Prism Use in Adult Diplopia

Kammi B. Gunton; A'sha Brown

Disclosures

Curr Opin Ophthalmol. 2012;23(5):400-404. 

In This Article

Vertical Deviations

There are many causes for vertical diplopia. Prism use in fourth nerve palsy, skew deviations, decompensated childhood strabismus, thyroid eye disease, and blowout fractions will be covered in this section.

Fourth Nerve Palsies

Vertical deviations are often more disabling in adults because of low vertical fusional amplitudes. Although the typical prism prescribed for horizontal deviations is generally 50% of the total deviation, a greater percentage of the total deviation is needed for vertical strabismus. Incomitance in fourth nerve palsies is particularly difficult to address with prisms. In fact, some studies have suggested that prism should not be attempted in patients with fourth nerve palsy because of the incomitance.[6] A recent review of fourth nerve palsies showed good outcomes with prism.[2] In this study, adults with acquired fourth nerve palsy had an average vertical deviation in primary position of 5.5 prism diopters. Most patients did not have an accompanying horizontal deviation. These patients required the full 5.5 prism diopters of correction to relieve the diplopia, consistent with poor vertical fusional amplitudes. In the same review, patients with symptomatic congenital fourth nerve palsies had larger deviations in primary with a mean deviation of 8.3 prism diopters. These patients required a mean prismatic correction of 6 prism diopters or 73% of their total deviation. In another review of patients with both congenital and acquired fourth nerve palsies, the mean deviation in primary was 7.7 prism diopters and a mean correction of 6 prism diopters in Fresnel prism was prescribed.[1]

Successful use of prism was subjectively reported by Tamhankar et al.[7] as completely satisfied, mostly satisfied (with some residual diplopia or asthenopia), or unsatisfactory because of persistent diplopia. In this retrospective review, all patients included in the study were treated with prism, probably resulting in a physician bias of patient selection.[2] Prism would only be prescribed if the physician felt the patient was likely to be satisfied. Nevertheless, with these criteria for success, 75% of patients with congenital fourth nerve palsy were completely satisfied and 92% were completely or mostly satisfied. In patients with acquired fourth nerve palsy, 78% were completely satisfied with prism correction and 86% were completely or mostly satisfied.[2] In the Fresnel study, 50% of patients continued with Fresnel prism correction permanently.[1] High success rates may result from adequate management of patient expectations. In addition, patients with congenital fourth nerve palsies have high vertical fusional amplitudes, allowing for better fusion in gazes in which the deviation is not fully corrected with prisms.

Skew and Decompensated Childhood Strabismus

A similar study of patients with skew deviation found that prism correction for on average 92% of the total vertical deviation in primary position resulted in 100% satisfaction with prism treatment in a small group of patients.[2] The mean vertical deviation in primary position was small (5.5 prism diopters), and the total mean correction was essentially the total deviation (6.1 prism diopters). In patients with decompensated strabismus, the mean vertical deviation was even smaller (4.0 prism diopters) with full prismatic correction given.[2] Patients with decompensated strabismus also had horizontal deviations, and oblique prism was attempted. Possibly because of the combination of vertical and horizontal prism, these patients reported a lower prism satisfaction rate of 85%. In another study of patients with vertical diplopia from long-term disruption of fusion, most patients had a combination of horizontal and vertical deviations.[8] Horizontal deviations were managed with exercises to increase horizontal fusional vergences. Vertical deviations were treated with prism. Successful resolution of diplopia was reported in three of the five patients in this report.

Thyroid Eye Disease

Patients with thyroid eye disease-related strabismus also often have incomitant deviations because of greater disease involvement of the inferior and medial rectus muscles. The average prismatic correction for thyroid eye disease patients was 9.2 prism diopters, with 72% of cases needing vertical prism.[1] Fresnel prism adequately corrected the diplopia in primary position for all but one patient, although the satisfaction with prism was reduced in this incomitant condition with only 55% of patients reporting complete satisfaction.

Patients with thyroid eye disease following inferior rectus recession may also present with diplopia limited to downgaze. Options to correct this situation include Fresnel prism in the bifocal segment, separate reading glasses with prism, ground-in prism in the bifocal segment by slab-off, unequal bifocal heights with induced prism, or occlusion of the bifocal segment for the nondominant eye. Fresnel prism in the bifocal segment is often not tolerated in these patients because of image blur.[9] In Kushner's [9] study, only 11% of patients were satisfied with this treatment. Ground-in prism in the bifocal segment using slab-off or reverse slab-off technique was also poorly tolerated because of the increasing deviation in progressive downgaze (17% success).[9] The most successful treatment for this condition was raising the bifocal segment in the spectacles and switching progressive-type bifocals for classical bifocal segments.[9]

Blowout Fractures

Patients with diplopia associated with blowout fractures have the additional treatment option of orbital fracture repair. Diplopia may occur from entrapment of the muscle, muscle or soft-tissue edema, muscle fibrosis, or associated cranial nerve palsies. In cases of entrapment of the inferior or medial rectus muscle, release of the muscle and fracture repair should be instituted usually within 48 h of the injury. The reported incidence of diplopia following blowout fractures varies from 57 to 86%.[10,11] In a review of diplopic cases, 63–74% of patients had elimination of the diplopia with orbital fracture repair [10,12]. In another study, diplopia was eliminated in 89% of patients with orbital fracture repair alone.[13] Alternatively, strabismus surgery can be delayed from the time of injury by several months to allow improvements in periorbital tissue and extraocular muscle edema and hemorrhage. The mean time to strabismus surgery following trauma was 10 months in Ceylan et al.'s[12] cohort. Eighteen percentage of all the patients required strabismus surgery. Persistent diplopia remained in 2% of patients in a large cohort with blowout fractures following orbital repair from Spain.[2] Eight percent of Ceylan's patients were successfully treated with prism without strabismus surgery.[12]

In patients undergoing inferior rectus recessions for diplopia from orbital floor fracture, postoperative persistent diplopia in downgaze may occur if the involved inferior rectus muscle is partially paralyzed or suffers a flap tear from the orbital fracture. This results in a hypertropia of the involved eye in downgaze. The treatment options then become the same as for thyroid patients with the similar complaint of diplopia in downgaze only.

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