To flatten the lens to cornea relationship in a gas permeable lens fit with parameters of 42.50-3.00 9.5, which lens should be ordered?

To understand why ordering a lens with the parameters of 42.50-3.00 9.0 is the appropriate choice to flatten the lens to cornea relationship in this scenario, consider the specific adjustments that need to be made to achieve the desired fit.

In this case, the goal is to flatten the lens in relation to the cornea, which typically involves either increasing the base curve or reducing the power of the lens. The original lens has a base curve of 42.50, and to achieve a flatter fit, you would ideally want to maintain or decrease the curvature slightly.

Ordering a lens with a base curve of 42.50 but a reduced thickness (the 9.0 measurement) retains the baseline curvature while slightly reducing the vault over the cornea, which provides a flatter relationship overall. The power is adjusted to a less negative value, which will also help achieve the intended fit.

Other choices either maintain or increase the curvature or change the lens parameters in such a way that they do not effectively achieve the intended flattening. For instance, a base curve of 43.0 or 43.50 would be steeper, leading to a more pronounced fitting relationship that is the opposite of what is desired.