How does the power of a dry contact lens compare with its power when resting on the tear layer of the eye? Explain.
The combination of the lens and the tear film on the eye provides the total power of the contact lens or liquid lens power. A portion of the lens, surrounded by the peripheral fitting curves acts as the optical zone of the contact lenses.
The tear layer has less effect on contact lens power, if lens is in perfect alignment onto the cornea. The degree of clearance of the lens enables the tear film to have a power effect on cornea/tear/lens system. Inadequate watery layer in the tear film causes dry eyes. As such the contact lenses become uncomfortable to wear.