H J Simonsz

Erasmus MC, Rotterdam, South Holland, Netherlands

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Publications (69)61.8 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We present the Delft Assessment Instrument for Strabismus in Young children (DAISY) a device designed to measure angles of strabismus in young children fast and accurately. Daisy allows for unrestrained head movements by the mean of a triple camera vision system that simultaneously estimates the head rotation and the eye pose. The device combines two different methods to record bilateral eye position: corneal reflections (Purkinje images) and pupillary images. Detailed results are provided on three orthotropic subjects (age 25-27). Three different conditions were tested: (i) gaze ahead, (ii) gaze ahead with different head rotations and (iii) fixed head with different eye positions. Systematic errors occurred between subjects that need further study. The system reached sufficient accuracy to be applied for the measurement of angles of strabismus, almost independent from the head pose.
    IEEE transactions on bio-medical engineering 02/2013; · 2.15 Impact Factor
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    ABSTRACT: BACKGROUND: We previously demonstrated that compliance with occlusion therapy for amblyopia was improved by the use of an educational programme, especially in children of parents of foreign origin and who spoke Dutch poorly. The programme consisted of: (i) a cartoon story for amblyopic children that explained without words why they should patch, (ii) a calendar with reward stickers, and (iii) an information leaflet for parents. In the current study, we assessed the individual effect of each component on compliance. METHODS: We recruited 120 3- to 6-year-old children who lived in a low socio-economic status (SES) area in The Hague and were starting occlusion therapy for the first time. They were randomised to receive one of the components (three intervention groups), or a picture to colour (control group). The randomisation was blinded for treating orthoptist and researcher. Compliance was measured electronically using the Occlusion Dose Monitor (ODM). Primary outcome was percentage of compliance (actual/prescribed occlusion time). Secondary outcome was absolute occlusion hours per day. Parental fluency in Dutch was rated on a five-point scale. RESULTS: Compliance could be measured electronically in 88 of the 120 children; in 32 others, it failed for various reasons. Parental fluency in Dutch was moderate or worse in 36.4 % (p = 0.327). Average compliance was 55 % standard deviation (SD) 40 (n = 18) in the control group, 89 % SD 25 in the group receiving the educational cartoon (n = 25, P = 0.002 compared with control group), 67 % SD 33 (n = 24, P = 0.301) in the reward-calendar group and 73 % SD 40 (n = 21, P = 0.119) in the parent-information-leaflet group. On average, children in the control group occluded 1:46 SD1:19 hours/day, 2:33 SD 1:18 hours/day in the group receiving the educational cartoon, 1:59 SD 1:13 hours/day in the reward-calendar group and 2:18 SD 1:13 hours/day in the parent-information-leaflet group. No child who received the cartoon story occluded less than 1 hour per day, against seven in the reward-calendar group, five in the parent-information-leaflet group and five in the control group. CONCLUSIONS: Although all three components of the programme improved compliance with occlusion therapy in children in low-SES areas, the educational cartoon had the strongest effect, as it explained without words to a 4- to 5-year-old child why it should wear the eye patch.
    Albrecht von Graæes Archiv für Ophthalmologie 07/2012; · 1.93 Impact Factor
  • H J Simonsz
    Strabismus 03/2012; 20(1):42.
  • H J Simonsz, G H Kolling
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    ABSTRACT: Infantile esotropia (IE) is defined as an esotropia before the age of 6 months, with a large angle, latent nystagmus, dissociated vertical deviation, limitation of abduction, and reduced binocular vision, without neurological disorder. Prematurity, low birth weight, and low Apgar scores are significant risk factors for IE. US standard age of first surgery is 12-18 months, in Europe 2-3 years. The only study to date with prospectively assigned early- and late-surgery groups and evaluation according to intention-to-treat, was the European Early vs. Late Infantile Strabismus Surgery Study (ELISSS). In that study 13.5% of children operated around 20 months vs. 3.9% (P = 0.001) of those operated around 49 months had gross stereopsis (Titmus Housefly) at age 6. The reoperation rate was 28.7% in children operated early vs. 24.6% in those operated late. Unexpectedly, 8% in the early group vs. 20% in the late group had not been operated at age 6, although all had been eligible for surgery at baseline at 11 SD 3.7 months. In most of these children the angle of strabismus decreased spontaneously. In a meta-regression analysis of the ELISSS and 12 other studies we found that reoperation rates were 60-80% for children first operated around age 1 and 25% for children operated around age 4. Based on these findings, the endpoints to consider when contemplating best age for surgery in an individual child with IE should be: (1) degree of binocular vision restored or retained, (2) postoperative angle and long-term stability of the angle and (3) number of operations needed or chance of spontaneous regression. IE is characterized by lack of binocular connections in the visual cortex that cannot develop, e.g. because the eyes squint, or do not develop, e.g. after perinatal hypoxia. As the cause of IE, whether motor or sensory, is a determinant of surgical outcome, a subdivision of IE according to cause is needed. As similarities exist between IE and cerebral palsy we propose to adapt the working definition formulated by the Surveillance of Cerebral Palsy in Europe and define IE as "a group of permanent, but not unchanging, disorders with strabismus and disability of fusional vergence and binocular vision, due to a nonprogressive interference, lesion, or maldevelopment of the immature brain, the orbit, the eyes, or its muscles, that can be differentiated according to location, extent, and timing of the period of development."
    European journal of paediatric neurology: EJPN: official journal of the European Paediatric Neurology Society 05/2011; 15(3):205-8. · 2.01 Impact Factor
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    ABSTRACT: We previously found that compliance with occlusion therapy for amblyopia is poor, especially among children of non-native parents who spoke Dutch poorly and who were low educated. We investigated conception, awareness, attitude, and actions to deal with noncompliance among Dutch orthoptists. Orthoptists working in non-native, low socioeconomic status (SES) areas and a selection of orthoptists working elsewhere in the Netherlands were studied. They were observed in their practice, received a structured questionnaire, and underwent a semi-structured interview. Finally, a short survey was sent to all working orthoptists in the Netherlands. Nine orthoptists working in non-native, low-SES areas and 23 working elsewhere in the Netherlands participated. One hundred and fifty-one orthoptists returned the short survey. Major discrepancies existed in conception, awareness, and attitude. Opinions differed on what should be defined as noncompliance and on what causes noncompliance. Some orthoptists found noncompliance annoying, unpleasant, and hard to imagine, others were more understanding. Many pitied the noncompliant child. Almost all thought that the success of occlusion therapy lies both with the parents and the orthoptist, but one third thought that noncompliance was not solely their responsibility. Patients' compliance was estimated at 69.3% in non-native, low-SES areas (electronically, 52% had been measured), at 74.1% by the other 23 orthoptists, and at 73.8% in the short survey. Actions to improve compliance were diverse; some increased occlusion hours whereas others decreased them. In non-native, low-SES areas, 22% spoke Dutch moderately to none; the allotted time for a patient's first visit was 21'; the time spent on explaining to the parents was 2'30" and to the child 10". In practices of the other 23 orthoptists, 6% spoke Dutch moderately to none (P<0.0001), the time for a patient's first visit was 27'24" (P=0.47), and the periods spent explaining were 2'51" (P=0.59) and 26" (P=0.17), respectively. Conception, awareness, attitude, and actions to deal with noncompliance varied among orthoptists. In non-native, low-SES areas, time spent on explanation was shorter, despite a lower fluency in Dutch among the parents.
    Strabismus 12/2010; 18(4):146-66.
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    ABSTRACT: According to the ROTAS study most of the improvement in visual acuity (VA) during amblyopia therapy of children aged 3 to 8 years occurs during the first 6 to 8 weeks . Sattler reported a VA gain in 11-year olds even during the second year of treatment . So far there are no standards concerning the intensity and duration of the treatment of patients older than 7 years of age. After a report on electronic monitoring of occlusion treatment in patients aged 7 to 16 years for 4 months , we now analyse whether this age group benefits from a longer-lasting treatment. In this pilot study the progression of VA was analysed in 11 patients (age range 7.18 to 15.76 years; median 11.42 years) during 12 months of occlusion therapy (types of amblyopia: 5 anisometropic, 1 strabismic, 5 combined). The daily occlusion times were recorded using the occlusion dose monitor (ODM) . At the beginning of treatment the prescription of the occlusion regime (median) was 6 h/d (range 4 to 7 h/d), the (decimal) VA 0.2 (range 0.02 to 0.63) for single and 0.16 (range 0.02 to 0.8) for crowded optotypes. The recorded occlusion time (median) was 4.4 h/d during the 12 months of treatment, the VA gain (median) was 0.4 log units for single (range 0.2 to 0.7 log units) and 0.3 for crowded optotypes (range--0.1 to 0.6). During the period of 4 to 12 months of treatment (received occlusion 4.12 h/d) the VA gain was 0.1 log units for single and for crowded optotypes. The maximum VA gain during the interval of 4 to 12 months of treatment was 0.2 log units, both single and crowded. The interocular difference for crowded VA (median) decreased from 0.9 to 0.6 log units during treatment, however only one patient achieved an interocular difference of < 0.2 log units. The patients presented here were able to integrate daily occlusion lasting several hours and the electronic monitoring of occlusion treatment into their daily routine over a period of 12 months. During this period the VA of all included types of amblyopia improved significantly, both from a clinical and statistical point of view. Further long-term studies using ODMs with larger groups of patients may identify factors for success of treatment, reveal the long-term stability of the improvement and contribute to a standardised treatment in this age group.
    Klinische Monatsblätter für Augenheilkunde 10/2010; 227(10):774-81. · 0.70 Impact Factor
  • H J Simonsz, M J C Eijkemans
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    ABSTRACT: In the Early vs. Late Infantile Strabismus Surgery Study (ELISSS), 13.5% of children operated at 20 months vs. 3.9% of those operated at age 4 had gross binocular vision (Titmus Housefly). Reoperation rates were 28.7% in the former vs. 24.6% in the latter group and, although all were eligible for surgery at baseline at 11 SD 3.7 months, 8% in the early group vs. 20% in the late group were never operated, mostly because their angle decreased spontaneously. We assessed the predictive value of age, angle, and refraction in these matters. The ELISSS reoperation rates were first compared with those found in nine series of consecutive cases in nine university clinics operated during one particular year, between 6 and 23 years previously. Logistic regression was used to estimate the effect of postoperative angle and clinic on the chance of reoperation. Secondly, a meta-regression analysis was done of these and other reported reoperation rates. The mean age at operation and the mean duration of follow-up were regressed on the logistically transformed reported reoperation rates. Finally, to estimate the chance of spontaneous decrease of the angle without surgery, a random-effects model was fitted on the 6-monthly orthoptic measurements of angle and refraction in the ELISSS that antedated surgery, loss to follow-up, or final examination. In the random-effects model (see online-only supplement link or visit, www.simonsz.net), for ELISSS patients the random effect was defined as the deviation of the average angle, the fixed effect. A vector was defined based on age and spherical equivalent of the patient. The variance around the prediction consisted of uncertainty in the estimations, random effects, and residuals. In the retrospective study, 204 patients who had been first operated between 6 and 23 years previously were eligible. A reoperation had been performed in 32 (19.3%) of the remaining 166 children who were 4.33 SD 1.35 years old at first surgery. The reoperation rate was 7.3% for those with a postoperative angle of -4° to +4° (N = 82), 25% for postoperative divergence > 5°, and 29% for postoperative convergence 10° to 14°. Strabismologists overestimated the reoperation rates at double. In the meta-regression analysis, 12 studies were included. Reoperation rates were between 60% and 80% for children first operated around age 1 and approximately 25% for children operated around age 4 (best fit: -0.221 Ln [age in months] + 1.1069; R(2) = 0.5725). Finally, in the predictions of random-effects model, a small angle at age 1 and hyperopia of approximately +4 increased the chance of spontaneous decrease of the angle into a microstrabismus. The benefit of early surgery for gross binocular vision is balanced by a higher reoperation rate and an occasional child being operated that would have had a spontaneous decrease into a microstrabismus without surgery. The fact that, in the ELISSS, hyperopia was associated with a decrease of the angle underscores the benefit of early refractive correction.
    Strabismus 09/2010; 18(3):87-97.
  • H J Simonsz
    Strabismus 09/2010; 18(3):116.
  • H J Simonsz
    Strabismus 03/2010; 18(1):1-2.
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    ABSTRACT: To analyse psychological causes for low compliance with occlusion therapy for amblyopia. In a randomised trial, the effect of an educational programme on electronically measured compliance had been assessed. 149 families who participated in this trial completed a questionnaire based on the Protection Motivation Theory after 8 months of treatment. Families with compliance less than 20% of prescribed occlusion hours were interviewed to better understand their cause for non-compliance. Poor compliance was most strongly associated with a high degree of distress (p<0.001), followed by low perception of vulnerability (p = 0.014), increased stigma (p = 0.017) and logistical problems with treatment (p = 0.044). Of 44 families with electronically measured compliance less than 20%, 28 could be interviewed. The interviews confirmed that lack of knowledge, distress and logistical problems resulted in non-compliance. Poor parental knowledge, distress and difficulties implementing treatment seemed to be associated with non-compliance. For the same domains, the scores were more favourable for families who had received the educational programme than for those who had not.
    The British journal of ophthalmology 08/2009; 93(11):1499-503. · 2.92 Impact Factor
  • M.V. Joosse, H.J. Simonsz, P.T.V.M. de Jong
    Strabismus 07/2009; 8(2).
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    ABSTRACT: Infantile esotropia, a common form of strabismus, is treated either by bilateral recession (BR) or by unilateral recession-resection (RR). Differences in degree of alignment achieved by these two procedures have not previously been examined in a randomised controlled trial. Controlled, randomised multicentre trial. 12 university clinics. 124 patients were randomly assigned to either BR or RR. Standardised protocol prescribed that the total relocation of the muscles, in millimetres, was calculated by dividing the preoperative latent angle of strabismus at distance, in degrees, by 1.6. Alignment assessed as the variation of the postoperative angle of strabismus during alternating cover. The mean preoperative latent angle of strabismus at distance fixation was +17.2 degrees (SD 4.4) for BR and +17.5 degrees (4.0) for RR. The mean postoperative angle of strabismus at distance was +2.3 degrees (5.1) for BR and +2.9 degrees (3.5) for RR (p = 0.46 for reduction in the angle and p = 0.22 for the within-group variation). The mean reduction in the angle of strabismus was 1.41 degrees (0.45) per millimetre of muscle relocation for RR and 1.47 (0.50) for BR (p = 0.50 for reduction in the angle). Alignment was associated with postoperative binocular vision (p = 0.001) in both groups. No statistically significant difference was found between BR and RR as surgery for infantile esotropia.
    The British journal of ophthalmology 04/2009; 93(7):954-7. · 2.92 Impact Factor
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    ABSTRACT: 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.
    Strabismus 01/2009; 17(4):158-64.
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    ABSTRACT: 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. 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. 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 degrees upgaze and downgaze was evaluated. 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) degrees in the working direction of the transposition, either upgaze or downgaze, 6.2 (4.5) degrees in gaze ahead, and 3.3 (4.4) degrees out of the working direction. Four patients had to be reoperated in the short term, one because of overcorrection and three because of undercorrection. 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.
    The British journal of ophthalmology 03/2008; 92(2):245-51. · 2.92 Impact Factor
  • Von Pflugk, H J Simonsz
    Strabismus 01/2008; 16(3):125-8.
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    ABSTRACT: Opinions differ on the course of the visual acuity in the amblyopic eye after cessation of occlusion therapy. This study evaluated visual acuity in a historical cohort treated for amblyopia with occlusion therapy 30-35 years ago. Between 1968 and 1975, 1250 patients had been treated by the orthoptist in the Waterland Hospital in Purmerend, The Netherlands. Of these, 471 received occlusion treatment for amblyopia (prevalence 5.0%, after comparison with the local birth rate). We were able to contact 203 of these patients, 137 were orthoptically re-examined in 2003. We correlated the current visual acuity with the cause of amblyopia, the age at start and end of treatment, the visual acuity at start and end of treatment, fixation, binocular vision and refractive errors. Mean age at the start of treatment was 5.4 +/- 1.9 years, 7.4 +/- 1.7 years at the end and 37 +/- 2.7 years at follow-up. Current visual acuity in the amblyopic eye was correlated with a low visual acuity at the start (p < 0.0001) and end (p < 0.0001) of occlusion therapy, an eccentric fixation (p < 0.0001), and the cause of amblyopia (p = 0.005). At the end of the treatment, patients with a strabismic amblyopia (n = 98) had a visual acuity in the amblyopic eye of 0.29 logMAR +/- 0.3, and in 2003 0.27 +/- 0.3 logMAR. In patients with an anisometropic amblyopia (> 1 D, n = 16) visual acuity had decreased from 0.17 +/- 0.23 logMAR to 0.21 logMAR +/- 0.23. In patients with both strabismic and anisometropic amblyopia (n = 23), visual acuity had decreased from 0.52 logMAR +/- 0.54 to 0.65 logMAR +/- 0.54. Overall, acuity had decreased in 54 patients (39%) after cessation of treatment. Of these, 18 patients had an acuity decrease to less than 50% of their acuity at the end of treatment. In 15 of these 18 patients anisohypermetropia had increased. A decrease in visual acuity after cessation of occlusion therapy occurred in patients with a combined cause of amblyopia or with an increase in anisohypermetropia.
    Klinische Monatsblätter für Augenheilkunde 01/2007; 224(1):40-6. · 0.67 Impact Factor
  • Klinische Monatsblätter für Augenheilkunde 01/2007; 224(1):40-46. · 0.67 Impact Factor
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    ABSTRACT: During the 1970s, as part of his work for a doctor's thesis in which he described the development of the human orbit in great detail, the first author established the largest anatomical collection of embryonic and fetal orbits ever. Unfortunately, he died before the thesis could be finished. The thousands of sections have now been scanned at high resolution and made publicly available on the Internet at www.visible-orbit.org; 3-D reconstruction software is being developed. The Discussion and part of the 'Methods' section of this thesis are published in translation in this article. The conclusions of the first author at the time read as follows: (1) initially, the developing orbit is vaguely indicated by condensations in the mesenchymal connective tissue area; (2) in this connective tissue area, chondral, osseous and muscular structures develop and grow until, in the fully developed stage, the orbital content is surrounded by bony surfaces with a thin layer of connective tissue as periosteum, and by a muscle fragment; (3) the embryonic and early fetal phase, during which one can only speak of a 'regio orbitalis,' is followed by a period in which we can speak of a primordial orbit; (4) the phase of the primordial orbit extends until after birth; (5) the surface area of all orbital walls increases more or less linearly; (6) the 'musculus orbitalis Mülleri' occupies a special place in the orbital wall; (7) the so-called 'regio craniolateralis' is the primordium, which, in the fully developed stage, is occupied by the thick intersection of the frontolateral and the horizontal part of the frontal bone; (8) in the frontal plane, the shape of the primordial orbit, as well as that of the fully developed orbit, is more or less round; (9) the prenatal development of an eye socket is a complex event, characterized by changes in composition, shape and size of the orbital wall; and (10) the orbit can only be denoted by the term "eye socket" when it is fully developed. At the end of the thesis, he also presented the following postulates: (1) in the prenatal orbit, the development of the so-called 'periorbita' is at the forefront; (2) the mutual rotation of the orbital axes and the frontalization of the eyes from approx. 180 degrees in the early prenatal stages to approx. 50 degrees in adulthood do not seem to be caused by mechanical influences of the surrounding tissue; (3) the pterygopalatine fossa and the 'cavum cerebri' are not part of the orbit at any developmental stage; (4) in the prenatal skull, the inferior nasal concha, which forms part of the maxilla in the fully developed skull, is part of the 'capsula nasalis'; and (5) in order to achieve normal development of the eye socket in microphthalmus and anophthalmus, the normal orbital content should be restored.
    Strabismus 04/2006; 14(1):51-6.
  • H J Simonsz, G H Kolling, K Unnebrink
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    ABSTRACT: 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. 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. 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 degrees and 10 degrees , 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. 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.
    Strabismus 01/2006; 13(4):169-99.
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    ABSTRACT: Connective tissue bands connect the horizontal rectus muscles at the level of the posterior pole to the orbital wall. These bands, referred to as pulley bands or faisseaux tendineux, purportedly act like springs to keep the rectus muscle bellies in place during eye movement out of the plane of the muscle. We examined the mechanical properties of these bands in human specimens obtained during surgery. In addition, we examined eye motility and stability of rectus muscles in a patient who had no functional pulley bands. Exenterations were carried out on two patients with sebaceous gland carcinoma. Pulley bands were identified and force-elongation behavior was examined with a forceps and a force gauge. Stability of rectus muscles was examined in a patient with severe Crouzon's syndrome by orbital CT scans and during surgery under local, eye drop, anesthesia. The pulley bands showed leash-like mechanical behavior: they were slack over approximately 10mm and became taut when stretched further. In the patient with Crouzon's syndrome, both CT and observation of the muscle during surgery showed little sideways displacement of the muscle bellies in eye movement out of the plane of the muscle, despite the lack of functional pulley bands. The leash-like mechanical behavior of the pulley bands seems unsuited for stabilization of the muscle bellies. The patient with Crouzon's syndrome had relatively good eye motility and stable rectus muscle paths despite the lack of functional pulley bands.
    Vision Research 10/2005; 45(20):2710-4. · 2.38 Impact Factor

Publication Stats

484 Citations
61.80 Total Impact Points


  • 2004–2012
    • Erasmus MC
      • • Department of Ophthalmology
      • • Research Group for Public Health
      Rotterdam, South Holland, Netherlands
  • 2009
    • Netherlands Institute for Neuroscience
      Amsterdamo, North Holland, Netherlands
  • 2005
    • Delft University Of Technology
      • Department of Biomechanical Engineering
      Delft, South Holland, Netherlands
  • 2000–2005
    • Erasmus Universiteit Rotterdam
      • Department of Ophthalmology
      Rotterdam, South Holland, Netherlands
  • 1998
    • Universität Heidelberg
      • Department of Medical Biometry
      Heidelberg, Baden-Wuerttemberg, Germany
  • 1991–1993
    • Kantonsspital St. Gallen
      San Gallo, Saint Gallen, Switzerland
  • 1989
    • University of Amsterdam
      Amsterdamo, North Holland, Netherlands
  • 1988
    • Justus-Liebig-Universität Gießen
      Gieben, Hesse, Germany