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Tomographic and biomechanical index (TBI) in a sample of asymmetric keratoconic corneas: pilot study

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Session Details

Session Title: Presented Poster Session: Glaucoma and Imaging

Venue: Poster Village: Pod 3

First Author: : J.Salgado-Borges PORTUGAL

Co Author(s): :    A. Siva   F. Esteves   E. Nunes   A. Queiros   J. Gonzalez-Meijome  

Abstract Details


To compare the values of the biomechanical, tomographic and combined indices in a set of keratoconic corneas and the contralateral corneas not affected clinical and tomographicaly by the disease.


Hospital Privado da Boa Nova, Porto, Portugal.


The Corvis ST and Petacam (Oculus, Wetzlar) were used to conduct a bioomechcanial analysis of the corneal properties and tomographic properties, respectively. The more recent algorithms to derive the corneal biomechanical index (CBI) from Corvis and the Belin-Ambrosio deviation index BAD D from Pentacam were used. Using the combined information the Tomographic and Biomechanical index (TBI) was derived for the keratoconic corneas and the contralateral non-affected corneas. Wilcoxon non-parametric test was used to compared tomographic and biomechanical parameters between both eyes of the subjects.


Both corneas from 8 patients with unilateral keratoconus were included in the study (4 males, 4 females; 26.63±10.29 years). Mean maximum keratometric reading (Kmax) was 56.54±10.27D and 45.95±2.38D, in keratoconus and normal corneas, respectively (p=0.012). Thinnest corneal thickness was significantly thinner in the keratoconic eye compared to non-affected eye (476.50±69.14 vs 517.88±43.58 microns, p=0.017). The CBI parameter was significantly higher in keratoconic group (0.82±0.37 vs 0.25±0.34 p=0.018) and also regards to the BAD D value (0.82±0.37 vs 0.25±0.34, p=0.017). The TBI index was also higher in keratoconic group but the difference was marginally significant (0.90±0.28 vs 0.58±0.45, p=0.043).


In 5 of the eyes considered non-affected by the disease using classical definitions, at least two out of the three indices (CBI, BAD D and TBI) were considered borderline or indicative of pathology. The indices provided by the combined analysis of Pentacam and Corvis ST might be of help in classifying borderline cases typically assumed as normal non-pathological corneas. This study should be expanded to a larger sample to confirm the findings.

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