| 1. |
- Frisén, Lars, 1939, et al.
(author)
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A simple relationship between the probability distribution of visual acuity and the density of retinal output channels.
- 1976
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In: Acta ophthalmologica. - 0001-639X. ; 54:4, s. 437-44
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Journal article (peer-reviewed)abstract
- Throughout the retina, the parameters of the probability distribution of visual acuity for monochromatic interference fringes are closely proportional to the number of retinal ganglion cells per degree of visual angle. There are no simple relationships to receptor spatial frequencies. These findings suggest that neuro-retinal acuity is determined principally by the spatial frequency of neural output channels.
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| 2. |
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| 3. |
- Frisén, Lars, 1939, et al.
(author)
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How good is normal visual acuity?. A study of letter acuity thresholds as a function of age.
- 1981
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In: Albrecht von Graefes Archiv fur klinische und experimentelle Ophthalmologie. Albrecht von Graefe's archive for clinical and experimental ophthalmology. - 0065-6100. ; 215:3, s. 149-57
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Journal article (peer-reviewed)abstract
- Visual acuity levels were studied in 100 normal subjects of different ages, using a finely graduated letter chart under carefully optimized test conditions. Each line on the chart contained 10 letters of similar difficulty, arranged in random order. A statistical analysis of different response criteria showed a clear superiority of fractional criteria (e.g. 50% correct responses) over the traditional 100% correct requirement. The average difference between right and left eyes was 0.04 +/- 0.15 (decimal notation). Regression analysis of the dependence of visual acuity on age showed a monotonic rise towards the age of 25 years, and a gradual decline thereafter. The most marked decline occurred after the age of 60. Age-dependent confidence intervals were tabulated. The results indicate that minor modifications of the conventional test procedure can enhance the diagnostic potential considerably.
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| 4. |
- Frisén, Lars, 1939, et al.
(author)
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Micropsia and visual acuity in macular edema. A study of the neuro-retinal basis of visual acuity.
- 1979
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In: Albrecht von Graefes Archiv fur klinische und experimentelle Ophthalmologie. Albrecht von Graefe's archive for clinical and experimental ophthalmology. - 0065-6100. ; 210:2, s. 69-77
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Journal article (peer-reviewed)abstract
- Relative micropsia was measured by a matching technique in patients with unilateral, benign, macular edema. Quantitative assessment of foveolar micropsia to be a sensitive indicator of receptor displacement in this disorder, and may be a useful tool both for diagnosing and for monitoring macular edema. Parallel measurements of grating acuity showed a close proportionality between acuity and micropsia parameters. This result validates a new quantitative theory for the neuro-retinal basis of visual acuity. The theory allows prediction of the proportion of working visual neurons in patients with impaired acuity due to diseases that produce a diffuse loss, or disconnection, of macular cones. Our results indicate that so-called normal visual acuity (1.0 or 20/20) requires no more than 44% of the normal quantity of fovelar, neuro-retinal channels.
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| 5. |
- Frisén, Lars, 1939, et al.
(author)
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Objective recognition of abnormal isopters.
- 1975
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In: Acta ophthalmologica. - 0001-639X. ; 53:3, s. 378-92
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Journal article (peer-reviewed)abstract
- We have examined the hypothesis that normal and only normal isopters of the central visual field are elliptical, except for random deviations. Statistical methods capable of recognizing small deviations from elliptical shape have been developed. Theses methods have been devised to meet the special demands of clinical testing of visual fields and require only simple calculations. The qualities of these methods were examined by theoretical analysis, by large-scale simulations, and by experimental comparison with subjective evaluations. The new methods proved very useful in these examinations. A clinical study using a servo-equipped Goldman perimeter demonstrated that normal central isopters are elliptical enough for the proposed test characteristic to be of practical value in clinical work. The method allows an objective recognition of abnormal isopters with a high degree of sensitivity.
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| 6. |
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| 7. |
- Blomsterwall, Elisabeth, et al.
(author)
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Postural function and subjective eye level in patients with idiopathic normal pressure hydrocephalus.
- 2011
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In: Journal of neurology. - : Springer Science and Business Media LLC. - 1432-1459 .- 0340-5354. ; 258:7, s. 1341-6
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Journal article (peer-reviewed)abstract
- Disturbance of posture is a frequent indication of idiopathic normal pressure hydrocephalus (iNPH) and is characterised by an increased sway in the frontal and sagittal planes. Further, iNPH patients with increased backward sway are known to have a defective perception of the subjective visual vertical (SVV), with the upper portion of an articulated rod tilted towards themselves. The objective of the present study was to compare subjective eye level (SEL) with actual eye level (EL) and compare this data with SVV and postural function. Twenty iNPH patients and ten normal controls estimated SEL by placing an adjustable horizontal line at EL. Sway pattern and SVV were also examined as previously described. The patients presented larger errors on downward as compared to upward line adjustments; all patients also presented a SVV tilted towards them. The patients swayed more in the sagittal than in the frontal plane at a higher speed than the normal controls, and they were relatively less helped by their vision. This is in accordance with the tendency to fall backwards seen in many iNPH patients. iNPH patients have a tendency to place SEL higher than EL and this, together with examination of SVV and sway pattern, suggests defective internal processing of gravicentric information.
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| 8. |
- Frisén, Lars, 1939, et al.
(author)
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A primer of ophthalmic computer graphics.
- 1990
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In: Documenta ophthalmologica. Advances in ophthalmology. - 0012-4486. ; 74:4, s. 337-50
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Journal article (peer-reviewed)abstract
- Computer graphics offers an unprecedented opportunity to probe new and old ideas in vision testing, without going to the expense of building dedicated equipment. However, the large variety of computer hardware is bewildering and only occasionally can commercial software tools be used. This mini review of the basic principles of computer graphics on personal computers is intended to help the newcomer to the field.
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| 9. |
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| 10. |
- Frisén, Lars, 1939
(author)
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Acuity perimetry: estimation of neural channels.
- 1988
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In: International ophthalmology. - 0165-5701. ; 12:3, s. 169-74
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Journal article (peer-reviewed)abstract
- 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.
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| 11. |
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| 12. |
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| 13. |
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| 14. |
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| 15. |
- Frisén, Lars, 1939, et al.
(author)
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Binocular summation in humans: evidence for a hierarchic model.
- 1988
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In: The Journal of physiology. - 0022-3751. ; 402, s. 773-82
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Journal article (peer-reviewed)abstract
- 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.
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| 16. |
- Frisén, Lars, 1939, et al.
(author)
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Characterization of vigabatrin-associated optic atrophy.
- 2003
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In: Acta ophthalmologica Scandinavica. - : Wiley. - 1395-3907. ; 81:5, s. 466-73
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Journal article (peer-reviewed)abstract
- To report the discovery of a previously unknown form of optic atrophy associated with use of the anti-epileptic drug vigabatrin.We conducted a retrospective analysis of digitally enhanced ocular fundus photographs, kinetic visual field maps and treatment parameters for 25 patients, who were selected to represent a large spectrum of visual field defects.In all, 21 patients (84%) evidenced subtle, diffuse atrophy of the retinal nerve fibre layer, in a pattern accessible to scoring. Atrophy scores correlated with visual field remains and cumulative vigabatrin doses. A pathophysiological model is proposed that involves the lengths of intraocular (unmyelinated) retinal ganglion cell axons.Optic atrophy attests to the irreversible nature of vigabatrin's visual toxicity. Ocular fundus imaging should prove useful for objectively monitoring vigabatrin-treated subjects for visual toxicity.
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| 17. |
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| 18. |
- Frisén, Lars, 1939, et al.
(author)
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Communicating exophthalmos: a sign of bilateral orbital roof defects.
- 1978
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In: Acta neurochirurgica. - 0001-6268. ; 41:1-3, s. 157-61
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Journal article (peer-reviewed)abstract
- The term communicating exophthalmos is suggested for a condition where manual retropulsion of one eye results in proptosis of the other eye. This sign was observed in a patient with bilateral pulsating exophthalmos. The pulsating exophthalmos was ascribed to orbital roof defects in combination with post-traumatic hydrocephalus. It was controlled by a shunting procedure.
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| 19. |
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| 20. |
- Frisén, Lars, 1939
(author)
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Computerized perimetry: possibilities for individual adaptation and feedback.
- 1988
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In: Documenta ophthalmologica. Advances in ophthalmology. - 0012-4486. ; 69:1, s. 3-9
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Journal article (peer-reviewed)abstract
- 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.
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| 21. |
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| 22. |
- Frisén, Lars, 1939, et al.
(author)
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Cyclic compression of the intracranial optic nerve: patterns of visual failure and recovery.
- 1976
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In: Journal of neurology, neurosurgery, and psychiatry. - 0022-3050. ; 39:11, s. 1109-13
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Journal article (peer-reviewed)abstract
- A patient with a cystic craniopharyngioma below the right optic nerve had several recurrences requiring surgery. Finally the cyst was connected with a subcutaneous reservoir by means of a fine catheter. Symptoms of optic nerve compression recurred more than 50 times during the following year, and were relieved within seconds upon drainage of the reservoir. In each cycle, a drop in visual acuity preceded a measurable change in the visual field. The pattern of field changes was an increasingly severe, uniform depression. Optic nerve ischaemia induced by compression was probably the most important factor causing visual failure in this case.
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| 23. |
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| 24. |
- Frisén, Lars, 1939, et al.
(author)
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Detection of extracranial carotid stenosis by computed tomography.
- 1979
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In: Lancet (London, England). - 0140-6736. ; 1:8130, s. 1319-20
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Journal article (peer-reviewed)abstract
- Ten patients with transient ischaemic attacks (T.I.A.) within the carotid territory were examined by aortic-arch angiography and computed tomography (C.T.) of the neck. C.T. showed evidence of carotid calcifications in all 17 angiographically abnormal arteries, and there was no evidence of calcification in the 3 normal arteries. C.T. of the neck promises to be a useful technique for the investigation of patients with T.I.A.s.
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| 25. |
- Frisén, Lars, 1939
(author)
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Deviations of the visual upright in three dimensions in disorders of the brainstem: a clinical exploration.
- 2010
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In: Brain : a journal of neurology. - : Oxford University Press (OUP). - 1460-2156. ; 133:12, s. 3541-3551
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Journal article (peer-reviewed)abstract
- Deviations of the subjective visual vertical in the roll or fronto-parallel plane occur commonly in disorders of the brainstem and have been extensively explored. In contrast, little is known about deviations in other directions. The present retrospective study focused on deviations in the pitch (sagittal) direction in 176 patients with a wide variety of disorders. The test task was to set a self-illuminated rod in the apparent upright position, in total darkness. Abnormal results (outside±4°) were recorded in 58% of the subjects. Negative (top backward) deviations were the most common, particularly with mass lesions in the pineal region, obstructive hydrocephalus, cerebellar lesions and crowding at the craniocervical junction. Positive and negative deviations were about equally common with focal intra-axial lesions. Negative deviations appeared related to dorsal locations of lesions and vice versa. Normal pressure hydrocephalus, Parkinson's disease and progressive supranuclear palsy were associated with smaller deviations, without a clear directional preponderance, and a larger individual variability. Most subjects lacked overt clinical corollaries. The most common ocular signs were aqueduct syndromes (n=17) and ocular tilt reactions (n=12), which were associated with deviations in 47 and 92% of instances, respectively. Subjective corollaries of deviation were never reported, not even by those subjects who showed a dramatic improvement upon resolution of the underlying condition. Deviations were also assessed in roll in a subgroup of 40 patients with focal lesions. Thirty subjects returned abnormal results: 13% in roll, 47% in pitch and 40% in pitch and roll. The direction of roll deviation appeared primarily related to laterality, with clockwise deviations with right-sided lesions and vice versa. All subjects with ocular tilt reactions had combined pitch and roll deviations, implying a common neural substrate. Correlation analyses, geometrical modelling and experimental self-observations indicated that deviations in pitch were attributable to cyclotorsional asymmetries between the eyes. The frequent co-existence of abnormal pitch and roll results implies that the true axis of deviation in focal brainstem disorders commonly falls outside traditional reference planes. The term 'visual upright in three dimensions' is suggested to identify unrestricted measurements, preserving the established term 'visual vertical' for measurements confined to the roll plane. Assessment of the visual upright in three dimensions provides a new, quantitative angle on brainstem disorders. The test appears useful for identifying a ubiquitous yet clinically silent feature of brainstem disease and also for monitoring the evolution of underlying conditions. More detailed explorations appear well motivated.
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