Keratoconus treatment options have expanded considerably. In the past, patients would be fitted with gas permeable lenses until they could no longer tolerate them or see well enough to function, at which time a corneal transplant would be performed. With the use of scleral lenses and a growing number of optometrists skilled at fitting this modality, patients are able to function longer prior to needing surgery. Crosslinking is now implemented earlier in the course of the disease, with fewer actually progressing to severe disease, requiring transplantation. Intacs are also helpful in changing the corneal shape to increase visual function.

Keratoconus treatment options have expanded considerably. In the past, patients would be fitted with gas permeable lenses until they could no longer tolerate them or see well enough to function, at which time a corneal transplant would be performed. With the use of scleral lenses and a growing number of optometrists skilled at fitting this modality, patients are able to function longer prior to needing surgery. Crosslinking is now implemented earlier in the course of the disease, with fewer actually progressing to severe disease, requiring transplantation. Intacs are also helpful in changing the corneal shape to increase visual function.

Surgeries that avoid full corneal transplantation are advantageous for patients, will experience less rejection, less need for chronic steroid usage, and quicker visual recovery. These include deep anterior lamellar keratoplasty (DALK) and Bowman’s layer transplantation. DALK, while leaving the endothelium intact, does weaken the corneal structure and is associated with intraoperative and postoperative complications.

Bowman’s layer transplantation has fewer complications and is a less invasive surgery. Bowman’s membrane fragmentation occurs in advance keratoconus. Based upon this pathological finding, it was thought that partial restoration using a mid-stromal BLT of an isolated Bowman’s layer graft may flatten the cornea. The purpose of the BLT is to reinforce the thin cornea and support it structurally. (2) The purpose of Bowman’s layer is not fully understood. Keratorefractive surgery patients undergoing PRK have none without demise. It was suggested that it may be the strongest biomechanical element of the cornea, after the anterior third.

Bowman’s layer transplantation was first described in 2014. In this technique, an isolated Bowman’s layer graft is positioned between the layers of stroma. It is a sutureless procedure, involving an acellular graft, potentially reducing complications of penetrating keratoplasty and DALK. While crosslinking is indicated for eyes with mild to moderate keratoconus, Bowman’s layer transplantation is indicated for the eye with moderate to severe keratoconus, when crosslinking and INTACS are less likely to be beneficial.

Bowman’s grafts are prepared from donor corneas not suitable for PK less than 24 hours old, or from donor buttons endothelium removed for endothelial keratoplasty. Placement into the host cornea begins with a superior conjunctival peritomy. Just outside the limbus, a partial thickness scleral tunnel is created, dissecting into the clear cornea. A paracentensis is then created, and the anterior chamber is filled with air. A stromal pocket is manually dissected over 360 degrees to the limbus. A depth of 50% is preferred to minimize perforation during the procedure. The graft is prepared using alcohol and balanced salt solution, stained with Trypan blue for visibility, and placed on the corneal glide for placement in the pocket. The glide is inserted and once the graft is inside the pocket, the glide is removed. The graft is unfolded and positioned. BSS is used to normalize ocular pressure. The conjunctiva is repositioned over the superior limbus and the eye is patched without suturing. Topical antibiotics are used for 7 days, with topical steroids typically four times per day for 30 days, then tapered.

Clinical outcomes are promising. Flattening of Kmax of an average of 8.5D within the first postoperative month, followed by stabilization of the ectasia has been reported. Reported complications include hydrops and perforation of Descemets membrane. ie., If perforation occurs, the procedure may be stopped, the corneal allowed to heal for another attempt later, or the procedure may be changed to a penetrating keratoplasty at the surgeon’s discretion.

A recent case illustrates the concept: a 24-year-old black male presented with advanced, progressive keratoconus in his left eye. Best spectacle-corrected visual acuity measured 20/30, but maximum keratometry (Kmax) was assessed at 62.9 diopters (D), increased from 57.1 D and 52.1 D two years previously, respectively. A decision was made to proceed with BL transplantation, which was performed as described above. No intra- or postoperative complications were experienced. Three months postoperatively, best spectacle-corrected vision was unchanged at 20/30. However, the steepest keratometry values were reduced, from 62.9D to 58.3D. The graft was almost imperceptible by slit-lamp examination (Figure 1; yellow arrows indicate the graft’s lateral border), and the eye appeared quiet and comfortable, without the need for postoperative steroid or antibiotic medication. In the three years since the surgery, Kmax and corneal thickness have been stable in the operated eye, despite a history of relentless progression before surgery.

Special thank you to Dr. Jack Parker, Birmingham, AL for his assistance with this article and case presentation.


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  4. van Dijk K, Parker J, Tong CM, Ham L, Lie JT, Groeneveld-van Beek EA, et al. Midstromal isolated Bowman layer graft for reduction of advanced keratoconus: a technique to postpone penetrating or deep anterior lamellar keratoplasty. JAMA Ophthalmol. 2014;132:495–501.

  5. van Dijk K, Liarakos VS, Parker J, Ham L, Lie JT, Groeneveld-van Beek EA, et al. Bowman layer transplantation to reduce and stabilize progressive, advanced keratoconus. Ophthalmology. 2015;122:909–17.

  6. Zygoura V, Birbal RS, van Dijk K, Parker JS, Baydoun L, Dapena I, et al. Validity of Bowman layer transplantation for keratoconus: visual performance at 5-7 years. Acta Ophthalmol. 2018; https://doi.org/10.1111/aos.13745.

  7. van Dijk K, Parker J, Tong CM, Ham L, Lie JT, Groeneveld-van Beek EA, et al. Midstromal isolated Bowman layer graft for reduction of advanced keratoconus: a technique to postpone penetrating or deep anterior lamellar keratoplasty. JAMA Ophthalmol. 2014;132:495–501

  8. van Dijk K, Liarakos VS, Parker J, Ham L, Lie JT, Groeneveld-van Beek EA, et al. Bowman layer transplantation to reduce and stabilize progressive, advanced keratoconus. Ophthalmology. 2015;122:909–17.