Calculation of IOL Power Using Average Equivalent Keratometry Readings in Eyes With Nonprogressive Keratoconus
Narrative Responses:
Purpose
Patients suffering from cataracts with coexisting keratoconus presents a unique challenge due to inaccuracy of keratometry measurements and erroneous prediction of effective lens position resulting in imprecise intraocular lens (IOL) power calculation. We report predictably successful visual outcome in both eyes of a patient with cataracts and non-progressive keratoconus.
Methods
IOL calculations by SRK-T formula using keratometry measurements by IOLMaster were performed, and repeated using Pentacam EKR values, averaged over the central 1-4 mm optical zones. The post-operative target refraction was mild myopia. IOL powers calculated using the average EKR were chosen for implantation. Best corrected visual acuity (BCVA) and spherical equivalent of refraction (SE) were measured 1 month following surgery, and compared to the target refraction (TR). IOL powers calculated using keratometry measurements by IOLMaster were compared to the selected IOL powers calculated using average EKR values.
Results
Cataract surgery was performed on both eyes of a 62 years old female. At 1 month, the BCVA was 20/20 in the right eye and 20/40 in the left eye which also developed an epiretinal membrane. The spherically equivalent refraction and its corresponding target refraction was -0.63 and -0.62 in the right eye, and -0.87 and -0.40 diopters in the left eye respectively. The mean IOL power using IOLMaster keratometry was lower than that by EKR measurements by 1.75 diopters.
Conclusion
IOL calculation using EKR values averaged over central 1-4 mm optical zones is an accurate method in patients with non-progressive keratoconus. Refractive outcome is more predictable, and approximates the target refraction better than use of traditional biometric methods. However, larger studies are needed to establish the validity of this method.