Twenty-four hours intraocular pressure in keratoconic eyes assessed by applanation tonometry and Tono-Pen AVIA

● AIM: To assess intraocular pressure(IOP) during the daily curve of intraocular pressure(DCPo) in keratoconic eyes and compare Goldmann applanation tonometer(GAT), without and with astigmatism correction(n GAT and c GAT) and Tono-Pen AVIA(TPA) assessment methods. ● METHODS: Thirty-nine keratoconic eyes of 24 patients were assessed. DCPo was evaluated with five IOP measurements; four were performed with a GAT(n GAT and c GAT), and a Tono-Pen AVIA(TPA) at various times throughout the day. ● RESULTS: Mean IOP DCPo values(mm Hg) were: n GAT, 9.9±2.6; c GAT, 11.3±2.6; TPA 12.3±3.1. Mean IOP DCPo differences(mm Hg) and Spearman’s correlation coefficients were as follows: c GATc-n GAT, 1.32±1.31, rs=0.879(P<0.01); c GAT-TPA,-1.02±2.08, rs=0.723(P<0.01); and n GAT-TPA,-2.35±2.23, rs=0.730(P<0.01). Bland-Altman analysis for agreement between c GAT-TPA and n GAT-TPA mean IOP DCPo measurements revealed a mean difference of 1.02(95%CI, 0.35-1.70) and 2.35(95%CI, 1.62-3.07) mm Hg, respectively. Regression analysis yielded the following equation: TPA IOP=5.49+0.775×c GAT-0.015×ACD-0.299×corneal astig matism, which allowed us to infer TPA IOP values from other parameters. ● CONCLUSION: In keratoconic eyes, IOP peaks of DCPo measurements are identified at 6 a.m., independent of the tonometer. The mean DCPo values are: TPA>c GAT>n GAT. IOP TPA measures are predictive of c GAT values, adjusted according to anterior chamber depth and corneal astigmatism.