Findings from a recent study published in the American Journal of Ophthalmology outlined the clinical outcomes after Bowman layer (BL) onlay grafting to treat progressive advanced keratoconus (KC).
Give me some background first.
Until recently, advanced cases of KC required invasive procedures such as deep anterior lamellar keratoplasty (DALK) or penetrating keratoplasty (PK).
However, in 2011, a minimally invasive procedure called BL inlay transplantation was established, in which a donor BL is positioned within the stromal pocket.
Talk about BL onlay grafting.
More recently, this procedure was further developed to become BL onlay grafting, which uses an acellular graft—preventing the risk of microperforation and reducing the risk of allograft rejection.
In this epi-off technique, following the removal of the epithelium, a single or double BL graft is “stretched” onto the corneal surface, allowed to dry in, and subsequently, a soft bandage lens is placed until the graft re-epithelializes.
Is this the first study on BL onlay grafting?
Nope—a previous study from 2021 led by the same research group demonstrated that this procedure is a feasible surgical technique that provided up to -5D of corneal flattening in eyes with advanced KC.
Now, talk about the study.
In this prospective, interventional case series, investigators included 21 eyes of 20 patients who underwent BL onlay grafting and followed up with patients postoperatively from 6-36 months (mean 21±11 months).
The cohort was divided into two subgroups based on the stage of the participants’ KC progression, as measured by preoperative maximum keratometry (Kmax).
The preoperative Kmax for group 1 (less advanced KC) was <69D (n=7) and >69D (n=14) for group 2 (more advanced KC).
Anything else?
Investigators recorded and analyzed key parameters for the entire cohort and both subgroups, such as:
- Best spectacle- and/or best contact lens-corrected visual acuity (BSCVA/BCLVA)
- Corneal tomography
- Postoperative complication rates
Findings?
Of note, all 21 surgeries were uneventful; broadly, the Kmax changed from 76±12D preoperatively to 72±12D during the follow-up period (P=0.015).
Further, the Kmax decreased by 6D in group 2 (P=0.002) but remained unchanged in group 1.
What about BSCVA and BCLVA?
In group 1, the average BSCVA remained stable, and in group 2, BSCVA improved from the preoperative measurement of 0.8±0.4 to 0.4±0.2 logMAR postoperatively (P=0.032).
For both groups, the BCLVA remained stable (P>0.05).
Any postoperative complications?
During the first few postoperative weeks, two eyes needed BL graft repositioning after accidental bandage lens removal, and four eyes underwent BL retransplantation due to incomplete re-epithelialization.
In addition, one eye underwent BL regrafting 12 months postoperatively following traumatic corneal erosion.
Ultimately, all eyes demonstrated a completely re-epithelialized graft at the last available follow-up.
Expert opinion?
Per the study authors, “BL onlay grafting seems especially effective for patients with very steep and thin corneas who still have a subjectively acceptable visual performance with scleral lenses.”
“This new technique may therefore be a promising alternative compared to more invasive treatment options for this challenging group of patients,” they added.
Take home.
These findings indicate that BL onlay grafting is an extraocular, minimally invasive technique that can provide up to -6D of corneal flattening in eyes with advanced progressive KC.
This could potentially allow for continued scleral contact lens wear and, consequently, preserve the BCLVA.