Final answer:
A multifocal contact lens is designed to provide corrective features for different vision distances in one lens. They are especially useful for presbyopia. Optometrists can adjust their power, measured in diopters, to correct for specific vision needs.
Step-by-step explanation:
A multifocal contact lens is designed to provide correction for multiple vision distances in a single lens. This type of lens has different optical powers to correct presbyopia, the age-related loss of near focusing ability. The design of multifocal contacts may vary, with some having a gradual change in power from the center to the edge of the lens, similar to progressive eyeglass lenses, and others having distinct zones for near, intermediate, and distance vision. The lenses work by optimizing the power selections based on where the eye is looking through the contact lens. Skilled optometrists will adjust the power of these contacts to suit the specific visual needs of their patients.
Consider the situation where the curvature of the contact lens does not match the curvature of the cornea. Here, the tear layer between the lens and the cornea can function as an additional lens. For instance, if the tear layer is thinner in the center than at the edges, it can act with negative optical power. Optometrists measure optical power in diopters (D). The right adjustment of diopters by an optometrist can correct various eye conditions, like myopia or hyperopia, ensuring a patient's comfort and clear vision.