Influence of Anterior Biometry on Corneal Biomechanical Stiffness of Glaucomatous Eyes Treated With Chronic Medication or Filtration Surgery Sushma Tejwani, MD,*† Mathew Francis, MTech,‡ Shoruba Dinakaran, MD,* Vijna Kamath, MD,* Bhavinkumar Tilva, MD,* Raunak K. Das, PhD,† Rohit Shetty, MD, PhD, FRCS,§ and Abhijit Sinha Roy, PhD‡ Précis: Anterior chamber depth, IOP, and thickness confounded the assessment of corneal biomechanical properties with noncontact applanation in glaucoma eyes. Compared with normal eyes, glau- coma eyes, which underwent long-term treatment or filtration sur- gery, had similar properties. Purpose: The purpose of this study was to evaluate corneal stiffness in primary angle-closure (PACG) and primary open-angle (POAG) glaucoma eyes that were subgrouped on the basis of the type of topical medication and filtration surgery using noncontact applanation. Methods: All eyes were retrospectively reviewed for intraocular pressure (IOP) with Corvis-ST (OCULUS Optikgerate Gmbh, Germany). Nonglaucoma (n = 140), PACG (n = 102 under medi- cation), and POAG (n = 154 under medication) eyes were included. Corneal stiffness was calculated using deformation amplitude and a biomechanical model. Multivariate analyses were performed, which evaluated the effect of systemic conditions (diabetes and hyper- tension), the effect of medication (prostaglandins or beta blockers or combined), and the effect of filtration surgery (PACG: n = 23; POAG: n = 26). Age, IOP, central corneal thickness (CCT), refractive error, and anterior chamber depth (ACD) were covariates. Results: Diabetes and hypertension did not alter corneal stiffness of glaucoma eyes compared with nonglaucoma eyes (P > 0.05). Cor- neal stiffness of POAG and nonglaucoma eyes was similar but significantly different from the stiffness of PACG eyes (P = 0.002), irrespective of the type of topical medication. This difference was strongly correlated with ACD (P = 0.003) in addition to IOP and CCT. In eyes treated with filtration surgery, ACD (P = 0.04) again impacted the trends between nonglaucoma and glaucoma eyes. Conclusions: Medication or filtration surgery did not affect the cor- neal biomechanical parameters differentially from nonglaucoma eyes. However, IOP, CCT, and ACD strongly affected corneal bio- mechanical parameters in the same glaucoma eyes. Key Words: glaucoma, angle closure, Open angle, biomechanics, Intraocular pressure, prostaglandins, beta-blockers, cornea, applanation (J Glaucoma 2019;28:626–632) N oncontact corneal applanation with an air puff is one of the most common methods to measure intraocular pressure (IOP). Accurate IOP measurement is challenging in glaucoma patients with abnormal IOP due to the inter- relationship between the corneal elastic modulus, thickness, and in vivo IOP. 1 However, IOP becomes near normal after treatment with medication or surgery. Therefore, bio- mechanical properties of the cornea play a critical role in the accurate determination of IOP in glaucoma patients, both before and after treatment. 1,2 The ocular response analyzer (ORA; Reichert Inc., NY) was the first clinical device used to assess corneal biomechanical properties in glaucomatous eyes. The ORA revealed different biomechanical properties of the cornea (corneal hysteresis or CH and corneal resist- ance factor or CRF) in glaucomatous eyes compared with normal eyes. 2–6 However, results were discordant between studies on glaucomatous eyes after ocular features (axial length, central corneal thickness or CCT, and IOP) were accounted for in multivariate models. 2,5,6 This implied that the changes in CH and CRF of glaucomatous eyes may be influenced by alterations in other ocular structures, and actual changes in biomechanical properties were not cap- tured by the ORA. As the correlation between in vivo corneal stiffness and ORA indices was unknown, a newer device, called Corvis-ST (OCULUS Optikgerate Gmbh, Wetzlar, Germany), was intro- duced to assess glaucomatous eyes. 7–14 Corvis-ST provided real- time deformation data of the cornea during the applanation process. These deformation data were converted to a definition of corneal and extracorneal stiffness in recent studies using a novel biomechanical model. 15,16 When evaluated with Corvis-ST, cor- neal stiffness was reduced in both eyes with myopia 15 and keratoconus. 16 Another confounder in glaucoma patients was the use of topical medications to reduce IOP. Some reports suggested that medications such as prostaglandins (PG) and beta-blockers (BB) may also affect corneal biomechanical properties and IOP measurement, 12,13 although the measured indices were not adjusted for ocular features, such as axial length, anterior chamber depth, and myopia, in one study. 12 Therefore, the aim of this study was to assess corneal and extracorneal stiffness in a large population of primary angle-closure (PACG) and primary open-angle (POAG) glaucoma Received for publication June 24, 2018; accepted March 8, 2019. From the Departments of *Glaucoma Services; §Cornea Services, Narayana Nethralaya; ‡Imaging, Biomechanics, and Mathematical Modeling Solutions Lab, Narayana Nethralaya Foundation, Ban- galore, Karnataka; and †School of Biosciences and Technology, Vellore Institute of Technology, Vellore, Tamil Nadu, India. Supported by Indo-German Science and Technology Center, Department of Science and Technology, India, grant number SIBAC. A.S.R.: has intellectual property on biomechanical modeling of the eye through Cleveland Clinic Innovations, US. The remaining authors declare that they have nothing to disclose. Reprints: Abhijit S. Roy, PhD, Narayana Nethralaya, Narayana Health City, #258A Hosur Road, Bommasandra, Bangalore 560099, Kar- nataka, India (e-mail: asroy27@yahoo.com). Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved. DOI: 10.1097/IJG.0000000000001247 ORIGINAL STUDY 626 | www.glaucomajournal.com J Glaucoma  Volume 28, Number 7, July 2019 Copyright r 2019 Wolters Kluwer Health, Inc. All rights reserved.