Phonon dynamics in MoSi2N4: insights from DFT calculations.

We have reported the density functional theory investigations on the monolayered, 2 layered and bulk MoSi2N4 in three structural modifications called α1 [Y.-L. Hong, et al., Chemical Vapor Deposition of Layered Two-Dimensional MoSi2N4 Materials, Science, 2020, 369(6504), 670-674, DOI: 10.1126/science.abb7023], α2 and α3 [Y. Yin, Q. Gong, M. Yi and W. Guo, Emerging Versatile Two-Dimensional MoSi2N4 Family, Adv. Funct. Mater., 2023, 2214050, DOI: 10.1002/adfm.202214050]. We showed that in the case of monolayers the difference in total energies is less than 0.1 eV between α1 and α3 phases, and less than 0.2 eV between α1 and α2 geometries. The most energetically favorable layer stacking for the bulk structures of each phase was investigated. All considered modifications are dynamically stable from a single layer to a bulk structure in energetically favorable stacking. Raman spectra for the monolayered, 2 layered and bulk structures were simulated and the vibrational analysis was performed. The main difference in the obtained spectra is associated with the position of the strongest band which depends on the Mo-N bond length. According to the obtained data, we can conclude that the Raman line at 348 cm-1 in the experimental spectra of MoSi2N4 can have more complex explanation than just Γ-point Raman-active vibration as was discussed before in [Y.-L. Hong, et al., Chemical Vapor Deposition of Layered Two-Dimensional MoSi2N4 Materials, Science, 2020, 369(6504), 670-674, DOI: 10.1126/science.abb7023].

[Correction of refractive disorders after surgical treatment of recurrent pterygium (case study)]. / Korrektsiya refraktsionnykh narushenii posle khirurgicheskogo lecheniya retsidiviruyushchego pterigiuma (klinicheskoe nablyudenie).

Lamellar keratoplasty is the most effective and safe method of surgical treatment of recurrent pterygium, providing restoration of the corneal frame and optical properties and a high anti-relapse effect due to the barrier properties of the lamellar graft. However, potential postoperative changes in the regularity of the anterior and posterior surfaces of the cornea (especially in case of advanced stage of fibrovascular tissue growth) do not always allow achieving high functional results of treatment. The article presents a clinical case that demonstrates the effectiveness and safety of excimer laser correction of refractive disorders after surgical treatment of pterygium.

[Clinical and morphological characteristics of corneal epithelial dystrophy (clinical observations)]. / Kliniko-morfologicheskie kharakteristiki epitelial'noi distrofii rogovitsy (klinicheskie nablyudeniya).

This paper presents clinical observations that can be regarded as degeneration of the basement membrane of the corneal epithelium. Difficulties in identifying such forms of corneal dystrophies, on the one hand, are associated with limitation and polymorphism of the clinical picture, and, on the other hand, with insufficient information content of the basic diagnostic methods (i.e. the methods used during the initial examination). The presented clinical cases allow singling out the alarming and pathognomonic signs of the disease in the diagnostic algorithm. In the first case, attention should be paid to biomicroscopic changes in the superficial layers of the cornea and the optical defects, which can be regarded as a manifestation of an irregularity of corneal refraction. Identification of pathognomonic signs of the disease is possible on the basis of a detailed, close-to-morphological study of the structure of superficial corneal layers using confocal microscopy and optical coherence tomography. At the same time, the localization of the detected changes at the level of epithelial basement membrane and its basal sections is of crucial significance for substantiating the diagnosis. In addition, according to the literature data, recurrent erosions of the cornea of unclear etiology should be attributed to presumptive signs of degenerative changes in the basement membrane of the epithelium.

[Comparative assessment of functional outcomes of different endothelial keratoplasty techniques]. / Sravnitel'naya otsenka funktsional'nykh rezul'tatov razlichnykh tekhnologii endotelial'noi keratoplastiki.

PURPOSE: Comparative analysis of the higher-order aberrations (HOA) of the cornea after endothelial keratoplasty (EK) using DSAEK and DMEK techniques; evaluation of the correlation between higher-order corneal aberrations and functional outcomes of the treatment. MATERIAL AND METHODS: The study included 47 patients (59 eyes). The main group consisted of 35 patients (35 eyes) with bullous keratopathy and Fuchs' endothelial dystrophy; among them, 19 patients underwent endothelial keratoplasty using the DSAEK technique and 16 - DMEK technique. The control group included 12 patients (24 eyes) of corresponding age without corneal pathology. Standard and special examination tests were performed before, as well as 6 and 12 months after the operation, including computed tomography and aberrometry of the cornea using the Pentacam HR system. Same tests were performed in the control group. RESULTS: The values of the main HOA of the anterior corneal surface: RMS coma (Z3±1, Z5±1), RMS spherical aberration (SA; Z40, Z60) and RMS HOA (Z3-6) 6 months after different EK techniques were statistically significantly higher than in the control group. A statistically significantly lower induction of aberrations of the posterior corneal surface after DMEK technique was revealed. Analysis of the final aberration pattern 6 months after surgery did not reveal any statistically significant differences in the values of the main (RMS coma, RMS SA, RMS HOA) total corneal aberrations after DSAEK and DMEK. A negative correlation was revealed between the best corrected visual acuity (BCVA) and HOA; however, it was statistically significant only for individual aberration values: RMS HOA (Z3-6) of the posterior corneal aberrations after DMEK (r= -0.634, p=0.049), and RMS coma (Z3±1, Z5±1) of the cornea after DSAEK (r= -0.57, p=0.042). CONCLUSION: Comparative analysis of total corneal HOA did not reveal a statistically significant difference in the main parameters: RMS coma, RMS SA, RMS HOA in patients after DSAEK and DMEK surgeries. Correlation analysis did not reveal any statistically significant effects of most aberrations on the functional outcomes of the treatment.

[Refractive changes after different modifications of endothelial keratoplasty]. / Refraktsionnye izmeneniia posle razlichnykh modifikatsii éndotelial'noi keratoplastiki.

PURPOSE: To evaluate changes in clinical refraction after Descemet Stripping Automated Endothelial Keratoplasty (DSAEK) and Descemet Membrane Endothelial Keratoplasty (DMEK), and assess their correlation to the thickness of the transplant. MATERIAL AND METHODS: The main study group included 40 patients (40 eyes) after DSAEK and 20 patients (20 eyes) after DMEK, the control group consisted of 20 patients (20 eyes) without any corneal pathologies or history of surgical treatment. In addition to standard examination, patients of the main group had central corneal thickness and transplant thickness regularly measured; they were also monitored by optical coherence tomography (Optovue, U.S.A.), computed tomography and aberrometry of the cornea performed on Pentacam device. The control group had the same examination regimen. RESULTS: Best corrected visual acuity after 6 months was on average 0.2 higher in DMEK patients compared to those who underwent DSAEK; after one year - 0.1 higher. Clinical refraction data shows presence of hypermetropic changes after DSAEK surgery. Induced astigmatism after one year was 0.4 Diopters in DSAEK patients, but did not exceed 0.1 Diopters in DMEK patients. Stabilization of the corneal thickness in DMEK group occurred on the 3-4th month, in DSAEK group - 6-7th month. Certain values of higher-order aberrations (3-6) and root-mean-square deviation (RMS) of the wave-front of anterior corneal surface in DSAEK and DMEK groups were higher than in the control group. Aberrations on the posterior corneal surface in DMEK group were significantly lower than in DSAEK group. There were no statistically significant differences in 'final' RMS higher-order aberrations between DMEK and DSAEK groups.

[Peripheral lamellar keratoplasty in treatment of relapsing pterygium]. / Perifericheskaia posloinaia keratoplastika v lechenii retsidiviruiushchego pterigiuma.

PURPOSE: To evaluate the effectiveness and safety of peripheral lamellar keratoplasty (LKP) for treating relapsing pterygium. MATERIAL AND METHODS: The study was conducted in the period of 2007-2017 and included 84 patients (91 eyes) with stage II-IV relapsing pterygium. Best corrected visual acuity (BCVA) before the surgery was in average 0.65±0.28 (0.01 to 1.0). Astigmatism varied from 0.5 to 6.5 D (mean 3.41±2.06). All patients underwent pterygium removal surgery followed by LKP. The analyzed parameters included visual acuity, refraction error before and after the surgery, frequency of relapses and post-operative complications. RESULTS: The follow-up period was 4 months to 10 years (mean 30.9±25.4 months). BCVA after the surgery was 0.1-1.2 (mean 0.83±0.24), post-operative astigmatism - 0 to 3.5 D (1.08±0.62). BCVA has improved and remained stable in 86 (94.5%) out of 91 eyes, decrease of visual acuity was observed in 5 cases (5.5%). Frequent relapse of pterygium happened in 5 cases (5.5%), was non-progressing and required no surgical treatment. CONCLUSION: LKP is an effective and safe method of surgical treatment of relapsing pterygium that provides good optical, tectonic and anti-relapsing results thanks to barrier properties of the layered transplant.

[Corneal dystrophies]. / Distrofii rogovitsy.

The article reviews modern clinical, morphological, and genetic aspects of corneal dystrophies based on the most recent international classification updated in 2015. Corneal dystrophies is a group of slow progressing, non-inflammatory corneal pathologies, most of which are characterized by variability of the associated traits. The existence of such pathologies makes important their differential diagnosis from acute inflammatory processes of various etiology, which require urgent therapy. Conservative treatment suitable for dystrophies is usually associated with disorders of the anterior corneal surface and employ symptomatic tactic (lubricants, epithelizing agents, soft contact lenses). No effective etiopathogenetically targeted treatment is currently known. In cases with significant visual acuity decrease, it is possible to perform phototherapeutic keratectomy, abrasive polishing of Bowman's membrane with diamond bur and various types of keratoplasty depending on the depth of involvement.

[Taxonomic Composition of Lake Baikal Bacterioneuston Communities].

The taxonomic composition of microbial communities of Lake Baikal surface microlayer was studied by pyrosequencing of the 16S rDNA amplicons. Statistically reliable differences were found between bacterioneuston of the shallow and deep-water stations. The shallow station community was characterized by higher diversity than the deep-water one. While bacterioneuston communities were shown to be less diverse than the water column communities, their diversity was comparable to that of other biofilm associations. Microbial communities of Lake Baikal surface microlayer were shown to be similar to those of the water column in the composition of predominant phyla, while differing considerably at the genus level. Bacterioneuston of Lake Baikal was comparable to microbial communities of the surface microlayer of other freshwater basins, although it was characterized by high abundance of the Alphaproteobacteria and Verrucomicrobia. High abundance of photoheterotrophs compared to the water column communities of other freshwater basins was another distinctive feature of Lake Baikal bacterioneuston. Our results showed the Lake Baikal surface microlayer to be a specific microbial community with low species diversity and relatively high abundance of photoheterotrophic microorganisms.

[Diversity and Physiological and Biochemical Properties of Heterotrophic Bacteria. Isolated from Lake Baikal Neuston.]

For heterotrophic microorganisms (44 strains) isolated-from the surface film of Lake Baikal, iden- tification was carried out and their. physiological and biochemical characteristics were determined. Com- pared to the water column, diversity of cultured heterotrophs was low, indicating formation of stable micro- bial communities at the air-water interphase interface. Heterotrophic bacteria isolated from the surface mi- crolayer exhibited the enzymatic activity comparable to that for strains form other biofilm associations. Deinococcusfi6us strain NA202 'vas the most active component of the community, capable of utilization of the broadest spectrum of mono- and disaccharides,'sugars, and amino acids. This strain possessed the highest diversity of extracellular enzymes and was the most resistant to UV radiation. The physiological and bio- chemical properties of this strain may-be responsible for its adaptation to survival in extreme conditions of the surface microlayer. Our results improve our understanding of occurrence of UV-resistant strains in freshwater ecosystems.

[Phylogenetic analysis of bacteria of extreme ecosystems].

Phylogenetic analysis of aerobic chemoorganotrophic bacteria of the two extreme regions (Dead Sea and West Antarctic) was performed on the basis of the nucleotide sequences of the 16S rRNA gene. Thermotolerant and halotolerant spore-forming bacteria 7t1 and 7t3 of terrestrial ecosystems Dead Sea identified as Bacillus licheniformis and B. subtilis subsp. subtilis, respectively. Taking into account remote location of thermotolerant strain 6t1 from closely related strains in the cluster Staphylococcus, 6t1 strain can be regarded as Staphylococcus sp. In terrestrial ecosystems, Galindez Island (Antarctic) detected taxonomically diverse psychrotolerant bacteria. From ornithogenic soil were isolated Micrococcus luteus O-1 and Microbacterium trichothecenolyticum O-3. Strains 4r5, 5r5 and 40r5, isolated from grass and lichens, can be referred to the genus Frondihabitans. These strains are taxonomically and ecologically isolated and on the tree diagram form the joint cluster with three isolates Frondihabitans sp., isolated from the lichen Austrian Alps, and psychrotolerant associated with plants F. cladoniiphilus CafT13(T). Isolates from black lichen in the different stationary observation points on the south side of a vertical cliff identified as: Rhodococcus fascians 181n3, Sporosarcina aquimarina O-7, Staphylococcus sp. 0-10. From orange biofilm of fouling on top of the vertical cliff isolated Arthrobacter sp. 28r5g1, from the moss-- Serratia sp. 6r1g. According to the results, Frondihabitans strains most frequently encountered among chemoorganotrophic aerobic bacteria in the Antarctic phytocenoses.

[Molecular-genetic detection of a nonpathogenic genotype of Spironucleus barkhanus (Diplomonadida: Hexamitidae) in the black Baikal grayling (Thymallus arcticus baicalensis Dybowski, 1874)].

A nonpathogenic genotype of Spironucleus barkhanus (Diplomonadida: Hexamitidae) has been revealed for the first time in the Baikal grayling (Salmoniformes: Thymallidae) by molecular-genetic methods. Sequences corresponding to a fragment of the gene encoding the small ribosomal subunit RNA (SSU rRNA) have been obtained. The genotype of S. barkhanus from Baikal fish is identical to that characteristic of the parasite found in freshwater salmonid fishes.

[Investigation of the impact of pterygium on ocular optic system aberration. Communication 1. Relationship of induced aberrations to the stage of pterygium].

The authors made a study in two areas: they investigated corneal aberrations in patients from different age groups in health; analyzed the corneal aberration pattern at different stages of pterygium in the matched age groups; and comparatively estimated values in pterygium and in health in the similar age groups. High-order aberrations (HOA) of the corneal were studied in 45 patients (84 eyes) aged 20 to 76 years. The corneal aberration pattern was analyzed in 44 patients (55 eyes) aged 25 to 74 years who had pterygium of different stages. The study covered patients with Stages II (24 eyes), III (n=20), and IV (n=11). The results of corneal HOA in health suggest that coma aberrations significantly increase with age while the rise of spherical aberrations is not decisive. Comparative analysis of aberrations in health and in pterygium of different stages showed that its stage II causes no significant changes in the corneal aberration pattern; the characteristic features of the latter in Stages III and IV pterygium are increases in trefoil and aberrations of the fourth and fifth orders: tetra- and pentafoil, secondary trefoil. The increase in the above parameters is proportional to the stage of pterygium. The comprehensive examination of patients with pterygium of different stages should comprise a study of corneal HOA, it is required for more detailed evaluation of disorders induced by the extent of pterygium, which in turn makes it possible to optimize the latter's removing technology.

[Investigation of the impact of pterygium on ocular optic system aberration. Communication 2. New approaches to reducing aberrations during surgical treatment for pterygium].

The authors made a detailed comparative analysis of the aberration pattern of the cornea as a result of surgical treatment for pterygium, by applying various technologies. Forty-four patients (55 eyes) with primary Stages II to IV pterygium were examined. According to the surgical techniques, the patients were divided into 2 groups: (1) those in whom pterygium was surgically removed, followed by abrasive microsurgery and plastic repair with an autoconjunctiva (29 eyes) (a control group); (2) those who had undergone surgical pterygium removal, abrasive microsurgery, and plastic repair with an autoconjunctiva, followed by phototherapeutic eximer laser keratoablation (26 eyes). The study has revealed that phototherapeutic eximer laser ablation of the cornea after surgical excision and abrasive treatment of the corneal bed in Stages II to IV pterygium causes a considerable reduction in the level of aberrations of higher orders. The expedience of phototherapeutic keratoablation as part of multimodality treatment for Stages III and IV pterygium, which has been shown by the aberration analysis, is only one of the first steps in evaluating the efficiency of this technology of surgical treatment for pterygium. Studies involving an integrated clinicofunctional and ophthalmoergonomic assessment of this treatment technology should be continued, which makes it possible to evaluate the clinical efficiency of this procedure and to define a place of the presented technology in the surgical treatment of pterygium.

[Indications for optimized refractive keratoablation. Communication 1. Dependence on the grade of myopia and baseline high-order aberrations].

The authors made a detailed comparative analysis of the aberration pattern of patients before and after aspheric individualized keratoablation (ORK-CAM) and the LASIK operation by routine technology, by taking into account the grade of correctable myopia and the size of baseline high-order aberrations (HOA). Investigations were made in 2 groups: 1) 20 patients (39 eyes) who had undergone routine ablation (a study group); 2) 19 patients (38 eyes) who had aspheric individualized keratoablation (a control group). The findings suggest that individualized aspheric keratoablation is effective in patients with mild and moderate myopia with varying baseline HOA. In addition, a relationship was found between the results of standard and optimized correction and one more key parameter of the aberration pattern, namely the magnitude of 4th-order spherical aberration that should be also taken into account on choosing an eximer laser correction technology. There is an outstanding question whether it is expedient to perform ORK-CAM in patients with high-grade myopia. The above problems require that further studies be continued and will be considered in part 2 of the present investigation.

[Indications for optimized refractive keratoablation. Communication 2. Dependence on baseline spherical aberrations].

The authors made a detailed comparative analysis of the aberration pattern of patients before and after aspheric individualized keratoablation (ORK-CAM) and the LASIK operation by routine technology, by taking into account the magnitude of 4th-order spherical aberration. Investigations were made in 2 groups: 1) 20 patients (39 eyes) who had undergone routine ablation (a study group); 2) 19 patients (38 eyes) who had aspheric individualized keratoablation (a control group). The detailed comparative analysis of the aberration pattern in patients after eximer laser correction by different technologies yielded major criteria predetermining the choice of an eximer laser correction technology. Indications for routine and individualized aspheric keratoablation are defined. Further studies of the impact of high-order aberrations on different visual functions are required to solve the vexed questions whether it is aberrationally expedient to choose laser correction. Ophthalmo-ergonomic studies should be also performed to provide a clinical verification of the consistency of the proposed concept of the indications and the choice of the optimal technology of eximer laser correction.

[Evaluation of the efficiency of aspheric eximer laser keratoablation (a preliminary communication)].

The authors have evaluated the efficiency of aspheric customized keratoablation (ORK-CAM) versus LASIK operation by the routine technology. The studies were conducted in 2 groups: 1) 11 patients (22 eyes) who had undergone aspheric individualized keratoablation (a study group); 2) 13 patients (24 eyes) who had LASIK operation by the routine technology (a control group). After aspheric individualized correction, the clinical and functional results were comparable in visual acuity and correction accuracy with those after routine laser operations. After optimized ablation, there was a statistically significantly less increase in spheric aberration, cumulative high-grade aberrations than after routine LASIK operation. Questioning about visual comfort revealed that aspheric individualized keratoablation was effective in solving characteristic optical problems. The studies have yielded encouraging preliminary results. Further complex studies are required for comprehensive evaluation of the efficiency of aspheric keratoablation.

[Comparative clinical study of the standard lasik operation versus optimized ORK "Corwave" keratoablation (a preliminary communication)].

The efficiency of primary ORK "Corwave" versus LASIK operation was evaluated. Studies were conducted in 2 groups: 1) 12 patients (34 eyes) with bilateral ORK "Corwave" (a study group); 2) 18 patients (36 years) undergone bilateral LASIK by the conventional technology (a control group). The following parameters: uncorrected visual acuity, values of refraction 1 and 3 months after surgery; high-order aberrations (values of RMS coma, spherical aberrations, RMS HOA of orders 3 to 6), spatial contrast sensitivity, blindness sensitivity, questionnaire data on visual comfort, were studied for comparative evaluation of the results of eximer laser correction made by different technologies. In the acuity of vision and in the accuracy of correction of refractive disorders, the clinical and functional results following the optimized correction by the "Corwave" technology were comparable with those after standard laser operations. After ORK "Corwave", spatial contrast sensitivity was found to tend to improve at average and high frequencies. After optimized ablation, the increase in high-order aberrations was less than that after traditional LASIK in terms of all three analyzed parameters; however, this difference was statistically insignificant. The questionnaire test for visual comfort revealed that ORK was effective in overcoming the characteristic optical problems: visual disorders were detected in fewer cases after optimized correction.