Measurement of spectacle lenses using wavefront aberration in real view condition

Freeform gradient index progressive addition lens raytrace performance evaluation

Raytrace evaluation capable of evaluating progressive addition lens (PAL) designs with freeform surface and gradient index (GRIN) contributions is presented. The method is validated on an analytically generated PAL start design and on optimized surface designs. Surface raytrace evaluations are compared with the surface-geometric evaluation commonly presented for freeform surface PAL designs. The evaluation is also tested on analytically generated freeform GRIN PAL designs with spherical and plano surfaces. The raytrace method agrees with the analytic performance and surface-geometric performance near the center of the lens and deviates at the edge of the lens, due to ray obliquity with the surfaces and aggregate contributions of surfaces and/or GRIN. These deviations are expected, as the raytrace model accounts for more physical contributions to optical performance, including pupil diameter and eye position. This raytrace method enables the evaluation of lens performance contributions other than from polished surfaces on homogeneous materials, enabling further exploration of GRIN in PAL designs.

Diopter measurement based on an artificial neural network

The measurement of the diopters of spectacle lenses using an artificial neural network is proposed in this paper. A diopter is measured by obtaining the distances between the spots imaged by a charge-coupled device (CCD) during a Hartmann test. Backpropagation (BP) and a radial basis function (RBF) algorithm are applied to train the BP and RBF neural networks, respectively. A set of -20D to 20D spectacle lenses is used to test the proposed method. When comparing the diopter measurement results of the RBF neural network with those of the BP neural network, the former exhibited higher stability and lower errors. In addition, the errors of diopter measurement are not against the system error measured by an auto-focimeter due to the increase of curvature of spectacle lenses. These results indicated that RBF neural network has better performance in diopter detection, and it can overcome the system error caused by the change of lens curvature in auto-focimeter measurement.

Null screens to evaluate the shape of freeform surfaces: progressive addition lenses

We propose a method for measuring the shape of freeform surfaces such as Progressive Addition Lenses (PAL). It is based on optical deflectometry by considering a non-uniform pattern of spots computed by using the null-screen method. This pattern is displayed on a flat LCD monitor being reflected on the freeform under test and whose image is recorded on a CCD camera placed at a predefined off-axis position. We use one image to calibrate the experimental setup and another to measure the freeform surface. We develop an iterative algorithm to retrieve the surface under test and calculate the spherical and cylindrical dioptric powers of the frontal freeform of a commercial PAL under test.

Optical performance of progressive addition lenses (PALs) with astigmatic prescription

The progressive addition lens (PAL) is a spectacle lens design with progressive refractive power changes across the lens surface to provide sharp vision at different viewing distances for patients with reduced accommodative strength. It has gained in popularity not just for presbyopic patients, but also patients with occupational (office, driving, or digital device) and therapeutic (e.g., myopia control) needs. However, despite the increasing prevalence of astigmatism in adults > 40 years old who rely on PAL correction, no metric is available to reflect the optical variation in PALs with astigmatic prescriptions. Based on recent studies, four novel optical metrics sensitive to variation of refractive power across the lens surface of PALs have been developed. These metrics were used to compare the optical performance of PALs of various prescriptions, designs, and manufacturers. For each lens, the refractive power profile was first measured with a Moire-deflectometry-based instrument.The data was then exported and analyzed using a two-dimensional error map for each of the four metrics. The results revealed significant impacts of astigmatic prescription, providing evidence for the usefulness of these metrics in quantifying the optical performance of PALs for patients with astigmatic prescriptions.

Method for evaluating ophthalmic lens based on Eye-Lens-Object optical system

We propose an evaluation method to judge the fitting extent to ophthalmic lens for the individual wearer. An Eye-Lens-Object optical system is set according to wearer's visual performance and the characteristic of ophthalmic lens assembly. A visual reference surface is proposed to calculate the object distance. The RMS radius of the spot diagram and MTF average value from optical design software Zemax are regarded as the criterion of assessing the image quality on the retina. Three cases are simulated to verify that our method is effective. The wearers can experience a comfortable wearing feeling when the evaluation method is used during the design of ophthalmic lens. The validity of our method is demonstrated to instruct designing the progressive addition lens with the freeform surface.