Eyeworld

EW CORNEA 20 August 2011 C ertain factors can affect the curvature of the cornea, altering its rigid- ity, as in the case of radial keratotomy (RK), thermokeratoplasty, and, in some cases, after the implantation of an IOL. We turned our attention to the crosslinking effect, which can in- crease the rigidity of the cornea. We conducted several experiments to verify the possibility of local effects on collagen, which would increase the rigidity of the corneal area. Our device, with the help of a diaphragm, projects a beam of ultra- violet (UV) radiation on the cornea in almost any shape. A UV beam in the form of a star is projected onto gelatin (partly hydrolyzed collagen) and impregnated with riboflavin. After 5 minutes, all of the riboflavin in the irradiated region is subject to full chemical decomposition. Later, after mild drying of the gelatin sur- face, the crosslinking zone appears. This photolithography effect of local crosslinking (LCXL) has high preci- sion and resolution. We use the term "photolithography" here because it is the technical term used by manu- facturers of electronic chips when using radiation to change the prop- erties of a material. LCXL was applied to the cornea in patients with refractive errors. In these cases, the basic crosslinking parameters were: riboflavin soaking corneal time, the radiation power, and exposure time. For a local reduc- tion in myopia, we used radiation in the form of circular segments. For local enhancement of refraction we used radiation of a radial zone, which are segments formed by UV irradiation on a cornea that practi- cally do not affect the stability or re- sistance of PK scars. Therefore, rigidity is restored in the field of healthy tissue and PK scars are seg- mented. As a result, the "radial" zones are formed as well as the re- fractive effect. To achieve a refractive effect on a hyperopic eye, it is neces- sary to project the "radial" segment in the form of narrow strips and al- ternate the stripes with increased and normal rigidity. For myopic ef- fect of correction, it is necessary to project with circular/ring segments. For astigmatism correction, it is pos- sible to project separately or in a combination of radial and circular segments in certain axes. Clinical studies were conducted using similar technology by three surgeons in three different hospitals (Sergei I. Anisimov, M.D., Moscow; Andrei V. Zolotorevski, M.D., Moscow; and Mikhail D. Pozharitskiy, M.D., Italy). LCXL was applied in three sce- narios: 1. Local ectasia after LASIK 2. Hyperopic shift after previous RK 3. Myopic astigmatism All patients had a pronounced refractive effect. Patient M, aged 56, from the first group, presented with keratoectasia after LASIK, which manifested in the form of irregular astigmatism. This astigmatism could not be fully corrected by eyeglasses, and visual acuity did not exceed 20/200. The technology of LCXL has the ability to project customized pat- terns of UV light on the cornea to customize the topographic effect on each patient. Patient M had two zones of topographically identifiable ectasia, creating irregular astigmatism. These zones were exposed on the perime- ter of the topography. UV radiation was projected through the di- aphragms in the form of circular seg- ments. One week after radiation with two circular zones, the curvature of the ectasia zone was decreased by 1.5 D. Irregular keratometric read- ings were also decreased in a 3-mm zone by nearly 1.5 D. Uncorrected visual acuity of this patient increased from 20/200 to 20/40 and rose to 20/25 in a week. In the second group of patients, hyperopic shift after RK in five pa- tients ranged from 5.0-6.5 D (aver- age 5.75 D). The cylindrical component ranged from 2.5-3.0 D. Radiation of de-epithelized cornea was performed in the local area of ectasia. Although irradiation was carried out in the form of ring seg- ments, the actual impact was a ra- dial zone because the entire cornea was segmented by radial keratotomy incisions. The central zone is blocked by the diaphragm in the form of round spots and is not sub- jected to irradiation by UV radia- tion. Corneal topography after LCXL revealed a significant increase in corneal curvature in the optical zone up to 5 D. Results in the third group with complex myopic astigmatism were represented by patient N, 27 years old. After UV radiation using pro- jected ring segments, refraction of the central cornea decreased to 4 D. The uncorrected visual acuity of this patient increased from 20/400 to 20/20; thus, the use of LCXL in pa- tients with iatrogenic or natural re- fractive anomalies can significantly improve their uncorrected visual acuity. EW Editors' note: Drs. Anisimov, Pozharitskiy, and Zolotorevski have no financial interests related to their studies. Contact information S.I. Anisimov: xen3744@yandex.ru by S.I. Anisimov, M.D., and C. Yu. Anisimov, M.D. Local crosslinking: New correction possibility for refractive anomalies Corneal continued from page 18 such as airline pilots, practicing sur- geons, and others. The patient that got him started on DMEK was a multifocal patient who had had a presbyopia-correcting lens success- fully implanted in one eye. The other eye had corneal edema and a multifocal IOL. "DSEK would have cleared the edema but would have been unlikely to produce visual acuities in the 20/20 to 20/25 range, and that patient would have had a hyperopic shift that would most likely need to be addressed with an additional procedure, glasses, or contacts," Dr. Vroman said. "After DMEK the patient was 20/20, J1 plus, and has remained that way for over 2 years with no correction." Overall, Dr. Vroman sees DMEK as something that can help a select group of patients but that is likely to evolve. "I think DMEK is a step- ping stone to a procedure that will be some hybrid between DSEK and DMEK," he said. Ultimately he thinks that this will be replaced by something that is more reproducible and that can routinely achieve bet- ter acuities, yet can be attained with a technique that everyone can mas- ter. EW Editors' note: Drs. Chan and Vroman have no financial interests related to their comments. Contact information Chan: clara.chan@gmail.com Vroman: drvromen@carolinacataract.com 18-21 Cornea_EW August 2011-FINAL_Layout 1 4/2/14 3:32 PM Page 20

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