Huib Simonsz

Final Report of the Early vs. Late Infantile Strabismus Surgery Study (ELISSS), a Controlled, Prospective, Multicenter Study

Background: The optimal age for surgery for infantile esotropia is controversial. Proponents of early surgery believe that further loss of binocular vision can be prevented by early surgery, a minority believes that binocular vision can even be restored by early surgery. The ELISSS compared early with late surgery in a prospective, controlled, non-randomized, multicenter trial. Methods: Fifty-eight clinics recruited children aged 6–18 months for the study. Each clinic operated all eligible children either ‘early’, i.e. at age 6–24 months, or ‘late’, i.e. at age 32–60 months. At baseline the angle of strabismus, refraction, degree of amblyopia and limitation of abduction were assessed. Intermediate examinations took place every six months. Children were evaluated at age six in the presence of independent observers. Primary endpoints were (i) level of binocular vision, (ii) manifest angle of strabismus at distance and (iii) remaining amblyopia. Secondary endpoints were number of operations, vertical strabismus, angle at near and the influence of surgical technique. Results: A total of 231 children were recruited for early and 301 for late surgery. Age at entry examination was 11.1 months (SD 3.7 months) in the early group and 10.9 (SD 3.7) months in the late group. Refraction, amblyopia and limitation of abduction were distributed equally in the early and late groups, but the angle of strabismus was slightly larger in the early group. Dropout-rates were 26.0% in the early and 22.3% in the late group. At age six, 13.5% of the early vs. 3.9% of the late group recognized the Titmus Housefly; 3.0% of the early and 3.9% of the late group had stereopsis beyond Titmus Housefly. No significant difference was found for angle of strabismus. 35.1% of the early group and 34.8% of the late group did not have an angle between 0° and 10°, the thresholds set for re-operation. For ratio of the visual acuities (remaining amblyopia) there was a small but significant advantage for the early group. There was hardly any correlation between the baseline parameters and the primary endpoints. Children scheduled for early surgery had first been operated at 20 (SD 8.4) months, but 8.2% had not been operated at age six. Children scheduled for late surgery had been operated at 49.1 (SD 12.7) months, but 20.1% had not been operated at age six. The number of operations per child was 1.18 (SD 0.67) in the early and 0.99 (SD 0.64) in the late group. Age at recruitment, age that strabismus reportedly had started and refraction at entry examination were similar among operated and non-operated children. Only the angle of strabismus at entry predicted, to some extent, whether a child had been operated at age six. Discussion: Children operated early had better gross stereopsis at age six as compared to children operated late. They had been operated more frequently, however, and a substantial number of children in both groups had not been operated at all.

Risk of bilateral visual impairment in individuals with amblyopia: the Rotterdam study

Background: The excess risk of bilateral visual impairment (BVI; bilateral visual acuity <0.5) among individuals with amblyopia is an argument for screening for amblyopia, but data are scarce. Methods: The risk was estimated by determining the incidence of BVI in the Rotterdam Study, a population-based cohort of subjects aged 55 years or over (n  =  5220), including 192 individuals with amblyopia (3.7%). Using a multistate lifetable, the lifetime risk and excess period spent with BVI were determined. Results: The relative risk of BVI for amblyopes was 2.6 (95% confidence interval 1.4–4.5). For individuals with amblyopia, the lifetime risk of BVI was 18%, whereas they lived on average 7.2 years with BVI. For non-amblyopic individuals, these figures were 10% and 6.7 years, respectively. Conclusion: Amblyopia nearly doubles the lifetime risk of BVI and affected individuals spent an extra six months with BVI. This study provides data for future cost-effectiveness analyses.

A finite-element analysis model of orbital biomechanics

To reach a better understanding of the suspension of the eye in the orbit, an orbital mechanics model based upon finite-element analysis (FEA) has been developed. The FEA model developed contains few prior assumptions or constraints (e.g., the position of the eye in the orbit), allowing modeling of complex three-dimensional tissue interactions; unlike most current models of eye motility. Active eye movements and forced ductions were simulated and showed that the supporting action of the orbital fat plays an important role in the suspension of the eye in the orbit and in stabilization of rectus muscle paths.

A preliminary report about the relation between visual acuity increase and compliance in patching therapy for amblyopia.

PURPOSE The aim of this study was to establish a relation between visual acuity increase and compliance in children who have been prescribed patching therapy for their amblyopic eye. METHODS AND MATERIALS In 14 new amblyopic children (mean age 4.3 ± 1.9 years) compliance was measured electronically during one week, six months after starting patching therapy, with an Occlusion Dose Monitor (ODM), distributed through house visits. The children were diagnosed with anisometropia (5), strabismus (4) and anisometropia and strabismus (5). The degree of amblyopia was expressed as the ratio between the acuity of the amblyopic eye and the acuity of the good eye. Satisfactory increase in acuity was assessed by means of the following three criteria: acuity amblyopic eye / acuity good eye >75%, acuity exceeding 0.5 E-chart, three lines LogMAR acuity increase. RESULTS Fourteen reliable recordings were obtained, which showed that children who did not patch, or were patched inconsistently, did not reach satisfactory acuity increase. CONCLUSION There is indeed a statistically significant relation between acuity increase and measured compliance.

Up- and downshoot in adduction after monocular patching in normal volunteers.

Upshoot-in-adduction and downshoot-in-adduction are non-paretic motility disorders that usually accompany a horizontal squint in children, together with V- or A-pattern motility. Upshoot-in-adduction may sometime mimic a superior oblique palsy. The authors have found that even in healthy volunteers these motility disorders can be found and made manifest by patching. One eye of complaint-free volunteers with full stereopsis was patched for three days. Then the eye movements of the patched eye were recorded with the search coil technique, first before taking the patch off and secondly after putting the patch on the other eye. The latter registration served as reference for the first registration. It was found that 11 out of 18 volunteers had developed an upshoot-in-adduction of the patched eye. In five cases no directional change was found whereas two cases had developed a downshoot-in-adduction. It seems that up- and downshoot-in-adduction are latent motility disorders that become manifest after disruption of fusion. In addition, the authors found undershooting saccades and postsaccadic drift of the patched eyes.

Dissociated vertical deviation and eye torsion: Relation to disparity-induced vertical vergence

We studied the relation between vertical eye movements and binocular torsion in five subjects with dissociated vertical deviation (DVD). During trials, subject viewed a well illuminated Snellen letter chart, with both eyes uncovered during 4 seconds, Subsequently, DVD was induced by covering one eye during 4 seconds. Finally, both eyes were uncovered during 4 seconds. Several trials were recorded for each subject and covered eye. Eye movements were measured with scleral coils. We found that in all subjects, the vertical divergence followed an exponential course with a time constant of 0.67 ± 0.14 seconds on average. In three of the five subjects this vertical divergence was associated with binocular torsion (cycloversion), partly, in the form of a cycloversional nystagmus. The time course of the vertical divergence as well as the direction and nystagmic nature of the cycloversion was similar to the behaviour that was previously observed in disparity induced vertical vergence in normal subjects. In two of the subjects, the torsion that was associated with the vertical divergence was monocular. Our results indicate that DVD and disparity induced vertical vergence share the same characteristics. In addition, they demonstrate that extorsion associated with the elevation in DVD possibly but not necessarily points at a dissociated torsional deviation.

Robinson's Computerized Strabismus Model Comes of Age

In this article we review our further development of D.A. Robinsons computerized strabismus model. First, an extensive literature study has been carried out to get more accurate data on the anatomy of the average eye and the eye muscles, and about how these vary with age and with refraction. Secondly, the force-length relations that represent the mechanical characteristics of the eye muscles in the model have been determined more accurately in vivo recently, and the model was changed accordingly. Thirdly, many parameters that were free in the original model and not derived from in vivo measurements were replaced by derivatives from in vivo measurements or made redundant. Fourthly, the ease of operation was improved greatly and the algorithms were made so much faster that a calculation for nine positions of gaze now takes ten seconds on a handheld HP 200LX Palmtop. The predictions of the model compared well with clinical results in horizontal muscle surgery, oblique muscle surgery, forced duction tests and abducens, oculomotor or trochlear palsies. Consequently, complex strabismus surgery in our clinic is now guided by the predictions of the computerized model.

Caudal or cranial partial tenotomy of the horizontal rectus muscles in A and V pattern strabismus

Background: When performing a recession with vertical transposition of the insertions of the horizontal muscles in patients with A or V pattern strabismus, there is a risk of overcorrection in those with a relatively small angle of strabismus and almost-straight eyes in either upgaze or downgaze. Aim: To determine whether a caudal or cranial partial tenotomy of the horizontal rectus would be sufficient to reduce the horizontal angle in gaze ahead and minimise the risk of overcorrection in gaze direction, either up or down, with the smallest horizontal deviation. Methods: A retrospective evaluation was performed of patients who had a caudal or cranial partial tenotomy of the horizontal rectus between January 1996 and January 2006. Patients were excluded if they had undergone previous surgery and or required additional oblique-muscle surgery. The reduction in the horizontal angle of strabismus in gaze ahead and in 25° upgaze and downgaze was evaluated. Results: Fifty-two patients were included, 16 with A-eso pattern, 12 with V-eso pattern, 7 with A-exo pattern, and 17 with V-exo pattern. Their age at operation ranged from 2 to 80 years (median 16). The mean (SD) reduction in the horizontal angle was 8.1 (4.5)° in the working direction of the transposition, either upgaze or downgaze, 6.2 (4.5)° in gaze ahead, and 3.3 (4.4)° out of the working direction. Four patients had to be reoperated in the short term, one because of overcorrection and three because of undercorrection. Conclusion: In patients with A or V pattern strabismus and an almost-straight eye position in either upgaze or downgaze, a partial tenotomy of the horizontal rectus is an effective treatment, with minimal risk of overcorrection.

Nightblindness-associated transient tonic downgaze (NATTD) in infant boys with chin-up head posture

Eleven infant boys presented with chin-up head posture, tonic downgaze and, on attempted upgaze, large-amplitude upward saccades with deceleration during the slow phase downward. The gaze-evoked upward saccades disappeared at the age of 2 or 3 years. In addition, they had high-frequency, small-amplitude horizontal pendular nystagmus that remained. Among these infant boys were 2 pairs of maternally related half-brothers, 2 cousins, and 2 siblings. Visual acuity ranged from 0.1 to 0.6, ERG-amplitudes (both A- and B-wave) were reduced, and severe myopia was found in 5 cases. Eight boys had CACNA1F mutations, and 1 boy had a NYX mutation, compatible with incomplete or complete congenital stationary nightblindness (iCSNB or cCSNB), respectively. This points to a defective synapse between the rod and the ON-bipolar cell causing the motility disorder: CACNA1F is located on the rod side of this synapse, whereas NYX is located on the side of the ON-bipolar cell. The coexistence of horizontal and vertical nystagmus has been previously described in dark-reared cats.

Sociocultural and psychological determinants in migrants for noncompliance with occlusion therapy for amblyopia

BackgroundCompliance with occlusion therapy for amblyopia in children is low when their parents have a low level of education, speak Dutch poorly, or originate from another country. We determined how sociocultural and psychological determinants affect compliance.MethodsIncluded were amblyopic children between the ages of 3 and 6, living in low socio-economic status (SES) areas. Compliance with occlusion therapy was measured electronically. Their parents completed an oral questionnaire, based on the “Social Position & Use of Social Services by Migrants and Natives” questionnaire that included demographics and questions on issues like education, employment, religion and social contacts. Parental fluency in Dutch was rated on a five-point scale. Regression analysis was used to describe the relationship between the level of compliance and sociocultural and psychological determinants.ResultsData from 45 children and their parents were analyzed. Mean electronically measured compliance was 56 ± 44 percent. Children whose parents had close contact with their neighbors or who were highly dependent on their family demonstrated low levels of compliance. Children of parents who were members of a club and who had positive conceptualizations of Dutch society showed high levels of compliance. Poor compliance was also associated with low income, depression, and when patching interfered with the child’s outdoor activity. Religion was not associated with compliance.ConclusionsPoor compliance with occlusion therapy seems correlated with indicators of social cohesion. High social cohesion at micro level, i.e., family, neighbors and friends, and low social cohesion on macro level, i.e., Dutch society, are associated with noncompliance. However, such parents tend to speak Dutch poorly, so it is difficult to determine its actual cause.