Comparison of Placido disc and Scheimpflug image-derived topography-guided excimer laser surface normalization combined with higher fluence CXL: the Athens Protocol, in progressive keratoconus

Abstract

Background: The purpose of this study was to compare the safety and efficacy of two alternative corneal topography data sources used in topography-guided excimer laser normalization, combined with corneal collagen cross-linking in the management of keratoconus using the Athens protocol, ie, a Placido disc imaging device and a Scheimpflug imaging device.

Methods: A total of 181 consecutive patients with keratoconus who underwent the Athens protocol between 2008 and 2011 were studied preoperatively and at months 1, 3, 6, and 12 postoperatively for visual acuity, keratometry, and anterior surface corneal irregularity indices. Two groups were formed, depending on the primary source used for topoguided photoablation, ie, group A (Placido disc) and group B (Scheimpflug rotating camera). One-year changes in visual acuity, keratometry, and seven anterior surface corneal irregularity indices were studied in each group.

Results: Changes in visual acuity, expressed as the difference between postoperative and preoperative corrected distance visual acuity were +0.12 ± 0.20 (range +0.60 to -0.45) for group A and +0.19 ± 0.20 (range +0.75 to -0.30) for group B. In group A, K1 (flat keratometry) changed from 45.202 ± 3.782 D to 43.022 ± 3.819 D, indicating a flattening of -2.18 D, and K2 (steep keratometry) changed from 48.670 ± 4.066 D to 45.865 ± 4.794 D, indicating a flattening of -2.805 D. In group B, K1 (flat keratometry) changed from 46.213 ± 4.082 D to 43.190 ± 4.398 D, indicating a flattening of -3.023 D, and K2 (steep keratometry) changed from 50.774 ± 5.210 D to 46.380 ± 5.006 D, indicating a flattening of -4.394 D. For group A, the index of surface variance decreased to -5.07% and the index of height decentration to -26.81%. In group B, the index of surface variance decreased to -18.35% and the index of height decentration to -39.03%. These reductions indicate that the corneal surface became less irregular (index of surface variance) and the "cone" flatter and more central (index of height decentration) postoperatively.

Conclusion: Of the two sources of primary corneal data, the Scheimpflug rotating camera (Oculyzer™) for topography-guided normalization treatment with the WaveLight excimer laser platform appeared to provide more statistically significant improvement than the Placido disc topographer (Topolyzer™). Overall, the Athens protocol, aiming both to halt progression of keratoconic ectasia and to improve corneal topometry and visual performance, produced safe and satisfactory refractive, keratometric, and topometric results. The observed changes in visual acuity, along with keratometric flattening and topometric improvement, are suggestive of overall postoperative improvement.

Keywords: Athens protocol; EX500 excimer laser; WaveLight/Alcon excimer laser; anterior Pentacam indices; cross-linking; higher fluence collagen cross-linking; keratoconus.

Figure 1

Box plots of corrected distance visual acuity, expressed as decimals. Top, preoperative and postoperative values for both groups. Bottom, gain/loss expressed as difference between postoperative minus preoperative corrected distance visual acuity. Notes: Box plots are showing median level indicated by ⊗, average symbol ⊕, 95% median confidence range box (black borderline boxes), and interquartile intervals range box (red borderline boxes). Abbreviation: CDVA, corrected distance visual acuity.

Figure 2

(A) Box plot describing induced changes (preoperative versus postoperative values) for anterior flat (top) and steep (bottom) keratometry (in diopters, D) for group A (Placido). (B) Box plot describing induced changes (preoperative versus postoperative values) for anterior flat (top) and steep (bottom) keratometry (in diopters, D) for group B (Scheimpflug). Notes: Median level is indicated by ⊗, average by ⊕, the 95% median confidence range box by the red borderline, and the interquartile intervals range box by the black borderline.

Figure 3

Top, box plot of preoperative ISV, and bottom, preoperative IHD versus keratoconus grading, as produced by the Oculyzer software. Notes: Median level is indicated by ⊗, average by ⊕, the 95% median confidence range box by the lack borderline, and the interquartile intervals range box by the red borderline. Abbreviations: IHD, index of height decentration; ISV, index of surface variance.

Figure 4

Box plot describing changes (preoperative versus postoperative values) induced for ISV in the two groups: top, group A, Placido; bottom, group B, Scheimpflug. Notes: ⊗, median level; ⊕, average; red borderline, 95% median confidence range box; black borderline, interquartile intervals range box. Abbreviation: ISV, index of surface variance.

Figure 5

Box plot describing changes (preoperative versus postoperative values) induced for IHD for the two groups: top, group A, Placido; bottom, group B, Scheimpflug. Notes: ⊗, median level; ⊕, average; red borderline, 95% median confidence range box; black borderline, interquartile intervals range box. Abbreviations: IHD, the index of height decentration; ISV, index of surface variance.

Figure 6

(A) Box plot describing preoperative versus postoperative changes in IHD induced for the subgroups. Top, group A1 (Placido low) indicating less affected keratoconic eyes; bottom, group A2 (Placido high) indicating more affected keratoconic eyes. (B) Box plot describing preoperative versus postoperative changes in IHD induced for the subgroups. Top, group B1 (Scheimpflug low) indicating less affected keratoconic eyes; bottom, group B2 (Scheimpflug high) indicating more affected keratoconic eyes. Notes: ⊗, median level; ⊕, average; red borderline, 95% median confidence range box; black borderline, interquartile intervals range box. Abbreviation: IHD, index of height decentration.