Fellow eye parameter substitution for IOL calculation in APAC

This retrospective study investigated whether substituting fellow-eye biometric parameters reduced postoperative hyperopic prediction error after cataract surgery in eyes with acute primary angle closure (APAC). Thirty-six patients (72 eyes) who underwent bilateral cataract surgery for unilateral APAC and the fellow eye were included. For APAC eyes, refractive prediction error (PE) at 1 month postoperatively using the standard method was compared with that calculated by substitution methods in which keratometry (K) and/or axial length (AL) were primarily replaced with corresponding fellow-eye values. Multiple linear regression was performed, with the change in PE between the standard and substitution methods (ΔPE) as the dependent variable, and interocular differences in K (ΔK) and AL (ΔAL) as explanatory variables. Receiver operating characteristic (ROC) curve analysis explored thresholds of ΔK and ΔAL associated with a > 0.50 D reduction in hyperopic PE after substitution. With the SRK/T formula, the mean PE decreased from + 0.61 ± 0.73 D (standard) to + 0.27 ± 0.93 D with combined K + AL substitution (p = 0.045). Barrett Universal II formula showed a similar trend without reaching statistical significance. ΔPE was significantly associated with ΔAL in SRK/T (β = 2.45, p < 0.001) and with both ΔK (β = 0.77, p < 0.001) and ΔAL (β = 2.77, p < 0.001) in Barrett Universal II. ROC analysis identified a ΔAL threshold of + 0.23 mm as an exploratory cutoff. Substituting fellow-eye AL during IOL power calculation may reduce hyperopic PE in APAC. What is known ・In eyes with acute primary angle closure (APAC), IOL power calculation at the time of cataract surgery often results in postoperative hyperopic prediction error due to transient axial length (AL) elongation under elevated intraocular pressure. ・Short AL eyes tend to show higher interocular symmetry compared to long AL eyes. What is new ・Substituting the fellow-eye AL for that of the APAC eye in IOL power calculation may reduce postoperative hyperopic prediction error. ・An APAC-eye AL exceeding the fellow-eye AL by approximately 0.23 mm may serve as an exploratory indicator for considering AL substitution.