Comparison of different methods to calculate the axial length measured by optical biometry.

Purpose: To compare axial length (AL) measurements in long eyes by 2 swept-source optical coherence tomography (SS-OCT) biometers, one based on the group refractive index (IOLMaster 700, Zeiss) and the other based on sum of segments (Argos, Movu Inc.), and compare these measurements with previously published methods to optimize AL.

Setting: G.B. Bietti Foundation I.R.C.C.S., Rome, Italy.

Design: Prospective case series.

Methods: AL was measured with both optical biometers in patients with myopia (AL > 24.0 mm) and compared with the values obtained with Wang-Koch adjustment, polynomial equations for the Holladay 1 and 2 formulas, and Cooke-modified AL (CMAL).

Results: In 102 eyes of 55 subjects, a statistically significant difference (P < .0001) was found among the 6 AL values. Posttest revealed that Argos measurements (26.90 ± 1.61 mm) were significantly lower compared with those provided by all methods (P < .001) but CMAL, whereas IOLMaster 700 measurements (27.01 ± 1.65) were higher (P < .001). No difference was found between the 2 Holladay equations. CMAL values did not reveal any difference compared with those of the Argos, but a proportional bias showed that in longer eyes, CMAL provided smaller values (P < .0001, r = -0.7221). AL overestimation by the IOLMaster 700 AL compared with the Argos was higher, the longer the eye was (P < .0001, r = 0.6959, r2 = 0.4842).

Conclusions: The SS-OCT optical biometer based on the group refractive index overestimates AL compared with the device using segmented AL. CMAL provides the measurements closest to those of the device using segmented AL.