What is a way to test to see if a lens is inverted?

The taco test is used to determine if a contact lens is inverted. This test involves taking the lens and gently squeezing it between the thumb and index finger to see how it behaves. When the lens is not inverted, it forms a "taco" shape, curving outward on both sides. If the lens is inverted, it will not take this shape and may instead have a flatter profile.

This method effectively distinguishes between an inverted and correctly oriented lens, ensuring that the practitioner can confirm proper insertion before fitting the lens on a patient or ensuring its correct use. The other methods listed may not be standard or effective approaches for testing lens orientation in the context of contact lens fitting.