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- Eklund, Anders, et al.
(författare)
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An applanation resonator sensor for measuring intraocular pressure using combined continuous force and area measurement
- 2003
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Ingår i: Investigative Ophthalmology and Visual Science. - : Association for Research in Vision and Ophthalmology (ARVO). - 0146-0404 .- 1552-5783. ; 44:7, s. 3017-24
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: For diagnostic purposes and for follow-up after treatment, it is important to have simple and reliable methods for measuring intraocular pressure (IOP). The purpose of this study was to develop a new applanation method for IOP measurement that uses combined continuous force and area measurement and to develop and evaluate an applanation resonator sensor (ARS) tonometer based on that method. METHODS: The tonometer was developed and evaluated in an in vitro porcine eye model, in which enucleated eyes were pressurized with a saline column. A model assuming that the applanation principle is valid over a certain interval of contact area was proposed. Continuous contact area was measured with a resonator sensor device, and contact force was measured with a force transducer, both mounted together in one probe. Reference IOP was measured in the vitreous chamber (IOP(VC)) with a standard fluid pressure transducer. RESULTS: An optimization algorithm determined the applanation interval that was optimal for calculating IOP(ARS). The corresponding time interval was 30 +/- 3 to 77 +/- 4 ms (mean +/- SD, n = 418) after initial contact. The proposed model showed a degree of explanation of R(2 [supi]) = 0.991 (n = 410, six eyes), corresponding to a correlation of r = 0.995 (n = 410) between IOP(ARS) and IOP(VC). The within-eyes precision (i.e., 95% confidence interval for the residuals between IOP(ARS) and IOP(VC)) was +/- 1.8 mm Hg (n = 410, six eyes). CONCLUSIONS: In this study, the ARS method for measuring IOP was evaluated in an in vitro porcine eye model and showed high precision. The ARS method is, to the authors' knowledge, the first to combine simultaneous, continuous sampling of both parameters included in the applanation principle: force and area. Consequently, there is a potential for reducing errors in clinical IOP tonometry.
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- Rosén, Robert, et al.
(författare)
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Influence of Optical Defocus on Peripheral Vision
- 2011
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Ingår i: Investigative Ophthalmology and Visual Science. - : Association for Research in Vision and Ophthalmology (ARVO). - 0146-0404 .- 1552-5783. ; 52:1, s. 318-323
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE. Peripheral optical corrections are often thought to give few visual benefits beyond improved detection acuity. However, patients with central visual field loss seem to benefit from peripheral correction, and animal studies suggest a role for peripheral vision in the development of myopia. This study was conducted to bridge this gap by systematically studying the sensitivity to optical defocus in a wide range of peripheral visual tasks. METHODS. The spatial frequency threshold for detection and resolution in high and low contrast with stationary and drifting gratings were measured off-axis (20 nasal visual field) in five subjects with a peripheral optical correction that was varied systematically +/- 4 D. RESULTS. All visual tasks, except high-contrast resolution, were sensitive to optical defocus, particularly low-contrast resolution with an increase of up to 0.227 logMAR/D. The two myopic subjects exhibited a very low sensitivity to defocus by negative lenses for low-contrast tasks, whereas all subjects were equally affected by myopic defocus. Contrary to expectations, drifting gratings made little difference overall. CONCLUSIONS. Optical defocus as low as 1 D has a large impact on most peripheral visual tasks, with high-contrast resolution being the exception. Since the everyday visual scenery consists of objects at different contrast levels, it is understandable that persons with central visual field loss are helped by correction of peripheral refractive errors. The asymmetry in sensitivity to peripheral optical defocus in low-contrast tasks that was experienced by the myopic subjects in this study merits further investigation.
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