Lesson · ABO
Dispensing and verification
Checking finished glasses against the ANSI Z80.1 tolerances, impact testing, vertical imbalance and the everyday frame adjustments.
After this lesson you can
About 12 minutes- Neutralize a finished lens and compare it with the Rx
- Pick the right Z80.1 tolerance for sphere, cylinder, axis and add
- Spot a vertical imbalance at the reading level
- Fix the common fit complaints with the right adjustment
Verifying finished glasses
- Focus the lensometer eyepiece for your own eye before every job.
- Read the sphere, then turn to the second meridian for the cylinder and read the axis.
- Check the OC or prism reference point against the PD and any prescribed prism.
- For multifocals, read the add through the segment from the front surface.
- Compare each value with the Rx using the tolerance for that power.
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ANSI Z80.1 tolerances
Tolerances depend on how strong the lens is. Look up the power in the right table, then check whether the measured value is within that much of the ordered one.
| Power (D) | Tolerance |
|---|---|
| 0.00 to 6.50 | ± 0.13 D |
| 6.75 and over | ± 2 % |
| Cylinder (D) | Tolerance |
|---|---|
| 0.00 to 2.00 | ± 0.13 D |
| 2.25 to 4.50 | ± 0.15 D |
| 4.75 and over | ± 4 % |
| Cylinder (D) | Axis tolerance |
|---|---|
| 0.25 | ± 14° |
| 0.50 | ± 7° |
| 0.75 | ± 5° |
| 1.00 to 1.50 | ± 3° |
| 1.75 and over | ± 2° |
| Add (D) | Tolerance |
|---|---|
| 0.00 to 4.00 | ± 0.12 D |
| 4.25 and over | ± 0.18 D |
Is it within tolerance?
Ordered −3.25 DS single vision; the lensometer reads −3.37.
- 3.25 D is in the first sphere band: ± 0.13 D.
- The difference is 0.12 D, which is within 0.13.
Answer: Passes
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Impact resistance
| Eyewear | Test |
|---|---|
| Dress eyewear | 5/8-inch steel ball dropped 50 inches |
| Safety eyewear (basic impact) | 1-inch steel ball dropped 50 inches |
Vertical imbalance at near
When the two eyes have different powers in the vertical meridian, reading below the OCs gives each eye a different amount of vertical prism. Work each eye with Prentice’s rule and compare.
Imbalance at the reading level
OD −1.00 DS, OS −4.00 DS; the patient reads 10 mm below the OCs.
- OD: 1 × 10 ÷ 10 = 1.00 Δ BD
- OS: 4 × 10 ÷ 10 = 4.00 Δ BD
- Same base direction, so subtract: 3.00 Δ
Answer: 3.00 Δ vertical imbalance
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Frame adjustments
Most fit complaints have a standard fix. Warm plastic frames before bending them; adjust metal frames at the pad arms and hinges.
| Complaint | Adjustment |
|---|---|
| Pinching on the nose (metal) | Open the pads so they sit flat on the nose |
| Sliding down (metal) | Bring the pads closer together |
| Sliding down (plastic) | Bend the temple ends down and in a little |
| Too tight behind the ears | Relax the temple bends upward and out |
| Left lens sits higher | Bend the right temple down at the hinge |
| Right lens sits higher | Bend the left temple down at the hinge |
| Left lens closer to the face | Angle the left temple in or the right temple out |
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