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Review Refractive Surgery
Surface Ablation Techniques for Myopia – A
Review of the Advances Over the Past 25 Years
Department of Ophthalmology, Aarhus University Hospital NBG, Aarhus, Denmark
P hotorefractive 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.
Keywords Photorefractive 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.
Received: 21 April 2017
Accepted: 15 June 2017
Citation: European Ophthalmic Review,
2017;11(1):31–4 Corresponding Author: Jesper Hjortdal, Department
of Ophthalmology, Building 10, 2nd floor, Aarhus
University Hospital NBG, 8000 Aarhus C, Denmark.
Photorefractive keratectomy (PRK) is the first laser-based technique that aimed to change the
refractive power of the cornea. The principle of excimer laser ablation of the cornea is based on
controlled emission of 193 nm pulses generated from excited dimers of argon fluoride (ArF) gases.
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. 13–15 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 lasers
Directing the location of the excimer laser rays is essential to change the surface shape of
the cornea in a controlled way. The first lasers were based on a scanning slit of excimer laser
pulses, which was modified by a mechanical aperture built into a suction device. The resulting
ablation of the cornea resulted in a stepwise change in the surface shape of the corneal stroma,
but these steps were smoothed by the healed corneal epithelium, making a smooth surface
and tear film. Simultaneously, wide-field excimer lasers were introduced. These lasers ablated
the full diameter of the ablation zone simultaneously, and the change in shape was based on
controlling a differential efficiency between central and peripheral rays. After a few years, most
excimer lasers became based on using a flying spot of small size, which in a controlled way could
reshape the corneal surface into almost any shape. Thus, myopia, hyperopia, astigmatism and
even irregular astigmatism could in principle be corrected, if the flying laser spot was controlled
properly. Today, all excimer lasers on the market are based on the flying spot principle, but the
repetition rate of the lasers vary.
The original surface ablation technique
Originally, PRK was performed as follows. After topical anaesthesia, the patient was placed on
the excimer laser bed, the eye to be treated was draped and a speculum inserted. The corneal
epithelium was removed centrally using a spatula. The patient was then asked to look at a central
fixation light in the excimer laser, and the eye was manually kept in a steady position using a
suction device, and laser ablation was initiated. The diameter of the ablation zone was typically
small, often less than 5 mm. 12 After ablation, the eye was treated with antibiotic drops and steroids.
The epithelium typically healed within a few days. Over time, development of superficial haze in the
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