Table 1.
Definitions of vector parameters17
| Vector parameter | Definition |
|---|---|
| IRC (D) | The vector difference between the preoperative astigmatic correction vector and the target postoperative cylinder vector. |
| If the target refractive state is emmetropia, the IRC vector is equal to the preoperative astigmatic correction vector | |
| SIRC (D) | The vector difference between the preoperative and postoperative astigmatic correction vectors. SIRC represents the achieved correction |
| EV (D) | The vector difference between the IRC and SIRC. When the refractive target is emmetropia, the EV is identical to the postoperative astigmatic correction vector |
| ER | The proportion of the intended correction that was not successfully treated (|EV|/|IRC|) |
| CR | The ratio of the achieved correction magnitude to the required correction (|SIRC|/|IRC|). A ratio of 1 is ideal, whereas <1 implies undercorrection and >1 implies excessive application of the treatment |
| EM (D) | The arithmetic difference of the magnitudes between SIRC and IRC (|IRC|–|SIRC|) |
| EA (°) | The angular difference between the achieved treatment and the intended treatment. The EA is negative if the SIRC is clockwise from the IRC and positive if the SIRC is counterclockwise from the IRC |
Abbreviations: IRC, intended refractive correction; D, diopter; SIRC, surgically induced refractive correction; EV, error vector; ER, error ratio; CR, correction ratio; EM, error of magnitude; EA, error of angle.