J Korean Ophthalmol Soc.  2014 Jan;55(1):85-92.

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

• Jeong JH
• Kim SG
• Lee HJ
• Lee SH
• Cha DM

Abstract

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.

Keyword

Effective lens position; Hoffer Q formula; IOL formula comparison; SRK/T formula

MeSH Terms

Anterior Chamber
Astigmatism
Biometry
Cataract
Lenses, Intraocular
Prospective Studies
Tertiary Care Centers

Figure

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  Figure 1. Distribution frequency was illustrated in histogram with normal distribution curve. In histogram, 37 cases (12.1%) had axial length shorter than 22 mm, and 239 cases (78.3%) ranged between 22 and 25 mm, and 29 cases (9.5%) were longer than 25 mm.

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  Figure 2. For the selected IOL power, the disparity between the 2 formulas (expected disparity between formulas, EDF) was calculated by subtracting the expected refraction value obtained using the SRK/T formula from that obtained using the Hoffer Q formula. The 365 cases were divided into 3 groups according to their EDF value (A: EDF ＞ 0.4 D, B: -0.4 D ≤ EDF ≤ 0.4 D, C: EDF ＜ -0.4 D). The scatterplot of the corneal curvatures and axial lengths showed clear discrimination among the EDF subgroups. EDF subgroup A (red circle), B (green circle), C (blue circle).

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  Figure 3. The EDF values were plotted against the axial length, and showed an R value of 0.417, by using a linear regression model (p = 0.000). The EDF values show large amplitude of variation even in middle axial length range (22-25 mm). * EDF (expected disparity between formulas) was calculated by subtracting the expected refraction value obtained using the SRK/T formula from that obtained using the Hoffer Q formula.

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  Figure 4. The EDF* values were plotted against the products of corneal curvature and axial length, and showed an r2 value of 0.855, by using a quadratic curve estimation (p = 0.000). * EDF (expected disparity between formulas) was calculated by subtracting the expected refraction value obtained using the SRK/T formula from that obtained using the Hoffer Q formula.

Reference

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