Biomechanics Sergei E. Avetisov, MD, PhD; Ivan A. Novikov; Irina A. Bubnova, MD; Alexei A. Antonov, MD; Vladimir I. Siplivyi, MD To propose a new approach for the study of corneal biomechanics using the Reichert Ocular Response Analyzer (ORA) database, which is based on changes in velocity retardation in the central cornea at the peak of flattening. The ORA applanation curve was analyzed using a mathematical technique, which allowed calculation of the elasticity coefficient (Ke), which is primarily characteristic of the elastic properties of the cornea. Elasticity coefficient values were obtained in patients with presumably different biomechanical properties of the cornea: “normal” cornea (71 eyes, normal group), keratoconus (34 eyes, keratoconus group), LASIK (36 eyes, LASIK group), and glaucoma with elevated and compensated intraocular pressure (IOP) (38 eyes, glaucoma group). The mean Ke value in the normal group was 11.05±1.6, and the corneal thickness correlation coefficient r² was 0.48. In the keratoconus group, the mean Ke value was 4.91±1.87 and the corneal thickness correlation coefficient r² was 0.47. In the LASIK group, Ke and r² were 5.99±1.18 and 0.39, respectively. In the glaucoma group, the same eyes that experienced a two-fold reduction in IOP developed a statistically significant reduction in the Ke (1.06 times lower), whereas their corneal hysteresis value increased 1.25 times. The elasticity coefficient calculated using the ORA applanation curve can be used in the evaluation of corneal biomechanical properties. From the Research Institute of Eye Diseases of the Russian Academy of Medical Sciences, Moscow, Russia. Supported by a grant from the Russian Foundation for Basic Research, “Elaboration of methods of mathematical simulation, of experimental and clinical research of biomechanical (strength) properties of cornea” (07-04-01710-a). The authors have no financial interest in the materials presented herein. Correspondence: Irina A. Bubnova, MD, 11-a Rossolimo St, Moscow, Russia, 119021. Tel: 79166209921; Fax: 74992480125; E-mail: bubnovai@mail.ru 10.3928/1081597X-20091030-01 To propose a new approach for the study of corneal biomechanics using the Reichert Ocular Response Analyzer (ORA) database, which is based on changes in velocity retardation in the central cornea at the peak of flattening. The ORA applanation curve was analyzed using a mathematical technique, which allowed calculation of the elasticity coefficient (Ke), which is primarily characteristic of the elastic properties of the cornea. Elasticity coefficient values were obtained in patients with presumably different biomechanical properties of the cornea: “normal” cornea (71 eyes, normal group), keratoconus (34 eyes, keratoconus group), LASIK (36 eyes, LASIK group), and glaucoma with elevated and compensated intraocular pressure (IOP) (38 eyes, glaucoma group). The mean Ke value in the normal group was 11.05±1.6, and the corneal thickness correlation coefficient r² was 0.48. In the keratoconus group, the mean Ke value was 4.91±1.87 and the corneal thickness correlation coefficient r² was 0.47. In the LASIK group, Ke and r² were 5.99±1.18 and 0.39, respectively. In the glaucoma group, the same eyes that experienced a two-fold reduction in IOP developed a statistically significant reduction in the Ke (1.06 times lower), whereas their corneal hysteresis value increased 1.25 times. The elasticity coefficient calculated using the ORA applanation curve can be used in the evaluation of corneal biomechanical properties. From the Research Institute of Eye Diseases of the Russian Academy of Medical Sciences, Moscow, Russia. Supported by a grant from the Russian Foundation for Basic Research, “Elaboration of methods of mathematical simulation, of experimental and clinical research of biomechanical (strength) properties of cornea” (07-04-01710-a). The authors have no financial interest in the materials presented herein. Correspondence: Irina A. Bubnova, MD, 11-a Rossolimo St, Moscow, Russia, 119021. Tel: 79166209921; Fax: 74992480125; E-mail: bubnovai@mail.ru

Medical article медицинская статья

Most foreign authors currently recommend the protocol and charts developed for the Early Treatment Diabetic Retinopathy Study (ETDRS) as the gold standard for evaluation of visual acuity (VA) in clinical trials and studies. Not every medical facility has equipment required for performing visometry by that method, while Sivtsev tables are found universally. To compare ETDRS and the more common Sivtsev visometry methods. The study included 100 volunteers - students of the Sechenov University. All participants were examined for VA in both eyes without correction using ETDRS "R" chart and Sivtsev table. Visometry with "R" ETDRS chart involved calculation of the number of named letters, then the number was translated into logarithmic notation by the conventional method. Sivtsev visometry findings were translated into logarithmic notation by two methods: first - standard, line-by-line, second - experimental, letter-by-letter. Subjects were divided into two groups: high VA (higher than 0.4 in decimal scale) and low VA - everyone else. The best agreement with ETDRS was found in letter-by-letter method of Sivtsev table interpretation, especially in the group with high VA with the lowest 95% limits of agreement (LoA) of ±0.157 logMAR, or 8 letters on ETDRS. Clinically significant were also LoA in comparison of ETDRS with line-by-line calculation method in the group with high VA and in letter-by-letter method without dividing groups by VA. The use of Sivtsev table in standardized multicenter studies is only reasonable when the ETDRS charts are unavailable.