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Topographic Central Corneal
Power Adjustment Method.1,2,3
The Topographic Central Corneal Power Adjustment Method of post-LASIK
corneal power estimation was originated by Doug Koch and Li Wang and is based
on determining the central power of the cornea using either the Zeiss Humphrey
Atlas topographer or the adjusted effective refractive power (EffRPadj)
of the Holladay Diagnostic Summary of the EyeSys Corneal Analysis System.
Using this technique, the 1, 2, 3 and 4 mm power values of the Numerical
View of the Zeiss Humphrey Atlas topographer are averaged together and used
as the central corneal power value (Ccp). As an alternative, the adjusted
effective refractive power (EffRPadj) of the Holladay Diagnostic
Summary of the EyeSys Corneal Analysis System can be used.
This value is then reduced by 19% for every diopter of myopia corrected
by LASIK. We have added the 3 mm and the 4 mm power values from the Numerical
View of the Zeiss Humphrey Atlas topographer to this calculation based on
the fact that Holladay has found that sampling the 4.0 mm central cornea
for the post-LASIK eye has returned very good results with the Oculus Pentacam.3 Our
own clinical results have also shown an increase in accuracy by doing this.
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CCP
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+
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(ΔD x 0.19) = Post-LASIK adjusted
corneal power
 Where...
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CCP
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= |
the EffRPadj, or the averaged Zeiss Atlas central
corneal power, and...
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ΔD
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= |
the refractive change after LASIK at the spectacle plane.
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The topographic central corneal power adjustment method for the right eye would be:
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If the averaged topographic central corneal power is 41.97 D, and...
The change in refractive power at the spectacle plane is -5.38 D, then...
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CCP
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+ |
(ΔD x 0.19) |
= Post-LASIK adjusted corneal power |
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41.97 D |
+ |
(-5.38 x 0.19) |
= 40.95 D |
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The topographic central corneal power adjustment method for the left eye would be:
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If the averaged topographic central corneal power is 42.61 D, and...
The change in refractive power at the spectacle plane is -4.00 D, then...
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CCP
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+ |
(ΔD x 0.19) |
= Post-LASIK adjusted corneal power |
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42.61 D |
+ |
(-4.00 x 0.19) |
= 41.85 D |
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Using this technique for estimating central corneal power, the following IOL powers are recommended by the Holladay 2 Formula:
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SN60WF |
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Target Refraction |
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Right |
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+16.50 D |
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Plano |
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+17.00 D |
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-0.38 D |
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Left |
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+16.00 D |
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Plano |
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+16.50 D |
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-0.38 D |
References
1. Koch, D., Wang I. Calculating IOL power in eyes that have had refractive
surgery. J Cataract Refract Surg 2003 29(11) 2039-2042.
2. Wang L, Booth MA, Koch DD. Comparison of intraocular lens power calculations
methods in eyes that have undergone LASIK. Ophthalmology 2004 111(10) 1825-1831.
3. Personal communication, April, 2006. Jack Holladay, MD, Houston, Texas.
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