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Biomedical subjects

M Abrahamsson

Publications and source records attributed to M Abrahamsson.

At least 37 records · Page 2Linked to original sources
PubMed1997

[Dim the light! Glare problems in a world with ever increasing demands on visual acuity].

Ocular tissue transparency is dependent on the regular lattice configuration of lens and corneal fibres of uniform diameter. Ageing is associated with degeneration of both lens and cornea, which lose some of their structural order and eventually their transparency, though this process is not uniform. The structural changes are local and result in ocular media opacities. When the opacities increase in number and extension, they begin to affect visual acuity. As the loss of acuity becomes clinically significant, we speak of clinically relevant cataract. Retinal exposure to light diffused by intraocular light scattering induces optical glare, one of two forms of glare. The other form is transient glare--i.e., glare due to adaptation problems in an environment with rapidly changing ambient luminance. Contemporary society is characterised by increasing emphasis on visual information in such forms as texts, icons, signs and symbols. The computer revolution has been accompanied by further stress on the importance of the detection and interpretation of written instructions.

Adaptation, Ocular↗
PubMed1996

[Can we identify risk groups for the development of amblyopia and strabismus?].

In the nordic countries 2 to 4% of the population squint and 3 to 5% develop amblyopia. Identification of these children can be done through a general visual screening at a proper age or by selective screening of high risk groups. Several risk factors can be identified: heredity, failure to emmetropize and high hyperopia at the age of 1 year.

Amblyopia↗
PubMed1996

Changes of visual function and visual ability in daily life following cataract surgery.

We conducted a prospective study of 56 patients aged 70 to 79 years undergoing cataract surgery, in order to determine the impact of surgery on subjective and objective measurements of visual ability. In 46 cases we could obtain all necessary data. Binocular visual acuity, near vision and contrast sensitivity improved due to surgery. Self-assessed ability to perform visually related tasks was examined in form of a questionnaire. The results show that there was no simple relationship between objective measurements and perceived visual ability. An impairment in preoperative visual acuity cannot be related to a specific loss of visual ability. In order to increase the quality of cataract surgery more subtly, subjective aspects of vision must be taken into consideration when operation is decided upon and in the evaluation of the results.

Activities of Daily Living↗
PubMed1996

Natural history of infantile anisometropia.

AIMS/BACKGROUND: In a previous study longitudinal changes of anisometropia were investigated. It was shown that anisometropia arises and vanishes during the emmetropisation process and that the associated risk for amblyopia is low. The aim of this study was to follow acuity and refraction longitudinally in children with marked anisometropia at 1 year of age. METHODS: Refractive errors and visual acuity were estimated every sixth month for a selected group of 20 children with marked anisometropia > or = 3.0 D (spherical equivalent) at 1 year of age from approximately 3 to 10 years of age. RESULTS: The children could be classified into three groups. In six subjects the anisometropia increased (mean 1.4 D) and they all developed amblyopia. The remaining children could be classified into two groups of equal size. One group developed no amblyopia and the anisometropia decreased with a mean of 3.0 D. The seven remaining children developed amblyopia and/or strabismus; the mean anisometropia decrease was 1.2 D. CONCLUSION: Anisometropia at 1 year of age that is larger or equal to 3.0 D will in 90% of the cases still be there at 10 years of age. There is a substantial risk of this group developing amblyopia (60%).

Amblyopia↗
PubMed1996

Transillumination of iris and subnormal visual acuity--ocular albinism?

BACKGROUND: A common clinical sign in children with subnormal visual acuity or slow visual development was iris transillumination. This was used as the inclusion criterion in a study of children shown to have a subnormal visual acuity in a general health examination at age 4 years. METHODS: Refraction values, stereopsis, fundus photography, macular and nerve head appearance, and visual evoked response (VER) recordings were studied in 18 children. The clinical results were compared with 64 controls referred to the eye clinic because of subnormal vision from the general health examination or from school health care. RESULTS: Eight children had VERs showing asymmetry typical for albinism. Another four had only small asymmetries on the VER, indicating a lower degree of decussation abnormality. No simple correlation of visual acuity, degree of iris transillumination, stereopsis, or macular pathology and VER asymmetries were found. However, marked iris transillumination in all four quadrants, absence of a foveal reflex, and low visual acuity were weakly correlated. CONCLUSIONS: In a rather homogeneous group of children with iris transillumination and subnormal visual acuity eight of 18 had typical albino VERs. The findings of small atypical VER asymmetries in four children and no asymmetry in six children suggest that albinism may be considered as a description of a heterogeneous group of conditions including maximal decussation rate (100%) in the chiasma to a condition with almost normal (> or = 50%) decussation rate.

Adolescent↗
PubMed1995

The 'light scattering factor'. Importance of stimulus geometry, contrast definition, and adaptation.

PURPOSE: Paulsson and Sjöstrand have suggested that the light scattering factor (LSF) can be estimated by using the equation: LSF = L/E (M2/M1-1). Here L is the space average luminance of the target, E is the illuminance of the glare source, and M2 and M1 are modulation contrast thresholds in the presence and absence of the glare source. To compensate for change of adaptation. Abrahamsson and Sjöstrand later modified the above equation by introducing a correction factor (CF): LSF = L/E ((CF) (M2/M1-1). The purpose of this study is to analyze the validity of the above equations. METHODS: The importance of stimulus geometry, contrast definition, background luminance, and glare illumination is studied through theoretical analysis and comparison with earlier studies. Stimulus geometry and contrast definition are studied through optical modeling. Adaptation is modeled according to the laws of Weber and DeVries-Rose. RESULTS: The choice of contrast definition may corrupt the result by a factor of 2. At background luminance levels above approximately 10 cd/m2, the Paulsson-Sjöstrand equation agrees well with theory. At lower background levels, the Abrahamsson-Sjöstrand equation is used with correction factors derived from adaptation measurements. Using this equation and earlier published data from glare testing performed at 2 cd/m2, the results are found to be in fair agreement with the light scattering theory. CONCLUSIONS: Glare testing using the Paulsson-Sjöstrand equation is found to be valid as long as the measurements are performed at high luminance levels (above 10 cd/m2), with targets of low spatiotemporal frequencies (e.g., 2 cpd and 1 Hz) and with the use of a properly chosen definition of contrast. At lower luminance levels, the Abrahamsson-Sjöstrand equation may be used with well-derived correction factors.

Adaptation, Ocular↗
PubMed1995

Excretion of amino acid residues from diets based on low-fibre wheat or high-fibre rye bread in human subjects with ileostomies.

OBJECTIVES: The effect of consumption of a wheat-flour bread-based low-fibre diet (13.6 g/day fibre per portion) or a rye bran bread and whole-grain rye crispbread-based high-fibre diet (43.5 g/day fibre per portion) on the ileal excretion of amino acid residues and crude protein was studied. DESIGN: The study was performed as a cross-over design. SETTING: The subjects were studied as outpatients except on the sampling days when all subjects were admitted to the research ward and stayed in a nearby patient hotel overnight. SUBJECTS: Six men and two women, all proctocolectomised for ulcerative colitis, volunteered to participate in the study. INTERVENTIONS: During each dietary period of 3 weeks, food and excreta were collected and analysed on days 3, 17 and 18. RESULTS: The excretion of crude protein and amino acids (free and bound) was generally higher during the high-fibre diet period, although the relative proportion of amino acids was similar in the ileal effluents from the two diets. The apparent digestibilities of crude protein and all amino acids except histidine, tyrosine and proline were significantly (P < 0.05) lower during the high-fibre diet period. CONCLUSION: It was indicated that the effect of the high-fibre rye-based diet was a generally impaired ileal amino acid absorption.

Aged↗
PubMed1995

Excretion of amino acid residues from diets based on wheat flour or oat bran in human subjects with ileostomies.

OBJECTIVES: The effect of consumption of a wheat-flour bread-based low-fibre diet (7.8 g/day fibre; 1.0 portion) or the same diet in which the wheat bread was exchange for a bread based on oat bran with a high fibre content (31.9 g/day fibre; 1.0 portion) on the ileal excretion of amino acid residues and crude protein was studied. DESIGN: The study was performed as a cross-over design. SETTING: The subjects were studied as outpatients except on the sampling days when all subjects were admitted to the research ward and stayed in a nearby patient hotel overnight. SUBJECTS: Seven men and three women, all proctocolectomised for ulcerative colitis, volunteered to participate in the study. One female subject was withdrawn from the study because of inflammation of the ileal stoma. INTERVENTIONS: During each dietary period of 3 weeks, food and excreta were collected and analysed on days 3 and 17. RESULTS: No significant differences in excretion of crude protein or amino acids (free and bound) were found between the two sampling days. Intake as well as excretion of all analysed amino acids was higher during the high-fibre diet period, although the relative proportion of amino acids was comparable in the two diets and their corresponding ileal effluents. Aspartic acid, glycine, threonine, alanine and serine were found in considerably higher relative proportions in the effluents from the subjects when they consumed each of the two diets than their concentrations in the diets. The apparent digestibilities were significantly (P < 0.05) lower for all analysed amino acids during the high-fibre diet period. Aspartic acid (10.7%), alanine (9.9%) and glycine (8.5%) showed a more pronounced decrease than the mean decrease in amino acid digestibility (6.6%) when subjects consumed the high-fibre diet. CONCLUSION: Intake of the oat bran high-fibre diet resulted in significantly lower amino acid and crude protein digestibility. The relative amino acid proportions in the diets and their corresponding excretas were, however, comparable for the two diets.

Aged↗
PubMed1994

Patterned light flash evoked short latency activity in the visual system of visually normal and in amblyopic subjects.

In a previous experimental study on anaesthetized cat it was shown that a short latency (35-40 ms) cortical potential changed polarity due to the presence or absence of a pattern in the flash stimulus. The results suggested one pathway of neuronal activation in the cortex to a pattern that was within the level of resolution and another to patterns that were not. It was implied that a similar difference in impulse transmission to pattern and non-pattern stimuli may be recorded in humans. The present paper describes recordings of the short-latency visual evoked response to varying light flash checkerboard pattern stimuli of high intensity in visually normal and amblyopic children and adults. When stimulating the normal eye a visual evoked response potential with a peak latency between 35 to 40 ms showed a polarity change to patterned compared to non-patterned stimulation. The visual evoked response resolution limit could be correlated to a visual acuity of 0.5 and below. In amblyopic eyes the shift in polarity was recorded at the acuity limit level. The latency of the pattern depending potential was increased in patients with amblyopia compared to normal, but not directly related to amblyopic degree. It is concluded that the short latency, visual evoked response that mainly represents the retino-geniculo-cortical activation may be used to estimate visual resolution below 0.5 in acuity level.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Refraction changes in children developing convergent or divergent strabismus.

Strabismus and amblyopia were studied in a cohort of children born in 1979 or 1980 in the area of Västerås, Sweden. Forty percent of the children had participated in a voluntary eye examination at 1 year of age. All children diagnosed as strabismic and/or amblyopic between 1979 and 1988 at any of the three eye clinics in the area were included in this study. Strabismic cases were mostly detected by the parents while microstrabismus and straight eye amblyopia were found at the general 4 years of age screening at children's health centres. In 57 cases with (n = 31) and without amblyopia (n = 41) it was possible to obtain several refraction values between 1 and 6 years of age. In this study we concentrated on manifest esotropia and exotropia. The aim of the study was to describe changes of refraction before and after onset of strabismus and to establish risk indicators that identified populations at risk of developing strabismus. We found that patients with esotropia show a more pronounced hypermetropia than exotropic cases at the time of detection of strabismus. This difference becomes more definite over time, since hypermetropia increased in the deviating eye in the esotropic cases while refractive errors remained stationary in most of the exotropic eyes. It was also apparent that anisometropia frequently developed after onset of strabismus in esotropic cases in contrast to exotropic cases. An increasing refractive error in the deviating esotropic eye could be combined with an emmetropisation of the fixating eye.

Anisometropia↗
PubMed1992

[Contrast sensitivity and glare].

The ability of the visual system to detect the information presented to the eye in form of spatial or temporal contrast can be characterized by the contrast sensitivity function (CSF). CSF measurements can be used to visualize loss in visual capacity in patients with different diseases and to monitor recovery of vision. In the clinic CSF is most commonly used to evaluate disability glare in patients with cataract.

Adaptation, Ocular↗
PubMed1991

Evaluation of a clinical glare test based on estimation of intraocular light scatter.

A glare test based on psychophysical estimation of intraocular light scatter and using a flickering, annular glare source was evaluated. The parameters determining the accuracy of the test were studied. In particular the influence of background light and flicker frequency were investigated and optimum values for best accuracy were found. Based on these findings a versatile and simple apparatus was constructed. Forty patients with various degrees of cataract were investigated in a clinical study. Patients, who subjectively experience severe glare problems, indeed show high glare values as measured with the apparatus. No obvious relation between visual acuity and glare score was found. In comparison with glare tests using a stationary glare source the use of a flickering glare source is advantageous in terms of sensitivity and accuracy.

Adult↗
PubMed1991

Flashed pattern-induced activity in the visual system: I. The short latency evoked response recorded from the cat visual cortex.

Previous methods for estimating visual acuity have used the visual evoked response conventionally the late visual evoked response components or the steady-state potential. The present experiments were undertaken to evaluate the possible use of short latency flashed pattern evoked responses in estimating pattern dependent activity in the cat visual system. Recordings were made from the skull bone and the dura above the primary visual cortex and intracortically. The visual evoked responses to patterned (checks) and non-patterned light flashes of high intensity and short duration were recorded. The visual evoked response activity recorded from the cortical surface had an onset latency of 14-15 ms. The initial positive-negative potential sequences of the responses were similar for patterned and non-patterned stimuli, however a difference was recorded from 35-40 ms after stimulus. The smallest check size which separated a pattern from a non-pattern VER was in the order of 10 min of arc. The results indicate that the short-latency cortical VER may be used to estimate visual resolution.

Animals↗
PubMed1990

Risk factors in amblyopia.

Any intervention to prevent serious amblyopia is based on the knowledge about normal versus subnormal visual development. Our ability to predict with high degree of certainty which children will develop amblyopia will be dependent on the characteristics of various risk factors for initiating the development of squint or amblyopia. We have used longitudinal studies of population based cohorts of young children to define some of these risk factors such as refractive errors. Three hundred and ten children with an astigmatism greater than or equal to 1.0 D at one year of age were refracted yearly between the age one and four years. Astigmatism and anisometropia were found to be highly variable during infancy and early childhood. Longitudinal follow-up seems to be needed to separate the normal from the abnormal refraction development, which initiates the development of the amblyopia. Children with constant or increasing astigmatism or anisometropia between one and four years were 'at risk'. In parallel we have studied important factors for successful treatment of amblyopia. Based on these findings we conclude that a population screening at four years of age seems to be advantageous in Sweden in order detect and successfully treat most cases of amblyopia.

Age Factors↗
PubMed1990

A longitudinal study of a population based sample of astigmatic children. I. Refraction and amblyopia.

The refraction changes in 310 children with astigmatism greater than or equal to 1.0 D in at least one eye at one year of age were followed during a period of 3 years. At the age 4 years amblyopia was found in 23 children (7%). The refraction data of these children were compared to the rest of the sample. We found that an increasing astigmatism during the test period was associated with an increased risk to develop amblyopia. The majority of children (n = 280) showed a decrease of their astigmatism, whereas all cases with a marked amblyopia (V.A. less than 0.5) or binocular amblyopia, except one, had an increasing or unchanged astigmatism during the age period 1 to 4 years. Strabismus and oblique astigmatism at any time during the test period was also strongly related to amblyopia. The incidence of strabismus (1%) was unexpectedly low. The study also showed that independent of age there was no simple relationship between amblyopia and refraction errors measured at a single test session. The main conclusion of this study is that failure of emmetropization may play an important role in visual development.

Amblyopia↗
PubMed1990

A longitudinal study of a population based sample of astigmatic children. II. The changeability of anisometropia.

The variability of anisometropi in a sample of 310 children with astigmatism at the age of 1 year was longitudinally studied during a 3-year period between 1 and 4 years of age. The prevalence of anisometropia of 1 D or more at each year level was rather stable. When individual cases were examined we found that between the first and the last test session 19 of the 33 children with anisometropia at the first test session had become non-anisometropic and were substituted with 14 new cases which were non-anisometropic at the age of 1 year. In general, less than half of the cases, at all levels of anisometropia, remained anisometropic throughout the whole test period. We also found that children with anisometropia persisting through the whole test period were at considerable risk, about one out of four, of developing amblyopia. There was no simple relationship, however, between anisometropia at a certain age level between 1 and 4 years and amblyopia and/or strabismus. Non-persisting anisometropia in an emmetropizing eye is in most cases a benign sign and not connected with an increased risk for developing amblyopia.

Aging↗
PubMed1990

A new glare test based on low contrast letters--evaluation in cataract patients.

A new simple glare test was designed and evaluated regarding clinical usefulness and reproducibility. The ability to recognize letters of equal size and varying contrast was determined with the absence and presence of glare sources above and below the letters. Ten patients with cataract, visual acuity of at least 0.3 and glare problems, and three age matched controls were tested, as well as one patient with glare complaints and exophoria, one with lens subluxation and one with cataract and no glare problem. The test was found to be cheap and simple to produce and useful for clinical testing. Normal eyes had no detectable reduction of letter contrast sensibility with glare. All cataractous eyes had a letter contrast sensitivity without glare that was well below that of the controls and under glare conditions they all had a drop in visual function that was unrelated to their visual acuity. The reproducibility was of a magnitude similar to that of other low contrast letter tests. Our conclusion is that this test will be a valuable tool in the evaluation of cataract patients providing information not only about glare-induced visual loss but also about contrast sensitivity, separating eyes with increased intraocular light scattering from normal eyes.

Adult↗