Contrast sensitivity testing in clinical practice.
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Contrast Sensitivity↗
Biomedical subjects
L Hyvärinen
Publications and source records attributed to L Hyvärinen.
Pulmonary deposition and clinical response of 99mTc-labelled salbutamol delivered from a novel multiple dose powder inhaler.
Pulmonary deposition of 99mTc-labelled sulbutamol was determined after delivery from a novel multiple dose powder inhaler (Easyhaler). The clinical efficacy of the inhalation powder, evaluated simultaneously with gamma camera detection, was compared with that obtained after drug delivery from a metered dose inhaler-spacer combination. The study was performed as an open, non-randomized cross-over trial. A single dose of radiolabelled inhalation powder was inhaled on the first and the inhalation aerosol, as control, on the second study day. Sulbutamol sulphate was labelled with 99mtechnetium, and the inhalation powder was formulated by mixing radioactive drug particles with carrier material. Aerodynamic properties of the radiolabelled inhalation powder were similar to those of the unlabelled salbutamol powder. Delivered dose from the breath-actuated powder inhaler was adjusted to be equal to two puffs from a conventional aerosol actuator with a short plastic mouthpiece. Twelve non-smoking asthmatic patients participated in the trial. The mean pulmonary deposition of 24% was obtained after drug delivery from Easyhaler powder inhaler. Clinical efficacy of the medications was similar in terms of area under the FEV1 curve, maximum FEV1 and the improvement ratio. Thus it can be suggested that powder delivery from Easyhaler powder inhaler and the aerosol delivery through the spacer are equally effective.
Adult↗
Contrast sensitivity in amblyopia. III. Effect of occlusion.
Contrast sensitivity of 26 children (mean age 9 years) was measured using vertical gratings during the course of pleoptic treatment. A statistically highly significant improvement in the vision of amblyopic eyes occurred during intensive treatment in the hospital. Occlusion of the amblyopic eye (inverse occlusion) before the pleoptic treatment did not effect the function of the amblyopic eyes. During 8-week occlusion of the dominant eye (direct occlusion) after pleoptic treatment changes in the vision of the amblyopic eyes were statistically insignificant. In some patients there was change in contrast sensitivity without a corresponding change in visual acuity. The contrast sensitivity of the dominant eye decreased markedly during occlusion in 12 patients. After a continuous occlusion of only 2 weeks there was a statistically significant decrease at spatial frequency 6 c/deg. There was no simultaneous decrease of visual acuity; thus the change can be called 'hidden occlusion amblyopia'. An additional 8-week occlusion did not cause any statistically significant decrease in contrast sensitivity, but visual acuity of 2 patients decreased slightly, a sign of beginning occlusion amblyopia. The changes disappeared during 'Einschleich'-occlusion or penalization except in one child whose previously dominant eye became non-dominant and slightly amblyopic.
Adolescent↗
Contrast sensitivity in amblyopia. IV. Assessment of vision using vertical and horizontal gratings and optotypes at different contrast levels.
The contrast sensitivity of 49 amblyopic children (mean age 9 years) was measured in the beginning and at the end of a treatment period using both vertical gratings and optotypes (LH-4 contrast test) at 2, 3, 5 and 75% contrast. The contrast sensitivity of 37 patients was also measure using horizontal gratings. The contrast sensitivity of the dominant eyes measured with vertical gratings was generally higher than when measured with horizontal gratings. The difference was statistically significant at spatial frequencies 1 and 6 c/deg. A similar difference was present in the amblyopic eyes only at the spatial frequency 1 c/deg both before and after the treatment. Individual variation was great; in a given patient the relationship between the two measurements varied from one spatial frequency to the next. It has been shown in earlier investigations that contrast sensitivity measurements using gratings reveal important new information in the study of amblyopia. Both tests, used in this investigation, measure visual function in the low contrast domain and improve follow-up of the changes in vision during treatment of amblyopia when used in addition to visual acuity measurements. Low contrast optotype test seems to measure contrast sensitivity in amblyopia closely similarly to the grating test. The slight difference in detecting a 'hidden occlusion amblyopia' at the intermediate spatial frequencies needs further study.
Adolescent↗
Persistent behavioural blindness after early visual deprivation and active visual rehabilitation: a case report.
Early long lasting binocular deprivation results in behavioural blindness in both man and experimental animals. However, few reported cases show that visual rehabilitation may improve visual behaviour. A 34-year-old man who had experienced 30 years of binocular deprivation due to bilateral cataracts received visual rehabilitation for one year. The rehabilitation included training in eye-hand co-ordination, recognition of objects, evaluation of distance and size, and mobility training. Despite signs of recovery of visual functions the patient never started to use vision in his normal life. The negative outcome of the rehabilitation is partly attributed to the patient's motivational problems and to the relatively short rehabilitation time. Visual rehabilitation may be successful when started immediately after the corrective operation on the eyes when the level of motivation is also high.
Adult↗
Visual illusion mimicking dyslexia. A case history.
A 14-year-old girl with reading difficulties was found to have an unusual illusory movement of objects in the central visual field. The movement could be blocked by using a 26 mm Visolette magnifier with an arrow pasted on its lower surface to function as a reference point. After having read with help of this arrangement for 19 months the girl suddenly could see normally and has now been able to read without difficulties for over 3 years. We report the first documented case of visual illusion as the cause of reading difficulty which disappeared at the age of 15 years, thus years after the maturation of visual functions is thought to be completed. Although visual illusion like the one presented here must be rare, it should be diagnosed, because the treatment is totally different from that of usual dyslexia.
Adolescent↗
Classification of visual impairment and disability.
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Accommodation, Ocular↗
Contrast sensitivity in evaluation of visual impairment due to diabetes.
Spatial contrast sensitivity of 19 diabetics with different degrees of visual impairment was studied. It was found that contrast sensitivity at intermediate and low spatial frequencies may decrease without corresponding loss of visual acuity. In advanced cases of diabetes the opposite may be true: contrast sensitivity was better than expected on the basis of visual acuity. Thus both visual acuity and contrast sensitivity measurements are useful in the evaluation of the nature of visual impairment due to diabetic eye disease.
Color Perception Tests↗
Contrast sensitivity in evaluation of visual impairment due to macular degeneration and optic nerve lesions.
Spatial contrast sensitivity was investigated in a group of 17 patients with macular degeneration or optic atrophy. It has been reported earlier that patients with optic atrophy may have reduced contrast sensitivity at low spatial frequencies without decrease of visual acuity, a phenomenon called 'hidden visual loss'. The present study shows that also the opposite may be true: patients with macular degeneration or optic atrophy may have greatly decreased visual acuity and yet normal or nearly normal contrast sensitivity at low spatial frequencies and reasonably good sensitivity at intermediate spatial frequencies. This phenomenon could be called 'hidden vision'. In normal individuals and many visually impaired patients the spatial contrast sensitivity at high and intermediate spatial frequencies is equal when measured using grating fields of different size. In patients with central scotoma due to macular degeneration or optic atrophy contrast sensitivity is dependent on the size of the grating field: the maximal contrast sensitivity is higher when larger grating fields are used. The size of the smallest grating field that is needed for normal contrast sensitivity values at low spatial frequencies is one measure of visual impairment in this group of patients. Another measure of the function of the eccentric viewing area is the grating acuity which may also vary as a function of the grating field size.
Humans↗
Contrast sensitivity in monocular glaucoma.
The results of this selected group of glaucoma patients demonstrate that the effect of glaucoma on the contrast sensitivity can be assessed only after careful exclusion of all other causes for decrease in contrast sensitivity. Further development of methods is necessary.
Aged↗
Higher functions and plasticity in visual pathways.
A summary of the visual pathways in the brain is presented as a basis for considering abnormalities in this system. The role of the cortical associative regions in visual function is briefly delineated. A short summary of experiments describing plastic properties of the visual pathways at early age is also presented, and experiments describing neural and behavioural changes after binocular deprivation are reviewed. It is concluded that early visual deprivation leads to a profound alteration of the associative systems of the brain and that in monkeys and humans these changes are difficult to remedy later. Therefore early detection and correction of visual abnormalities is very important as well as early compensation using other forms of sensory communication.
Adult↗
Contrast sensitivity in visually impaired children.
Spatial contrast sensitivity may decrease differently at different spatial frequencies when vision is impaired. Patients with central acidoma may have normal or decreased sensitivity at low spatial frequencies, their Snellen acuity often is lower than grating acuity estimated on the basis of contrast sensitivity values. In retinitis pigmentosa contrast sensitivity may decrease at the low spatial frequencies already in the early teens. Because the ability to discern low contrasts is important in daily living, spatial contrast sensitivity measurements should become a part of clinical evaluation of vision.
Adolescent↗
Visual rehabilitation after long lasting early blindness.
A 23-year-old woman, blinded at an early age due to retinopathy of prematurity and cataract was successfully operated. After the operation the patient was behaviourally blind. Visual rehabilitation was started 9 months later and lasted 1 1/2 years. During this time the visual behaviour of the patient improved. Quantitative tests were designed to depict the progress. The functional improvement of the patient is in agreement with the findings of animal studies; binocular deprivation during the critical period of development causes behavioural blindness, which is partially recoverable. The result of this study indicates that the visual rehabilitation facilitates the process of recovery. The progress in visual behaviour is likely to reflect an improvement of the function of the associative systems of the brain.
Adult↗
Topographic instability of spatial vision as a cause of dyslectic disorder: a case study.
A case of severe disorder of spatial perception with concomitant dyslexia is described. The patient, a 15-yr-old girl, has a systematic tendency to misperceive the spatial order of symbols or objects lying on the same horizontal level and within a few degrees of visual angle. The syndrome includes a spatial extinction phenomenon in which an object in her left visual field disturbs the perception of another object in the corresponding symmetry point of her right visual field. The order reversal symptom was abolished if the letters presented for her were shown for less than 15 msec. The disorder is probably due to a pathological interhemispheric interference in the processing of visual topographic information.
Adolescent↗
[Local treatment of allergic conjunctivitis].
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Conjunctivitis↗
Resolution of gratings oriented along and across meridians in peripheral vision.
Grating resolution was measured at various locations of the visual field for four grating orientations. As an instance of the oblique effect, vertical and horizontal gratings produced the highest resolution values in the central area. At eccentricities larger than about 20 deg, the oblique effect was replaced by a meridional resolution effect, in which resolution was systematically best for meridionally oriented grating bars and worst for grating bars perpendicular to the visual-field meridians. The origin of the effect seems to be neural because it was not caused by peripheral refractive errors or optical distortion of the peripheral retinal image.
Humans↗
[Contrast sensitivity in macular and optic nerve degeneration].
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Humans↗
Early visual deprivation alters modality of neuronal responses in area 19 of monkey cortex.
Monkeys deprived on vision during the first year of life by lid suture appear functionally blind after the opening of the eyes, but move actively in familiar surroundings using somesthetic cues. Microelectrode recordings of multiple unit activity in the associative visual cortical area 19 of deprived monkeys indicated that 20% of the neuron groups studies responded only during active somatic exploration. In normal animals all neuron groups studied responses exclusively to visual stimuli, but in the deprived animals only 40% of them did. Visual deprivation alters the synaptic pathways to visual associative cortex enhancing the efficiency of those inputs that can mediate somatic information to this region.
Animals↗