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255 NeuroRehabilitation 27 (2010) 255–259 DOI 10.3233/NRE-2010-0606 IOS Press A new prism use for treatment of cyclo-deviation in trochlear nerve injury Thomas Politzer∗ , Mark Cilo and Alan Weintraub Craig Hospital, Englewood, CO, USA Abstract. Visual problems are common in patients with severe TBI [1]. Diplopia is among the most frustrating of visual disturbances for patients, due to its functional consequences. This is further compounded by often slow, and at times, incomplete or partial recovery over six months or longer. Ocular cranial nerve injuries (particularly trochlear nerve) occur in 0.2%–1.4% of severe TBI patients [2]. This paper presents a new prism treatment application for treating rotational diplopia arising from Trochlear nerve injury. 1. Background Diplopia is a serious and often intolerable visual condition that occurs following an acquired, decompensated, and/or non-suppressed strabismus [2]. Not only is the diplopia itself a problem, but it frequently has a negative effect on rehabilitation therapy in other domains (i.e. speech and language, cognition, perception, mobility, and activities of daily living or ADL). For these reasons, it is important to diagnose and treat diplopia as soon as possible. Of particular difficulty and frustration is the treatment of a rotational [torsional] deviation. Most commonly the rotational deviation is outward (excyclotorsion) and is caused from damage to the Trochlear Nerve (CNIV). The Trochlear Nerve innervates the superior oblique muscle whose action is to lower the gaze of the eye when it is adducted and to in-cyclo rotate the eye in all positions except for adduction. Trochlear nerve palsy has been mentioned in ophthalmology texts dating back to the mid nineteenth century. Historically, it received little attention until Bielschowsky, in 1935, correctly reported that trochlear nerve palsy was the most common cause of vertical diplopia and introduced his classic head-tilt test [3]. ∗ Addresss for correspondence: Dr. T. Politzer, Craig Hospital, 3425 S Clarkson St., Englewood, CO 80113, USA. E-mail: tpolitzer @msn.com. Many treatments have been used over the years to correct, or reduce diplopia from an acquired strabismus. These have included lenses, prisms, patching, surgery and medication. Most of these approaches have been used for over 50 years. Unfortunately, the non commitant [variable depending on direction of gaze] and torsional deviation resulting from Trochlear Nerve injury make it particularly refractive to successful treatment. 2. Signs and symptoms Patients with an acquired Trochlear Nerve injury will typically complain of a variable vertical, angular and tilted diplopia. This is especially prominent in down gaze. The patient frequently exhibits a head tilt away from the affected side. Visual acuity should not be affected and there is rarely pain. However, obtaining reliable complaints from TBI patients is difficult, due to their confusion or aphasia or other neurological deficits; thus the subjective experience of their diplopia is difficult to elicit. 3. Anatomy and pathophysiology The Trochlear Nerve nucleus is located in the dorsal aspect of the midbrain. It is the only Cranial Nerve to exit the brainstem dorsally. The nerve travels a long ISSN 1053-8135/10/$27.50 2010 – IOS Press and the authors. All rights reserved 256 T. Politzer et al. / A new prism use for treatment of cyclo-deviation in trochlear nerve injury course. From the nucleus, fibers traverse the subarachnoid space, the cavernous sinus, the superior orbital fissure to the orbit and then innervate the superior oblique muscle [4]. The Trochlear Nerve is particularly vulnerable to trauma as it exits the brain stem. Closed head injury is the most common cause of Trochlear Nerve palsy [4] Khawam and co-workers reviewed 3000 cases of strabismus, in which there were 40 cases of acquired superior oblique palsy. Sixty-eight per cent of the acquired superior oblique palsies were caused by closed-head trauma. Uncertain etiology was noted in 20 per cent, and the remainders were from stroke, diabetes, brain tumor, ethmoiditis, and mastoiditis [6] Von Noorden reviewed 270 cases of superior oblique paralysis and found that 40 percent were congenital, 34 percent were traumatic, 23 percent were idiopathic and 3 percent were due to other causes such as vascular disease, tumors or myasthenia gravis. Frequently no definitive cause was identified [5]. 4. Evaluation With the presentation of new onset diplopia caused by a Trochlear Nerve palsy, it should be determined if the palsy is acute, or from a latent disorder that has decompensated. Newly acquired palsy requires detailed evaluation including neurologic examination and neuro imaging. The Park three-step test is used in evaluation of vertical diplopia caused by a paretic cyclovertical muscle [7] Each step reduces by half the number of possible affected muscles until only 1 remains. The Bielschowsky head-tilt test stimulates intorsion of the globe on the side to which the head is tilted and extorsion of globe on the side away from which the head is tilted. The presence of an excyclotorsion can be determined by using a single or double Maddox rod test. 5. Historical treatment Patching an eye that deviates and causes diplopia has been used for over a hundred years. Full patching will relieve the diplopia, but causes a 25% to 30% reduction of peripheral vision to the patched side and eliminates binocular stereoscopic vision. The “Spot Patch” [Politzer] is a method of partial patching without these limitations [8]. Prisms have been used with good success for patients with diplopia without torsional component. Non commitance of deviation will, however, reduce the effectiveness of prism therapy. Botulinum toxin has been studied in treatment of Trochlear Nerve palsy. Use of this agent as primary therapy has not been satisfactory [3]. In the 1970s, Knapp developed a surgical approach for superior oblique palsy [9] Plager described a tailored treatment plan that evolved from Knapp’s recommendations, with some additions based on more recent operative algorithms [10] The modified Harada-Ito procedure is useful for patients with large excyclotorsional deviation [3]. 6. Prognosis Prognosis of trochlear nerve palsy varies depending on etiology. According to records collected at the Mayo Clinic over the past 40 years the following has been found. Recovery is most likely in patients whose superior oblique palsy is secondary to microvascular disease. Idiopathic cases have greater than 50% likelihood of spontaneous recovery. Most cases resolve within weeks to months, with the vast majority completely recovering by 6 months. Some cases may resolve slowly over the course of a year. Patients with TBI were less likely to recovery; yet, nearly 50% of these patients showed some degree of improvement [9]. Cases due to aneurysm or neoplasm were least likely to have functional recovery. Unfortunately, partial recovery may only alter or diminish, but not eliminate all aspects of the diplopia [10]. 7. The cyclo prism While surgery may or may not ultimately be the method indicated for treatment of diplopia from a Trochlear Nerve Palsy there are several issues to consider. Most importantly is how to help the patient during the time period when the patient is having diplopia. It will be more bothersome when superimposed on other neurologic deficits. It can affect recovery and interfere in other areas including functional cognition, mobility and activities of daily living. When there is a rotational deviation, the use of prisms has been ineffective up to now. Prism bends light in a linear fashion, but what is needed is a rotational bend. It has been discovered that tilting a prism 10 to 15 T. Politzer et al. / A new prism use for treatment of cyclo-deviation in trochlear nerve injury 257 Fig. 1. Left Retro Tilt. degrees around the axis passing from its apex to the base gives a two dimensional displacement of approximately 8 degrees. For example: a 2 diopter base out prism tilted so the bottom is moved out relative to the top [retroscopic tilt] gives the perception of the viewed object in an “in-cyclo” rotated manner [to compensate for an ex-cyclo deviation]. A base in prism tilted so the top is moved out relative to the bottom [pantoscopic tilt] also gives the perception of the viewed object in an “in-cyclo” rotated manner. A base down prism angled so the outer lateral side of the prism is moved away from the patient this will give the perception of incyclorotation. From a clinical and visual perspective, this two-dimension displacement closely simulates a rotational displacement and has been found to be effective in compensating for a cyclo-deviation. Once the cyclo deviating eye is determined [or both as with bilateral Trochlear Nerve palsy] then measurements to determine the amount of prism to neutralize are done with a trial frame. Combinations of prism are used until the least amount of prism that gives a range of single vision is determined. The appropriate amount of tilt can be obtained by “X’ing” or twisting the eyeglass frame the required amount as noted in these photos (Figs 1 and 2). 8. Case reports T.K. was a 57 year old male when he suffered acute bilateral cerebellar and right occipital ischemic strokes. He complained of intermittent double and “tilted” vi- sion. Additional symptoms included dizziness and he was unable to perform his in hospital vestibular therapy because of his vision. Uncorrected distance visual acuity was 10/15 right eye and 10/20 left eye. Cover test showed a very small angle left hyper phoria. Maddox rod testing showed a gaze dependent variable left excyclo deviation. Ocular fixations were intact without nystagmus. Ductions and versions were full. Pursuits were noteworthy for a +2 ataxia. Saccades were intact. Convergence was 4 inches. Pupil reflexes were intact direct, consensual and to accommodation with no afferent defect. Visual field testing was full. External and fundus exams were unremarkable. Binocular testing showed elimination of the “tilted” vision with 2 base out retro tilt prism left eye. With prism in place vestibular exercises were done easily and without complaint. T.K. was diagnosed with a mild Fourth Nerve palsy left eye. He was prescribed 2 base-out prism retro tilt left eye to be worn during therapy and while ambulating. Follow-up was scheduled for two weeks. T.K. was re-examined 10 days later. The therapist reported he had discontinued wearing the prism. T.K. reported they helped significantly at first and then he did not feel he needed them after about a week. He no longer had any complaints of “tilted” vision, or dizziness. Testing showed resolution of the excyclo deviation. A.B. was a 23 year old male when first examined. He had sustained a TBI with diffuse axonal injury one month prior from falling down some stairs. His chief visual complaint was of constant double and tilted vision. 258 T. Politzer et al. / A new prism use for treatment of cyclo-deviation in trochlear nerve injury Fig. 2. Left Panto Tilt. Examination was completely normal except for a non commitant left hyper excyclo deviation consistent with left Trochlear nerve palsy. Prism was trialed and he was able to achieve a moderate range of single straight vision with 3 base up prism right eye and 4 base down lateral tilt left eye. This was placed on a temporary eye glass frame with Fresnell prisms. Therapy was prescribed to enhance the range of single vision. In most acute care rehabilitation hospitals, the occupational therapist is charged with addressing vision. In hospitals with a vision clinic therapy is typically done by the patients’ primary occupational therapist. While OT’s are taught the basics of vision in school, the OT’s in our clinics have received additional post graduate training in vision rehabilitation. Resources are available through different organizations and individuals (Appendix 1). At subsequent follow-up visits the amount of prism was reduced and therapy continued. At discharge he had single vision 80% of the time to all but far lower right gaze. He was dispensed a retainer prism and has not regressed. scopic vision, and places the cornea at risk in TBI patients. A novel prism application has now been defined that can help the patient achieve greater relief from diplopia from Trochlear nerve involvement. Even for patients who might spontaneously improve with time, it is an effective tool to manage symptoms during their recovery. For TBI patients engaged in a comprehensive, in-patient rehabilitation program, a reduction in their diplopia will have significant positive impact on all other aspects of their treatment, thus facilitating functional progress and overall improvement in vision and quality of life. Appendix 1 Resources for post graduate education in vision rehabilitation 1. Neuro-Optometric Rehabilitation Association (a) www.nora.cc 2. College of Optometrists in Vision Development (a) www.covd.org 9. Conclusion Diplopia resulting from a Trochlear Nerve is a difficult strabismus to treat. 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Cause and prognosis in 1,000 cases. 1: s.l., Archives of Ophthalmology 99 (January 1981), 76–79. Copyright of NeuroRehabilitation is the property of IOS Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.