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Biomedical subjects

H J Simonsz

Publications and source records attributed to H J Simonsz.

At least 37 records · Page 2Linked to original sources
PubMed1998

A prospective 10 year follow up study of patients with neurofibromatosis type 1.

OBJECTIVE: To establish the prevalence and incidence of symptoms and complications in children with neurofibromatosis type 1 (NF1) and to assess possible risk factors for the development of complications. DESIGN: A 10 year prospective multidisciplinary follow up study. PATIENTS: One hundred and fifty children diagnosed with NF1 according to criteria set by the National Institutes of Health. RESULTS: In 62 of 150 children (41.3%) complications were present, including 42 (28.0%) children with one complication, 18 (12.0%) with two complications, and two (1.3%) with three complications (mean (SD) duration of follow up 4.9 (3.8) years). Ninety five of the 150 children presented without complications (follow up, 340.8 person-years). The incidence of complications was 2.4/100 person-years in this group. An association was found between behavioural problems and the presence of complications. CONCLUSION: This is the largest single centre case series of NF1 affected children followed until 18 years of age. Children with NF1, including those initially presenting without complications, should have regular clinical examinations.

Adolescent↗
PubMed1998

The Early vs Late Infantile Strabismus Surgery Study: do sources for bias exist in this non-randomised trial? Early vs Late Infantile Strabismus Surgery Study Group.

BACKGROUND: The Early vs Late Infantile Strabismus Surgery Study Group investigates whether early or late surgery is preferable in infantile convergent strabismus, in a non-randomised, prospective, multicentre clinical trial. The current state of the study after end of recruitment is reported here, focusing on the question of possible sources for bias in this non-randomised trial. METHOD: The prognostic factors were analysed at baseline in order to check for imbalances between the two treatment groups. Reasons for possible differences are discussed. RESULTS: There is no evidence for clinically relevant inhomogeneities between the two groups concerning the distribution of the three prognostic factors spherical equivalent, degree of amblyopia, and limitation of abduction. The fourth prognostic factor, horizontal angle of squint, differs significantly between the two groups. CONCLUSION: In the analysis of the final results we may have to account for differences in angle of squint at baseline by its inclusion as a covariate or by stratification.

Age Distribution↗
PubMed1997

Quantitative perimetry under binocular viewing conditions in microstrabismus.

In order to elucidate the type, size and depth of suppression scotomata in microstrabismus and small angle convergent strabismus, we performed binocular static perimetry in 14 subjects with strabismus and four normal observers. The strabismic cases had an objective angle of convergent squint between 1 and 8 deg, visual acuity between 0.1 and 1.25, and limited stereopsis. During testing the subjects fused pictures on two Friedmann visual field analyzers. Right and left eyes were studied separately under both monocular and binocular viewing conditions. In five strabismics a suppression scotoma was found in the squinting eye, with a diameter of 5-30 deg and a depth ranging from 4 to 14 dB. No suppression scotomata could be detected in the nine other subjects nor in the four normal observers. In conclusion, only 36% of subjects with strabismus were found to have a suppression scotoma. These scotomata were centered around the fixation point of the squinting eye, in some cases also encompassing the foveal area, and varying in depth and size.

Adult↗
PubMed1997

Endocrinologic disorders and optic pathway gliomas in children with neurofibromatosis type 1.

OBJECTIVE: To establish the prevalence of endocrinologic disorders in children with neurofibromatosis type 1 (NF1) and the relationship between these disorders and cerebral abnormalities on magnetic resonance imaging. DESIGN: A prospective follow-up study. Setting. A multidisciplinary neurofibromatosis clinic. PATIENTS: A total of 122 children diagnosed with NF1 according to diagnostic criteria set by the National Institutes of Health. RESULTS: Central precocious puberty (CPP) was diagnosed in 3 children and growth hormone deficiency (GHD) in 3 children. Optic pathway gliomas were observed in 15 children; in 9 of the 15 cases, the optic chiasm was involved. Of the 3 children with CPP, only 1 showed a chiasma glioma on magnetic resonance imaging. In 1 case with GHD, an optic chiasm glioma was detected on neuroimaging. Two of the 9 children with an optic chiasm glioma presented with CPP or GHD. CONCLUSIONS: It has been suggested that CPP in children with NF1 is found exclusively in the presence of a chiasma glioma. We conclude that chiasma glioma may not be obligatory in children with NF1 and CPP or GHD. Moreover, we report a prevalence of GHD in children with NF1 of 2.5%, which has not been established earlier.

Brain↗
PubMed1992

Kearns-Sayre's syndrome developing in a boy who survived pearson's syndrome caused by mitochondrial DNA deletion.

A 7-year-old boy presented with bilateral ptosis and atypical retinitis pigmentosa. Before age two, he had had an Fe-refractory anemia, with neutropenia and thrombopenia. Just prior to the ophthalmic examination, the patient developed lactate acidosis, muscular hypotonia, ataxia and increased protein in the spinal fluid. Pancytopenia, pancreas dysfunction and growth retardation are the main features of Pearson's syndrome, most children not surviving beyond age three. The cause of Pearson's syndrome in our patient turned out to be a 5 kb deletion in the mitochondrial DNA. Similar deletions have been described in the Kearns-Sayre syndrome. It seems that children who survive the initial phase of Pearson's syndrome, may develop Kearns-Sayre syndrome.

Child↗
PubMed1992

Costs and methods of preventive visual screening and the relation between esotropia and increasing hypermetropia.

Atkinson has shown that early correction of hypermetropia reduces the incidence of esotropia. If esotropia is reduced by prescribing glasses early, the rate of esotropia-induced amblyopia can be similarly reduced; this would have important economic consequences. We have studied (1) how costs compare to benefits in early visual screening, (2) how videorefraction as used by Atkinson compares to retinoscopy, and (3) whether esotropia is more likely to occur in children who have increasing as opposed to decreasing hypermetropia. The costs of the study so far have been high. It was exceedingly difficult to get all infants invited, come to the clinic and examined. Videorefraction did not compare favourably with retinoscopy in terms of costs and precision, whereas the amount of skill and time needed was approximately equal. The third question, whether esotropia is more likely to occur in children who have increasing as opposed to decreasing hypermetropia, arose from the controversy whether, in the general population, refraction increases or decreases during the first years of life. We found that papers reporting a decrease of hypermetropia in early childhood were studies of large cross-sections of the general population, whereas papers that reported an initial increase originated from ophthalmological practices or strabismus departments. These conflicting results could be reconciled by assuming a population bias: if esotropia is more likely to occur in children with increasing hypermetropia, children with increasing hypermetropia will preferentially be seen by ophthalmologists. It seems natural that children with increasing hypermetropia are more likely to squint, because additional accommodation, needed to overcome increasing hypermetropia, will inevitably confer additional convergence. This relationship has meanwhile been confirmed by others.

Amblyopia↗
PubMed1992

Misdirected regeneration of abducens nerve neurons into the parasympathetic pupillary pathway.

A 16-year-old girl suffered a severe head trauma with paralyses of the right oculomotor, trochlear, and abducens nerves. Three years later, only the abducens nerve had recovered. The pupil did not react to light or near. However, the diameter of the pupil correlated with horizontal gaze: with the gaze to the left, the diameter of the pupil was 8 mm, with the gaze straight ahead, 6 mm, and with the gaze to the right, 4 mm. With saccades to the right, the pupil started to constrict immediately and reached its smallest diameter after about 2 s. We conclude that the constriction of the pupil was due to misdirected regeneration of abducens nerve neurons into the parasympathetic pathway of the oculomotor nerve.

Abducens Nerve↗
PubMed1992

[Length-tension measurement of oblique eye muscles in strabismus operations for differentiating trochlear paralysis and strabismus sursoadductorius].

In a group of patients with a motility typical of a superior oblique palsy (a hypertropia increasing in adduction, in down-gaze and on head-tilt, a V-pattern and an excyclotropia), we recorded length-tension diagrams of oblique eye muscles during strabismus surgery. In 14 cases a length-tension recording was made during surgery in general anaesthesia, before and after intravenous administration of succinylcholine, that produces a fierce contraction of eye muscles. Among 14 patients that had eye motilities compatible with a superior oblique muscle palsy, 7 indeed had a non-contracting superior oblique muscle, but others had oblique muscles that contracted vividly. We also made length-tension diagrams of oblique eye muscles during strabismus surgery with local, tetracain eye-drop anaesthesia. Here, the recording was made three times, while the patient looked ahead, into the field of action of the muscle and out of the field of action of the muscle. Some patients indeed had a non-contracting superior oblique muscle and a stiff inferior oblique muscle, but others had superior oblique muscles that contracted vividly, despite an eye motility typical of a superior oblique palsy, with a positive Bielschowsky head-tilt test. This finding confirms the assumption of Kaufmann, Kolling and others that these cases have a non-paretic motility disorder. Viirre et al. found in normal monkeys that disruption of fusion by one week of occlusion of one eye allowed abberrations of conjugate horizontal and vertical eye movement like upshoot-in-adduction to become manifest.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Covering one eye in fixation-disparity measurement causes slight movement of fellow eye.

In the subjective measurement of fixation disparity (FD), the subject fuses contours presented in the peripheral macular areas of both eyes (fusion lock). The position of the eyes relative to each other is monitored by means of two haploscopically seen vertical lines presented in the central macular area, one above and one below a binocularly seen horizontal line. The subject is instructed to shift one of the vertical lines horizontally until the two are aligned, while fixating their intersection with the horizontal line. It has recently been questioned whether the foveolae really are pointed towards the perceived intersection. In this study, we monitored the position of one eye while intermittently covering the fellow eye, while the subject maintained fixation of the intersection of the remaining vertical line and the horizontal line. We found slight differences in position of the measured eye, depending on whether the other eye was covered or not, i.e. depending on the presence or absence of fusion in the macular periphery. These differences were more pronounced in the non-dominant eye.

Adult↗
PubMed1991

[Behavior of the other eye in measuring fixation disparity].

In the subjective measurement of FD, the proband fuses contours presented in the peripheral macular areas of both eyes ('fusion lock'). The position of both eyes relative to each other is monitored by means of two haploscopically seen vertical lines presented in the central visual field, one above and one below a binocularly seen horizontal line. The subject is instructed to shift one of the vertical lines horizontally until the two are aligned, while fixating their intersection with the horizontal line. It has recently been questioned whether the foveolae really are pointed at the perceived intersection. To investigate this matter, we registered the position of one eye while intermittently covering the fellow eye, while the subject maintained fixation of the intersection. We found slight differences in monocular eye position depending on the presence or absence of fusion in the macular periphery, confirming earlier findings in part. These differences were more pronounced in the nondominant eye.

Adult↗
PubMed1990

19th century mechanical models of eye movements, Donders' law, Listing's law and Helmholtz' direction circles.

Donders, Ruete, von Graefe, von Helmholtz, Listing, Volkmann and many others have provided the broad outline of an answer to the question how the eye rotates during eye movements. Many mechanical models of eye movements, ophthalmotropes, have been constructed and studied in the nineteenth century. These models have primarily served to explain Donders' and Listing's Laws on the nature of eye movements. As both Donders' Law and Listing's Law are easier to understand when seen against the background of the coordinate systems used to describe eye movements, all of the coordinate systems currently in use in the diagnosis and treatment of strabismus are described. In addition, the reader is introduced to a coordinate system based on von Helmholtz' direction circles, circles describing the direction of the horizontal and vertical retinal meridians in all positions of gaze.

Eye Movements↗
PubMed1990

A reexamination of end-point and rebound nystagmus in normals.

In order to detail the characteristics of end-point (EPN) and rebound nystagmus (RN), two series of experiments were performed with infrared oculography for measurement of horizontal eye movements. Experiment 1 consisted of EPN recordings during sustained lateral gaze (40 degrees and 50 degrees) in 20 normal subjects. Experiment 2 consisted of recordings of RN in 5 normal subjects. Nine of 20 subjects demonstrated a jerk EPN. EPN almost always appeared immediately and was sustained for 15-25 sec. In Experiment 2, RN occurred in 5 of the 5 subjects who demonstrated EPN. The mean amplitude of RN was always less than that of EPN, and decayed over a 5-10-sec time period. The experiment demonstrated that RN can be evoked in normals even when a fixation target, in a fully lit room, is present.

Adult↗
PubMed1989

Increased muscle tension and reduced elasticity of affected muscles in recent-onset Graves' disease caused primarily by active muscle contraction.

In 3 patients with Graves' disease of recent onset, length-tension diagrams were made during surgery for squint under eyedrop anesthesia. The affected muscles were found to be very stiff when the other eye looked straight ahead. It was expected that these stiff muscles would be able to shorten to some extent but would be unable to lengthen, due to fibrosis of the muscle. We found that the affected muscles did not shorten very much when the other eye looked into the field of action of the muscle. Unexpectedly however, they lengthened considerably when the other eye looked out of the field of action of the muscle. This finding implies that the raised muscle tension and reduced elasticity of affected muscles in these cases of Graves' disease of recent onset were primarily caused by active muscle contraction, not by fibrosis.

Diplopia↗
PubMed1989

The effect of prolonged monocular occlusion on latent nystagmus in the treatment of amblyopia.

We recorded eye movements in 5 patients with latent nystagmus (LN) before and after 2 days of occlusion of the better eye. The slow-phase speed of the nystagmus (SPS) was in general, before occlusion, lower when the better eye fixated but, after occlusion, lower when the worse eye fixated. However, the sum of SPS during right fixation and SPS during left fixation remained constant. Oscillopsia complaints gradually disappeared during the period of occlusion. These findings indicate that the difference between the SPS during fixation with the right eye and the SPS during fixation with the left eye in LN patients is caused by a compensatory drift that decreases LN during fixation with the better eye but increases LN during fixation with the worse eye. During occlusion, this compensatory drift changes its direction and magnitude slowly over days. Hence, occlusion of the better eye in children with amblyopia and LN should be prescribed only in days per week, not in hours per day.

Adolescent↗
PubMed1989

Preoperative prism adaptation test in normosensoric strabismus.

In 19 patients with normosensoric esotropia, the squint angles measured with the alternate cover test were compared with those after prolonged prismatic correction of the squint angle and with those after prolonged occlusion of one eye. All patients showed an increase of the squint angle after prism adaptation. The angle was generally smaller after diagnostic occlusion of one eye than after prism adaptation. We assume that the increase in the squint angle after prism adaptation is caused by an anomalous sensorial relationship between the two eyes that was not detected with the usual psychophysical tests. Surgery tailored to the squint angle after prism adaptation seems advisable in patients with normosensoric esotropia.

Adaptation, Ocular↗
PubMed1989

The effect of prolonged monocular occlusion on latent nystagmus in the treatment of amblyopia.

We recorded eye movements in 8 patients with latent nystagmus (LN) before and after 2 days of occlusion of the better eye. The slow-phase speed of the nystagmus (SPS) during fixation with the worse eye became lower after 2 days of occlusion of the better eye. However, the SPS during fixation with the better eye became higher after 2 days of occlusion of the better eye. The sum of SPS during fixation with the better eye and SPS during fixation with the worse eye remained the same. Oscillopsia complaints gradually disappeared over days during the occlusion. It seems likely that the alteration of the LN during prolonged monocular vision is caused by a slow-velocity bias of the neural integrator, a compensatory drift, generated by the flocculus using retinal-slip information. The difference between SPS during fixation with the better eye and SPS during fixation with the amblyopic eye in LN patients with amblyopia is probably also caused by this compensatory drift. As the compensatory drift changes its direction and magnitude slowly over days, it seems advisable to occlude the better eye in children with amblyopia and LN during days per week, and not during hours per day.

Adaptation, Ocular↗