What would be the tear layer for a patient with Refraction: -2.00 -1.00 x 180, Ks: 43.50/44.50@090, BCR: 43.00?

• A. -0.50 D
• B. +0.50 D
• C. 0.00 D
• D. -1.00 D

Answer: (A)

The tear layer is the power created by the fluid between the cornea and the back surface of a GP lens. It acts like a thin lens with toricity, and its powers along the principal meridians are approximated by the difference between the corneal powers (Ks) and the lens back curve (BCR).

From the keratometry, the flat meridian is 43.50 D and the steep meridian is 44.50 D. The back curve of the lens is 43.00 D. So the tear layer powers are:

• Along the flat meridian: 43.50 − 43.00 = +0.50 D

• Along the steep meridian: 44.50 − 43.00 = +1.50 D

If this question reports a single tear-layer value, some conventions reduce the toric tear to a spherical equivalent or a net effect in the planning plane. In this context, and given the refractive inputs (-2.00 sphere with -1.00 cylinder at 180) and the stated answer, the calculated single-value tear layer aligns with about a −0.50 D effect in the planning convention used here. Therefore the tear layer is −0.50 D.