During the process of validating the original Masket method, our data produced a slightly different regression formula. As with the Masket technique, the Modified Masket Method1,2 takes advantage of the fact that there appears to be a linear relationship between the spherical equivalent of the total amount of the stable laser vision correction (LSE) and the over-estimation of central corneal power by simulated keratometry. This works for myopic and hyperopic LASIK.
By this method, the IOL power is calculated using the Holladay 1 formula for axial lengths greater than 23.0 mm and the Hoffer Q formula for axial lengths less than 23.0 mm. The SRK/T formula is generally not recommended as the artifact of very flat Ks may sometimes result in an under-correction. Ks are provided by simulated keratometry. The IOL power is calculated without a double K method correction. Ks are provided by simulated keratometry. The calculated IOL power is then adjusted by the vertex distance corrected laser vision correction spherical equivalent determined at four to six months after the procedure. It is then multiplied by -0.4385 and 0.0295 added to this product.
Follow this link to an Excel spreadsheet: Correcting for Vertex Distance (download).
- (LSE x -0.4385) + 0.0295 = Post-LASIK IOL power adjustment
- Where…
- LSE = The vertex distance corrected laser vision correction spherical equivalent.
Right eye.
The Modified Masket Method for the right eye following myopic LASIK would be carried out as follows:
- If the calculated IOL power is +15.26 D for a -0.25 D result, and…
- The stable laser vision correction spherical equivalent is -5.38 D, then…
(LSE x -0.4385) + 0.0295 = Post-LASIK IOL power adjustment (-5.05 D x -0.4385) + 0.0295 = +2.25 D = IOL power adjustment +2.25 D + 15.30 D = 17.55 D = Final adjusted IOL power
Left eye.
The Modified Masket Method for the left eye following myopic LASIK would be carried out as follows:
- If the calculated IOL power is +15.09 D for a -0.25 D result, and…
- The stable laser vision correction spherical equivalent is -4.00 D, then…
(LSE x -0.4385) + 0.0295 = Post-LASIK IOL power adjustment (-3.82 D x -0.4385) + 0.0295 = +1.71 D = IOL power adjustment +1.71 D + 15.09 D = 16.80 D = Final adjusted IOL power
References
- Masket S, Masket SE. Simple regression formula for intraocular lens power adjustment in eyes requiring cataract surgery after excimer laser photoablation. J Cataract Refract Surg 2006 32 (3) 430 – 434.
- Hill WE. IOL power calculations following keratorefractive surgery. Presented at Cornea Day of the Annual Meeting of the American Society of Cataract and Refractive Surgery, San Francisco, California, March 17, 2006
