Determining Corneal Power after Hyperopic LASIK.
For eyes that have undergone hyperopic LASIK, the central corneal power estimation technique is much easier than for myopic LASIK. This is thought to be due to the fact that the ablation takes place outside the central cornea.
An interesting feature of hyperopic LASIK is that following this procedure, the ratio between the posterior and anterior corneal radii is increased, much like what is seen following radial keratotomy. For this reason, it is possible to use a similar method of central corneal power estimation. It is intriguing that a myopic incisional technique (RK) and a hyperopic ablative technique (hyperopic LASIK), would alter the posterior : anterior corneal radii ratio in much the same way.
Zeiss Humphrey Atlas topographer
Based on the experience of Drs. Wang, Jackson and Koch, the average of the 1 mm, 2 mm and 3 mm annular power rings of the Numerical View of the Zeiss Humphrey Atlas topographer is sufficiently accurate to serve as a reasonable estimate of central corneal power following hyperopic LASIK. However, depending on the amount of hyperopic laser vision correction, a correction to the average of the 1 mm, 2mm, and 3mm annular power ring value must be made.
| LASIK-Induced Refractive Correction (D) |
Adjustment for Hyperopic LASIK (D) Atlas AnnCP |
| 0.5 | -0.30 |
| 1.0 | -0.20 |
| 1.5 | -0.11 |
| 2.0 | -0.01 |
| 2.5 | 0.08 |
| 3.0 | 0.18 |
| 3.5 | 0.27 |
| 4.0 | 0.37 |
| 4.5 | 0.46 |
| 5.0 | 0.56 |
| 5.5 | 0.65 |
| 6.0 | 0.75 |
From: JCRS 2002; 28:954 – 961
EyeSys Corneal Analysis System
As an alternative, Drs. Wang, Jackson and Koch have shown that the effective refractive power (EffRP) of the EyeSys Corneal Analysis System also works well.¹ Notice that this technique is very similar to what is currently recommended for estimating the central corneal power following radial keratotomy. As well, for this method, a small correction needs to be made to the effective refractive power (EffRP).
| LASIK-Induced Refractive Correction (D) |
Adjustment for Hyperopic LASIK (D) EyeSys EffRP |
| 0.5 | -0.20 |
| 1.0 | -0.12 |
| 1.5 | -0.04 |
| 2.0 | -0.04 |
| 2.5 | 0.13 |
| 3.0 | 0.21 |
| 3.5 | 0.29 |
| 4.0 | 0.37 |
| 4.5 | 0.45 |
| 5.0 | 0.53 |
| 5.5 | 0.61 |
| 6.0 | 0.69 |
From: JCRS 2002; 28:954 – 961
Double K method correction
Remember that some form of a “double K method” correction is still required for IOL power calculations following hyperopic LASIK in order to avoid a refractive surprise. This can be done by checking the “Previous RK, LASIK, etc.” box on the Holladay 2 formula (contained within the Holladay IOL Consultant), or by using a hyperopic “double K method” IOL power correction table based on the work of Aramberri for any of the three popular 3rd generation, 2-variable formulas.
Haigis-L formula
The recently introduced hyperopic version of the Haigis-L formula is also very useful for patients who have undergone prior hyperopic LASIK. It is a purely objective methodology that uses small zone keratometry and requires no prior historical information.
- Wang L, Jackson DW, Koch DD. Methods of estimating corneal refractive power after hyperopic laser in situ keratomileusis. J Cataract Refract Surg. 2002; 28:954 – 961.
