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Biomedical subjects

J Ygge

Publications and source records attributed to J Ygge.

At least 19 recordsLinked to original sources
PubMed2006

Intra-individual variability of saccadic velocity measured with the infrared reflection and magnetic scleral search coil methods.

BACKGROUND: The infrared (IR) and the magnetic scleral search coil (MSC) systems for eye tracking were studied with regard to the intra-individual variability in saccadic eye movement recordings. METHOD: Three healthy subjects performed similar saccadic eye movement tasks at five different occasions with both the IR (Orbit XY-1000) and the MSC (Skalar Medical) techniques. The maximum velocity (VMAX) and slope constant (C) of the main sequence plots were analyzed with regard to the coefficient of variation (CV) and the intraclass correlation coefficient (Ricc). In addition, the possible reasons for variability in the IR recordings, especially different causes for noise, were analyzed and discussed. RESULTS: The main sequence data showed intra-individual variation with both recording systems, but the coefficient of variation was higher for VMAX with the IR compared to the MSC method. Ricc analysis showed that 36% of the variance of VMAX and 49% of the variance of C resulted from intra-individual variability in recordings of the IR system. The corresponding results for the MSC recordings regarding VMAX and C were 48% and 88%. CONCLUSIONS: Saccadic eye movement recordings yielded a larger intra-individual variability with the IR system than with the MSC system. The effect that the MSC annulus may have on the ocular motor command signal and the possible low pass filter caused by the coil slipping on the surface of the eye may partly explain the relatively lower velocity in the MSC recordings. Also, noise in the IR recordings induces peaks of eye velocity, which can be reduced considerably by filtering. However, the variability in the recordings, which was larger in the IR than in the MSC recordings, did not seem to be decreased by filtering. The basic level of noise in the recordings was not clearly associated with the amount of reduction of VMAX when the IR recordings were filtered. We suggest that artefacts of the saccadic signal, which can be related to changes in the reflecting surface of the eyes and eyelids, are important factors for explaining the variability and high-velocity peaks in the IR recordings. Lighting conditions was confirmed as a cause for noise, but temperature and air humidity changes in the goggles were not suspected to influence data in the normal experimental setting. Although noise, shortcomings of the recording technique and procedure may offer explanations for the intra-individual variability, the calibration procedure and changes in attention and fatigue of the subject should also be considered.

Adult↗
PubMed2005

A comparison between the magnetic scleral search coil and infrared reflection methods for saccadic eye movement analysis.

BACKGROUND: A non-invasive eye tracking system, based on pulsed infrared light (IR), was compared with the magnetic scleral search coil method (MSC) for saccadic eye movement recordings. METHODS: Ten normal subjects performed horizontal and vertical saccades recorded with both methods. Eight recordings were complete and analysed for maximum peak velocity (V(MAX)) and constant (C) of the main sequence curve. RESULTS: The IR recordings showed significantly higher peak velocity values than the MSC system and generally more inter-individual variability. No significant difference regarding peak velocity was detected between abducting and adducting saccades or between upward and downward saccades with either of the systems. Horizontal saccades had higher peak velocities with both techniques. CONCLUSIONS: Comparison of the main sequence plots of the IR and MSC eye tracking techniques reveals that the IR system yields higher values of maximum peak velocity and the constant, the differences being similar for eye movements in different directions. There are various possible explanations for the lower maximum velocity of the MSC recordings, e.g. slipping of the coil annulus on the surface of the eye and a change of the oculomotor command signal induced by wearing the coil. Also, artefacts associated with the IR recording system may cause over-estimations of the saccadic velocity and, furthermore, contribute to the higher variability of the IR recordings.

Adult↗
PubMed2002

Visual and perceptual characteristics, ocular motility and strabismus in children with periventricular leukomalacia.

The immature visual system is vulnerable to adverse events. Periventricular leukomalacia (PVL), an end-stage lesion after hypoxia-ischemia at gestational age 24-34 weeks affecting the visual radiation, has become a principal cause of visual impairment in children. Cerebral visual dysfunction caused by PVL is characterized by delayed visual maturation, subnormal visual acuity, crowding, visual field defects, and visual perceptual-cognitive problems. Magnetic resonance imaging is the method of choice for diagnosing this brain lesion, which is associated with optic disk abnormalities, strabismus, nystagmus, and deficient visually guided eye movements. Children with PVL may present to the ophthalmologist within a clinical spectrum from severe visual impairment in combination with cerebral palsy to only early-onset esotropia, normal intellectual level and no cerebral palsy. Optimal educational and habilitational strategies need to be developed to meet the needs for this group of children.

Adolescent↗
PubMed2001

A child with muscle-eye-brain disease. Ophthalmological and neurological characteristics.

PURPOSE: To describe a child with Muscle-Eye-Brain disease (MEB), one of three types of congenital muscular dystrophy associated with ocular abnormalities. METHODS: Case report. RESULTS: The child showed severe visual impairment due to progressive myopia and retinal degeneration, a pachygyria-type of migration disorder of the brain with a nodular cortical surface, i.e. cobblestone cortex, as well as muscular weakness and severe mental retardation. CONCLUSION: Ophthalmological assessments are important to help to diagnose and follow children with congenital muscular dystrophy.

Abnormalities, Multiple↗
PubMed2001

Symptoms, findings and treatment in patients with dehiscence of the superior semicircular canal.

Recently Minor and co-workers described patients with sound- and pressure-induced vertigo due to dehiscence of the superior semicircular canal. Identifying patients with this 'new' vestibular entity is important, not only because the symptoms are sometimes very incapacitating, but also because they can be treated. We present symptoms and findings in eight such patients, all of whom reported pressure-induced vertigo that increased during periods of upper respiratory infections. Pulse-synchronous tinnitus and gaze instability during head movements were also common complaints. All patients lateralized Weber's test to the symptomatic ear. In some of the patients the audiogram also revealed a small conductive hearing loss. However, the stapedius reflexes were always normal. A vertical/torsional eye movement related to the superior semicircular canal was seen in most of the patients in response to pressure changes and/or sound stimulation. One patient also had superior canal-related positioning nystagmus. Testing vestibular evoked myogenic potentials revealed in all patients a vestibular hypersensitivity to sounds. In the coronal high-resolution 1-mm section CT scans the dehiscence was visible on 1 to 4 sections. Moreover, the skull base was rather thin in this area and cortical bone separating the middle ear and the antrum from the middle cranial fossa was absent in many of the patients. Two of the patients have undergone plugging of the superior semicircular canal using a transmastoid approach and both patients were relieved of the pressure-induced symptoms.

Adult↗
PubMed2000

Ophthalmological findings in children with congenital toxoplasmosis. Report from a Swedish prospective screening study of congenital toxoplasmosis with two years of follow-up.

UNLABELLED: Congenital toxoplasmosis may lead to severe visual impairment or neurological sequelae in the child. PURPOSE: To study the severity of the primary and late ophthalmological dysfunction during a prospective incidence study of congenital toxoplasmosis in the Stockholm and Skåne counties. METHODS: Blood collected on phenylketonuria (PKU) cards from 40,978 consecutively born children were investigated for antitoxoplasma antibodies. Children with verified congenital toxoplasmosis were treated for 12 months with antiparasitic therapy and followed ophthalmologically, neurologically and serologically every third month. RESULTS: Three children had congenital toxoplasmosis. Two of these were asymptomatic at birth and would have escaped early detection without screening. One child had unilateral severe visual impairment and CNS involvement. The incidence of congenital toxoplasmosis was less than 1:10,000. CONCLUSION: Neonatal screening is of importance to diagnose asymptomatic infected children with congenital toxoplasmosis as treatment has been shown to reduce long-term sequelae. Ophthalmological investigations should start early and continue in co-operation with paediatricians.

Adult↗
PubMed1999

Visual and ocular outcome in children after prenatal exposure to antiepileptic drugs.

PURPOSE: To prospectively study the incidence of structural and/or functional ophthalmological abnormalities in the offspring to an unselected population of women with epilepsy, subjected to a well controlled antiepileptic drug (AED) treatment during pregnancy. METHODS: Forty-three children prenatally exposed to antiepileptic drugs and 47 controls were included. Blinded ophthalmological examinations including fundus photography were performed at a median age of 7 years and 4 months. RESULTS: No major eye anomalies were found except in one child in the exposed group who had nystagmus and low vision. The visual acuity was lower in the eye with lowest acuity among the exposed children (p < 0.05). No other significant difference was found between the two groups. CONCLUSION: The results suggest that a well-controlled treatment with AEDs, preferably monotherapy, during pregnancy does not have any major adverse effects on the development of the eye and ophthalmological functions.

Anterior Eye Segment↗
PubMed1998

Nystagmus in periventricular leucomalacia.

BACKGROUND/AIMS: Periventricular leucomalacia (PVL) is a lesion in the immature brain involving the optic radiation. Children with PVL have visual problems including crowding, visual field defects, strabismus, and visual perceptual/cognitive deficits, together with nystagmus. They often have optic nerve hypoplasia seen either as small discs or as large cupping of normal sized optic discs. This study aimed to perform eye movement recordings in a group of children with PVL in order to characterise and classify the nystagmus. METHODS: 19 children with PVL on cerebral imaging underwent eye movement recordings with the Ober-2 infrared reflection technique. RESULTS: 16 of the 19 subjects had horizontal nystagmus. CONCLUSION: The present study shows that nystagmus is commonly seen in children with PVL.

Adolescent↗
PubMed1997

Visual impairment and dyslexia in childhood.

Although visual screening programs seem to be more and more effective, we face new problems with visual dysfunction that are not always detected in the visual screening programs. Many children born prematurely develop cerebral visual impairment. These children suffer from a cognitive visual impairment, causing them to have problems with orientation and visual perception. Brain impairment also seems to be relevant for the dyslexia syndrome, which continues to fascinate and puzzle many researchers. New findings in visual brain function cast light on these questions and might ultimately answer a few of the mysterious findings in dyslexia.

Child↗
PubMed1995

Control of vertical eye alignment in three-dimensional space.

A target that is nearer to one eye than the other subtends a larger visual angle in the closer eye. Consequently, when making saccades between vertically separated targets that are closer to one eye, there is a vertical retinal disparity that must be overcome by a change in the relative alignment of the eyes. We recorded eye movements in three normal subjects and showed that in such viewing circumstances subjects made unequal vertical saccades that led to a rapid change (peak velocity up to 30 deg/sec) in vertical eye alignment. On average, 81% of the required change in alignment occurred within the saccade for downward movements and 47% for upward movements. Such unequal vertical saccades occurred independently of immediate disparity cues; saccades remained unequal when refixing to the remembered locations of the vertically-oriented targets, or even when the natural vertical disparity was nullified by a prism. On the other hand, when subjects wore the nullifying prism in front of the inferior visual field of the left eye for 8-20 hr, they showed a decrease in saccade disconjugacy (to 12-35% of the preadaptation value) to targets closer to the left eye in the inferior but not in the superior visual field. We suggest that the brain develops a three-dimensional map (horizontal, vertical, depth) for vertical saccade yoking, which is under adaptive control, and which is used to preprogram automatically the relative excursions of the eyes during vertical saccades as a function of the current and the desired point of regard.

Adaptation, Ocular↗
PubMed1993

Visual functions in a Swedish population of dyslexic and normally reading children.

Eighty-six 9-year old dyslexic children were carefully matched to controls with regard to age, sex, class in school, and intelligence and thorough visual functions tests and eye examinations were performed. As a group the dyslexic pupils exhibited a lower distance as well as near visual acuity both with monocular and binocular viewing. Furthermore, the dyslexic pupils had a lower contrast sensitivity at the lower and higher spatial frequencies. These differences were all statistically significant. However, no statistically significant differences between the two groups could be observed regarding refractive errors or contrast sensitivity in the middle spatial frequency range. Although some eyes were amblyopic, any severe eye anomalies or diseases were not found in any of the investigated children.

Child↗
PubMed1993

Oculomotor functions in a Swedish population of dyslexic and normally reading children.

Eighty-six nine-year-old dyslexic children were matched to control children with regard to age, sex, class in school, and intelligence. Orthoptic and eye movement analysis were performed on all children. It was concluded that the dyslexic pupils did not differ significantly from control children in terms of strabismus, accommodation, stereo acuity, vergence function or ocular dominance. Eye movement recordings did not show any qualitative differences between the groups in vergence dynamics during synoptophore investigations.

Accommodation, Ocular↗
PubMed1992

Dyslexia; ophthalmological aspects 1991.

Dyslexia or specific reading disability is an important and frequent handicap afflicting 5-10% of the population. It is basically a disorder of acquisition of written language, probably due to a poorly developed phonological awareness, which in turn may be neurologically related. As anatomical correlates symmetry of the planum temporale and ectopies in the cerebral cortex have been suggested. Functional correlates are discovered with brain electrical mapping and stimulation of brain structures during neuro surgery. From an ophthalmological point of view there are no relations between dyslexia and ocular problems including refractive errors and accommodation, problems of binocular control and stereopsis, eye dominance instability etc. However, contrast sensitivity seems to be reduced in dyslexics for the middle range of spatial frequencies, which may be related to impaired function of the 'transient' visual system. With regard to eye movements, there is no firm experimental proof for any disturbances in dyslexia, be it with the different movement systems or in the best movement direction. 'Backward saccades' or regressions are typical not only for dyslexic reading but in all types of reading when comprehension is poor. Although there is no treatment for dyslexia itself that can be based on ophthalmological findings, the ophthalmologist must after careful examination discover and treat any ocular, orthoptic or neuroophthalmological problem that may make reading difficult for the dyslexic child. The ophthalmologist must explain to the child and the parents that dyslexia usually has no ophthalmological or visual cause but is a disability with a neurobiological background, still unknown, in which the only efficient treatment is within the area of pedagogy.

Dyslexia↗
PubMed1991

[Prevention of cellular foreign body reactions to lens implants].

A heparin-surface-modified PMMA IOL has recently been developed in order to give the IOL a hydrophilic surface and to reduce postoperative inflammatory reactions in the eye. It is known that severe inflammation accompanies a tremendous increase in leucocytes in IOLs. A foreign-body reaction is characterized by the formation of histiocytic giant cells. The topical administration of corticosteroids, or the surface passivation of IOLs, cannot prevent a foreign-body reaction. Specular microscopy was used for in vivo investigation of cellular reaction in IOL surface of heparin-surface-modified lenses versus regular PMMA lenses. The double-masked and randomized study included 53 patients investigated 1 week and 1 month postoperatively. Small, round, and spindle-shaped cells were the cells most frequently observed after 1 week. These cells were identified in all cases. They were found in a higher density on the surface of the control lenses (43 cells/mm2) than on the heparin-surface-modified lenses (25 cells/mm2). Giant cells were found in two patients after 1 week; both of these patients belonged to the control group. Small, round, and spindle-shaped cells were also seen in all patients 1 month postoperatively. Again, they were found in a higher frequency on the control lenses (38 cells/mm2) than on the heparin-surface-modified lenses (13 cells/mm2). Giant cells were found in 18 patients 1 month postoperatively. They were found exclusively on the control lenses; the difference was significant (p less than 0.0001).

Follow-Up Studies↗