A 2D flatter K makes a tear lens of what power?

A 2D flatter K makes a tear lens of what power?

• A. -4 D
• B. 0 D
• C. +2 D
• D. -2 D

Answer: (D)

When a contact lens sits on the eye, the tear film between the cornea and the lens acts as its own thin lens, adding or subtracting optical power from the system depending on how the two curved surfaces compare. The tear layer tends to oppose the curvature difference between the cornea and the lens. If the cornea is 2 diopters flatter than the lens, the tear film that fills the gap takes on a shape that provides negative power of the same magnitude. In other words, the tear lens acts as a minus 2 diopter lens. This is because a flatter surface between the eye and the lens creates a diverging effect, reducing the overall convergence produced by the cornea and lens combination. So the tear lens power in this scenario is -2 D.

When a contact lens sits on the eye, the tear film between the cornea and the lens acts as its own thin lens, adding or subtracting optical power from the system depending on how the two curved surfaces compare. The tear layer tends to oppose the curvature difference between the cornea and the lens.

If the cornea is 2 diopters flatter than the lens, the tear film that fills the gap takes on a shape that provides negative power of the same magnitude. In other words, the tear lens acts as a minus 2 diopter lens. This is because a flatter surface between the eye and the lens creates a diverging effect, reducing the overall convergence produced by the cornea and lens combination.

So the tear lens power in this scenario is -2 D.