When recording the keratometry reading, the horizontal power reading is taken from the left side of the instrument; the vertical power reading is taken from the right side.

• A. Horizontal from left side; vertical from right side
• B. Horizontal from right side; vertical from left side
• C. Horizontal from top; vertical from bottom
• D. Horizontal from left side; vertical from top

Answer: (A)

Keratometry records curvature along two principal meridians, and the instrument is laid out so that each meridian is associated with a specific side of the instrument’s scales. The horizontal meridian uses the left-side scale, while the vertical meridian uses the right-side scale. This design keeps the readings consistent as you rotate the instrument to measure different meridians and helps you document the two keratometry powers accurately. Readings from the opposite sides would misalign the meridians with the scales, and using top or bottom would not match how the device is calibrated for these measurements.