Purpose To evaluate the relationship between lens parameters and spherical equivalent refraction in the development of nuclear cataract following pars plana vitrectomy (PPV). Methods This prospective cohort study included patients who were scheduled for unilateral PPV surgery. All patients underwent subjective refraction, ocular biometry, and swept-source anterior segment optical coherence tomography (SS-ASOCT) before and after PPV. Lens power and equivalent refractive index were calculated based on the Bennett and Lensmaker formula, and lens nuclear density was quantified based on SS-ASOCT images. Results A total of 110 patients who developed nuclear cataract after PPV were included in the analysis, with a mean follow-up of 10.38 +/- 3.12 months. The operated eyes showed a myopia refractive shift (-2.81 +/- 2.36D), along with an increase in lens power, lens refractive index, and lens thickness, as well as a protruding of the radius of posterior lens surface. Multivariate linear regression analysis showed that the lens power was the main factor contributing to the myopic refractive shift (R-squared: 0.80, P < 0.001). Additionally, the refractive index of the lens was found to be the primary determinant of changes in the refractive power of lens (R-squared: 0.98, P < 0.001). Lens density showed a linear correlation with both the refractive index and lens power (correlation coefficient: 0.48 and 0.50, respectively). Conclusions Changes in lens refractive index are the main cause of lenticular myopia induced by nuclear cataract after PPV. Lens density can be used to assess the change of lens refractive index and lens power in vivo. Key Messages What is known center dot Lenticular myopia, with some changes in lens parameters, is the main cause of refractive changes following nuclear cataract development. What is new center dot During the development of lenticular myopia, the lens showed a thicker lens thickness, steeperradius ofposterior lens surface,shallower anterior chamber depth, as well as decreased lens tilt and decentration. center dot The refractive index of the lens is the main cause of lenticular myopia after pars plana vitrectomy.The correlation between the nuclear density and refractive index offers the possibility of an assessment of refractive index in vivo.