Excimer laser photorefractive keratectomy (PRK) for myopia and astigmatism

doi:10.1016/S0161-6420(99)90085-4

Ophthalmology

Volume 106, Issue 2, 1 February 1999, Pages 422-437

https://doi.org/10.1016/S0161-6420(99)90085-4 Get rights and content

Abstract

The purpose of the Committee on Ophthalmic Procedures Assessment is to evaluate on a scientific basis new and existing ophthalmic tests, devices, and procedures for their safety, efficacy, clinical effectiveness, and appropriate uses. Evaluations include examination of available literature, epidemiologic analyses when appropriate, and compilation of opinions from recognized experts and other interested parties. After appropriate review by all contributors, including legal counsel, assessments are submitted to the Academy’s Board of Trustees for consideration as official Academy policy.

Introduction

The field of ophthalmology has been evolving at a rapid pace as new technology continues to be integrated into everyday clinical practice. The process of integration is a long, complex one that involves scientific innovators, industry, clinical investigators, and regulatory agencies. The dissemination of accurate, prompt, and comprehensive information is critical in order for practicing ophthalmologists to evaluate new advances fairly.

The American Academy of Ophthalmology (AAO) implemented the Ophthalmic Procedure Preliminary Assessment (OPPA) in 1996 to evaluate new and rapidly evolving technology. The goal of the OPPA is to review the scientific literature to distill what is well established about the technology and to help define and refine the important questions to be answered by future investigations, recognizing that emerging technology is characterized by rapid change and expanding clinical indications.

The process for creating this assessment on excimer laser photorefractive keratectomy (PRK) involved writing an outline, which was reviewed by the seven-member Ophthalmic Procedures Assessment (OPA) committee. The peer-reviewed literature was analyzed and all possible relevant articles were selected, 285 in all. Members of the committee evaluated the articles for relevance to this OPPA and divided them into high, medium, and low categories based on the quality of study methodology. A methodologist reviewed all of the relevant articles and assigned a good, fair, or poor quality rating. A high-quality study is one in which the design of the study allowed the issue to be addressed, and one that was performed on the population of interest, executed in such a manner as to produce accurate and reliable data, and analyzed using appropriate statistical methods. Less highly-ranked studies lack one or more of these components. High-quality studies were given more weight for the purpose of this OPPA. Ophthalmic organizations and industry groups with interests in PRK also were contacted for their input. OPA committee members and other AAO committees reviewed drafts of this OPPA prior to formal approval by the Board of Trustees.

PRK is a procedure that is used to treat myopia and astigmatism by surgically modifying the anterior surface of the cornea to flatten the corneal curvature. The Academy selected excimer laser PRK as the topic for this OPPA because it is a relatively new procedure that is used widely around the world and becoming increasingly popular in the United States. The procedure received Food and Drug Administration (FDA) premarket approval for one laser in the fall of 1995 and for a second laser in the spring of 1996 to treat myopia, and for one laser in the spring of 1997 and another in early 1998 to treat astigmatism. A third laser received FDA approval in late 1998 for myopia and astigmatism correction. However, both hardware and software are still undergoing technical adjustments, and the surgical technique and postoperative care for the myopic patient are still being refined. There are multiple refractive surgery alternatives to PRK. Some options have been extensively studied, such as radial keratotomy,1 and many have undergone less scientific scrutiny, such as ALK, laser in-situ keratomileusis (LASIK), intracorneal ring, clear lens extraction, and phakic intraocular lenses. More accurate and reproducible data on all these refractive surgery choices will only improve our ability to treat patients in the best way possible.

This OPPA on PRK for myopia and astigmatism will review the following:

1.
Excimer laser technology, animal studies, and early human studies to describe the basis for early optimism regarding PRK
2.
Current indications for PRK
3.
Results of appropriate peer-reviewed literature on PRK
4.
Various adjunctive treatments after PRK
5.
Complications of PRK
6.
Ongoing studies involving PRK
7.
Important questions about PRK to be answered by future investigations

Section snippets

Technological and historical background

The term “excimer” is a contraction of “excited dimer,” an energized molecule of two like components, which was the original concept of how these rare gas-halide lasers functioned. Clinical excimer lasers use argon and fluorine gases to generate ultraviolet light with a wavelength of 193 nm. The energy from this wavelength of light is high enough to break the molecular bonds in the cornea and remove tissue. While various wavelengths of light can be produced depending on the gases used (e.g.,

Results of excimer laser photorefractive keratectomy

A large number of articles on the results of excimer laser PRK have been published in the peer-reviewed literature. Many of the studies described results utilizing machines that are no longer in use (e.g., the Taunton excimer laser), newer machines that are not FDA approved and consequently not readily available in the United States (e.g., Chiron, Nidek, and Novatec), or older techniques such as using nitrogen gas flow over the cornea during the ablation (as VISX did initially) or ablation

Postoperative management

Postoperative treatment after PRK varies greatly from surgeon to surgeon. Both Summit and VISX recommend topical antibiotics until the epithelial defect heals, but additional medications and treatments are more controversial. Many physicians use a bandage soft contact lens and/or topical nonsteroidal anti-inflammatory (NSAID) agents to reduce postoperative pain. It is not known if a tightly fitted or a loosely fitted contact lens yields more comfort and better healing. One study using a ProTek

Corneal topographic analysis

Over the past decade, clinicians have found computerized videokeratographic analysis of corneal curvature to be extremely helpful both before and after refractive surgery. Prior to refractive surgery, corneal topography helps determine whether a cornea is regular or irregular, possibly demonstrating signs of contact lens warpage or early keratoconus. After refractive surgery, it can be used to evaluate centration of the ablation, irregular astigmatism, and central islands.

Lin27 reviewed corneal

Complications

Seiler et al35 prospectively studied PRK complications in 193 eyes of 146 patients for up to 2 years postoperatively. Kim et al36 retrospectively reviewed PRK complication data on 2920 eyes of 1821 patients, also up to 2 years postoperatively. These two studies, the Summit and VISX FDA submission data, the Phase III results using the Summit ExciMed UV 200 LA Excimer Laser,37 and other smaller studies and reports are the primary sources for this section.

Future developments in excimer laser photorefractive keratectomy

Many of the newest technological developments in PRK (including scanning slit lasers and flying-spot lasers that are being used extensively outside the U.S.) are not widely available in the U.S. because they have not received FDA premarket approval. Scanning slit lasers generate a slit beam that is smaller than broad-beam lasers. The slit beam is scanned over the surface to alter the lasing profile, improving the smoothness of the ablated cornea and allowing for larger-diameter ablation zones.

Important issues to be addressed

Despite all the published peer-reviewed studies on PRK, numerous questions remain:

•
What is the long-term stability of eyes many years after PRK?
•
What is the maximum amount of myopia and of astigmatism effectively treated with PRK? What is the maximum amount of myopia and of astigmatism safely treated with PRK?
•
What is the best method to remove the epithelium? Is a manual debridement, laser-scrape, or transepithelial approach best? Should epithelial toxic solutions, such as alcohol or 4% lidocaine,

Conclusion

PRK is a well-accepted procedure in the United States and around the world, backed by a large volume of published research. The techniques used in the published research and described in this report are already superseded by newer techniques that require quantitative evaluation. Many of the earlier complications and poorer visual function results have been largely resolved by using a larger ablation zone, a multizone technique, and other improvements since the initial FDA trials. It appears to

References (79)

R.A Del Pero et al.
A refractive and histopathologic study of excimer laser keratectomy in primates
Am J Ophthalmol
(1990)
D Epstein et al.
Twenty-four-month follow-up of excimer laser photorefractive keratectomy for myopia. Refractive and visual acuity results
Ophthalmology
(1994)
D.K Williams
Multizone photorefractive keratectomy for high and very high myopialong-term results
J Cataract Refract Surg
(1997)
J.L Alio et al.
Complications of photorefractive keratectomy for myopiatwo year follow-up of 3000 cases
J Cataract Refract Surg
(1998)
H Higa et al.
Predictability of excimer laser treatment of myopia and astigmatism by the VISX Twenty-Twenty. Melbourne Excimer Laser Group
J Cataract Refract Surg
(1997)
C.A McCarty et al.
Comparison of results of excimer laser correction of all degrees of myopia at 12 months postoperatively. The Melbourne Excimer Laser Group
Am J Ophthalmol
(1996)
E Maguen et al.
Results of excimer laser photorefractive keratectomy for the correction of myopia
Ophthalmology
(1994)
A.R Talley et al.
Results one year after using the 193-nm excimer laser for photorefractive keratectomy in mild to moderate myopia
Am J Ophthalmol
(1994)
S.C Schallhorn et al.
Preliminary results of photorefractive keratectomy in active-duty United States Navy personnel
Ophthalmology
(1996)
I Kremer et al.
One-year follow-up results of photorefractive keratectomy for low, moderate, and high primary astigmatism
Ophthalmology
(1996)

P.G Mardelli et al.

The effect of excimer laser photorefractive keratectomy on intraocular pressure measurements using the Goldmann applanation tonometer

Ophthalmology

(1997)

D.S Gartry et al.

Retreatment for significant regression after excimer laser photorefractive keratectomy. A prospective, randomized, masked trial

Ophthalmology

(1998)

Cited by (78)

Ocular higher-order aberrations changes after implantable collamer lens implantation for high myopic astigmatism
2018, Journal of Current Ophthalmology
To investigate the changes in higher-order aberrations (HOAs) induced by the implantation of implantable collamer lenses (ICLs) and Toric ICL (TICL) in eyes with high myopia and high myopic astigmatism.
We investigated 33 eyes of 18 consecutive patients (in a prospective, interventional case series study), with spherical equivalent errors of −6.00 to −21.09 diopters (D) and cylindrical errors of −0.5 to −4.75 D, who underwent ICL and TICL implantation. Before and after 5 days, 2 and 6 months of surgery, the uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), defocus and adverse events of the surgery were assessed. Ocular HOAs were also evaluated by Hartmann-Shack aberrometry (Technolas PV, Rochester, New York, USA) before and after 6 months of surgery.
At 6.0 months after surgery, the UCVA and BCVA in 40% and 66.7% of eyes were 20/20, respectively. Mean defocus refraction and astigmatism was reduced to −0.66 and 0.65 D from −12.79 and 2.18 at baseline, respectively. For a 6 mm pupil, HOAs were not significantly changed, merely from 0.417 ± 0.162 μ before surgery to 0.393 ± 0.119 μ after surgery (P = 0.45). Spherical aberration (Z400) increased significantly (P = 00.0). Surgical induced astigmatism was lower than 0.25 D, and there were no changes in trefoils and coma aberration. No vision-threatening complications occurred during the observation period.
This study shows that the ICL and TICL performed well in correcting high myopic astigmatism without significant changes in HOAs during a 6-month observation period, although the spherical aberration (Z400) increased significantly.
Outcomes after implantable collamer lens surgery in a Canadian cohort
2017, Canadian Journal of Ophthalmology
To describe refractive outcomes and complications after implantable collamer lens (ICL) implantation.
Retrospective, interventional case series.
A database search of ICL surgeries over a 5-year period (2009–2013) was conducted, and 83 eyes of 44 patients were included. The Visian ICL (STAAR Surgical, Monrovia, Calif.) was used in all eyes. The primary outcome measure was postoperative uncorrected distance acuity (UCDA). Secondary outcomes include predictability, safety, and adverse events.
Mean age was 31 years, and 59% of patients were female. Mean observation time was 14.9 months. Mean manifest refractive spherical equivalent (MRSE) was −11.1 ± 3.24 D preoperatively and −0.18 D ± 0.57 D postoperatively. Mean astigmatism was −1.90 ± 1.34 D, and 82% of eyes received toric ICLs, 93.4% of eyes achieved 20/40 UCDA, and 50.8% achieved 20/20 at last observation; 67.1% and 89.5% of eyes had MRSE within 0.5 and 1.00 D of target refraction, respectively. Safety index was 1.16 and overall improvement of 0.060 logMAR was observed. Eight (10.5%) eyes had residual astigmatism with 5 (6.5%) requiring laser enhancement. Glare and haloes were reported in 6 eyes (7.9%). Three eyes developed cataract. One eye had a retinal detachment.
Toric and nontoric ICL implantations show promising refractive outcomes and acceptable safety in moderate to high myopes and can be considered for patients who are noncandidates for refractive laser surgery.
Rendre compte des résultats réfractifs de l’implantation d’une lentille de Collamer® (ICL) et des complications observées après l’intervention.
Examen rétrospectif d’une série d’interventions
On a procédé à l’examen d’une série de chirurgies d’implantation d’ICL répertoriées dans une base de données au cours d’une période de 5 ans (de 2009 à 2013), effectuées sur 83 yeux chez 44 patients. Les lentilles Visian ICL (STAAR Surgical, Monrovia, Californie) ont été utilisées dans tous les yeux. Le principal paramètre d’évaluation était l’acuité visuelle de loin (AVL) non corrigée postopératoire. Les paramètres secondaires comprenaient la prévisibilité, l’innocuité et les effets indésirables.
L’âge moyen des sujets était de 31 ans; 59 % d’entre eux étaient des femmes. La durée moyenne de la période d’observation était de 14,9 mois. L’équivalent sphérique de réfraction manifeste (ESRM) moyen était de −11,1 ± 3,24 D avant l’intervention, et de -0,18 D ± 0,57 D après celle-ci. L’astigmatisme moyen était de −1,90 ± 1,34 D. On a implanté une ICL torique dans 82 % des yeux. On a obtenu une AVL non corrigée de 20/40 pour 93,4 % des yeux, et de 20/20 pour 50,8 % des yeux à la dernière observation. L’ESRM était à ≤ 0,5 D et à ≤ 1,00 D de la réfraction cible pour 67,1 % et 89,5 % des yeux, respectivement. L’indice d’innocuité était de 1,16, et une amélioration globale de 0,060 logMAR a été observée. Un astigmatisme résiduel a été noté dans 8 (10,5 %) yeux, dont 5 (6,5 %) ont nécessité une correction au laser. On a signalé de l’éblouissement et des halos dans 6 yeux (7,9 %), la formation de cataractes dans 3 yeux et un décollement de rétine dans 1 œil.
L’implantation d’ICL toriques et non toriques a donné des résultats réfractifs prometteurs et fait preuve d’un tableau d’innocuité acceptable en présence de myopie modérée ou forte. Elle est envisageable chez les patients qui ne sont pas admissibles à la chirurgie réfractive au laser.
Managing residual refractive error after cataract surgery
2015, Journal of Cataract and Refractive Surgery
Citation Excerpt :
Keratorefractive approaches comprise (1) laser vision correction with laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK), (2) laser vision correction after implantation of a multifocal IOL, and (3) arcuate keratotomy after cataract surgery. The proven safety, efficacy, predictability, and stability of excimer laser surgery for the correction of a wide range of refractive errors30–33 make LASIK and PRK good options for treating pseudophakic ametropia. Combining keratorefractive surgery with intraocular surgery emerged first as a refractive paradigm coined “bioptics” in the late 1990s by Güell and Vázquez.34
We present a review of keratorefractive and intraocular approaches to managing residual astigmatic and spherical refractive error after cataract surgery, including laser in situ keratomileusis (LASIK), photorefractive keratectomy (PRK), arcuate keratotomy, intraocular lens (IOL) exchange, piggyback IOLs, and light-adjustable IOLs. Currently available literature suggests that laser vision correction, whether LASIK or PRK, yields more effective and predictable outcomes than intraocular surgery. Piggyback IOLs with a rounded-edge profile implanted in the sulcus may be superior to IOL exchange, but both options present potential risks that likely outweigh the refractive benefits except in cases with large residual spherical errors. The light-adjustable IOL may provide an ideal treatment to pseudophakic ametropia by obviating the need for secondary invasive procedures after cataract surgery, but it is not widely available nor has it been sufficiently studied.
Dr. Manche has equity in Calhoun Vision, Inc., Krypton Vision, Refresh Innovations, Inc., Seros Medical, LLC, and Veralas, Inc. He is a consultant to Oculeve, Inc., Best Doctors, and Gerson Lehrman. Dr. Sáles has no financial or proprietary interest in any material or method mentioned.
Phakic Intraocular Lens Implantation for the Correction of Myopia. A Report by the American Academy of Ophthalmology
2009, Ophthalmology
Citation Excerpt :
Keratorefractive surgeries, such as photorefractive keratectomy and LASIK, have limitations when used for the correction of high refractive errors.1–4
To review the published literature for evaluation of the safety and outcomes of phakic intraocular lens (pIOL) implantation for the correction of myopia and myopic astigmatism.
Literature searches of the PubMed and Cochrane Library databases were conducted on October 7, 2007, and July 14, 2008. The PubMed search was limited to the English language; the Cochrane Library was searched without language limitations. The searches retrieved 261 references. Of these, panel members chose 85 papers that they considered to be of high or medium clinical relevance to this assessment. The panel methodologist rated the articles according to the strength of evidence.
Two pIOLs have been approved by the US Food and Drug Administration (FDA): one iris-fixated pIOL and one posterior-chamber IOL. In FDA trials of iris-fixated pIOLs, uncorrected visual acuity (UCVA) was ≥20/40 in 84% and ≥20/20 in 31% after 3 years. In FDA trials of posterior-chamber pIOLs, UCVA was ≥20/40 in 81% and ≥20/20 in 41%. Satisfaction with the quality of vision with both types of pIOLs was generally high. Toric anterior- and posterior-chamber pIOLs have shown improved clinical results in European trials compared with spherical pIOLs. Comparative studies showed pIOLs to provide better best spectacle-corrected visual acuity (BSCVA) and refractive predictability and stability compared with LASIK and photorefractive keratectomy and to have a lower risk of retinal detachment compared with refractive lens exchange. Reported complications and long-term safety concerns include endothelial cell loss, cataract formation, secondary glaucoma (pupillary block, pigment dispersion), iris atrophy (pupil ovalization), and traumatic dislocation.
Phakic IOL implantation is effective in the correction of myopia and myopic astigmatism. In cases of high myopia of −8 diopters or more, pIOLs may provide a better visual outcome than keratorefractive surgeries and better safety than refractive lens exchange. The short-term rates of complications and loss of BSCVA are acceptable. Comprehensive preoperative evaluation and long-term postoperative follow-up examinations are needed to monitor for and prevent serious complications, and to establish long-term safety.
Proprietary or commercial disclosure may be found after the references.
Outcomes of laser refractive surgery for myopia
2009, Journal of Cataract and Refractive Surgery
Citation Excerpt :
Formation of subepithelial haze peaking at 3 to 6 months postoperatively and followed by progressive clearing up to 12 months was fairly common in PRK studies,64,65 but rarely observed in LASIK studies. Central islands that resulted in BCVA loss were, in the past, sometimes seen during the first few months after PRK procedures using the older broad-beam laser technology.53,64,65 These central islands often resolved by 12 months, reversing their effect on the BCVA loss observed earlier.
Many advances have been made in laser refractive surgery, and this review examines how they have affected treatment outcomes in individuals with varying degrees of myopia (law, moderate, and high). Studies with a minimum follow-up of 1 year with at least 2 of the 3 major outcome measures—efficacy, stability, and safety—were reviewed, and how the findings were affected by differences in ethnicity was assessed.
Higher-order aberrations after wavefront-optimized photorefractive keratectomy and laser in situ keratomileusis
2009, Journal of Cataract and Refractive Surgery
To analyze the changes in higher-order aberrations (HOAs) that occur after wavefront-optimized photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK).
Emory Eye Center and Emory Vision, Atlanta, Georgia, USA.
This retrospective analysis comprised eyes that had PRK or LASIK from June 2004 through October 2005. Postoperative outcome measures included 3-month uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), manifest refraction spherical equivalent (MRSE), changes in the root mean square (RMS) and grouped coefficient HOAs (microns) measured with a corneal analyzer, and subjective assessment of visual aberrations.
One hundred consecutive eyes of 54 patients had PRK, and 100 contemporaneous consecutive eyes of 71 patients had LASIK. The PRK and LASIK populations were similar in general demographics, preoperative HOAs, and postoperative UCVA and BSCVA. The mean MRSE was slightly hyperopic after PRK (mean +0.11 diopters [D]) and slightly myopic after LASIK (mean −0.19 D) (P<.0001). There were no statistically significant changes in RMS or grouped coefficient HOA values after PRK or LASIK, nor were there significant differences in postoperative RMS or grouped coefficient HOA values between PRK and LASIK. One percent of PRK and LASIK patients reported a subjective increase in postoperative visual aberrations; 5% reported a subjective improvement postoperatively.
Wavefront-optimized excimer laser surgery did not induce significant HOAs after PRK or LASIK. The 2 techniques were equally efficacious and had equivalent postoperative HOA profiles.

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¹: Prepared by the Committee on Ophthalmic Procedures Assessment Refractive Surgery Panel, Christopher J. Rapuano, MD, Chair, and approved by the American Academy of Ophthalmology’s Board of Trustees December 14, 1998.

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Ophthalmic procedure preliminary assessmentExcimer laser photorefractive keratectomy (PRK) for myopia and astigmatism1

Abstract

Introduction

Section snippets

Technological and historical background

Results of excimer laser photorefractive keratectomy

Postoperative management

Corneal topographic analysis

Complications

Future developments in excimer laser photorefractive keratectomy

Important issues to be addressed

Conclusion

Am J Ophthalmol

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Ophthalmic procedure preliminary assessment
Excimer laser photorefractive keratectomy (PRK) for myopia and astigmatism¹