Impact of anterior chamber depth to axial length ratio on conventional intraocular lens power calculation formulas performance in axial myopia

Purpose: To evaluate the effects of the ratio of anterior chamber depth to axial length (ACD/AL), as well as axial length (AL) itself, on the accuracy of conventional intraocular lens (IOL) power calculation formulas in eyes with axial myopia.Methods: This retrospective cross-sectional study included 60 eyes from 44 patients with an AL greater than 25.0 mm who underwent uncomplicated phacoemulsification with IOL implantation. Eyes were categorized into high and low AL groups using an AL threshold of 27.0 mm, and into high and low ACD/AL groups based on the median ACD/AL value of 13.4. The median absolute errors (MedAEs) predicted by the Sanders-Retzlaff-Kraff theoretical (SRK/T) and Haigis formulas were compared according to AL and ACD/AL groupings.Results: In the low ACD/AL group and in the high AL group, the MedAEs predicted by the Haigis formula were lower than those predicted by the SRK/T formula (P=0.002 and P=0.012, respectively). The MedAEs predicted by both the SRK/T and Haigis formulas were significantly lower in the high ACD/AL group than in the low ACD/AL group (P<0.001 and P=0.010, respectively). In contrast, no significant difference was observed between the low and high AL groups in the MedAEs predicted by the Haigis formula. When the ACD/AL ratio was less than 13.4, postoperative refractive outcomes were more hyperopic with both formulas.Conclusion: In eyes with a long AL and a relatively shallow ACD, the Haigis formula demonstrated superior accuracy among conventional IOL power calculation formulas. Under these anatomical conditions, targeting slightly more myopic postoperative refractions may therefore be advisable.