Eyeworld

JUN 2012

EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.

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52 EWInternational June 2012 Characteristics of trans-PRK performed by the Profile 500 laser by Alexander I. Myagkikh, Ph.D., Eugene V. Makurin, and Eugene L. Subbotin Approach in Russia reveals another way to perform PRK I n 2000 at the VII Ophthalmol- ogists' Conference of Russia, the fifth-generation Profile 500 excimer laser was introduced. Developed in Russia, Profile 500 uses the technique (also devel- oped in Russia) of photorefractive keratectomy (PRK), which does not require pre-op de-epithelialization of the cornea.1 The impressive results with the Profile 500 (The Center for Physics Instrument-Making in the General Physics Institute, Russian Science Academy, Troitsk, Moscow Region, Russia) were reported in some scientific papers but were not widely discussed. This was likely be- cause complications were not imme- diately seen after operation of the Profile 500. In addition, after the introduction of the Profile 500 into medical practice, no decision was made about the registration of the official name (trans-PRK) of this va- riety of PRK. More confusion ensued when results conducted by different researchers were not immediately comparable. We have found many biases against the use of PRK have no solid grounds. To accurately discuss and under- stand differences in PRK perform- ance technology, the authors propose the following definition of the subject: Trans-PRK involves a working element of action on the cornea that exclusively involves an impulse-modu- lated excimer laser ray, which has a width equal to the width of the opera- tion zone and regulated Gaussian radial distribution of energy density in the cross-section of the ray. A physical pattern of action of the Profile 500 on the cornea has been reported elsewhere.2,3 The first clinical observations of some hun- dred operated eyes also are described elsewhere.4 In this article, we will re- port on how the new physical prin- ciples forming the basis of trans-PRK are expressed in surgical results. These results reflect data from more than 6,000 operations performed in Vladivostok, Russia, by surgeons at Ost-Optic K Co. Ltd., who used the Profile 500 installation. Figure 1. Trans-PRK haze Transepithelial effect Kind of haze (post-op) 1-3 months More than 4 months Subepithelial opalescence 34.45% 0.1 in center 0.5 in center 1.0 in center 1.5 in center 0.00% At all treated areas 28.98% 0.05% 0.05% 0.99% 0.5 on edge of treated area 0.05% 1.5 on edge of treated area 0.58% Table 1. Trans-PRK. Hazes at various post-op periods 1.38% 0.06% 1.65% 0.00% 0.00% 0.00% 0.00% 0.03% With trans-PRK, there is no need for the preliminary stage of epithelium removal. The time of full epithelial- ization with trans-PRK is 1.5-2 days without using any additional means to protect the corneal epithelium. This takes about twice as long with PRK with mechanical or chemical re- moval of the epithelium. With trans- PRK, blepharospasm is observed for no more than 2 days. Because the patient experiences only moderate pain, it is safe to perform the opera- tion on both eyes in the same day. As there is no mechanical damage to the epithelium, there is a very even margin of operation field that mini- mizes the probability of the occur- rence of a mixed corneal syndrome. This is aided by smoothness of the treated surface of the cornea, which is first, a consequence of the absence of mechanical action on the epithe- lium and Bowman's membrane, and second, the action from a laser ray does not worsen the properties of the corneal surface because the ray has an equal distribution of energy density. The same factors reduce the risk for the development of superfi- cial corneal haze (notwithstanding haze that arises in 36.8% cases that then resolves without any treat- ment). In other cases, resolution oc- curs after a course of therapy is prescribed (Figure 1). Wide ray The point of using a wide ray is that every laser pulse contains full infor- mation on treatment, and a final re- Figure 2. Trans-PRK. Value of correction: Sph –6.0, best spectacle-corrected visual acuity pre-op. The uncorrected visual acuity 3 months later was –0.9. The patient was an 18-year-old female

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