SMILE or implant for hyperopia?
Intrastromal lenticule implantation may be a future treatment for hyperopia, but SMILE more effective now
Dan Z Reinstein MD
The advent of intrastromal implantation of femtosecond laser-sculpted lenticules has brought refractive surgery full circle to José Barraquer’s original idea of tissue additive corneal re-shaping, Dan Z Reinstein MD told the 38th Congress of the ESCRS.
“The accuracy and repeatability of the VisuMax femtosecond laser has made Barraquer’s concept a reality,” announced Prof Reinstein, Medical Director of London Vision Clinic, London, UK. The concept of tissue additive corneal refractive surgery dates back to 1980 when Dr Barraquer in his textbook on keratomileusis introduced a technique for myopia or hyperopia he called pocket intrastromal keratophakia, wherein a lathed disc of stroma is inserted into a lamellar pocket dissected in the cornea.
However, it was not until 2004 that the procedure was revived, this time in a new form that involved mechanical de-epithelialisation, lamellar microkeratotomy, hyperopic LASIK and a circumferential side-cut to remove the lenticule. The lenticule was then placed beneath a LASIK-style flap in the patients’ eye (Jankov et al, J Refract Surg Jan-Feb 2004;20(1):79-84).
In a hyperopic and amblyopic eye that had undergone previous refractive surgeries, the endokeratoplasty procedure improved mean best spectacle-corrected visual acuity from 20/200 to 20/70 and improved manifest refraction from +8.00 -1.00 x 130 to +1.00 -2.25 x 120 at two months postoperatively. Corneal topography showed a more regular cornea with increased curvature in all meridians. Central corneal thickness increased to 600µm.
The next attempt was in 2015 where a +10.00D lenticule obtained from a myopic small-incision lenticule extraction (SMILE®) procedure was implanted into an aphakic eye of a patient who had undergone removal of a congenital cataract in childhood. The patient’s hyperopia improved from a preoperative value of +12.00D to +1.00D at two days postoperatively, but regressed to +8.00D at four months (Pradhan et al. J Refract Surg. 2015;31:60).
Prof Reinstein noted that the reason for the regression was that although the front surface had steepened by the desired amount, the back surface had flattened, causing a hyperopic shift. Subsequent finite element model analysis using OptimEyes software predicted both the anterior and posterior corneal changes, he added (Studer et al. J Refract Surg.2015;480-486).
In another study, intrastromally implanted cryopreserved lenticules were used to treat eight hyperopic eyes and one aphakic eye. The postoperative residual spherical equivalent was +4.10D for the aphakic eye and had a mean value of +0.60D in the hyperopic eyes. None of the eyes showed evidence of rejection or loss of corrected distance visual acuity (CDVA) (Ganesh et al, J Refract Surg. 2015;31: 374-9).
One patient developed interface haze in both eyes at the end of six months, Dr Reinstein noted. However, lenticule exchange restored corneal clarity. One eye that underwent implantation of a -9.50D lenticule to correct +9.00D of hyperopia had a postoperative residual refraction of +2.50D. Relaxation of Bowman’s membrane using a Barren’s trephine reduced the hyperopia to +0.75D.
Dr Reinstein noted that research into the use of intrastromal lenticule implantation continues for a variety of indications including hyperopia, high astigmatism, presbyopia and, perhaps most importantly, keratoconus.
HYPEROPIC SMILE SHOWING PROMISE
Meanwhile, hyperopic SMILE® may hold more immediate prospects for the treatment of hyperopes than intrastromal lenticular implantation. Recent studies show that hyperopic SMILE® produces results comparable to those of hyperopic LASIK in terms of safety, visual outcome and refractive predictability, Dr Reinstein said.
He cited a prospective study in which he and his associates performed hyperopic SMILE® in a series of 93 eyes with a maximum attempted hyperopic meridian between +1.00D and +7.00D. Initial phase safety studies showed that treatment centration was similar to hyperopic LASIK (Pradhan et al, J Refract Surg. 2017;150-156), as were topographic optical zone diameter and spherical aberration induction (Pradhan et al, J Refract Surg. 2017;370-376). The optical zone diameter was 6.3-to-6.7mm, with a 2.0mm transition zone, 30μm minimum thickness and 120μm cap thickness (Pradhan et al, J Refract Surg. 2019;442-450).
At 12 months’ follow-up, the spherical equivalent was within ±0.50D of target refraction in 59% of eyes and within ±1.00D of target in 76% of eyes. There was also no significant difference between spherical equivalent at one day postoperatively and at the last follow-up visit.
In addition, among 37 eyes targeted for emmetropia, postoperative uncorrected distance visual acuity (UDVA) was the same or better than postoperative CDVA in 78% and was within one line of CDVA in 86%. Overall, at 12 months’ follow-up 17% of eyes lost one line of CDVA and no eyes lost two or more lines.Furthermore, vector analysis showed that the refractive cylinder was corrected within 0.50D of target in 95% of eyes and within 1.00D of target in 99% of eyes.
“Lenticule removal and implantation has shown promise, for keratoconus and corneal transplant, However, for hyperopia, SMILE® has shown promising early results,” Dr Reinstein added.
Dan Z Reinstein: Dzr@londonvisionclinic.com