Criteria for optimally prescribed spectacles
| Spectacle component | Tolerance limits* |
| Spherical power (most plus power) | ±0.50 D |
| Cylindrical power | ±0.50 D |
| Cylindrical axis (if baseline cylinder power ≤ −0.50 DC) | ±7° |
| Cylindrical axis (if baseline > −0.50 DC to ≤ −1.50 DC) | ±5° |
| Cylindrical axis (if baseline > −1.50 DC) | ±2° |
| Horizontal prism | <1 prism dioptre (in/out direction) |
| Vertical prism | <0.50 prism dioptre (up/down direction) |
*Development and testing of the tolerance limits are described in Lee et al.5