Scheimpflug Corneal Topographer and Combined Placido Disc and Anterior Segment OCT Measurements of Corneal Topography Before and After LASIK
Narrative Responses:
Purpose
To compare the measurements of cornea topography and pachymetry before and after laser in situ keratomileusis (LASIK) using two different technologies—Scheimpflug imaging using Pentacam (Oculus) and combined Placido imaging and Optical Coherence Tomography imaging using Visante Omni (Carl Zeiss).
Methods
In a prospective study, 50 eyes of 25 patients were measured using Pentacam and Visante Omni best-fit toric ellipsoid before and after LASIK. The mean difference (Visante – Pentacam), standard deviation (SD), 95% limits of agreement (LOA) were calculated and Bland–Altman plots were constructed for anterior cornea curvature (ACC), posterior cornea curvature (PCC), anterior cornea elevation (ACE), posterior cornea elevation (PCC) and pachymetry of the thinnest point.
Results
Mean difference (MD) for pre-op ranged from 0.12D to 0.52D for ACC and PCC, 0.68µm to 1.16µm ACE and PCE, and -10.08 µm for pachymetry. 95%LOA ranged from 0.53 to 1.88D for ACC and PCC, 4.76µm to 14.3µm for ACE and PCE, and 32.30µm for pachymetry. Post-operatively, MD ranged from -0.31D to 0.17D for ACC and PCC, -1.96 µm to 2.52µm for ACE and PCE, and was -6.12µm for pachymetry. 95%LOA ranged from 0.50 to 5.80D for ACC and PCC, was 9.81µm to 16.69µm for ACE and PCE and 36.36µm for pachymetry. 92-100% of the cases fell within the 95%LOA.
Conclusion
We found a high degree of accuracy between the Pentacam and Visante Omni for cornea analysis. The Visante Omni under-measures pachymetry compared to the Pentacam and over-measures the other values but these differences are clinically insignificant. Both machines seem to perform equally well in pre-and post-LASIK cornea measurements.