Multi-toric optical element to compensate ocular astigmatism with increased tolerance under rotation.

A new, to the best of our knowledge, optical element designed to compensate regular astigmatism while exhibiting increased tolerance to rotational misalignment is introduced. The element incorporates an optical design based on concentric annular regions with slightly different cylindrical axis angular positions. To assess visual quality performance as a function of rotation, retinal image simulation and clinical assessments with an adaptive optics visual simulator were carried out. The results demonstrate the superior performance of the newly proposed element in the presence of rotational errors when compared to traditional solutions.

Repeatability and Reproducibility of Virtual Subjective Refraction.

PURPOSE: To establish the repeatability and reproducibility of a virtual refraction process using simulated retinal images. METHODS: With simulation software, aberrated images corresponding with each step of the refraction process were calculated following the typical protocol of conventional subjective refraction. Fifty external examiners judged simulated retinal images until the best sphero-cylindrical refraction and the best visual acuity were achieved starting from the aberrometry data of three patients. Data analyses were performed to assess repeatability and reproducibility of the virtual refraction as a function of pupil size and aberrometric profile of different patients. RESULTS: SD values achieved in three components of refraction (M, J0, and J45) are lower than 0.25D in repeatability analysis. Regarding reproducibility, we found SD values lower than 0.25D in the most cases. When the results of virtual refraction with different pupil diameters (4 and 6 mm) were compared, the mean of differences (MoD) obtained were not clinically significant (less than 0.25D). Only one of the aberrometry profiles with high uncorrected astigmatism shows poor results for the M component in reproducibility and pupil size dependence analysis. In all cases, vision achieved was better than 0 logMAR. A comparison between the compensation obtained with virtual and conventional subjective refraction was made as an example of this application, showing good quality retinal images in both processes. CONCLUSIONS: The present study shows that virtual refraction has similar levels of precision as conventional subjective refraction. Moreover, virtual refraction has also shown that when high low order astigmatism is present, the refraction result is less precise and highly dependent on pupil size.

Retinal Image Simulation of Subjective Refraction Techniques.

Refraction techniques make it possible to determine the most appropriate sphero-cylindrical lens prescription to achieve the best possible visual quality. Among these techniques, subjective refraction (i.e., patient's response-guided refraction) is the most commonly used approach. In this context, this paper's main goal is to present a simulation software that implements in a virtual manner various subjective-refraction techniques--including Jackson's Cross-Cylinder test (JCC)--relying all on the observation of computer-generated retinal images. This software has also been used to evaluate visual quality when the JCC test is performed in multifocal-contact-lens wearers. The results reveal this software's usefulness to simulate the retinal image quality that a particular visual compensation provides. Moreover, it can help to gain a deeper insight and to improve existing refraction techniques and it can be used for simulated training.

Sphero-cylindrical error for oblique gaze as a function of the position of the centre of rotation of the eye.

PURPOSE: New designs of ophthalmic lenses customised for particular wearing conditions (e.g., vertex distance or wrap tilt angle) have emerged during the last few years. However, there is limited information about the extent of any improvement in visual quality of these products. The aim of this work was to determine whether customisation according to the centre of rotation of the eye (CRE) improves visual quality for oblique gaze in monofocal spherical lenses. METHODS: Conventional spherical lenses were designed by numerical ray tracing with back vertex powers (BVP) ranging from +8 to -8 dioptres (D) and base curves from 0 to 8 D. The wavefront error at oblique gaze (40°) was computed for each design with CRE positions from 20 to 35 mm. Sphero-cylindrical (SC) error was calculated using wavefront Zernike coefficients, considering only monochromatic aberrations. Visual acuity in logMAR was estimated following the Raasch empirical regression model. RESULTS: SC error and visual acuity maps were calculated for each BVP as a function of base curves and CRE in a graded colour scale. From SC error maps maximum spherical and cylindrical errors (MSE and MCE) of 1.49 D and -1.24 D respectively were found for BVP from 0 to -2 D, 2.27 D and -1.90 D for BVP from -2 D to -4 D, 2.59 D and -2.20 D for lenses from -4 D to -6 D and 2.63 D and -2.28 D for lenses from -6 D to -8 D. Concerning positive lenses, we obtained MSE and MCE of 0.37 D and -1.35 D respectively for lenses from 0 D to +2 D, 0.39 D and -2.23 D for lenses from +2 D to +4 D and 0.36 D and -2.73 D for lenses from +4 D to +6 D. Regarding visual acuity maps for 40° oblique gaze, significant loss of visual acuity (>0.30 logMAR, Snellen 6/12, 20/40, decimal 0.50) was found for BVP as low as -2 D. Clinically negligible high order aberration levels (equivalent spherical power <0.25 D) were found for all cases. CONCLUSIONS: We calculated SC error and visual acuity maps as a function of base curves and CRE position for a set of spherical lenses at oblique gaze. These maps could be useful as a clinical guide to select the best base as a function of CRE and BVP for each patient. It was found that negative lenses with low BVP provided high SC error when they were designed with low bases. However, high BVP negative lenses with low SC error were found for medium bases and low CRE or for low bases and high CRE positions. In the case of positive lenses, the dependence of SC error with CRE position was less noticeable. Finally, high order aberrations did not have a significant influence over visual quality.