Long-Term Evaluation of Complications and Results of Photorefractive Keratectomy in Myopia: An 8-Year Follow-Up

Investigation of corneal epithelial thickness and irregularity by optical coherence tomography after transepithelial photorefractive keratectomy

CLINICAL RELEVANCE

Corneal epithelial healing after refractive surgery is a clinically significant issue, especially for surface ablation procedures, and this can be monitored using optical coherence tomography (OCT).

BACKGROUND

The aim of this work is to investigate the corneal epithelial thickness and irregularity by OCT after transepithelial photorefractive keratectomy (t-PRK) and analyse its correlation with visual and refractive outcomes.

METHODS

Patients aged ≥18 years with myopia, with or without astigmatism, who underwent t-PRK between May 2020 and August 2021 were included. All participants were subjected to complete ophthalmic examinations and OCT pachymetry at every follow-up visit. Patients were followed up at 1 week and 1, 3, and 6 months postoperatively.

RESULTS

A total of 67 patients (126 eyes) were enrolled in this study. One month postoperatively, spherical equivalent refraction and visual acuity achieved preliminary stability. However, central corneal epithelial thickness (CCET) and standard deviation of the corneal epithelial thickness (SDcet) took 3-6 months to progressive recovery. Patients with higher baseline spherical equivalent refraction were associated with slower epithelial recovery. At every follow-up time point, a significant superior-inferior difference in the minimum corneal epithelial thickness area was observed. Higher stromal haze was correlated with higher spherical equivalent refraction (both baseline and residual) but had no relation with visual outcomes. There was a significant correlation between higher CCET with a better uncorrected distance visual acuity and lower corneal epithelial thickness irregularity.

CONCLUSIONS

CCET and SDcet measured by OCT seem to be a good auxiliary indicator for reflecting the status of corneal wound recovery after t-PRK surgery. However, a well-designed randomised control study is needed to confirm the study results.

The 18-Month Outcomes of a Contralateral, Randomized, Prospective Clinical Trial Comparing Photorefractive Keratectomy and SMILE for Myopia

PURPOSE

To compare clinical outcomes and patient satisfaction of photorefractive keratectomy (PRK) and small incision lenticule extraction (SMILE) for myopia.

METHODS

This contralateral, randomized, prospective clinical trial included 86 eyes of 43 patients diagnosed as having spherical equivalent (SE) from -1.00 to -8.00 diopters (D). One eye of each patient was randomly allocated to receive either PRK with 0.02% mitomycin C or SMILE. Visual acuity measurement, slit-lamp microscopy, manifest and cycloplegic refraction, Scheimpflug corneal tomography, contrast sensitivity assessment, ocular wavefront aberrometry, and a satisfaction questionnaire were performed preoperatively and during an 18-month follow-up.

RESULTS

Forty-three eyes of each group completed the study. After 18 months of follow-up, eyes treated with PRK and SMILE showed comparable results regarding uncorrected distance visual acuity (-0.12 ± 0.07 and -0.25 ± 0.09, respectively), safety, efficacy, contrast sensitivity, and ocular wavefront aberrometry. For predictability, eyes treated with PRK had a statistically lower residual spherical equivalent when compared with eyes treated with SMILE. Residual astigmatism of 0.50 D or less was achieved in 95% of the PRK group and 81% of the SMILE group. At the 1-month follow-up visit, the PRK group presented worse evaluation in relation to vision and foreign body sensation when compared to the SMILE group.

CONCLUSIONS

Both PRK and SMILE presented as safe and effective strategies for treating myopia with comparative clinical results. Eyes treated with PRK showed lower spherical equivalent and residual astigmatism. In the first month, eyes treated with SMILE showed less foreign body sensation and faster visual recovery. [J Refract Surg. 2023;39(3):180-186.].

[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.

TGF beta -1, -2 and -3 in the modulation of fibrosis in the cornea and other organs

The TGF beta-1, -2 and -3 isoforms are transcribed from different genes but bind to the same receptors and signal through the same canonical and non-canonical signal transduction pathways. There are numerous regulatory mechanisms controlling the action of each isoform that include the organ-specific cells producing latent TGF beta growth factors, multiple effectors that activate the isoforms, ECM-associated SLRPs and basement membrane components that modulate the activity and localization of the isoforms, other interactive cytokine-growth factor receptor systems, such as PDGF and CTGF, TGF beta receptor expression on target cells, including myofibroblast precursors, receptor binding competition, positive and negative signal transduction effectors, and transcription and translational regulatory mechanisms. While there has long been the view that TGF beta-1and TGF beta-2 are pro-fibrotic, while TGF beta-3 is anti-fibrotic, this review suggests that view is too simplistic, at least in adult tissues, since TGF beta-3 shares far more similarities in its modulation of fibrotic gene expression with TGF beta-1 and TGF beta-2, than it does differences, and often the differences are subtle. Rather, TGF beta-3 should be seen as a fibro-modulatory partner to the other two isoforms that modulates a nuanced and better controlled response to injury. The complex interplay between the three isoforms and numerous interactive proteins, in the context of the cellular milieu, controls regenerative non-fibrotic vs. fibrotic healing in a response to injury in a particular organ, as well as the resolution of fibrosis, when that occurs.

Visual outcomes of sterile corneal infiltrates after photorefractive keratectomy

Purpose:

Sterile infiltrates following laser refractive surgery is an uncommon complication. This study was undertaken to analyze the visual outcomes of sterile infiltrates following photorefractive keratectomy (PRK).

Methods:

This retrospective study included 14 eyes that developed sterile infiltrates following PRK out of a total of 6280 eyes that underwent PRK between 2014 and 2017. Medical records of these patients, including patient demographics, characteristics of the infiltrate, presenting visual acuity, and treatment outcomes were recorded and analyzed.

Results:

The incidence of sterile corneal infiltrates post-PRK in our study was 0.22% (14/6280). The mean age of the patients was 27.42 ± 4.87 years. The uncorrected visual acuity (UCVA) at presentation was 0.49 ± 0.13 log MAR units. The mean size of the infiltrate was 3.22 ± 2.85 mm². All cases were successfully managed medically with topical steroids. The mean UCVA and best-corrected visual acuity (BCVA) at the last follow-up visit were 0.08 ± 0.08 and 0.05 ± 0.07 log MAR units, respectively. The mean time taken for resolution of the infiltrate was 8.91 ± 4.57 days.

Conclusion:

Sterile infiltrates following PRK can be effectively treated with aggressive topical steroids. The outcome is generally favorable and does not require surgical intervention if treatment is instituted early.

Integrating binocular vision assessment in refractive surgery work-up: Proposition and protocol

Refractive surgeries are one of most commonly performed surgeries for correcting visual impairment due to refractive errors. With the increase in demand for refractive surgeries, there is an enormous strain on the operating surgeon for delivering ideal outcomes i.e 20/20 visual acuity. Regression, under-correction and ectasia are the most dreaded complications post-refractive correction, for the surgeon as well as the patient. They have significant effects on the quantity of the vision and most importantly on the quality of life of the patient. With the advent of digital era and jobs requiring the eyes being glued to the screen for hours there has been a surge in the patients presenting with complaints of asthenopia, glare, halos, and difficulty in focusing; pointing towards diagnosis of non-strabismic binocular vision anomalies (NSBVA). NSBVA in a postrefractive surgery patient may masquerade as regression or under-correction. However, timely diagnosis of NSBVA in such patients would prevent the greater harm caused by wrongful re-correction. Home- and office-based vision therapy results in improvement in visual acuity in a large majority of these patients. This preferred practice pattern intends to guide the refractive surgeons to diagnose and treat the postrefractive surgery NSBVA following a case-based and algorithmic approach. It also emphasizes the inclusion of the binocular vision assessment as a part of the pre-operative workup for patients undergoing refractive procedures.

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.

Early Refractive and Clinical Outcomes of High-Myopic Photorefractive Keratectomy as an Alternative to LASIK Surgery in Eyes with High Preoperative Percentage of Tissue Altered

Objective

To analyze the safety and efficacy of high-myopic PRK as an alternative to LASIK surgery in patients with a high preoperative percentage tissue altered (PTA).

Design

Retrospective interventional case series.

Participants

Charts of 256 consecutive eyes that underwent PRK with application of mitomycin-C 0.02% for high myopia were retrospectively reviewed.

Methods

Refractive (refraction and refractive accuracy) and visual outcomes (uncorrected and corrected visual acuities), as well as occurrence of haze in the eyes with preoperative PTA expected to be higher than 40% with a 110-micron flap if undergoing LASIK surgery, were analyzed.

Results

Mean follow-up was 7.3 ± 4.8 months. A total of 187 of 256 eyes (73.0%) were included in the analysis because they were expected to have a PTA greater than 40%, should they have undergone LASIK surgery. The actual mean PTA of those eyes following PRK was 31.8 ± 2.2%, and none had a PTA ≥ 40%. UDVA of 20/16, 20/20, and 20/25 or better was achieved in 1.2% (2 eyes), 65.5% (112 eyes), and 85.4% (146 eyes), respectively. The percentage of eyes with postoperative SE within ±0.5 D and ±1.0 D of planned SE was 71% and 93%, respectively. None of the eyes lost 2 or more lines of CDVA. The rate of stromal haze, managed successfully with topical steroids only, was 4.8%.

Conclusion

High-myopic PRK with application of mitomycin-C in the eyes at risk of developing ectasia because of high preoperative PTA was demonstrated to be a safe and effective alternative to the LASIK procedure.

Studying the factors related to refractive error regression after PRK surgery

Backgtound

Photorefractive keratectomy (PRK) is used for a wide range of refractive errors such as low to moderate myopia, hyperopia and astigmatism. While many improvements have been made in laser application and accuracy as well as the modes of corneal flap removal, and although the results are somewhat predictable, regression of refractive errors is still a common complaint among the patients undergoing refractive surgery with Excimer Laser. We aimed to determine related factors of regression following photorefractive keratectomy (PRK) in different types of refractive errors.

Methods

This cross-sectional study included patients who had undergone PRK more than 6 months previously and investigated refractive error regression and related factors. The participants were those who had PRK eye surgery for the first time from 2013 to 2016 using Technolas 217z100. A refraction value of spherical equivalent > 0.75 D after cycloplegic refraction was defined as refractive error regression.

Results

A total of 293 eyes on 150 subjects were studied. The preoperative refractive error of the eyes were as follows: 5.5% were myopic, 1% were hyperopic, 4.8% had astigmatism, 76% had myopic astigmatism and 12.6% had hyperopic astigmatism. Regressed and non-regressed eyes were assessed using the generalized estimating equations for the probabilistic variables of demographic characteristics, topography and eye refraction. The variables of simulated keratometry astigmatism (simK) (OR = 2.8; p = 0.04), 5 mm irregularity (OR = 3.56; p = 0.01) and sphere value (OR = 1.98; p = 0.01) were significantly related to refractive error regression. There was no significant relationship between the regressed and non-regressed eyes of the same person (p ≥ 0.05).

Conclusion

There was a positive relationship between the increase of 5 mm irregularity, simK, sphere value before surgery and refractive error regression. Age, sex and type of refraction error of the patient and the expertise of the PRK surgeon could change the general results; therefore, not all cases should be dealt with identically.

Visual performance after excimer laser photorefractive keratectomy for high myopia

PURPOSE:

To evaluate the efficacy, safety, predictability, and visual performance of excimer laser photorefractive keratectomy (PRK) for myopia greater than −8 diopters (D).

METHODS:

Fifty-four patients (104 eyes) with myopia from −8D to −13D and cylinder up to −4D received surface ablation technique with the Allegretto wave version 1009-1 excimer laser to correct their refractive error. The patients were examined on days 1, 3, 7, and 14 and 1, 3, 6, and 12 months postoperatively. Visual acuity, manifest refraction, corneal haze, topography, intraocular pressure, contrast sensitivity, and wavefront aberration were evaluated.

RESULTS:

Twelve months postoperatively, 95% of eyes were within 1D of the intended correction. In addition, 94% of eyes had attained uncorrected distance visual acuity of 20/25 or better, and 98% of eyes had improved or remained their corrected distance visual acuity. All eyes exhibited barely detectable corneal haze which peaked during the 1^st month with a gradual reduction in the 3^rd month. Ninety-five percent of patients had no or only mild degree of night glare.

CONCLUSIONS:

Excimer laser PRK is an effective and predictive treatment for high myopia greater than −8D with or without astigmatism up to −4D. The incidence of complication is low. All patients who are candidates for laser in situ keratomileusis can be candidates for surface ablation, especially those with preoperative thinner cornea or higher risk of corneal flap complications.

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.

New drug delivery system for corneal administration of mitomycin-C

PURPOSE

To develop a new corneal release system to deliver optimum amounts of mitomycin-C (MMC) during the perioperative period of photorefractive keratectomy (PRK).

SETTING

Ophthalmos S/A, São Paulo, Brazil.

DESIGN

Experimental study.

METHODS

An in vitro experimental design was developed for studying a new MMC delivery system at a drug concentration of 0.02%. Whatman sterile filter paper disks with a diameter of 8.0 mm were impregnated with MMC solution. After drying, the disks were placed on agar plates seeded with Staphylococcus epidermidis; this was followed by instillation of a drop of sterile water. After 1 minute, the disks were removed and the plates were incubated for 48 hours at 35°C. The mean volume of the drops delivered from regular eyedrop bottles was determined, and the inhibition zone (in millimeters) was correlated with the amount of MMC loaded onto the disks.

RESULTS

Analysis of the inhibition zones produced by MMC indicated that 16 μg was the optimum dose to be incorporated in the disks. The mean volume of a drop delivered from eyedrop bottles was 37.7 μL. One minute after the application of a single drop of a balanced salt solution, the system released an adequate concentration of MMC for PRK.

CONCLUSION

A new delivery system for MMC was successfully developed for application during photorefractive keratectomy.

FINANCIAL DISCLOSURE

Dr. de Souza Lima Filho is the managing director of Ophtalmos S/A. Drs. de Souza Lima Filho, Irochima Pinheiro, and Oréfice have exclusive rights to intellectual property of this invention secured by a patent application filed with the Instituto Nacional da Propriedade Industrial.

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.

The results of photorefractive keratectomy with Mitomycin-C in myopia correction after 5 years

Objective:

To evaluate the results of photorefractive keratectomy (PRK) with mitomycin C in myopia correction after five years.

Methods:

This is a cross sectional study which included 145 eyes of 74 patients in 18 to 51 years age group that were undergoing Photorefractive keratectomy with mitomycin C using Allegretto Wave Eye-Q 400-Hz excimer laser platform in Markazi Eye Center, Tehran, Iran. All the surgical procedures were performed by the same surgeon. After five years follow-up evaluation including BCVA, UCVA, Refractive error measurement and external eye examination was performed.

Results:

The mean diopter of spherical equivalent before surgery was -3.40±1.73. The following findings were obtained after 5 years follow up visit: The mean spherical equivalent value: -0.08±0.40, the mean: Log MARUCVA: 0.02±0.07, the mean Log MAR BCVA: 0.00±0.04.

Conclusion:

PRK is an effective, safe and predictable method used to correct myopia. The wave front-optimized algorithm of the Allegretto Wave Eye-Q 400-Hz excimer laser platform demonstrated good refractive and visual results. Presence of variables such as gender, age and astigmatism before operation have no significant impact on the result of this operation.

Risk factors of regression and undercorrection in photorefractive keratectomy: a case-control study

AIM

To determine risk factors of regression and undercorrection following photorefractive keratectomy (PRK) in myopia or myopic astigmatism.

METHODS

A case-control study was designed in which eyes with an indication for re-treatment (RT) were defined as cases; primary criteria for RT indication, as assessed at least 9mo postoperatively, included an uncorrected distance visual acuity (UDVA) of 20/30 or worse and a stable refraction for more than 3mo. Additional considerations included optical quality symptoms and significant higher order aberrations (HOAs). Controls were chosen from the same cohort of operated eyes which had complete post-operative follow up data beyond 9mo and did not need RT. The cohort included patients who had undergone PRK by the Tissue-Saving (TS) ablation profile of Technolas 217z100 excimer laser (Bausch & Lomb, Rochester, NY, USA). Mitomycin C had been used in all of the primary procedures.

RESULTS

We had 70 case eyes and 158 control eyes, and they were comparable in terms of age, sex and follow-up time (P values: 0.58, 1.00 and 0.89, respectively). Pre-operative spherical equivalent of more than -5.00 diopter (D), intended optical zone (OZ) diameter of less than 6.00 mm and ocular fixation instability during laser ablation were associated with RT indications (all P values <0.001). These factors maintained their significance in the multiple logistic regression model with odd ratios of 6.12, 6.71 and 7.89, respectively.

CONCLUSION

Higher refractive correction (>-5.00 D), smaller OZ (<6.00 mm) and unstable fixation during laser ablation of PRK for myopia and myopic astigmatism were found to be strong predictors of undercorrection and regression.

Management of residual refractive error after laser in situ keratomileusis and photorefractive keratectomy

PURPOSE OF REVIEW

To review the various steps and methods in managing residual refractive error after laser in situ keratomileusis and photorefractive keratectomy (PRK).

RECENT FINDINGS

Past studies have shown the efficacy and safety of flap relifts over recuts and for surface ablation over the flap. Other previous and also more recent studies show the use of a femtosecond laser for side cuts only. Recently, the creation of a femtosecond mini flap has been described. New studies also demonstrate the use of collagen cross-linking in postrefractive surgery ectasia.

SUMMARY

Residual refractive error is a known complication after both laser in situ keratomileusis and PRK. A systematic approach should be taken to manage this complication starting with a thorough evaluation to determine if an enhancement is indicated and if so, which method will be the safest and most efficacious for the patient.

Corneal curvature gradient map: a new corneal topography map to predict the corneal healing process

PURPOSE

To evaluate a new curvature gradient topography map to predict postoperative corneal remodeling.

METHODS

In this retrospective study, 32 eyes of 16 patients with myopia underwent excimer ablation surgery with a postoperative high curvature gradient. The new curvature gradient map (acquired immediately postoperatively) shows the difference between the curvatures of two points over the distance between them; it was compared to the tangential curvature difference map between 1 and 12 months postoperatively to determine their relationship. Corneas were divided into 12 regions for analysis: four 90°-wide sectors centered on 0°, 90°, 180°, and 270°. There were three subdivisions in each sector: central (radius: 0 to 2.75 mm), paracentral (radius: 2.75 to 3.25 mm), and peripheral (radius: 3.25 to 4.5 mm). Linear regression analysis was performed by region.

RESULTS

The following regions had significant relationships between the initial curvature gradient and curvature difference between 1 and 12 months postoperatively: the paracentral zone of the 90° sector (P = .0145; R(2) = 0.1832) and both the central (P = .0034; R(2) = 0.2522) and paracentral (P = .0452; R(2) = 0.1271) zones of the 270° sector. The greatest average initial tangential curvature was in the 270° sector.

CONCLUSIONS

The initial curvature gradient after surgery predicted change in tangential curvature over the subsequent 12 months in areas where initial tangential curvature was greatest. When the curvature gradient was high, the surface curvature modification remained in progress months after surgery.

The posterior chamber phakic refractive lens (PRL): a review

Implantation of phakic intraocular lenses (pIOLs) is a reversible refractive procedure, preserving the patient's accommodative function with minimal induction of higher order aberrations compared with corneal photoablative procedures. Despite this, as an intraocular procedure, it has potential risks such as cataracts, chronic uveitis, pupil ovalization, corneal endothelial cell loss, pigmentary dispersion syndrome, pupillary block glaucoma, astigmatism, or endophthalmitis. Currently, only two models of posterior chamber pIOLs are commercially available, the implantable collammer lens (STAAR Surgical Co.) and the phakic refractive lens (PRL; Zeiss Meditec). The number of published reports on the latter is very low, and some concerns still remain about its long-term safety. The present article reviews the published literature on the outcomes after PRL implantation in order to provide a general overview and evaluate its real potential as a surgical refractive option.

Prospective, randomized, fellow eye comparison of WaveLight Allegretto Wave Eye-Q versus VISX CustomVueTM STAR S4 IRTM in photorefractive keratectomy: analysis of visual outcomes and higher-order aberrations

Background

The purpose of this study was to compare differences in visual outcomes, higher-order aberrations, contrast sensitivity, and dry eye in patients undergoing photorefractive keratectomy using wavefront-guided VISX CustomVue™ and wavefront-optimized WaveLight^® Allegretto platforms.

Methods

In this randomized, prospective, single-masked, fellow-eye study, photorefractive keratectomy was performed on 46 eyes from 23 patients, with one eye randomized to WaveLight Allegretto, and the fellow eye receiving VISX CustomVue. Three-month postoperative outcome measures included uncorrected distance visual acuity, corrected distance visual acuity, refractive error, root mean square of total and grouped higher-order aberrations, contrast sensitivity, and Schirmer’s testing.

Results

Mean values for uncorrected distance visual acuity (logMAR) were −0.03 ± 0.07 and −0.06 ± 0.09 in the wavefront-optimized and wavefront-guided groups, respectively (P = 0.121). Uncorrected distance visual acuity of 20/20 or better was achieved in 91% of eyes receiving wavefront-guided photorefractive keratectomy, and 87% of eyes receiving wavefront-optimized photorefractive keratectomy, whereas uncorrected distance visual acuity of 20/15 was achieved in 35% of the wavefront-optimized group and 64% of the wavefront-guided group (P ≥ 0.296). While root mean square of total higher-order aberration, coma, and trefoil tended to increase in the wavefront-optimized group (P = 0.091, P = 0.115, P = 0.459, respectively), only spherical aberration increased significantly (P = 0.014). Similar increases were found in wavefront- guided root mean square of total higher-order aberration (P = 0.113), coma (P = 0.403), trefoil (P = 0.603), and spherical aberration (P = 0.014). There was no significant difference in spherical aberration change when comparing the two platforms. The wavefront-guided group showed an increase in contrast sensitivity at 12 cycles per degree (P = 0.013).

Conclusion

Both VISX CustomVue and WaveLight Allegretto platforms performed equally in terms of visual acuity, safety, and predictability in photorefractive keratectomy. The wavefront-guided group showed slightly improved contrast sensitivity. Both lasers induced a comparable degree of statistically significant spherical aberration, and tended to increase other higher-order aberration measures as well.

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.