Which formula gives the radius of a GP lens when the base curve diopters are known?

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Multiple Choice

Which formula gives the radius of a GP lens when the base curve diopters are known?

Explanation:
Understanding how curvature expressed as diopters relates to a physical radius is key. In keratometry, the curvature (in diopters) and the radius (in millimeters) are linked by the equation D = 337.5 / R_mm. To get the radius from the diopters, you solve for R_mm: R_mm = 337.5 / D. So the radius is found by dividing 337.5 by the base-curve diopters, giving a result in millimeters. The constant 337.5 comes from the tear film refractive index used in keratometry and the conversion from meters to millimeters; note that a higher diopter means a steeper curve and thus a smaller radius.

Understanding how curvature expressed as diopters relates to a physical radius is key. In keratometry, the curvature (in diopters) and the radius (in millimeters) are linked by the equation D = 337.5 / R_mm. To get the radius from the diopters, you solve for R_mm: R_mm = 337.5 / D. So the radius is found by dividing 337.5 by the base-curve diopters, giving a result in millimeters. The constant 337.5 comes from the tear film refractive index used in keratometry and the conversion from meters to millimeters; note that a higher diopter means a steeper curve and thus a smaller radius.

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