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Biomedical subjects

G Lennerstrand

Publications and source records attributed to G Lennerstrand.

16 recordsLinked to original sources
PubMed1992

Regressed retinopathy of prematurity: the relationship between clinical risk factors of the newborn period and regressed retinopathy of prematurity severity in a preterm born population of Stockholm county 1976-81.

In a retrospective study, clinical risk factors of the neonatal period were correlated with the severity of regressed retinopathy of prematurity (ROP) in a population of preterm infants (bw less than 1500 g and or gestational age less than 33 weeks). At the age of 5-11 years 134 out of 528 preterm born infants (25.4%) were found to be under ophthalmic care. Reliable information on eye fundus status could be obtained in 105 of them. Regressed ROP was found in 61, the moderate form in 48 (9.1%) and the severe form in 13 (2.5%) patients. Twelve patients (2.3%) had visual acuity of less than 0.3 on the worst eye and two (0.4%) of these patients were blind from ROP. Twenty-four clinical factors of the newborn period were correlated with the severity of regressed ROP. The results suggest that long oxygen exposure in combination with other factors interfering with retinal vasotonus are associated with the degree of the disease developed.

Birth Weight↗
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↗
PubMed1979

Contractile properties of extraocular muscle in cats reared with monocular lid closure and artificial squint.

Kittens were raised with amblyopia by monocular lid suture or esotropia by transection of extraocular muscles in one eye at the age of 2--3 weeks. Isometric contractions in the inferior oblique muscle were recorded at 20 weeks or at adult age, and the results were compared with those of similarly aged cats with normal visual development. The speed of contraction and the fatigue resistance was reduced in the lid sutured animals. In the esotropic cats studied, fatigue resistance was also reduced but the speed of contraction did not change much. It is suggested that the postnatal eye muscle development can be modified by manipulation of the visual input at an early age. Presumably the impaired binocular vision in the lid sutured and esotropic cats reduced the demand for fusion vergences, and this might be reflected in the changes of eye muscle properties. In monocularly lid sutured cats, eye muscle changes were the same on both sides, suggesting that amblyopia per se did not affect eye muscle development.

Age Factors↗
PubMed1979

Age variations in normal human contrast sensitivity.

The visual contrast sensitivity (the reciprocal of contrast threshold) was studied as a function of age. Psychophysical measurements of binocular and monocular contrast thresholds were made for 33 normal observers at spatial frequencies within the range 0.5 to 40 cycles/degree. The observers were divided into three different age groups: young, middle-aged, and old subjects with the age ranges 6--10 years, 20--40 years, and 60--70 years, respectively. All observers had healthy eyes, normal vision, and Snellen visual acuity of 1.0 or better in both eyes. In all groups, contrast sensitivity for binocular and monocular viewing peaked at a spatial frequency around 3--5 cycles/degree and showed the typical attenuation at low and high spatial frequencies. The binocular contrast sensitivity was higher than the monocular. There was no significant difference between young and middle-aged subjects with regard to contrast sensitivity. Subjects aged 60 years or more showed significantly lower contrast sensitivity than younger subjects for most spatial frequencies above 4 cycles/degree. We may thus conclude that both the binocular and monocular contrast sensitivity seemed independent of age within the range of 6 to 40 years. For higher ages studied (above 60 years), there was a loss of sensitivity in the middle and high frequency regions.

Adolescent↗
PubMed1979

Contractile properties of extraocular muscle in Siamese cat.

Siamese cats are albinos with poor visual resolution and severely impaired binocular vision. Eey muscle phyiology was studied in Siamese cats as a part of a more extensive project on eye muscle properties in cats with deficient binocular vision. Isometric contractions of the inferior oblique muscle were recorded in response to single and repetitive muscle nerve stimulation. Speed of contraction, measured as twitch contraction time, fusion frequency and rate of tetanic tension rise, was lower in Siamese than in normal cats. Eye muscles of Siamese cats fatiqued more easily to continuous activation than normal cat eye mucle. These functional changes have also been found in cats with binocular defects from monocular lid suture, but were much more marked in Siamese cats. It is suggested that the eye muscle changes represent muscular adaptations to genetically caused impairments of binocular vision and visual resolution in Siamese cats.

Albinism↗
PubMed1978

The postnatal development of the inferior oblique muscle of the cat. I. Isometric twitch and tetanic properties.

The postnatal development of the inferior oblique muscle in the cat has been studied with physiological and histochemical techniques. This paper describes the changes with age in isometric twitch and tetanic response characteristics. The twitch amplitude increased and the twitch contraction time (ct) and half-relaxation time (hrt) decreased almost linearly from birth to adulthood. The relation between the strength of nerve stimulation and twitch ct and hrt changed during development with a threshold slow response appearing at 10 weeks. Twitch responses in cats 6 weeks of age or older were of longer duration than in younger cats, in spite of the longer ct and hrt in young cats. Fusion frequency of the tetanic response reached a constant level in muscles 6 weeks or older. The maximum rate of tension rise remained the same from birth to 6 weeks of age and later increased markedly up to 20 weeks of age. The contracture induced by succinylcholine was the same in muscles of all ages. These data were related to previous findings on the postnatal development of fast and slow muscles and motor units in the hindlimb of the cat. A differentiation of the development of fast and slow eye muscle fibers is suggested. Slow fibres seemed to have completed their maturation at about ten weeks of age, while the development of fast fibre properties continued, probably up to the adult stage.

Age Factors↗
PubMed1978

The postnatal development of the inferior oblique muscle of the cat. II. Effects of repetitive stimulation on isometric tension responses.

The changes with postnatal age in post-tetanic potentiation (PTP) and fatigue of the inferior oblique muscle have been studied in the cat. PTP of the twitch amplitude increased steadily with age up to 20 weeks after birth. Twitch contraction time (ct) and half relaxation time (hrt) was not significantly changed. The potentiation of the tetanic response also became more prominent with age. The young muscles (10 weeks and below) were slightly more susceptible to fatigue than older muscles, but recovery was rapid in muscles of all ages. Intensive stimulation induced post-tetanic depression of twitch responses in muscles older than 1 week, but none in the muscles of new-born cats. Ct and hrt were greatly prolonged in muscles above six weeks of age. In these muscles, but never in the very youngest, repetitive firing could be observed in response to post-tetanic single nerve stimulation. The results are compared with those obtained in similar experiments on hind-limb muscles by other workers. They further support the idea, raised in a previous paper, that slow eye muscle fibres develop quicker and reach maturity earlier than fast fibres.

Age Factors↗
PubMed1978

Binocular interaction studied with visual evoked responses (VER) in humans with normal or impaired binocular vision.

In an attempt to evaluate binocular functions in an objective manner, visual evoked responses (VER) were recorded in sixteen subjects, six with normal binocular functions and ten with various degrees of squint and binocular impairment. The two eyes were stimulated monocularly or dioptically with a polaroid checker board pattern viewed through rotating polaroid discs. The rate of pattern reversal was 7 per sec for one eye and 10 per sec for the other, allowing stimulus locked responses to be recorded from each eye individually, even during dioptic viewing. In normal subjects the VER of each eye to binocular stimulation were reduced to half or less of the monocular value. The reduction was much smaller in humans with impaired binocular vision, at least for the dominant eye. In stereoblind subjects the response of the dominant eye was the same for monocular and binocular stimulation. The VER changes might reflect binocular interaction in visual cortex neurons, which probably are binocular in normal subjects but driven only from one eye in stereoblind subjects.

Adolescent↗
PubMed1978

Some observations on visual evoked responses (VER) to dichoptic stimulation.

The possibility that the interocular depression of VER seen with dioptic stimulation, might reflect alternate suppression or binocular rivalry, unnoticed by the test subjects, was investigated in VER experiments using dichoptic stimulation with patterns of dissimilar form. Red and blue grating and checker board patterns were produced on a colour TV screen. Appropriate filtering allowed the two eyes to be stimulated separately. Provided the patterns were dissimilar enough to produce binocular rivalry, no interocular depression was noticed in the VER. The interocular depression became larger as the patterns were made similar in size and reached a maximum for patterns identical in shape. Thus the interocular depression of the VERs reported for dioptic stimulation did not seeem to be related to binocular rivalry. The results also give electrophysiological support to the notion of spartial frequency and orientation selective channels in the human visual system.

Adult↗
PubMed1978

Mechanical properties of succinylcholine activated muscle fibers in the inferior oblique muscle of the cat.

To determine the mechanical properties of the multi-innervated fibres in inferior oblique muscle of the cat, these fibers were selectively activated by means of an intravenous injection of succinylcholine chloride (Sch). For small sinusoidal length changes (+/- 1 mm) of low frequency, tension in the Sch activated muscle exhibited a component that was sensitive to the direction of stretch but was independent of the velocity. At higher frequencies of length change (16 Hz) a form of negative friction was observed. Negative friction had not been previously noted in mammalian muscles, although a similar friction was observed both in the muscles of insects and amphibians. These properties were expressed in the form of a simple mechanical model.

Animals↗
PubMed1977

Morphology of motor units in cat extraocular nodule.

Muscle fibers from single motor units in cat inferior oblique were marked iontophoretically with procion red injected through an intracellular pipette. The fibers were isolated by dissection and characterized by electron microscopy. A fiber in a slow motor unit with non-conducted electrical responses showed slow fiber morphology of the amphibia-type. Fast, twitch motor units contained fibers with twitch fiber morphology. Thus, a good correlation between muscle fiber structure and function was obtained in these eye motor units, examined with both physiological and morphological techniques.

Animals↗
PubMed1977

Contractile and histochemical properties of the inferior oblique muscle in the rat and in the cat.

Mechanical and histochemical properties of inferior oblique muscles(IO) were compared in adult albino rat and pigmented cat. The twitch contraction times and the fusion frequencies were about the same in both species indicating similar contractile properties of the fast contracting fibers. Rat IO seemed to contain fewer slowly contracting fibers than cat IO; half-decay time of the twitch was shorter in rat than in cat muscles and fusion started at higher stimulus frequencies. Fatique resistance was lower in rat than in rat than in cat. Post-tetanic potentiation occurred in the cat but not in the rat IO. Almost all fibers of rat IO were rich in myofibrillar ATPase. In cat IO most fibers showed high myofibrillar ATPase activity, but some fibers in the global layer had moderate to small amounts of this enzyme. This correlates well with the physiological differencies between cat and rat IO.

Adenosine Triphosphatases↗
PubMed1977

Extraocular muscle fibers: ultrastructural identification of iontophoretically labeled fibers contracting in response to succinylcholine.

Cat extraocular muscle fibers (from the superior rectus or inferior oblique) were penetrated in vivo with Procion red-filled glass microelectrodes. When stable penetrations were obtained, succinylcholine (Sch), 8 to 20 microng, was injected into the femoral vein. In some fibers, a depolarization-repolarization response was obtained with the same time course (2 min.) as the total muscle contraction. The depolarizing fibers were labeled iontophoretically. The ultrastructural characteristics of five depolarizing fibers and three control (nondepolarizing) fibers were then studied. The fibers that did not depolarize to Sch had the characteristics of singly innervated cells, whereas those sensitive to Sch had morphological characteristics of multi-innervated fibers.

Animals↗
PubMed1976

Motor unit responses in the lateral rectus muscle of the cat: intracellular current injection of abducens nucleus neurons.

Single motor units of the cat's lateral rectus muscle were activated with short intracellular current pulses delivered through an intracellular micropipette penetrating a single motoneuron, and the mechanical responses in the muscle were recorded. Lateral rectus unit responses fell within the same range as those obtained earlier with extracellular stimulation of inferior oblique units, confirming that in the latter case single and not multiple motor units had been studied. It was also found that both fast and slow contracting muscle units were connected to fast conducting, large size motoneurons. The organization of motor unit recruitment in eye movements would thus seem different from the recruitment pattern in limb muscles. Intracellular stimulation of abducens nucleus "interneurons" did not initiate contractions at the ipsilateral lateral rectus muscle. These "interneuron", therefore did not appear to have excitatory inputs to the abducens motoneurons, but may be involved in relaying information to the other extraocular muscle nuclei or to other brain centers.

Abducens Nerve↗
PubMed1975

Absence of polyneuronal innervation in cat extraocular muscles.

1. Polyneuronal innervation is known to occur in several types of vertebrate muscle, including mammalian muscle spindle (Gray, 1957). Previous work had led to the suggestion that the multiply innervated cat extraocular muscles were similarly polyneuronally innervated. 2. The presence of polyneuronal innervation in fibres that show propagated conduction was explored in the two muscles innervated by the abducens nerve: the lateral rectus (which contains multiply innervated fibres) and the retractor bulbus (which does not). 3. Under conditions of twitch and tetanic stimulation, the sum of individual tensions from the two nerve branches was compared with the tension elicited from the whole nerve. An analysis of variance indicated that the lateral rectus and the retractor bulbus did not differ significantly in terms of tension excess. The twitch condition yielded a small but statistically significant (P smaller than 0-01) amount of tension excess, whereas the tetanic condition did not. 4. Twitches elicited by stimulation of one branch of the abducens nerve showed slight potentiation when preceded by a tetanic stimulation to the other nerve branch. This effect could be ready differentiated from the post-tetanic potentiation elicited by applying both twitch and tetanic stimuli to the whole nerve. 5. Muscle fatigue produced by intensive stimulation of one nerve branch did not decrease the amplitude of the tetanic contraction elicited by stimulation of the other branch. In fact, instead of crossed fatigue, a small but significant (P smaller than 0-05) potentiation was observed. 6. Analysis of the results of the three tests led to the conclusion that polyneuronal innervation could not be demonstrated in cat extraocular muslce fibers that showed propagated conduction. Thus, the end-to-end muscle fibre junctions (Floyd, 1970) apparently do not transmit conducted impulses.

Abducens Nerve↗