Chemotherapy drugs, used in cancer treatments, may change the timing of a vision condition known as presbyopia. Presbyopia is the inability to focus the eye on close objects, by a process called accommodation. It is caused by an increase in the stiffness of the lens of the eye that occurs naturally with aging. Currently, there are no known treatments that can be used to prevent or delay presbyopia. As a result, the risk, in later life, of having this condition is essentially 100%.