Figure 1a. Muscle light used for testing.
Figure 1b. Neutralizing prism and red lens used to determine prismatic prescription.
By Richard London, M.A., O.D., F.A.A.O.
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Diplopia is a distressing symptom that can greatly compromise a patient’s quality of life. It also provides the clinician with unique challenges because a sudden onset of diplopia may be the harbinger of significant medical problems. Diplopia can be idiopathic, due to neural dysfunction, or it can result from mechanical eye movement restrictions. Following any required medical treatment, efficient prescription of prisms, lenses, and/or vision therapy for the management of diplopia can greatly improve patient comfort and visual function.
In recent years, the subspecialty of Rehabilitative Optometry has been recognized as offering an important service to an underserved population. Although most vision care specialists currently think of Rehabilitative Optometry as dealing primarily with head trauma patients (as opposed to the earlier connotation of Low Vision), I prefer to use the term to refer to any disruption of vision in the largest sense, and especially to disruption of binocular vision resulting from pathology or trauma. Using this definition, a great many cases encountered in modern optometric practices may be included.
Acquired oculomotor deviations can have profound consequences on binocularity and patient comfort. Most patients with oculomotor deviations who present in a general practice have a stable, neuromuscular bias for their problem (e.g., a phoria or intermittent strabismus) that they are able to control with fusional vergence. Chronic necessity for utilizing this controlling vergence can lead to symptoms or avoidance of symptom-provoking tasks. Fortunately, these problems can usually be alleviated by the judicious application of small amounts of prism power, plus or minus lens powers, or vision therapy.
A challenge for the clinician is to differentiate oculomotor causes of diplopia from diplopia caused by etiologies requiring medical treatment. Some congenital or long standing deviations and all acquired oculomotor deviations must be rigorously evaluated to determine their cause.
In general, oculomotor deviations can result from idiopathic, mechanically restrictive, and neural dysfunction causes. (Table 1)
Table 1. Causes of Oculomotor Deviations
It is important to realize that the clinician's appreciation of a patient's condition is often different from the patient's. Although patients may be concerned about their "vision" in the broad sense and their cosmetic appearance, the clinician often has health concerns at the top of his or her concern list. Determination of deviation cause is very important because many acquired oculomotor deviations require medical management, and appropriate medical management should be established prior to any optometric treatment. Medical management can treat the underlying etiology and can potentially stabilize the angle of deviation.
The cardinal rule for managing diplopia must be: save the life, save the eye, restore the function. In addition, before intervening the clinician should always keep in mind the admonition to "Do no harm."
Frequently, a solution to a patient's immediate discomfort may lead to greater long-term difficulties. For example, prescribing full-time prism wear for a recent onset sixth nerve palsy may relieve the diplopia, but it can also allow a secondary contracture of the medial rectus in the affected eye to develop. This would lead to significantly greater obstacles in the final remediation. Secondary muscle contractures should be aggressively avoided.
There are several clinical approaches for preventing contractures (Table 2).
Table 2: Options For Preventing Secondary Contractures
Alternate occlusion is a time-tested procedure for prevention of contracture by forcing each eye to attempt movement through its full range. The patient initially places an occluder over the unaffected eye for several hours a day. The patch is later placed over the paretic eye to prevent an extraocular muscle contracture in the good eye.
Some clinicians suggest that simply occluding the affected eye reduces symptoms and is likely to have better compliance. They suggest that motility should not be compromised by this procedure because Hering’s Law predicts that movement of the good eye should result in corresponding movement of the paretic eye. Unfortunately, this is not consistent with clinical experience. The innervation resulting from moving the good eye is often insufficient to cause the paretic eye to move fully into the affected field.
Although there have been no studies to demonstrate effectiveness, I prefer to leave the occluder off for part of the time when the patient is in a safe, secure environment, e.g., at home. My impression is that diplopic perception serves as a stimulus for the brain to maintain its efforts to establish binocular fusion, possibly by stimulating fusional vergence.
An alternative patching approach for patients with lateral rectus paresis involves the use of asymmetric binasal occluders with the larger coverage area over the unaffected, fixating eye. (A template to help position binasal occluders is available from Bernell Inc., http://www.bernell.com.) This encourages alternation and stimulation of the paretic eye throughout the day. Clear contact paper (see below) is my material of choice for this option. The benefit of binasal occlusion is that the patient does not need to remember to alternate the occluder throughout the day. Use of bitemporal occluders for patients with medial rectus paresis is not recommended because it cuts down the peripheral field and puts the patient at risk when crossing the street - or even when navigating around tables and cabinets in the house.
A second optometric approach to prevent secondary contracture involves using yoked prism with the prism base opposite to the affected nerve. In the case of a left lateral rectus palsy, the patient would wear base right prism in the amount of approximately 15 prism diopters. Base-out prism would be given before the right eye, and base-in before the left. This provides a continual challenge to the paretic muscle to move into the affected field.
Unfortunately, techniques that require patching or even using therapeutic prism spectacles require patient compliance. This is not always easy to obtain because many patients have multiple health-related problems. Some patients may also have concurrent cognitive or memory difficulties.
Botox® injection into the antagonist muscle (i.e., with left lateral rectus palsy, inject the left medial rectus) does not depend on patient compliance. The goal of this technique is to chemically relax the unopposed muscle that is prone to contracture. Over time as the Botox® wears off, the palsied nerve may have recovered some function.
Remember that very small amounts of vertical misalignment, amounts easily ignored in horizontal misalignment, may impede single, clear, comfortable binocular vision. (1, 2) Therefore, when symptoms are present, intervention (often in the form of prism prescription) must be considered for any detectable amount of vertical deviation.
Many acquired oculomotor deviations are incomitant. This adds an additional level of complexity to the therapeutic options because a correction that attains alignment in one position of gaze may over- or under-correct in other positions.
When a patient has an oculomotor deviation that results in diplopia, the clinician can adopt one of two strategies for remediation. He or she can either provide help for the patient to comfortably fuse the images together, or he or she can eliminate one of the images to make the patient comfortably monocular.
All therapeutic options are based on one of these two strategies or a combination of them. Listed below are the strategies for implementing the options in clinical practice. (Table 3)
Table 3: Management Options For Patients With Diplopia
If a patient is capable of sensory fusion, several options are available to make the task more comfortable. Ergonomic modifications, prism, lenses, vision therapy, medical and surgical intervention all provide viable alternatives in various cases.
Often, rather simple changes in the immediate environment offer great relief from the symptom of diplopia. Placement of work material in a fused field, e.g., raising or lowering the position of a VDT screen, is a simple but effective technique. Use of a slant board to read or learning to read in a chin-down position may also be very helpful for patients who are diplopic in downgaze or have a gaze palsy.
Learning to pursue targets "with your nose" rather than with eye movements can be useful with patients who have incomitant deviations. I usually find that giving the patient practice in-office using head movements to follow a Marsden ball or some other basic therapy techniques greatly aids in learning to track effectively.
A useful motto for the remediation of binocular dysfunction is that "Sensory fusion is the best orthoptics." By providing an environment conducive to sensory fusion, motor fusion often improves on its own. However, I recommend temporizing 6 to 12 months prior to providing full-time prismatic correction. The intention is to decrease the chance of developing a secondary contracture, which can occur by allowing the unchallenged antagonist of the paretic muscle to remain tight. As the nerve heals, there should be a progression in the ability to move the eye further into the affected field of action. The angle of deviation may also reduce during healing.
By keeping the eyes in the fused position demanded by full-time prism, even if the nerve function improves, the patient must maintain the same angle determined by the prism in order to avoid diplopia. This could have the consequence that the patient “owns” the deviation permanently, and the antagonist to the paretic muscle may not relax over time, even when the paretic muscle improves its function.
In acquired strabismus, a good rule of thumb is to not give the full prescription to be worn full-time wear for a minimum of 6 months, and, if improvement in the angle is noted on follow-up visits, waiting up to a year is common. The idea is to prevent the strabismic eye from getting too "comfortable" in its turned position. If the eye is not challenged to move, secondary muscle contracture of the antagonist is the likely result.
Following determination of the deviation angle, the clinician must decide whether to prescribe full or partial compensation. In general, patients with phorias and intermittent tropias are given partially compensating prisms, whereas constant strabismus requires full compensation.
A simple clinical procedure for arriving at a suitable prism prescription requires only a red glass and a muscle light. (A muscle light is simply a discrete point light source, e.g., a transilluminator or penlight that can be used for directing the eyes into different positions of gaze.)
A partial prescription may be obtained by having the patient fixate the muscle light with the nonparetic eye. With good ambient light in the room, a red lens is then placed in front of one eye (usually the paretic eye) and prism power is added over the red lens until the red and white images of the muscle light fuse. (Figures 1a, 1b) The resulting partial prescription should allow peripheral fusion of large room objects and possibly a reduction in the angle of deviation.
Determination of full compensation power follows the same procedure, but the room is kept as dark as possible except for the muscle light. This eliminates any fusion potential and should reveal the maximum deviation.
Figure 1a. Muscle light used for testing.
Figure 1b. Neutralizing prism and red lens used to determine prismatic prescription.
At times, the clinician may suspect that there is a latent deviation that is not being revealed by cover testing or the red lens test. This is possible in patients with long-standing latent deviations that have increased in magnitude due to decompensation of vergence ability over time. (3) The patient may be able to hold the deviation in check by using peripheral fusion during testing, yet be uncomfortable or diplopic when fatigued. If this is suspected, a prolonged occlusion test may be performed. One eye is patched for 45 minutes to an hour while the patient is allowed to read in the waiting room.
When the patient is brought back to the exam room, the clinician must be careful not to allow both eyes to view a target simultaneously. Ask the patient to close both eyes. Remove the patch, and place the testing instrument (an occluder, red lens, or Maddox rod) before one eye. Only when everything is in place should the patient be told to open the eyes. Use the red lens or Maddox rod to determine the prim power required to obtain fusion. This may reveal a higher magnitude of deviation, which the patient must routinely overcome to remain binocular, and provide the prism power that should be prescribed. I find prolonged occlusion testing to be particularly useful for assessing vertical deviations.
The goal of the clinician should be to provide immediate comfort with prism, but also to wean off as much power as possible until the minimum amount of prism required to allow comfortable binocularity is obtained. A procedure for "dribbling off" or weaning prism power is presented in Table 4. (4)
Table 4: Procedure For "Dribbling Off" Prism Power
Due to the inherent incomitant nature of acquired deviations, prisms are normally prescribed to allow fusion in the position of gaze that the patient uses for normal tasks. Therefore, patients may require different glasses for work, driving, golf, etc., with a different prism power in each.
Alternatively, options are available to vary prism power (and base orientation) within a single pair of glasses. Fresnel membrane prisms may be cut and applied as sector prisms. (Figure 2) This will put the power only where it is required. Unfortunately, Fresnel prisms, especially in higher powers, reduce contrast and degrade visual acuity. (5) However, the patient may have to accept this compromise. (Table 5)
Another option is to utilize clip-ons to allow prisms (6) (or adds) to be applied to existing spectacles. Some clip-ons, such as those made by Just Match-It (http://www.justmatchit.com), fit most spectacles and are constructed with screws that permit easy insertion of a prism or plus lens.
Table 5. Prism Advantages and Disadvantages
Figure 2. Sector Fresnel prism used to prevent vertical diplopia in a patient with thyroid myopathy.
Perhaps the most well known manner for varying the prism power in a lens involves the use of slab-off, which provides base-up prism in downgaze. This is prescribed for the most myopic or least plus eye. Unfortunately, the amount of prism available through traditional slab-off is limited by the power of the patient’s lens. A newer variation is the prefabricated slab-off that provides base-down prism power in front of either eye. By combining these options, a wide range of near and/or downgaze vertical imbalances may be compensated.
When a larger vertical prism prescription is required at distance than at near, slab-offs may be used to decrease or cancel out the prism effect at near. For example, if 3 diopters of base-up prism in front of the left eye is required for comfortable fusion at distance but none is needed for near, a 3 diopter prism base-down prefabricated slab-off placed in the left lens would provide the needed prism at both distances.
Remember that patients who have significant anisometropic prescriptions will experience induced prism between the two eyes when looking away from the optical center of the lens, further impeding alignment.
Although most patients prefer to wear an optimum refractive correction, certain patients benefit particularly from lenses that provide maximum visual acuity. For example, patients with fragile fusion caused by cataracts, intraocular lens (IOL) implants, anisometropia, or intermittent strabismus with astigmatic error all respond positively to the clearest possible retinal image.
Occasionally, additional dioptric power may be used to help a diplopic patient fuse. For pre-presbyopes, an over-minused prescription can help to control divergence excess intermittent exotropia. (7) A bifocal may be needed to remove the additional accommodative demand for close work if the patient becomes symptomatic or esophoric at near. Again, the management plan should include attempting to slowly wean the patient off the over-minus lenses, usually at the rate of 0.50 diopters of sphere power every 4 to 6 weeks.
Although not a common presentation in late-onset, acquired strabismus with diplopia, using a higher add power than expected for a patient's age may permit easier fusion at near if there is an eso deviation. This type of prescription provides good leverage for some patients and is very useful for accommodative esotropia in general.
Probably the most common mistake clinicians make in treating vertical or cyclovertical deviations is to forget about the difficulty patients have using traditional bifocals. Many vertical deviations increase in downgaze so patients may be so misaligned by the time they look the down 10 mm into bifocal segments that one eye is looking through a segment while the other is bisecting the segment line. Attempts to rectify this problem and establish bifixation in downgaze include conventional slab-off prism, pre-fabricated slab-off, or Fresnel prisms placed over the segment. If the cyclo component manifests more in downgaze, as is common with some superior oblique or bilateral superior oblique palsies, occlusion of one bifocal segment or monovision correction at near may be indicated (see below).
A second option is to permit the patient to see clearly at near without needing to look into the affected downgaze area. Prescribing single vision near spectacles and encouraging the patient to hold material a bit higher than normal may accomplish this.
Alternatively, having the patient tip his or her chin so the eyes will look slightly in upgaze may be all that is needed to avoid the problematic field.
A yoked 10 to 15 diopter base-down prism placed in each lens will allow patients who can neither hold material up nor tip their chin (possibly due to neck problems) to benefit from a single vision prescription. A trial with Fresnel prisms can be useful and may be all that is required for management. Slant reading boards are also helpful.
Compu Specs® (http://www.uniqueoptical.com) have replaced the no longer available (in the US) Focal Change® and Hi - Rise 2® frames. (Hi Rise 2 Frames were distributed by Englehardt Nominees Party Ltd., Edwardston, South Australia.) Each of these provide a novel alternative to separate pairs of spectacles.
The Compu Specs® work (Figure 3) by having two magnets located in each nose pad that allow normal positioning of the distance and near add for most purposes, but they also allow lenses to be elevated so that the bifocal segment can be utilized in primary gaze. These frames are extremely useful for patients who have diplopia in downgaze or a gaze palsy affecting downgaze. (They are also useful for patients without binocular vision problems who need help with intermediate distance tasks such as computer use, cooking, or even reading in bed when the head is at an angle.)
Figure 3. Compu Specs® adjustable frames spectacles in normal (left) and raised (right) nose pad positions.
Head trauma can result in an accommodative spasm called post-traumatic pseudo-myopia. (8) It is important for the clinician to be aware of this condition. A patient may report a decrease in visual acuity at distance that is corrected with an increase in myopic prescription. There will be a sizeable reduction in myopia between the non-cyclopleged retinoscopy or refraction and the cyclopleged findings. The most common pattern in these cases is a persistent bilateral pseudomyopia, and minus lens correction is often necessary.
There are many simple and practical vision therapy procedures that can easily be implemented in a primary care office to assist a patient in managing diplopia.
Some basic principles involved in managing patients with acquired brain injury are worth reviewing before discussing treatment of the diplopia often associated with these cases. First, it is important to remember that there is both an acute and a chronic phase associated with acquired brain injury. The acute phase is usually considered to occur within the first month following injury. Treatment during this phase is thought to result in the best and quickest outcome. After 35 days the condition is considered chronic, and although progress is certainly possible, it often takes longer to achieve results.
The clinician providing vision therapy for this patient population should be prepared for the criticism that “the patients you think you helped would probably have gotten better anyway, and your intervention probably did little good.” This criticism is largely unfounded, and it is widely believed in many of the fields that co-manage brain injury patients, e.g., occupational therapy, physical therapy, and physiatry (physical medicine), that early intervention is the option of choice.
Frequently patients with acquired brain injury have many concurrent physical, cognitive, and emotional problems. When treating brain injury patients, the clinician must realize that these patients often have limited energy and concentration.
When faced with patients having multiple, overwhelming problems, it is my suggestion that vision care providers utilize one of the more passive treatment options listed in this course until the professions that do not have passive options have made progress with their “piece of the puzzle.”
Passive options include prisms, lens, occlusion, etc. When the patient has made progress with other activities of daily living, active vision therapy can be attempted. Coordination with other providers to effectively co-manage brain injury patients is critical for optimum results.
The clinician should make an assessment of the patient’s cognitive abilities and take that assessment into account when planning an active therapy program. Can the patient understand or remember the exercises? Is he or she able to routinely incorporate exercises into the daily schedule? If not, is there a support person who can be relied upon to foster the therapy? Sometimes cooperation with the rehabilitative team can ensure that the vision therapy exercises are included in the rehabilitation schedule. My experience has been that occupational therapists have been particularly helpful in this endeavor.
Patients with frontal lobe damage may have a frustrating (for the clinician and everyone else around them) lack of awareness of their defects. This makes motivating these patients to do daily exercises extremely difficult. Neglect or visual extinction, inattention to information in one hemifield (usually left) of personal and extra-personal space, which is found most frequently in non-dominant (usually right) parietal or upper temporal lobe lesions also adds a significant level of difficulty to therapy. These problems typically remove the patient from the realm of general optometric practice.
Never-the-less, there is much the general clinician can do to improve the quality of life for these patients. A decision must be made regarding whether to attempt the enhancement of damaged skills, or to attempt the development of new ones. The role of repetition during therapy cannot be over-emphasized. Skills must be practiced until they are second nature.
Be very clear to the patient and their support person what can reasonably be expected as an outcome of therapy. In general, the goal of therapy is to reach the patient’s full remaining potential. It is unlikely they will return to the level they formerly obtained (or think they obtained). This must be reinforced often during the treatment program.
Pay attention to details during therapy. Check to be sure that the spectacle prescription hasn’t changed and that the patient remembers to wear his or her correction. Training should proceed slowly, especially at first. Avoid patient frustration and build confidence. Everyone wants to be cured yesterday. Patient patience is often in short supply. Be clear from the start that this is a process of retraining, and that it will take time. Remember that patients must expend a great deal of conscious effort doing things they used to take for granted so their endurance is often quite limited.
Vision therapy for brain injured patients with diplopia should be directed at avoiding secondary contractures, maintaining good ocular motility, and, whenever possible and practical, reestablishing binocularity. For many brain injured patients, one of the few joys left to them is reading so with compromised visual abilities their quality of life is severely compromised.
For purposes of this course, only vision therapy exercises directed at minimizing diplopia and improving ocular motility will be addressed. Coexisting problems of acquired brain injury such as treatment of visual field defects, neglect, and perceptual processing problems are beyond the scope of the course.
Incorporating ocular motility exercises while the dominant eye is occluded may assist in preventing secondary contractures. Having the patient watch television and turn his or her head an inch (2.5 cm) or so opposite to the restricted field can be a simple and effective initial approach to therapy. If the patient has a right lateral rectus palsy, turning the head slightly to the left while maintaining fixation on the TV causes some relaxation of the right medial rectus while stimulating the right lateral rectus. After 5 to 10 minutes, the patient can attempt to turn the head another inch (2.5 cm). Remember that when viewing a distant target, turning the head one inch (2.5 cm) results in a substantial shift in fixation. If possible, this exercise should be carried out for half an hour several times daily.
Developing smooth eye movements is frequently an initial step in training ocular motility. The well-known Marsden ball (Figure 4) is easy to make and is quite useful. Often it is best to start with the patient seated, especially if there are vestibular difficulties. The string is fixed to the ceiling, the ball set at eyelevel, and it is swung first horizontally, then on the “Z” axis, and finally diagonally.
The patient occludes one eye, usually the poorer eye first in order to develop familiarity with the task, and is encouraged to carefully track the ball with their opened eye. To help ensure accurate fixation, the patient can be asked to point at the ball as it swings. He or she can also aim a small flashlight or laser pointer at the ball during its movement, or can hold a ring made out of a bent hanger under the ball as it moves to encourage accuracy. Of course these techniques depend on the degree of motor control the patient has available.
Figure 4. The Marsden ball. Sometimes letters or numbers are added to improve fixation accuracy.
Following success while seated, the patient should be encouraged to follow the ball while standing or moving (with support as needed). The goal is to make eye movements more facile when standing or walking without the patient losing balance.
Smaller smooth movements can be practiced with small fixation targets held closer to the patient and moved in an “H” or figure eight pattern. Groffman or Visual Tracing Sheets (available at www.bernell.com) (Figure 5) can also be used to encourage eye movement and attention at near. Although they do not truly train pursuit movements (a moving target is required for that), they are quite useful for enhancing the range of eye movement.
Figure 5. A sample of visual tracings. The patient is required to “visually trace” the line from the letter to the number to which it connects. Ultimately the patient should be able to complete this using only vision, however a finger or pointer may be permitted initially.
The other type of eye movement to be enhanced is fast saccadic movement. “Four-corner saccades” is an exercise that teaches large eye movements. The patient is seated in the center of a room. A support person standing behind the patient shines a flashlight beam into different corners of the facing wall. The patient must make an appropriate eye movement to fixate the light. (This assumes the patient has no visual field loss.) It is often helpful to have the patient place a beanbag on his or her head to keep from using excessive head motions during this training exercise. The exercise assumes a reasonable degree of ocular motility.
Once the patient is able to comfortably make large eye movements, the therapy should be directed towards making the shorter, more precise movements needed for reading. Tasks such as Michigan or Ann Arbor Tracking® (Ann Arbor Tracking books are available at http://www.bernell.com) and PerCon Saccades® (PerCon Inc., Akron, Ohio) are very useful introductory techniques. Again, begin with the patient monocular.
Using Michigan Tracking, the patient must simply circle each letter in the alphabet in order as it occurs in a jumble of nonsense words. Begin in the upper right and start with the letter “a.” (Figure 6) Continue in order until the paragraph is completed. If no letters are skipped, the last letter circled should be a “z”. When accuracy is satisfactory, timing the task can be used to monitor progress and increase difficulty.
Figure 6. Michigan Tracking Test
For the clinician who wants to attempt therapy with patients having have hemianopic visual field cuts that interfere with reading, the same tracking program can be used with modification. Turning the page 90 degrees and having the patient practice scanning vertically can greatly improve reading skills.
PerCon Saccades® use letters or numbers presented in columns. (Figure 7). The patient is told that while fixating on a flagged (underlined) number, he or she should still able to see the next flagged number by using peripheral vision. This peripheral awareness guides the direction and length of the next saccade. To add a level of complexity, the task can be timed. Later, it is often useful to flag words in newspapers or magazines with red underlining. Usually underlining one or two words per sentence is adequate. The patient can then practice these skills during a normal activity of daily living, i.e., reading.
Figure 7. A page from PerCon Saccades®. Note the underlined (flagged) numbers. These are the markers to be fixated on successive saccades.
I have found several video programs to be of particular value for the patient who wants to improve reading skills: versions of guided readers and tachistoscopic therapy. This is by no means an exclusive list, but computer versions of guided readers are offered by Vision Builder (http://www.visionbuilder.no/), Ultimate Speed Reader (http://www.knowledgeadventure.com/), and Reading Plus (http://www.readingplus.com). The first two programs are available on CDs, whereas Reading Plus is available for download on the Internet.
The guided reader programs all use some form of moving mask to reveal reading material. (Figure 8) The speed of the movement (and sometimes the size) of the mask can be varied depending on the abilities of the patient. Some programs allow the patient to load their own reading material for added interest.
The purpose of guided readers is to direct speed and direction of eye movements when viewing cognitively demanding material. Each of the three listed programs contains additional useful vision exercises.
Figure 8. Two views of the moving mask of the guided reader program on Vision Builder.
Monocular eye movement therapy is usually an early step in treating patients with acquired diplopia. Additionally, the clinician should not forget that pre-presbyopic patients with acquired oculomotor deviations may simultaneously have problems with accommodation that are very amenable to vision therapy. Addressing these accommodative dysfunctions with exercises or lenses might help relieve symptoms.
Monocular accommodative push-ups are often valuable. I suggest having the patient use his or her normal reading material in order to maintain interest. Starting at arm’s length, the material should be slowly moved toward the face until it can no longer be cleared. It is then brought back to the starting point and the procedure repeated. I suggest starting with 5 minutes for each eye three times daily. When the range improves, accommodative facility (jumps) can be added by simply having the patient move the material as previously described until it is at the limit of clarity, then shift gaze to a calendar or Hart chart (Figure 9) at least 10 feet (3 meters) away. Following relaxation of accommodation, the reading material is brought in again from arm’s length and the cycle repeated.
An investment in plus/minus flippers can also be very helpful. Using the flippers, the patient monocularly reads his or her choice of material at the normal reading distance. The plus lens is placed in front of the reading eye, and, if the print can be cleared, the patient reads a sentence silently. The lens is then flipped to the minus side and the patient reads the next sentence. This alternation of lenses continues sentence by sentence. Using his or her preferred reading material and flipping the lenses by sentence rather than after each word helps maintain interest and compliance.
Flippers are usually available with equal plus and minus powers. (http://www.bernell.com) For example, one side will have +1.00 diopter lenses and the other will have -1.00 diopter lenses. Using the flippers will produce a 2 diopter change in accommodation when clearing one side and flipping to the other.
Start with a flipper power that the patient can succeed in clearing in the office remembering that during the actual exercise sustaining ability becomes challenged. This exercise should be continued for a minimum of 10 minutes, working up to 20 minutes per session.
Figure 9. The Hart Chart, which can be used as a distance target to relax accommodation.
More aggressive vision therapy can help to maintain fusion and improve binocularity in certain acquired deviations. The goal is to establish good sensory fusion in one position of gaze, then slowly work to expand the zone of fusion. Patients with restrictive changes or who have constant paralytic strabismus are not appropriate candidates for motor fusion therapy. However, they may benefit from sensory fusion techniques in conjunction with other management options. Tranaglyphs, vectographs, and computer orthoptics are all useful techniques to extend motor fusion ranges.
When improvement of ocular motility is recalcitrant or when fusion is possible in only one position of gaze, it is still possible to improve quality of life through practical techniques. Often the easiest and most useful form of vision therapy for patients with acquired oculomotor deviation involves making some of the ergonomic changes previously described. These include modification of head posture, use of head rather than eye movements into certain positions of gaze, and changing the work place so that the patient does not have to look into the affected field.
My impression is that a frequently overlooked but potent aspect of vision therapy involves improvement of attention (especially, but not exclusively visual attention). This skill can generalize to other activities and is a significant bonus associated with successful vision therapy.
Several medical and surgical options are available to help eliminate diplopia and reestablish fusion. Botox®, is a mild concentration of botulinum toxin that has several established uses in acquired and early onset strabismus. (9,10) In recent onset palsy, injection of Botox® into the antagonist muscle prevents secondary contracture from developing as the affected nerve heals. In the case of a right lateral rectus palsy, this would require an injection into the right medial rectus. The technique has the distinct advantage of being independent of patient compliance. As the Botox® begins to wear off after three to six months, the palsy may also begin to resolve, and the patient may end up close enough to the ortho position to regain fusion.
The most favorable conditions for which the use of Botox® can help to establish binocularity involve patients with good, established sensory fusion prior to the trauma and a comitant, horizontal deviation. Botox® does less well in establishing fusion with incomitant deviations, fibrotic restrictions, and vertical deviations. However, in diplopic cases, the goal is not the immediate reestablishment of fusion through use of Botox®, but rather prevention of secondary contracture. Fusion in these cases results from a combination of chemical relaxation of the antagonist muscle and neural recovery of the agonist.
Side-effects of Botox® injections result from spill over of the drug to adjacent muscles. Vertical deviation and ptosis are the most common side-effects; fortunately, they are temporary.
Patients with myasthenia gravis who respond positively to edrophonium (Enlon®, formerly Tensilon®) testing are routinely put on a trial of Mestinon® (oral pyridostigmine bromide), which is a long-lasting acetylcholinesterase inhibitor. Unfortunately, results are better with systemic symptoms than with the ocular symptoms.
Extraocular muscle surgery options are dependent on the etiology of the deviation and the extent of the muscle involvement. As a general rule, recent onset strabismus must be allowed to stabilize prior to surgery, which usually takes a minimum of 6 months and frequently can take a year. This period of time is also necessary to allow the nerve to heal.
In my experience, the ability of the surgeon to position the eyes close to alignment increases the likelihood that further treatment (e.g., prism, lenses, therapy) can improve binocular function.
One of the most useful surgical contributions to diplopia management involves eliminating torsional components in superior oblique palsy. Torsion is a major obstacle to fusion and very difficult to manage.
When a palsy does not recover and an extra ocular muscle is incapable of moving the eye into the affected field, adjacent muscles can sometimes be transposed to provide some function. For example, with a left lateral rectus palsy, the left superior and left inferior rectus can be transposed to near the insertion of the faulty muscle to provide some abduction.
Thyroid myopathy provides the surgeon with a number of difficulties. When there is an exophthalmos and/or optic nerve compression along with muscle restrictions, a decompression surgery can be performed prior to extraocular muscle surgery. (Figures 10a and 10b) Decompression surgery changes the shape of the orbit and allows the globe to assume a more normal position.
As the globe is moved back into its normal relationship within the orbit, the taunt extra ocular muscles may be slightly relaxed, which can eliminate or modify the need for muscle surgery. This concept is very important for the optometrist to understand because the referral for decompression surgery is normally to an oculo-plastic surgeon, whereas a strabismus surgeon typically does the muscle alignment work.
Figure 10a. Grave's patient showing exophthalmos.
Figure 10b. Same patient following decompression surgery.
Restriction of the inferior rectus muscle is the most common muscle anomaly in thyroid myopathy. Surgical correction normally involves a recession of the inferior rectus. One unfortunate consequence of this surgery can be a significant "A" pattern with a large exo deviation on downgaze. (11) This is because the depressor muscles have greater horizontal force than the elevator muscles. When the inferior rectus is weakened, the relatively stronger superior oblique pulls the eye outward. The lower lid may also droop following recession of the inferior rectus. (11) This can be avoided by reattaching the Ligament of Lockwood to the lid at a position 15 mm from the limbus.
When a patient is either unable to fuse or not able to support sensory fusion with good motor fusion over an effective range, a viable option is to make the patient monocular. While this goes against the instincts of many clinicians, I have determined that "Being efficiently monocular is better than being inefficiently binocular." Options to make a patient monocular include occlusion, monovision correction, and reverse prism.
Occlusion is the traditional last resort for patients who cannot attain comfortable fusion and who cannot adapt to a monovision correction. Opaque patches are effective but are quite unsightly and are routinely rejected by patients. Use of translucent occluders is just about as effective and much better cosmetically. This type of occlusion can be provided through the use of frosted lenses, clear nail polish applied directly to the lens, (12) cellophane tape, clear contact paper (4) (Figure 11), Bangerter Foils® (13), or Bernell Occlusion Foils®. All may be used over the whole lens, and all, except for frosted lenses, may be used in a sector or as a circular patch near the center of the lens. (Figure 12) Occluders can be placed over one bifocal segment for patients unable to fuse while reading or above the segment line for patients who have diplopia only at distance.
I prefer to use contact paper because it is so easy to apply and remove, and it is readily available. Frosted lenses and nail polish are not as easily modified. Cellophane tape is difficult to cut into small segments and often requires the use of acetone to remove sticky residue.
Foils come in various levels of opacity so visual acuity can be predictably reduced. This is quite useful in the treatment of amblyopia and suppression, but for management of diplopia maximum density is required. Foils are easy to work with but are not as readily available to patients as contact paper. They also cost more. Clear contact paper is sold in the shelving department of most hardware stores and is very inexpensive. Removal is easy, leaving virtually no residue.
I trace circles using coins of various sizes on the contact paper and then cut them out. Having marked out on the spectacles the area where the diplopia begins, I place a large circle on the lens. If diplopia is relieved, I can remove the contact paper circle and try the next smaller size. I continue this process until the smallest patch that will relieve the diplopia is found.
This process allows the patient to remain asymptomatic, look cosmetically acceptable, and maintain a reasonable amount of his or her peripheral visual field. The use of circular occluders not only eliminates troublesome diplopia, but it also prevents many potential accidents such as banging into tables or counters.
Figure 11. Clear contact paper.
Figure 12. Clear contact paper used as a central occluder to eliminate diplopia.
For those patients who need occlusion, want the best cosmetic appearance, and have reasonable dexterity, opaque occluding contact lenses are available. (14) (Figure 13) A fogging element of +2.00 to +4.00 diopter is usually incorporated into the lens to compensate for any residual light transmission through the lens.
A fully-opaque occluding contact lens (Figure 13) can be used for patients with dark irides, however patients with lighter irides will appear to have a large anisocoria. For these patients, a true cosmetic contact lens may have to be fabricated. Remember that the increased cosmesis offered by an occluding contact lens has the negative side-effect of reducing the visual field.
Figure 13. An opaque occluding contact lens used to eliminate diplopia.
Some patients attempt to provide their own physiological occlusion by developing a unilateral ptosis. Use of an occluding contact lens can eliminate the need for ptosis, thereby reducing another source of strain and poor cosmesis.
Occlusion can be an important tool in the diagnosis of subtle cyclovertical deviation (15) and for the prevention of secondary contractures in recent palsies. In the case of a recent right superior oblique palsy, use of alternate occlusion for several hours daily can help prevent contracture of the ipsilateral (right) inferior oblique. It can also help to prevent contracture of the contralateral (left) inferior rectus (inhibitional palsy of the contralateral antagonist, i.e., the left superior rectus). This inhibitional palsy of the contralateral antagonist only occurs when the paretic eye is used for fixation ("fixation duress").
Personally, I do not like to prescribe full time occlusion, even with alternation. As stated above, I believe that diplopia is usually such a negative experience that it may serve as a great motivator (consciously and/or subconsciously) to reestablish fusion.
Many patients who would benefit from single vision spectacles for distance and near work reject this option because they do not want to carry two separate pairs of glasses (distance and near) with them at all times. For these patients, as well as for those who do not have an acceptable range over which fusion may be maintained, I have found monovision correction to be a viable option. (16) In fact, it is the best option for many patients.
Rather than attempting to establish fused, comfortable vision when there is a limited range of gaze, the monovision option, by not forcing the patient to deal with the issue of fusion at all, allows him or her comfortable vision in most positions of gaze with only one pair of spectacles or contact lenses.
Table 6 lists certain guidelines I have developed for use of monovision in patients with diplopia or fragile binocularity. Flexibility is the key for the clinician, and shifting between these guidelines or other ideas is often necessary to obtain a successful prescription. Patients who can fuse in primary gaze will often feel better having a pair of distance spectacles (or ones that will compensate for the “near” eye”), which they can keep in their car for driving.
Table 6: Guidelines For The Monovision Correction Of Diplopia (Assuming nearly equal best corrected vision)
Monovision correction does not need to be prescribed only as a single vision distance lens along with a single vision near lens. A variant that I have found very useful when the patient has fusion in primary gaze at one distance is to provide a prescription of monovision at one distance only. For instance, if the patient has fusion at distance but is diplopic at near, I might give the distance prescription for each eye and a near segment only for the eye that has better motility in downgaze. (4) (Figures 14, 15) This variant allows fusion in primary gaze and monovision in the troublesome downgaze position.
It is not always necessary to eliminate a bifocal segment in one lens. If a flat top is used, a very low power can be placed in front of the “distance” eye. This approach can be used for patients who have fusion at near but who are diplopic at distance. One lens can be made using only the near prescription and the other with the distance prescription and a near bifocal. Of course, a progressive addition lens could also be used in front of the “near” eye.
Figure 14. Spectacles with a bifocal only for the left eye. This provides binocular vision in primary gaze and monovision in near downgaze.
Figure 15. Patient wearing spectacles similar to those shown in Figure 14.
Most patients are able to suspend the blurred second image quite readily. For those who cannot, a simple training procedure may help. Instruct the patient to place a card or occluder over the near eye while watching television. After ten to twenty minutes, remove the occluder while still watching the program. This may be repeated if necessary. The same procedure can be used when reading. Cover the distance eye for ten to twenty minutes, and then remove the cover while continuing the reading task. Use of this technique as needed during the first week following prescription of a monovision correction will usually facilitate the patient's adaptation.
A small number of patients who experience close proximity of their diplopic images prefer to have prism incorporated into the monovision prescription to permit peripheral fusion.
Prism For Patients Unable To Fuse
Reverse prisms, i.e., base-in for esotropia, or base-up for an eye with superior oblique palsy, can be useful for the management of several conditions.
When a patient has very poor acuity in one eye, reverse prism placed before the strabismic eye only may establish better cosmesis. Usually, however, cosmetic prism is prescribed as base-right or base-left. Base-right prism means that base-in prism is prescribed before the left eye and base-out prism is placed before the right eye. The prism in front of the straight eye causes a version movement that actually helps turn out the strabismic eye. The prism in front of the turned eye moves the position of angle lambda therefore making the eye look straighter. A good starting point is 7 to 8 prism diopters for each eye. (Figures 17a and 17b) Using prisms or lenses to achieve improved cosmesis has been referred to as "optical surgery."
Figure 16a. Patient without prism.
Figure 16b. Prism used for "Optical Surgery."
Figure 17a. Patient before yoked prism prescription.
Figure 17b. Patient wearing base-left yoked prism.
Finally, prisms can be used monocularly for patients who have such compromised motility that they must assume a dramatic head turn to be able to look “straight ahead.” Here the prism (usually Fresnel because of the magnitude) is not used to obtain fusion but rather to allow the patient to maintain a normal head posture and still see what is in front of him or her. Thus, for a patient with a large exotropia in one eye and a hypotropia in the fellow eye, a base-in prism would be placed in front of the exotropic eye and base-up prism placed before the hypotropic eye. This should permit a straightened head posture and may help prevent skeletal muscular problems for the patient.
Whether you are a patient suffering from diplopia or a doctor caring for a diplopic patient, frustration is frequently encountered. If the clinician can keep in mind the two strategies -- make the patient comfortably fused, or make the patient comfortably monocular -- the task of caring for these challenging patients becomes much more manageable. By using all the tools at our disposal (lenses, prisms, vision therapy, occlusion, and appropriate referral), we can potentially improve the quality of life for the vast majority of patients with diplopia.
1. Percival AS. The Prescribing of Spectacles, 3rd. ed (rewritten) Bristol, England: John Wright & Sons 1928
2. London R, and Wick B. Correction of the vertical associated phoria effect on the horizontal forced-vergence fixation disparity curve. In Problems in Optometry, London R ed. Ocular Vertical and Cyclovertical Deviations. Lippincott. 1992: 646 – 651
3. Marton HB. Some clinical aspects of heterophoria. Br J Physiol Opt 1954: 11: 170 - 175
4. London R. Special forms of vertical and cyclovertical deviation. . In Problems in Optometry, London R ed. Ocular Vertical and Cyclovertical Deviations. Lippincott. 1992: 587 – 606
5. Adams AJ, Kapash RJ, Barkan E : Visual performance and optical properties of Fresnel membrane prisms. I. Distortion. Am J Optom Arch Am Acad Optom 48: 289 –297, 1971
6. Cotter SA, Frantz KA. Practical considerations in prism implementation. In: Clinical Uses of Prism A Spectrum of Applications, Cotter ed. Mosby 1995: 59 - 83
7. Caltrider, Nieca, and Jampolsky A. Overcorrecting minus lens therapy for treatment of intermittent exotropia. Ophthalmology 1983; 79: 1160 – 1165
8. London R, Wick B, Kirschen D. Post-Traumatic Pseudomyopia
Optometry 2003: 74: 111 - 117
9. Scott AB. Botulinum toxin injection into extraocular muscles as an alternative to strabismus surgery. Ophthalmology 1980: 87: 1044 – 1049.
10. Scott AB, Magoon EH, McNeer KW, et al: Botulinum treatment of childhood strabismus. Ophthalmology 1990; 97: 1434
11. Jampolsky A. Vertical muscle surgery. Audio Digest Vol 23 No. 23 1985 (transcript)
12. Kirschen D, Flom MC. Monocular central field occlusion for intractable diplopia. Am J Optom Physiol Opt 1977; 54: 325 – 331
13.Silverberg, M., Schuler, E., Veronneau-Troutman, S., Wald, K.
Schlossman, A., Medow, N. Nonsurgical management of binocular diplopia induced by macular pathology. Arch Ophthalmol 1999: 900-3
14. Burger D, London R. Clinical applications of opaque, soft contact lenses. J Am Optom Assoc 1993; 64: 176-180
15. Roy RR, Zeitner DK, Yolton RL. Use of prolonged monocular occlusion to assess latent vertical imbalace. In Problems in Optometry, London R ed. Ocular Vertical and Cyclovertical Deviations. Lippincott. 1992: 565 – 577
16. London R. Monovision correction for diplopia. J Am Optom Assoc. 1987; 58:568 - 570
Contact this author:
Richard London
Pacific University College of Optometry
2043 College Way
Forest Grove OR 97116
londonr@pacificu.edu
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