Journal d'ophtalmologie clinique et expérimentale
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Correlation of Tono-Pen and Pneumatonometer Measurements from Four Scleral Quadrants with Intraocular Pressure Measurements from the Cornea

Tak Yee Tania Tai, Kateki Vinod and Noga Harizman

Objective: To assess whether Tono-Pen and pneumatonometer measurements obtained from the sclera correlate to intraocular pressure measurements obtained from the cornea.
Methods: This is a prospective, cross-sectional study, conducted at the New York Eye and Ear Infirmary of Mount Sinai. Patients were randomized to have their left or right eye included in the study. Exclusion criteria included prior intraocular surgery (except uncomplicated cataract extraction), uveitis, corneal or scleral thinning, central corneal thickness <500 μm or >575 μm, and hyperopia greater than +2 diopters or myopia greater than -4 diopters. Goldmann applanation tonometry, Tono-Pen and pneumatonometer measurements were obtained from the cornea. Tono-Pen and pneumatonometer measurements were obtained from the sclera in the superonasal, superotemporal, inferonasal, and inferotemporal quadrants. Product moment correlation and linear regression were used to examine correlations between the measurements.
Results: 50 eyes of 50 patients were enrolled. The scleral intraocular pressure measurements (S-IOP) differed significantly from the corneal intraocular pressure (C-IOP) readings. Moderate correlation was found between the pneumatonometer readings from the superotemporal (r=0.64, P<0.01) and inferotemporal (r=0.64, P<0.01) quadrants with the Goldmann C-IOP, with the following linear relationships, respectively: C-IOP=(0.52 × superotemporal S-IOP)+1.35, and C-IOP=(0.41 × inferotemporal S-IOP)+0.88. A combined superotemporal pneumatonometer S-IOP of >30 mmHg and an inferotemporal pneumatonometer S-IOP of >39 mmHg was 92.3% (95% Confidence Interval [CI] 63.9%, 98.7%) sensitive and 94.6% (CI 81.8%, 99.2%) specific for a C-IOP ≥ 20 mmHg with positive likelihood ratio of 17.1 (CI 4.4-66.3).
Conclusion: S-IOP measurements, especially from the superotemporal and inferotemporal quadrants, can provide useful information about intraocular pressure in eyes in which accurate C-IOP measurements cannot be obtained.