PubMed · 15180590
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Kurt Simons. 2004. Hyperopia, accommodative dysfunction and reading.. https://pubmed.ncbi.nlm.nih.gov/15180590/
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BACKGROUND: Photorefraction can be carried out in both eyes simultaneously from a distance and is therefore suitable for examination of children. This study evaluated the accuracy of a commercially available photo-refractometer (Power Refractor, Plusoptix, Erlangen, Germany) and investigated whether the working distance relaxes the accommodation sufficiently without cycloplegia. METHODS: Photo-refractometer readings were compared to cycloplegic retinoscopy. Because of the limited working range the group of patients consisted of low and moderate ametropic eyes within a spherical power of -7.0 to +5.0 D. One hundred and ninety-two eyes from 104 patients (2-81 years) were photo-refracted under cycloplegia. A subgroup of 83 eyes from 46 patients was additionally refracted without cycloplegia. RESULTS: Under cycloplegia, the Power Refractor measured the spherical equivalent slightly below that of cycloplegic retinoscopy (too much minus). The mean difference in spherical equivalent was -0.12+/-0.91 D (SD). The mean difference of cylindrical power was -0.17+/-0.73 D. The mean weighted axis difference was 0.61+/-0.71 D which is comparable to an axis deviation of 18 degrees at a cylinder power of 1.00 D. Without cycloplegia, the mean difference of the spherical equivalent was -0.73+/-1.25 D. The mean difference of cylindrical power was -0.20+/-0.65 D. The mean weighted axis difference was 0.44+/-0.58 D which is comparable to an axis deviation of 13 degrees at a cylinder power of 1.00 D. CONCLUSIONS: Without cycloplegia, the spherical equivalent of the Power Refractor tends to be underestimated due to uncontrolled accommodation, especially in children. Cycloplegia improves the accuracy in evaluating the spherical equivalent, but decreases the accuracy of cylinder power and axis.
PURPOSE: The principal ability of potentially accommodative IOLs is based on an axial shift of the IOL optics induced by the ciliary body action in interaction with a reversible change in haptic angulation. The aim of this study was to investigate the accommodative performance of this new IOL generation. METHOD: The authors have designed a test device to study IOL performance experimentally. These results were extrapolated to the in vivo situation in patients with accommodative implants. RESULTS: The 3D high-resolution presentation of the anterior segment of the eye allows a separation of the IOL haptic elements. In vitro and in the selected in vivo cases a change in haptic angulation <10 degrees in combination with a maximal IOL shift of 0.5 mm was found. CONCLUSIONS: The simulation model used in combination with 3D ultrasound biomicroscopy provides information about the potential of accommodative IOL designs. Conclusions corresponding to changes in haptic angulation during accommodation can be drawn and applied to the in vivo situation.
The objective was to measure the change in shape of the aging human crystalline eye lens in vivo during accommodation. Scheimpflug images were made of 65 subjects between 16 and 51 years of age, who were able to accommodate at least 1D. The Scheimpflug images were corrected for distortion due to the geometry of the camera and the refraction of the cornea and anterior lens surface, which is necessary to determine the real shape of the lens. To ensure accurate correction for the refraction of the anterior lens surface, the refractive index of the crystalline lens must be determined. Therefore, axial length was also measured, which made it possible to calculate the equivalent refractive index of the lens and possible changes in this index during accommodation. The results show that during accommodation there is a decrease in both the anterior and the posterior radius of the lens, although the change in mm per diopter of the latter is much smaller. The increase in lens thickness with accommodation is higher than the decrease in the anterior chamber depth, indicating that the posterior lens surface moves backwards with accommodation. During accommodation the anterior lens surface becomes more hyperbolic. Furthermore, an increase in the equivalent refractive index during accommodation was determined.