New treatment
Stromal donor implant with CXL may improve VA in keratoconus patients with central cones
Howard Larkin
Published: Thursday, September 1, 2016
BETTER VISION
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: brar_sheetal@yahoo.co.inTags: corneal crosslinking, donor stromal lenticules, visual outcomes
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