Research on refractive power calculation formula of intraocular lens based on the principle of double thick lens
Mengdi Yan1, Juntao Zhang2, Shiming Wang1
1Department of Ophthalmology, Ningbo Municipal Hospital of Traditional Chinese Medicine, Affiliated Hospital of Zhejiang Chinese Medical University, Ningbo, Zhejiang, China.
Introduction:
This study aimed to develop and validate a novel formula for calculating intraocular lens (IOL) refractive power based on Gaussian optics and thick-lens imaging.
Methods:
This study was conducted at Ningbo Traditional Chinese Medicine Hospital between October 2021 and October 2023. A total of 54 patients (84 eyes) with age-related cataracts (ARC) undergoing phacoemulsification and IOL implantation were included. The effective lens position was defined as (ACD + W × preoperative LT), where ACD is the anterior chamber depth and LT is the lens thickness. A new IOL power calculation formula was derived using stepwise multiple linear regression, incorporating key ocular parameters including axial length (adjusted for central corneal thickness), keratometry, and the effective lens position. The performance of the new formula was compared with five established formulas: Barrett Universal II, Haigis, Hoffer Q, SRK/T, and Holladay I. For each formula, we compared the mean and median predicted error (PE), the mean and median absolute predicted error (APE), and the proportions of eyes with within ±0.25 D, ±0.50 D, and ±1.00 D.
Results:
The newly developed formula demonstrated excellent bias control, with a median prediction error of 0.060 D that was not statistically different from zero (p = 0.480). In contrast, the Barrett Universal II (0.450 D, p = 0.006), Hoffer Q (0.280 D, p = 0.024), and SRK/T (0.515 D, p = 0.0004) showed significant hyperopic shifts. The mean error of the new formula (0.071 D) was significantly lower than that of Barrett Universal II, Hoffer Q, and Holladay I formulas (all p < 0.01) and comparable to that of the Haigis formula (p = 0.226). Its accuracy (mean absolute error, 0.461 D) was comparable to that of all other formulas. The new formula achieved the highest proportion of eyes within ±0.25 D (43.3%), outperforming all other formulas.
Discussion:
The proposed IOL calculation formula, which is based on a double-thick-lens imaging model, provides improved control of systematic bias and competitive predictive accuracy. This approach offers a promising framework for clinical applications of personal IOL power calculations.
