While postoperative visual acuity is generally favorable in most patients who undergo keratoplasty, recalcitrant elevated IOP, both in the presence and absence of previous glaucoma, is a frequently encountered finding that may cause irreversible damage, both to the optic nerve and the keratoplasty itself. In fact, according to one study, post-keratoplasty glaucoma is the most frequent cause of ocular morbidity following keratoplasty.1 Additionally, another study showed the 10-year cumulative incidence of elevated IOP and elevated IOP requiring treatment in post-keratoplasty patients was 46.5% and 38.7%, respectively.2
           Due to the vulnerable condition of the eye following keratoplasty, it is crucial that treatment options for post-keratoplasty glaucoma demonstrate their efficacy in reducing IOP, while also minimizing damage to the corneal graft. Ab-interno canaloplasty (ABiC) may fit the bill here. In fact, I was part of a team that recently published in Cornea3 the results of a retrospective 12-month study that investigated the clinical outcomes and safety profile of ABiC using a specific device in post-keratoplasty eyes.³ 
            Here, I discuss why ABiC is beneficial for post-keratoplasty glaucoma, and I provide 24-month data on the safety and efficacy of the procedure. 
 
"Due to the vulnerable condition of the eye following keratoplasty, it is crucial that treatment options for post-keratoplasty glaucoma demonstrate their efficacy in reducing IOP, while also minimizing damage to the corneal graft."

ABiC Benefits
            ABiC is a MIGS procedure that does not involve tissue destruction and/or leaves an implant in the eye. Specifically, it allows surgeons to treat the conventional outflow pathways while maintaining a low-risk profile.^2,3 
            For the corneal surgeon, ABiC represents a procedure that can effectively reduce the IOP while maintaining angle anatomy if future glaucoma surgery with a glaucoma specialist is required. More importantly, ABiC is a procedure that corneal surgeons can easily learn with knowledge of angle anatomy and experience with surgical gonioscopy.
 
“ABiC uses a tissue-sparing and stent-free approach to provide corneal surgeons with an effective option to maintain corneal graft survivability while effectively lowering IOP and preventing irreversible ocular damage.”
 
24-Month Data
            In a study comprised of 12 eyes that underwent ABiC as a standalone procedure (canaloplasty-alone) and 5 eyes that underwent canaloplasty combined with phaco (canaloplasty+phaco), IOP was reduced in the eyes treated with ABiC, and this reduction was sustained two years after the procedure (See Table 1). 
            Other findings: No patients experienced loss in visual acuity, worsening of corneal edema or subsequent graft failure. Additionally, one patient had a hyphema that required washout, one patient required additional glaucoma surgery, and the reduction in the number of glaucoma medications required appeared to be transient, given that a significant number of patients needed topical medications even though they continued to maintain favorable IOPs. The good news for keratoplasty patients is that the results observed in this longer-term study, in terms of IOP reduction and preservation of visual acuity, are consistent with the published results of research into canaloplasty performed on normal glaucoma patients.4,5
 
Know Your ABiC
            Without prompt intervention, elevated IOP can result in corneal tissue and/or optic nerve damage. While the former is reversible with repeat keratoplasty, the latter may cause irreversible vision loss. As my glaucoma colleagues like to remind me: “You can replace the cornea, but you can’t replace the optic nerve!” ABiC uses a tissue-sparing and stent-free approach to provide corneal surgeons with an effective option to maintain corneal graft survivability while effectively lowering IOP and preventing irreversible ocular damage. This procedure can be readily performed by surgeons with a familiarity with angle anatomy. CP

References:

1. Al-Mahmood AM, Al-Swailem SA, Edward DP. Glaucoma and corneal transplant procedures. J Ophthalmol. 2012;2012:576394. doi:10.1155/2012/576394