Intraocular Lens Power Calculation After Radial Keratotomy
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.