Correlations between intraocular pressure (IOP) measurements taken by Goldmann aplanation tonometry (GAT) and Tono-Pen AVIA® during daily curve of IOP (DCPo) in keratoconic eyes.

Abstract

Purpose : Appropriate IOP evaluation in keratoconic eyes remains a challenge. This study aims to assess correlations between IOP measurements obtained by GAT and Tono-Pen AVIA® during DCPo

Methods : The diagnostic keratoconus criteria was (1 sign or a combination of signs): Munson’s sign; biomicroscopic signs: stromal thinning, conical protrusion, Fleischer ring, Vogt striae; and an abnormal retinoscopy reflex. The diagnosis was confirmed with Oculus Pentacam. Exclusion criteria were: acute corneal hydrops, corneal scarring, penetrating/lamellar keratoplasty, keratitis, corneal rings, or cross-linking. Each DCPo consisted of 5 IOP measurements performed with GAT and Tono-Pen AVIA® at 9:00am, 11:00am, 6:00pm and 10:00pm and in the morning of the following day at 6:00am with Perkins tonometer with patient in a supine position in bed and in darkness and before he had stood up. Because of corneal astigmatism, the GAT prism red line was placed at the prism degree mark (flattest meridian/minus cylinder) to correct IOP measurement (GATc); also, measurements without these corrections were done (uGAT). Average IOP and standard deviation were calculated. Paired-t test, Spearman correlation, and regression analysis were done.

Results : Thirty-nine eyes from 24 patients, mean age of 23.4±7.7 years, were included. The mean Pentacam findings: k average: 50.3±5.3D; k maximum: 58.1±6.9D; astigmatism: 4.8±2.6; Badd: 8.7±5.0; central corneal thickness: 469±75. Mean IOP was 11.2±2.5mmHg (range, 5 to 18) via GATc, 9.9±2.5mmHg (range, 5 to 14) with uGAT and 12.2±3.1mmHg (range, 6 to 20) with Tono-Pen AVIA®. By Paired-t test, mean difference between GATc and uGAT measurements was 1.32mmHg (P<0.001); between GATc and AVIA was -1.02mmHg (P<0.001), and between uGAT and AVIA was -2.35mmHg (P<0.001). Spearman correlation coefficient for GATc versus uGAT IOP was 0.87 (P<0.01); 0.72 for GATc versus AVIA (P<0.01), and 0.73 for uGAT versus AVIA (P<0.01). Using regression analysis, IOP taken by AVIA may be predicted from GATc IOP via the following equation: IOP (Tono-Pen AVIA) = 5.579+0.763xGATc-0.016xACD-0.296xCornealAstig; R²= 0.725 (P<0.001).

Conclusions : In keratoconic eyes, IOP taken by Tono-Pen can be estimated using measurement obtained from GATc. Statistical significant correlations were found between IOP measurements obtained with both tonometers.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.