title: Effect of Intraocular Pressure and Anisotropy on the Optical Properties of the Cornea: A Study Using Polarization Sensitive Optical Coherence Tomography.
abstract: OBJECTIVE
  We hypothesize that because of the anisotropic properties of the cornea, there should be a nonuniform change in birefringence with an increase in intraocular pressure (IOP). In this in vitro study, anisotropic properties, stress distribution within the cornea, and the effect of IOP on changes in stress level were investigated.
  
  
  METHODS
  Button inflation tests for deformation with polarization sensitive optical coherence tomography were used to demonstrate optical and material anisotropy on ex vivo human corneas.
  
  
  METHODS
  Inflation tests were performed on human donor corneoscleral rims. Using a turntable and hydrostatic column, each corneoscleral rim was subjected to a hydrostatic pressure of 0, 10, 15, and 20 mm Hg. At each pressure step, 4 scans at 0, 45, 90, and 135 degrees were taken by a polarization sensitive optical coherence tomography system, and the birefringence images and normal intensity-based images were recorded; images were later compiled for analysis.
  
  
  RESULTS
  The retardation changed with the axis of orientation (P [T ≤ t] 1-tailed = 0.025) and IOP (P [T ≤ t] 1-tailed = 0.019). Optical thickness of the cornea decreased with increasing IOP.
  
  
  CONCLUSIONS
  The optical properties of the cornea are modified with change in IOP. This is not uniform because of distinct anisotropic properties. Anisotropic properties may unpredictably affect the optical quality of cornea during or after the surgeries. Changes in corneal birefringence can be also used as a tool for measuring the IOP of the eye.
authors.affiliation: From the *Cornea and Anterior Segment Services, L. V. Prasad Eye Institute, Hyderabad; and †Laser Biomedical Applications & Instrumentation Division, Raja Ramanna centre for Advanced Technology, Indore, India; ‡Biomedical Engineering and Ophthalmology, The Ohio State University, Columbus, OH; and §Mechanical Engineering, Ujjain Engineering College, Ujjain, India.
authors.forename: Ashutosh
authors.initials: A
authors.lastname: Richhariya
authors.forename: Yogesh
authors.initials: Y
authors.lastname: Verma
authors.forename: Divakar K
authors.initials: DK
authors.lastname: Rao
authors.forename: Cynthia J
authors.initials: CJ
authors.lastname: Roberts
authors.forename: Ashraf M
authors.initials: AM
authors.lastname: Mahmoud
authors.forename: Virender S
authors.initials: VS
authors.lastname: Sangwan
authors.forename: Sunil
authors.initials: S
authors.lastname: Punjabi
authors.forename: Pradeep K
authors.initials: PK
authors.lastname: Gupta