Upon initial insertion of a GP lens, the patient complains about flare. To correct this problem, the fitter should choose a lens with a/an:

When a patient experiences flare upon the initial insertion of a gas permeable (GP) lens, it typically indicates that there is an issue with the lens design in relation to how light is entering the eye. Choosing a lens with an increased optical zone helps to enhance the central area of the lens that contributes to clearer vision and reduced optical aberrations.

An increased optical zone allows for better light passage and can help minimize flare by providing a larger area that aligns better with the pupil's diameter and the corneal curvature. This is particularly beneficial if the flare results from lens-induced optical distortions or poor alignment with the eye.

In contrast, adjusting the base curve, whether increased or flattened, primarily affects how the lens sits on the eye, altering the fit and possibly impacting comfort but not directly addressing the light performance that contributes to flare. Additionally, a decreased optical zone could compound the issue rather than resolve it, as it would limit the area through which light can pass effectively. Therefore, opting for a lens with an increased optical zone is the most effective solution to alleviate flare issues in this context.