Liudmila S. Pateyuk

Efficient delivery of instilled drugs into the corneal stroma and intraocular tissues remains a major challenge in ophthalmic pharmacology. Existing enhancers of transmucosal and transepithelial permeability are often toxic and fail to overcome ocular surface barriers effectively. Dynamic modulation of ocular surface acidity during drug instillation represents a promising approach for gentle “opening” of these barriers and enhancing the bioavailability of certain classes of drugs. Purpose. This study aimed to develop a pharmaceutically acceptable eye drop vehicle based on an overloaded pH buffer capable of dynamically regulating ocular surface acidity and thereby ensuring effective and safe transmucosal and transepithelial delivery of substances. Material and methods. This pilot study included six rabbits (four groups). The permeability of copper (Cu²+) and neodymium (Nd³+) ions was investigated; these ions were selected as models due to their high affinity for mucins and the epithelium. The ions were delivered into the corneal stroma using a vehicle based on an overloaded pH buffer and phosphate-buffered saline (PBS). Stromal concentrations were assessed as follows: Cu — by atomic absorption spectrometry, Nd — by energy-dispersive spectrometry. The absence of toxic reactions was confirmed by biomicroscopy. Results. The eye drop vehicle based on an overloaded pH buffer increased the stromal copper concentration by 1.6-fold compared to PBS (0.54 vs 0.33 mg/kg). The new vehicle enabled significant accumulation of Nd in the corneal stroma at 0.39 wt% [0.36—0.43 wt.%], whereas with PBS the stromal Nd level was measured at 0.07 wt.% [0.07—0.08 wt.%] (below the detection threshold of p<0.001). Conclusions. The eye drop vehicle based on an overloaded pH buffer provides a physiological and significant enhancement of transmucosal and transepithelial transport of cationic substances without inducing ocular tissue damage. This approach may increase drug bioavailability, reduce the required initial dose of active components in dosage forms, decrease toxic burden, and eliminate the need for toxic permeability enhancers in ophthalmic formulations.

Introduction. The structural approach to studying the mechanism of accommodation and its age-related changes focuses on analyzing morphometric parameters (size, shape, and position) of the crystalline lens as the key element responsible for changes in clinical refraction during accommodation. The latest-generation swept-source (SS) anterior segment optical coherence tomography (AS-OCT) device CASIA2 (Tomey, Japan) enables near-screening evaluation of lens shape and position both at baseline and under accommodative stimulus. In the latter case, the integrated optical system provides lens-induced accommodative stress directly in the examined eye. Purpose. This study aimed to evaluate age-related changes in various morphometric parameters of the lens measured by CASIA2 OCT under accommodative stimulus. Material and methods. The study cohort comprised 74 healthy volunteers (123 eyes, i.e., clinical observations) aged 20—85 years. The exclusion criteria were clinically significant refractive errors and ocular diseases. Three groups were formed according to age: 20—30 years, 31—50 years, and >51 years (43, 33, and 47 clinical observations, respectively). Scanning was performed under conditions of relative accommodative rest and during accommodative stimulus. In the latter case, a lens-induced method of accommodative stimulus was used, employing a −5.0 D negative spherical lens and a fixation target in the form of a radial figure integrated into the optical system of the CASIA2 OCT device. Results. Analysis of the entire cohort (n=123) revealed significant changes in morphometric parameters of the lens under accommodative stimulus, including a decrease in the radius of curvature of the anterior (p=0.003) and posterior (p=0.045) lens surfaces, an increase in lens thickness (p=0.011) and nuclear thickness (p=0.007), as well as a reduction in lens diameter (p=0.026) and anterior chamber depth (p=0.033). The radius of curvature of the anterior lens surface under relative accommodative rest in Group 1 (20—30 years) was significantly higher (p=0.00) than in Groups 2 (31—50 years) and 3 (>51 years), with median values of 11.62, 9.47, and 9.25 mm, respectively. The magnitude of changes in lens curvature radius significantly decreased with increasing age for both the anterior and posterior surfaces. Baseline lens thickness and nuclear thickness increased significantly with age and also demonstrated an increase under accommodative stimulus across all age groups. A statistically significant correlation with age was found for the radius of curvature of the anterior surface (r=−0.371; p=0.00) and the posterior surface (r=−0.224; p=0.013), as well as for lens thickness (r=0.268; p=0.003). Conclusion. Anterior segment OCT using the CASIA2 system is a highly informative method for assessing morphometric parameters of the crystalline lens under conditions of relative accommodative rest and lens-induced accommodative stress. Under accommodative stress, statistically significant changes included a decrease in the radius of curvature of the anterior and posterior lens surfaces, an increase in lens thickness and nuclear thickness, and a decrease in lens diameter and anterior chamber depth. Analysis of the magnitude of changes induced by accommodative stimulus and their correlation with age demonstrated statistically significant negative associations between age and the radius of curvature of the anterior and posterior lens surfaces, and a positive association with lens thickness.

Background. Etiology and pathogenesis research of such a corneal disease as keratoconus is rather difficult due to the impossibility to study the underlying ultrastructural and molecular cornea changes in vivo and in animal models.The aim. To evaluate zinc relevance in the biomechanical properties of the corneal stroma – by means of in vitro keratoconus cell model.Materials and methods. In this experimental study, normal and keratoconic cell models of the corneal stroma were exampled – three-dimensional tissue-engineered structures of corneal fibrocytes obtained from healthy donors keratocytes and grown on standard and zinc-depleted nutrient media, respectively. The biomechanical properties of tissue-engineered structures modeling the normal and keratoconic corneal stroma were evaluated by means of the atomic force microscope nanoindentation. Additionally, histological assessment of the obtained cell models and immunohistochemical analysis of type I collagen were performed.Results. According to the study of five samples of each of the corneal stroma models, a statistically significant difference in viscoplastic biomechanical properties was shown: the effective Young’s modulus of the normal and keratoconic models was 9.9 [5.4; 15.6] and 10.3 [6.1; 14.8] kPa, respectively. The in “healthy” group cell cultures thickness was 17.67 ± 1.32 and 18.10 ± 1.22 microns for two and four weeks of cultivation, respectively; in the “keratoconus” group, in a zinc depleted medium, the cell cultures thickness was 21.25 ± 8.39 and 25.55 ± 5.67 microns at the same time of cultivation, respectively. The extracellular component with an excess collagen fraction prevails in the structure of the latter.Conclusion. The data obtained confirms the modern keratoconus etiology and pathogenesis concept – the biomechanical function deterioration of the keratoconic cornea is a consequence of copper, iron and zinc mineral dysmetabolism in its stroma.

Neurotrophic keratitis is a frequent complication of neurosurgical interventions caused by a loss of corneal sensitivity due to damage of the trigeminal nerve pathway. The article presents a clinical case of a successful treatment of a neurotrophic corneal ulcer developed after removal of a giant trigeminal neurinoma. Treatment with autologous serum instillations made it possible to achieve ulcer healing and unstable corneal epithelialization. Stable epithelialization was achieved after temporary replacement of the autologous serum topical application with recombinant human nerve growth factor. In addition to ulcer healing and complete corneal epithelialization, regeneration of nerve fibers was noted (according to cornea confocal microscopy data).

Keratoconus is an ectatic corneal disease, resulting in loss of visual functions in young population. Diagnosis of the disease at a moderate stage with a typical progressive clinical course is not particularly difficult; however, the diagnosis verification in a few cases is rather troublesome. This literature review systematizes modern conceptions to the keratoconus diagnosis, outlines current approaches to patients examining and diagnostics results assessing. The clinical manifestations (complaints, anamnesis data, visometry and autorefractokeratometry results) at the early stages of keratoconus with its non-progressive course are similar to ordinary myopia and regular myopic astigmatism; as a result, it is quite difficult to suspect the disease in such cases. With progressive keratoconus course, as corneal protrusion develops, the disease acquires features specific for gradual irregular corneal myopic astigmatism growth. Currently valuable pathognomonic slit-lamp signs of keratoconus are Fleischer’s ring, stromal Vogt’s striae and focal thinning of the cornea in the ectasia apex. Nowadays the gold standard of keratoconus diagnosis and screening is comprehensive examination of the cornea by means of modern computer optical scanning (Scheimpflug camera in particular) keratoanalyzers, combining keratoscopy (Placido’s disc) and keratotomography. The keratoanalyzers original software generates maps and calculates irregularity indices of the cornea shape (keratotopography), refractive power (keratometry) and thickness (keratopachimetry), as well as values the probability and stage of corneal protrusion. Such diagnostic platforms provide differential diagnosis and verification of keratoconus at the earliest signs of the topographic stage of the disease; to date, there are no effective methods, that can reliably confirm or exclude ultrastructural changes at the pretopographic stage of keratoconus.

This review analyzes the primary etiological factors of diffuse lamellar keratitis following various laser corneal refractive surgery techniques. The use of advanced diagnostic methods such as optical coherence tomography, confocal microscopy, and immunohistochemical methods has allowed for the identification of the main pathogenetic mechanisms underlying this condition, which will help improve the prevention, as well as assist with the development of optimal treatment strategies for this complication.

The scientific and practical interest in studying the biomechanical characteristics of the lens capsule, on the one hand, is associated with its anatomical significance in modern microinvasive phaco surgery, and on the other hand, with investigation of the mechanisms of lens curvature changes during accommodation. Selective study of the biomechanical properties of the lens capsule aims to identify characteristics of various regions and surfaces of the capsule. Purpose. This study is a comparative analysis of age-related changes in the biomechanical properties of the anterior (AC) and posterior (PC) lens capsules in humans. Material and methods. The study analyzed 73 pairs of central fragments of the AC and PC of the lens, obtained from donor (cadaver) eyes and through anterior and posterior capsulorhexis during microinvasive phaco surgery (38 and 35 paired samples, respectively). Planned biomechanical testing followed a previously developed protocol for examining the anterior capsule, including determination of the Young’s modulus using atomic force microscopy. Results. Comparing the Young’s modulus of lens capsule samples from donor eyes and microinvasive phaco surgery revealed no significant differences in mean values, indirectly indicating minimal postmortem impact on the biomechanical properties of the capsule. General biomechanical patterns observed in the human lens capsule show the Young’s modulus (stiffness) is higher in the AC than the PC, and higher on the inner than the outer surface for both the AC and PC. Age-related changes are associated with an increase in stiffness on the outer surface and its decrease on the inner surface, more pronounced in the AC. Conclusion. The obtained results indicate the need for further investigation into the role of capsule biomechanics in age-related accommodative disorders.

Cataract phacoemulsification with intraocular lens implantation significantly affects the morphology of the anterior chamber angle (ACA) and contributes to a reduction of intraocular pressure (IOP). PURPOSE This study investigates the changes in anterior chamber angle configuration and IOP level before and after cataract surgery in primary open-angle glaucoma (POAG) eyes, and assesses its possible relationship with the axial length of the eye. MATERIAL AND METHODS The study included 38 patients with immature senile cataract and compensated unoperated stage I-II POAG. Patients underwent anterior segment optical coherence tomography (AS-OCT) with measurement of the angle opening distance (AOD₇₅₀) and trabecular-iris space area (TISA₇₅₀) before and six weeks after the surgery, as well as axial length and corneal-compensated IOP (IOP_cc). RESULTS After the surgery 92.11% of patients showed a decrease in IOP_cc an average of 1.84±1.95 mm Hg (by 12.33±10.21% of the baseline); the maximum decrease in the IOP_cc level was 8.35 mm Hg (by 40.97% of the baseline). AS-OCT data indicates that cataract phacoemulsification causes an increase in anterior chamber angle width: AOD₇₅₀ increased from 0.510±0.175 to 0.771±0.156 mm, and TISA₇₅₀ increased from 0.266±0.090 to 0.494±0.096 mm². The strongest correlations were found between the axial length, postoperative TISA₇₅₀ increase (Δ%TISA₇₅₀) and postoperative IOP_cc reduction (Δ% IOP_cc). Postoperatively, specific changes could be observed in the trabecular meshwork in 28.95% of cases in the form of elongation and strain of the membrane. CONCLUSIONS Cataract extraction contributes to a significant reduction in IOP due to anterior chamber angle expansion, trabecular meshwork stretching, and improved aqueous outflow.

INTRODUCTION: Certain mineral elements dismetabolism is known to play an important part in the pathogenesis of the corneal degenerative and dystrophic diseases, as metalloenzymes participate in connective tissues metabolism affecting their properties. Thus, in keratoconus corneal tissue is depleted in iron, copper and zinc, what could be the underlying cause of cornea biomechanical properties impairment. Keratoconus modeling is complicated and practically not reproducible in animals, therefore cell models elaboration is very much in demand. Definite mineral elements content must be reduced in order to simulate pathological changes specific for keratoconic corneas. PURPOSE: The aim of this study was an elaboration of a cell model suitable for keratoconus pathogenesis research. This goal achieving involved solving the following tasks: 1) to develop a tissue-engineered system that mimic healthy corneal stroma; 2) to develop a technique for selective depletion of the nutrient medium by mineral elements involved in keratoconus pathogenesis; 3) to assess the possibility of the designed tissue-engineered system growth in the depleted nutrient medium. MATERIAL AND METHODS: The study was carried out with the primary culture of human keratocytes, which were used to build tissue-engineered systems of three types: on silicone, on a membrane, without a carrier. Cell cultures morphology was evaluated by light and electron microscopy. The nutrient media were zinc depleted via decationization of fetal bovine serum using two types of ion-exchange resins; mineral elements concentrations were evaluated by means of inductively coupled plasma mass spectrometry. RESULTS: The tissue system engineered without a carrier in form of cell sheet was chosen as the most convenient model. The decationization of the serum by means of Chelex 100 resin was shown to be a successful method for tenfold zinc concentration reduction in the nutrient medium. Keratocytes cultivation in the form of cell sheet on a zinc-depleted medium was successfully approved. CONCLUSION: Elaborated tissue-engineered system could be considered as a model of the corneal stroma under specific for keratoconus conditions of zinc depletion.

Представлены результаты, полученные на нескольких типах модельных культур. Из тканей структур переднего сегмента глаза были получены первичные культуры эпителиоцитов роговицы и фибробластоподобные клетки из зоны лимба. На них проведены тесты по определению цитотоксичности антиглаукомных препаратов и апробирован способ протекции. Выполнен сравнительный анализ регенераторного потенциала различных дериватов крови. На культуре эндотелиоцитов in vitro показана корреляция между степенью повреждающего воздействия гипотензивных препаратов различных групп и содержанием в их составе консерванта бензалкония хлорида. Кератоциты роговицы использовали для создания клеточного пласта, отражающего основные черты строения стромы и подходящего для проведения биомеханических тестов. На культуре фибробластов носослезного протока протестирована антифибротическая активность лекарственного препарата. Проведенные исследования иллюстрируют возможность применения клеточных культур в качестве информативного модельного объекта для изучения патогенеза офтальмологических заболеваний и тестирования препаратов.