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Tak Yee Tania Tai, Noga Harizman; Comparison of Tono-Pen and Pneumotonometer Measurements from Scleral Locations with Intraocular Pressure Measurements from the Cornea. Invest. Ophthalmol. Vis. Sci. 2014;55(13):129.
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Intraocular pressure (IOP) assessment by measurements on the cornea may not be possible in patients with severe corneal pathology or keratoprosthetic implants. The purpose of this study is to assess whether Tono-Pen and pneumotonometer measurements on the sclera show correlation with IOP measurements on the cornea using these two devices, as well as Goldmann applanation tonometry.
This is a prospective study. Subjects were randomized to have their left or right eye included in the study. The following measurements were obtained from the study eyes: IOP measurement on the cornea using Goldmann applanation, followed by Tono-Pen and pneumotonometer; IOP measurements on the sclera were taken between 3-5mm posterior to the limbus in each quadrant (superonasal, superotemporal, inferonasal and inferotemporal) using pneumotonometer and Tono-Pen. At least 2 acceptable measurements were obtained from each location, using each applanation modality. Product moment and linear regressions were used to examine correlations between measurements.
50 eyes (25 right eyes, 25 left eyes) of 50 subjects (23 males, 27 females) were enrolled. Intraobserver reliability of the scleral IOP (S-IOP) measurements was high with the superotemporal and inferotemporal pneumotonometer measurements being the most reliable (Cronbach’s alpha of 0.95 for measurements from both locations). The S-IOP measurements differed significantly from the corneal IOP (C-IOP) readings; however, moderate correlation was found between the pneumotonometer readings from the superotemporal (r=0.64, P<0.01) and inferotemporal (r=0.64, P<0.01) quadrants with the Goldmann C-IOP. A combined superotemporal pneumotonometer S-IOP of ≥30 mmHg and an inferotemporal pneumotonometer S-IOP of ≥39 mmHg was 84.6% (95% confidence interval [CI] 53.7%, 97.3%) sensitive and 91.9% (95% CI 77.0%, 97.9%) specific for a C-IOP ≥20 with positive likelihood ratio of 10.4 (95% CI 3.4-31.6).
These findings suggest that S-IOP measurements may be an alternate method, other than digital palpation, to provide useful information about IOP in eyes which accurate corneal measurements cannot be obtained. Research into novel IOP measurement devices that do not rely on a clear native cornea will be helpful in managing glaucoma in patients with severe corneal disease or keratoprosthetic implants.
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