Article Text
Abstract
Purpose We describe the spontaneous resolution of hypertropia in a subset of patients with preoperative exotropia and hypertropia, who underwent surgery for intermittent exotropia alone.
Design This was a retrospective case series.
Methods The charts were reviewed of 17 patients who underwent surgical correction for an intermittent exotropia, who additionally were noted on preoperative exam to have greater than 5 prism dioptres of vertical deviation in primary position. Patients were excluded if they had prior strabismus surgery, dissociated vertical deviation, and paretic or restrictive deviations.
Results All patients were documented to have complete resolution of any vertical deviation in any field of gaze. This effect was noted to persist.
Conclusions We propose that the measured distance hypertropia, which is coincident with intermittent exotropia, even with the appearance of superior oblique dysfunction or inferior oblique overaction, is not created by a true vertical or cyclovertical muscle imbalance. Further, that the reduction of the hypertropia at near fixation predicts its resolution with horizontal muscle surgery. Therefore, vertical surgery should not be performed to address the coincident vertical deviation in these patients.
- Muscles
- Treatment Surgery
- Physiology
Statistics from Altmetric.com
Introduction
The combination of a vertical deviation coexisting with a horizontal exotropic deviation has been described; however, it poses a challenge when attempting to restore ocular alignment and binocular function in determining the best treatment for the vertical deviation component. This report analyses the surgical manifestations of patients with intermittent exotropia who additionally present with a clinically significant hypertropia, unrelated to oblique dysfunction, dissociated vertical deviation or paretic muscle. We have defined ‘clinically significant’ vertical deviations as those with a magnitude of 5 prism dioptres or greater in primary position, regardless of the magnitude of deviation in other fields of gaze.1 Previously, 5 prism dioptres was determined as the baseline, which may initiate contemplation of surgical intervention, even if asymptomatic.2 We describe, in these patients, the spontaneous resolution of hypertropia when the exotropic deviation alone is surgically corrected.
Only a few reports have focused on the surgical implications and response of the hypertropia that can coexist with basic intermittent exotropia.3–5 Moore and Stockbridge6 was probably the first to describe the phenomenon of the resolution of hypertropia during preoperative prism adaptation testing for intermittent exotropia. Kushner3 reported on a series of 30 patients with simulated superior oblique palsy and intermittent exotropia, 83% of whom responded with resolution of the hypertropia when the exotropia was corrected. Finally, Cho4 described this in a series of 93 patients with intermittent exotropia. Jampolsky5 described the ‘rising eye’ of the exotropic eye in abduction, which he attributed to oblique dysfunction. However, little description is given for the preoperative clinical characteristics of the patients in all of these studies. Both surgical series also included patients with as little as 1 prism dioptre of vertical deviation preoperatively.
We describe the spontaneous resolution of hypertropia associated with intermittent exotropia in a consecutive group of patients treated surgically for the intermittent exotropia alone. Additionally, we describe preoperative factors, which may help to predict this ‘spontaneous resolution’ of hypertropia, and define it as a clinical entity in association with intermittent exotropia in our patients. In order to guide the surgical correction of these patients, we have limited our study to patients with 5 prism dioptres or greater of hypertropia in primary position, associated with intermittent exotropia.
Finally, we propose the mechanism whereby the near-distance disparity is accounted for and correlate this mechanism to a component of the near response7 that has previously not been a recognised associated component of that response.
Methods
Records were searched for all patients less than 18 years of age who underwent surgical correction for intermittent exotropia by one surgeon (MCS) at the University of Wisconsin Madison from 1/2002 to 12/2012. All patient records were reviewed for the preoperative presence of a vertical deviation. Patients were eliminated from the study if they had the presence of DVD; diagnosis of either surgical consecutive exotropia or spontaneous consecutive exotropia; or constant exotropia. Exclusion criteria also included mechanical or restrictive strabismus, neurologic disorders, visual acuity worse than 20/30 in the poorer seeing eye, anisometropia greater than 2.75 dioptres, hypermetropia greater than 3.75 dioptres in the worse eye and previous or concurrent vertical muscle surgery.
214 charts were reviewed of patients meeting inclusion criteria undergoing surgical correction of intermittent exotropia. No patient who met inclusion criteria was excluded because of a follow-up of less than 5 weeks. 38 patients were noted to have a preoperative vertical deviation in primary position measurements. In 14 patients the vertical deviation in primary position was 4 prism dioptres or less. Five patients had concurrent vertical muscle surgery, two were diagnosed with superior oblique palsy and three were previously reported and included in this study.1 A retrospective case review was conducted of the remaining 17 patients.
All patients underwent complete orthoptic examination, alternate cover testing in primary position determining the magnitude of vertical and horizontal angle of deviation at near (33 cm) and distance (6 m). All patients had cover testing performed in five cardinal fields, and at near, and with appropriate cycloplegic refraction. Stereopsis was tested with Titmus circle or animal stereogram. No patient was treated preoperatively or postoperatively with over-minus spectacle correction. All patients underwent passive forced duction testing to rule out restrictive strabismus under general anesthaesia at the time of surgery.
Surgical correction consisted of bilateral lateral rectus recession (n=4), recession of the lateral rectus and resection of the medial rectus same eye (n=13). No vertical shifting of the muscle reinsertion was made in any case. Fourteen patients had at least 6 months follow-up data.
University of Wisconsin Institutional Review Board approval was obtained and informed consent was obtained from the patient or parents. This study also was in compliance with Health Insurance Portability and Accountability Act regulations.
Results
Seventeen patients met the inclusion criteria for the study; the patients’ average age, in years, at surgery was 7 (range 2–18 years) and 47% were female (table 1).
The characteristics of the preoperative evaluation in our patients included:
The average preoperative intermittent exotropic deviation was 25 prism dioptres at distance fixation, and 22 prism dioptres near fixation. The average hypertropic deviation was 8 prism dioptres at distance (range 5–14) and 1.1 prism dioptres at near (range 0–9). The subjects manifested a relative absence of a vertical deviation in the near measurement; 13 of the 17 patients had no measurable near hypertropia while the exotropic deviation at near was manifested. Of the patients who were old enough for stereo testing, the average preoperative measurement was 150 s stereo arc acuity (range 40–400) and the postoperative measurement was 90 s stereo acuity.
The vertical deviation was comitant in 11 of the 17 patients. Two patients were too young to get accurate measurements in side gaze. One had apparent incomitance and is discussed below, the other appeared comitant, but not included in the 11 listed. Of these 11 patients, the hypertropic distance deviation did not change by more than 2 prism dioptres in side gaze, vertical gaze or head tilt. Additionally, the hypertropia when one eye was fixing was equivalent to the hypotropia when the other eye was fixing in 7 of 11 patients where this was recorded.
The vertical deviation was incomitant in 30% (5) of the patients and positive for the Bielschowsky three-step test;8 these patients had 4 to 13 pd of increasing hypertropia in adduction and on head tilt to the ipsilateral side. In addition, the patients with this pattern of incomitant hypertropia all had over elevation of the hypertropic eye in the field of adduction—pseudo inferior oblique dysfunction. Preoperatively, 4 of 5 of these patients could cooperate for testing and had neither measurable subjective torsion with double Maddox Rod test nor vertical diplopia with prism correction for the exotropia alone. Additionally, none had objective torsion or manifested a compensatory head posture or head tilt. We considered these patients to have simulated superior oblique palsy.3
The preoperative measurements for the hypertropia at distance and near are recorded in table 1. No patient manifested hypertropia or intermittent hypertropia in any field of gaze postoperatively. Additionally, only one patient of the 17 had a measureable distance hyperphoria 6 months postoperatively (table 2).
The exotropic deviation was less than 6 prism dioptres at 6 months in all patients except one, who had a mild recurrent intermittent exotropic deviation, without recurrence of the hypertropia. One patient was overcorrected and required partial reversal of the lateral rectus recession, thereafter maintaining good alignment.
Discussion
The findings in our report are dramatic in that the tropic vertical deviation presents preoperatively in all patients with intermittent exotropic deviations underwent complete spontaneous resolution with surgical treatment of the horizontal component alone. The finding was a complete resolution of the deviation in all fields of gaze, not just improved control or asymptomatic residual deviation. In the patients with simulated superior oblique palsy, this suggests that the vertical deviation, even with the appearance of superior oblique dysfunction or inferior oblique overaction, is not related to oblique muscle imbalance postoperatively.
The maximum hypertropic distance deviation in primary position in this report to spontaneously resolve was 14 prism dioptres. However, larger deviations have been noted to respond with the same effect. In a case not presented here, the subject had a preoperative hypertropia of 25 prism dioptres at distance fixation and 0 prism dioptres at near fixation. Her surgical correction effectively was horizontal surgery alone; she remained without a vertical deviation postoperatively for over 15 years (personal communication BJKushner).
This finding has been noted before;3 ,4 however, the magnitude of the effect, the fact that the effect was total, the effect in other fields of gaze and the duration of the effect were not fully elucidated. Kushner warned against vertical or cyclovertical surgery in this situation. We have previously described a high rate of overcorrection of the vertical deviation when the surgical plan involves operating for the hypertropic component in intermittent exotropia.1 Indeed, Moore et al described the same resolution of the vertical component when patients undergo preoperative prism adaptation for the horizontal deviation alone. Therefore, it seems that surgery is not a necessary component to provide evidence for this effect.
Jampolsky's5 ‘rising eye’ of exotropia has similar features in that the abducting eye will manifest a hypertropia dependent of the eye that is fixing. The non-fixing eye in this syndrome always shows a hyperdeviation that increases as the eye goes further into abduction. In contrast, we did not see the same horizontal incomitance of progressive hypertropia the further into abduction the eye travelled. In fact, the 30% of patients we had with incomitant hypertropia were of an opposite pattern of greater hypertropia in adduction. He attributes the rising eye to longstanding exotropia; our average age at surgery was 7 years old. Further, the mechanism proposed the oblique imbalance and/or superior rectus overaction as creating the rising eye hypertropia as the eye travels into abduction would persist after surgical correction of the exotropia, which is not what we found.
An additional observation noted was the distance-near disparity of the hypertropia in this particular group of patients, which likely stems from a known association of the normal amplitude of vertical motor vergence in association with near fixation.9 ,10 The description of a central mechanism to preprogramme vertical alignment has be shown to be highly associated in near-viewing, disparity-driven, testing. Even without visual fixation clues, the visual system can remember the appropriate vertical location and appropriately maintain a vertical eye position.11 This feature of the ocular system has been termed ‘memory’.11 Our data confirm a vertical vergence adaptation with near fixation that has this memory effect of the near response. All of the patients in this study had reduced near vertical deviation. In fact, in 75% of the patients, the near vertical deviation was absent at the same time that the near exotropia was manifesting despite distance hypertropia of as much as 14 prism dioptres. Since the near exotropic deviation is intermittent and vertical vergence ability and memory is instituted at near, it may be that the vision system ‘remembers’ the correct altitudinal positioning along vertical despite a deficient localisation along the horizontal (manifested exotropia). This group of patients having a deficiency of horizontal near alignment, however, seems to be manifesting the remaining components of the near response. This vertical vergence mechanism for near fixation must be a part of the near response originally described by Donders,12 which includes convergence, accommodation and miosis.
Why only a fraction (16% in our study) of patients with an intermittently tropic horizontal distance deviation manifest a distance hypertropia as well is unclear. Possibly the resting status of most patients’ extraocular muscles produces no inherent vertical imbalance. Possibly this cohort of patients with intermittent exotropic distance deviations have an asymmetric innervation input in the two compartments of the lateral rectus muscle as described by Peng et al,13 which could create a small vertical deviation.
In our surgical patients with intermittent exotropia and hypertropia, we will attempt a short trial of distance prism adaptation for the horizontal deviation alone. If the distance hypertropia resolves (as is most often the case), we do not operate for a vertical misalignment. If the hypertropia persists in distance fixation and is associated with vertical diplopia awareness, further evaluation of the hypertropia is necessary. Our data confirm that the absence of subjective torsion or compensatory head posture, along with an absence of near hypertropia when near exotropia manifests, is a predictor of the postoperative resolution of hypertropia in association with horizontal muscle surgery alone for basic intermittent exotropia.
Footnotes
-
Contributors Conception and design: MCS. Conducting study: MCS. Collection of data: MCS, TJD. Analysis of data: MCS, TJD. Interpretation of results: MCS. Drafting of manuscript: MCS. Approval of manuscript: MCS.
-
Funding Funded in part by an unrestricted grant from Research to Prevent Blindness.
-
Competing interests None.
-
Patient consent Obtained.
-
Ethics approval University of Wisconsin IRB.
-
Provenance and peer review Not commissioned; externally peer reviewed.