Ten-year follow-up of photorefractive keratectomy for myopia of less than -6 diopters

Surface ablation outcomes in high myopia with different epithelium removal techniques

PURPOSE

To study the outcomes of alcohol-assisted photorefractive keratectomy (PRK) when compared with transepithelial PRK (TransPRK) using 2 software programs, with or without SmartPulse Technology (SmartSurfACE), in high myopia.

SETTING

Vissum Miranza, University Miguel Hernandez, Alicante, Spain.

DESIGN

Retrospective, consecutive, case series.

METHODS

High myopic eyes undergoing surface ablation were included. The main inclusion criteria were preoperative spherical equivalent (SE) above -5.50 diopters (D) and no other ocular surgeries. Mitomycin-C was used in all the surgeries. The outcomes were analyzed using the 6-month follow-up visit data.

RESULTS

135 eyes were included. Alcohol-assisted PRK was performed in 65 eyes, transepithelial PRK (TransPRK1) in 32 eyes, and TransPRK2 in 38 eyes. The mean all groups preoperative sphere, cylinder, and SE were -6.00 ± 0.87 D, -1.13 ± 1.03 D, and -6.57 ± 0.69 D, respectively. The mean efficacy index in the alcohol-assisted PRK group was 0.91 ± 0.18 compared with 0.98 ± 0.1 and 0.98 ± 0.12 in the TransPRK1 and TransPRK2, respectively (P = .027). The mean safety index in alcohol-assisted PRK was 0.99 ± 0.05, whereas it was 1 ± 0.06 in the TransPRK1 and 0.99 ± 0.08 in the TransPRK2 (P = .780). A final SE of ± 0.50 D was achieved in 96.9% of eyes in the TransPRK1 group and in 100% eyes in the TransPRK2 group compared with 73.8% in the alcohol-assisted PRK group (P < .001).

CONCLUSIONS

Surface ablation with the Amaris 500 excimer laser with flying spot pattern and mitomycin C use showed adequate refractive outcomes in high myopia correction in the 3 groups. TransPRK with or without SmartPulse Technology achieved statistically significant better outcomes than alcohol-assisted PRK in refractive predictability and efficacy.

[Regression and ablation profiles in corneal refractive surgery]

Regression after corneal refractive surgery is a complex phenomenon which seems inevitable. The choice of surgical technique has very little influence on regression for low myopia or myopic astigmatism. However, LASIK and SMILE are the two techniques of choice in the correction of high myopia. LASIK is also better for the correction of hyperopia, hyperopic astigmatism and mixed astigmatism. Intraoperatively, the choice of a wide optical zone and adherence to a thick residual stromal bed provide stability. Regression may also be reduced by modulating anti-inflammatory therapy, treating dry eye, and using mitomycin C in PKR. In all cases, obtaining keratometry during patient follow-up helps to identify the cause of the regression. The objective of this review is to synthesize recent data from the literature on regression in refractive surgery as a function of the ablation profiles used.

Twenty-Year Follow-Up of Excimer Laser Photorefractive Keratectomy: A Retrospective Observational Study

Introduction

Photorefractive keratectomy (PRK) was introduced in the late 1980s to correct myopia. The purpose of this study was to assess its long-term efficacy and safety, analyzing patients with at least 20-year follow-up.

Methods

This retrospective observational study was carried out on 85 eyes of 54 patients (33 females) that underwent PRK between 1991 and 1998 (mean age 32.62 ± 9.74, range 18–55 years). Both preoperatively and postoperatively, patients underwent a complete ophthalmological evaluation, including uncorrected and corrected distance visual acuity, slit-lamp, intraocular pressure, dilated fundus, and corneal topographic examinations. The outcome assessment was made by comparing the preoperative refraction, as spherical equivalent, with the postoperative ones, taking into account the planned refractive correction. Safety and efficacy indices were also calculated. All the data were evaluated with a paired t test.

Results

The mean attempted correction as spherical equivalent was – 5.64 ± 3.01 D (range – 1.00 to – 15.00 D), while the mean achieved correction after 20 years was – 4.30 ± 3.13 D (range – 1.88 to – 14.25 D), with a significant statistical difference (p < 0.01).

The mean expected refractive outcome was – 0.27 ± 0.81 D (range – 4.00 to + 1.25 D). The mean difference between achieved and attempted treatment was 1.33 ± 1.92 D (range – 4.25 to + 6.25 D), with a significant difference (p < 0.01).

The safety index was 1.00 and the efficacy index was 0.63.

Conclusion

The results provided by this study highlight that the procedure could be considered safe, with no long-term sight-threatening complications such as late ectasia or haze.

Main Complications of Photorefractive Keratectomy and their Management

Photorefractive keratectomy (PRK) was the first surface ablation procedure introduced for the treatment of refractive errors and has been proven to be effective and safe. In some cases, however, the patient may not be totally satisfied with the final result and retreatment may be necessary. We performed a literature review to describe the main conditions that may arise following PRK that may require retreatment and new promising techniques to allow customized and effective treatments for patients. There is currently no gold standard for retreatment of residual refractive error after PRK. The surgeon must take into account the patient's history and type of problem when choosing the most appropriate technique. LASIK and PRK are the main options. Haze can be treated with good results with phototherapeutic keratectomy and mytomicin C. High order aberrations and decentration may be addressed with topographically-guided excimer photoablation or with wavefront-guided PRK.

Long-term evaluation of corneal sub-basal nerve recovery after photorefractive keratectomy and influence of pars plana vitrectomy

The corneal sub-basal nerve (SBN) plexus is destroyed during photorefractive keratectomy (PRK) and its recovery is still a matter of debate. In vivo confocal microscopy (IVCM) was used to evaluate SBN plexus in 23 patients at a distance of 10-25 years (mean 15.6 years) from myopic PRK. Because 8 out of the 23 PRK patients underwent pars plana vitrectomy (PPV) for rhegmatogenous retinal detachment, IVCM was also performed on those patients 6 months after PPV. Thirteen patients matched for age and myopia served as controls (non-PRK). SBN plexus was markedly reduced after PRK compared with non-PRK eyes and showed a slow, continuous but incomplete recovery up to the end of our follow-up (range 10-25 years). PRK and non-PRK eyes showed a marked reduction in SBN density 6 months after PPV, thus demonstrating a detrimental effect exerted by PPV on SBN plexus.

Bioptics for high hyperopia with combined multifocal intraocular lens implantation and excimer ablation in young patients

PURPOSE

To analyze the visual and refractive outcome of the bioptics procedure combining multifocal intraocular lens implantation and excimer laser surgery in young patients with high hyperopic eyes not suitable for a single surgical procedure.

METHODS

This retrospective case series included 10 eyes of five patients (age range 18-30 years) with high hyperopia (spherical equivalent +8.51 ± 0.85 diopters (D)). They had been treated with serial multifocal intraocular lens implantation followed 6 weeks later by laser in situ keratomileusis for residual hyperopia. Uncorrected distance visual acuity, uncorrected near visual acuity, corrected distance visual acuity, corrected near visual acuity, and manifest refraction were evaluated before surgeries, after multifocal intraocular lens implantation, and 3 months post laser in situ keratomileusis.

RESULTS

No patients were lost to follow-up (6 months). The mean spherical equivalent decreased to +2.05 ± 1.33 D after multifocal intraocular lens implantation and to -0.10 ± 0.58 D after the laser in situ keratomileusis procedure. Success of the procedures was determined by uncorrected visual acuity. LogMAR uncorrected distance visual acuity improved by a total of more than six lines from 1.05 ± 0.18 LogMAR to 0.46 ± 0.12 LogMAR post multifocal intraocular lens implantation and to 0.15 ± 0.06 LogMAR after both surgeries. The LogMAR uncorrected near visual acuity increased by 0.81 ± 0.82 LogMAR after lens implantation due to loss of accommodation, and all eyes reached a LogMAR of 0 at 1 month postoperatively following laser in situ keratomileusis.

CONCLUSIONS

A bioptics approach involving multifocal intraocular lens followed 6 weeks later by a laser in situ keratomileusis procedure for the correction of very high hyperopia enabled the resolution of the residual refractive error in young very high hyperopic patients.

Long-term Follow-up of LASEK With Mitomycin C Performed to Correct Myopia in Thin Corneas

PURPOSE

To evaluate the long-term outcomes of laser-assisted subepithelial keratomileusis (LASEK) with intraoperative use of mitomycin C (MMC) performed on thin corneas for the correction of myopia.

METHODS

This retrospective cohort study included 100 eyes with a preoperative central corneal thickness (CCT) thinner than 500 μm that underwent LASEK + MMC with at least 6 years of follow-up. Stability of visual acuity and refraction and the efficacy, safety, and predictability at the examinations 3 months and the last annual postoperative visit were analyzed.

RESULTS

Preoperative CCT was 482.9 ± 14.7 μm (range: 433 to 499 μm). Mean preoperative spherical equivalent was -4.09 ± 2.3 diopters (D). At the 3-month postoperative visit, mean CCT was 419.79 ± 32.6 μm. The residual spherical equivalent showed a statistically significant regression (P = .001) in the comparison between the 3-month and the last annual postoperative visit. The efficacy index showed a significant decrease (P = .01) and the safety index remained stable around 0.96. Six or more years after the surgery, 85 eyes (85%) were within ±0.50 D and 94 eyes (94%) eyes were within ±1.00 D of emmetropia. The topography did not show signs of secondary corneal ectasia in any eye.

CONCLUSIONS

LASEK with intraoperative use of MMC seems to be safe, effective, and predictable to correct myopia in corneas thinner than 500 μm and with normal preoperative topography, providing good visual and refractive outcomes with no topographic signs of corneal ectasia in a mean 6.5-year follow-up. [J Refract Surg. 2017;33(12):813-819.].

Comparison of laser in situ ketatomileusis and photorefractive keratectomy for myopia using a mixed-effects model

Purpose

To compare the results of laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) for myopia using a mixed-effects model.

Methods

This comparative retrospective study was conducted in 1,127 eyes of 579 patients after LASIK and 270 eyes of 144 patients after PRK who had two or more postoperative follow-ups after 3 months. Uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), manifest refractive spherical equivalent (MRSE), percentage of eyes within ± 0.5 diopters (D) and ± 1.0 D of targeted refraction, and central corneal thickness were compared between PRK and LASIK groups using a mixed-effects model.

Results

Compared with the LASIK group, UCVA in the PRK group was significantly worse in the initial year but was significantly better after 4 years. The average BSCVA was not significantly different between the LASIK and PRK groups after 4 years. The average gain of BSCVA in the PRK group was significantly larger than that of the LASIK group after 2 years. MRSE in the LASIK and PRK groups showed a gradual myopic shift until 6 years after surgery. After 6 years, MRSE in the PRK group remained stable whereas MRSE in the LASIK group continued a myopic shift. The percentages of eyes within ± 0.5 D or ± 1.0 D in the LASIK group were significantly higher than those in the PRK group at 3 months but were significantly lower than those in the PRK group at 10 years.

Conclusions

PRK for myopia shows better efficacy than LASIK for myopia after 4 years.

Photorefractive Keratectomy for Residual Myopia after Myopic Laser In Situ Keratomileusis

Purpose. To evaluate the safety, efficacy, and predictability of photorefractive keratectomy (PRK) on the corneal flap for correction of residual myopia following myopic laser in situ keratomileusis (LASIK). Patients and Methods. A retrospective study on eyes retreated by PRK on the corneal flap for residual myopia after LASIK. All eyes had no enough stroma after LASIK sufficient for LASIK enhancement. Data included spherical equivalent (SE), uncorrected and best corrected visual acuity (UCVA and BCVA), central pachymetry, corneal higher order aberrations (HOAs), corneal hysteresis (CH), corneal resistance factor (CRF), and corneal haze. Results. The study included 64 eyes. Before PRK, the mean central pachymetry was 400.21 ± 7.8 μm, the mean SE was -1.74 ± 0.51 D, and the mean UCVA and BCVA were 0.35 ± 0.18 and 0.91 ± 0.07, respectively. 12 months postoperatively, the mean central corneal thickness was 382.41 ± 2.61 μm, the mean SE was -0.18 ± 0.32 D (P < 0.01), and the mean UCVA and BCVA were 0.78 ± 0.14 (P = 0.01) and 0.92 ± 0.13 (P > 0.5), respectively. The safety index was 1.01 and the efficacy index was 0.86. No significant change was observed in corneal HOAs. Conclusions. Residual myopia less than 3 D after LASIK could be safely and effectively treated by PRK and mitomycin C with a high predictability. This prevents postoperative ectasia and avoids the flap related complications but has no significant effect on HOAs.

One-year visual outcome of small incision lenticule extraction (SMILE) surgery in high myopic eyes: retrospective cohort study

OBJECTIVE

To determine whether the long-term visual outcome of small incision lenticule extraction (SMILE) surgery is consistent with the short-term results in high myopic eyes.

DESIGN

Retrospective cohort study; data collected from 8 August 2011 to 31 August 2015.

SETTING

Single refractive surgery centre.

PARTICIPANTS

A total of 156 eyes were studied: 65 eyes of 39 subjects (22 female/17 male) in the high myopic group (manifest refraction spherical equivalent (MRSE) ≥-6.0 D), and 91 eyes of 54 subjects (29 female/25 male) in the control group (MRSE <-6.0 D). The inclusion criteria were subjects who had follow-ups after 1 day, 1 week, 1 month, 3, 6 months and 1 year with the manifest refraction, uncorrected and corrected distance visual acuity (UDVA/CDVA). There were no statistically significant differences between the two groups in the subjects' gender, age, or cylindrical dioptre, preoperatively (p=0.835, p=0.055, p=0.341, respectively).

PRIMARY AND SECONDARY OUTCOME MEASURES

UDVA, refractive stability, safety index (postoperative CDVA/preoperative CDVA), and predictability (the percentage of eyes within ±0.50 D).

RESULTS

In both groups, the 1-year UDVA and safety index were significantly better than results at 1 day (high myopic group: p=0.035, p<0.001; control group: p<0.016, p<0.001); the 1-year predictability showed no significant difference with the short-term results (p=1.00 in both groups). In the high myopic eyes, the 1-year MRSE was significantly worse than the short-term result (p=0.048). To correct it, the added magnitude (D) for the high myopic eyes may equal 0.13×Attempted SE (D)-0.66 D. However, the postoperative MRSE showed no differences from 1 day to 1 year (p=0.612) in the control group.

CONCLUSIONS

The 1-year visual outcomes were better than the short-term results after the SMILE surgery on the visual acuity and safety. However, the high myopic eyes suffered a significant regression at 1 year, which may be corrected by adding additional magnitude to the SE for high myopic eyes.

Four-year observation of predictability and stability of small incision lenticule extraction

BACKGROUND

To investigate long-term refractive outcomes, wavefront aberrations and quality of life after small incision lenticule extraction (SMILE) for moderate to high myopia.

METHODS

A total of 26 patients (47 eyes) with preoperative mean spherical equivalent (SE) of -6.30 ± 1.47 diopters (D) who underwent SMILE were recruited. The measurements included uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), manifest refraction, wavefront aberrations, and quality of life.

RESULTS

At 4 years postoperatively, UDVA was better than or equal to 20/20 in 92 % of eyes. The efficacy index was 1.07 ± 0.16. 89 % of eyes were within ± 0.5 D of the intended refractive target. No eye lost any Snellen lines. The safety index was 1.16 ± 0.14. No significant changes of SE occurred among postoperative follow-ups at months 1, 3, 6 and years 1, 2, 4 (P > 0.05, Scheffe test). Higher-order aberrations, coma, spherical aberration and higher-order astigmatism increased postoperatively, and no significant changes of aberrations were detected among the 1-month, 6-month or 4-year follow-ups postoperatively (37 eyes). Compared to the spectacles group, the surgery group showed a significantly higher total score on quality of life (45.71 ± 2.61 vs 39.96 ± 3.56, P < 0.001).

CONCLUSIONS

SMILE provides a predictable and stable correction of moderate to high myopia as documented by long-term follow-up.

Long-Term Clinical Outcomes of Myopic Patients Having Thin Residual Corneal Thickness after Excimer Laser Surface Ablation

PURPOSE

To investigate and compare the long-term safety, efficacy, and accuracy of PRK (photorefractive keratectomy) and LASEK (laser epithelial keratomileusis) in myopic corneas having residual corneal thickness less than 400 micron meters (µm).

METHODS

The medical reports of the patients who had undergone excimer laser surface ablation between 2007-2011 and had a residual corneal thickness less than 400 µm were retrospectively reviewed.

RESULTS

Forty-two eyes of 42 patients with a mean age of 28.79±7.76 years were enrolled into the study. Twenty-two PRK and 20 LASEK procedures were performed. The mean follow-up time was 45.00±11.80 months. At the end of follow-up, no ectasia was detected. Nineteen percent of eyes had trace haze. No eyes lost any lines in corrected distance visual acuity. Eighty-one percent of the patients had an uncorrected distance visual acuity better than 20/40. The regression rate was 16.7%. Sixty-two percent of eyes were within ±1.00 D. The safety and efficacy indexes were 1.19±0.42 and 1.00±0.40, respectively. There was not any difference between LASEK and PRK regarding achieved spherical equivalent refraction, haze ratio, visual acuity, safety, efficacy, and regression.

CONCLUSIONS

Both PRK and LASEK are safe and effective in myopic corneas having thin residual thickness.

Corneal wound healing after laser vision correction

Any trauma can trigger a cascade of responses in tissues, with the purpose of safeguarding the integrity of the organ affected by the trauma and of preventing possible damage to nearby organs. Subsequently, the body tries to restore the function of the organ affected. The introduction of the excimer laser for keratorefractive surgery has changed the treatment landscape for correcting refractive errors, such as myopia, hyperopia, and astigmatism. In recent years, with the increased understanding of the basic science of refractive errors, higher-order aberrations, biomechanics, and the biology of corneal wound healing, a reduction in the surgical complications of keratorefractive surgery has been achieved. The understanding of the cascade of events involved in the corneal wound healing process and the examination of how corneal wound healing influences corneal biomechanics and optics are crucial to improving the efficacy and safety of laser vision correction.

Fifteen years follow-up of photorefractive keratectomy up to 10 D of myopia: outcomes and analysis of the refractive regression

PURPOSE

To evaluate outcomes of photorefractive keratectomy up to -10.00 D of myopia and -4.50 of astigmatism and to develop a predictive model for the refractive changes in the long term.

SETTING

Vissum Corporation and Miguel Hernandez University (Alicante, Spain).

DESIGN

Retrospective-prospective observational series of cases.

METHODS

This study included 33 eyes of 33 patients aged 46.79±7.04 years (range 40-57) operated with the VISX 20/20 excimer laser with optical zones of 6 mm. No mitomycin C was used in any of these cases. The minimum follow-up was 15 years. The main outcome measures were: uncorrected and corrected distance visual acuity, manifest refraction and corneal topography. Linear regression models were developed from the observed refractive changes over time.

RESULTS

Safety and efficacy indexes at 15 years were 1.18 and 0.83, respectively. No statistically significant differences were detected for any keratometric variable during the follow-up (p≥0.103). 15 years after the surgery 54.55% of the eyes were within ±1.00 D of spherical equivalent and 84.85% within ±2.00 D. The uncorrected distance visual acuity at 15 years was 20/25 or better in 60.6% of the eyes and 20/40 or better in 72.73% of the eyes. The correlation between the attempted and the achieved refractions was r=0.948 (p<0.001) at 1 year, and r=0.821 (p<0.001) at 15 years. No corneal ectasia was detected in any case during the follow-up.

CONCLUSIONS

Photorefractive keratectomy is a safe refractive procedure in the long term within the range of myopia currently considered suitable for its use, although its efficacy decreases with time, especially, in high myopia. The model developed predicts a myopic regression of 2.00 D at 15 years for an ablation depth of 130 µm.

Four-year visual outcomes after photorefractive keratectomy in pilots with low-moderate myopia

BACKGROUND

The photorefractive keratectomy (PRK) is approved for Air Force pilots in several nations. The occupational environments of pilots in the Air Force are unique, including extremely high altitude, low oxygen tension, high ultraviolet light exposure and high G-force load. The short-term efficacy and safety of PRK for pilots are documented. However, the study for long-term visual and refractive outcomes of PRK in pilots is limited.

OBJECTIVE

To investigate the long-term visual and refractive outcomes in a 4-year follow-up period after PRK in pilots with low to moderate myopia.

METHODS

Thirty-eight eyes of 20 subjects that underwent PRK and recruited to Air Force pilot were evaluated preoperatively and at 3, 6, 12, 24, and 48 months postoperatively.

RESULTS

The mean patient age was 21.42±0.75 years. The mean preoperative manifest refraction spherical equivalent (SE) was -1.51±1.15 diopters (D). At 4 years postoperatively, the mean SE was -0.29±0.51, 89.5% of eyes achieved 20/20 or better Snellen uncorrected visual acuity, 71.1% of eyes were within ±0.50 D of emmetropia. The refraction stabilised by 6 months and was maintained up to the 4-year follow-up stage.

CONCLUSIONS

PRK for pilots with low to moderate myopia is safe and effective in the long term. High-altitude environmental stress exposure has no effect on the refractive stability after PRK.

TRIAL REGISTRATION NUMBER

ROKAF-ASMC-2015-IRB-002.

Photorefractive keratectomy results in myopic patients with thin cornea eyes

BACKGROUND

To evaluate the results of visual acuity and quality, and corneal integrity in myopic patients with a thin cornea who received photorefractive keratectomy (PRK).

MATERIALS AND METHODS

In this before-after interventional study, 30 myopic eyes with a myopia -3.76 ± 1.72 (-6.50 to -1.25) D and a corneal thickness of 486.03 ± 11.93 (452-499) μm at the thinnest point received PRK. In myopia was more than 4D, mitomycin C was used with PRK. The surgery was performed with an excimer laser (VISX STAR, Abbott Medical Optics, Abbott Park, US).

RESULTS

The safety and the efficacy index of the surgery was 1.01 ± 0.05 and 1.00 ± 0.05 in these patients, respectively. All the patients were within ±0.5D of emmetropia 1 year after the surgery. Mesopic contrast sensitivity (CS) had a significant increase in two spatial frequencies of six (P = 0.003) and 12 (P = 0.003). Total coma (P < 0.001), spherical aberration (P < 0.001), and total higher-order aberrations (HOA) (P < 0.001) also showed a significant increase. Corneal hysteresis (P < 0.001) and corneal resistance factor (P < 0.001) showed a significant decrease after 1 year.

CONCLUSION

PRK is a safe, effective, and predictable procedure with desirable effects on mesopic CS in patients with corneal thickness <500 μm, which increases HOAs and decreases corneal integrity proportionate to its value before the procedure.

Impact of laser refractive surgery on ocular alignment in myopic patients

PURPOSE

To evaluate the impact of myopic keratorefractive surgery on ocular alignment.

METHODS

This prospective study included 194 eyes of 97 myopic patients undergoing laser refractive surgery. All patients received a complete ophthalmic examination with particular attention to ocular alignment before and 3 months after surgery.

RESULTS

Patients with a mean age of 26.6 years and a mean refractive error of -4.83 diopters (D) myopia were treated. Asymptomatic ocular misalignment was present preoperatively in 46 (47%) patients: a small-angle heterophoria (1-8 prism diopters, PD) in 36%; and a large-angle heterophoria (>8 PD)/heterotropia in 11%. Postoperatively, the change in angles of 10 PD or greater occurred in 3% for distance and 6% for near fixation: in 7% of the patients with orthophoria, in 3% of those with a small-angle heterophoria, and in 18% of those with a large-angle heterophoria/heterotropia. No patient developed diplopia. The preoperative magnitude of myopia or postoperative refractive status was not related to the change in ocular alignment. The higher anisometropia was associated with a decrease in deviation (P=0.041 for distance and P=0.002 for near fixation), whereas the further near point of convergence tended to be related with an increase in near deviation (P=0.055).

CONCLUSIONS

Myopic refractive surgery may cause a change in ocular alignment, especially in cases with a large-angle heterophoria/heterotropia. There is also a chance of improvement of misalignment in patients with anisometropia.

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.

CONCLUSION

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.

CONCLUSION

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.

Long-term comparison of laser in situ keratomileusis versus laser surface ablation in corneas thinner than 470 μm

PURPOSE

To compare long-term refractive and visual outcomes of laser in situ keratomileusis (LASIK) and laser surface ablation in eyes with corneas thinner than 470 μm.

SETTING

Private clinics, Spain.

DESIGN

Comparative case series.

METHODS

The study comprised eyes with myopic error and corneas thinner than 470 μm that had at least 2.9 years of postoperative follow-up between September 2001 and June 2007. The main outcome measures were safety, efficacy, predictability, and complications.

RESULTS

The mean central corneal thickness was 462.0 μm (range 440 to 469 μm) in the LASIK group (n = 40) and 458.1 μm (range 420 to 469 μm) in the laser surface ablation group (n = 88). All eyes had normal preoperative topography. In the LASIK group after a mean follow-up of 5.1 years ± 1.5 (SD), the safety index was 1.07, efficacy was 0.99, and predictability (± 1.00 diopter [D]) was 0.93. In the laser surface ablation group after a mean follow-up of 4.8 ± 1.3 years, the safety index was 1.01, efficacy was 0.93, and predictability (± 1.00 D) was 0.92. The mean residual corneal bed thickness in all eyes was 345 ± 25 μm (range 270 to 399 μm). No major complications occurred. The safety index was better in the LASIK group than in the laser surface ablation group.

CONCLUSION

Both techniques were effective, safe, and predictable in eyes with corneas thinner than 470 μm, normal preoperative topography, and a residual corneal bed thickness greater than 250 μm.

Mitomycin C: biological effects and use in refractive surgery

PURPOSE

To provide an overview of the safety and efficacy of mitomycin C (MMC) as adjuvant therapy after refractive surgery procedures.

METHODS

Literature review.

RESULTS

Over the past 10 years, MMC has been used by refractive surgeons to prophylactically decrease haze after surface ablation procedures and therapeutically in the treatment of preexisting haze. Development of MMC treatments has had a significant role in the revival of surface ablation techniques. We reviewed the literature regarding mechanism of action of MMC, its role in modulating wound healing after refractive surgery, and its safety and efficacy as adjuvant therapy applied after primary photorefractive keratectomy surgery or after photorefractive keratectomy re-treatment after laser in situ keratomileusis and other corneal surgeries and disorders. The drug is a potent mitotic inhibitor that effectively blocks keratocyte activation, proliferation, and myofibroblast differentiation. Many studies have suggested that MMC is safe and effective in doses used by anterior surface surgeons, although there continue to be concerns regarding long-term safety. After initial depletion of anterior keratocytes, keratocyte density seems to return to normal 6 to 12 months after the use of MMC when corneas are examined with the confocal microscope. Most clinical studies found no difference between preoperative and postoperative corneal endothelial cell densities when MMC 0.02% was applied during refractive surgery, with exposure time of 2 minutes or less.

CONCLUSIONS

After more than 10 years of use, MMC has been found to be effective when used for prevention and treatment of corneal haze. Questions remain regarding optimal treatment parameters and long-term safety.

Evaluation of the Long-Term Effects of Photorefractive Keratectomy Correction for Myopia in China

Purpose

To evaluate the long-term effects of photorefractive keratectomy (PRK) correction for myopia in China.

Methods

A comprehensive literature research was conducted in 2 Chinese databases and PubMed. Statistical analysis was performed using the RevMan 4.2 software.

Results

Seven prospective studies involving 2,796 eyes were included. The follow-up period was 5 to 11 years. Meta-analysis showed efficacies in low to moderate myopia that surpassed those in high myopia, and pooled odds ratios were 9.14 (95% confidence interval [CI] 4.37–19.11) in the proportion of eyes with uncorrected visual acuity (UCVA) ≥20/20 and 5.61 (95% CI 3.97–7.93) in the proportion of eyes with UCVA ≥20/40. More than 10 years post operation, 82.0% had 20/20 or better UCVA and 96.1% had 20/40 or better in the ≤-6.00 D myopia group. Among patients with >-6.00 D myopia, 31.7% had 20/20 or better UCVA and 80.4% had 20/40 or better. Moreover, 82.1% and 46.4% of the treated eyes were within ±1.0 D of target refraction in the low to moderate myopia and high myopia group, respectively. About 1.4%-3.5% of eyes lost ≥2 lines of best spectacle-corrected visual acuity, and 0.6%-4.1% of eyes had grade 1 corneal haze.

Conclusions

Photorefractive keratectomy for myopia is an effective and safe procedure for the long term in China. The efficacy and predictability of PRK in low to moderate myopia are better than in high myopia.

Analysis of the reasons for not undergoing laser corneal refractive surgery in 611 patients

To determine and analyze the reasons for patients not undergoing laser corneal refractive surgery. A retrospective observational study was conducted to analyze the reasons for not undergoing laser corneal refractive surgery in 611 patients. In this study, 611 (14.34%) among 4,262 enrolled patients did not undergo laser corneal refractive surgery. Among these 611 patients, the common reasons for not undergoing laser corneal refractive surgery were concern about the surgery (366 patients, 59.90%), insufficient corneal thickness (72 patients, 11.78%), too high corneal refractive power (36 patients, 5.89%), dry eye (33 patients, 5.40%), high intraocular pressure (22 patients, 3.60%), poor corrected visual acuity (25 patients, 4.09%), retinal diseases (23 patients, 3.76%) and others (34 patients, 5.56%). The concern about surgery is the primary factor for the patients not undergoing laser corneal refractive surgery.

Surface ablation techniques

The ongoing quest for a safe, simple, effective, minimally invasive, and stable refractive surgical procedure to correct refractive errors has stimulated the development of surface ablation techniques and laser in situ keratomileusis. In this review, we describe the history, patient assessment, techniques, outcomes, and complications of surface ablation (photorefractive keratectomy, laser-assisted sub-epithelial keratectomy, epithelial laser-assisted in situ keratomileusis) and compare the results of various surface techniques. Surface ablation procedures will continue to evolve, with potential improvements in outcomes accompanying future sophisticated ablation profiles and laser technology.

Long-term follow-up of photorefractive keratectomy for myopia: Comparative study of excimer lasers

PURPOSE

To compare the long-term results of photorefractive keratectomy (PRK) for low to moderate myopia performed using a broad-beam laser system or a scanning-slit laser system.

SETTING

Department of Ophthalmology, University of Helsinki, Helsinki, Finland.

DESIGN

Case-control study.

METHODS

This follow-up study comprised eyes with myopia (-1.25 to -7.00 diopters [D]) or myopic astigmatism (astigmatism lower than -2.50 D) corrected by PRK using a broad-beam (Visx) or scanning-slit (Nidek) laser. Follow-up included a visit at 3 months and at more than 8 years. The uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), and manifest refraction were recorded.

RESULTS

The broad-beam group comprised 27 eyes and the scanning-slit group, 34 eyes. At the last postoperative follow-up, the UDVA was 0.0 or better in 55% of eyes in the broad-beam group and 65% of eyes in the scanning-slit group. The CDVA was 0.0 or better in all eyes in the broad-beam group and 96% of eyes in the scanning-slit group. Regarding predictability, 48% and 73% of the eyes, respectively, were within ±0.50 D of the intended spherical equivalent refraction. There were no statistically significant differences between the 2 laser groups in any preoperative or postoperative parameter.

CONCLUSION

There were no significant differences in UDVA, CDVA, or SE after PRK for low to moderate myopia between the broad-beam laser system and the scanning-slit laser system.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Efficacy of surface ablation retreatments using mitomycin C

PURPOSE

To evaluate the visual and refractive results and the incidence of complications after laser subepithelial keratectomy (LASEK) enhancement using mitomycin C (MMC) after a previous LASEK procedure with MMC.

DESIGN

Retrospective, noncomparative, interventional case series.

METHODS

Setting was Vissum Santa Hortensia, Madrid, Spain. We performed a retrospective study of LASEK-treated eyes that received intraoperative MMC for 30 seconds and that needed an enhancement procedure. LASEK retreatment with MMC 0.02%, applied for 60 seconds, was performed 3 to 6 months after the initial surgery. We measured the visual and refractive results 3 months after the enhancement and the incidence of complications.

RESULTS

Eighty-two eyes were included in the study. The preoperative data were best spectacle-corrected visual acuity (BSCVA) 1.08 +/- 0.19, sphere -4.68 +/- 2.8 diopters (D), and cylinder -1.30 +/- 1.20 D. Three to 6 months postoperatively, before enhancement, the uncorrected VA (UCVA) was 0.59 +/- 0.2; the BSCVA, 0.976 +/- 0.2; the residual sphere, +0.17 +/- 0.7 D, and the cylinder, -0.39 +/- 0.5 D. Three months after retreatment, the UCVA was 0.93 +/- 0.1; the BSCVA, 0.977 +/- 0.1; the residual sphere, 0.09 +/- 0.3 D; and the residual cylinder, -0.2 +/- 0.3 D. The safety index after retreatment was 1.01 +/- 0.1, and the efficacy index was 0.96 +/- 0.1. No haze, no delay in epithelial healing, and no case of endothelial decompensation were detected.

CONCLUSION

Surface ablation retreatment using MMC seems to be effective to correct residual refractive errors after an initial surgery with MMC.

Ten-year follow-up of photorefractive keratectomy for myopia

BACKGROUND

The aim of this study is to evaluate the long-term (10-year) outcome of excimer laser photorefractive keratectomy (PRK) on myopic eyes.

METHODS

This retrospective study included 42 eyes of 29 patients (13 male, 16 female; mean age 33.4 years, range 21 to 60) who were treated with myopic PRK at St. Luke's International Hospital, Tokyo, Japan, from May 1 1995 to December 31 1998, and followed up for more than 10 years. The main outcome measures were efficacy, predictability, stability, safety, and complications. We also evaluated the progress of intraocular pressure, corneal thickness, and endothelial cell density after the surgery. The cases of retreatments were excluded from this study.

RESULTS

Ten years after the surgery, 17 eyes (40%) had 20/20 vision or better, and 35 eyes (81%) had 20/40 or better. With regard to the refractive predictability, 55 percent of the eyes were within ± 1.0D and 76% were within ± 2.0D, 10 years after the surgery. There was myopic regression with a mean change in refraction of-0.51 ± 1.78D. Best spectacle-corrected visual acuity (BCVA) was unchanged or improved in 95%, and only two eyes lost 1 line of BCVA. The mean corneal haze score was 0.19 ± 0.40, and the decreasing rate of endothelial cell was 8.30 ± 9.94% at 10 years, which was slightly higher than the spontaneous decreasing rate with age.

CONCLUSIONS

PRK is safe and effective in refraction even 10 years after surgery; however, further long-term follow-up is needed to evaluate the decreasing of endothelial cells.

Comparison between femtosecond laser-assisted sub-Bowman keratomileusis vs laser subepithelial keratectomy to correct myopia

PURPOSE

To compare femtosecond laser sub-Bowman keratomileusis (FSBK) vs laser subepithelial keratectomy (LASEK) to correct myopia.

DESIGN

Retrospective, nonrandomized, interventional, comparative case series.

METHODS

Two thousand one hundred and eight eyes were included in the study. We compared 1,072 eyes treated with FSBK vs 1,036 eyes treated with LASEK with or without mitomycin C (MMC). Visual and refractive results were evaluated 1 day, 1 week, and 1 and 3 months postoperatively.

RESULTS

Preoperative mean sphere and best spectacle-corrected visual acuity (BSCVA) were -3.93 diopters (D) vs -3.87 D (P = .5) and 1.12 vs 1.12 (P = .8) in FSBK and LASEK, respectively. Uncorrected visual acuity (UCVA) was 0.92 vs 0.62, 0.98 vs 0.78, 0.96 vs 0.91, and 1.06 vs 1.03 in FSBK and LASEK, respectively, at 1 day, 1 week, and 1 and 3 months after surgery (P < .01 for all comparisons). Three months postoperatively, BSCVA was 1.13 and 1.10, respectively (P = .001). At that moment, 20 eyes (1.93%) in the LASEK group vs 9 eyes (0.84%) in the FSBK group had lost 2 or more lines of BSCVA. Ten eyes (0.96%) in the LASEK group gained 2 or more lines of BSCVA, whereas 3 eyes (0.28%) in the FSBK group gained 2 lines. Six months postoperatively, only 2 LASEK eyes (0.19%) showed loss of 2 or more lines of BSCVA, compared to 3 FSBK-treated eyes (0.28%).

CONCLUSION

Both FSBK and LASEK are safe and effective procedures to correct myopia. Slightly better visual and refractive results were observed in FSBK-treated eyes in a 3-month follow-up.

Comparison of the changes in corneal biomechanical properties after photorefractive keratectomy and laser in situ keratomileusis

PURPOSE

To compare the postoperative biomechanical properties of the cornea after photorefractive keratectomy (PRK) and after laser in situ keratomileusis (LASIK) in eyes with myopia.

METHODS

We retrospectively examined 27 eyes of 16 patients undergoing PRK and 31 eyes of 16 patients undergoing LASIK for the correction of myopia. Corneal hysteresis (CH) and corneal resistance factor (CRF) were measured with Ocular Response Analyzer before and 3 months after surgery. We also investigated the relationship between these biomechanical changes and the amount of myopic correction.

RESULTS

The CH was decreased significantly from 10.8 +/- 1.3 (mean +/- SD) mmHg to 9.2 +/- 1.6 mmHg after PRK (P < 0.001), and from 10.8 +/- 1.4 mmHg to 8.6 +/- 0.9 mmHg after LASIK (P < 0.001). The CRF was also decreased significantly, from 10.3 +/- 1.5 mmHg to 8.4 +/- 1.8 mmHg after PRK (P < 0.001), and from 10.3 +/- 1.5 mmHg to 7.7 +/- 1.3 mmHg after LASIK (P < 0.001). The amount of decrease in CH and CRF was significantly larger after LASIK than after PRK (P = 0.04). There was a significant correlation between the amount of myopic correction and changes in biomechanical properties after PRK (r = -0.61, P < 0.01 for CH, r = -0.41, P < 0.05 for CRF) and LASIK (r = -0.37, P < 0.05 for CH, r = -0.45, P < 0.05 for CRF).

CONCLUSIONS

Both PRK and LASIK can affect the biomechanical strength of the cornea depending on the amount of myopic correction. The amount of biomechanical changes is larger after LASIK than after PRK. From a biomechanical viewpoint, PRK may be a less invasive surgical approach for the correction of myopia than LASIK.

Mitomycin C in corneal refractive surgery

Mitomycin C has played a deciding role in the current revival of excimer laser surface ablation techniques. We review the literature regarding mechanism of action of mitomycin C, histological effects on the cornea, and indications, dose, exposure time, and toxicity of mitomycin C in corneal refractive surgery. Mitomycin C is an alkylating agent with cytotoxic and antiproliferative effects that reduces the myofibroblast repopulation after laser surface ablation and, therefore, reduces the risk of postoperative corneal haze. It is used prophylactically to avoid haze after primary surface ablation and therapeutically to treat pre-existing haze. There is no definite evidence that establishes an exact diopter limit or ablation depth at which to apply prophylactic mitomycin C. It is usually applied at a concentration of 0.2mg/ml (0.02%) for 12 to 120 seconds over the ablated stroma, although some studies suggest that lower concentrations (0.01%, 0.002%) could also be effective in preventing haze when treating low to moderate myopia. This dose of mitomycin C has not been associated with any clinically relevant epithelial corneal toxicity. Its effect on the endothelium is more controversial: two studies report a decrease in endothelial cell density, but the majority of reports suggest that the endothelium is not altered. Regarding mitomycin C's effect on keratocyte population, although animal studies report keratocyte depletion after its use, longer follow-up suggested that the initial keratocyte depletion does not persist over time.

Seven-year follow-up of LASIK for myopia

PURPOSE

To assess the long-term refractive results, subjective parameters, and late sequelae of LASIK.

METHODS

A retrospective follow-up study was conducted on 38 eyes of 21 patients (17 with bilateral treatment and 4 with unilateral treatment) who had LASIK surgery between 1999 and 2000. Laser ablations were done with an excimer laser (VISX STAR and STAR S2). Follow-up was 2 months, 2 years, and > 7 years postoperatively. Uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), manifest refraction, indirect ophthalmoscopy, and wavefront analysis were measured at the last follow-up and a questionnaire was answered.

RESULTS

Postoperatively, BSCVA < or = 0.0 (logMAR) was obtained in 91%, 100%, and 89% of eyes at 2 months, 2 years, and at last follow-up, respectively. Postoperative spherical equivalent refraction within +/- 0.50 diopters (D) was obtained in 75%, 63%, and 42% of eyes at 2 months, 2 years, and 7 to 8 years, respectively. At 2 months and 2 years, 83% of eyes were within +/- 1.00 D, which decreased to 42% at 7 to 8 years. Mean spherical equivalent refraction at 2 months was -0.41 D, at 2 years -0.57 D, and at 7 to 8 years continued to decrease to -1.38 D. Patient satisfaction was high--100% of patients would have LASIK again.

CONCLUSIONS

LASIK outcomes tend to shift toward undercorrection over time. Postoperative ectasia was not noted 7 to 8 years after LASIK. All patients were satisfied with the postoperative results although emmetropia was not reached.

Ten-year follow-up of excimer laser surface ablation for myopia in thin corneas

PURPOSE

To evaluate the long-term outcomes of excimer laser surface ablation performed on thin corneas.

DESIGN

Retrospective study.

METHODS

We included in the study 75 eyes (49 patients) with a preoperative central corneal thickness (CCT) thinner than 500 mum that had undergone surface ablation to correct their myopia and that had at least 10 years of follow-up. We evaluated the stability of visual acuity (VA) and refraction, the predictability, corneal keratometry, safety, efficacy, and postoperative complications at the examinations 3 months and 1, 2, 5, and 10 years after surgery.

RESULTS

Preoperative CCT was 481.54 +/- 15.7 microm (range, 438 to 499 microm). Preoperative spherical equivalent was -6.12 +/- 2.67 diopters (D) (range, -2 to -14 D). The best spectacle-corrected VA significantly improved (P < .01) during the follow-up. The uncorrected VA showed significant improvement in all visits when compared with the 3-month postoperative visit. Both the sphere and cylinder showed a slight but significant regression (P < .01) only in the comparison between 3 months and 10 years after the surgery. Ten years after the surgery, 30 eyes (40%) were within 0.50 D and 43 eyes (57.33%) were within 1.00 D of emmetropia. The safety index improved over the 10 year period and was always higher than 0.9. The efficacy index remained stable around 0.8. The topography did not show signs of corneal ectasia and the keratometry showed no increase in corneal power. Thirty eyes (40%) needed enhancement.

CONCLUSION

Surface ablation seems to be safe and effective to correct myopia in corneas thinner than 500 microm, with stable visual and refractive outcomes in a 10-year follow-up.

Comparison between three- and six-month postoperative refractive and visual results after laser epithelial keratomileusis with mitomycin C

PURPOSE

To compare the residual refraction and visual results between the three- and six-month postoperative visits to detect the optimal moment for enhancement after myopic laser epithelial keratomileusis (LASEK) with mitomycin C (MMC).

DESIGN

Nonrandomized, interventional, prospective study.

METHODS

One hundred and forty-one consecutive eyes that underwent LASEK with MMC to correct their myopia using the Esiris excimer laser (Schwind Eye Tech Solutions, Kleinostheim, Germany), and that showed three months postoperatively a residual defect or a suboptimal uncorrected visual acuity (UCVA) or best spectacle-corrected visual acuity (BSCVA) were included in the study. We compared the residual spherical refraction and cylinder, the UCVA, and the BSCVA between the three- and six-month postoperative examinations.

RESULTS

Preoperative spherical refraction was -5.2 +/- 2.90 diopters (D). Preoperative cylinder was -1.66 +/- 1.20 D. The residual sphere was +0.43 +/- 0.90 D three months and +0.21 +/- 0.90 D six months after surgery (P = .0001). The cylinder was -0.71 +/- 0.60 D and -0.67 +/- 0.60 D, respectively (P = .4). The UCVA was 0.75 +/- 0.2 and 0.81 +/- 0.2 (P = .0001) and the BSCVA was 0.94 +/- 0.1 and 1.01 +/- 0.1 (P = .0001), respectively. Those patients with a myopic defect (sphere or cylinder) three months postoperatively did not show any significant change in UCVA or refractive defect six months after surgery, while those with a hyperopic defect (sphere or cylinder) showed an improvement in UCVA and residual refraction six months postoperatively (P < .05).

CONCLUSIONS

Our results suggest that retreatment after myopic LASEK with MMC may be performed three months after surgery when the residual refraction is myopic, but it seems wise to wait at least six months after surgery when the residual refraction is hyperopic.