The results of calculation and development of a device aimed at forming a laser beam with an annular intensity distribution and spatial mode homogenisation, as well as approbation of this device for biological phantoms and eyes in ex vivo experiments with laser non-ablative correction of the cornea profile, are presented. The radiation intensities and thermal field distributions on the surfaces of a phantom and isolated rabbit’s eye are investigated. The absence of significant heating in the central region of eye is confirmed. It is shown that this device can be used for laser impact in order to change symmetrically eye’s refraction.

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

To develop a new approach to morphometric analysis of corneal nerve fibers (CNF) and to evaluate their age-related changes in type 1 and type 2 diabetes mellitus patients. The study enrolled 150 participants (300 eyes) aged from 13 to 83 years, of them 37 type 1 diabetes patients (74 eyes), 51 type 2 diabetes patients (102 eyes), and 62 healthy volunteers (124 eyes). All participants were examined with HRT III Rostock Corneal Module (Heidelberg Engineering GmbH). Digital images thus obtained were analyzed with specially developed original software that automatically computes coefficients of CNF orientation symmetry and anisotropy. A strong inverse correlation has been found between the coefficient of CNF orientation anisotropy and glycated hemoglobin levels (r = -0.83, p < 0.001 and r = -0.79, p < 0.005 in patients with type 1 and type 2 diabetes respectively) as well as the duration of the disease (r = -0,7, p < 0.005 and r = -0.72, p < 0.001, type 1 and type 2 diabetes respectively). On the contrary, the coefficient of CNF orientation symmetry has been shown to be directly correlated with both glycated hemoglobin levels (r = 0.64, p < 0.005 and r = 0.78, p < 0.05, type 1 and type 2 diabetes respectively) and the duration of the disease (r = 0.62, p < 0.05 and r = 0.73, p < 0.05, type 1 and type 2 diabetes respectively). Interocular asymmetry in both coefficients was found in diabetic patients but not in the controls. On the basis of the proposed coefficients, age-related changes in corneal nerve fibers orientation have been determined. Normally, the degree of CNF tortuosity increases with age. The rate of this increase is the highest before the age of 35-40. As shown, type 1 diabetes is associated with low coefficients of CNF orientation anisotropy and high coefficients of CNF orientation symmetry as compared to type 2 diabetes in the same age group. As suggested by the results, the two proposed coefficients that describe the state of corneal nerve fibers can possibly be used for diagnosis and monitoring of diabetic peripheral neuropathy (DPN). However, to produce enough evidence, further studies should be conducted.