Contributing factors to corneal deformation in air puff measurements

8 pags., 5 figs., 2 tabs.PURPOSE. Air puff systems have been presented recently to measure corneal biomechanical properties in vivo. In our study we tested the influence of several factors on corneal deformation to an air puff: IOP, corneal rigidity, dehydration, presence of sclera, and in vivo versus in vitro conditions. METHODS. We used 14 freshly enucleated porcine eyes and five human donor eyes for in vitro experiments; nine human eyes were used for in vivo experiments. Corneal deformation was studied as a function of: IOP ranging from 15 to 45 mm Hg (in vitro); dehydration after riboflavin-dextran instillation (in vitro); corneal rigidity after standard ultraviolet (UV) corneal crosslinking (CXL, in vitro); boundary conditions, that is effect of the presence of the sclera (comparing corneal buttons and whole globes in vitro in pigs); and effect of ocular muscles (comparing human whole globes in vitro and in vivo). The temporal corneal deformation was characterized by the apex indentation across time, the maximal indentation depth, and the temporal symmetry (comparing inward versus outward deformation). The spatial corneal profile was characterized by the peak distance at maximal deformation. RESULTS. Temporal and spatial deformation profiles were very sensitive to the IOP (P < 0.001). The sclera slightly affected the temporal symmetry, while the ocular muscles drastically changed the amount of corneal recovery. CXL produced a significant (P=0.001) reduction of the cornea indentation (by a factor of 1.41), and a change in the temporal symmetry of the corneal deformation profile (by a factor of 1.65), indicating a change in the viscoelastic properties with treatment. CONCLUSIONS. Corneal deformation following an air puff allows the measurement of dynamic properties, which are essential for the characterization of corneal biomechanics. © 2013 The Association for Research in Vision and Ophthalmology, Inc.Supported by Spanish Government FIS2011-25637 (SM) and FPIBES-2009-024560 Predoctoral Fellowship (SK). The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007–2013)/ERC Grant Agreement number 294099. The authors alone are responsible for the content and writing of the paper