Posters

Preliminary findings for wavefront-guided transepithelial photorefractive keratectomy combined with corneal collagen cross-linking for stage II-III keratoconus using the SCHWIND Amaris 750S excimer laser

Poster Details

First Author: B.Allan UK

Co Author(s):    D. Gore              

Abstract Details

Purpose:

Combining transepithelial photorefractive keratectomy (TransPRK) with corneal collagen cross-linking (CXL) for keratoconus may provide enhanced spectacle corrected distance visual acuity (CDVA) in comparison with CXL alone. The Schwind Amaris excimer laser platform (Schwind GmbH, Kleinostheim, Germany) is capable of topography guided and aberrometry (wavefront) guided ablation to treat irregular astigmatism, and has a unique tissue saving algorithm designed to target higher order aberrations without any compensatory additional tissue removal to regulate induced changes in sphere and cylinder. Here we present preliminary findings from a prospective case series of patients with keratoconus treated with combined wavefront guided TransPRK and CXL.

Setting:

Moorfields Eye Hospital, London

Methods:

Predicted maximum depth and total volume of corneal stromal tissue removal was compared at the maximum optical zone diameter between wavefront guided PRK with and without the Amaris tissue saving algorithm, and between topography guided and wavefront guided PRK with the tissue saving algorithm applied. In patients with stage II-III keratoconus and Snellen CDVA≤6/6, TransPRK using the programming modality with the lowest predicted depth of tissue removal was applied in combination with CXL using a rapid protocol (10 minutes riboflavin soak, Vibex Rapid (Avedro Inc, Waltham MA); 30mW/cm2 total energy delivered over 8 minutes using pulsed light: 1.5 sec on - 1.5 sec off).

Results:

To date, 4 eyes of 2 patients with CDVA≤6/6 have been treated. In all eyes, the predicted depth/volume (mean 32µm/682nl) of tissue removal was lowest with wavefront guided treatment and the tissue saving algorithm. The mean reduction in predicted depth/volume of tissue removal using the tissue saving algorithm in wavefront guided treatment was 46µm/1623nl. The mean reduction in predicted depth/volume of tissue removal using wavefront guided rather than topography guided treatment was 20µm/298nl. The optical zone diameter was 7mm in all cases with a total ablation diameter of 7.65 to 8.13mm. To date, 3 month visual results are available for 1 eye. CDVA improved 3 lines from 6/15 to 6/7.5 after treatment. Coma (at 6mm) improved from 2.87D preoperatively to 0.85D.

Conclusions:

Early results indicate that corneal stromal tissue removal can be minimized in wide optical zone combined PRK and CXL for keratoconus by using wavefront guided in preference to topography guided treatment, and a tissue saving algorithm which targets irregular astigmatism only. Further study is required to confirm our early findings, and long-term review is required monitor corneal shape stability using the novel approach to simultaneous combined CXL and PRK for keratoconus described here. FINANCIAL INTEREST: NONE