Moran Eye Center, University of Utah Histopathology of Intraoperative Cauterization in Keratoconus: Can Cautery be Combined with Deep Anterior Lamellar Keratoplasty? Yousuf M. Khalifa, Don Davis, Surekha Maddula, Peter Ness, Nick Mamalis, Majid Moshirfar, Mark D. Mifflin Moran Eye Center, University of Utah Salt Lake City, UT, USA The authors have no financial interest in the subject matter of this poster.

Introduction Intraoperative corneal cautery prior to trephination in keratoconus penetrating keratoplasty has been shown to decrease postoperative myopia and astigmatism1 Deep anterior lamellar keratoplasty (DALK) is a technique to selectively remove diseased corneal stroma while maintaining donor endothelium2 Busin M, Zambianchi L, Franceschelli F, et al. Intraoperative cauterization of the cornea can reduce postkeratoplasty refractive error in patients with keratoconus. Ophthalmology 1998; 105(8):1524-9. Fontana L, Parente G, Tassinari G. Clinical outcomes after deep anterior lamellar keratoplasty using the big bubble technique in patients with keratoconus. Am J Ophthalmol 2007; 143(1):117-124.

Introduction cont’d DALK Technically more demanding, typically a big bubble is used to separate Descemet’s membrane from stroma Postoperative refractive outcomes similar to PKP3 Benefits: Reduced risk of infection, less risk of wound dehiscence, no risk of endothelial rejection Can intraoperative corneal cautery be combined with DALK? Does the cautery depth appear to be too deep for the big bubble technique? Does it damage endothelium? 3. Javadi MA, Feizi S, Yazdani S, Mirbabaee F. Deep anterior lamellar keratoplasy versus penetrating keratoplasty for keratoconus: a clinical trial. Cornea 2010 (Epub)

Purpose To evaluate intraoperative corneal cautery depth and its effect on the endothelium in keratoconus patients. Methods Consecutive cauterized and non-cauterized keratoconic corneal buttons (n=129) from 2006 to 2009 were retrospectively evaluated using light microscopy and H&E stains Measurements of corneal thickness and cautery depth were made along with morphologic assessment of the underlying endothelium. Three fresh corneas were prospectively assessed with scanning electron microscopy and vital staining to visualize endothelial viability.

Non-cauterized corneal button Results Non-cauterized corneal button Noncauterized corneal button stained with hematoxyalin and eosin (100X). Note the focal discontinuities in Bowman layer; this feature is diagnostic for keratoconus (arrow). Endothelium are flattened and difficult to visualize, but present in this picture. The architecture in this photomicrograph is preserved.

Intraoperative Cautery Appearance Results Intraoperative Cautery Appearance

Cauterized Corneal Histopathology B Cauterized corneal button stained with hematoxyalin and eosin (40X). Note Coagulated epithelium (E), burn through Bowman’s layer (B), and stromal condensation under the cautery. Extent of stromal architectural changes are easily visualized in this specimen (arrow). Note large folds in Descemet’s membrane (D). This specimen was one of the few with complete absence of endothelium under areas of cautery (L). L D Cauterized Corneal button stained with hematoxylin and eosin (40X). Note the cauterized epithelium (E), and condensation of stroma under the burn (arrows) denoting changes in stromal architecture (staining more eosinophilic). Artificial corneal folds are also seen (F). Endothelial cells are also visualized directly under the cautery marks and no folds in Descemet’s membrane exist. E F F L L

Corneal Histopathology Measurements Results Corneal Histopathology Measurements   Peripheral Corneal Thickness (μm) Mean, ±S.D., (Range) Central Corneal Thickness (μm) Mean, ±S.D., (Range) Endothelial Cell Count Mean, ±S.D., (Range) Cauterized Corneas (n = 53) 562, ±140, (353-965) 407, ±115, (210-757) 28, ±11, (0-45) Non-Cauterized Corneas (n = 76) 574, ±191, (262-1468) 360, ±152, (140-1177) 31, ±11, (0-45) Student t-Test p- Values p=0.61 p=0.07 p= 0.23 Cautery depth (μm) Mean, ±S.D., (Range) Mean Percentage of Corneal Burn Depth 195, ±65, (63-323) 48%

Scanning Electron Microscopy Photomicrographs B S C Scanning Electron Microscopy Photomicrographs B A. En face view of the corneal epithelial cautery marks (C) B. Cross sectional view of cornea directly beneath cauterized epithelium (E). Note how cautery flattens the corneal curvature and Bowman layer (B). Stromal condensation is noted directly underlying the cautery mark (arrows), C. High magnification view of photo B highlighting coagulated epithelium (E), condensed, rigid Bowman layer (B), and underlying stroma (S). With light cautery some burns appear to affect only Bowman layer (not seen here). E B

Corneal Endothelium Vital Staining * † A Corneal Endothelium Vital Staining B C * Vital staining with Trypan blue followed by Alizaren red of three keratoconic corneas that were intraoperatively cauterized (A-C) showing healthy endothelium underlying epithelial cauthery. The hazy black marks in the background are cautery marks, and purple marks are intraoperative ink marks. Distinct areas of red (*) denoted epithelial death with denuded basement membrane showing. Blue nuclei (†) are from damaged/stunned endothelium. Smudgy red marks are artifactual Alizaren red staining (arrow only). Note endothelial damage is not associated with burn cautery marks but is random as is seen after penetrating keratoplasty.

Conclusions Epithelial corneal cautery variably condenses and flattens corneal stromal architecture. Endothelium underlying light to moderate corneal epithelial cautery is frequently viable after cautery. Corneal cautery architectural changes are likely less than 50 percent depth. There is no significant difference between pathological endothelial cell counts of cauterized and non-cauterized corneas. Cautery increases folding of Descemet’s membrane, but rarely changes Descemet’s membrane microscopic architecture.

Conclusions (cont’d) Corneal epithelial cautery coupled with DALK could be a viable treatment option for keratoconus and needs to be studied. Intraoperative corneal cautery could have other surgical indications such as peripheral cautery combine with epithelial debridement and bandage contact lens to treat keratoconus in the third world.