Photorefractive keratectomy: A technique for laser refractive surgery

Munnerlyn, Charles R.; Koons, Stephen J.; Marshall, John

doi:10.1016/s0886-3350(88)80063-4

Cited by 682 publications

(245 citation statements)

References 8 publications

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“…8 The change in the asphericity expected due to this ablation algorithm accounted for 87.2% of the increase in the p-factor. The additional increase may be due to factors such as decentration, type of laser, optical role of the flap, wound healing, biomechanical effects, technical procedures, and reflection losses of the laser on the cornea.…”

Section: Discussionmentioning

confidence: 92%

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Changes in corneal asphericity after laser in situ keratomileusis

Anera

Jiménez

Barco

et al. 2003

Journal of Cataract and Refractive Surgery

101

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Purpose:To analyze the origin of the changes in corneal asphericity (p-factor) after laser in situ keratomileusis (LASIK) and the effect of postsurgery asphericity on contrast-sensitivity function (CSF) under photopic conditions. Setting: Department of Optics, University of Granada, Granada, Spain. Methods:The p-factor and CSF (best corrected before surgery and 1, 3, and 6 months after surgery) were measured in 24 eyes.Results: An increase in the p-factor after LASIK was noted; there was an 87.2% change in the asphericity using the paraxial formula of Munnerlyn and coauthors. Other factors such as decentration, type of laser, optical role of the flap, wound healing, biomechanical effects, technical procedures, and reflection losses of the laser on the cornea could account for the greater than expected increase (12.8%) in the p-factor. The CSF measurements deteriorated after LASIK; the change was significant (PϽ.05) in patients with myopia worse than Ϫ4.0 diopters at frequencies of 9.2, 12, 15, and 20 cycles per degree. Conclusion:The increase in corneal asphericity after surgery, greater with a higher degree of myopia, and the deterioration in CSF with high myopia justify new ablation algorithms and further study of the variables that could modify the ablation unpredictably.

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Section: Discussionmentioning

confidence: 92%

“…Experimental studies also show changes in postsurgery corneal asphericity; ie, the anterior cornea's change from prolate to oblate. 1,6,7 Except those for customized corneal ablation, most ablation algorithms, although proprietary, are based on the paraxial formula of Munnerlyn and coauthors, 8 in which the ablation depth, s(y), is given by s͑y͒ ϭ 4Dy …”

mentioning

confidence: 99%

Changes in corneal asphericity after laser in situ keratomileusis

Anera

Jiménez

Barco

et al. 2003

Journal of Cataract and Refractive Surgery

101

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“…The first ablation algorithms were based on the Munnerlyn formula, 41 which was a spherical algorithm. As the diameter of the ablation zones in early lasers was small, many patients experienced considerable night vision disturbances when the pupil was larger.…”

Section: Laser Ablation Algorithmsmentioning

confidence: 99%

Surface Ablation Techniques for Myopia – A Review of the Advances Over the Past 25 Years

Hjortdal¹

2017

European Ophthalmic Review

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Photorefractive keratectomy for correction of myopia was the first excimer laser-based technique to be developed. During the last 25 years, excimer lasers have improved technologically, several variations of the technique have been developed and pre-and postoperative pharmaceutical therapies have been investigated. This review article summarises these developments and the published meta-analyses on comparison of surface ablation techniques and laser in situ keratomileusis. The main conclusion is that there seem to be no differences between the clinical results obtained with the different variations of surface ablation techniques. KeywordsPhotorefractive keratectomy, laser in situ keratomileusis (LASIK), refractive surgical procedures, myopia, excimer laser Disclosure: Jesper Hjortdal discloses that Aarhus University Hospital has signed a research support agreement with Carl Zeiss Meditec, Jena Germany. No funding was received in the publication of this article. This study involves a review of the literature and did not involve any studies with human or animal subjects performed by any of the authors.Authorship: All named authors meet the International Committee of Medical Journal Editors (ICMJE) criteria for authorship of this manuscript, take responsibility for the integrity of the work as a whole, and have given final approval to the version to be published.Open Access: This article is published under the Creative Commons Attribution Noncommercial License, which permits any non-commercial use, distribution, adaptation and reproduction provided the original author(s) and source are given appropriate credit. When such a gas is put under electrical stimulation and high pressure, the excited compound can give up its excess energy by undergoing spontaneous emission, which very quickly (on the order of a picosecond) dissociates back into two unbound atoms. Directing the emitted light towards, for example, biological materials will result in ablation of surface molecules. In the early 1980s it was shown that using this approach biological materials, including the cornea, could be incised using the excimer laser.1-3 After short time, it was realised that actual surface ablation of the corneal stroma was possible after removal of the corneal epithelium 4 and that the resulting surface was very smooth. 5 In 1987, excimer laser-based keratotomy was performed in a human eye, 6 but it was the surface ablation application that pushed development of excimer lasers. 7,8 The first preliminary results in human eyes were published the late 1980s 9-12 and excimer lasers became commercially available around 1990. In the early 1990s larger follow-up series of patients undergoing PRK for myopia were published. [13][14][15] Since then, many modifications of PRK have been introduced, and a common uniting name for all these techniques is 'surface ablation'. This review will focus on surface ablation for myopia. Development of excimer lasersDirecting the location of the excimer laser rays is essential to change the surface shape of the ...

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“…Geometrically, correction of myopia is fairly simple and the necessary lenticule shape to be removed was calculated many years ago by Munnerlyn et al 57 Although this calculation ignores aspects related to the aspheric shape of the cornea, the formula has been widely used, also as a basis for intrastromal refractive surgery. In correction of astigmatism and hyperopia, the actual correcting tissue removal will end abruptly.…”

Section: Treatment Of Astigmatism and Hyperopiamentioning

confidence: 99%

New Developments in the Lenticule Extraction Procedure

Hjortdal¹,

Ivarsen²

2014

European Ophthalmic Review

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31Over the last few years, surgical extraction of a refractive lenticule, or ReLEx ® , has evolved as a new treatment in the field of keratorefractive surgery. Currently, the VisuMax ® femtosecond (FS) laser (Carl Zeiss Meditec, Jena, Germany) is the only platform to offer this treatment.The 500 kHz VisuMax laser generates very fast pulses (10 -15 s range) in the near-infrared spectrum. Depending on the specific laser settings, each pulse conveys approximately 150 nJ, which causes localised photodisruption at the focal point. The generated plasma expands, creating a cavitation bubble, and, as individual cavitation bubbles fuse, the stroma is cut with a minimum of collateral damage. The VisuMax FS laser uses a high numerical aperture and a concave contact glass to focus the laser pulses with very high precision. Thus, laser spots of approximately 1 μm diameter are placed with a defined distance of 2-5 μm in a spiral pattern. To ensure centration on the visual axis, the patient fixates on a blinking light and suction is applied at the limbus to maintain stability of the eye. Initially, the posterior refractive surface of the lenticule is cut, followed by creation of the plano anterior surface, which is slightly enlarged in diameter to facilitate surgical manipulation.This review article reviews the current state of the technique, updated clinical results, 1 experimental studies and, finally, presents some of the challenges that need to be addressed by new technologies.Depending on the method used to access the lenticule, ReLEx can be split into FLEx, in which a laser-assisted in situ keratomileusis ( In contrast to LASIK, ReLEx is a one-laser approach, where the critical laser treatment is performed on the intact cornea rather than on exposed corneal stroma. Consequently, the potential variability associated with the excimer laser photoablation is avoided.In addition, the minimally invasive SMILE treatment has several theoretical advantages over flap-based treatments, including little trauma to the corneal surface, less corneal denervation and better biomechanical strength due to an almost intact anterior stroma. Since AbstractFor the last 20 years controlled excimer laser ablation of corneal tissue, either directly from the corneal stromal surface or from the corneal interior after creation of a superficial corneal flap, has become widely used to correct myopia, hyperopia and astigmatism.Recently, an intrastromal refractive procedure whereby a tissue lenticule is cut free in the corneal stroma by a femtosecond laser and removed through a small peripheral incision has been introduced. The procedure avoids creation of a corneal flap and the potential associated risks while avoiding the slow visual recovery of surface ablation procedures. The all-femtosecond-based flap-free intracorneal refractive procedure has been documented to be a predictable, efficient and safe procedure for correction of myopia and astigmatism. Technological developments related to further improved cutting quality, hyperopic and individualise...

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Photorefractive keratectomy: A technique for laser refractive surgery

Cited by 682 publications

References 8 publications

Changes in corneal asphericity after laser in situ keratomileusis

Changes in corneal asphericity after laser in situ keratomileusis

Surface Ablation Techniques for Myopia – A Review of the Advances Over the Past 25 Years

New Developments in the Lenticule Extraction Procedure

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