[The effect of keratoconus-associated refractive errors on the results of tomographic methods of studying the posterior structures of the eye]. / Vliyanie opticheskikh narushenii pri keratokonuse na rezul'taty tomograficheskikh metodov issledovaniya struktur zadnego segmenta glaza.

PURPOSE: The study assesses the potential influence of refractive errors in keratoconus (KC) on the results of tomographic methods of studying the structures of the posterior eye segment. MATERIAL AND METHODS: The study included 30 patients with bilateral stabilized KC of stages I-IV in classification by M. Amsler. Spherical and cylindrical components of refractions were determined using automatic refractometry, keratometry measurements - based on scanning keratotopography with Scheimpflug analyzer. Aberrometry was performed to evaluate corneal wave front according to the following parameters: root mean square for lower order aberrations (RMS LOA), root mean square for higher order aberrations (RMS HOA), vertical trefoil, vertical coma, horizontal coma and spherical aberrations. Optical coherence tomography (OCT) and laser confocal scanning ophthalmoscopy (HRT 3) data was used in morphometric analysis of the optic nerve head and peripapillary retina. The following morphometric parameters were analyzed: optic nerve head (ONH) area, optic disc cup area, optic disc cup volume, ratio of optic disc cup area to ONH area, neuroretinal rim area, neuroretinal rim volume, peripapillary retinal nerve fiber layer (RNFL) thickness. All studies were performed first without correction, and 30 minutes after installing customized scleral hard contact lenses (SHCL). RESULTS: Compensation of the refractive errors characteristic for KC was achieved as expected with contact correction. OCT revealed a general trend for reduction in the area and volume of the optic disc cupping, ratio of area to volume of the optic disc cupping, as well as an increase in other parameters. As such, with correction the values for area and volume of the neuroretinal rim according to OCT were 2.2 and 13%, HRT 3 - 18 and 51.6%; comparable increase in mean RNFL thickness - 2.8 and 28.5%, respectively (p<0.001). According to HRT 3 data, the area and volume of optic disc cupping statistically significantly decreased (by 21 and 28%, respectively), while OCT showed statistically significant decrease only in cupping area (by 5.7%). The ratio of cupping to ONH area decreased by 6.6 and 23% relative to the initial data obtained with OCT and HRT 3, respectively. Significant decrease in ONH area amid SHCL correction was observed only with HRT 3. The revealed changes in morphometric parameters were analyzed using the fundamental principles of physiological optics. Changes in interference pattern and, consequently, morphometric parameters of structures of the eye fundus in KC are of multifactorial nature, and are mostly associated with refractive and wave artefacts occurring when the rays pass through the irregular corneal surface and cannot be optically compensated by the device. The use of SHCL as means for making the optic system relatively regular can significantly decrease the artefacts in morphometric measurements. CONCLUSION: The results obtained in this study demonstrate the practicality of tomographic examination in KC with contact correction. The optimal choice is custom-fit SHCL, which along with proper correction of refractive errors also ensures stable position of the lens on the cornea. In standard examination specialists should take into account the «false¼ decrease in parameters of the peripapillary retinal nerve fiber layer and increase in ONH cupping.

[Keratoconus: main lines of research]. / Keratokonus: osnovnye napravleniya issledovanii.

Keratoconus (KC) research focuses on studying pathogenesis, advancing diagnostic techniques and methods of correction and treatment. The working hypothesis for KC etiopathogenesis is based on abnormalities in distribution of microelements in the cornea and its potential influence on the processes of stromal collagen disorganization. Improvement of early diagnosis of KC is associated with evaluation of microstructural changes in the cornea using computerized methods such as Scheimpflug camera and high-definition optical methods for visualization of initial signs of a pigment ring. The main optimization directions of KC contact correction are associated with increasing gas permeability of the material, improving lens design and methods of lens fitting. Customized fitting of gas-permeable scleral hard contact lenses with consideration of topographic features of the anterior corneal surface allows achieving stable lens positioning and preserving the tear gap between the lens and the cornea. Alternative methods of correcting the refraction component of KC are associated with surgical interventions involving increase in corneal volume in the paracentral area. Implantation of corneal ring segments should be considered as an alternative to correction of refractive errors in cases with unsatisfactory individual subjective tolerance and insufficient patient compliance with contact correction. Femtolaser-assisted implantation of intrastromal allotransplants along with a decrease in the degree of spherical and astigmatic components of refractive errors contribute to prevention of KC progression. Advancement of techniques of corneal collagen cross-linking for prevention of KC progression is aimed at reducing the risk of developing post-operative complications directly related to the extent of intraoperative deepithelization. Limiting corneal ectatic area by implantation of intrastromal allotransplants can be considered an alternative approach. Deep anterior lamellar keratoplasty and penetrating keratoplasty are the surgeries of choice in replacing altered corneal layers in KC. With regard to the modern trends in selective keratoplasty, selective replacement of the cornea in lamellar keratoplasty reduces the rate of injuries and the risk of tissue reaction.

[Cell cultures - model object for experimental studies in ophthalmology]. / Kletochnye kul'tury ­ model'nyi ob"ekt dlya eksperimental'nykh issledovanii v oftal'mologii.

The article presents results obtained on several types of model cultures. Primary cultures of corneal epithelial cells and fibroblast-like cells from the limbus were obtained from the tissues of the anterior eye segment. Tests were performed on these cultures to determine the cytotoxicity of antiglaucoma drugs and to trial a protection method. In addition, a comparative analysis of the regenerative potential of various blood derivatives was carried out. An in vitro culture of endotheliocytes showed a correlation between the degree of damaging effects of antiglaucoma drugs of various groups and the content of the preservative benzalkonium chloride in their composition. Corneal keratocytes were used to create a cell sheet reflecting the main structural features of the stroma and suitable for biomechanical tests. The antifibrotic activity of the drugs was tested on the culture of fibroblasts from the nasolacrimal duct. The conducted studies demonstrate that cell cultures can be used as an informative model object for researching the pathogenesis of ophthalmic diseases and for testing drugs.

[On refraction shift after trabeculectomy]. / K voprosu ob izmeneniyakh refraktsii posle trabekulektomii.

PURPOSE: To determine the factors affecting the shift of refraction after trabeculectomy. MATERIAL AND METHODS: The study included 42 patients who were examined prior to trabeculectomy and at the following timepoints: 1 week, 1 month and 3 months after surgery. Examination included tonometry with assessment of corneal biomechanical properties, keratorefractometry with vector analysis, and biometry. The obtained data was processed for regression analysis and to find the possible correlations. RESULTS: All significant correlations between the measured parameters only occur on week 1. Postoperative spherical component of refraction (sphere) correlates negatively both with preoperative axial length (AL) and anterior chamber depth (ACD) (r=-0.699 and r=-0.458, p<0.05) and postoperative AL and ACD (r= -0.767 and r= -0.415, p<0.011). Dependence of sphere on AL is also expressed as a regression model. The magnitude of AL change depends on the magnitude of intraocular pressure (IOP) change (r=0.729, p<0.0001) and correlates negatively with postoperative IOP (r=-0.454, p=0.009) and baseline corneal hysteresis (CH; r= -0.482, p=0.009). Dependence of AL on IOP is also expressed as a regression model. The magnitudes of sphere and cylinder shifts correlate negatively with each other (r=-0.416, p=0.038). Keratometry reveals that the overall cylinder value correlates with the corneal cylinder, and so do the magnitudes of their shifts (r=0.589 and r=0.574, p<0.0001). Dependence of corneal hysteresis on IOP is expressed as a regression model; however, neither tonometric nor biomechanical corneal properties correlate with refraction. CONCLUSIONS: Sphere correlates negatively with AL and ACD. In turn, AL is related to the reduction in IOP. This dependence is likely the most important one for the refraction shift after trabeculectomy. No correlations were found for the change of astigmatism.

[Precorneal tear film after corneal collagen cross-linking in keratoconus (preliminary report)]. / Sostoyanie prekorneal'noi sleznoi plenki posle krosslinkinga rogovichnogo kollagena pri keratokonuse (predvaritel'noe soobshchenie).

PURPOSE: To study the condition of precorneal tear film in keratoconus patients after corneal collagen cross-linking (CXL). MATERIAL AND METHODS: The study enrolled 24 patients (30 eyes) with stages I-III progressive keratoconus. All study patients underwent standard (Dresden) protocol CXL. Patients were examined before the surgery and 1 week, 1 month, and 3 months postoperatively. The condition of precorneal tear film was evaluated based on the results of Norn test (the tear film break-up time), Schirmer test, Jones test, optical coherence tomography based lacrimal meniscometry, and improved tearscopy. RESULTS: One month after CXL, patients with keratoconus experienced transient changes in the precorneal tear film condition - the tear film break-up time was reduced, the tear secretion was elevated, the lacrimal meniscus biometry parameters were increased, and the thickness of the tear film lipid layer was decreased. CONCLUSION: Corneal changes resulting from CXL lead to transient disorders of the mucin and lipid layers of the precorneal tear film, which requires adequate tear substitute therapy in the postoperative period.

[Results of optical coherence tomography of the retina and optic nerve in keratoconus]. / Rezul'taty opticheskoi kogerentnoi tomografii setchatki i zritel'nogo nerva pri keratokonuse.

The article reviews the results of optical coherence tomography (OCT) of the retina and optic nerve in patients with keratoconus (KC). This research direction is premised by the possibility that changes in the retina and optic nerve are associated with KC, as well as the potential influence of significant changes in axial eye length, disorders of corneal refraction and increased level of aberrations on the quality of visualization of these ocular structures. Results of the conducted studies were conflicting, but in all they indicated a possibility of OCT findings to be altered in KC patients. Therefore, the question of changing the parameters for OCT of the retina and optic nerve requires further investigation. The main problem that needs solving with evidence based medical research can be phrased as follows: are the changes in OCT findings observed in KC patients the consequence of changes in the retina and optic nerve associated with this disorder, or potential effect of aberrations and irregular astigmatism on the quality of visualization of the studied structures?

[Results of confocal microscopy of the cornea after bandage therapeutic-optical keratoplasty in keratoconus]. / Rezul'taty konfokal'noi mikroskopii rogovitsy posle bandazhnoi lechebno-opticheskoi keratoplastiki pri keratokonuse.

Bandage therapeutic-optical keratoplasty (BTOK) is one of the modern methods of surgical treatment of keratoconus (KC) that allows to improve visual functions by changing keratotopographic and pachymetric parameters of the cornea in the zone of ectasia. Long-term results show that changes also affect the central part of the cornea, which tends to flatten. PURPOSE: To compare the light confocal microscopy appearance of the cornea before and after BTOK surgery. MATERIAL AND METHODS: We examined 15 patients (15 eyes) with progressive keratoconus (7 eyes with Amsler stage I KC and 8 eyes with Amsler stage III KC), who subsequently underwent BTOCK surgery. Using the Confoscan-4 confocal light microscope (Nidek, Japan), we studied the structure of central and paracentral cornea. The exact zone of interest was determined individually depending on the location of the graft. RESULTS: In all cases, morphological changes in the cornea characteristic of the stage II and III KC were detected. Twelve months after the operation, there was an increase in the transparency of intercellular substance of the stroma with a clearer visualization of keratocyte nuclei in the optical zone as well as at the site of the graft. In the area of interface, tissue compaction in the form of diffuse fibrosis with local scar formation could be seen. Neither significant changes in the cell structure, nor a decrease in cell density were found in the central part of ectasia and the areas of clear visualization of the endothelium under the graft. Additional postoperative assessment of the level of corneal light scattering indicated a tendency towards restoration of stromal transparency and optical uniformity. CONCLUSION: As a result of interlayer graft implantation in the zone of corneal ectasia, a tendency to structural improvement in its central and paracentral parts was revealed. Local fibrosis in the interface area can indirectly indicate biomechanical «strengthening¼ of this zone.

[The effects of corneal collagen cross-linking on the corneal structure in keratoconus]. / Vliyanie krosslinkinga rogovichnogo kollagena na strukturu rogovitsy pri keratokonuse.

The article reviews the key information regarding morphological changes in keratoconic corneas and dramatic alterations of the corneal tissue induced by corneal cross-linking according to data obtained with in vivo corneal confocal microscopy, presents basic information on keratoconus visualization techniques widely used for diagnosis, monitoring of ectasia, as well as efficacy assessment of its treatment, and lists basic principles of corneal cross-linking procedure and confocal microscopy with consideration of morphology specifics of keratoconic corneas. The article also discusses prospective benefits of further research and longitudinal studies aimed to define the origin of keratoconus and to develop advanced corneal cross-linking protocols.

[Phacosurgery features in keratoconus]. / Osobennosti fakokhirurgii pri keratokonuse.

The review summarizes the results of surgical treatment of cataracts in patients with keratoconus. The major challenges of phacosurgery in keratoconus are associated with intraocular lens (IOL) power calculation, choice of the most appropriate IOL model and additional interventions required to stabilize keratectasia and reduce corneal irregularity.

[Secondary dry eye syndrome after keratorefractive surgeries and approaches to its treatment and prevention]. / Vtorichnyi sindrom 'sukhogo glaza' posle keratorefraktsionnykh vmeshatel'stv i podkhody k lecheniiu i profilaktike.

The article reviews the particularities of development and pathogenesis of secondary dry eye syndrome (DES) after refractive surgeries including a complex of problems related to changes in tear film content, damage of eye surface and neurotrophic epitheliopathy. Additionally, modern algorithms of treatment and prevention of secondary DES in patients after refractive surgeries are described. Despite the transient nature of the changes, excimer-laser surgery can lead to lasting deficiencies of eye surface in some patients. Therefore, intensive and early treatment of secondary DES during the early follow-up period after refractive surgery may significantly reduce risks of tear dysfunction and neurotrophic epitheliopathy development in the long term.

[Reducing cytotoxic action of the preservative employed in ophthalmic hypotensive medications with tear replacement therapy]. / Snizhenie tsitotoksicheskogo deistviia konservanta v sostave oftal'mogipotenzivnykh preparatov s pomoshch'iu slezozamestitel'noi terapii.

PURPOSE: to assess the possibilities of reducing the cytotoxic effect of benzalkonium chloride (a preservative used in ophthalmic hypotensive drugs) with the help of tear replacement therapy. MATERIAL AND METHODS: The study included 28 patients (56 eyes) who had been using antiglaucomatous drugs containing benzalkonium chloride as a preservative for various periods (from 2 months to 17 years). The examination was performed in the setting of compensated IOP. In addition to hypotensive topical medication regimen, all patients were prescribed Stilavit eye drops. Subjects were examined prior to the prescription of artificial tears and after 1, 3 and 6 months of its usage. Effectiveness of the treatment was evaluated with biomicroscopy, Norn's test, Jones test, tearscopy, OCT-meniscometry, confocal microscopy, and impression cytology. RESULTS: The use of 'Stilavit' artificial tears in combination with antiglaucoma drugs led to an improvement of the corneal epithelium condition in 85% of cases, a statistically significant increase in the mean values of precorneal tear film rupture time after 1, 3 and 6 months by 26%, 61.2% and 85.8% respectively. Maximum increase of main tear production level was achieved after 3 months of treatment (increased by 43.5%), and was accompanied by 18.6% rise of the lower tear meniscus height after 3 months; in 6 months it raised by 29.4%. A tendency for restoration of the lipid layer of the tear film was observed. According to confocal microscopy and impression cytology, positive dynamics in the condition of corneal epithelium and conjunctival epithelial layer were present. CONCLUSION: The study results justify the use of tear replacement therapy, in particular the tear substitute Stilavit, as an additional protective agent for glaucoma treatment regimen.