Corneal biomechanics with CORVIS-ST in post-keratoplasty corneas

Comparative evaluation of the corneal biomechanical parameters by the dynamic corneal response imaging with CORVIS-ST ST in normal and post-keratoplasty eyes.

Cross-sectional observational study of CORVIS-ST imaging of 150 normal corneas and 150 post-keratoplasty corneas was done to evaluate corneal biomechanics of normal Asian-Indian corneas and post-keratoplasty corneas. Data on demographic details, postoperative period, visual acuity (UCVA, BCVA) (logmar units), refraction, axial length (D), corneal topography Scheimpflug's imaging with Pentacam [Anterior-K1(AK1), Anterior-K2 (AK2), Posterior-K1(PK1), PosteriorK2(PK2), Mean keratometry (Kmean), Keratometry maximum (Kmax), Q-value, D-value, Thinnest pachymetry (TP), Corneal elevation [anterior (CE ant) and posterior (CE post)], CORVIS-ST imaging (bIOP, 1 st and 2 nd Appl time HCT, 1 st Appl length, DA, TBI, CBI, HC rad, Vel in and out, DA ratio, IR, Inv CR, SSI, SPA1, ARTh) were recorded.

Comparative evaluation of CORVIS-ST in 150 normal corneas [mean age 32.54 ± 10 (9-68) years] and 150 post-keratoplasty corneas [mean age 35.14 ± 16.96 (8-72) years; PK (58), DSAEK (29), DALK (58), HALK (8), and SALK (3)] noted 18 parameters (bIOP, 1 st and 2 nd Appl time HCT, 1 st Appl length, DA, TBI, CBI, HC rad, Vel in and out, DA ratio, IR, Inv CR, SSI, SPA1, ARTh) and showed that 12 of these were statistically different in post-keratoplasty corneas. Parameters of DA, TBI, CBI, IR, and Inv CR were higher, whereas HC rad, SSI, SPA1, and ARTh showed significantly lesser values in post-keratoplasty corneas as compared to normal corneas. Subgroup analysis (PK, DSAEK, DALK, HALK) showed eyes that underwent DSAEK had biomechanical values closest to that of normal corneas. Post-DALK in comparison to post-PK corneas showed significantly higher values in CBI and IR, and lower values in HC rad, SSI, and ARTh (0.87 ± 0.17, 9.9 ± 3.5, 0.85 ± 0.25, 190.92 ± 119.06 and 0.71 ± 0.25, 8.19 ± 1.92, 1.02 ± 0.38, and 340.90 ± 178.37, respectively). Correlational analysis showed significant mild positive correlation of CBI with corneal curvature in normal and post-PK corneas ( P = 0.004 and 0.040, respectively).

Post-keratoplasty corneas were seen to have lesser biomechanical strength as compared to normal corneas. Post-DSAEK corneas had a better biomechanical strength than other groups and closest biomechanics to normal corneas. Post-DALK in comparison to post-PK corneas showed a lower biomechanical strength in our study.