There are described an excimer laser unit and a method of controlling the unit to perform cornea ablation to reduce presbyopia, wherein the excimer laser unit is controlled to form on the cornea a photoablative pattern inducing a fourth-order ocular aberration, in particular a positive spherical aberration. More specifically, an aberrometric map of the eye is first acquired indicating the visual defects of the eye, which include second-order visual defects such as hypermetropia, astigmatism, and myopia, and higher-order visual defects such as spherical aberration if the detected spherical aberration is negative, it is reduced by numerically increasing its absolute value to obtain an overcorrect photoablative inducing positive spherical aberration conversely, if the detected spherical aberration is positive, its sign is changed and its absolute value increased numerically to obtain an overcorrect photoablative pattern inducing positive spherical aberration and the photoablative pattern so generated is supplied to the excimer laser unit for implementation on the cornea.
