Purpose
To evaluate long-term outcomes of surgical treatment for abnormal head positioning (AHP) associated with infantile nystagmus syndrome (INS).
Design
Retrospective observational case series.
Methods
Review of 150 patients who underwent surgery for AHP associated with nystagmus. Outcomes included head positioning, duction limitations, and strabismus, and were evaluated several times postoperatively. Successful collapse of AHP was defined as being ≤10°.
Results
Thirty-one patients had surgery for AHP in the pitch (chin up/down) position, whereas 119 had surgery for a horizontal AHP. In addition, 54 underwent 50%-60% augmentation, 19 underwent 40% augmentation, 5 underwent less than 40% augmentation. Thirty-eight had surgical dose modified to correct strabismus, and 3 underwent surgery different from standard Kestenbaum procedures. Collapse of AHP: At the 1-3-week follow-up (n = 131), 125 patients (95%) had collapse of AHP. The percentage trended down at the 2-5-month (91%, n = 106) and 2-year follow-ups (83%, n = 57). However, at 5 and 10 years, it was 93% (n = 42) and 93% (n = 14), respectively, due to reoperation in a small minority. Over- and undercorrection: At 1-3 weeks, 5% of patients were overcorrected whereas 0% were undercorrected. Over- and undercorrection rates peaked at 2 years postoperatively. Ten years out, there were no overcorrections and 7% undercorrections. Four percent of patients required reoperation for overcorrection (mean 2.7 years) and 5% did for undercorrection (mean 3.9 years).
Conclusion
Surgery for the head positioning associated with INS produces excellent outcomes throughout 10 years postoperatively. Overcorrection presents early and resolves either over time or with additional surgery. Undercorrection develops later and can persist despite reoperation.
Patients with infantile nystagmus syndrome (INS) often develop an abnormal head position, where the amplitude of nystagmus is reduced to a minimum. Surgical treatment of abnormal head positioning (AHP) associated with INS has progressed since the first surgeries were proposed in the early 1950s. Anderson postulated that there was a relative overaction of the muscles driving the slow phase of nystagmus and proposed a 2-muscle surgery to recess these muscles. Goto suggested an underaction of the muscles driving the fast phase of nystagmus and proposed a bilateral resection of the muscles driving the fast phase. Kestenbaum independently proposed a 4-muscle surgery that combined both Anderson and Goto’s recessions and resections to move the globe in the direction of the head turn.
Subsequent modifications of Kestenbaum’s numbers have been proposed, including Parks’ classic maximum, which described a resection and recession of a sum total of 13 per eye (5-6-7-8 rule). Parks suggested that this was the maximum surgery that could be done without risking rotational deficits. Since then, augmentations of increasing magnitude have been proposed, and others have shown success with 40% or 60% augmentations of Parks’ numbers, depending on the degree of the head positioning. , Others have described modifications for head positioning that occurs in the pitch (chin up/chin down) and torsional (head tilt) position.
We sought to report long-term efficacy of surgical treatment of compensatory head positioning in congenital nystagmus. We performed a retrospective, observational study of the long-term efficacy of surgical correction of AHP associated with nystagmus.
Methods
A retrospective chart review was performed on 150 patients who underwent eye muscle surgery for AHP associated with nystagmus at Vanderbilt Eye Institute between 1995 and 2018. This study was deemed IRB exempt by the Vanderbilt Institutional Review Board (IRB), and all data collection was in conformity with county, federal, or state laws, and was in adherence to the tenets of the Declaration of Helsinki.
Head position, duction limitation, strabismus (if present), and visual acuity were evaluated at the preoperative visit, 1-3 weeks postoperatively, 2-5 months postoperatively, 2 years (±6 months), 5 years (±9 months), 10 years (±1 year) postoperatively, and at the last follow-up visit.
Horizontal head position was approximated by the attending physician and recorded in degrees and subsequently categorized into minimal (≤10 degrees of straight), mild (11°-29°), moderate (30°-44°), and severe (≥45°). Vertical head posturing was approximated by observation and divided into 3 categories (instead of 4) of minimal (1°-15°), moderate (16°-30°), and severe (31° or more). We did not use a goniometer to measure head position as it was not standard practice at that time in our clinic. Postoperatively, a collapse of head positioning to minimal was considered a successful surgery. Ductions and versions were graded from –4 to + 4, with –2 to –1 considered a mild duction limitation and –3 to –4 considered a severe duction limitation. Magnitude of strabismus (if present) was measured in prism diopters (PD) using simultaneous prism and cover test and prism and alternating cover test. Strabismus was defined as a manifest deviation that exceeded 8 prism diopters.
In a verbal child, binocular visual acuity was recorded using an age-appropriate optotype acuity and converted to logMAR (logarithm of minimal angle of resolution). When binocular vision was not recorded, the visual acuity of the better-seeing eye was converted to logMAR. In a preverbal child, the central-steady-maintained method was used to evaluate visual acuity.
For patients with horizontal preoperative head positioning, graded surgery was performed depending on the magnitude of baseline head positioning. A 50%-60% augmentation of Parks’ maximum was done if preoperative head positioning was severe. A 40% augmentation was done if the preoperative head positioning was moderate. Unlike in horizontal cases, surgical planning for vertical cases represented maximal doses of recession-resection of vertical recti or weakening of both agonist muscles depending on the procedure.
When strabismus coexisted with abnormal head posturing, surgery was performed on the fixating eye based on the head position, but decreased in magnitude if the proposed surgery would worsen the strabismus.
Wilcoxon signed rank tests were used to evaluate for changes in visual acuity over time.
Results
Ninety-three patients were male and 57 were female. Mean age at surgery was 8.1 years. Of the 150 patients, 31 had surgery for AHP in the pitch (chin up/down) position, and 119 had surgery for a horizontal AHP. Fifty-five patients underwent 50%-60% augmentation, 19 underwent 40% augmentation, and 5 underwent less than 40% augmentation; 37 patients had surgery modified for strabismus, and 3 underwent nonstandard procedures. Of these, 2 were modified Anderson procedures and 1 was a Kestenbaum reoperation with unknown prior surgery. A total of 57 patients has sensory abnormalities, 88 patients had idiopathic congenital nystagmus, and 5 had acquired forms of nystagmus.
Of 150 patients, 132 patients presented for their 1-3-week follow-up, 107 patients presented for their 2-5-month follow-up, 57 patients presented for 2-year (±6 months) follow-up, 42 patients presented for 5-year (±9 months) follow-up, and 14 were seen 10 years (±1 year) postoperatively. Overall, only 21% of patients required a second operation.
Preoperative head positioning
Preoperatively, 93 (62%) had severe head positioning, 22 (15%) had moderate head positioning, and 3 (2%) had mild head positioning. Given the retrospective nature of this study, 31 patients (21%) had a head positioning that was reported in direction but not quantified, and 1 patient did not have any reported baseline head position reported despite having surgery for a vertical head position.
Collapse of AHP Outcomes
Collapse of head positioning was defined as resolution of head positioning to within 10 degrees of straight for horizontal cases, and within 15 degrees of straight for vertical cases. At the 1-3-week follow-up (n = 132), 126 patients (95%) had collapse of AHP. The success rate trended down during the 2-5-month (91%, n = 107) and 2-year follow-ups (82%, n = 57). However, at 5 and 10 years, 93% (n = 42) and 93% (n = 14) of patients had successful collapse of head positioning, respectively, due to several patients having reoperation.
Over- and Undercorrection of AHP Outcomes
At 1-3 weeks, 5% of patients were overcorrected, whereas none were undercorrected. Over- and undercorrection rates peaked at 2 years postoperatively at 11% and 7%, respectively. Ten years out, none were overcorrected and 7% were undercorrected. Six patients (4%) required reoperation for overcorrection (mean 2.7 years later), and 7 patients (5%) did for undercorrection (mean 3.9 years later) ( Figure 1 ).
Duction limitations
Significant duction limitations were noted in 9% of patients at the 2-5-month visit, in 10% of patients at the 2-year visit, in 5% of patients in the 5-year visit, and in no patients in the 10-year visit. Minor duction limitations were noted in 63% of patients at the 2-5-month visit, in 60% of patients at the 2-year visit, in 68% of patients in the 5-year visit, and in 60% of patients at the 10-year visit.
Development of Strabismus
Overall, a total of 6.7% of patients developed a new strabismus with an average magnitude of 18.7 PD. Only 5% of horizontal cases had an induced strabismus with an average magnitude of 10.3 PD. However, 13% of patients with pitch head positioning developed new strabismus with an average of 31.3 PD esodeviation. Most of these patients had induced V pattern esotropia, resulting from vertical recession resection procedures. The overall reoperation rate due to new strabismus was 3.3%.
Visual Acuity (BV)
Mean visual acuity is summarized in Table 1 . Overall, there was no statistically significant change in visual acuity at 1-3 weeks, 2-5 months, 2 years, 5 years, and 10 years compared with preoperatively as calculated by the Wilcoxon signed rank test.
