Accuracy of Intraocular Lens Power Calculations According to Corneal Curvature in Short Eyes

PURPOSE: To evaluate the accuracy of intraocular lens (IOL) power calculations between Hoffer Q and other formulas according to corneal curvature by comparing the results of cataract surgery and calculation of chosen formulas in short axial lengths. METHODS: We performed a retrospective analysis of patients who underwent cataract surgery from January 1st, 2012 to June 12th, 2012. The patients were selected if their axial length was below 23.00 mm and 77 patients (90 eyes) were included in the present study. The patients were divided into 2 groups according to mean corneal curvature below 44.0 D and over 45.0 D. IOL power was calculated using the Hoffer Q and SRK II, SRK-T and Holladay I formulas and the error between the calculations and refractive outcome of cataract surgery were measured. The accuracy of each formula was evaluated by comparing the error between the 2 groups. RESULTS: Hoffer Q formula showed a higher predictive accuracy than other formulas regardless of corneal curvature in eyes with short axial lengths (p < 0.001, p = 0.023). Particularly, SRK II, SRK-T and Holladay I showed a lower predictive accuracy in eyes with flat corneal curvature than Hoffer Q (p < 0.001, p = 0.215). CONCLUSIONS: In eyes with short axial lengths, preoperative predicted IOL power calculations showed better accuracy with Hoffer Q formula than SRK II, SRK-T and Holladay I formulas. SRK II, SRK-T and Holladay I formulas showed a lower predictive accuracy in flat corneal curvature eyes than steep corneal curvature eyes with short axial lengths. We hypothesize that SRK II, SRK-T and Holladay I tend to underestimate effective lens position in eyes with short axial lengths indicating Hoffer Q formula is more accurate.

Theoretical and Clinical Comparison of the Hoffer Q and SRK/T Formulas

PURPOSE: To evaluate the biometric conditions causing increased disparity in the calculation of intraocular lens (IOL) power between the Hoffer Q and SRK/T formulas. METHODS: A prospective comparative study was conducted on 365 uneventful, cataract surgeries performed at a tertiary care center by one surgeon. The IOL power was calculated using both the Hoffer Q and SRK/T formulas with A-scan biometry. For a selected IOL power, the expected disparity between the 2 formulas (EDF) was measured and the EDF value was used to categorize the cases. The resultant error associated with each formula was determined at postoperative 6 weeks. KAL was defined as the product of mean corneal power (K) and axial length (AL). Postoperative errors of both formulas were calculated and their association with preoperative biometry measurements analyzed. RESULTS: In 17.8% of the cases, the EDF was larger than 0.4 D, possibly leading to different IOL diopter recommendations. The EDF value and the product of corneal curvature and axial length were significantly correlated (R2 = 0.855, p < 0.001). Multiple regression analysis of causative preoperative biometric factors on the postoperative formula errors showed that astigmatism, anterior chamber depth (ACD), and lens thickness (LT) were significantly associated with Hoffer Q error and SRK/T error. CONCLUSIONS: Overall, both formulas performed very well when recommending the correct IOL power. The cause of disparity between the predicted refraction for the 2 formulas was more associated with KAL than K or AL alone. Astigmatism, ACD, and LT were the causative factors for the postoperative errors in both formulas.

Comparison of the Hoffer Q and SRK-II fomulas in IOL Power Calculation

Although most available IOL power calculation formulas perform accurately for eyes of average axial length, they have been shown to be inaccurate for eyes that have unusually short and long axial length. To compare the prediction accuracy of new Hoffer Q with SRK-II formula, we reviewed, retrospectively, a series of 225 ECCE with PCL implantation cases, including 106 Hoffer Q group and 119 SRK-II group, each of which was further divided into subgroups based on axial length. The Hoffer Q formula overestimated the refraction and resulted in more myopic shift and was less accurate than SRK-II in all length eyes, except short length eyes. In short length eyes, both formulas had similar mean error and mean absolute error but Hoffer Q formula was more accurate than the SRK-II in +/- 0.5D prediction proportion.