CPO Study Guide 2026

The lensometer inker stamps dots marking the optical center (and flanking reference points) so the lens is correctly aligned during edging and frame mounting.

While a keratometer measures only a few central points on the cornea, a corneal topographer maps the curvature of the entire corneal surface. This provides a much more detailed view, which is essential for detecting irregular astigmatism, keratoconus, and for planning refractive surgery.

A special calibration bar is used to check the accuracy of a Goldmann tonometer at three specific settings: 0, 2, and 6. This corresponds to 0, 20, and 60 mm Hg. This check should be performed regularly to ensure accurate intraocular pressure measurements.

ANSI Z80.1 specifies a tolerance of ±0.12 D for add power; a discrepancy greater than this requires the lenses to be returned to the laboratory for remake.

These are classic symptoms of a retinal detachment, which is a medical emergency. The flashes are caused by the retina pulling away from its underlying tissue, and the 'curtain' represents the area of the retina that has detached and is no longer functioning.

Topography maps use a color scale to represent corneal power, which is related to curvature. Hot colors (reds, oranges) indicate steeper areas with higher power, while cool colors (blues, greens) indicate flatter areas with lower power.