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Biomedical subjects

G Lennerstrand

Publications and source records attributed to G Lennerstrand.

At least 19 recordsLinked to original sources
PubMed1999

Eye position changes induced by neck muscle vibration in strabismic subjects.

BACKGROUND: In normal subjects vibratory stimulation of neck muscle proprioceptors can induce eye position change and visual illusory movement. The direction of apparent movement is vertical when the back muscles of the neck are stimulated and horizontal when lateral-rotation muscles are stimulated. The effect of muscle proprioceptor stimulation in individuals with defects in binocular vision, such as strabismus, has not been studied previously and is the subject of the present report. METHODS: In 23 strabismic patients with different levels of binocular vision, 70-Hz mechanical vibration was applied to three groups of neck muscles under both dark and normal light conditions, and eye position changes were recorded for each eye using an infrared reflection technique. The dominant eye fixated on a target while the non-dominant eye was covered. RESULTS: When the back muscles were stimulated, eye position changed in a downward direction, as previously demonstrated in the normal subjects. However, in strabismic subjects with poor binocular vision, stimulation of the horizontal rotation neck muscles resulted in eye position changes generally to the same side regardless of the muscle group activated. This differed from normal subjects, where the direction of the eye position changes is related to the group of muscles stimulated. The direction and amplitude of the eye position changes were the same under dark and light conditions. CONCLUSION: Proprioceptive information from neck muscles plays an important role in regulation of gaze direction. The difference that exists between normal subjects and strabismic patients is most likely related to differences in binocular function.

Adolescent↗
PubMed1999

Assessment of visual acuity in children aged 1 1/2-6 years, with normal and subnormal vision.

The aim of the study was to assess different visual acuity tests in the age group 1 1/2-6 years in 105 children with assumed normal vision, visual impairment due to ocular disease or strabismus. Acuity tasks for young children can be divided into three subtypes according to the kind of stimulus used. For "detection acuity", the stimulus should be detected or distinguished from the background, as assessed with the Stycar Rolling Balls. For "resolution acuity", the stimulus pattern should be resolved, as assessed with the Preferential Looking procedure (Teller Acuity Cards). For "recognition acuity", the stimulus must be recognized by the subject as assessed with the BUST-D symbol test, Sheridan Gardiner (S-G) single letters, LH single symbols and line tests, and also the HVOT test. Different acuity values were obtained with regard to detection, resolution and recognition acuities. Assessment with the Stycar Rolling Balls only gave a rough estimate of the visual function. There was an overestimation of the acuity values in all groups of children when using the Preferential Looking technique. Good agreement was found between the LH line and HVOT tests. The BUST-D test, S-G single letters, and LH single symbols gave slightly better acuity values than linear recognition tests. A "crowding ratio" was calculated by dividing the single optotype acuity by the linear acuity, and also by dividing the grating acuity by the optotype linear and single acuity. The crowding ratio varied in the individual children and in the different groups, being highest for strabismic amblyopia. The general conclusion is that reliable visual acuity measurements were not obtained until the visual acuity could be assessed with a recognition test using linear letters or symbols.

Adult↗
PubMed1998

Changes in conceptions of meaning, effects and treatment of amblyopia. A phenomenographic analysis of interview data from parents of amblyopic children.

The research reported is an experimental study on the effects of intensified education of parents of children with amblyopia on their understanding of the nature of the defect, its origins and treatment. Parents in the control group were exposed to the ordinary information provided at two departments of paediatric ophthalmology, whereas parents in the experimental group, attending the same clinics, were asked to read a booklet aiming at enhancing their understanding of amblyopia and its treatment. Experimental as well as control subjects were thereafter interviewed about their understanding of the meaning of amblyopia and amblyopia-related phenomena. Data were generated in single subject, semi-structured, in-depth interviews which were taped and transcribed in extenso. The interviews were analyzed according to the phenomenographic approach: i.e. the outcome is a description of the various conceptions that emerged in the interviews. In almost all cases the categories of meaning could be hierarchically ordered with regard to the level of understanding implied. Parallel to the interviews the subjects had also filled out a questionnaire assessing general and specific attitudes towards disease and treatment (the Health Belief Model, HBM). The results reveal a superior understanding among parents in the experimental group. The experimental group had also changed attitudes towards disease and treatment in a direction that would favour compliance, more than could be observed in the control group. The outcome is discussed in terms of the role of understanding for a compliant behaviour. It is also emphasised that health care personnel would profit from being aware of the nature of common misconceptions of diseases and their treatment, in the sense that they would be better prepared for entering instructional dialogues with patients or, as in this case, other persons responsible for the management of prescriptions provided.

Adult↗
PubMed1998

Treatment of strabismus and nystagmus with botulinum toxin type A. An evaluation of effects and complications.

PURPOSE: Injection of botulinum toxin type A into eye muscles leads to a temporary paralysis and the effects have been evaluated in strabismus or nystagmus. METHOD: A total of 112 patients with different types of concomitant and paralytic strabismus and acquired nystagmus were treated with botulinum toxin, according to well-established indications. RESULTS: The lasting effects of the injections on strabismic angle were largest in esotropia, consecutive exotropia and abducens palsy, and amounted to, on an average, 12 prism diopters or 6 degrees. The larger the strabismus the better was the effect. Repeated injections reduced the angle further. In complex nystagmus forms retrobulbar injections could be used. The side effects were mostly due to spread of botulinum toxin to the levator, producing ptosis (8%), or the inferior rectus muscle, causing vertical strabismus (10%). On an average 42% of the patients were later operated for strabismus and nystagmus. CONCLUSION: Injection of botulinum toxin A into eye muscles is a valuable adjunct to surgery in the treatment of strabismus and nystagmus.

Adult↗
PubMed1998

Effects of neck muscle proprioceptive activation on the dynamics of monocularly driven horizontal vergence movements.

PURPOSE: The dynamics of accommodative vergence responses were studied to accommodative stimuli combined with the activation of neck muscle proprioception. METHODS: Accommodative stimulation was done with a LED bar. The stimuli were presented monocularly in a stepwise and a sinusoidal mode to either the dominant or the non-dominant eye with the other eye covered. The neck proprioceptors were activated by vibration on the neck muscles which turn the head horizontally. Eye movements were recorded with an infra-red reflection system in both eyes. RESULTS: Vibration of the neck muscles shortened the time constant of the accommodative vergence movement in the covered eye to square wave stimulation when the non-dominant eye was fixating the targets. The gain factor to sine wave stimulation was higher when the non-dominant eye was fixating. CONCLUSION: Extraretinal signals from neck proprioception influenced not only the static eye position, but also the dynamics of monocularly driven accommodative vergence movements, when the non-dominant eye was the viewing eye.

Accommodation, Ocular↗
PubMed1998

Screening for visual and ocular disorders in children, evaluation of the system in Sweden.

The aim of this study was to evaluate the visual screening system in Sweden. We have made a retrospective investigation of the results of screening for ocular disease and visual impairment of all children born in 1982 in three Swedish communities. The records from screening examinations from 0 to 10 y and from diagnostic follow-up at the departments of ophthalmology that the children were referred to were inspected. The data were used to evaluate the efficiency of the Swedish visual screening system. The study included 3126 children. The attendance rate at the 4-y examination was better than 99%. The sensitivity of the 4- and 5.5-y screening examinations was on the average 92% and the specificity was 97%. The average number of false negative cases at 4 y was 5.6 in 1000 (0.56%). With this screening and subsequent diagnosis and treatment, the prevalence of amblyopia at different levels of visual acuity at the age of 10 y was: 0.06% with visual acuity < or = 0.1, 0.9% with visual acuity < or = 0.5 and 1.7% with visual acuity < or = 0.7. In spite of largely unchanged pressure of amblyogenic factors in the population, the prevalence of deep and moderate amblyopia has been markedly reduced by screening and early treatment.

Amblyopia↗
PubMed1997

Reduced activity in the extrastriate visual cortex of individuals with strabismic amblyopia.

In order to examine the relationship between reduced visual acuity in human strabismic amblyopia and the cortical activation pattern, we studied, by use of positron emission tomography (PET) and the H2(15)O bolus technique, changes in the regional cerebral blood flow (rCBF) induced by monocular visual stimulation of 8 individuals with this disorder. Individual amblyopic thresholds for monocular detection of the checkerboard pattern were employed as stimuli for both eyes during PET scans. Statistical analysis of subtracted images showed significant increases in rCBF (P < 0.05) by the stimulation of the sound eye localized bilaterally to Brodmann's areas (BAs) 17-19. The cortical response evoked by the amblyopic eye was significantly reduced (P < 0.05) in the ipsilateral BAs 18, 19. These results suggest that the reduction in contrast sensitivity (pattern vision) in amblyopia is coupled with deactivation in identifiable regions of occipital visual areas, including ipsilateral BAs 18,19.

Adult↗
PubMed1997

Effects of eye muscle proprioceptive activation on eye position in normal and exotropic subjects.

BACKGROUND: Activation of muscle spindles by vibration of eye muscles is known to induce illusory movements of fixated targets, but the effects on eye position have not been studied, either in normal subjects or in patients with exotropia. METHODS: Eye position was recorded from the covered, non-dominant eye with an infrared system in 11 subjects with normal eyes and binocular vision and in 10 patients with exotropia and abnormal binocular function. Activation of eye muscle spindles was done by vibration at 70 Hz of the inferior and lateral rectus muscles of the dominant eye, fixating a light-emitting diode in subdued light. RESULTS: Vibratory activation of proprioceptors in the inferior rectus muscle induced an eye movement mainly directed upward in both normal and exotropic subjects. The magnitude of the movement was on average 2.7 deg in normals and 2.4 deg in exotropes. Lateral rectus vibration induced a movement that was mainly temporally directed (abduction) of an average 2.1 deg in normal subjects, but a nasally directed (adduction) movement of 4.2 deg in exotropic subjects. In normal subjects the eye movement is of the same direction as the earlier reported visual illusory movements induced by the same type of proprioceptive activation, but in exotropic subjects the movements is in the opposite direction. CONCLUSIONS: Proprioceptive activation of eye muscles affects eye position, and the results also indicate that signals from eye muscles are processed differently in normals and strabismics, probably depending on the level of binocular function.

Adult↗
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↗
PubMed1996

Properties of eye movements induced by activation of neck muscle proprioceptors.

BACKGROUND: We have previously reported that neck muscle vibration can induce visual illusory movements and eye movements under subdued ambient illumination in human subjects with the head and body fixed. The subjects viewed a fixation light with one eye and the other eye was covered. The eye movements were recorded with an infrared system mounted in goggles attached to the head of the subject. METHODS: In order to further examine the properties of these cervico-ocular reactions and reveal any artefacts in the eye movement recordings, we have studied (1) the effect of increasing the ambient light, which made visual illusory movements disappear, (2) the timing between the illusory movement and the eye movement in subdued light, (3) the effect of viewing the target through a pin-hole, which would reveal artefacts due to head movement, and (4) the effect of mounting the eye movement recording system on the head support, which would allow recording to the absolute eye position change. RESULTS: The results of these experiments showed no significant difference from those that were reported previously. Eye movements of about the same amplitude were induced in both eyes under all conditions, and there was no time difference in the occurrence of visual illusory movements and eye movements. CONCLUSION: The results of this study confirm that neck muscle vibration can induce eye position changes. This seems to confirm that the proprioceptive messages originating in the neck muscles are processed together with visual information of eye position in determining gaze direction.

Adult↗
PubMed1996

Results of treatment of amblyopia with a screening program for early detection.

The Swedish program for early intervention in children with visual dysfunction, was evaluated with respect to the results of treatment of amblyopia. One hundred and seventy-two amblyopic children were examined before and at 6, 12 and 18 months after the beginning of treatment. The mean visual acuity of the amblyopic eye was 0.76 and the mean ratio of visual acuity between the two eyes was 0.75 or better in all types of amblyopia. Children with strabismic amblyopia showed slightly poorer treatment results than the other types, in spite of the fact that their amblyopia had been detected earlier than the others. The results attest to the importance of careful screening of monocular visual acuity in all children, which in Sweden occurs at 4 years of age. This provides a good basis for detection and treatment of amblyopia. Only one child in the group had a visual acuity at 0.2 and may therefore be at risk for visual handicap if the better eye should be lost later in life.

Amblyopia↗
PubMed1995

Dynamics of accommodative vergence movements controlled by the dominant and non-dominant eye.

Accommodative vergence responses to accommodative stimuli presented at three different amplitudes in a stepwise and a sinusoidal mode to either the dominant or the non-dominant eye were studied. The motor control loop was opened by one eye viewing the target and the other eye covered. Each eye was stimulated monocularly and eye movements were recorded with an infra-red reflection system. Latency and time constant of the accommodative vergence response to step stimulation or the phase of the vergence response to sine wave stimulation, did not vary systematically with stimulus amplitude or eye stimulated. However, the gain of the accommodative vergence movements was highest in the non-dominant eye at a particular stimulus amplitude. This suggested that accommodative vergence angles can vary depending on which eye is leading and driving the accommodative vergence system in a specific fixation situation.

Accommodation, Ocular↗
PubMed1995

Eye movements in normal subjects induced by vibratory activation of neck muscle proprioceptors.

Versional eye movements, induced by neck muscle vibration at 70 Hz in 8 normal subjects, were recorded with infrared reflection technique in each eye separately with one eye fixating a target and the other covered. The direction of eye movements was horizontal when the sternocleidomastoid muscle on one side of the neck and the splenius on the other side were activated, and downward when both splenii muscles were vibrated. The direction was the same as that of the illusory movements of the target also induced by the vibration. These findings would imply that the proprioceptive messages originating in the neck muscles are processed together with visual information of eye position in determining gaze direction.

Eye Movements↗
PubMed1995

Screening for ocular dysfunction in children: approaching a common program.

According to the general principles of screening, detection of visual impairment in children is worthwhile, since the condition is a serious health problem, reliable diagnostic tests are available and effective treatment is possible in most instances of ocular and visual dysfunction. However, an evaluation of the screening procedures has not been properly done and the cost-benefit of screening has not been studied. The aim of the present study is to perform a systematic analysis of the screening programs for detection of visual dysfunction. In the screening two parts can be separated, one that concerns the more serious ocular and visual conditions which have to be discovered by general survey methods very early in life, and one that involves detection of less serious conditions, mainly amblyopia, which can be diagnosed by testing for monocular reduction of visual acuity at about 3-4 years of age. The performance characteristics of the screening programs used in Sweden and Canada were evaluated and found to be very favourable. Based on the analysis and the evaluation, recommendations are made on programs for vision screening in children that could be applied more widely. The program could involve all or parts of the following: 1) A careful inspection of the eyes in the neonatal period and preferably also examination of the red reflex with the ophthalmoscope. 2) Children at high risk for ocular and visual disorder, i.e. those born prematurely before 32 weeks of age, or with genetic disease, hearing deficit and/or neurological and mental disorder, should be examined at the proper age by an ophthalmologist. 3) All staff at pediatric departments and child health care centers should be familiar with the visual development of the normal baby and should be alerted to the various symptoms and signs which first warn parents that there may be a visual defect. An inspection of the eyes to detect squint should be part of all pediatric examinations. 4) A screening test of monocular visual acuity in 4 year-old children can be reliably performed by non-ophthalmic personnel after proper training. The screening test should be repeated by school nurses during the first grade of school, and at regular intervals during the school years. 5) The children that screen positively should be seen by ophthalmologists, and in some cases by orthoptists, without undue delay for diagnosis and treatment.

Child↗
PubMed1994

Vertical saccadic velocity and force development in superior oblique palsy.

Vertical saccadic movements recorded with electrooculography (EOG) and force development measured by means of a contact lens-strain gauge technique were investigated in 13 patients with a clinical diagnosis of unilateral superior oblique palsy (SOP) and 10 normal subjects. Upward and downward movements from the horizontal level to 5, 10 and 20 deg of deviation with monocular fixation were made in the 20 deg abduction and adduction fields of gaze. Peak velocity (Vp) and the ratio of downward over upward movement (VpD/U) of the paretic eye (PE) and the sound eye (SE) of the patients were compared with the values of the covered, non-fixating eye (CE) and the fixating eye (FE) of the normals respectively. Peak tension (Fp), steady-state tension (Fs) and the ratios of downward over upward movement (Fp D/U, Fs D/U) of PE were compared with the values of CE. Comparisons were done (a) between normals and the whole group of 13 patients, (b) between normals and two subgroups of five patients with acquired and five with congenital SOP, (c) and between the subgroups. Mean Vp for the whole group of SOP showed reduced values from normals in many directions of gaze. However, mean Fp and ratios of Vp D/U and Fp D/U were not different in SOP and normals, and such measures could not be used to differentiate SOP from normal eye muscles in the sample of patients studied. Clear differences were seen in the comparisons between normals and the subtypes of SOP. Vp was significantly reduced in PE for the downward movements in the adduction field of gaze, more marked in acquired than in congenital SOP. Slowing of upward saccades was also found in the congenital group. This may be due to adaptational changes in concomitization of congenital paretic strabismus. Fp for downward saccade, and Vp D/U and Fp D/U were lower for PE in the acquired than in congenital SOP and normals in the lower adduction field of gaze, where the superior oblique has its main action. A linear relation was found between Vp and Fp of downward saccades for the congenital group in the lower adduction of gaze, but the slope was steeper than in normals. However, in acquired SOP the relationship was non-linear, which indicates a force production different from that of a normal muscle. Vertical saccadic velocity and force development measured at 20 deg adduction could reveal weakness of the superior oblique muscle and the imbalance of agonist-antagonist actions in the paretic eye.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1994

Eye proprioception and visual localization in humans: influence of ocular dominance and visual context.

It has been previously established that the application of low amplitude mechanical vibrations to the inferior rectus muscle of human subjects results in an illusory upward movement of a luminous spot fixated in total darkness, and in a corresponding overshooting of the target when the subject is asked to point to this spot. In the first experiment described here, we compared the effects of applying vibrations to each eye separately and to both eyes simultaneously, under monocular and binocular viewing conditions, in left- and right-eyed subjects. The results confirmed that proprioceptive signals arising from both eyes are involved in egocentric visual localization. A proprioceptive dominance was observed however since vibration of the dominant eye gave rise to larger pointing displacements. In addition, whichever eye was stimulated, the pointing shift induced by vibrating a covered eye was of smaller amplitude than that which occurred when vibrations were applied to the viewing eye. The second experiment showed that both the vibration induced illusions and the pointing shifts disappeared in a structured visual context, which suggests that the processes involved when the target is viewed in darkness might differ from those occurring in structured surroundings.

Eye Movements↗