What is the lacrimal lens power of a -4.00 sph soft contact lens? (repeated question variant)

• A. -4.00D
• B. -2.00D
• C. 0D
• D. +4.00D

Answer: (C)

The lacrimal lens refers to the tear film that sits between the back surface of the contact lens and the cornea. Its power depends on the curvature of those two refracting surfaces and the small thickness of the tear layer. In soft contact lens wear, the tear film is extremely thin and the two opposing refracting surfaces are close together, with only modest refractive index changes. Because of this, the tear layer contributes essentially no net dioptric power. Put simply, the tear film acts almost like a neutral layer in this setup.

So, even though the contact lens itself has a power of -4.00 D to correct the refraction, the lacrimal (tear) lens power remains about zero. That’s why the lacrimal lens power is approximately 0 diopters.