A Prospective Trial Comparing Scleral Pneumotonometry to Goldmann Applanation Tonometry Sara Duke, MD, Usiwoma Abugo, BS, Shuchi Patel MD Loyola University Medical Center, Department of Ophthalmology, Maywood IL References Introduction Conclusions Current devices used to estimate intraocular pressure (IOP) perform the measurements on the cornea. This is not possible in some patients such as those with a keratoprosthesis or other corneal pathology. Glaucoma is known to occur in about 75% of patients following a keratoprosthesis, but accurate pressure readings to monitor for progression are not possible. Thus, we sought to determine if a predictable relationship exists between Goldmann applanation tonometry (GAT) and scleral pneumotonometry (PT) to provide an accurate and reliable assessment of intraocular pressure (IOP) via scleral measurements. Scleral PT shows consistently higher IOP measurements than the corneal IOP measurements from the same eye Scleral PT has a statistically significant positive correlation to corneal PT, however it does not correlate to GAT The difference between scleral PT and GAT did not correlate with SE, CCT or AL individually Scleral PT may be a useful method of IOP measurement when SE, AL and CCT are taken into consideration concomitantly Further studies are needed with a larger number of participants in order to create an equation which may be able to provide IOP as a function of scleral PT measurements Acknowledgement: The Richard A. Perritt Charitable Foundation. 1. Chew HF, Ayers BD, Hammersmith KM et al. Boston keratoprosthesis outcomes and complications. Cornea 2009 Oct;28(9): Barraza RA, Sit AJ. Investigation to determine a relationship between scleral and corneal tonometry. ARVO poster presentation; May 02, Eisenberg DL, Sherman BG, McKeown CA, Schuman JS. Tonometery in adults and children: a manometric evaluation of pneumatonometry, applanation and TonoPen in vitro and in vivo. Ophthalmology: vol 105; Erlich JR, Haseltine S, Shimmyo M, Radcliffe NM. Evaluation of agreements between intraocular pressure measurements using GAT and Goldmann correlated intraocular pressure by Reichert’s ocular response analyzer. Eye: 2010; Shen CC, Downs J, Mansberger SL. Assessment of intraocular pressure along the limbus and sclera using contact and indentation tonometry. ARVO poster presentation; May 02, Abstract Purpose To determine if scleral pneumotonometry (PT) will provide an accurate and reliable assessment of intraocular pressure (IOP) either directly or via a predictable relationship such that IOP can be extrapolated from scleral measurement. Methods A prospective non-randomized trial of individuals 18 years of age and older. Each had his/her IOP measured with the Goldmann applanation tonometer (GAT) first, then corneal PT and finally scleral PT. The patient’s age, gender, ocular history, refractive error, current medications and pachymetry were recorded. Pearson’s correlation was used for statistical analysis. Results 107 eyes from 54 patients (32-87 years old) have been examined to date. Mean GAT IOP was mmHg while mean corneal PT was mmHg. Mean difference between corneal PT and GAT was 3.39 mmHg (SD 2.29). Mean scleral PT was mmHg with an average difference between scleral PT and GAT of mmHg (SD 9.74). Mean spherical equivalent refraction (SE) was D, mean CCT was µm, mean AL was mm. A correlation plot between scleral PT and corneal PT reveals a statistically significant positive correlation (r 0.196, p 0.047), but the plot between scleral PT and GAT shows no statistically significant correlation (r 0.084, p 0.359). The difference between scleral PT and GAT did not correlate with SE (r 0.08, p 0.46), CCT (r -0.11, p 0.34) or AL (r 0.01, p 0.98). Conclusions Scleral PT has shown consistently higher IOP measurements than the corneal IOP measurements. While scleral PT has a statistically significant positive correlation to corneal PT, it unfortunately does not correlate well to the gold standard of IOP measurement, GAT. Initial analysis has been unable to account for this discrepancy by factoring in SE, CCT or AL separately. With further data collection and analysis we hope to determine if an equation could be formulated that would provide the true IOP as a function of scleral PT measurements by taking SE, AL and CCT into consideration concomitantly. Methods IRB approved, prospective case control study 54 patients who presented to the Loyola University Hospital outpatient ophthalmology clinic for routine examination Patients were provided appropriate informed consent and were aware of the risks and benefits of participation The first IOP measurement was taken on the central cornea with a Goldmann applanation tonometer AT900® (Haag-Streit International) The second IOP measurement was taken on the central cornea with a Model 30 Classic Pneumatonometer (Reichert Ophthalmic Instruments) The third and final IOP measurement was taken on the inferotemporal scleral approximately 2 mm from the limbus with the same Model 30 Classic Pneumatonometer (Reichert Ophthalmic Instruments) Corneal pachymetry was measured with the DGH Model 555 PACHETTE 3 (DGH Technology Inc) The patient’s age, gender, ocular history, refractive error, and current medications were recorded Pearson’s correlation was used for statistical analysis Data Results AverageStandard Deviation Range GAT (mmHg) – 24 Corneal PT (mmHg) – 28 Scleral PT (mmHg) – 52.5 Spherical Equivalent (D) – CCT (µm) – 727 Axial Length (mm) – Scleral PT vs GAT Pearson r P value (two-tailed) Scleral PT vs Corneal PT Pearson r P value (two-tailed) 0.047