Commentary: Femtosecond laser-assisted stromal implants for keratoconus - Customized treatment for the future!

Penetrating keratoplasty (PK) and deep anterior lamellar keratoplasty (DALK) are well-established treatments for advanced keratoconus with excellent long-term outcomes. Intrastromal corneal ring segments (ICRS) implantation is sometimes done to delay corneal grafting. However, both transplants and ICRS have their own set of complications, some of which are eye threatening.[1]

Over the past few years, newer partial lamellar grafts are being explored – Bowman’s membrane transplantation (BMT)[23] and various types of stromal additive surgeries.[456] Using the ability of the femtosecond laser (FSL) to make precise and customized cuts, these surgeries are being explored more.

BMT was described by Zygoura et al.[3] in the early 2010s with encouraging mid- to long-term outcomes. BMT offers flattening of the ectatic cornea, thereby leading to some visual improvement and potentially delaying a transplant. In a recent article, Oganesyan et al.[7] suggest using Descemet’s membrane as an alternative to BMT.

The stromal additive surgeries tackle two key clinical features of keratoconus – adding to the thin cornea and flattening the steep cornea. It is often combined with collagen cross-linking to prevent disease progression. The general principle of stromal additive surgery is to make FSL-guided pockets or circular channels in the stroma at different depths. Stromal implant or ring segments are then implanted in the respective space. However, the source of stromal tissue and the method of preparation are different for each surgeon. Some authors advocate doing a simultaneous collagen cross-linking. The techniques are summarized in Table 1. Surgeons have experimented with the ideal implant shape and depth to achieve maximum flattening and to improve the corneal topography. Some of which has resulted in significant hyperopic shifts too!

Table 1

Summary of the technical steps of various femtosecond laser-assisted stromal implantation surgeries

Author	Tissue source	Donor shape	Implant depth	Simultaneous cross-linking
Jacob et al.[6]	Donor corneal tissue	Ring segment	50% of minimum pachymetry	Yes
Ganesh and Brar[4]	SMILE lenticule	Annular	100 µ	Yes
Jadidi and Mosavi[5]	Custom FSL cut lenticule	Circular or crescentic	250 µ	No
Jafarinasab and Hadi[8]	DSAEK anterior cap	Ring segment or crescentic (for pellucid)	300-400 µ	No

SMILE=small-incision lenticule extraction, DSAEK=Descemet’s stripping automated endothelial keratoplasty

An interesting article by Jafarinasab and Hadi[8] describes the outcomes of FSL-assisted implantation of biological ring segments made from DSAEK (Descemet’s stripping automated endothelial keratoplasty) anterior caps. In the current publication, simultaneous cross-linking was not done, and the authors plan to do it at a later date if and when progression is noted.

Some authors have used otherwise discarded corneal tissue to make the stromal grafts.[48] Although a small number, this still saves a few corneal donor tissues.

The economic aspect discussed by Jafarinasab and Hadi[8] may or may not hold true in all cases. In some parts of the world, the surgical cost of DALK might cost less than an FSL cut combined with cross-linking. Also, there is always the theoretical risk that keratoconus might progress after these newer stromal additive surgeries, and these eyes will need PK or DALK. So the combined surgical cost will be much more.

Femtolaser assisted stromal additive keratoplasty (FASAK) is one of the new avenues in the treatment of keratoconus. As with all new advances, only time will tell whether these will eventually become part of standard therapy. Unlike ICRS, there is no nomogram currently to determine the size, shape, and depth of stromal implants corresponding to keratoconus parameters. Probably that is a Herculean task, too, given that all these bioimplants behave differently. Perhaps in the future we can have engineered customized stromal (or even biosynthetic) implants to neutralize both the refractive error and the aberrations; that combined with cross-linking may be a minimally invasive surgical treatment for keratoconus. The possibilities are exciting!