Assessment of Ocular Magnification in Relation to Biometric Parameters and Measurement Techniques: A Prospective Study.

Purpose: The aim of this study was to evaluate the effects of factors such as axial length (AL), spherical equivalent (SE), and keratometry (K) on longitudinal and lateral magnification and their impact on Bruch's membrane opening (BMO)-fovea distance and central foveal thickness (CFT) measurements.

Methods: This prospective cross-sectional study included 437 eyes of 437 healthy participants aged 18 to 50 years with best corrected visual acuity of 20/20 or better. Participants were divided into three groups according to their refractive status: myopia (< -0.50 diopters [D]), emmetropia (-0.50 to +0.50 D), and hypermetropia (>+0.50 D). BMO-fovea distance and CFT were measured using a Topcon swept-source optical coherence tomography SS-OCT device, first without taking into account the magnification of the eye and then by incorporating individual AL, SE, and K into the system. Measurement errors greater than 5% were considered significant.

Results: Longitudinal and lateral magnification affected BMO-fovea distance and CFT differently. Image size correction was required in 60% of BMO-fovea and 41% of CFT measurements. BMO-fovea distance was significantly influenced by lateral magnification, whereas CFT remained largely unchanged, indicating its primary association with longitudinal magnification. The highest correction need was observed in hypermetropic (87.7%) and short AL eyes (66.1%).

Conclusions: It has been demonstrated that BMO-fovea distance is sensitive to lateral magnification, whereas CFT is mainly affected by longitudinal magnification. Neglecting these effects, particularly in hypermetropic and short AL eyes, may lead to significant measurement errors. These findings highlight the necessity of considering both longitudinal and lateral magnification corrections in retinal imaging.