Investigation of the myopic outcomes of the newer intraocular lens power calculation formulas in Korean patients with long eyes

Abstract

This study investigated the underlying causes of the myopic outcomes of the optic-based newer formulas (Barrett Universal II, EVO 2.0, Kane, Hoffer-QST and PEARL-DGS) in long Korean eyes with Alcon TFNT intraocular lens (IOL) implantation. Postoperative data from 3100 randomly selected eyes of 3100 patients were analyzed to compare the reference back-calculated effective lens positions (ELPs) based on the Haigis formula using conventional axial length (AL) and Cooke-modified AL (CMAL) with the predicted ELP of each single- and triple-optimized Haigis formula applied to AL- and CMAL. Contrary to the AL-applied Haigis formula, the predicted ELP curve of the CMAL-applied, single-optimized Haigis formula, simulating the methods of the newer formulas, exhibited a significant upward deviation from the back-calculated ELP in long eyes. The relationship between the AL and anterior chamber depth in our long-eyed population differed from that in the base population of the PEARL-DGS formula. The myopic outcomes in long eyes appeared to stem from the substantial overestimation of the postoperative IOL position with AL modification, leading to the implantation of inappropriately higher-powered IOLs. This discrepancy may be attributed to the ethnic differences in ocular biometrics, particularly the relatively smaller anterior segment in East Asian patients with long AL.

Keywords: Anterior chamber depth; Axial length modification; East Asian; Ethnic ocular biometric differences; Intraocular lens calculation formula accuracy; Myopia.

Figure 1

Comparison between the back-calculated ELP versus the predicted ELP of the Haigis formula, with single and triple optimization. Mean ELP values are plotted against conventional AL values rounded to 0.5 mm. (a) Haigis formula with the conventional AL application, single-optimized (a0/a1/a2 constants: 1.523/0.4/0.1), (b) Haigis formula with the conventional AL application, triple-optimized (a0/a1/a2 constants: 1.304/0.442/0.104), (c) Haigis formula with the Cooke-modified axial length application, single-optimized (a0/a1/a2 constants: 1.556/0.4/0.1), (d) Haigis formula with the Cooke-modified axial length application, triple-optimized (a0/a1/a2 constants: 3.526/0.523/0).

Figure 2

Comparison between the back-calculated theoretical internal lens position (TILP) versus predicted TILP in the PEARL-DGS formula training population (figure derived from reference 19, the units of measurement were revised for consistency.) Mean TILP values are plotted against conventional AL values rounded to 0.25 mm. (a) In the long eyes, the back-calculated TILP is higher than the predicted TILP, which is contrary to our data (see Fig. 1c), (b) After AL input correction, in the long eyes, the predicted TILP is pushed upwards to fit the back-calculated TILP. This refinement would lead to more myopic deviation in our population’s long eyes. AL = axial length; TILP = theoretical internal lens position.

Figure 3

The relationship between the AL and the anterior chamber depth (ACD). Mean ACD values are plotted against conventional AL values rounded to 0.5 mm. (a) A: Relationship in our population (n = 3100), (b) B: Relationship in the PEARL-DGS formula training population (n = 4242, data from the formula author, image has been modified for easier comparison by us and confirmed for usage by the formula author).

Figure 4

An eye model based on the mean values of the long-eye subgroup. Upper half: Eye model applying Haigis formula, single-optimized and AL-applied (HSAL). Lower half: Eye model applying Haigis formula, single-optimized and CMAL-applied (HSCL). AL = axial length; CMAL = Cooke-modified axial length; ELP = Effective lens position; HSAL = Haigis formula, single-optimized and AL-applied; HSCL = Haigis formula, single-optimized and CMAL-applied; IOL = Intraocular lens; SE = Spherical equivalent; TK = Total keratometry.

Figure 5

Mean prediction error changes of each formula according to AL (figure derived from Reference 33, and modified to enhance visual clarity). EVO: Emmetropia Verifying Optical formula; Hoffer QST: Hoffer Q/Savini/Taroni formula; RBF: Hill Radial Basis Function formula.

Figure 6

Ethnic Variations in Ocular Biometric Characteristics and their Impact on Refractive Outcomes in Long Axial Length Range. (a) Long Eyes in Caucasian patients with bigger anterior segments, (b) Long Eyes in East Asian patients with smaller anterior segments. Blue-colored hemicircle: Eye model with conventional AL. Red-colored hemicircle: Eye model with modified AL, approximating true AL. Blue-colored triangle: Lower-powered IOL and its longer focal length.Red-colored triangle: Higher-powered IOL and its shorter focal length. AL = axial length; IOL = Intraocular lens.