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Biomedical subjects

L Frisén

Publications and source records attributed to L Frisén.

At least 37 records · Page 2Linked to original sources
PubMed1991

High-pass resolution perimetry and age-related loss of visual pathway neurons.

The normal, age-related decline of results of high-pass resolution perimetry (HRP) predicts a loss of approximately 9,000 retino-cortical neural channels per year of age, or about 1 channel each hour. Previously published counts of numbers of neurons in the optic nerve indicate a loss of approximately 5,000 neurons per year. The HRP results can be accounted for by postulating that neurons are lost at the same rate also in the geniculo-striate visual pathway.

Adolescent↗
PubMed1990

Decompression of the orbit using a lateral rhinotomy approach in patients with malignant endocrine exophthalmos.

Malignant endocrine exophthalmos is a complication seen in 1-2% of patients treated for thyrotoxicosis. A variety of surgical techniques have been used to prevent loss of vision due to compression of the optic nerve. In this study, nine patients with rapidly diminishing vision were operated upon using a lateral rhinotomy technique creating the largest possible space for expansion into the nose and decompressing the optic nerve far back in the orbit. In all patients the vision was improved 1 year after surgery and the proptosis was decreased.

Adult↗
PubMed1988

Acuity perimetry: estimation of neural channels.

Measurements of peripheral visual acuity allow quantitative estimations of retino-cortical neural channels. Analysis of results from high-pass resolution perimetry revealed that about 2/3 of all channels are contained within 30 degrees of visual field eccentricity and that loss of 1/3 raises the average threshold level about 1 decibel. The analytical procedure can be applied to any type of visual field defect.

Adolescent↗
PubMed1988

Computerized perimetry: possibilities for individual adaptation and feedback.

Computerized perimetry is often poorly accepted by the tested subjects, presumably because of sparse feedback and lack of adaptation to individual capacity. Several remedies are suggested, including visual response feedback, active correction of erroneous responses, various fixation prompts, and continuous adaptation to current reaction time. Intuitively intelligible result displays are also desirable. A novel format representing threshold level by symbol size may meet this need.

Cues↗
PubMed1988

Perimetric variability: importance of criterion level.

Perimetry suffers from considerable variability of results. A new technique for estimating individual criterion levels in normal subjects exposes the important role of psychological variables. The analysis depends on features peculiar to acuity perimetry. It can be accommodated in the regular examination. The results can be used to compensate for practice effects in serial examinations and to tighten the range of normal limits. The reduction in variation between normal subjects amounted to 57 per cent.

Adolescent↗
PubMed1988

Sahlgren's Saturation Test for acquired dyschromatopsia: increased lightness enhances sensitivity.

Sahlgren's Saturation Test (SST) is a simple sorting test designed for the detection and grading of acquired color vision defects. Like other pigment-based color vision tests, the SST color samples have medium lightness, i.e., they belong to the intermediate part of the gray scale. We tested normal controls and subjects with congenital or acquired dyschromatopsia with five SST versions that differed only in the amount of lightness. The sensitivity of the test increased considerably with increasing lightness. Therefore, the lightness level of SST has now been changed from 30 to 10 Natural Color System units.

Color↗
PubMed1988

Binocular summation in humans: evidence for a hierarchic model.

1. Binocular summation was studied in human subjects using a batter of vision tests. Two tests assessed detection, another three acuity, one hyperacuity and one pattern recognition. 2. The magnitude of summation was consistent with, or exceeded, the level predicted from quadratic summation for both detection tests. 3. The summation factor was significantly smaller in the resolution tests than in the detection tests. Hyperacuity showed a large individual variation. 4. Spatial filtering of acuity targets did not influence summation. 5. No summation was found in the pattern recognition test. 6. It is argued that the degree of summation is related to the complexity of the visual task. A simple task yields a larger binocular summation than a more complex one. This may be related to the level of processing in the primary visual cortex.

Adult↗
PubMed1987

Clinical observations of effects on central nervous system in patients with acute facial palsy.

Twenty-eight consecutive patients with acute unilateral facial palsy were examined with special reference to clinical signs of central nervous system involvement. The clinical investigation in the acute stage of the disease showed that only seven patients had solitary facial nerve dysfunction, while the remaining patients had evidence of more widespread disease involvement. The most frequent finding was a trigeminal dysfunction of the paretic side, as shown by paresthesia and sensibility disturbance corresponding to the sensoritrigeminal area, as well as a dysfunction of the trigeminal component of the corneal reflex of the paretic side. Three patients showed migrating symptoms that were suggestive of a brain-stem disorder. In addition, four patients had an optic neuropathy, while an abnormal brain-stem audiometry response was demonstrated in five patients. The outcome of acute facial palsy one to two years after onset, however, could not be predicted from the clinical central nervous system signs. The degree of the palsy in the acute stage of the disease still seemed to be one of the most important prognostic factors. It is concluded that acute facial palsy is not a single entity, but rather a feature of different neurologic conditions.

Acute Disease↗
PubMed1987

High-pass resolution targets in peripheral vision.

Visual acuity was measured at 10 degree intervals on the horizontal meridian in two normal subjects, using high-pass spatial frequency filtered test targets in a computer graphics display. The close similarity between detection and recognition thresholds resulted in quick and reliable measurements. Peripheral acuity was proportional to local retinal ganglion cell separation. High-pass targets appear to be nearly ideal for clinical perimetry because of the easy test task and the possibility of interpreting results in terms of numbers of functional neuroretinal channels. The major limitation appears to be a somewhat fuzzy definition of small, circumscribed defects.

Adult↗
PubMed1986

Vanishing optotypes. New type of acuity test letters.

Acuity test letters generated on a television monitor were studied with regard to detection and resolution thresholds, both for the native configurations and after high-pass spatial frequency filtering. Comparisons were made with printed acuity charts of different contrast. Filtering diminished the interval between detection and resolution thresholds. Under some circumstances, a small (1 dB, about 26%) increment in size could make a previously invisible optotype clearly visible, or vice versa. The term vanishing optotype is suggested for acuity targets with this peculiar property. Vanishing optotypes do not seem useful for routine clinical acuity testing, but they may be advantageous, for example, in preferential looking-acuity tests for infants and visual field examinations. Like the present tests, such novel applications can be generated relatively easily on personal computers.

Adult↗
PubMed1986

Posttraumatic seesaw nystagmus abolished by ethanol ingestion.

We describe a patient who was left with a midchiasmal injury and bitemporal hemianopia after head trauma. Four months later, she developed typical seesaw nystagmus and moderate hydrocephalus. Lumbar punctures did not affect the nystagmus, but a temporary cessation was documented after ingestion of ethanol.

Adult↗
PubMed1986

The cerebral ocular pursuit pathways. A clinicoradiological study of small-field optokinetic nystagmus.

Optokinetic nystagmus was tested in patients with intracerebral tumors restricted to one hemisphere, by using a simple, hand-held drum and visual evaluation of symmetry of horizontal response. Computed tomographic mapping revealed that lesions associated with asymmetric optokinetic nystagmus involved the posterior hemisphere. The critical region appeared to extend from the posterior splenium and the anteromedial occipital lobe to the posterior internal capsule. It seemed to course below the posterior horn of the ventricular system, then turn anteriorly, and finally medially, above the temporal horn. It is argued that the posterior extremity of this C-shaped region contains the ipsilateral and contralateral visual inputs to a parietal cortex control over ipsilateral smooth eye movements, and that the anterior extremity contains the efferent motor command pathways destined to the brain stem.

Adolescent↗
PubMed1984

Visual acuity in optic atrophy: a quantitative clinicopathological analysis.

Analysis of clinicopathological data from 14 eyes with optic atrophy from various causes revealed a simple relationship between visual acuity and the number of surviving axons in the temporal quadrant of the optic nerve head. This provides support for the theory that the minimum angle of resolution (inverse of visual acuity) is directly proportional to the spatial separation of transmitting foveal cones. The theory allows estimation of the functional fraction of foveocortical neural channels from clinical acuity measurements.

Adult↗
PubMed1984

Narrowing of the retinal arterioles in descending optic atrophy. A quantitative clinical study.

Measurements were made on fundus photographs of the diameters of retinal arterioles in a series of cases with various nonvascular lesions of the anterior visual pathways, before and after the development of fundus signs of optic atrophy. A simple method was devised for reliable estimation of the diameter of the central retinal artery whenever this vessel could not be measured directly: this allowed comparisons to be made between different eyes, irrespective of individual variations in arteriolar branching patterns. Atrophy was consistently associated with a decrease in central retinal artery caliber, averaging 24% in eyes developing total optic atrophy, and 17% in eyes with hemi-atrophy. Normal controls showed a maximum side difference of 8%.

Adolescent↗
PubMed1984

Episodic astigmatism heralding generalized myopathy: report of a case managed with a new type of soft contact lens.

A 29-year-old woman presented with marked variations in refraction. A few minutes of physical exertion or reading at a close distance induced up to 2D of myopia and 2D of myopic astigmatism, which regressed upon resting with closed eyes. Cycloplegic agents did not affect the refractive changes, which were shown to be due to variations in corneal curvatures. The eyes were otherwise clinically normal. A few months later the patient developed signs of a progressive, generalized myopathy of unknown origin. The muscular disease was resistant to treatment. The refractive changes were effectively controlled by means of a new type of soft contact lens, with a semi-rigid center.

Adult↗
PubMed1983

Fundus changes in acute malnutritional optic neuropathy.

A peculiar dilation and tortuosity of small retinal vessels within the arcuate areas of the retinal nerve fiber layer occurred in a series of patients with acute malnutritional optic neuropathy ("tobacco-alcohol amblyopia"). These evanescent vascular abnormalities may be caused by arteriovenous shunting. They seem to be specific indicators of the early phase of this disease.

Acute Disease↗