Corneal Biomechanical Properties in Keratoconic, Myopic, and Hypeopic Eyes as Measured With Scheimpflug-Based Tonometer

Tuesday, April 29, 2014: 10:11 AM
Room 151A (Boston Convention and Exhibition Center)
David Zadok, MD, Assaf Harofe Medical Center, Zerifin, Israel
Nadav Shoshany, MD, Assaf Harofe Medical Center, Tel Aviv, Israel

Narrative Responses:

Purpose
To evaluate corneal biomechanical properties in myopic, hyperopic and keratoconic eyes as measured with the CorVis ST (Corneal Visualization Scheimpflug Technology, CorVis ST; Oculus Optikgeräte, Inc.) a newly developed Scheimpflug-based noncontact tonometer with features of visualization and measurement of the corneal deformation response to an air impulse.

Methods
One hundred fifty seven participants, including keratoconus (KCN) patients (36 cases),  myopic (MY) patients (109 cases) and hyperopic (HY) patients (12 patients) were enrolled. Corneal biomechanical properties measurements were obtained with the Corvis ST by two experienced clinicians. One eye was selected randomly for further study. Statistical analysis was performed using a Student T-test.  Logistic regression was used in order to control for confounders ((IOP, pachymetry, and first applanation time) and to identify optimal combinations of parameters for keratoconus detection.

Results
In the KCN vs. MY comparison, the first applanation deflection amplitude (0.089±0.017 and 0.099±0.039 mm, respectively) and the simulated non-contact first applanation time (NTSIM-A1) (7.412±0.331 and 7.66±0.745 ms, respectively) were different statistically significant (p<0.029, p<0.007 respectively). They were remained significant when using logistic regression to control for confounders (OR 7.72e-09 CI[1.14e-16, 5.25e-01] p<0.042, OR 5.28 CI[1.04, 2.68e+01] p<0.045). In the KCN vs. HY no parameter was found to be statistically significantly different after controlling for confounders. No one parameter or a combination of parameters that is useful for differentiation between the three groups was found.

Conclusion
Two parameters were found to facilitate early distinction of keratoconus from myopia. However, the parameters and their combinations overlapped significantly and could not provide proper distinction between keratoconic and non-myopic eyes. Therefore, the findings can only be used as an adjunct to a thorough clinical examination and customary diagnostic tools.