The precision of ophthalmic biometry using calipers

Objective The purpose of the study is to determine the precision of whole globe and cornea measurements acquired using calipers, and to quantify the intraoperator and interoperator variance. Design Experimental study. Participants Ten human donor eyes. Methods Ten human eyes (donor age, 16–54 years) were obtained between 18.5 and 66.5 hours postmortem. The horizontal and vertical diameters and the anteroposterior length of the globe were measured using a digital Vernier caliper. The horizontal and vertical diameters of the cornea were measured using both a digital Vernier caliper and a Castroviejo caliper. The measurements were performed by 3 operators with 5 repeat measurements for each dimension. Results No significant differences were observed between measurements of globe anteroposterior length, horizontal diameter, and vertical diameter. Horizontal corneal diameter was greater than vertical diameter with all instruments and all operators. Variability of either instrument did not change with measurement object scale, and was similar across all operators. No significant differences were observed between the variabilities of the 2 devices. The mean intraoperator SD was 0.127 ± 0.023 mm with the digital caliper and 0.094 ± 0.056 mm with the Castroviejo caliper. Conclusions The precision of commercially available calipers in ophthalmic biometry measurements is limited to approximately 0.1 mm.