A Keratometer measures the central ______ mm of the cornea.

A Keratometer measures the central ______ mm of the cornea.

• A. 2
• B. 3
• C. 4
• D. 5

Answer: (B)

Keratometry focuses on the curvature of the cornea in the central 3 mm. This zone is used because it’s the most regular part of the cornea and the portion that most strongly determines refractive power and is most important for fitting contact lenses. The instrument projects mire patterns onto the cornea and analyzes the reflected image to calculate the radius of curvature of that central area. Moving outward beyond about 3 mm introduces more peripheral variation and measurement inaccuracy, so the standard measurement is the central 3 mm.

Keratometry focuses on the curvature of the cornea in the central 3 mm. This zone is used because it’s the most regular part of the cornea and the portion that most strongly determines refractive power and is most important for fitting contact lenses. The instrument projects mire patterns onto the cornea and analyzes the reflected image to calculate the radius of curvature of that central area. Moving outward beyond about 3 mm introduces more peripheral variation and measurement inaccuracy, so the standard measurement is the central 3 mm.