AbstractsBiology & Animal Science

The Influence of IOP, Corneal Stiffness, and Sclera on Corneal Deformation Response to an Air Puff Using the CorVis ST

by Kimberly M Metzler

Institution: The Ohio State University
Department: Biomedical Engineering
Degree: MS
Year: 2015
Keywords: Biomedical Engineering; cornea; biomechanics; crosslinking; deformation response; CorVis ST; air puff
Record ID: 2062589
Full text PDF: http://rave.ohiolink.edu/etdc/view?acc_num=osu1418479307


Corneal biomechanics provides useful insight into the fields of refractive surgery and disease screening and management. The CorVis ST is a new device with the potential to provide clinical evaluation of in vivo corneas, but the precise impact of intraocular pressure (IOP) and corneal stiffness is not known. Additionally, the influence that the sclera has on deformation response has not been previously evaluated. The two studies presented use corneal deformation response parameters determined by the CorVis ST to analyze the difference between control and experimental groups. Twenty-four eyes of twelve human donors were obtained in matched pairs to determine if the mounting methods (i.e., chamber vs whole eye) influence corneal deformation response to an air puff. One eye of each pair was kept as an intact whole globe (WG group), while the cornea of the fellow eye was mounted in a rigid artificial anterior chamber (AC group). Internal pressure was set to 10, 20, 30, 40, and 50mmHg. Deformation response to the device’s air puff was captured at each pressure for both groups. With matched internal pressures, differences in deformation response were observed between groups for several response parameters. The AC group exhibited stiffer behavior than the WG group. For all pressures examined, corneas in the AC group had smaller deformation amplitudes at highest concavity as well as slower velocities at the second applanation. Several other parameters were found to be significantly different between groups as well.Ten eyes of five human donors were used to evaluate if human decorin core protein treatment had a stiffening effect on the cornea. One eye of each pair was treated while the other served as the control. Internal pressure was set to 15, 20, 30, 40, and 50 mmHg, with several air puff examinations performed at each pressure level. Stiffer behavior was observed in the treated corneas, with treatment having a significant effect on maximum deformation amplitude, velocity at the first applanation, and length of the second applanation. Porcine corneas were also used to assess if the treatment had a stiffening effect measured by uniaxial tensile tests. Strips of the treated and untreated porcine corneas underwent dynamic mechanical analysis and ramp testing. Treated corneas had significantly higher secant modulus at 5 and 6% strain, consistent with a treatment induced stiffening effect observed from the human data. These two studies identified deformation response parameters associated with changes in boundary conditions and corneal stiffness. The results have implications on interpreting in vivo air puff examinations, since the corneal deformation response is determined by a complex interplay of several parameters. Additionally, identifying deformation parameters sensitive to increased corneal stiffness may be useful in screening and management of diseases associated with corneal stiffness change.