Stromal donor implant with CXL may improve VA in keratoconus patients with central cones
Implanting modified donor stromal lenticules extracted during small incision lenticule extraction (SMILE) procedures into the corneas of keratoconus patients with central cones may improve visual outcomes, Sri Ganesh MBBS, MS, DNB told the 2016 ASCRS•ASOA Symposium & Congress in New Orleans, USA.
Combined with accelerated corneal crosslinking (A-CXL), the doughnut-shaped implant flattens the central cornea while elevating the mid-periphery, improving overall asphericity and aberrations.
In a pilot study involving six eyes in six keratoconus patients, mean best corrected visual acuity (BCVA) improved from 20/80 to 20/40, with four patients gaining two or more lines, and uncorrected visual acuity (UCVA) improved in all eyes six months after surgery, said Dr Ganesh, who is Chairman and Managing Director at Nethradhama Super Specialty Eye Hospital, Bangalore, India.
Safety also was excellent, with no significant difference in endothelial cell density before and after surgery, and no evidence of haze, infection or graft rejection in any patient, Dr Ganesh reported. Without the risk of extrusions or infections seen with intracorneal rings, or the pain of conventional CXL (C-CXL), the procedure may become a feasible keratoconus treatment option, though larger and longer studies are needed, he added.
While CXL often stops keratoconus progression, it does not eliminate topographic aberrations, or correct refractive errors. As a result, most patients must wear glasses or contact lenses or even gas-permeable rigid contacts, to achieve satisfactory vision after CXL, Dr Ganesh noted. Various treatments are combined with CXL to correct visual errors, but each has its drawbacks, Dr Ganesh said.
Dr Ganesh had success treating hyperopic patients by implanting into their corneas cryopreserved stromal lenticules collected from patients undergoing small-incision refractive lenticule extraction (ReLEx SMILE) for myopia (Cornea 2014;33:1355-1362). Thicker in the centre, the implanted tissue predictably increased corneal power without inducing significant higher order aberrations (HOAs), and because it was additive it resisted regression.
Dr Ganesh postulated that a similar tissue-adding approach might benefit keratoconus patients. However, the thick centres of available lenticules, which are exclusively from myopic SMILE treatments, might actually worsen aberrations due to central cornea cones.
However, with a 3.0mm hole cut in the centre with a trephine, leaving a doughnut shape, the donor lenticule is the right shape to add bulk where it is needed – in the mid-peripheral cornea, Dr Ganesh said. Inserted through a 2.0mm to 4.0mm incision into a pocket cut 100 microns deep in the cornea with a femtosecond laser, this flattens the central cone and steepens the cornea around it. With the proper thickness, the added tissue also can correct refractive errors.
Combining the procedure with A-CXL helps further helps to stabilise the result. Riboflavin solution injected into the pocket does away with the need to remove the epithelium. UV radiation is delivered at 30mW for 3.3 minutes.
In the six eyes in Dr Ganesh’s exploratory study, conducted with colleague Sheetal Brar MBBS, MS, FPRS, FC, adding the doughnut-shaped lenticule increased mean mid-peripheral pachymetry from 480.0 ± 23.3 microns to 525.9 ± 23.0 microns six months after surgery. Mean astigmatism also was reduced from -3.37 ± 1.64D to -2.62 ± 1.53.
Asphericity was reduced from a hyperprolate Q value of -1.61 to a more normal -0.55, Dr Ganesh said. Total HOAs were also reduced, often by more than half.
Though the results are promising, the procedure has some limitations, Dr Ganesh said. It is only effective for keratoconus with central cones, and in mild to moderate cases, with Kmax of <58D, no Vogt’s striae or apical scarring, he said. Nomograms also need refinement, and elevation topography might be used as a guide. Positives include better quality of vision, low risk of allogeneic rejection, and the procedure is reversible. However, long-term follow-up is needed to establish safety, efficacy and effects on corneal stabilisation, he concluded.
Sri Ganesh, Contact – Sheetal Brar: firstname.lastname@example.org