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Corneal biomechanics in different keratoconus grades: a pilot study with a new device

Poster Details

First Author: P.Cristina SPAIN

Co Author(s):    M. Díez Ajenjo   C. García Domene           

Abstract Details



Purpose:

To analyze if the new device Corvis ST has any parameter to discriminate between incipient and advanced keratoconus patients

Setting:

Cornea and Refractive Surgery Unit. FISABIO Oftalmología Médica (FOM), Valencia, Spain

Methods:

We evaluated 20 eyes with keratoconus. We evaluated best corrected visual acuity (BCVA) with decimal optotypes. We measured corneal topography with Pentacam (Oculus, Wetzler, Germany). With topographies, we classificated keratoconus patients in two groups: incipient group (steeper meridian less than 47.2D, 12 patients, 33 + 13 years old) and moderate keratoconus (steeper meridian more than 47.2D, 8 patients, 40 + 12 years old). To evaluate corneal biomechanics we used a Corvis ST (Oculus, Wetzler, Germany). This device studies the dynamic corneal deformation during a controlled air pulse. The air pulse forces the cornea inwards through a first applanation into a concavity phase until it achieves the highest concavity (HC). The cornea undergoes a second applanation before achieving its natural shape when the air pulse ends. The moment, applanation length and velocity at first and second applanations were identified. The peak distance, deformation amplitude and the radius of curvature are also measured in the HC image. Pachymetry is calculated at the apex. Intraocular pressure (IOP) is calculated based on the timing of the first applanation. Statistical analyses were performed using the SPSS software. We made a non-parametric comparative Kolmogorov-Smirnov test. Two samples were different if p value was less than 0.05

Results:

Mean power of steeper meridian in incipient keratoconus group was 46+3 D and mean power of flattest meridian was 44+2 D. In moderate keratoconus group mean steeper meridian was 52+3 D and flattest meridian was 48+3 D. These power differences were statistically significant (p=0.028). BCVA for incipient keratoconus group was 0.9+0.2 decimal unit and for moderate keratoconus group was 0.6+0.2 decimal unit, without statistical differences (p=0.10). IOP was higher in moderate group (11.8+1.9 mmn Hg) than in incipient group (9.5+2.9 mm Hg), and pachymetry was higher in incipient group (507+40 m) than in moderate group (498+46 m), but these data were not statistically significant (p=0.15 and p=0.61 respectively). With Corvis ST, we observed that corneal deformation velocity was higher in moderate group and corneal recovery velocity was lower, and applanation length was higher in incipient group. But these observations were only significative for recovery velocity (p=0.028) and corneal deformation (p=0.046). We also observed significative differences in HC time (p=0.047), that it is higher in moderate group. Peak distance at HC was higher in incipient group, but this data was not statistically significant (p=0.09).

Conclusions:

Studying corneal biomechanics with Corvis ST, we can differentiate between incipient keratoconus and moderate keratoconus, but only in a few parameters. We can distinguish both groups in first applanations length, corneal recovery velocity, and HC time. These results may indicate that in incipient keratoconus, the cornea is more deformable, and it is more quick to achieve its natural shape in incipient group than in moderate group. But, it will be necessary to measure more patients to confirm these results. FINANCIAL INTEREST: NONE

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