Strabismus surgery in children: the prospects for binocular single vision

A Dichoptic Optokinetic Nystagmus Paradigm for Interocular Suppression Quantification in Intermittent Exotropia

Purposes: To investigate the effectiveness of a dichoptic optokinetic nystagmus (dOKN) test to objectively quantify interocular suppression in intermittent exotropia (IXT) patients during the states of orthotropia and exodeviation.

Methods: The OKN motion in subjects (15 controls and 59 IXT subjects) who viewed dichoptic oppositely moving gratings with different contrast ratios was monitored and recorded by an eye tracker. Interocular suppression in control subjects was induced using neutral density (ND) filters. The OKN direction ratios were fitted to examine the changes of interocular suppression in subjects under different viewing states. Two established interocular suppression tests (phase and motion) were conducted for a comparative study.

Results: The dOKN test, which requires a minimal response from subjects, could accurately quantify the interocular suppression in both IXT and control subjects, which is in line with the established interocular suppression tests. Overall, although comparative, the strength of interocular suppression detected by the dOKN test (0.171 ± 0.088) was stronger than those of the phase (0.293 ± 0.081) and the motion tests (0.212 ± 0.068) in the control subjects with 1.5 ND filters. In IXT patients, when their eyes kept aligned, the dOKN test (0.58 ± 0.09) measured deeper visual suppression compared with the phase (0.73 ± 0.17) or the motion test (0.65 ± 0.14). Interestingly, strong interocular suppression (dOKN: 0.15 ± 0.12) was observed in IXT subjects during the periods of exodeviation, irrespective of their binocular visual function as measured by synoptophore.

Conclusion: The dOKN test provides efficient and objective quantification of interocular suppression in IXT, and demonstrates how it fluctuates under different eye positions.

A comparison of surgical outcomes between pre-and full-term patients with exotropia

PURPOSE

To compare the surgical outcomes between pre- and full-term patients with exotropia and to examine the factors associated with surgical outcomes.

METHODS

This retrospective study included 48 pre- and 432 full-term patients with basic-type exotropia who underwent unilateral or bilateral lateral rectus muscle (ULR or BLR) recession. Preoperative characteristics and surgical outcomes were compared between the pre- and full-term infants. Additionally, factors affecting the surgical outcomes were evaluated in all patients.

RESULTS

The preoperative characteristics were significantly different between the pre- and full-term groups in terms of neurodevelopmental disabilities (p = 0.020). There were no significant differences between the pre- and full-term groups in terms of the success, overcorrection, and recurrence rates after the mean follow-up period of 34.6 ± 13.9 months (p = 0.697). The major cause of surgical failure was recurrence in both groups. Pre-term birth was not a risk factor for overcorrection and recurrence. However, regardless of the pre- or full-term birth status, the presence of neurodevelopmental disabilities significantly affected final overcorrection (p = 0.004).

CONCLUSIONS

Pre-term patients with exotropia showed similar surgical outcomes to full-term controls. The presence of neurodevelopmental disabilities was a risk factor for final overcorrection.

Long-term surgical outcomes of infantile-onset esotropia in preterm patients compared with full-term patients

BACKGROUND/AIMS

To compare surgical outcomes between preterm and full-term patients with infantile-onset esotropia.

METHODS

This study included 56 preterm and 162 full-term patients with infantile-onset esotropia who underwent strabismus surgery. The extent of surgery was reduced by 0.5 mm per muscle in preterm patients who were born at <30 weeks of gestation. Surgical outcomes over time, including surgical success, overcorrection rate, undercorrection rate and surgical dose-response were compared between preterm and full-term patients.

RESULTS

The Cox proportional hazards regression model and competing risk analysis showed no statistically significant differences in the rate of surgical success or undercorrection over time between preterm and full-term patients. However, the final overcorrection rate was greater in preterm children than in full-term children (p=0.019). The average surgical dose-response was 3.99 prism dioptres (PD)/mm in full-term children and 4.40 PD/mm in preterm children.

CONCLUSIONS

The results of this study showed a favourable outcome using a mildly reduced amount of surgery in preterm patients with infantile-onset esotropia. Surgical dose-response was significantly greater in preterm patients than in full-term patients.

Outcome of monocular surgery for horizontal strabismus in Hyderabad

BACKGROUND AND OBJECTIVE

Squint surgery is frequently performed successfully in Hyderabad. However, no study in any detail has been performed on the outcome of monocular surgery for horizontal squint in the region. This study aims to determine the results of monocular surgery for horizontal trabismus.

DESIGN

Retrospective/observational study.

SUBJECTS AND METHODS

The study was conducted on patients aged under 45 years, presenting with horizontal strabismus and undergoing monocular squint surgery. Anterior segment slit lamp examination, and if possible, posterior segment examination with 90 diopter (D) and 78 D fundoscopes was performed. Angle of deviation was measured. Patients were divided into two groups (esotropia and exotropia). Investigations were performed. Surgery was done under general anesthesia. A second surgical procedure was performed after six months for any residual deviations.

RESULTS

After squint surgery, patients in group 1 (79%) and in group 2 (73.3%) had residual deviation of less than 15 prism diopters (PD). The preoperative deviations of 60 PD or less illustrated excellent domino effects with residual deviation of fewer than 15 PD. Three patients with successive deviation underwent a second surgery with excellent outcomes.

CONCLUSION

Few extraocular muscles can be prevented due to monocular squint surgery when multiple surgeries are needed.

Bimedial hang-back recession— outcomes and surgical response

AIM

To report outcomes and identify factors affecting surgical response for constant esotropia using 'hang-back' bimedial rectus recession.

STUDY TYPE

Retrospective case series analysis.

METHODS

Patients managed by a single surgeon over a 4-year study period were categorized into esotropia types: infantile, partially accommodative, nonaccommodative and secondary esotropia. Postoperative alignment was compared between types, and regression modelling used to examine factors predicting surgical response.

RESULTS

In all, 95% (18/19) of children with partially accommodative esotropia achieved postoperative deviation <15 prism dioptres from orthotropia, compared to 56% (15/27) of children with infantile esotropia, 69% (11/16) of children with non-accommodative esotropia and all (2/2) of those with secondary esotropia. Surgical response (Delta/mm recession performed) increased with the magnitude of both preoperative deviation (P<0.001) and anisometropia (P<0.001); the effect of deviation on surgical response was reduced by amblyopia (P=0.02). Age at surgery was statistically associated (P=0.002) but had negligible clinical effect on response.

CONCLUSIONS

Surgical response to hang-back recession may be partially predicted by preoperative factors.

Surgery and botulinum toxin in congenital esotropia

BACKGROUND

In a previous study we investigated the advantages and drawbacks of early and delayed injection of botulinum toxin as primary treatment of infantile esotropia with nystagmus in abduction (IENA). We carried out a further study to investigate the role and efficacy of surgery in this condition and to determine the possible effect of previous injection of both medial recti with botulinum toxin in patients requiring a final horizontal surgical correction.

METHODS

Review of the records of 44 patients (24 girls and 20 boys) with IENA seen between 1979 and 1998 who had undergone at least one horizontal surgical procedure. The outcomes in the 16 patients who had previously received botulinum toxin were compared with those in the 28 patients for whom surgery was the primary treatment.

RESULTS

There was a negative correlation between the pretreatment esotropic angle and age (Pearson's r = -0.45, p < 0.05). The first visit to a surgical specialist took place very late (mean age 43 months [standard deviation (SD) 39 months]). Of the 35 children seen during the period in which botulinum toxin was available, 20 (57%) had additional factors inducing unsteadiness of binocular vision (e.g., moderate to severe initial relative amblyopia, initial ametropia). Administration of 5 units of botulinum toxin before 18 months of age destabilized dissociated vertical deviation. Overall, 39 patients (89%) had a final residual deviation of less than 10 prism dioptres. The first surgical correction was horizontal and vertical-torsional in 30 patients (68%). A total of 23 patients (52%) required some retreatment (botulinum toxin or surgery or both). Children treated initially with botulinum toxin had less surgery than those with initial surgery (mean recession or resection 8.9 mm [SD 4.5 mm] vs. 14.2 mm [SD 4.0 mm]) as well as fewer horizontal muscles operated (mean 1.6 [SD 0.6] vs. 2.3 [SD 0.6]).

INTERPRETATION

Surgery with or without further interventions is a reasonable approach for IENA with delayed diagnosis and in cases associated with unsteadiness of binocular vision or with nonhorizontal deviations. Initial treatment with botulinum toxin, injected into both medial recti, is effective, reducing the amount of further horizontal surgery and favouring postoperative stability, except in children under 18 months, in whom injection of 5 units induces unbalanced dissociated vertical deviation.

Effect of late surgery for acquired esotropia on visual evoked potential

PURPOSE

To asses the effect of strabismus surgery on visual evoked potential (VEP) amplitude after age 5 years in children with acquired esotropia.

METHODS

Visual evoked potentials to binocular and monocular pattern reversal stimulation were recorded in 10 children aged 5 to 6 years before and 3 months after surgical correction of their esotropia. Visual function (fusion) was tested by synoptophore after strabismus surgery. Electrophysiological and clinical data were correlated following surgical intervention.

RESULTS

A significant increase in pattern VEP amplitudes was noted following strabismus surgery. Visual evoked potential changes were most prominent on binocular stimulation. Binocular fusion showed similarly significant improvement after intervention. Postoperative VEP data, however, were not consistently correlated with functional improvement.

CONCLUSION

Surgical intervention in esotropia, even if performed years beyond the end of the classical critical period, can have a strong effect on binocular VEPs and a beneficial effect on the development of binocular fusion.

Prospective multicentre study of the accuracy of surgery for horizontal strabismus

Eight centres throughout the United Kingdom cooperated with a prospective evaluation of the accuracy of surgery for horizontal strabismus. The eight centres were divided into four with a specialist interest in strabismus and four offering a general ophthalmic service. Each participating surgeon was asked to indicate the anticipated outcome of surgery and, thereafter, orthoptic examinations were made post-operatively to determine the actual outcome. Two hundred and five cases were included in the study and it is hoped the results will serve as useful guidelines for those departments wishing to undertake audit of their own strabismus surgery. There was no statistically significant difference in the accuracy of surgical alignment achieved by strabismus specialists and general ophthalmologists.

The outcome of strabismus surgery in childhood exotropia

The results of squint surgery in 42 children with primary, non-paralytic, childhood exotropia are analysed. A 'favourable outcome', defined as a final alignment for near and distance within +/- 10 dioptres of straight, or within +/- 20 dioptres of straight with evidence of binocular single vision, was achieved in 39 (93%) children. The factors affecting the final outcome are discussed, including age of onset, age at the time of surgery, preoperative and post-operative amblyopia, refractive error, anisometropia, the surgical procedures used, and postoperative ocular alignment.

Results of early surgery for infantile esotropia in normal and neurologically impaired infants

A prospective study was performed over a 4-year period of 56 infants presenting with infantile esotropia to assess development of binocularity after surgical alignment before 2 years of age. In 50% of cases infantile esotropia was associated with neurological problems or prematurity. Forty-three cases have undergone surgery (mean age 15.7 months +/- 3.46); 86% were aligned (+/- 10 dioptres) at 2 years. Eighty-seven per cent of normal children and 74% of children with neurological problems or prematurity were aligned at last follow-up (mean 27.2 months since surgery). Tests of fusion and stereopsis have to date been possible upon 21 'successfully' aligned infants and although most have evidence of peripheral sensory fusion none showed stereopsis to more than one test. Although early surgery achieves a good cosmetic result in normal children and those with neurological problems, our findings question its ability to promote the development of even gross stereopsis in most children.