Advanced Refracting Techniques

The Diopter Cross

The Diopter Cross

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What It’s Used For

• This cross target is used during near testing and ADD power determination.

• When you place a near card with this symbol in front of the patient, at 40 cm, you ask the patient if the horizontal and vertical lines are equally clear.

• If vertical lines look darker or clearer → patient may need more minus (or less plus).

• If horizontal lines look clearer → patient may need more plus.

By adjusting sphere power while the patient views the cross, you determine the near add power required for balanced clarity at near.

The diopter cross / cross target, used to calculate and refine ADD power at near during refraction.

Optical corneal alignment device (10)

The Optical Corneal Alignment Device

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The Optical Corneal Alignment Device (OCAD) is a built-in feature on most modern phoropters that helps ensure the instrument is positioned correctly in relation to the patient’s eyes. Proper alignment is essential for accuracy in refraction.

Purpose

• Ensures the phoropter optical axis is aligned with the patient’s visual axis.

• Minimizes measurement errors from head tilt, vertical/horizontal decentration, or improper positioning.

• Improves comfort for the patient and reproducibility of refraction results.

What It Looks Like

• Usually a small optical target or illuminated reticule located on the sides of the phoropter.

• Appears as a main vertical line with other vertical lines next to it.

• The main vertical line corresponds to a vertex distance of 13.25mm. Each vertical line to the right of the main vertical line equals

• Align the main vertical line with the patient’s corneal apex.

• Each vertical line to the right of the main line corresponds to an additional 2mm of vertex distance (in addition to the 13.25mm.)
  
  

How It Works

1. Seat the patient properly with head straight, chin on rest, forehead against the bar.

2. While standing in front of the patient, look through the OCAD viewer on the phoropter (you must have your eye verrrry close to the OCAD to see the lines.*

3. You’ll see each eye from its side..

4. Adjust the phoropter’s Forehead rest until the corneal apexes are on the long line of the alignment device for each eye.

5. Lock or stabilize the phoropter in place.

*How To use the optical corneal alignment device

Why It Matters

• Even small misalignments (2–3 mm) can introduce cylinder axis errors or prismatic effects during refraction.

• Particularly important in patients with higher refractive errors, prism corrections, or when performing Jackson cross-cylinder refinements.

• Consistent use improves both accuracy and efficiency of refraction.

The optical corneal alignment device on a phoropter is a simple but critical feature used to center the patient’s visual axis with the phoropter’s optical system, ensuring accurate, reproducible, and comfortable refractions.