Intraocular Lens Power Calculation After Radial Keratotomy

Friday, April 25, 2014
KIOSKS (Boston Convention and Exhibition Center)
Mikhail Kremeshkov, MD, IRTC Eye Microsurgery Ekaterinburg Center, Ekaterinburg, Russia
Alexey Ulyanov, MD, IRTC Eye Microsurgery Ekaterinburg Center, Ekaterinburg, Russia
Elena Titarenko, MD, IRTC Ekaterinburg Eye Microsurgery Center, Ekaterinburg, Russia

Narrative Responses:

Purpose
Estimation of  IOL calculation results using Hoffer Q, Best 1.0, ASCRS formulas in patients after radial keratotomy with Pentacam examination. Development of recommendations on preoperative patients investigation for more accurate IOL power calculation.

Methods
A retrospective analysis of   clinical cases of cataract surgery in patients after radial keratototomy was performed.  On the basis of manifest refraction after the operation IOL optic power was re-calculated for emmetropia.  Thus, the power of  the IOL “required” for aimed emmetropia was defined. Then, IOL power  was calculated  according to pre-operative investigation data using  Hoffer Q, Best 1.0, ASCRS formulas.  Calculation results were compared with “required” IOL power.  A group of 58 patients (64 eyes) formerly operated for myopia and myopic astigmatism was investigated.

Results
By  Pentacam images the patients were divided into 2 groups: group 1 – corneas with “pseudonormal”  equivalent refraction values distribution profile and group 2 – with “pathologic” profile.  “Pseudonormal” cornea was found in 18 eyes. “Pathologic” cornea was found in 46 eyes; this sample is parametric and statistically significant.  In group 1 the smallest error of IOL power calculation was achieved using ASCRS formula (0.7± 1.9 D).  Patients of group 2 were the most difficult in IOL power calculation, all the formulas were erroneous but the smallest error was achieved using   ASCRS (1.5±1.1 D) and Best 1.0 (1.8±1.4 D) formulas.

Conclusion
In patients after radial keratotomy it is necessary to estimate corneal refraction distribution  with Pentacam data  in 4maps Refractive and Holladay EKR modes. In “pseudonormal” distribution it is reasonable to calculate IOL power using ASCRS formula. In patients with “pathologic” profile calculation is individual,  post-operative results are difficult to predict.