Q: I am a 24 years old boy having -2 spherical and -1 cylindrical power in both the eyes. I have opted for contact lenses, but the doctor advised me lenses of power -2.5. Is it correct to wear lens of power -2.5?

A:Yes, what your contact lens specialist has advised is absolutely right because when we calculate effective power, we add spherical power + half of cylindrical power giving you -2.50 spherical. Most of the cylindrical defect arises from the corneal curvature at the front of the eye. When you wear contact lens, it is not just the contact lens power but the (capillary) fluid between the cornea and contact lens evens out the effect of corneal curvature and in effect works like a spherical lens. Not only it corrects the power, it also improves the quality and field of vision by equalising image size on the retina, which is closer to normal as compared to spectacle lens.