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Biomedical subjects

G Lennerstrand

Publications and source records attributed to G Lennerstrand.

At least 55 records · Page 3Linked to original sources
PubMed1989

Contrast sensitivity in macular degeneration and the relation to subjective visual impairment.

Contrast sensitivity was determined with electronic and computer equipment (Cadwell CTS 5000) and with optotype test charts (LH low contrast test) in 31 patients, aged 47-89, with macular degeneration, mostly of the age-related type. Values of maximal sensitivity and mean sensitivity in different spatial frequency bands were estimated. Visual acuity at distance and the magnification factor needed for reading were also determined. Each of these measures were correlated with a score obtained in a subjective evaluation of difficulties with visual discrimination and orientation. It was found that poor visual discrimination and orientation was better correlated with low contrast sensitivity than with low visual acuity. The outcome of the LH-test was a better predictor of orientation problems than the electronic test.

Aged↗
PubMed1989

Prevalence of refractive errors and ocular motility disorders in 5- to 10-year-old Swedish children born prematurely or at full-term.

Knowledge of the occurrence of visual and ocular problems in children is important when eye health care systems are designed. We have studied the prevalence of ocular changes in all children born prematurely during 1976-1981 in Stockholm county and compared the findings with those obtained in a random sample of full-term children from the same period and area.

Child↗
PubMed1988

Central motor control in concomitant strabismus.

Basic research in the field of oculomotor physiology has advanced rapidly during the last decade. The new knowledge has been largely incorporated into the research and the clinical practice of neurology and neuroophthalmology [14, 16], but the influence on strabismus research has been rather limited [15]. This presentation will point out the elements of basic research that are believed important for our understanding of concomitant strabismus. The description will concentrate on the role of different central motor factors, mainly brainstem mechanisms, in the genesis and development of infantile esotropia or convergent strabismus, i.e. strabismus with an early onset in life [8]. Strabismus of late onset seems less enigmatic, since it probably originates from abnormalities of the vergence system, particularly its coupling with accommodation.

Accommodation, Ocular↗
PubMed1987

Motoneuronal innervation and mechanical properties of extraocular muscles in the catfish, (Ictalurus punctatus).

Mechanical characteristics and electrical activity were studied in the extraocular muscles of the catfish, Ictalurus punctatus. The contractile properties were determined by stimulation of the individual muscle nerve branches to lateral and medial rectii and the superior and inferior oblique muscles. The speed of contraction was higher than in most other fish muscle, with a twitch contraction time of about 12 ms and a tetanus fusion frequency of 150-170 Hz in all four eye muscles. The fatigue resistance was also high. These properties were the same in fully innervated and partially innervated muscle, largely irrespective of what part of the muscle that was activated. Although different fibre types are known to exist in fish extraocular muscle, it was not possible to obtain functional separation of the mechanical force profile even in the lateral rectus with two distinct motoneuronal innervations. We suggest that polyneuronal innervation of the muscle fibres produces the mechanical responses. Since EMG activity during spontaneous eye movements was similar in the global and the orbital parts of the muscle, all types of fibres in fish extraocular muscle are probably recruited for all types of eye movements.

Animals↗
PubMed1986

Effects of surgery on the dominant eye in exodeviations.

It has been suggested that operating the dominant eye is a more effective way of treatment for exodeviations than the conventional non-dominant eye surgery. We have tested this idea in groups of children and adults with intermittent and constant exotropia. In a first group of 30 patients where the non-dominant eye was operated on, we found that our initial technique resulted in an undercorrection averaging 11 prism diopters. Modification of the technique, by increasing the relative amount of surgery on the non-dominant eye in another group of 41 patients, improved the results significantly in adult patients, but not in children. Operations on the dominant eye in a third group of 26 patients were no more successful than non-dominant eye surgery with the initial technique. Thus, we did not obtain better results in operations on the dominant eye with our technique than we did with surgery on the non-dominant eye.

Adolescent↗
PubMed1985

Contractile properties and histochemistry of extraocular muscle in the pigmented and the albino guinea pig.

The inferior oblique muscles of pigmented and albino guinea pigs were compared with respect to contractile and histochemical properties. No differences were found between the 2 kinds of animal in twitch and tetanic response or in fatigue properties. They also had the same fiber composition and fiber and capillary densities of their inferior obliques. These findings indicate that differences in eye muscle previously demonstrated and Siamese (albino) cats are related to the state of binocular vision and not to genetic variations between pigmented and albino animals.

Albinism↗
PubMed1985

Binocular interaction in the VEP to grating stimulation. II. Spatial frequency effects.

The size specificity of the binocular interaction in the VEP was investigated. VEPs elicited by sine wave gratings were recorded on 3 subjects, with the exception of one experiment where 6 subjects were tested. The recording technique made it possible to obtain responses from each eye, even during binocular stimulation. The VEP amplitude for each eye during monocular stimulation was compared with the response of the same eye during binocular stimulation. A low binocular/monocular ratio indicated a high binocular interaction. When each eye was stimulated by the same spatial frequency, the binocular interaction was highest in the spatial frequency band of 2-4 c/d. When each eye was stimulated by a different spatial frequency, the binocular interaction decreased as the frequencies were made progressively more unequal. The bandwidth at half amplitude was about 1 octave around the center frequency.

Evoked Potentials, Visual↗
PubMed1984

Postural sway and gait of children with convergent strabismus.

Postural sway and gait of 35 children with convergent strabismus were tested and compared with those of a control group. They were found to have a short stride-length and single-limb support time in walking, particularly at slow speeds. The girls had a large postural sway, but not the boys. The results suggest a common visuomotor disturbance of eye and limb motor-control.

Child↗
PubMed1984

Glare from outdoor high mast lighting: effects on visual acuity and contrast sensitivity in comparative studies of different floodlighting systems.

Glare effects on visual acuity and contrast sensitivity were studied at outdoor timber terminal work with conventional far-reaching floodlighting and with a new type of oblique floodlighting with an asymmetrical light distribution. The binocular work visual acuity of 19 volunteers was measured at 40, 55 and 80 per cent contrast and the contrast sensitivity of 14 volunteers at spatial frequencies of 0.5, 1, 2, 4, 8 and 16 cycles/degree. With the light source 15 degrees from the centre of the visual fields the visual acuity as well as the contrast sensitivity was consistently lower with the conventional type than the new type of floodlight . The results thus indicate that not only the vision of details is impaired by glare but also the contrast perception of sparse patterns. In standardized rating scales the timber terminal workers scored the difference in glare between the two floodlight systems as "great"--"very great".

Adult↗
PubMed1983

Visual testing with 'preferential looking' in mentally retarded children.

In 21 out of 26 children and young adults with mental retardation visual acuity could be successfully examined with operant preferential looking. There was a good correlation in this group of patients between ocular abnormalities demonstrated in an ophthalmological examination and the visual acuity results.

Adolescent↗
PubMed1983

Central and peripheral normal contrast sensitivity for static and dynamic sinusoidal gratings.

Contrast sensitivity for moving and stationary sine grating patterns was determined in central and peripheral parts of the visual field. The method was primarily developed as a possible screening procedure for visual defects in glaucoma. Contrast sensitivity to moving patterns seemed maximal both in central and in 10 degrees of eccentric viewing for square wave reversals of temporal frequencies 0.5-5 Hz. We selected 2Hz for the clinical procedure. Further, we have determined normal central and peripheral contrast sensitivity in 10 subjects 61-71 years-old, to serve as a basis for the glaucoma studies. We used this age group since glaucoma mainly affects elderly people. We confirmed that contrast sensitivity was higher for dynamic than for static presentation of gratings of low spatial frequencies (below 1 c/d) both centrally and peripherally. For patterns of medium or high spatial frequencies, dynamic and static stimuli were equally detectable. The absolute level of contrast sensitivity was higher centrally than peripherally in the interval 0.3-4 c/d. The lower visual hemifield exhibited greater sensitivity, for both static and dynamic gratings, than the upper one.

Adult↗
PubMed1983

Effects of amblyopia therapy on contrast sensitivity as reflected in the visuogram.

A quantitative evaluation of the Cambridge amblyopia treatment on contrast sensitivity was performed for 2 groups, one comprising 11 children with strabismic amblyopia (S) and another of 10 children with combined strabismic and anisometropic amblyopia (S & A). Contrast sensitivity deficits were expressed in dB CSL (Contrast Seeing Level) in relation to normal sensitivity of the same age group and represented in the form of visuograms. Mean contrast sensitivity losses in dB CSL were estimated within the low, medium and high spatial frequency ranges, as well as over the total frequency band. On an average S & A amblyopia was found to affect contrast sensitivity of all spatial frequencies, while S amblyopia affected mainly the higher frequency band, but to a smaller extent. After therapy average contrast sensitivity improved for both S and S & A groups, and reached the same, subnormal levels. The relation between highest resolvable spatial frequency (according to our method) and Snellen acuity was different for the 2 amblyopia groups. No correlation was found between improvements in contrast sensitivity and Snellen acuity, which is why both parameters should be estimated.

Adolescent↗
PubMed1983

Visual recovery after treatment for pituitary adenoma.

Visual functions were studied pre- and post-operatively in 128 patients treated for pituitary adenoma with operations by intracranial (89 patients) or transsphenoidal approach (39 patients). Most patients were given post-operative irradiation. Follow-up was 6 months or more. Visual field defects were seen pre-operatively in 85% of the patients operated intracranially and in 36% of the patients operated transsphenoidally. Visual acuity was reduced, at least in one eye, in 64% of the patients in the former group and in 26% of the latter group. Additional diagnostic information was obtained from recordings of visually evoked cortical potentials. After intracranial operations visual acuity was normalized or improved in 65% and visual fields in 82% of the patients with pre-operative visual defects. After transsphenoidal operations the corresponding values were 56% and 92%. A detailed analysis of the visual acuity showed that eyes with optic atrophy pre-operatively improved to a very limited extent. Other pre-operative ophthalmological disturbances were of much less prognostic significance. Improvement of vision was often gradual and could continue for more than a year after treatment. Even if visual acuity and visual fields had been completely restored, visually evoked cortical potentials could remain impaired, indicating that evoked potentials might be a very sensitive test for the evaluation of visual recovery.

Adenoma, Acidophil↗
PubMed1983

Clinical assessment of visual functions in infants and young children.

We report our experience with 2 new methods of assessing visual functions in children: grating acuity determination by means of preferential looking technique and contrast sensitivity measurements. Acuity determinations with preferential looking proved useful for evaluation of the effects of amblyopia treatment in young children (0-3 years) with esotropia and for monitoring visual development in children operated early for congenital cataract. We have also used these methods successfully for diagnostic acuity determinations in very young children or in older but mentally retarded children with suspected visual impairment. In 4-year-old children contrast thresholds were determined for sine wave gratings of different spatial frequencies displayed on an oscilloscope screen. The results were less reproducible than those obtained earlier in somewhat older children, and did not correlate as well as the results of other visual tests as in the older children.

Amblyopia↗
PubMed1983

Visual acuity testing with preferential looking in mental retardation.

Twenty-six mentally retarded children and young adults, most of them with severe neurological deficits, in the age range 5-24 years, were examined ophthalmologically, and their binocular visual acuities were tested with 'operant preferential looking' according to the technique of Mayer & Dobson (1980). Five of the subjects did not co-operate sufficiently for visual testing, although 3 had no ocular abnormalities that would affect binocular acuity. The visual acuity levels determined with 'preferential looking' ranged from 1.29 to 0.03 in the 21 subjects that could be tested. Two children with high myopia showed substantial increase in acuity with appropriate correction (from 0.1 to 1.06 in one child and from 0.05 to 0.31 in the other). Inability to fixate light or objects was found in subjects, who at acuity testing showed values of 0.15 or less. In patients with suspected or definite optic atrophy, visual acuities 0.28 or less were obtained. In general there was a good correlation between ophthalmological abnormalities (in fixation, pupil reactions to light, ocular motility, fundus appearance and refraction) and poor visual acuity. It is therefore concluded that visual acuity testing with 'preferential looking' techniques can give valid information on central visual function in mentally retarded children and young adults.

Adolescent↗
PubMed1983

Amblyopia in 4-year-old children treated with grating stimulation and full-time occlusion; a comparative study.

We have compared the effects on visual acuity and binocular functions of grating stimulation (CAM therapy) and full-time occlusion in 38 4-year-old, previously untreated amblyopic children. The patients were divided into subgroups with regard to amblyopia type and fixation pattern. We found that grating stimulation was slightly better than occlusion in improving visual acuity of anisometropic amblyopes with central fixation, but that both types of therapy were equally effective in strabismic amblyopia with central fixation and in amblyopia with eccentric fixation. However, maximal treatment effects were not reached with grating stimulation alone, as shown at follow-up after continued conventional therapy. Grating stimulation may be regarded as a valuable method at the initiation of treatment, particularly in anisometropic amblyopia, but it has to be supplemented with occlusion, which still must be regarded as the prime form of amblyopia therapy.

Amblyopia↗
PubMed1983

Recent advances in the management of amblyopia.

Methods of detection and treatment of amblyopia as a developmental visual defect are reviewed. Traditional occlusion therapy is compared with recent therapy techniques using square-wave grating patterns as stimuli to increase visual sensitivity. Both methods can help manage amblyopia particularly during stages of early visual development. It is found that the grating pattern stimuli are not in themselves therapeutic, but rather it is probably occlusion in combination with demanding visual tasks which help reduce amblyopia.

Amblyopia↗