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Modified Masket Method.1,2
During the process of validating the original Masket method, our data produced
a slightly different regression formula. As with the Masket method, this technique
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 for Correcting
for
Vertex Distance.
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(LSE x -0.4385) + 0.0295 = Post-LASIK IOL power adjustment
 Where...
LSE = The vertex distance corrected laser vision correction spherical
equivalent.
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The modified Masket method for the right eye would be carried out as follows:
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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 ...
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(LSE x -0.4385) |
+ |
0.0295 |
= |
Post-LASIK IOL power adjustment |
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(-5.05 D x -0.4385) |
+ |
0.0295 |
= |
+2.25 D = IOL power adjustment |
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+2.25 D |
+ |
15.30 D |
= |
17.55 D = Final adjusted IOL power |
The modified Masket method for the left eye would be carried out as follows:
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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 ...
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(LSE x -0.4385) |
+ |
0.0295 |
= |
Post-LASIK IOL power adjustment |
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(-3.82 D x -0.4385) |
+ |
0.0295 |
= |
+1.71 D = IOL power adjustment |
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+1.71 D |
+ |
15.09 D |
= |
16.80 D = Final adjusted IOL power |
References
1. 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.
2. 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
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