[Study of corneal morphological changes and light scattering rate in keratoconus].

The paper gives the results of studying the rate of light scattering by different corneal layers in keratoconus from confocal microscopy data. The study was conducted using a Confoscan-4 confocal microscope (Nidek, Japan). The rate of light scattering was estimated from the results of analyzing the densitometric curve, by applying a Z-scanning system. A total of 77 patients (136 eyes) with stages 1-4 keratoconus and 20 healthy individuals at the age of 16 to 20 years were examined. Confocal microscopy revealed corneal changes that were characteristic of different stages of keratoconus and a cause of its optical heterogeneity. As an epithelial lesion progressed, there was an obvious tendency towards increases in the scattering of light waves and in the range between their minimum and maximum values. Examination of corneal stromal layers revealed no statistically significant differences between the minimal level of light scattering in health and that in keratoconus in its different stages. However, there was an increase in the maximum level of light scattering due to the appearance of compact tissue portions with a higher reflectivity. The range between the minimum and maximum values was also increased. Comparison of the levels of light scattering by the posterior corneal epithelium established no statistically significant differences. Overall, increased light scattering by individual corneal microstructures and a distorted ratio between its minimum and maximum levels may be considered as a morphological component of aberrations that reduce the resolution of the eye optical system.

[Possibilities of compensation of optical aberrations in keratoconus with rigid gas-permeable contact lenses].

The paper gives the results of a study of ocular optical aberrations in keratoconus. Objective aberrometry was carried out with OPD Scan (Nidek, Japan). An additional computer program (OPD station) was used to evaluate the corneal wavefront. Examinations were made before and after application of a rigid gas-permeable lens (RGPL) to the eye. For the functional evaluation of the effectiveness of contact correction, the investigators used visometry and determined binocular visual functions, contrast sensitivity, and visual productivity. A total of 87 subjects (174 eyes) with keratoconus were examined. Stage 1 disease was found in 48 eyes, Stage 2 in 49 eyes, Stage 3 in 37 eyes, and Stage 4 in 40 eyes. Analyzing the results of the study could evaluation the effectiveness of keratoconus correction with RGPL. The use of the latter presents a possibility of compensating for optical aberrations, achieving their reduction practically to the one level irrespective of the stage of keratoconus with a slight increase in Stage 4 disease. In Stages 1-3, the mean aberration values of each type have very close values (without statistically significant differences between them). In Stage 1 keratoconus, RGPL can completely compensate for high-order corneal aberrations (including coma, trefoil, and spherical aberrations). Normalization of the wavefront promotes the achievement of high functional results of contact correct of refraction disorders in keratoconus, by applying RGPL.

[Confocal microscopy of the cornea. Communication 1. The normal morphological pattern].

The paper presents the results of life-time confocal microscopy using a Confoscan-4 confocal microscope (Nidek). The study was conducted on 10 healthy volunteers (20 eyes), which evaluated the specific features of the normal morphological pattern of the cornea. The morphological features of three types of anterior corneal epithelial (basal, wing, and spiny) cells were revealed. The possibilities of visualizing subbasal and stromal nerve fibers were assessed. Corneal stromal layers (these being anterior, anteromedian, median, and posterior) differing in the density of cellular elements, their shape, and orientation) were conventionally identified. In health, Bowman's and Descemet's membranes were not visualized as they were transparent and failed to reflect light. The posterior corneal epithelium was microscopically presented by a layer of light hexagonal or polygonal squamous cells with well-defined outlines. Thus, life-time corneal confocal microscopy is a highly informative noninvasive study.

[Confocal microscopy of the cornea. Communication 2. Morphological changes in keratoconus].

The paper presents the results of studying morphological changes in keratoconus by life-time confocal microscopy. A total of 50 patients (100 eyes) with grades 1-to-4 keratoconus were examined. The most pronounced changes were found in the corneal areas involved in an ectatic process. Four grades of epitheliopathy were conventionally identified in relation to the desquamation of superficial epitheliocytes, the change of their shape, impaired adhesion with the underlying layers, and transparency disorders. The indirect signs of altered Bowman's membrane were revealed. In early keratocons, the stroma showed hyperreflectivity of anterior layers, higher activated keratocytes, their changed shape and spatial orientation. The emergence of microstrium in the posterior stromal layers with their gradual spread to the midstroma and anterior stroma, abnormal transparency, and scarring were typical of the progress of the disease. There were processes of homogenization and fibrotization of stromal structure and fewer keratocytes. There might be changes in Descemet's membrane (undulating folds) and posterior epithelium (polymegatism, polymorphism, enlarged intercellular spaces, and cell apoptosis). Thus, confocal microscopy reveals certain regularities of a pathological process in keratoconus at different stages of the disease.

[Influence of long-term contact lens wear on the cornea according to the data confocal microscopy].

The paper presents the results of a comparative study of corneal morphological changes by lifetime confocal miscroscopy in the long-term use of various types of contact lenses (CLs). Twenty-two patients (44 eyes) were examined, of them 8 patients (16 eyes) had worn soft CLs (SCLs) for 10-25 years (mean 17 years). 8 (16 eyes) had used hard CLs (HCLs) made of polymethyl metacrylate for 17-30 years (mean 23 years), 6 (12 eyes) had worn HCLs for 15 to 30 years (mean 20 years), hard gas-permeable CLs (HGCLs) over the past 5-15 years. The findings suggest that long-term wear of corrective CLs may lead to significant structural impairments in different corneal layers. The most characteristic changes are different types of epitheliopathies and the emergence of the signs of stromal degeneration with formation of deposits. According to our evidence, the likelihood of the detected changes increases with the long use of SCLs and reduces with the wear of HCLs, HGCLs in particular, which allows the authors to recommend that SCLs be changed to HGCLs after long (more than 10-15-year) contact correction.