Bowman layer onlay grafting as a minimally invasive treatment for the most challenging cases in keratoconus.

To analyze the clinical outcomes after Bowman layer (BL) onlay grafting for the treatment of progressive, advanced keratoconus. Prospective, interventional case series. Twenty-one eyes underwent BL onlay grafting. After removing the epithelium, a single or double BL-graft was "stretched" onto the corneal surface, allowed to dry-in, and a soft bandage lens was placed until the graft was re-epithelialized. Best spectacle- and/or best contact lens-corrected visual acuity (BSCVA/BCLVA), corneal tomography, and postoperative complication rates were analyzed for the total group and two subgroups [Group 1: preoperative maximum keratometry (Kmax) <69D (n=7), Group 2: preoperative Kmax ≥69D (n=14)]. Follow-up ranged from 6-36 months (mean 21±11 months). All 21 surgeries were uneventful. Overall, Kmax changed from 76±12D preoperatively to 72±9D at 6-36 months postoperatively (P=0.015). Kmax decreased by 6D in Group 2 (P=0.002) but did not change in Group 1. Average BSCVA remained stable for Group 1 and improved from preoperatively 0.8±0.4 to 0.4±0.2 LogMAR postoperatively in Group 2 (P=0.032); BCLVA remained stable (P>0.05). Within the first postoperative weeks, two eyes required BL-graft re-positioning after inadvertent bandage lens removal and four eyes underwent BL re-transplantation for incomplete re-epithelialization. One eye underwent BL-regrafting 12-month postoperative after traumatic corneal erosion. All eyes showed a completely re-epithelialized graft at the last available follow-up. BL onlay grafting is a completely extraocular, minimally invasive surgical technique, providing up to -6D of corneal flattening in eyes with advanced progressive keratoconus, allowing for continued (scleral) contact lens wear and therefore preserving the BCLVA.

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