When cataract patients are treated surgically, they usually retain about 50 degrees of near vision and have a better quality of vision. Cataracts are treated with surgery, which involves the implantation of an IOL with a dioptric lens inside the eye. The implanted IOL needs to be calculated during the pre-surgical examination and usually preserves about 50 degrees of myopia for the patient after the surgery. This is because 50 diopters of myopia will have less of an impact on the patient’s distance vision, while at the same time helping to improve the patient’s near vision. If the implanted lenses are not preserved and the patient is completely orthokeratotic, the patient will have better distance vision but blurred near vision.