Past and present of corneal refractive surgery: a retrospective study of long-term results after photorefractive keratectomy and a prospective study of refractive lenticule extraction.

Surgical correction of refractive errors is becoming increasingly popular. In the 1990s, the excimer laser revolutionized the field of corneal refractive surgery with PRK and LASIK, and lately refractive lenticule extraction (ReLEx) of intracorneal tissue, using only a femtosecond laser, has become possible. Two new procedures were developed, ReLEx flex (FLEX) and ReLEx smile (SMILE). Until this thesis, only a few long-term studies of PRK with a relatively limited number of patients had been published; therefore, this thesis intended to retrospectively evaluate long-term outcomes after PRK for all degrees of myopia for a large number of patients. Furthermore, a prospective contralateral eye study comparing FLEX and SMILE, when treating high to moderate degrees of myopia, had not been performed prior to this study. This was the second aim of this thesis. In the first study, results from 160 PRK patients (289 eyes) were presented. Preoperative spherical equivalent ranged from -1.25 to -20.25 D, with 78% having low myopia (<-6 D). Average follow-up time was 16 years (range 13-19 years), making this the longest published follow-up study on PRK patients. Outcomes from eyes with low myopia were generally superior to outcomes from eyes with high myopia, at final follow-up. Seventy-two percent were within ± 1.00 D of target refraction, as compared to 47% of eyes with high myopia. However, results from a subgroup of unilateral treated PRK patients indicated that refraction at final follow-up was affected by myopic progression. Fifty percent of eyes with low myopia had uncorrected 20/20 distance visual acuity or better, as compared to 22% of eyes with high myopia. Haze did not occur if attempted corrections were <-4 D, and only eyes with high myopia lost two lines or more of CDVA (corrected distance visual acuity). Eighty-one per cent were satisfied or very satisfied with their surgery. The results support the continued use of the excimer laser for corneal surface ablation as a treatment option for correction of low degrees of myopia, and as the treatment of choice for subgroups of refractive patients (thin corneas, etc.). The results also highlight that treatment of higher degrees of myopia with standard PRK should only be done today under special circumstances, due to low refractive predictability, and high risk of corneal haze. Technological advances since then should be taken into account when comparing these results with contemporary techniques. In the second study, 35 patients were randomized to receive FLEX in one eye and SMILE in the other. Preoperative spherical equivalent refraction ranged from -6 to -10 D with low degrees of astigmatism. A total of 34 patients completed the 6 month follow-up period. Refractive and visual outcomes were very similar for the two methods, as well as tear film measurements and changes in corneal biomechanics. Ninety-seven percent were within ± 1.00 D of target refraction, no eyes lost two lines or more of CDVA, and contrast sensitivity was unaffected after both procedures. The changes in higher-order aberrations were also very similar. There were also no differences in tear film parameters 6 months after surgery, although less postoperative foreign body sensation was reported within the first week after surgery in SMILE eyes. Corneal sublayer pachymetry measurements demonstrated equally increased epithelial thickness 6 months after surgery. Contrary to expectations, it was not possible to measure the theoretical biomechanical advantages of a small corneal incision in SMILE as compared to a corneal flap in FLEX. The main differences between FLEX and SMILE were found when the corneal nerves and intraoperative complications were evaluated. Thus, corneal sensitivity was better preserved and corneal nerve morphology was less affected after SMILE, but intraoperative complications occurred more frequently, although without visual sequela. Finally, 97% were satisfied or very satisfied with both their surgeries. The results support the continued use of both FLEX and SMILE for treatment of up to high degrees of myopia. Overall, refractive and visual results for both procedures were good and similar, but from a biological point of view, the less invasive SMILE technique is more attractive, as demonstrated in this study, despite being slightly more surgically demanding than FLEX.

Vestergaard AH 《-》

Spherical and aspherical photorefractive keratectomy and laser in-situ keratomileusis for moderate to high myopia: two prospective, randomized clinical trials. Summit technology PRK-LASIK study group.

Steinert RF ，Hersh PS 《-》

Photorefractive keratectomy versus laser in situ keratomileusis for moderate to high myopia. A randomized prospective study.

Hersh PS ，Brint SF ，Maloney RK ，Durrie DS ，Gordon M ，Michelson MA ，Thompson VM ，Berkeley RB ，Schein OD ，Steinert RF ... -  《OPHTHALMOLOGY》

Long-term outcomes of photorefractive keratectomy for low to high myopia: 13 to 19 years of follow-up.

To evaluate long-term outcomes after photorefractive keratectomy (PRK). A retrospective follow-up study of patients who received PRK at 5.0- to 6.5-mm optical zones, using the Summit broad beam excimer laser (Summit Technology, Inc., Waltham, MA) at Odense University Hospital, Odense, Denmark, between 1992 and 1998. One randomly selected eye of each patient was used in the statistical analyses. Re-treated eyes were excluded. One hundred sixty eyes were included. Mean follow-up time was 16 years (range: 13 to 19 years). Mean preoperative spherical equivalent was -4.84 ± 2.95 diopters (D) (range: -20.25 to -1.25 D). At last follow-up examination, achieved refraction was -1.00 ± 1.56 D (range: -10.75 to +1.00 D) from attempted refraction, and the change in mean refractive error from 6 months postoperatively was less than 1.00 D. Results from a subgroup of unilateral treated patients indicated that myopic progression was the main reason for the residual refractive error. For eyes with low myopia (n = 124), the proportion of eyes within ± 1.0 D of attempted refraction was 72%, and for eyes with high myopia (-6.00 D or more, n = 36) it was 47%. Forty-five percent had uncorrected distance visual acuity of 20/20 or better at last follow-up examination. Three eyes (2%) lost two or more lines and 13 eyes (8%) gained two or more lines of corrected distance visual acuity. Fourteen percent had haze (grade 0.5 to 2). Eighty-one percent were satisfied with the surgery. PRK for low degrees of myopia seemed safe and effective up to 19 years after surgery with conventional broad beam laser ablation. Refractive predictability was significantly lower and the occurrence of haze was higher in eyes with high myopia.

Vestergaard AH ，Hjortdal JØ ，Ivarsen A ，Work K ，Grauslund J ，Sjølie AK ... -  《JOURNAL OF REFRACTIVE SURGERY》

Comparison of ReLEx SMILE and PRK in terms of visual and refractive outcomes for the correction of low myopia.

Ganesh S ，Brar S ，Patel U 《-》