Comparison of Placido Disk and Scheimpflug Generated Data in Topography-Guided Normalization in Keratoconus Combined With CXL Athens Protocol
Narrative Responses:
Purpose
To compare the safety and efficacy of two alternative corneal topography data sources employed in the topography - guided excimer laser normalization, combined with CXL, in the management of keratoconus with the Athens Protocol (AP) procedure, namely a Placido-disk imaging device and a Scheimpflug imaging device.
Methods
One hundred eighty-one (181) consecutive keratoconic cases subjected to the Athens Protocol procedure, were studied pre-operatively and 1, 3, 6, and 12-months postoperatively for visual acuity, keratometry, and anterior surface corneal indices. Two groups were formed, depending on the primary source for the topo-guided photoablation, namely a Placido disc, for group A (Placido), and a Scheimpflug rotating camera, for group B (Scheimpflug). The one-year changes in visual acuity, keratometric, and seven anterior-surface topometric indices were studied for both groups.
Results
For group A, K1 (flat) changed 45.202±3.782 D to 43.022±3.819, (-2.18 D flattening), and K2 (steep) changed 48.670±4.066 D to 45.865±4.794 D, (-2.805 D flattening). Respectively, for group B, K1 (flat) changed 46.213±4.082 D to 43.190±4.398 D, (-3.023 D flattening), and K2 (steep) changed 50.774±5.210 to 46.380±5.006 D, (-4.394 D flattening).
For group A, the index of surface variance (ISV) was reduced to -5.07% and the index of height decentration (IHD) to -26.81%. For group B, ISV reduced to -18.35% and IHD to -39.03%. These reductions indicate a less irregular corneal surface and a ‘flatter’ cone.
Conclusion
The Scheimpflug camera appears to provide better improvement when used instead of the Placido topographer for topography-guided treatments. The Athens Protocol procedure demonstrates safe and notable refractive, keratometric and topometric results. The observed changes, as well as keratometric flattening and topometric improvement are suggestive of the overall postoperative improvements.