When the tear layer is minus, what adjustment is typically required to neutralize the final spherical power?

• A. Add more minus power
• B. Add more plus power
• C. No adjustment
• D. Add more plus power (alternative phrasing)

Answer: (D)

The tear film between the cornea and the contact lens acts like a small lens and contributes to the eye’s overall refractive power. If that tear layer has minus power, it behaves as a diverging lens and reduces the eye’s net converging power. To bring the final spherical power back to the desired value, you compensate by increasing the lens power in the plus direction. In other words, you add more plus power to neutralize the negative tear-layer effect. For example, if the tear film adds -0.50 D of power, you would increase the lens power by +0.50 D to maintain the intended final correction. Adding more minus power or making no adjustment would not counteract the tear film’s negative effect, whereas adding plus power directly offsets it.