Biomedical subjects

Patricia A Piers

Publications and source records attributed to Patricia A Piers.

5 recordsLinked to original sources

PubMed2004

Eye models for the prediction of contrast vision in patients with new intraocular lens designs.

Theoretical calculations of the polychromatic modulation transfer function (MTF) and wave-front aberration were performed with physiological eye models. These eye models have an amount of spherical aberration that is representative of a normal population of pseudophakic eyes implanted with two different types of intraocular lens (IOL) made from high-refractive-index silicone. These theoretical calculations were compared with the measured contrast sensitivity function (CSF) under mesopic lighting conditions and with wave-front aberration (obtained with a Hartmann-Shack wave-front sensor) collected from 37 patients bilaterally implanted with the same types of lens. The relationships between the ocular wave-front aberration and the MTF predicted by the eye models and the CSF and the ocular wave-front aberration measured in eyes implanted with IOLs were investigated. The predicted improvements in MTF and wave-front aberration correlated well with the improvements measured in practice. Physiological eye models are therefore useful tools for IOL design.

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PubMed2004

Improved functional vision with a modified prolate intraocular lens.

PURPOSE: To evaluate whether the Tecnis Z9000 intraocular lens (IOL) (Pfizer) with a modified prolate anterior surface provides better quality of vision than a conventional spherical IOL. SETTING: Oregon Eye Institute, Eugene, Oregon, USA. METHODS: Patients presenting for cataract surgery who were randomly assigned to receive a Tecnis Z9000 IOL (Pfizer) or a Sensar OptiEdge AR40e IOL (AMO) in 1 eye were followed for 3 months postoperatively. The patient could elect to have the same type of IOL implanted in the fellow eye. The results of sine-wave grating contrast sensitivity testing under mesopic and photopic conditions were compared interindividually. RESULTS: Monocular comparison was made between the 2 IOL groups, which comprised 15 patients each. The Tecnis IOL provided significantly better contrast sensitivity at 6 cycles per degree (cpd) under photopic conditions and at 1.5 and 3 cpd under mesopic conditions. Seven patients with a Tecnis IOL and 9 patients with an AR40e IOL had subsequent implantation in the fellow eye. In all eyes, including fellow eyes, having IOL implantation, the Tecnis provided significantly better contrast sensitivity at 3 and 6 cpd under photopic conditions and at 1.5, 3, and 6 cpd under mesopic conditions. The mean contrast sensitivity in fellow eyes showed that the Tecnis IOL produced significantly better results at some spatial frequencies. CONCLUSIONS: Results show the Tecnis IOL with a modified prolate anterior surface may produce better contrast sensitivity than a standard spherical IOL under mesopic and photopic conditions. Because contrast sensitivity testing correlates well with functional vision, a goal of future research should be to evaluate patient performance using functional tests such as driving simulation.

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PubMed2004

Adaptive optics simulation of intraocular lenses with modified spherical aberration.

PURPOSE: Adaptive optics systems can be used to investigate the potential visual benefit associated with correcting ocular wave-front aberration. In this study, adaptive optics techniques were used to evaluate the potential advantages and disadvantages associated with intraocular lenses (IOLs) with modified spherical aberration profiles. METHODS: An adaptive optics vision simulator was constructed that allows psychophysical tests to be performed while viewing targets through any desired ocular wave-front profile. With this simulator, the subjective visual performance of four subjects was assessed by letter acuity and contrast sensitivity (at 3, 6, and 15 cyc/deg) for two different values of induced spherical aberration. The values of spherical aberration were chosen to reproduce two conditions: the average amount measured in pseudophakic patients with implanted IOLs having spherical surfaces and the complete correction of the individual's spherical aberration. Visual performance was assessed in both white and green light, at best focus and for defocus of +/-0.5 and +/-1.0 D. RESULTS: There was an average improvement in visual acuity associated with the correction of spherical aberration of 10% and 38% measured in white and green light, respectively. Similarly, average contrast sensitivity measurements improved 32% and 57% in white and green light. When spherical aberration was corrected, visual performance was as good as or better than for the normal spherical aberration case for defocus as large as +/-1 D. CONCLUSIONS: Correcting ocular spherical aberration improves spatial vision in the best-focus position without compromising the subjective tolerance to defocus.

Adult↗

PubMedDate not supplied

A new intraocular lens design to reduce spherical aberration of pseudophakic eyes.

PURPOSE: The aim of this study was to design and evaluate in the laboratory a new intraocular lens (IOL) intended to provide superior ocular optical quality by reducing spherical aberration. METHODS: Corneal topography measurements were performed on 71 cataract patients using an Orbscan I. The measured corneal surface shapes were used to determine the wavefront aberration of each cornea. A model cornea was then designed to reproduce the measured average spherical aberration. This model cornea was used to design IOLs having a fixed amount of negative spherical aberration that partially compensates for the average positive spherical aberration of the cornea. Theoretical and physical eye models were used to assess the expected improvement in optical quality of an eye implanted with this lens. RESULTS: Measurements of optical quality provided evidence that if this modified prolate IOL was centered within 0.4 mm and tilted less than 7 degrees, it would exceed the optical performance of a conventional spherical IOL. This improvement occurred without an apparent loss in depth of focus. CONCLUSION: A new IOL with a prolate anterior surface, designed to partially compensate for the average spherical aberration of the cornea, is intended to improve the ocular optical quality of pseudophakic patients.

Adult↗

PubMedDate not supplied

Prospective randomized trial of an anterior surface modified prolate intraocular lens.

PURPOSE: We compare the contrast sensitivity obtained with an anterior surface modified prolate intraocular lens with the contrast sensitivity obtained with a standard spherical intraocular lens. METHODS: Patients presenting for cataract surgery in one eye were randomized to receive either the Tecnis Z9000 intraocular lens (Pharmacia) or the AMO AR40e Opti-Edge intraocular lens (AMO). Sine wave grating contrast sensitivity testing under mesopic and photopic conditions served as the principal outcome measure. RESULTS: The Tecnis Z9000 intraocular lens provided statistically significantly better contrast sensitivity at 1.5 and 3 cycles per degree under mesopic conditions and at 6, 12 and 18 cycles per degree under photopic conditions. CONCLUSION: The use of a modified prolate intraocular lens during cataract surgery has the potential to improve contrast sensitivity under both mesopic and photopic conditions.

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