This study evaluates the impacts of milling on the hardness and optical transmission of PMMA lenses using experimental and mathematical models. Three milling parameters, i.e., spindle speed, depth of cut, and feed rate, were evaluated. The machining levels were obtained from experimental trials. The experiments were designed using the Taguchi method, giving out 16 experiments. Sixteen workpieces were investigated for Shore D Hardness and optical transmission before and after milling, and the change was computed. The experimental analysis identified a reduction in Shore D Hardness and optical transmission after milling. The mathematical analyses using Taguchi analysis and ANOVA found out that for the absolute minimum change in Shore D Hardness, the milling parameters should be 5000 rpm (spindle speed), 0.3 mm (depth of cut), and 0.05 m/min (feed rate). Similarly, for the optical transmission, the parameters should be a spindle speed of 3750 rpm, a depth of cut of 1.2 mm, and a feed rate of 0.1 m/min. The analysis further identified the depth of cut to be the most dominant milling parameter toward the Shore D Hardness and optical transmission of PMMA lenses with a percentage impact of 12.77 and 42.51%, respectively. Thus, this study presents a model for conventional milling of PMMA for optical applications.