Error of calibration in ophthalmic calipers: a source of significant clinical errors

Length measuring instruments are frequently used in ophthalmic surgery practice. For all subspecialties, calipers need to be accurate. This study was carried out to identify errors of calibration in ophthalmic calipers as a potential source of significant clinical errors.

This study is a descriptive research.

All Castroviejo calipers free of any visible damage and available to the ophthalmic surgeons in the operating room suites of our 2 affiliated hospitals were included. The caliper scale readings were compared to measurement markings on a standardized ruler at screening points of 1, 5, 10, and 15 mm on the ruler. Any caliper with a discrepancy of 0.5 mm or more at any set of these screening points went on to having further analysis.

Seventy-one calipers were examined, of which 30 (42%) showed at least 1 caliper scale reading discrepancy of ≥0.5 mm as compared to ruler measurements. Errors of at least 1 mm were found in 6 of 30 calipers (20%). The majority of calipers underestimated lengths 22/30 (73%), whereas 27% overestimated.

With close to half of the calipers inducing a 0.5 mm or more error, and with 20% of these at least 1 mm, significant clinical consequences could ensue: for example, in follow up of glaucomatous corneas in children, in measurements for anterior chamber intraocular lens sizing, in certain refractive surgery techniques, pars-plana sclerotomies, and intravitreal injection sites, or in measuring amounts in strabismus to name a few. Errors in calibration of ophthalmic calipers must be acknowledged and avoided.