Validating the use of U-tool as a novel method for measuring the corneal diameter in infants screened for congenital...

The Castroviejo caliper is routinely used for measuring the corneal diameter in patients with primary congenital glaucoma, but needs an examination under anesthesia (EUA) or sedation. A simple U-shaped tool was devised to aid in the estimation of the corneal diameters of patients in settings where an ophthalmic caliper is not available or EUA is not feasible.

Infants presenting to the congenital glaucoma clinic posted for EUA were recruited. The demographic details of the patients such as age, sex, and diagnosis were noted. A simple U-shaped tool was devised using three Schirmer strips or a printable ruler. Before the patient underwent a EUA, the corneal diameters were measured using the U-tool. During EUA, corneal diameters were measured using the Castroviejo caliper.

The mean age of infants was 6.7 ± 3.39 months (R = 1-12). The mean corneal diameter measured using the U-tool was 13.29 ± 1.33 mm and with Castroviejo caliper was 13.18 ± 1.39 mm. The difference between the corneal diameters measured using the two techniques was -0.114 mm with the Bland-Altman plot 95% Limits of agreement (LoA) from -0.965 to 0.737 mm. Corneal diameters measured with both instruments had a good correlation (Pearson's correlation coefficient = 0.95, P < 0.001).

U-tool can be used for screening congenital glaucoma by first-contact physicians or optometrists. It can also be used by ophthalmologists when EUA is delayed.