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

BackgroundThe 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.MethodsA 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.ResultsChanges 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.ConclusionOf 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.

Occupational safety measures and morbidity among welders in Vellore, Southern India

“…Placido's disk and Snellen's chart were used to examine the corneal surface and visual acuity, respectively. 25,26 Peak expiratory flow rates (PEFR) were measured using a hand-held peak flow meter calibrated by the Department of Physiology, Christian Medical College and Hospital, Vellore, India. Three readings were observed for each individual and the average of the three readings was computed.…”

Evaluation of Visual Acuity, Pachymetry and Anterior-Surface Irregularity in Keratoconus and Crosslinking Intervention Follow-up in 737 Cases

“…12,13 The same surgeon (AJK) performed the operations. Mean age or patients in this group, at the 6 months postoperative examination, was 31.2 ± 7.3 (20 to 57) years.…”

OCT corneal epithelial topographic asymmetry as a sensitive diagnostic tool for early and advancing keratoconus

“…KCN diagnosis was established by slit-lamp biomicroscopy for clinical signs of KCN, such as the pattern of opposing central and peripheral retinoscopic movements, the conical reflection on the nasal cornea under temporal lighting (Rizzutti’s sign), the Fleischer ring, “iron deposits” within the epithelium near the cone base, and finally the presence of Vogt’s striae 17. The KCN diagnosis was further confirmed by the WaveLight ® Oculyzer™ II (Alcon Surgical, Fort Worth, TX, USA) and a Pentacam High-Resolution Scheimpflug imaging camera (Oculus Optikgeräte, Wetzlar, Germany) 18. Quantitative data supporting the KCN diagnosis included keratometry >45.00 D and asymmetric topographic patterns.…”

“…Both of these indices have been recently studied in screening, classification, and clinical follow-up8,18,21,23 of keratoconic patients, indicating a robust correlation with KCN severity.…”