Excimer laser surface ablation procedures, such as photorefractive keratectomy (PRK) and laser-assisted subepithelial keratomileusis (LASEK), have become the technique of choice in corneas with inferior steepening on corneal topography without keratoconus, patients with thin central corneal thickness (CCT), those at risk for trauma, and those in whom epithelial problems are anticipated, such as patients with recurrent erosion syndrome or basement membrane disease.1
Although some studies have shown that LASIK performed in thin corneas with normal preoperative topography is a safe procedure when leaving a residual stromal bed thickness of more than 250 μm,2 several surgeons recommend not to perform LASIK in corneas with a preoperative CCT thinner than 500 μm1 (490 μm for other authors3) to decrease the alteration in the biomechanical strength of these corneas. Theoretically, surface ablation procedures would minimize the risk of having postoperative corneal ectasia because they leave a thicker residual stroma and thus may have less impact on the corneal biomechanical behavior than LASIK while obtaining similar refractive and visual results.4,5
Some studies have shown that surface ablation performed on thin corneas (CCT < 500 μm) is a safe and effective procedure to correct myopia, with stable refractive and visual results in the short- to long-term follow-up.2,6–12 Mitomycin C (MMC) modulates the corneal wound-healing response in surface ablation, thus reducing the risk of postoperative corneal haze formation.13 Nevertheless, the antiproliferative effect of MMC on the keratocytes has led some clinicians to fear that a long-term keratocyte depletion could potentially induce a secondary corneal instability.14,15
The question of whether the use of MMC facilitated the development of ectasia after surface ablation has not been completely answered yet, although, to our knowledge, no case has been reported so far. For this reason, and because of the relevance that this issue could have on surface ablation indications, we decided to evaluate the long-term safety and outcomes of LASEK with intraoperative MMC performed on thin corneas for the correction of myopia.
Patients and Methods
We performed a retrospective study of patients who underwent LASEK with intraoperative use of MMC to correct myopia (with or without astigmatism) and who had a preoperative CCT thinner than 500 μm. All study patients underwent a full ophthalmologic examination before surgery that included the measurement of the uncorrected distance visual acuity (UDVA), the corrected distance visual acuity (CDVA) including manifest and cycloplegic refractions, corneal keratometry and topography (CSO; Compagnia Instrumenti Oftalmici, Firenze, Italy), scanning-slit topography (Orbscan II; Bausch & Lomb, Rochester, NY), Scheimpflug corneal tomography (Pentacam; Oculus Optikgeräte, Wetzlar, Germany), ultrasound corneal pachymetry (DHG 5100 contact pachymeter; DHG Technology, Inc., Exton, PA), mesopic infrared pupillometry (Colvard Pupillometer; Oasis Medical, Inc., Glendora, CA), slit-lamp biomicroscopy, Goldmann tonometry (CT-80; Topcon, Tokyo, Japan), and funduscopy.
When evaluating for refractive surgery, we excluded patients with unstable refractions, those who had undergone any previous ocular surgery, keratoconus suspects (defined as any mild localized steepening seen with Placido corneal topography or slight bowing of the posterior corneal surface detected by corneal tomography), and those with ocular or systemic diseases, such as diabetes mellitus or connective tissue disorders that could interfere with the wound-healing process.
All patients provided written informed consent, and Institutional Review Board (Hospital La Princesa, Madrid, Spain) approval was obtained. The study was performed in accordance with the tenets of the Declaration of Helsinki.
We recorded the preoperative data (refraction, pachymetry, and corneal topography) and the postoperative data 3 months postoperatively and at each annual postoperative visit performed in our clinic. We compared the residual refraction between the 3-month and the last annual postoperative examination to detect a possible change in the refraction that would suggest secondary corneal ectasia. We also compared the topographic features between those examinations to detect any topographic sign suggesting corneal instability.
Postoperative corneal ectasia was defined as progressive steepening of corneal curvature inferiorly or centrally, progressive and significant increases in myopia, with or without increasing astigmatism, severe decrease in UDVA or CDVA, and progressive thinning of the cornea.
Given the fact that high percent tissue altered (PTA) has been recently described as a main risk factor for the development of corneal ectasia after LASIK in eyes with normal preoperative topography,16 we calculated PTA for our study population.
Two experienced surgeons (MG-G, MAT) performed all procedures. A povidone-iodine solution was applied to the skin and the conjunctiva, and a sterile surgical drape and a rigid eyelid speculum were positioned. All surgeries were performed using topical anesthesia with lidocaine 2%. A 20% alcohol solution diluted in balanced salt solution was instilled inside a 7-mm corneal trephine (ASICO, Westmont, IL) centered on the pupil and left for 40 seconds. A cellulose sponge was used to remove the alcohol and balanced salt solution was copiously instilled to rinse the ocular surface. The edges of the flap were dried with a sponge and the epithelial flap was peeled back with a crescent blade (Alcon Surgical, Orlando, FL), leaving a hinge at the 12-o'clock position. The stromal bed was dried with a sponge and the eye tracker was set in the center of the pupil.
The ablation was performed with the Esiris excimer laser (Schwind Eye Tech Solutions, Kleinostheim, Germany) using a PRK nomogram. Because no study has demonstrated yet the exact ablation depth below which there is no risk of haze, we arbitrarily set the cut-off for using prophylactic MMC at 50 μm of ablation depth, as previously reported.17 Due to the use of MMC, the programmed spherical ablation was 10% less than the intended correction to avoid overcorrection. Because the ablation depth exceeded 50 μm in all cases, a 7-mm round cellulose sponge soaked in MMC 0.02% was applied for 30 seconds over the ablated stroma, carefully avoiding leakage of the drug to the epithelial flap and the limbus. The stroma was then copiously rinsed with balanced salt solution and the epithelial flap was repositioned using the same cannula. A therapeutic soft contact lens (AcuVue; Johnson & Johnson Vision Care, Inc., Jacksonville, FL) was carefully placed on the eye and antibiotic drops (ciprofloxacin 3 mg/mL) and nonsteroidal anti-inflammatory drops (ketorolac trometamol 5 mg/mL) were applied.
The medications consisted of a topical antibiotic (ciprofloxacin 3 mg/mL; Oftacilox; Alcon Cusí surface ablation, El Masnou, Spain) and steroid (dexamethasone alcohol 1 mg/mL; Maxidex; Alcon Cusí surface ablation) drops four times daily during the first week postoperatively. Steroid drops were tapered over the subsequent 2 months: three times daily the first month, twice daily for the following 15 days, once daily for another 15 days, and then stopped. The therapeutic contact lens was removed 1 week after surgery.
Postoperative examinations were scheduled at 1 day, 1 week, 1 and 3 months, and at each annual postoperative visit after the surgery. At the 3-month and subsequent examinations, the optometrists refracted the patients and registered the UDVA, CDVA, keratometry, pachymetry, and corneal topography features with the CSO, Orbscan II, and Pentacam.
If an early re-treatment was needed, it was performed 3 months after the original procedure, and the CCT, topography, and refractive and visual results obtained 3 months after the enhancement were considered for analysis as the “3-month postoperative visit.”
The Statview+Graphics software (Abacus Concept, Inc., Cupertino, CA) was used for data analysis. The normality of the distributions was checked using the Kolmogorov–Smirnov test. Statistical comparisons were made using the unpaired two-tailed Student's t test, linear regression analysis, and multiple regression analysis. A P value of .05 or less was considered statistically significant. All continuous data are expressed as the mean ± the standard deviation. Although the minimum angle of resolution (logMAR) values of all visual acuity tests were used for the statistical analyses, we converted them to the more conventional Snellen quotation (decimal scale) throughout the text, using a visual acuity conversion chart.
One hundred consecutive eyes that underwent LASEK, fulfilled the inclusion criteria, and attended all scheduled follow-up visits were included in the study. Patients' preoperative data are shown in Table 1. Preoperative CCT was 482.9 ± 14.7 μm (range: 433 to 499 μm). The optical zone was 6 mm in all cases. The ablation depth was 63.1 ± 31.1 μm (range: 50 to 149 μm) and the mean PTA was 13.1% (range: 6.2% to 30.1%).
Preoperative Data of the 100 Eyes Treated With LASEK + MMC That Were Followed Up to 6 Years After Surgery
Table A (available in the online version of this article) shows the postoperative data. At the 3-month postoperative visit, mean CCT was 419.79 ± 32.6 μm (range: 340 to 485 μm). The last examination was performed 6.5 ± 1.3 years after surgery (range: 6 to 8 years). We found no statistically significant changes in the mean postoperative CCT during the follow-up. The UDVA showed a slight but statistically significant decrease (P = .02) when compared with the 3-month postoperative visit, whereas the CDVA remained stable during the follow-up. The residual spherical equivalent showed a statistically significant (P = .001) regression (the mean change in the residual spherical equivalent was only approximately −0.25 D) in the comparison between the 3-month and the last annual postoperative visits. This amount of change in the spherical equivalent is similar to that observed in other series analyzing the long-term stability of PRK performed to correct myopia without using MMC,11 and is so small that it is probably not clinically relevant in terms of visual function. Six or more years after the surgery, 85 eyes (85%) were within ±0.50 diopters (D) and 94 eyes (94%) eyes were within ±1.00 D of emmetropia. The efficacy index showed a statistically significant decrease, from 0.93 to 0.88 in the comparison between the 3-month and the last annual postoperative visits (P = .01). The safety index remained stable around 0.96 during the follow-up. Figure 1 presents the standard graphs for reporting refractive surgery at 3 months after the primary treatment and at the last annual postoperative examination.
Postoperative Data on the Long-term Follow-up of the 100 Eyes Treated With LASEK + MMC That Had a Preoperative CCT < 500 μm
(A) Cumulative histogram of uncorrected distance visual acuity of the 100 thin corneas treated with LASEK with mitomycin C at 3 months and at the last annual postoperative examination (≥ 6 years). (B) Changes in lines of corrected distance visual acuity 3 months and 6 or more years after LASEK with MMC performed in 100 corneas thinner than 500 μm. (C) Attempted versus achieved spherical equivalent refraction scatterplots of LASEK with the adjuvant use of mitomycin C to correct myopia in 100 thin corneas at 6 or more years postoperatively. The scatterplots include data after all primary treatments and after enhancements. The linear regression equation and coefficient of determination (r2) are displayed. (D) Predictability 6 years or more after LASEK with intraoperative MMC performed in 100 corneas thinner than 500 μm. (E) Refractive astigmatism preoperatively and 6 years or more after LASEK with MMC in thin corneas. (F) Stability of spherical equivalent refraction after primary LASEK with mitomycin C to correct myopia in thin corneas. All data at 3 months included all eyes after primary treatment and before enhancement. Data provided at 6, 7, and 8 years postoperatively included all eyes after primary treatment and after enhancement when needed. LASEK = laser-assisted subepithelial keratomileusis; MMC = mitomycin C; UDVA= uncorrected distance visual acuity; CDVA = corrected distance visual acuity; D = diopters; SD = standard deviation
The topography did not show signs of corneal ectasia in any eye during the follow-up. During the long-term follow-up, 8 eyes (8%) needed enhancement. The indications for re-treatment were early undercorrection in 7 eyes (7%) and late regression in 1 eye (1%).
We found a statistically significant increase (P = .0001) in the mean postoperative keratometry during the mean 6.5-year follow-up. The mean change in the keratometry between the 3-month and the last postoperative visits was +0.49 ± 0.72 D (range: −0.50 to +4.30 D). We detected an increase of 1.00 D or more in the mean keratometric values in only 12 eyes during the follow-up. In all of these cases, the residual spherical equivalent was −1.50 D or less and the topographies showed no sign of ectasia.
Linear regression analysis found a statistically significant correlation between the preoperative spherical equivalent and the change in the mean postoperative keratometry during the long-term follow-up (ie, the higher the preoperative spherical equivalent, the higher the increase in the mean postoperative keratometry); however, the correlation was weak (r2 = 0.05; P = .01) and therefore not clinically relevant.
Correlation between the mean preoperative keratometry and the change in the mean postoperative keratometry was significant (ie, flattest corneas tended to have a higher increase in the mean postoperative keratometry during the long-term follow-up); however, the correlation was weak (r2 = 0.04; P = .02) and therefore not clinically relevant.
Multiple regression analysis found a statistically significant correlation (r2 = 0.102; P = .005) among the preoperative spherical equivalent, the preoperative keratometry, and the change in the postoperative keratometry; that is, correction of higher myopias in the flattest corneas tended to induce a higher increase in the postoperative keratometry over time.
Linear regression analysis showed no statistically significant correlation (r2 = 0.03; P = .06) between the change in the postoperative spherical equivalent and the change in the postoperative keratometry; that is, there is no correlation between the postoperative myopic regression and the postoperative steepening of the cornea during the follow-up.
No intraoperative or early postoperative complications were detected and no case of haze greater than grade 1 (mild, not affecting visual acuity or refraction) was registered during any postoperative visit.
In the current study, LASEK with intraoperative MMC performed to correct myopia in thin corneas (preoperative CCT < 500 μm) with normal preoperative topography was safe, effective, and predictable, and obtained good refractive and topographic results during the mean 6.5-year follow-up. No eye developed postoperative corneal ectasia.
There are few studies of surface ablation performed on thin corneas. Hashemi et al.6 reported the results of LASEK performed in 68 corneas with a preoperative CCT of 455 to 499 μm to correct myopia from −1.50 to −8.75 D. They obtained good visual and refractive results, but the follow-up was limited to only 3 months. Vinciguerra et al.7 reported the results of phototherapeutic keratectomy performed in 48 very thin corneas (CCT range: 290 to 444 μm) resulting from complications of previous PRK. Postoperative CCT ranged from 264 to 414 μm and did not show signs of progressive thinning or refractive instability. The maximum postoperative follow-up was 5 years (64.5% of eyes). Kymionis et al.2 reported their results with PRK (without MMC) performed in 68 eyes with thin corneas (pre-operative CCT: 453 to 499 μm) to correct myopia (up to −6.75 D of spherical equivalent). The mean follow-up was 16 months (range: 12 to 36 months) and the authors did not detect any case of postoperative ectasia. De Benito-Llopis et al.8 showed that the visual and refractive results obtained 3 months after LASEK in 136 thin corneas (49 with MMC) to correct myopia up to −11.00 D were stable 15 months after surgery. Djodeyre et al.9 compared the refractive outcomes in 40 eyes that had LASIK and 88 eyes that had surface ablation (only one eye with MMC), all of them with a CCT thinner than 470 μm. In the surface ablation-group, postoperative CCT ranged from 315 to 444 μm and no case of postoperative ectasia was reported. After a mean 4.8-year follow-up, the efficacy and safety indexes were 0.93 and 1.01, respectively, and 92% of eyes were within ±1.00 D of emmetropia. Hashemi et al.10 reported good visual and refractive results with PRK performed in 30 thin corneas (preoperative CCT: 452 to 499 μm) to correct myopia from −1.25 to −6.50 D (MMC was used only in cases with myopia higher than −4.00 D) after a 12-month follow-up.
Only one study, performed by De Benito-Llopis et al.,11 reported on the long-term visual outcomes of surface ablation in thin corneas. The authors included 75 eyes with a preoperative CCT of 438 to 499 μm that underwent PRK to correct myopia up to −14.00 D and had at least 10 years of follow-up. They did not use intraoperative MMC in any case. Ten years after the surgery, 30 eyes (40%) were within ±0.50 D and 43 eyes (57.3%) were within ±1.00 D of emmetropia. The efficacy index remained stable around 0.8 and the safety index was higher than 0.9 during the follow-up. They did not report any case of postoperative corneal ectasia. The authors found a slight myopic regression during the follow-up that was not higher than that described in corneas with normal CCT 8 to 12 years after surface ablation.18–20 Interestingly, the efficacy, safety, predictability, and re-treatment rate were similar to that reported after surface ablation in corneas with normal thickness on a long-term follow-up.18–22
MMC has played a decisive role in the current revival of surface ablation procedures. This drug modulates the corneal wound-healing response, thus reducing the risk of postoperative corneal haze formation.13 However, the antiproliferative effect of MMC on the keratocytes has led some investigators to fear long-term keratocyte depletion14,15 that could potentially induce a secondary corneal instability, especially in thin corneas. Nevertheless, only one study has evaluated to date the long-term outcomes of surface ablation in thin corneas when adjuvant MMC is used. Naderi et al.12 recently reported the results of PRK with MMC in 74 thin corneas (preoperative CCT: 446 to 498 μm) to correct myopia up to −5.50 D (0.02% MMC was applied during 10 to 35 seconds depending on the preoperative refraction). Of the 74 eyes included, 23 eyes (31.1%), 33 eyes (44.6%), and 18 eyes (24.3%) were followed for 3, 4, and 5 years after the surgery, respectively. No cases of ectasia were detected during the mean 4-year follow-up.
Comparing the results of the current study with those previously published, several facts should be noted. First, it seems that surface ablation with MMC is a safe and effective procedure when it is performed in healthy corneas (normal preoperative topography), regardless of preoperative CCT. In fact, our results are similar to those reported by Diakonis et al.23 after surface ablation with MMC in corneas with normal CCT. Second, the adjuvant use of MMC when performing surface ablation in thin corneas does not seem to facilitate the development of corneal ectasia. In fact, it is noteworthy that our study found no clinically relevant changes in the postoperative CCT and keratometry that suggested secondary corneal instability, and the topography did not show signs of postoperative corneal ectasia in any eye during the long-term follow-up.
There have been few reports of ectasia after surface ablation and, interestingly, most of them either had preoperative signs of primary ectasia24,25 or did not have a complete preoperative examination to exclude the possibility of primary ectasia.26 In the review by Leccisotti24 of 6,453 eyes that had undergone PRK, postoperative ectasia was detected in only 5 eyes and all of them had preoperative topographical abnormalities or even a frank keratoconus in the fellow eye. However, only 2 of the 5 eyes had preoperative CCT less than 500 μm. Moreover, it is important to note that among all of the reported cases of ectasia after PRK, we found a much stronger relationship between the development of postoperative ectasia and preoperative abnormal corneal topography rather than preoperative CCT, as described by Randleman et al.27
Based on our results, preoperative CCT of less than 500 μm does not seem to be a risk factor for developing postoperative corneal ectasia27,28 after surface ablation in corneas with normal preoperative topography. On the other hand, although the importance of having a “thick enough” residual stromal bed after LASIK refractive surgery is widely accepted,27 no minimal “safe” residual stromal bed thickness has been proposed in surface ablation. In LASIK surgery, it has been suggested that a residual stromal bed thinner than 250 μm or a postoperative total CCT thinner than 400 μm should be avoided.29 In our series, the postoperative CCT ranged from 340 to 485 μm, with no signs of corneal instability. Moreover, it has been recently described that a PTA of 40% or higher is the main risk factor for the development of post-LASIK ectasia in corneas with normal preoperative topography.16 In the current study, PTA ranged from 6.2% to 30.1%, and no case of postoperative corneal ectasia was detected.
One limitation of the current study is that it was not controlled. Thus, a better study would have been randomizing all corneas in two refractive-matched groups, one with MMC and one without MMC. It is well accepted that MMC inhibits the corneal haze that may appear after surface ablation, especially in deep ablations (in our study the preoperative spherical equivalent ranged from −2.00 to −11.00 D). For this reason, and given the fact that even mild degrees of haze can influence the postoperative outcomes of surface ablation (refractive regression and loss of lines of CDVA), we routinely apply MMC in these cases, so a control group (without MMC) was not available.
LASEK with MMC seems to be a safe, effective, and predictable procedure to correct myopia in thin corneas (CCT < 500 μm) with normal preoperative topography, providing good visual and refractive outcomes with no topographic signs of corneal ectasia during a mean 6.5-year follow-up. More studies with a larger number of cases and longer follow-up are needed to further elucidate the maximum PTA and the minimum residual stromal bed thickness needed to avoid the risk of postoperative ectasia after surface ablation with the use of intraoperative MMC.
- Taneri S, Zieske JD, Azar DT. Evolution, techniques, clinical outcomes, and pathophysiology of LASEK: review of the literature. Surv Ophthalmol. 2004;49:576–602. doi:10.1016/S0039-6257(04)00135-3 [CrossRef]
- Kymionis GD, Bouzoukis D, Diakonis V, et al. Long-term results of thin corneas after refractive laser surgery. Am J Ophthalmol. 2007;144:181–185. doi:10.1016/j.ajo.2007.04.010 [CrossRef]
- Condon PI, O'Keefe M, Binder PS. Long-term results of laser in situ keratomileusis for high myopia: risk for ectasia. J Cataract Refract Surg. 2007;33:583–590. doi:10.1016/j.jcrs.2006.12.015 [CrossRef]
- de Benito-Llopis L, Teus MA, Sánchez-Pina JM, Hernández-Verdejo JL. Comparison between LASEK and LASIK for the correction of low myopia. J Refract Surg. 2007;23:139–145.
- Teus MA, de Benito-Llopis L, Sánchez-Pina JM. LASEK versus LASIK for the correction of moderate myopia. Optom Vis Sci. 2007;84:605–610. doi:10.1097/OPX.0b013e3180dc9a4f [CrossRef]
- Hashemi H, Fotouhi A, Sadeghi N, Payvar S, Foudazi H. Laser epithelial keratomileusis (LASEK) for myopia in patients with a thin cornea. J Refract Surg. 2004;20:90–91.
- Vinciguerra P, Munoz MI, Camesasca FI, Grizzi F, Roberts C. Long-term follow-up of ultrathin corneas after surface retreatment with phototherapeutic keratectomy. J Cataract Refract Surg. 2005;31:82–87. doi:10.1016/j.jcrs.2004.10.039 [CrossRef]
- de Benito-Llopis L, Teus MA, Sánchez-Pina JM, Fuentes I. Stability of laser epithelial keratomileusis with and without mitomycin C performed to correct myopia in thin corneas: a 15-month follow-up. Am J Ophthalmol. 2008;145:807–812. doi:10.1016/j.ajo.2008.01.013 [CrossRef]
- Djodeyre MR, Ortega-Usobiaga J, Beltran J, Baviera J. Long-term comparison of laser in situ keratomileusis versus laser surface ablation in corneas thinner than 470 μm. J Cataract Refract Surg. 2012;38:1034–1042. doi:10.1016/j.jcrs.2011.12.036 [CrossRef]
- Hashemi H, Miraftab M, Asgari S. Photorefractive keratectomy results in myopic patients with thin cornea eyes. Oman J Ophthalmol. 2015;8:24–27. doi:10.4103/0974-620X.149860 [CrossRef]
- de Benito-Llopis L, Alió JL, Ortiz D, Teus MA, Artola A. Ten-year follow-up of excimer laser surface ablation for myopia in thin corneas. Am J Ophthalmol. 2009;147:768–773. doi:10.1016/j.ajo.2008.12.022 [CrossRef]
- Naderi M, Ghadamgahi S, Jadidi K. Photorefractive keratectomy (PRK) is a safe and effective for patients with myopia and thin corneas. Med Hypothesis Discov Innov Ophthalmol. 2016;5:58–62.
- Teus MA, de Benito-Llopis L, Alió JL. Mitomycin C in refractive surgery. Surv Ophthalmol. 2009;54:487–502. doi:10.1016/j.survophthal.2009.04.002 [CrossRef]
- Netto MV, Mohan RR, Sinha S, Sharma A, Gupta PC, Wilson SE. Effect of prophylactic and therapeutic mitomycin C on corneal apoptosis, cellular proliferation, haze, and long-term keratocyte density in rabbits. J Refract Surg. 2006;22:562–574.
- Dupps WJ Jr, Wilson SE. Biomechanics and wound healing in the cornea. Exp Eye Res. 2006;83:709–720. doi:10.1016/j.exer.2006.03.015 [CrossRef]
- Santhiago MR, Smadja D, Gomes BF, et al. Association between the percent tissue altered and post-laser in situ keratomileusis ectasia in eyes with normal preoperative topography. Am J Ophthalmol. 2014;158:87–95. doi:10.1016/j.ajo.2014.04.002 [CrossRef]
- de Benito-Llopis L, Teus MA, Sánchez-Pina JM. Comparison between LASEK with MMC and LASIK for the correction of high myopia (−7.00 to −13.75 D). J Refract Surg. 2008;24:516–523.
- Alió JL, Muftuoglu O, Ortiz D, et al. Ten-year follow-up of photorefractive keratectomy for myopia of more than −6 diopters. Am J Ophthalmol. 2008;145:37–45. doi:10.1016/j.ajo.2007.09.009 [CrossRef]
- Rajan MS, Jaycock P, O'Brart D, Nystrom HH, Marshall J. A long-term study of photorefractive keratectomy: 12-year follow-up. Ophthalmology. 2004;111:1813–1824.
- O'Connor J, O'Keeffe M, Condon PI. Twelve-year follow-up of photorefractive keratectomy for low to moderate myopia. J Refract Surg. 2006;22:871–877.
- Alió JL, Muftuoglu O, Ortiz D, et al. Ten-year follow-up of photorefractive keratectomy for myopia of less than −6 diopters. Am J Ophthalmol. 2008;145:29–36. doi:10.1016/j.ajo.2007.09.007 [CrossRef]
- Pietilä J, Mäkinen P, Pajari T, et al. Eight-year follow-up of photorefractive keratectomy for myopia. J Refract Surg. 2004;20:110–115.
- Diakonis VF, Kankariya VP, Kymionis GD, et al. Long term followup of photorefractive keratectomy with adjuvant use of mitomycin C. J Ophthalmol. 2014;2014:821920. doi:10.1155/2014/821920 [CrossRef]
- Leccisotti A. Corneal ectasia after photorefractive keratectomy. Graefes Arch Clin Exp Ophthalmol. 2007;245:869–875. doi:10.1007/s00417-006-0507-z [CrossRef]
- Randleman JB, Caster AI, Banning CS, Stulting RD. Corneal ectasia after photorefractive keratectomy. J Cataract Refract Surg. 2006;32:1395–1398. doi:10.1016/j.jcrs.2006.02.078 [CrossRef]
- Kim H, Choi JS, Joo C-K. Corneal ectasia after PRK: clinicopathologic case report. Cornea. 2006;25:845–848. doi:10.1097/01.ico.0000224634.72309.43 [CrossRef]
- Randleman JB, Woodward M, Lynn MJ, Stulting RD. Risk assessment for ectasia after corneal refractive surgery. Ophthalmology. 2008;115:37–50. doi:10.1016/j.ophtha.2007.03.073 [CrossRef]
- Binder PS. Analysis of ectasia after laser in situ keratomileusis: risk factors. J Cataract Refract Surg. 2007;33:1530–1538. doi:10.1016/j.jcrs.2007.04.043 [CrossRef]
- Randleman JB. Post-laser in situ keratomileusis ectasia: current understanding and future directions. Curr Opin Ophthalmol. 2006;17:406–412. doi:10.1097/01.icu.0000233963.26628.f0 [CrossRef]
Preoperative Data of the 100 Eyes Treated With LASEK + MMC That Were Followed Up to 6 Years After Surgery
|Parameter||Mean ± Standard Deviation||Range|
|Age (y)||31.4 ± 6.1||19 to 55|
|Sphere (D)||−3.59 ± 2.30||−2.00 to −11.00|
|Cylinder (D)||−1.01 ± 1.00||0.00 to −4.75|
|Spherical equivalent (D)||−4.09 ± 2.30||−2.00 to −11.00|
|CDVA (decimal notation)||1.12 ± 0.2||0.7 to 1.25|
|Mean keratometry (D)||44.25 ± 1.60||39.125 to 47.375|
|CCT (μm)||482.9 ± 14.7||433 to 499|
|Endothelial cell count (cells/mm2)||2,472.3 ± 258.7||2,461.4 to 2,575.3|
Postoperative Data on the Long-term Follow-up of the 100 Eyes Treated With LASEK + MMC That Had a Preoperative CCT < 500 μma
|Parameter||3 Months Postoperative||Last Postoperative Visit||P|
|UDVA (range)||1.03 ± 0.2 (0.6 to 1.2)||0.97 ± 0.2 (0.3 to 1.2)||.02|
|CDVA (range)||1.06 ± 0.2 (0.6 to 1.2)||1.06 ± 0.1 (0.6 to 1.2)||.80|
|Sphere (D) (range)||0.13 ± 0.40 (+1.25 to −1.25)||−0.06 ± 0.40 (+1.25 to −1.25)||.001|
|Cylinder (D) (range)||−0.12 ± 0.30 (0.00 to −2.00)||−0.23 ± 0.50 (0.00 to −2.00)||.06|
|Spherical equivalent (D) (range)||0.07 ± 0.30 (+1.00 to −1.75)||−0.17 ± 0.40 (+1.00 to −1.50)||.001|
|Mean keratometry (D) (range)||40.56 ± 2.20 (33.50 to 46.00)||41.05 ± 2.10 (35.00 to 46.00)||.0001|
|CCT (μm)||419.79 ± 32.6 (340 to 485)||423.82 ± 33.4 (338 to 490)||.70|
|Endothelial cell count (cells/mm2)||2,466.5 ± 294.1||2,452.5 ± 226.8||.60|
|Efficacy index||0.93 ± 0.2||0.88 ± 0.2||.01|
|Safety index||0.96 ± 0.1||0.96 ± 0.1||.90|