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Research on the influence of the near vision area on the width of the astigmatism channel based on the minimization model

Freeform progressive addition lenses (PALs) are mainly divided into distance vision zone, near vision zone, astigmatism channel and peripheral astigmatism zone. The purpose of this study was to compare the effect of the width of the astigmatism channel by changing the near vision area of PALs on the basis of the minimal model method. The change of the near vision area was mainly achieved by changing the distribution function of the main curvature difference and the average curvature weight. Firstly, two weight distribution matrices of different near vision areas were designed, and the second-order partial differential equations of the minimized model were solved by the finite element method. The surface shape of two PALs was obtained. Secondly, the freeform verifier software (FFV) (ROTLEX, Israel) was used to simulate the shapes of the obtained surfaces, and used computer numerical control machine tools to process two groups of PALs. Finally, the Visionix VM-2500 lens measuring instrument was used to measure the PALs. The simulated and measured power and astigmatism distribution contours showed that the width of the astigmatism channel increased with the increase of the near vision area, however, the peripheral astigmatism was increased. Therefore, the near vision zone with an appropriate area can provide a reference for the optimal design of PALs.