Instability of ocular alignment in childhood esotropia

Multiple factors causing variability of alignment in childhood concomitant strabismus

PURPOSE

To investigate the potential factors related to variability of alignment in childhood concomitant strabismus.

DESIGN

Prospective inter-examiner (test-retest) reliability analysis.

METHODS

In total, 197 children with concomitant strabismus (57 esotropia, 140 exotropia) underwent repeat prism and alternate cover test (PACT) by two orthoptists who were certified by the study, and sensory tests were all performed once. We defined the alignment measurement as stable if the absolute value of the measurement difference between two orthoptists was within 10 prism diopters (PD), and unstable if the difference was 10 PD or greater. We analyzed the relationship between the measurement variability and sensory results, patient age, and angle of deviations.

RESULTS

The mean age of the esotropia and exotropia patients was 68.5 ± 26.3 months (range, 36-164 months) and 96.0 ± 33.7 months (range, 22-200 months), respectively, and there was a significant difference in suppression related variability of alignment, both at distance (P = 0.004) and at near (P = 0.046). Anisometropia also showed a significant difference at distance (P = 0.035) for variability of alignment, and there was no significant statistical effect of age on measurement variability in our study. Variability of alignment is positively associated with the angle of deviation, especially at distance (P = 0.021 for exotropia, P = 0.002 for esotropia) with more variability between observers with larger angles of misalignment.

CONCLUSION

Suppression is an important factor for variability of alignment in childhood concomitant strabismus. Other factors, such as anisometropia and a large angle of strabismus should be taken into account when evaluating binocular alignment.

The incidence, clinical features, and management of essential infantile esotropia in the United Kingdom. A British Ophthalmology Surveillance Unit (BOSU) study

BACKGROUND/OBJECTIVES

A national study was undertaken through the British ophthalmology surveillance unit (BOSU) to determine the incidence, presenting features and management of essential infantile esotropia (EIE) in the UK.

METHODS

Data from a prospective national observational study of newly diagnosed EIE presenting to clinicians in the United Kingdom over a 12-month period were collected. Cases with a confirmed diagnosis by a clinician of a constant, non-accommodative esotropia ≥20 prism dioptres (PD), presenting at ≤12 months, with no neurological or ocular abnormalities were identified through BOSU. Follow-up data were collected at 12 months.

RESULTS

A total of 57 cases were reported giving an incidence of EIE of 1 in 12,828 live births. The mean age of diagnosis and intervention were 7.05 ± 2.6 months (range 2-12) and 14.7 ± 4.9 months (range 6.5-28.1), respectively. Management was surgical in 59.6%, botulinum toxin alone in 22.8%, and 17.5% were observed. The preoperative angle of esotropia was smaller in the observation group (P = 0.04). The postoperative angle of esotropia was not statistically significant between botulinum toxin or surgery (P = 0.3), although the age of intervention was earlier in the botulinum group (P = 0.007). Early intervention (before 12 months of age) did not influence the post-intervention motor outcomes between 0 and 10 prism dioptres of esotropia (P = 0.78).

CONCLUSIONS

The incidence of EIE in the UK is considerably lower than reported in other population-based studies. The preferred method of treatment was surgical with earlier intervention in those treated with botulinum toxin. An early age of intervention (<12 months) did not influence motor outcomes.

Split-Tendon Medial Transposition of Lateral Rectus for Pediatric Complete Oculomotor Palsy

BACKGROUND

Split-tendon medial transposition of lateral rectus (STMTLR) for complete oculomotor palsy can correct large angles of exotropia in adults, but outcomes are variable, and complications are frequent. Only a few pediatric cases have been reported, and further insight is needed to assess the child's alignment outcomes and ability for postsurgical gain of function. The aim of our study is to report the outcomes of this surgical procedure in pediatric cases of complete oculomotor palsy.

METHODS

A retrospective review of outcomes was conducted on 5 consecutive patients with complete oculomotor palsy treated with STMTLR by a single surgeon (V.S.S.) between 2015 and 2021 at tertiary referral centers. Primary outcome was postoperative horizontal alignment, and secondary outcome was demonstration of gain-of-function activity in the field of action of the paretic medial rectus muscle.

RESULTS

Five cases of pediatric complete oculomotor palsy underwent surgical treatment with STMTLR. Subjects averaged 5.3 years old (range 10 months-16 years). Two were female. Etiologies were heterogeneous, and all presented with unilateral (n = 2) or bilateral complete oculomotor palsy with exodeviations ranging from 45 to >120 prism diopters. Two subjects had bilateral disease secondary to military tuberculosis with CNS involvement. A third subject presented iatrogenically with complete bilateral third nerve palsies secondary to removal of a nongerminomatous germ cell tumor (NGGCT) of the pineal gland. The 2 remaining subjects had monocular involvement in their right eye, 1 from compressive neuropathy after a cavernoma midbrain hemorrhage, and 1 from a congenital right oculomotor palsy. All patients were observed to have stable ocular alignment for a period of at least 6 months before surgery. Unilateral STMTLR was performed in all cases except the subject with NGGCT, in which bilateral STMTLR was performed. Measurement of alignment permanence out to 1-3 years postop resulted in an average correction of 40.83 prism diopters (range 37.5-45 prism diopters) per operated eye. Four of 5 subjects regained limited but active adduction eye movements, and the 2 unilateral cases demonstrated improved convergence. None of the subjects experienced significant complications.

CONCLUSIONS

STMTLR was a safe and effective approach for the surgical correction of complete pediatric oculomotor palsy in our case series. In addition, pediatric patients may benefit from STMTLR with immediate gain-of-function activity in the transposed lateral rectus muscle, which supports the hypothesis that children have a dynamic and adaptive neuroplasticity of visual target selection that predominates established agonist/antagonist neural signaling.

Interventions for intermittent exotropia

BACKGROUND

The clinical management of intermittent exotropia (X(T)) has been discussed extensively in the literature, yet there remains a lack of clarity regarding indications for intervention, the most effective form of treatment, and whether there is an optimal time in the evolution of the disease at which any given treatment should be carried out.

OBJECTIVES

The objective of this review was to analyze the effects of various surgical and non-surgical treatments in randomized controlled trials (RCTs) of participants with intermittent exotropia, and to report intervention criteria and determine whether the treatment effect varies by age and subtype of X(T).

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL; 2021, Issue 1), which contains the Cochrane Eyes and Vision Trials Register; Ovid MEDLINE; Ovid Embase; Latin American and Caribbean Health Science Information database (LILACS); the ISRCTN registry; ClinicalTrials.gov, and the WHO ICTRP. The date of the search was 20 January 2021. We performed manual searches of the British Orthoptic Journal up to 2002, and the proceedings of the European Strabismological Association (ESA), International Strabismological Association (ISA), and American Association for Pediatric Ophthalmology and Strabismus meeting (AAPOS) up to 2001.

SELECTION CRITERIA

We included RCTs of any surgical or non-surgical treatment for intermittent exotropia.

DATA COLLECTION AND ANALYSIS

We followed standard Cochrane methodology.

MAIN RESULTS

We included six RCTs, four of which took place in the United States, and the remaining two in Asia (Turkey, India). A total of 890 participants with basic or distance X(T) were included, most of whom were children aged 12 months to 10 years. Three of these six studies were from the 2013 version of this review. Overall, the included studies had a high risk of performance bias as masking of participants and personnel administering treatment was not possible. Two RCTs compared bilateral lateral rectus recession versus unilateral lateral rectus recession with medial rectus resection, but only one RCT (n = 197) reported on the primary outcomes of this review. Bilateral lateral rectus recession likely results in little difference in motor alignment at near (MD 1.00, 95% CI -2.69 to 4.69) and distance (MD 2.00, 95% CI -1.22 to 5.22) fixation as measured in pupillary distance using PACT (moderate-certainty evidence). Bilateral lateral rectus recession may result in little to no difference in stereoacuity at near fixation (risk ratio (RR) 0.77, 95% CI 0.35 to 1.71), adverse events (RR 7.36, 95% CI 0.39 to 140.65), or quality of life measures (low-certainty evidence). We conducted a meta-analysis of two RCTs comparing patching (n = 249) with active observation (n = 252), but were unable to conduct further meta-analyses due to the clinical and methodological heterogeneity in the remaining trials. We found evidence that patching was clinically more effective than active observation in improving motor alignment at near (mean difference (MD) -2.23, 95% confidence interval (CI) -4.02 to -0.44) and distance (MD -2.00, 95% CI -3.40 to -0.61) fixation as measured by prism and alternate cover test (PACT) at six months (high-certainty evidence). The evidence suggests that patching results in little to no difference in stereoacuity at near fixation (MD 0.00, 95% CI -0.07 to 0.07) (low-certainty evidence). Stereoacuity at distance, motor fusion test, and quality of life measures were not reported. Adverse events were also not reported, but study authors explained that they were not anticipated due to the non-surgical nature of patching. One RCT (n = 38) compared prism adaptation test with eye muscle surgery versus eye muscle surgery alone. No review outcomes were reported. One RCT (n = 60) compared lateral rectus recession and medial rectus plication versus lateral rectus recession and medial rectus resection. Lateral rectus recession and medial rectus plication may not improve motor alignment at distance (MD 0.66, 95% CI -1.06 to 2.38) (low-certainty evidence). The evidence for the effect of lateral rectus recession and medial rectus plication on motor fusion test performance is very uncertain (RR 0.92, 95% CI 0.48 to 1.74) (very low-certainty evidence).

AUTHORS' CONCLUSIONS

Patching confers a clinical benefit in children aged 12 months to 10 years of age with basic- or distance-type X(T) compared with active observation. There is insufficient evidence to determine whether interventions such as bilateral lateral rectus recession versus unilateral lateral rectus recession with medial rectus resection; lateral rectus recession and medial rectus plication versus lateral rectus recession and medial rectus resection; and prism adaptation test prior to eye muscle surgery versus eye muscle surgery alone may confer any benefit.

Combined passive and active treatment in strabismic amblyopia with accommodative component

BACKGROUND

Treatment of amblyopia in esotropic subjects with accommodative component currently consists of optical correction and subsequent occlusion, or penalisation, of the dominant eye. This treatment obtains a good outcome in visual acuity but poor outcomes in binocular vision. An intervention protocol that could improve the outcome of conventional treatment is presented.

METHODS

A retrospective study in subjects with amblyopia associated with both fully accommodative and partially accommodative esotropia is presented. Subjects were refracted under cycloplegia and treated with occlusion (passive therapy). Subjects who did not achieve orthotropia through optical correction (partially accommodative esotropia) performed an active therapy (full-time prismatic correction and subsequent fusional vergence therapy or surgery in larger angles > 12 prism dioptres). After treatment, the subjects were examined by a masked optometrist in an external ophthalmology clinic.

RESULTS

Twenty-six subjects (12 males and 14 females) aged from six to 13 years (median 8.50; interquartile range [IQR] 3) were included. Median age of detection was three years (IQR 1). All the subjects were hyperopic. In the baseline, median best-corrected visual acuity of the amblyopic eye was 0.40 logMAR (IQR 0.30) and 0.00 logMAR (IQR 0.01) in the dominant eye. After the treatment, the median best-corrected visual acuity in the amblyopic eye was 0.06 logMAR (IQR 0.08). These differences were statistically significant (p < 0.001). All subjects acquired stereoacuity equal or better than 800'' with the Randot Preschool Stereoacuity Test.

CONCLUSIONS

The proposed treatment highlights the management of amblyopia in esotropic subjects with accommodative component. This intervention protocol could help to determine if the treatment has to be passive (in fully accommodative esotropia) or a combination of passive and active therapies (in partially accommodative esotropia).

Eye alignment changes caused by sustained GDNF treatment of an extraocular muscle in infant non-human primates

The ability of sustained treatment of a single extraocular muscle with glial cell line-derived neurotrophic factor (GDNF) to produce a strabismus in infant non-human primates was tested. Six infant non-human primates received a pellet containing GDNF, releasing 2 µg/day for 90 days, on one medial rectus muscle. Eye alignment was assessed up to 6 months. Five of the six animals showed a slow decrease in eye misalignment from the significant exotropia present at birth, ending with approximately 10° of exotropia. Controls became orthotropic. Misalignment averaged 8° three months after treatment ended. After sustained GDNF treatment, few changes were seen in mean myofiber cross-sectional areas compared to age-matched naïve controls. Neuromuscular junction number was unaltered in the medial rectus muscles, but were significantly reduced in the untreated lateral recti. Neuromuscular junctions on slow fibers became multiply innervated after this sustained GDNF treatment. Pitx2-positive cells significantly decreased in treated and contralateral medial rectus muscles. Our study suggests that balanced GDNF signaling plays a role in normal development and maintenance of orthotropia. Sustained GDNF treatment of one medial rectus muscle resulted in a measurable misalignment largely maintained 3 months after treatment ended. Structural changes suggest mechanisms for producing an imbalance in muscle function.

Strabismus Surgery for Esotropia, Down Syndrome and Developmental Delay; Is an Altered Surgical Dose Required? A Literature Review

Background and Purpose:

There is a high rate of strabismus, in particular esotropia, in children with Down syndrome or developmental delay, which frequently requires surgical correction. A paper in 1994 advocated that the surgical dose be adjusted due to an altered response in these children. The aim of this literature review is to evaluate the available evidence to establish whether an altered surgical approach is required in either population.

Methods:

A literature review was conducted using PubMed and Web of Knowledge. Only English language papers were eligible for inclusion. The papers were collated in chronological order for analysis, and their references searched for further relevant papers. Forward citation searches were also undertaken.

Results:

A 2 × 2 comparison is made between publications on Down syndrome (in isolation) and developmental delay populations (including Down syndrome) with adjusted versus non-adjusted surgery. Published surgical success rates on esotropia from unaltered surgical doses range from 62.0%–85.7% (four papers) in the Down syndrome cohort, with none of the adjusted surgeries having a successful outcome. Surgical success rates from adjusted surgical doses in developmental delay cohort range from 37.5%–86.0% (seven papers), with one unadjusted surgical success rate of 76.0%. The results across the studies are summarised in a table and discussed.

Conclusions:

An exaggerated surgical effect in individuals with developmental delay has been reported, and this population may benefit from a reduced surgical dose. Published research does not support giving a reduced surgical dose in individuals with Down syndrome, but more research needs to be done to make a definitive conclusion.

LONG-TERM VARIABILITY OF STRABISMUS ANGLE IN NEUROLOGICALLY IMPAIRED PREMATURE INFANTS: A 12-YEAR FOLLOW UP

The aim of this retrospective study was to determine the strabismus angle variability and rationality of surgical treatment of strabismus in prematurely born children with neurological impairment during 12-year follow up. Eleven premature infants born in 2003 were included in the study and treated with equal conservative approach from 2005 until 2016. Initial esotropia was found in seven and exotropia in four of eleven children. Changes in the strabismus angle correlated significantly with aging of the children. In children with initial esotropia, the strabismus angle became less convergent (less positive), changed the orientation and became more divergent with aging. In those with initial exotropia, the angle became less divergent (more positive), changed the orientation and became more convergent. Moreover, a significant difference in the strabismus angle was found during the 12-year follow up. Based on our results, due to the variability in strabismus angle, we did not find enough evidence for optimal timing or rationality of strabismus surgery in neurologically impaired children born prematurely.

Variability of Ocular Deviation in Strabismus

IMPORTANCE

In strabismus, the fixating eye conveys the direction of gaze while the fellow eye points at a peripheral location in space. The stability of the eyes may be reduced by the absence of a common target.

OBJECTIVE

To quantify the stability of eye position in strabismus and to measure variability in the ocular deviation.

DESIGN, SETTING, AND PARTICIPANTS

From 2010 to 2014, a prospective comparative case study of 25 patients with alternating exotropia with normal visual acuity in each eye and 25 control individuals was conducted in a laboratory at a tertiary eye center. A video eye tracker was used to measure the position of each eye while participants alternated fixation on the center of a cross under dichoptic conditions or scanned pictures of natural scenes.

MAIN OUTCOMES AND MEASURES

Spatial and temporal variability in the position of the fixating eye and the nonfixating eye in patients with strabismus and control individuals, quantified by the log area of ellipses containing 95% of eye positions or mean SDs of eye position.

RESULTS

In the 25 patients with strabismus, the mean (SD) age was 28 (14) years (range, 8-55 years) and the mean (SD) ocular deviation was 14.2° (5.9°) (range, 4.4°-22.4°). In the patients with strabismus, the mean position variability (1.80 log units; 95% CI, 1.66-1.93) for the deviating eye was greater than for the fixating eye (1.26 log units; 95% CI, 1.17-1.35) (P < .001). The fixating eye of patients with strabismus was more variable in position than the fixating eye of individuals without strabismus (0.98 log units; 95% CI, 0.88-1.08) (P < .005).

CONCLUSIONS AND RELEVANCE

In patients with strabismus, even without amblyopia, the deviated eye is more variable in position than the fixating eye. Both eyes are less stable in position than the eyes of control individuals, which indicates that strabismus impairs the ability to fixate targets steadily. Saccades contribute to variability of the deviation angle because they are less conjugate in patients with strabismus.

The effect of reducing hyperopic correction in patients with accommodative esotropia

PURPOSE

To report a 2-year follow-up of a previously reported study of the effects of not correcting the total hyperopic refractive error in patients with accommodative esotropia.

METHODS

Consecutive patients with refractive accommodative esotropia were prescribed the maximal tolerable amount of spectacle undercorrection, up to -1.5 D, and were followed up for 2 years. One year after an initial undercorrection, the maximal tolerable undercorrection was reevaluated. We analyzed changes in visual acuity, angle of deviation, stereoacuity, and fusional ability during the follow-up period.

RESULTS

A total of 39 patients were included, of whom 1 was lost to follow-up. During the 2-year follow-up period, none of the patients had deterioration in visual acuity (right eye: 95% CI, -0.01 to -0.02; left eye: 95% CI, -0.10 to -0.03 [Wilcoxon signed rank test]), angle of deviation (at distance: 95% CI, -4.00 to 0.00; at near: 95% CI, -4.00 to 0.50), stereoacuity (95% CI, -0.55 to -0.10), or fusional ability. Small changes in the angle of deviation (2(Δ)-4(Δ)) were noted in 3 undercorrected patients.

CONCLUSIONS

We demonstrated stable eye alignment and binocular function 2 years after undercorrecting a hyperopic refractive error in patients with accommodative esotropia.

The maximal tolerable reduction in hyperopic correction in patients with refractive accommodative esotropia: a 6-month follow-up study

PURPOSE

To investigate the optimal amount of safe under-correction in patients with refractive accommodative esotropia.

DESIGN

Prospective noncomparative interventional case series.

METHODS

Patients with refractive accommodative esotropia wore trial glasses based on cycloplegic refraction, then -0.25 diopters (D) of minus sphere lenses were placed on both lenses of the trial glasses and the deviation was measured. Minus spheres of -0.25 D were continuously added until the angle of deviation increased; the minus spheres added just before the deviation increase were defined as the maximal tolerable amount of under-correction. A total of 38 patients were prescribed under-corrected spectacles up to -1.5 D and followed for 6 months.

RESULTS

Thirty-one patients underwent the maximal tolerable amount of under-correction and 7 underwent -1.5 D of under-correction. A mean -0.89 D of under-correction was performed. We observed no deterioration in visual acuity, stereoacuity, or fusional ability during the follow-up period in any of the patients. Small increase in the angle of deviation of 2 prism diopters was noted in 2 patients. The mean spherical equivalent refractive error of both eyes (P = .012) and age of onset (P = .006) showed strong positive correlations with the maximal tolerable amount of under-correction.

CONCLUSIONS

A reduction in hyperopic correction by the maximal tolerable amount of under-correction was performed without notable short-term side effects. The spherical equivalent refractive error and age of onset appear to be useful clinical indices in determining the appropriate amount of under-correction.

Intermittent exotropia: facts, opinions, and unknowns

INTRODUCTION

Intermittent exotropia (IXT) can be a controversial topic, often eliciting lively discussion. This lecture will discuss its definition, incidence, age of onset, presentation, natural variation, criteria for deterioration, goals of treatment, effectiveness of surgical treatment, types of surgical treatment, and unwanted effects of surgical treatment.

METHOD

Results from the scientific literature, opinions of respected colleagues, the opinion of the author, and the results of live polling of the audience during the John Pratt-Johnson lecture are presented.

RESULTS

IXT is defined as an exotropia that is present intermittently predominantly for distance. Its incidence is about 1% and it usually has an onset before age 5. Patients often present because of concern regarding the appearance of the eye misalignment. There is natural variation in the control of IXT, the angle of IXT, and the amount of stereopsis. Criteria that denote deterioration are increasing frequency of IXT, progressively and consistently increasing angle of IXT, loss of binocular vision, and increasing concern regarding the patient's appearance and its effect on social interaction. Goals of treatment are to retain equal or nearly equal vision, to obtain acceptable cosmesis, and to retain binocular vision. The long-term success of surgical treatment is not well proven. Persistent postoperative overcorrection is an unwanted effect of surgical treatment.

CONCLUSION

The inherent biologic variation that occurs when measuring the components of IXT makes it difficult to be dogmatic about IXT, particularly when trying to decide when deterioration is occurring.

Classifying stability of misalignment in children with esotropia using simulations

OBJECTIVE

To determine the sensitivity and specificity of several classification rules for stability and instability of angle in childhood esotropia.

METHODS

We conducted 10 000 Monte Carlo simulations of participants with no actual change in angle of esotropia during follow-up, where "observed" changes in ocular alignment were sampled from a distribution of measurement errors for the prism and alternate cover test. Additional simulations were conducted for a range of "true" changes (1.0, 2.5, 4.2, 5.0, 7.5, and 10.0 prism diopters [PD] per visit) with up to 10 follow-up visits. We then estimated sensitivities and specificities for specific rules for retrospectively classifying stability (all measurements within 0, 5, 10, or 15 PD) and instability (≥2 measurements differing by ≥10 PD, etc) across a fixed number of visits. Results were extended to classifying ocular alignment stability and instability prospectively based on a varying number of measurements.

RESULTS

For a series of 4 measurements, the rules that optimized sensitivity and specificity were "all measurements within 5 PD" for stability and "at least 2 measurements differing by 15 PD or more" for instability. For a series of 3 measurements, all 3 measurements needed to be identical to confirm stability.

CONCLUSIONS

We derived definitions of stability and instability in childhood esotropia using estimates of actual measurement error that may be useful for clinical practice and for future clinical studies of esotropia.

The relationship between preoperative alignment stability and postoperative motor outcomes in children with esotropia

PURPOSE

To examine the effect of preoperative alignment stability on postoperative motor outcomes in children who underwent surgery for esotropia.

METHODS

One hundred sixty-seven subjects (68 with infantile esotropia and 99 with acquired esotropia) aged less than 6 years had surgery after completing 18 weeks of follow-up as part of an observational study. Preoperative alignment was classified as stable, uncertain, or unstable, based on measurements taken at baseline and every 6 weeks for 18 weeks. Distance alignment measured by prism and alternate cover test was compared among stability classification groups at 6 weeks and 6 months after surgery.

RESULTS

Among subjects with infantile esotropia, median 6-week postoperative deviation was 2(Delta), 6(Delta), and 2(Delta) for subjects with stable, uncertain, and unstable preoperative alignment, respectively (p = 0.73 for stable vs unstable). Median 6-month postoperative deviation was 1(Delta), 9(Delta), and 1(Delta) for stable, uncertain, and unstable, respectively (p = 1.00 for stable vs unstable). Among subjects with acquired esotropia, median 6-week postoperative deviation was 6(Delta), 4(Delta), and 4(Delta) for subjects with stable, uncertain, and unstable preoperative alignment, respectively (p = 0.69 for stable vs unstable). Median 6-month postoperative deviation was 8(Delta), 4(Delta), and 6(Delta) for stable, uncertain, and unstable, respectively (p = 0.22 for stable vs unstable).

CONCLUSIONS

Postoperative alignment at 6 weeks and 6 months appears similar in children with stable versus unstable preoperative esotropia. Nevertheless, our finding should be interpreted with caution due to small sample size.

Interventions for intermittent exotropia

BACKGROUND

The clinical management of intermittent exotropia has been discussed frequently in the literature, but there is a lack of clarity regarding the indications for intervention, the most effective type and if there is a time point at which it should be carried out.

OBJECTIVES

The objective of this review was to analyse the effects of various surgical and non-surgical treatments in randomised trials of people with intermittent exotropia, to report intervention criteria and determine the significance of factors such as age with respect to outcome.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials - CENTRAL (which contains the Cochrane Eyes and Vision Group Trials Register) on The Cochrane Library (2006, Issue 1), MEDLINE (1966 to March 2006), EMBASE (1980 to March 2006) National Research Register (2006, Issue 1), PubMed (searched on 13 March 2006; last 90 days) and LILACS (Latin American and Caribbean Literature on Health Sciences) (1966 to 2002). We manually searched the British Orthoptic Journal, proceedings of the European Strabismological Association (ESA), International Strabismological Association (ISA) and American Academy of Paediatric Ophthalmology and Strabismus meeting (AAPOS). We contacted researchers who are active in the field for information about further published or unpublished studies. There were no language restrictions in the manual or electronic searches.

SELECTION CRITERIA

We included randomised controlled trials of any surgical or non-surgical treatment for intermittent exotropia.

DATA COLLECTION AND ANALYSIS

Each review author independently assessed study abstracts identified from the database and manual searches. Author analysis was then compared and full papers for appropriate studies were obtained.

MAIN RESULTS

We found one randomised trial that was eligible for inclusion. This trial showed that unilateral surgery was more effective than bilateral surgery for correcting basic intermittent exotropia.

AUTHORS' CONCLUSIONS

The available literature consists mainly of retrospective case reviews which are difficult to reliably interpret and analyse. The one randomised trial included found unilateral surgery more effective than bilateral for basic intermittent exotropia but there remains a need for more carefully planned clinical trials to be undertaken to improve the evidence base for the management of this condition.