What is the difference between centration and movement of a contact lens on blinking?

What is the difference between centration and movement of a contact lens on blinking?

• A. Centration refers to lens alignment over the pupil; movement is lens displacement with blink; both affect vision and comfort.
• B. Both terms refer to the lens surface coating.
• C. Centration is vertical movement; movement is horizontal.
• D. Centration is lens rotation; movement is lens tilt.

Answer: (C)

The main idea here is distinguishing where the lens sits versus how it moves with a blink. Centration is about the lens lining up over the pupil center on the cornea—the lens should sit centered so the pupil is visually properly covered. Movement is the lens sliding on the tear film when you blink; a small amount of downward displacement with each blink is normal and helps tear exchange, while too much movement or decentration can blur vision or feel uncomfortable. So the best concept is that centration is lens alignment over the pupil, while movement refers to the lens displacing with blinking; both factors influence vision clarity and comfort. The other ideas misstate centration as a surface coating or reduce movement to a single direction, which doesn’t reflect how lenses sit and shift on the eye.

The main idea here is distinguishing where the lens sits versus how it moves with a blink. Centration is about the lens lining up over the pupil center on the cornea—the lens should sit centered so the pupil is visually properly covered. Movement is the lens sliding on the tear film when you blink; a small amount of downward displacement with each blink is normal and helps tear exchange, while too much movement or decentration can blur vision or feel uncomfortable.

So the best concept is that centration is lens alignment over the pupil, while movement refers to the lens displacing with blinking; both factors influence vision clarity and comfort. The other ideas misstate centration as a surface coating or reduce movement to a single direction, which doesn’t reflect how lenses sit and shift on the eye.