| 1. |
- Beckman, Claes, 1962-
(författare)
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Comparison of three methods of evaluating glare.
- 1992
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Ingår i: Acta ophthalmologica. - 0001-639X. ; 70:1, s. 53-9
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Tidskriftsartikel (refereegranskat)abstract
- A Humphrey Automatic Refractor Model 570 was used to measure the impairment of visual acuity for low contrast optotypes as a result of glare for normal subjects and for subjects with cataracts. This was compared with a direct measure of intraocular light scatter as measured by a compensating technique and with a subjective assessment of glare determined by a questionnaire. Only a weak correlation (r = 0.28) was found between the decrease in low contrast letter acuity and intraocular light scatter. The subjective assessment of glare sensitivity was not correlated with the decrease in low contrast letter acuity, but correlated to some extent (r = 0.55) with the measurement of intraocular light scatter.
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| 2. |
- Beckman, Claes, 1962-
(författare)
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Comparison of two glare measurement methods through light scattering modeling.
- 1992
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Ingår i: Optometry and Vision Science. - : Ovid Technologies (Wolters Kluwer Health). - 1040-5488 .- 1538-9235. ; 69:7, s. 532-7
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Tidskriftsartikel (refereegranskat)abstract
- Two methods used for evaluation of glare in patients with opacities of the ocular media are compared. One is a low contrast letter test and the other is a direct light scattering meter. Theoretical expressions for the measures obtained from the two different glare tests are derived in terms of the point spread function. Measurements on healthy test persons wearing diffusive glasses with known light scattering properties were in good agreement with the theory. Data from 26 cataractous eyes are presented and discussed in light of the theory.
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| 3. |
- Beckman, Claes, 1962-
(författare)
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Disputing Viking navigation by polarized skylight.
- 1994
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Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 33:21, s. 4754-5
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Tidskriftsartikel (refereegranskat)abstract
- The widely held notion that the Vikings utilized polarization of skylight on overcast days for navigational purposes is demonstrated to have no scientific basis. The use of polarized skylight for navigation under partly cloudfree skies should be treated with caution and skepticism.
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| 4. |
- Beckman, Claes, 1962-, et al.
(författare)
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Disputing Viking Navigation by Polarized skylight
- 1993
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Ingår i: Light and Color in the Open Air, OSA Technical Digest Series (Optical Society of America, Washington, D.C., 1993. - Washington DC. ; , s. 34-37
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Konferensbidrag (refereegranskat)
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| 5. |
- Beckman, Claes, 1962-
(författare)
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Evaluation of a clinical glare test based on estimation of intraocular light scatter.
- 1991
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Ingår i: Optometry and Vision Science. - : Ovid Technologies (Wolters Kluwer Health). - 1040-5488 .- 1538-9235. ; 68:11, s. 881-7
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Beckman, Claes, 1962-
(författare)
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Fiber optic point-source for in vivo measurement of light transmission and scattering in the eye
- 1994
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Ingår i: OphthalmicTechnologies, Proc. SPIE 2126, 324-330 (Societ of Photo-Optical Engineers, Bellingham WA, 1994).. - Bellingham WA. ; , s. 324-330
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Konferensbidrag (refereegranskat)abstract
- A fiber optic point-source was designed for in vivo measurement of light transmission and scattering. The point-source consists of an optical fiber, with a core diameter of about 8 um, mounted in a stainless steel cannula. At the tip of the cannula the entrance face of a 1 mm micro prism is fixed. The hypotenuse face of the prism is coated with aluminum and acts as a mirror reflecting the light out through the exit face. The arrangement allows light fed into the optical fiber to be emitted in a direction perpendicular to the axis of the cannula. The cannula is bent to allow its in vivo introduction into the eye at the posterior pole. The prism is positioned close to the retina along the optical axis of the eye. The light is transmitted through the eye in a reversed beam path (from vitreous towards cornea). In the vitreous, the light source emits within a numerical aperture of about 0. 1 allowing the exiting light to be well confined through the dilated pupil. After careful calibration of the light source, accurate measurements can easily be performed by positioning detector equipment outside the eye. The small size of the point-source (in the range of the eye's resolution) allows measurement of light scatter at both wide and narrow angles. With this intraocular fiber optic technique, it is possible to perform several types of experiments, including measurements of light transmission and scattering, and also studies of fluorescence phenomena in different parts of the ocular media.
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| 7. |
- Beckman, Claes, 1962-
(författare)
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Glare and contrast sensitivity before and after Nd : YAG laser capsulotomy.
- 1994
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Ingår i: Acta ophthalmologica. - 0001-639X. ; 72:1, s. 27-32
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Tidskriftsartikel (refereegranskat)abstract
- The benefits of Nd:YAG laser capsulotomy on visual performance were evaluated in 13 patients with after-cataract following extracapsular cataract extraction. Besides clinical evaluation we measured: visual acuity, letter contrast sensitivity with and without the presence of a circular glare source (glare angle: 8 degrees). Finally, the patients were asked to evaluate their subjective glare problems. In all patients, visual acuity had decreased markedly compared to measurements 2 months after cataract surgery. Before capsulotomy we observed impaired letter contrast sensitivity and increased intraocular light scatter compared to normals. Following capsulotomy, VA and contrast sensitivity both improved by a factor of 2. The subjective glare problems diminished, although most patients showed minor decreases in intraocular light scatter. The limited glare induced loss of letter contrast sensitivity, present before capsulotomy, remained after treatment. Our study indicates that after-cataract impairs resolution and contrast sensitivity without necessarily causing a marked increase in light scatter as measured at a large angle.
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| 8. |
- Beckman, Claes, 1962-
(författare)
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Glare measurements before and after cataract surgery.
- 1993
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Ingår i: Acta ophthalmologica. - 0001-639X. ; 71:4, s. 471-6
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Tidskriftsartikel (refereegranskat)abstract
- The efficacy of cataract surgery in improving visual performance was evaluated in 10 patients by measuring changes in intraocular light scatter, contrast sensitivity and glare induced visual loss. Two different methods were used to estimate these functions before and after cataract extraction with implantation of a monofocal posterior intraocular lens. By one method intraocular light scattering was assessed. By the other, letter contrast sensitivity and glare induced visual loss were determined. Preoperatively most patients had various glare problems, glare induced visual loss and increased intraocular light scatter. Following surgery the letter contrast sensitivity increased by a factor of 3 or more (mean 4.3). The glare problems diminished or disappeared after surgery, although several patients still had increased intraocular light scattering and glare induced visual loss compared to normals. Postoperatively the contrast sensitivity both with and without glare had increased to a level where the glare induced visual loss did not create any visual problems.
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| 9. |
- Beckman, Claes, 1962-
(författare)
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Imaging through light scattering eye media : letter identification
- 1994
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Ingår i: Proc.SPIE. - : SPIE. ; 2079, s. 2079-2079
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Tidskriftsartikel (refereegranskat)abstract
- The influence of intraocular light scatter on letter identification in the absence and presence of glaring light is studied through computer simulations and simple experiments on healthy test subjects wearing diffusive glasses with known light scattering properties. An explicit expression for the point-spread function of a cataractous eye is used to calculate retinal images. For estimating resolution in the calculated images an assumed neural contrast sensitivity function is needed. The function used is derived from measurements by Campbell and Green. Experimental results are in agreement with theory. The analysis shows that visual acuity is quite insensitive even to substantial diffusive scattering provided that glare sources are not present in the field of view. Comparing measurements of ‘letter size’ with measurements of ‘letter contrast’ the latter method is found to measure intraocular light scattering more sensitively.
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| 10. |
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