Excimer Laser Refractive Surgery
This series of articles follows students undertaking the University of Ulster's E-learning course in cataract and refractive surgery. The nine courses presented in year 1 (for which we will continue to provide coverage) are covered through lectures and tutoring. Coursework is then followed by a second year of affiliated research projects. Within this course on excimer laser refractive surgery, lecturers covered techniques on (1) how to accelerate epithelial healing after PRK, (2) management of persistent epithelial defects following PRK, (3) causes of haze after PRK and its management, (4) the functions of different lasers, and (5) how to implement techniques for laser refractive surgery.
Lectures on this topic spurred discussion, including (1) the merits of LASIK versus LASEK, including whether patients choose LASEK because of safety issues or recommendation, (2) nomenclature, (3) the function and abilities of different lasers, (4) surgical knowledge on how to implement techniques with lasers, (5) use of mitomycin C (MMC) in surface ablations, such as when, where, how, and how not to use it, (6) if and when to treat hyperopes with LASIK or surface ablation with or without MMC, (7) management of congenital nystagmus or superficial scars, and (8) the impact of femtosecond lasers. In this article, we summarize the lectures that gave rise to these and other topics of discussion.
WEEK 1
Stefan Pieger, MSc, presented the basics of excimer laser application, including the original concept of excimer laser refractive correction.1 Since then, advances in knowledge, experience, and technology have evolved into the current endeavour: the correction of higher-order aberrations. Mr. Pieger addressed the principles of excimer lasers with regard to ablation profiles for myopia, hyperopia, and astigmatism, such as bitoric ablations (ie, combined steep and flat meridian ablations) for the treatment of mixed astigmatism, topography, and wavefront-guided treatments. Reference axis selection and eye-tracking methods were also highlighted.
Sudi Patel, PhD, FCOptom, and Johnny E. Moore, FRCOphth, PhD, presented a lecture on corneal wound healing and biomechanics. Corneal wound healing can be arbitrarily divided into epithelial and stromal wound healing; however, the two do not work independently. The lecture addressed the four recognized stages in epithelial healing: the latent phase, cell migration, cell proliferation, and adhesion. Corneal stromal wound healing was also explained and wound healing after corneal refractive procedures. Professors Patel and Moore also discussed pharmacological techniques that modify the healing responses in refractive surgery (eg, corticosteroids, MMC, NSAIDs, interferon, growth factors, caspase inhibitors). The latter part of the lecture concentrated on healing, the biomechanics of over- and under-correction, and regression of refractive error.
This discussion branched into areas of pain management and the use of topical anesthetics. A careful examination will help to decide if it is safe to use lubricants, antibiotics, patching, and bandage contact lenses. Emphasis was placed on the importance of evidence-based medicine when managing such cases.
WEEK 2
Michael Mrochen, PhD, discussed ablation profiles, including new aspheric, topography-guided, and wavefront-guided ablations. He also provided strategies for attempting to reduce spherical aberrations induced by the classical Munnerlyn profile, correcting aberrations induced by the anterior cornea, and correcting the aberrations of the whole eye. Students debated the benefits of an aspheric ablation and considered the future impact of a wavefront ablation in an eye in which the crystalline lens is removed.
Arthur Cummings, FRCS(Ed), and Sunil Shah, FRCOphth, FRCS(Ed), FBCLA, compared the costs, results, comfort, and safety of LASEK with those of LASIK and PRK. Students' and surgeons' personal experiences with LASEK and other surface ablation techniques were conflicting. Additionally, the lack of large, randomized prospective studies on LASEK versus PRK did not help answer the main question: Is LASEK less painful and less prone to haze? Participants discussed ablation profiles for mixed astigmatism (ie, bitoric, crossed cylinder, negative cylinder, positive cylinder). Participants concluded that bitoric ablation is the most popular because of its tissue-saving properties.
WEEK 3
Steven C. Schallhorn, MD, provided an introduction to LASIK, and Vikentia J. Katsanevaki, MD, PhD, and Ioannis G. Pallikaris, MD, PhD, presented an introduction to epi-LASIK. Compared with LASIK, epi-LASIK is less frequently used. The discussion focused on the drawbacks of epi-LASIK. One such drawback is that a living flap causes more pain and inflammation. Additionally, the separator is expensive and many surgeons discard the epithelial flap because it sometimes appears to hamper reepithelialization.
Surgeons discussed the acceptable limits of myopic and hyperopic ablation. Opinions differed, but surgeons agreed that a cornea should not be flatter than 35.00 to 36.00 D nor steeper than 48.00 to 49.00 D.
WEEK 4
Antonio Leccisotti, MD, PhD, reviewed the use of MMC in surface treatments. Surgeons are currently using various exposure times (10 to 60 seconds) and concentrations (usually 0.1 to 0.2 mg/mL). Corneal melting may occur if the wrong concentration is used; however, MMC appears to be safe in the short term. Professor Leccisotti discussed how different regions, habits, and populations use MMC with different thresholds. In Australia, some surgeons use it during every surface ablation. In southern Europe, it is used with ablations deeper than 70 µm or -4.00 D, whereas in Northern Europe, it is used with ablations deeper than 80 µm or -6.00 D. An adjustment in the nomogram is required because of the overcorrecting effect of MMC.
The principles of aberrometry were also introduced. Aberrations induced by keratoconus and centered and decentered ablations were reviewed, including the diagnosis of forme fruste keratoconus based upon both topographic changes and the aberration of coma.
WEEK 5
Dr. Cummings focused on aberrometers and the clinical aspects of aberrometry, describing monochromatic aberrations and their analysis with Zernike polynomials. Wavefront was introduced as the envelope of all points that have the same optical path length. The five principles of aberrometry (ie, Hartmann-Shack, Tscherning, ray tracing, spatially resolved refractometer, slit skiascopy) and the commercial machinery using these principles were described. Almost all laser platforms use a prolate ablation profile in their wavefront treatments—hence producing better results than standard procedures.2,3 Practical indications and examples of wavefront-guided treatments were also explained by Dr. Cummings.
Omar Hakim, MD, FRCSC, described technology requirements for wavefront-guided treatments, dealing with the objectives of customized treatments in relation to visual acuity, contrast sensitivity, and quality of vision. Eye tracking and iris registration were introduced by Paul P. van Saarloos, PhD.
Students debated marking the axis in patients with high astigmatism prior to ablation with the absence of cyclotorsion control by the eye tracker. Additionally, students discussed the treatment of a 22-year-old carpenter who had slow horizontal congenital nystagmus. Experienced surgeons have found a radial keratotomy fixation ring connected to a handle particularly useful to reduce movements in cases of nystagmus.
WEEK 6
Jorge L. Alió, MD, PhD, reviewed customized excimer laser ablation techniques, including wavefront-based ablation as a primary or secondary procedure. Students discussed if customized ablation in plain spherocylindrical treatment, a time-consuming and expensive technique, was justified. Some participants stressed the marketing involved by the term customized, but it was agreed that at least spherical aberrations deserve maximum attention.
Holger Lubatschowski, PhD, described the uses of femtosecond lasers, including creation of channels for intrastromal rings and corneal grafting, and modern mechanical microkeratomes, which can achieve equally thin flaps. The advantages and drawbacks of femtosecond flaps were questioned. Unique complications, such as transient light sensitivity, difficulty of separating the flap, and an opaque bubble layer, are infrequent and balanced by reproducibility and reduced occurrence of striae. Professor Lubatschowski also reviewed irregular cuts.
Antonio Leccisotti, MD, PhD, is a Visiting Professor at the School of Biomedical Sciences, University of Ulster, Coleraine, Northern Ireland, and Director of the Ophthalmic Department, Générale-de-Santé Toscana, Siena, Italy. Dr. Leccisotti states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +39 335 8118324; fax: +39 0577 578600; E-mail: leccisotti@libero.it.
Colm McAlinden, BSc(Hons), MCOptom, is an optometrist and refractive surgery PhD Student, School of Biomedical Sciences, University of Ulster, Coleraine, Northern Ireland. Mr. McAlinden may be reached at E-mail: colm.mcalinden@gmail.com.
Damien McConville, MSc, MBCS, FHEA, is a Learning Technologist at the Institute of Lifelong Learning, University of Ulster. Dr. McConville states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +44 0 2890368537; E-mail: d.mcconville@ulster.ac.uk.
Johnny E. Moore, FRCOphth, PhD, is a Visiting Professor at the School of Biomedical Sciences, University of Ulster, Coleraine, Northern Ireland, and Department of Ophthalmology, Mater Hospital, Belfast Hospital Trust Northern Ireland, and Director of Leeson Eye Institute, Dublin, Ireland. Dr. Moore states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +353 0 16674778; E-mail: johnnymoorebal@gmail.com.
Tara Moore, PhD, NTF, is a Course Director and Senior Lecturer at the School of Biomedical Sciences, University of Ulster, Coleraine, Northern Ireland. Dr. Moore states that she has no financial interest in the products or companies mentioned. She may be contacted at tel: +44 0 7793226873; E-mail: t.moore@ulster.ac.uk.
Sunil Shah, FRCOphth, FRCSEd, FBCLA, is a Visiting Professor at the School of Biomedical Sciences, University of Ulster, Coleraine, UK, Visiting Professor at the School of Life & Health Sciences, Aston University, Birmingham, UK, Medical Director, Midland Eye Institute, Solihull, UK, Consultant Ophthalmic Surgeon, Heart of England Foundation Trust, Birmingham, UK, and Consultant Ophthalmic Surgeon, Birmingham & Midland Eye Centre, Birmingham, UK. Dr. Shah states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +441217112020; fax: +441217114040; E-mail: sunilshah@doctors.net.uk.
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