable. If the alignment measures seem to be changing, the optometrist may consider modifying the prism amount. Before prescribing the final prism, it is also possible to extend the trial period by affixing a Fresnel prism to the patient's spectacles and rechecking a few days later. Yoked prism can be prescribed to reduce extraocular muscle contracture in patients with incomitant strabismus, or applied during the ocular calisthenics exercises.

When yoked prisms are prescribed, both prisms are oriented with the base in the same direction. (7) For instance, base left refers to a prism where the base is oriented to the patient's left side; the left eye prism base orients temporally while the right eye prism base orients nasally.


Where prismatic correction is unsuitable, occlusion may be considered using a patch on the skin or on the spectacle lens (see Figure 2), or by fitting a full occlusive contact lens. Unfortunately, using a patch or a full occlusive contact lens is particularly disadvantageous due to a loss of visual field. Nevertheless, in cases where occlusion is required, the weakest density Bangerter filter that alleviates symptoms in adults with untreatable diplopia should be prescribed. (8) Some advocate giving partial occlusion of the nonfixating eye rather than total occlusion in patients with diplopia. (9) The author suggests applying a 1cm circular cutout of translucent tape to the centre of the lens on the patient's non-fixating eye (see Figure 3). Partial occlusion using translucent tape covering one lens from the patient's nasal pupil margin to the frame's nasal rim can be considered, sparing the peripheral visual field. However, for therapeutic purposes, alternate full occlusion might reduce muscle contracture by forcing k each eye to attempt movement through its full range.

The patch or occlusion foil is usually placed over the patient's unaffected eye for some hours and then placed over the affected eye. In this way it is possible to avoid extraocular muscle contracture in the unaffected eye. Binasal occlusion with larger coverage over the healthy eye can be a solution for patients affected by lateral rectus palsy to encourage alternation and stimulation of the affected eye. By applying binasal occlusion, the amount of binocular visual input is reduced without decreasing the size of the entire visual field. Bitemporal occlusion, especially in elderly patients with medial rectus impairment, is not recommended as the partial patch may reduce the patient's peripheral vision and increase the risk of a fall. Fitting partially occlusive contact lenses (scotomatous contact lens) can be useful in neurological patients who complain of constant diplopia. (10) Bonci et al found that this type of intervention can be very effective at eliminating diplopia completely (see Figure 4). For untreatable diplopia, fully occlusive or a high plus powered contact lens might be considered. Monovision correction with glasses or contact lenses is another effective treatment to correct diplopia in adult patients with acquired small angle of strabismus (10[DELTA] or less). (11) Monovision requires using the distance correction in the dominant eye, and a +3.00 or +2.50 add in the non-dominant eye.

Vision therapy

VT has documented origins with orthoptic principles by the ophthalmologist Javal in 1865 and orthoptist Maddox in 1919., (12,13) Early pioneers such as Sheard, Percival and Skeffington also began their work in the early 1900s. (14) VT is considered as being an extension of traditional orthoptics. (15)

VT is a sequence of visually based activities to improve visual skills and processing. A typical VT program can include lenses, prisms and filters, along with special equipment and exercises that help to ameliorate the strength and effectiveness of the eye. In patients affected by diplopia due to extraocular imbalance VT aims to: reduce the muscle/s contracture and restore the normal muscle functionality in the paretic muscle/s; increase the range of fusion; increase the convergence and divergence range.

Ocular calisthenics exercises

Ocular calisthenics procedures can be applied in patients with incomitant strabismus to reduce muscle contracture in the paretic eye. It is crucial during ocular motor therapy that the patient has good feedback about what their body and head are doing while performing the task. (16) The patient is instructed to move the eye along the field of action of the muscle affected by palsy. The exercise is conducted monocularly, occluding the healthy eye, while the patient is asked to follow a wand. The practitioner can use either static or dynamic stimuli depending on the patient's ability. For example, in a patient with right cranial nerve (CN) VI palsy, the practitioner places different stimuli of varying sizes on the patient's right side. Starting with the largest target, the patient is instructed to look as far to the right side as possible and view the target. Once the patient has reached a good ability to detect the object on the right side, a Marsden ball (see Figure 5) can be used to extend the muscle's range of motion. The Marsden ball is made to oscillate along the field of action of the muscle affected by palsy. To increase the range of fusion, the targets are shown first where fusion is possible or easy to reach, and then targets are moved into the field of action of the affected muscle. Procedures to ameliorate the accuracy and speed of saccades, such as using a Hart chart can be considered in the VT program. A Hart chart consists of 10 columns of letters and each column contains 10 letters (see Figure 6). The training is performed at 3m from the chart. The patient is instructed to call out the first letter in column one and then the first letter in column 10, the second letter from the top in column one and the second letter from the top in column 10. The procedure is completed when the patient calls out all the letters from columns one and 10. The goal is to perform the task monocularly in 15 seconds. The optometrist should record errors made during the task. Asking to the patient to call out the letters in the inner columns increases the level of difficulty.

Reinforcement of fusion

VT using the binocular field can begin with peripheral fusion using vectograms or anaglyphs to improve fusion in individuals affected by incomitant strabismus. The patient is encouraged to be peripherally conscious and to appreciate the SILO effect (small--in, large out). As the disparity for an anaglyphic or vectographic target is increased, the crossed direction creates an image which appears paradoxically smaller, though it appears closer, and the uncrossed disparity image appears larger though it appears farther away. In practice, the author generally uses the OPT1 / fair, OPT2/circus and the OPT3/ stereo rope variable slides. The slides are used with red/blue-green goggles. The OPT1 (fair) slides are useful to improve flat fusion (see Figure 7). The OPT2 (circus) slides offer the possibility to stimulate stereopsis (see Figure 8). The different figures are printed with different prismatic values in base-out or base-in). The OPT3 (stereo rope) slides give an intense stereo-motivation and an increase of the accommodative stimulus while the patient tries to fuse the smaller figures (see Figure 9). The patient's dynamic fusional ability can be improved by performing exercises to increase both divergence and convergence demand. For this purpose, a Brock string can be very useful (see Figure 10). The string is held on the bridge of the nose, slightly below eye level while the opposite end of the string is tied to the door. The patient is asked to view a bead placed in an area where fusion is possible with only moderate effort. The practitioner subsequently occludes the normally deviating eye for one or two seconds and then removes the occlusion, instructing the patient to use peripheral awareness to obtain single vision. Once the patient achieves single vision quickly, the occlusion time can be increased. The same procedure is carried out in additional fields of gaze until fusion occurs quickly with minimum effort. This technique is then repeated in all remaining fields of gaze in which fusion is possible. However, if the patient is experiencing esotropia or exotropia, the bead should be moved inward (in case of esotropia) or outward (in case of exotropia) to seek a centration point. Once the centration point is found, patients with esotropia are encouraged to extend this range outward, while those patients affected by exotropia to reduce this range inward. In cases of vertical balance, patients may perceive the string as being on two different planes, one slightly lower then other. A small amount of vertical prism can be used to reduce vertical heterophoria or instructing the patient to tilt the head to orient the strings in the same plane. The patient then slowly reduces the head tilt while still attempting to maintain the strings in a level plane. Lifesaver and/or free fusion cards can be also added to the training programme to improve convergence and divergence ability (see Figure 11). The white card is useful to ameliorate convergence ability while the transparent card improves the divergence ability. Using the white card, a pencil is held centred between the bottom circles. The patient is instructed to look intently at the tip of the pencil and observe the circles on either side but without looking directly at them. The patient should continue to move the pencil and observe how the inner circles approach each other until they overlap and superimpose. At this point, they will then see three circles: one red; one green; and one in the middle under the pencil. At this point, the pencil is kept still and the patient is required to try to keep the circle in the middle clear, after which the pencil is removed. This procedure should be repeated at least three times a day. With the transparent card, a pencil is held behind the card, between the bottom circles. The patient observes the tip of the pencil, and as it is moved away, they should see three circles: one red; one green; and one in the middle. As with the white card, the patient is instructed to keep the middle circle clear.


Practitioners can play an essential role in rehabilitating patients with binocular vision anomalies to improve visual outcomes and the quality of life for these individuals.

Exam questions

Under the enhanced CET rules of the GOC, MCQs for this exam appear online at Please complete online by midnight on 23 August 2019. You will be unable to submit exams after this date. Please note that when taking an exam, the MCQs may require practitioners to apply additional knowledge that has not been covered in the related CET article.

CET points will be uploaded to the GOC within 10 working days. You will then need to log into your CET portfolio by clicking on 'MyGOC' on the GOC website ( to confirm your points.

* Fabrizio Bonci is the clinical optometry lead and vision therapist at Ocular-Optikus Clinic in Kecskemet, Hungary. He has mostly worked in eye clinics in Italy and was also a clinical research fellow at the Department of Clinical Neuroscience and Mental Health, Imperial College London, Charing Cross Hospital.


Visit, and click on the 'Related CET article' title to view the article and accompanying 'references' in full.

Course code: C-71252 Deadline: 23 August 2019_J

Learning objectives

Be able to elicit relevant detail from patients presenting with binocular vision anomalies (Group 1.1.2) Be able to manage patients presenting with diplopia (Group 8.1.7)

* Be able to elicit relevant detail from patients presenting with binocular vision anomalies (Group 1.1.2)

* Be able to understand the management of patients presenting with diplopia (Group 7.1.8)

Fabrizio Bonci Dip Optom (ITA)

Caption: Figure 1A Exotropia in a patient with uncorrected myopia; IB Overcorrection was prescribed to reduce the angle of strabismus

Caption: Figure 2 Full occlusion where tape is applied to the lens

Caption: Figure 3 Partial or spot occlusion

Caption: Figure 4 Partially occlusive contact lens

Caption: Figure 5 Marsden ball

Caption: Figure 6 Hart Chart

Caption: Figure 7 OPT1: fair

Caption: Figure 8 OPT2: circus

Caption: Figure 9 OPT3: stereo rope

Caption: Figure 10 VT using the Brock string and alternate occlusion

Caption: Figure 11 Lifesaver card
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Title Annotation:Binocular vision
Author:Bonci, Fabrizio
Publication:Optometry Today
Date:Jul 1, 2019
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