Contact lenses are used by millions of people worldwide to correct vision impairments. The mechanical interactions between the lens and the eye are not fully understood and difficult to access in the clinic. We developed a mathematical model of the mechanical interactions between the lens and the eye to predict the ocular stress load due to contact lens wear, accounting for the effect of intraocular pressure (IOP). The eye and lens models are coupled non-linearly via the suction pressure under the lens. We developed the reference configuration algorithm (RCA) that predicts iteratively the stress-free ocular reference configuration, given the desired eye shape in the presence of IOP. We conducted an analysis on the effects of IOP and the eye and lens shapes on the deformation and stress of the ocular surface due to contact lens wear. The final aim of this work is to improve contact lens design and fitting process by predicting ocular deformations and ocular stress load before wearing the lens.