OPTE: Refraction and Refractive Error Assessment

This domain tests the sequence, logic and endpoints of refraction: objective findings, subjective refinement, and how accommodation and vertex distance distort the result.

The sequence

1. Objective estimation (retinoscopy or autorefractor).
2. Sphere to best vision, then fog to relax accommodation.
3. Cylinder axis with the Jackson cross-cylinder, then cylinder power, then re-check axis.
4. Sphere refinement, then duochrome as a final check - clearer on red suggests more minus is needed, clearer on green suggests more plus.
5. Binocular balance and final acuity recording.

Rules worth memorising

• Subtract the working distance in dioptres from the sphere only: at 67 cm, subtract 1.50 D; at 50 cm, subtract 2.00 D.
• Correct vertex distance when the power exceeds about ±4.00 D.
• Anisometropia above roughly 1.00 D in a child warrants amblyopia surveillance; aniseikonia matters above ~2.50 D difference.
• Amplitude of accommodation declines with age; the push-up technique overestimates the near point.

Worked example

Retinoscopy at 67 cm shows neutrality with +1.50 DS. Working distance 1/0.67 = 1.50 D must be removed, so the net sphere is plano. If neutrality instead appears at +4.00 DS with the same working distance, the corrected sphere is +4.00 − 1.50 = +2.50 DS. Cylinder is subtracted from the sphere only, never from the axis or the cylinder value itself.

Traps

Subtracting the working distance from a cylinder; using the cross-cylinder before the axis is roughly correct; accepting a duochrome endpoint as precise rather than a coarse check; refracting a young hyperope without fogging, so latent hyperopia is missed.