FP448 : Prospective evaluation of graded Anderson procedure in idiopathic infantile nystagmus

Dr.Sandra Chandramouli, Dr.Shilpa Rao

Abstract

Aim: To study the efficacy of gradation in augmented Anderson procedure for correction of anomalous head posture (AHP) in idiopathic infantile nystagmus (IIN).

Methods: Thirty seven participants between 5 and 37 years of age having IIN with eccentric null position and anomalous head position were enrolled in an institution-based study. Best-corrected visual acuity (binocular, in both null position and primary position), anterior segment evaluation, fundus examination, ocular motility examination and stereopsis (using TNO for adults and older children, Titmus fly test for younger children)were recorded. In all cases augmented Anderson procedure with mild gradation in the recession of the yoke muscles was performed, depending on the initial head turn. AHP was recorded before and 1 and 3 months after surgery. Visual acuity(binocular, in the primary position) and stereopsis before and after surgery were also recorded.

Results: All participants had improvement in their anomalous head posture after surgery, which improved frommean value of 22.5 ±6.12 degrees of head turn preoperatively to 7.58 ± 3.62 degrees at 1 month postoperative review (p<0.001). The mean binocular visual acuity was seen to improve from 0.47 ± 0.15 preoperatively to 0.25 ± 0.17 after surgery(p<0.001).

Conclusion: The gradation inaugmented Anderson procedure based on the initial head turn is successful in correcting moderate AHP in patients having IIN. It has the added advantage ofpreserving ocular motility in smaller face turns and leaving behind 2 recti muscles for future surgeries.

Key words

Idiopathic infantile nystagmus, anomalous head posture, graded Anderson’s procedure

Introduction

Idiopathic infantile nystagmus (IIN) is a disorder of unknown etiology characterized by early presentation and producing horizontal, jerky, involuntary oscillations of the eye. Typically these patients have a null zone and dampening of the nystagmus on convergence. Adoption of anomalous head posture occurs to increase the visual function, in 20% to 70 % of the patients, due to an eccentric null zone (zone of minimal nystagmus intensity)¹.

Various surgical and nonsurgical treatment modalities have been tried for the correction of anomalous head posture and visual function in IIN.

Anderson’s procedure² involves recessions of horizontal yoke muscles, responsible for the slow phase of nystagmus. Over the years, multiple modifications have been performed on the original Anderson procedure such as 2 mm retroequatorial recession of yoke muscles (modified Anderson procedure) and augmented Anderson procedure (12 mm recession of lateral rectus, LR and 9 mm recession of medial rectus, MR).

In this study we have performed Anderson’s procedure in patients with IIN, in a graded manner. The amount of yoke muscle recession was decided individually in each case, based on the initial head turn, rather than maintaining the same surgical dose for all subjects.

Materials and methods

All patients withIIN and eccentric null zone presenting with AHP, who were above the age of 5 years and who underwent surgical correction for AHP, were included in a prospective study between January 2014 and December 2017, following approval from the Institutional Review Board.  Two of the participants includedin the study had manifest strabismus (exotropia) in primary gaze and their surgical plan included correction for strabismus, along with primary surgery (Anderson procedure). (participants 19 and 21). One patient underwent a second surgery (resection of yoke muscles), for the correction of residual AHP, following primary procedure. (Table 1, participant 3).

Details of all the participants are included in Table 1

Patients who had prior extraocular muscle surgery, those with cosmetically acceptable AHP(< 10 degrees of face turn), nystagmus secondary to sensory cause or neurological disorders or those who did not desire surgery were excluded from the study.

Distance and near visual acuity measurements (binocular, in both primary position and null position) were recorded by a masked examiner using Snellen’s chart or Sheridan Gardiner chart, depending on the patient’s age. The values obtained were converted to LogMAR using standard charts for the ease of statistical analysis. All patients underwent anterior segment evaluation, ocular motility evaluation, fundus examination and stereopsis recording using The Netherlands Organization for Applied Scientific Research (Lameris Instrumenten b.v., Utrecht, Netherlands) (TNO) charts in adults and Titmus fly test in younger children. Head turn was elicited by asking the patients to read the lowest line they could on the distance visual acuity chart (6 m) and the angle between the visual axis and the sagittal axis was recorded with a goniometer.

Patients underwent a modification of augmented Anderson’s procedure (after obtaining informed consent), where the amount of yoke muscle recession was graded based on the amount of head turn as follows

• 30 degrees of head turn- 12 mm of lateral rectus(LR) and 9 mm of medial rectus(MR)
• 20- 25 degrees of head turn- 11mm of LR and 8 mm of MR
• 15 degrees of head turn- 10 mm of LR and 7 mm of MR

All patients underwent surgical correction under general anesthesia and were reviewed 1 month and 3 months post operatively. The parameters recorded on review were amount of head turn, ocular motility, visual acuity (binocular, in primary position) and stereopsis.Patients also underwent video recording of pre and postoperative head postures for documentation of clinical findings.

Statistical analysis

Statistical analysis was performed using the software STATA 14.0 (Texas, USA). Wilcoxon signed rank test was used to assess the statistical significance of change in AHP (head turn) from the preoperative value to the amount of head turn seen 1 month post operatively.  Similarly the improvement in visual acuity in the primary position seen 1 month after surgery was calculated and its statistical significance was analyzed using Wilcoxon signed rank sum test.

Results

The study included 37 participants (26 males and 11 females). Mean age was 12.39 ±8.64years at the time of surgery and it ranged from 5 years to 49 years. Thirty five (94.59%) of the patients had idiopathic infantile nystagmus with AHP alone and 2 patients had associated strabismus along with IIN.

Details of the same are shown in Table 1.

Abnormal head posture

All participants had improvement in their head posture following surgery. The head turn decreased from mean value of 22.5 (±6.12) degrees preoperatively to 7.58(± 3.62) degrees at 1 month postoperative review. Preoperative median value of head turn was 20 degrees and showed a statistically significant improvement to 5 degrees after surgery (p < 0.001).

Visual acuity

The binocular visual acuity in primary position (LogMAR) was compared before and after the surgery to ascertain the shifting of null zone to primary position. The mean acuity was seen to have improved from 0.47 ± 0.15 preoperatively to 0.25 ± 0.17 after surgery. Median value of 0.50 (IQR 0.30- 0.60) improved to 0.25(0.10- 0.35), the change was seen to be statistically significant (p<0.001).

Ocular alignment and motility

All patients were orthotropic in primary gaze at the time of postoperative review. The 2 patients who underwent strabismus correction also attained good ocular alignment in the phoria range. There was no restriction of ocular movements in any patient following surgery.

Discussion

Multiple surgical and nonsurgical modalities have been tried in an attempt to alleviate the symptoms of IIN. Initial approaches included prescription of spectacles with prisms³, apex pointing towards the direction of neutral zone; Botox injections to recti muscles⁴, pharmacological therapy⁵, contact lenses and so on.

Surgeries for nystagmus were broadly classified into two categories; those for correction of head posture such as Anderson- Kestenbaum procedure and modified Anderson procedure, and those for improvement of the visual acuity- four horizontal muscle recession (Bietti and Bagolini⁶), artificial divergence⁷ and tenotomy of recti muscles⁸. Now it is known that most surgeries for nystagmus correct all aspects of visual function and AHP.

Surgical correction for treatment of anomalous head posture in nystagmus was suggested independently by Anderson and Kestenbaum⁹ in the year 1953 and Goto¹⁰ in 1954. Anderson postulated that the muscles acting in the slow phase of nystagmus overacted causing AHP and advised recession of the involved muscles. Goto attempted to address this problem by advising strengthening procedure for the muscles acting in the fast phase of nystagmus. Kestenbaum advocated a combined two-stage recession–resection of all four horizontal rectus muscles.

Augmented Anderson procedure is one of the many surgical options in patients with IIN.It has the advantage of being more physiological and offering opportunity for reversal or for additional surgery in the event of residual AHP following first surgery. There are a few studies in literature outlining the various aspects, modifications and outcomes of the procedure.

A study by Arroyo- Yllanes et al¹¹described the modified Anderson procedure in 21 patients with AHP. They performed 2 mm retroequatorial recessions on the horizontal recti muscles and found that this successfully corrects the AHP, mainly head turn and also the vertical and torsional components.

Following this, another prospectiveevaluation by Gupta et al¹², studied the effect of augmented Anderson procedure on 12 patients with IIN and AHP, where large recession of horizontal yoke muscles (12 mm for lateral rectus and 9 mm for medial rectus) was performed in all patients. Most of the participants included in this study had large head turns (30 degrees or more), hence the results of the above surgical dosage were found to be cosmetically and functionally acceptable.

The participants in our study exhibited a greater diversity in the amount of AHP at presentation, ranging from 15 degrees to 30 degrees or more, with most of the patients displaying a moderate degree of AHP. Hence we employed a modification of Anderson procedure, where the surgical dose was titrated based on the amount of initial head turn. We found that all the participants had statistically significant improvement in the head turn. Individual analysis of each patient shows that only one patient had undercorrection when corrected thus (Table number 1, participant 37). Two of the participants with large initial head turns (30 degrees or greater) had significant residual head turn (15 degrees or more) and were advised second surgery for residual AHP. One of them underwent resection of the antagonist muscles as a second surgery and had good surgical outcome.(Table 1, participant 3)

Another study conducted by Anand Kumar et al¹³evaluated the visual acuity in patients with IIN before and after the surgery. They found that all the patients, including those that underwent augmented Anderson’s procedure, demonstrated a measurable improvement in visual acuity. These results were similar to ours, indicating a shift of the eccentric null zone to the primary gaze.

One of the drawbacks of our study was the unavailability of stereopsis recordings. We were also unable to measure other characteristics of the nystagmus such as intensity and amplitude. In spite of the above lacunae in our study, we observed a modest improvement in head turn and most participantshad an improvement in binocular visual acuity in the primary position. Some of the participants also reported a subjective decrease in intensity of nystagmus.

In conclusion, we agree with Arroyo-Yllanes et aland Gupta et althat augmented/modified Anderson is the preferred surgical choice for correcting head posture because it is simpler with fewer number of muscles being operated on and it only deals with recession, which is more physiological and can be effectively reversed if need be.Addition of a grading algorithm to augmented Anderson procedure is helpful specifically in moderate (20° to 25°) head turn. The vision is seen to improve and the nystagmus dampens in the primary position with mild/minimal restriction of gaze. It is technically easier to perform in small children and patients with smaller or deep set eyes. It leaves behind 2 muscles, for further correction and allows for additional surgical procedures, such as correction for coexisting strabismus.

References

1. Hertle RW, Zhu X. Oculographic and clinical characterization of thirty-seven children with anomalous head postures, nystag­mus, and strabismus: the basis of a clinical algorithm. J AAPOS. 2000;4:25-32.
2. Anderson JR. Causes and treatment of congenital eccentric nys­tagmus. Br J Ophthalmol. 1953;37:267-281.
3. Metzger EL. Correction of congenital nystagmus. Am J Ophthalmol1950;33:1976.
4. Carruthers J. The treatment of congenital nystagmus with Botox. J PediatrOphthalmol Strabismus. 1995;32(5):306–308.
5. Kimberly Penix, Mark WSwanson, Dawn K DeCarlo1,2 Nystagmus in pediatric patients: interventions and patient-focused perspectives.Clinical Ophthalmology 2015:9 1527–1536
6. Bietti GB, Bagolini B. Traitement medico-chirurgical du nystag­mus. L’AnneeTherClinOphtalmol. 1960;11:268-293.
7. Cuppers C. Probleme der operativen T herapie des okularen Nys­tagmus. KlinMonatsblAugenheilkd. 1971;159:145-157.
8. Hertle RW, Dell’Osso LF, FitzGibbon EJ, Thompson D, Yang D, Mellow SD. Horizontal rectus tenotomy in patients with congenital nystagmus: results in 10 adults. Ophthalmology. 2003;110:2097-2105.
9. Kestenbaum A. New operation for nystagmus. Bull SocOphtalmol Fr. 1953;6:599-602.
10. Goto N. A study of optic nystagmus by electrooculogram. ActaSocOphthalmolJpn1954;58:851-5.
11. Arroyo-Yllanes ME, Fonte-Vazquez A, Perez-Perez JF. Modified Anderson procedure for correcting abnormal mixed head positive in nystagmus. Br J Ophthalmol2002;86:267-69.
12. Ritesh Gupta, Pradeep Sharma, Vimala Menon. A Prospective Clinical Evaluation of Augmented Anderson Procedure for Idiopathic Infantile Nystagmus. J AAPOS 2006;10:312-317
13. Anand Kumar, Shashikant Shetty, P. Vijayalakshmi, Richard W. Hertle. Improvement in Visual Acuity Following Surgery for Correction of Head Posture in Infantile Nystagmus Syndrome. J PediatrOphthalmol Strabismus 2011;48:341-346.
    

Subject number	Age (years)	Sex	Surgical dose	Pre op AHP	Post op AHP	Visual acuity (pre op)	Visual acuity (post op)
1	15	M	RLR 12 + LMR 9	30 L	<5 L	0.5	0.5
2	11	M	RLR 10 + LMR 7	15 L	<5 L	0.6	0.25
3	5	F	RLR 12 + LMR 9	30 L	10 L	0.6	0.35
			RMR 6rs + LLR 9rs	15 L	5 L	0.35	0.25
4	13	M	RLR 11 + LMR 8	20 L	5 L	0.3	0.25
5	10	F	LLR 10 + RMR 7	15 R	<5 R	0.3	0.25
6	7	M	LLR 11 + RMR 8	20 R	Nil	0.55	0.25
7	13	F	RLR 10 + LMR 7	15 L	5 L	0.3	0
8	10	M	LLR 11 + RMR 8	20 R	Nil	0.2	0
9	8	M	RLR 11 + LMR 8	20 L	10 L	0.5	0.25
10	8	M	LLR 12 + RMR 9	30 R	15 R	0.6	0.5
11	17	M	RLR 10 + LMR 7	15 L	<5 L	0.25	0.1
12	5	F	RLR 12 + LMR 9	30 L	10 L	0.6	0
13	16	M	RLR 11 + LMR 8	25 L	10 L	0.65	0
14	20	M	RLR 10 + LMR 7	15 L	<5 L	0.2	0
15	9	M	RLR 11 + LMR 8	25 L	<5 L	0.3	0
16	9	F	RLR 11 + LMR 8	20 L	<5 L	0.55	0.5
17	11	M	RLR 11 + LMR 8	25 L	10 L	0.5	0.3
18	11	M	LLR 11 + RMR 8	20 R	<5 R	0.8	0.2
19	9	F	RLR 11 + LMR 8 + RMR 7 rs	25 L	5 L	0.3	0.2
20	13	M	RLR 12 + LMR 9	35 L	<5 L	0.65	0.3
21	6	F	RLR 11 + LMR 8 + RMR 8 rs	20 L	Nil	0.55	0.5
22	21	M	RLR 11 + LMR 8	20 L	Nil	0.65	0.55
23	6	M	RLR 11 + LMR 8	20 L	<5 L	0.3	0.25
24	5	F	RLR 12 + LMR 9	35 L	15 L	0.6	0.35
25	11	F	RLR 11 + LMR 8	20 L	5 L	0.55	0.3
26	8	M	RLR 11 + LMR 8	20 L	10 L	0.5	0.3
27	8	M	RLR 12 + LMR 9	35 L	15 L	0.55	0.35
28	39	M	RLR 11 + LMR 8	25 L	<5 L	0.5	0.2
29	7	M	RLR 11 + LMR 8	20 L	<5 L	0.5	0.1
30	49	M	RLR 11 + LMR 8	20 L	Nil	0.3	0.1
31	8	M	RLR 12 + LMR 9	30 L	<5 L	0.5	0.2
32	13	F	LLR 10 + RMR 7	15 R	Nil	0.6	0.5
33	14	M	RLR 11 + LMR 8	20 L	<5 L	0.4	0.25
34	8	M	RLR 11 + LMR 8	25 L	10 L	0.5	0.5
35	14	M	RLR 12 + LMR 9	30 L	10 L	0.55	0.1
36	14	F	RLR 10 + LMR 7	15 L	Nil	0.4	0.4
37	15	M	RLR 11 + LMR 8	20 L	15 L	0.25	0

Table 1- Improvement in AHP and binocular visual acuity in primary gaze before and after the procedure. Preoperative and postoperative AHP (in degrees, right-R and left-L head turns). Surgical dose- recessions of yoke muscles, lateral rectus- LR, medial rectus- MR. (2 patients had resections, rs, of MR for correction of strabismus). Preoperative and postoperative visual acuity expressed in LogMAR.