[New approach to corneal nerve fibers morphometry in diabetes mellitus on the basis of confocal biomicroscopy]

[Confocal microscopy of the corneal nerve fibers]

This article presents the results of confocal microscopy of the corneal nerve fibers (CNF). The transparency of the cornea provides a unique potential for in vivo visualization of thin unmyelinated nerve fibers at the level close to morphological study. Modern software eliminates the need for manual tracing of the confocal image fragments, allows objectifying the process of assessment of CNF structure based on quantitative indicators characterizing the length, density and tortuosity of the main nerve trunks. Clinical application of structural analysis of the CNF has two potential directions associated with immediate tasks of ophthalmology, as well as with interdisciplinary affairs. In terms of ophthalmology, this primarily concerns various surgical interventions potentially affecting the state of the cornea, and chronic pathological processes in the cornea of different nature. Such studies could analyze the degree of changes in the CNF, or the particularities of corneal reinnervation. The potential for interdisciplinary studies lies in using CNF as biomarkers of systemic polyneuropathies. Relative simplicity, high level of direct visualization of the thin nerve fibers, and the obtained results allow recommending corneal confocal microscopy as a tool for primary screening and consequent monitoring of neuropathies in addition to the conventional methods.

[State of corneal nerve fibers in systemic amyloidosis]

The term systemic amyloidosis unites a group of diseases with a single pathogenetic mechanism involving diffuse deposition of a pathological fibrillar protein (amyloid) in the intercellular space of various organs. Among the systemic forms of amyloidosis, light chain amyloidosis (AL-amyloidosis) occurs most often in clinical practice, while transthyretin amyloidosis (TTR-amyloidosis) is its most common hereditary form. Laser corneal confocal microscopy (CCM) allows for in vivo and non-invasive assessment of the state of corneal nerve fibers (CNF).

PURPOSE

To assess the state of CNF in systemic amyloidosis by confocal microscopy data obtained in vivo.

MATERIAL AND METHODS

The main study group included 16 patients (6 men and 10 women, mean age 60.5±11.6 years) with morphologically confirmed primary AL-amyloidosis, and 14 patients (5 men and 9 women, mean age 59.4±11.3 years) with genetically and morphologically confirmed hereditary TTR-amyloidosis. The control group included 23 healthy volunteers of the same age range without any neurological pathologies. The state of CNF was assessed by in vivo CCM data recorded on the HRT III system and its consequently processing using authors' self-developed program Liner 1.2. The criteria for neuropathy intensity was the degree of CNF tortuosity characterized by coefficients of anisotropy (K_ΔL) and symmetry (K_sym) of CNF orientation.

RESULTS

According to the NIS scale, the manifestations of neuropathy in the subgroup of patients with TTR-amyloidosis were significantly more pronounced compared to AL-amyloidosis patients. The severity of clinical manifestations of neuropathy did not depend on the duration of TTR-amyloidosis and AL-amyloidosis (Spearman R r_s=0.21, p=0.58 and r_s= -0.49, p=0.055, respectively). Changes in the quantitative indicators (a decrease in the anisotropy coefficient and an increase in the symmetry coefficient of the fibers orientation) confirm increased tortuosity of CNF in systemic amyloidosis.

CONCLUSION

The clinical picture of systemic amyloidosis is characterized by polymorphism of neurological manifestations that include various symptoms of damage to the peripheral somatic and autonomic nervous system. In vivo CCM can be used to reveal qualitative and quantitative changes in CNF in patients with systemic amyloidosis. However, statistical unreliability of the identified quantitative changes allows considering the state of CNF in amyloidosis only as a component of the disease monitoring algorithm, but not as a biomarker of the disease.

[Association of polymorphic markers rs7947461 of the TRIM21 gene and rs33996649 of the PTPN22 gene with the risk of developing exogenous dry eye syndrome]

In this age of technological advancement, an increasing number of people is being exposed to external risk factors of damaging their ocular surface (wearing contact lenses, electromagnetic radiation from computers, mobile devices, etc.). However, the presence of external factors does not lead to a 100% risk of developing the dry eye disease (DED). The trigger mechanism in the development of autoimmune lesions of the ocular environment in some systemic diseases is known to be associated with molecular genetic factors. The search for molecular genetic disorders is based on the analysis of polymorphic markers of a number of genes responsible for the state of the eye surface.

PURPOSE

To study the relationship of polymorphic markers rs7947461 of the TRIM21 gene and rs33996649 of the PTPN22 gene with the risk of developing dry eye syndrome of exogenous etiology.

MATERIAL AND METHODS

The study included 57 people with exogenous risk factors for DED development. The control group included volunteers without a history of ophthalmic pathologies (n=75). Genotyping was done by real-time polymerase chain reaction followed by melting curve analysis. Statistical processing of data was done using the Statistica 6.1 RUS software for statistical analysis.

RESULTS

In the course of the study, 31 patients of the main group were diagnosed with DED and separated into the 1st subgroup; DED diagnosis was not confirmed in 26 patients, who were put into the 2nd subgroup. The 1st subgroup showed a significant increase in the frequency of predisposing genotypes of the TRIM21 and PTPN22 genes. The relative risk of developing DED turned out to be 2.5 and 4.86 times higher, respectively. In the 2nd subgroup, no statistically significant data was found on the presence of predisposing genotypes of polymorphic markers of the TRIM21 and PTPN22 genes (p=0.3).

CONCLUSION

The revealed association of polymorphic markers rs7947461 of the TRIM21 gene and rs33996649 of the PTPN22 gene with the risk of developing DED of exogenous etiology puts these loci as possible markers for diagnosing this pathology.

[First results of clinical diagnostic analysis of post-COVID peripheral neuropathy]

This analysis of ocular manifestations of the COVID-19 that can occur both in the acute and the post-COVID period focuses on pathological changes associated with hypercoagulation: thrombosis of the central retinal vein, occlusion of the central retinal artery, and decreased peripapillary perfusion. Potential changes in corneal nerve fibers (CNF) associated with coronavirus infection remain poorly understood. Meanwhile, previous studies have shown the possibility of using CNF as biomarkers of polyneuropathy (PNP).

PURPOSE

To study clinical and diagnostic features of post-COVID PNP.

MATERIAL AND METHODS

We examined 9 female patients aged 32 to 51 years who had suffered an infection caused by SARS-CoV-2 of varying severity. The patients were divided into two groups: the first consisted of 6 patients with clinical manifestations of PNP in the form of neuropathic pain, the second - 3 patients without clinical manifestations. Patients of group 1 underwent comprehensive examination including neurological examination, confocal microscopy of the cornea (in vivo CM), electroneuromyography (ENMG) of the nerves of the upper and lower extremities, quantitative sensory testing in the zone of painful sensations, while patients of group 2 only underwent in vivo CM.

RESULTS

All patients of the first group, within 5-40 days after the onset of infection caused by SARS-CoV-2, exhibited symptoms of damage to various parts of the nervous system (peripheral nerves, thoracic spinal roots, trigeminal nerve). The main - and in most cases the only - symptom of the disease was neuropathic pain syndrome. In Guillain-Barré syndrome, for the first time using in vivo CM, the following changes were revealed: enlargement of in Langerhans cells, shortening of CNF and their processes, presence of neuromas.

CONCLUSION

The standard neurological examination of patients with post-COVID neuropathy should be supplemented with special diagnostic methods for assessment of structural and functional state of the peripheral nerves. The in vivo CM method is capable of non-invasive assessment of changes in thin CNF and, with accumulation of empirical data, can be included in the algorithm for diagnosing post-COVID PNP.

[Methods and clinical significance of the condition of corneal nerve fibers]

The review provides basic information about embryology, structural features, biochemical composition, functions and classification of corneal nerve fibers, and describes anatomical, histological and functional diagnostic techniques for corneal nerves. Each method for analyzing the structure of the nerve fiber, its advantages and disadvantages are described in detail, including the history of the development of confocal microscopy (laser and light) and esthesiometry (contact and non-contact). The article also presents the criteria according to which the structure of the nerve fiber is estimated using laser confocal microscopy, and the shortcomings of these criteria. Additionally, the article reports on the futility of the use of modern esthesiometry methods.

State of corneal nerve fibers after laser-assisted in situ keratomileusis

PURPOSE

To assess the state of corneal nerve fibers (CNF) based on quantitative parameters after laser correction of myopia using LASIK.

MATERIAL AND METHODS

The study examined 141 eyes - 80 eyes with myopia and 61 emmetropic eyes. In 47 cases a microkeratome was used to form a corneal flap, and in 33 cases a femtosecond laser was used (LASIK and FemtoLASIK, respectively). Confocal microscopy was performed before, as well as 1, 3, and 6 months after correction. Objective analysis of CNF involved automatic calculation of the anisotropy (K_ΔL) and symmetry (K_sym) coefficients of CNF orientation in the Liner 1.2S software.

RESULTS

Lower values of K_ΔL were revealed in myopia as compared to emmetropia. Regardless of the method of flap formation, no CNF could be detected in the central cornea 1 month after myopia correction. In all cases after FemtoLASIK and in 2 cases after LASIK, CNF in the central cornea were first visualized after 3 months, and after 6 months CNF could be detected in all cases. At a similar observation time, CNF were visualized both after LASIK and after FemtoLASIK in the superior and inferior peripheral portions of the cornea. Analysis of long-term postoperative changes in K_ΔL and K_sym revealed a decrease in the former and an increase in the latter.

CONCLUSION

Evaluation of the state of CNF after corneal refractive correction should take into account the initial changes in CNF in myopia that are possibly associated with an increase in axial eye length. A more dynamic restoration of innervation was noted in cases where the flap was formed with the femtosecond laser, which may be explained by the fact that the mechanism of tissue separation when using this type of coherent radiation is gentler. Considering the changes in the quantitative indicators characterizing the state of CNF, the question of «completeness» of the restored CNF as a result of reinnervation remains open.

The Role of Polymorphic Markers rs1478604, rs2292305, and rs2228262 in THBS1 Gene in the Development of Autoimmune Dry Eye Syndrome

An association of polymorphic marker rs2228262 in the THBS1 gene with the risk of developing dry eye in Sjögren syndrome was revealed. Confocal microscopy data suggest that this polymorphic marker is responsible for the high probability of corneal nerve fiber lesion in Sjögren syndrome even in the absence of clinical and functional signs of dry eye syndrome. A significant correlation was established between polymorphic markers rs1478604, rs2228262 in THBS1 gene and the coefficients of anisotropy and orientation symmetry of corneal nerve fibers. These results allow considering these polymorphic markers as a genetic factor of predisposition to dry eye syndrome in patients with Sjögren syndrome.

[Phacosurgery effects on the condition of corneal nerve fibers]

The question of potential changes in the nerve fibers of the cornea induced by phacosurgery remains poorly investigated. This is a review of results of many individual studies aimed at assessing the condition of corneal nerve fibers following different techniques of cataract removal. The authors substantiate the necessity for structural analysis of fiber changes based on in vivo confocal microscopy of the cornea. Functional assessment of corneal sensitivity (esthesiometry) does not allow objective conclusions, for several reasons. Further studies on corneal nerve changes after phacosurgery could be directed at improving software products for objective quantitative assessment of corneal nerve fibers and analyzing long-term results of various phacosurgery techniques.

[Clinical and morphological changes in the eye in Fabry's disease (a clinical case study)]

The article presents a clinical case of Fabry's disease accompanied by changes in the eye and gives detailed description of standard ophthalmological examination and results of some modern methods of assessing macro- and micro-structure of certain ocular tissues. Fabry's disease (also known as Anderson-Fabry disease, diffuse angiokeratoma of the body, hereditary dystonic lipidosis) is a progressive hereditary multi-systemic disease; more specifically, it is a progressive congenital defect in the metabolism of tissues of the human body. It is included in the list of orphan diseases. One of its local manifestations is development of dystrophic changes in the structure of the cornea with tendency to progress. Early diagnosis of Fabry's disease is crucial, but its extensive and 'mixed' symptoms often mask the true causes of pathological changes, which leads to late diagnosis.

[Prognostic value of changes in the cornea and conjunctiva in diabetes mellitus]

Diabetes mellitus (DM) is the most common endocrine disease, and therefore a pressing medical and social problem. In many cases, ocular manifestations of DM are considered the particular cause of patients' disability. The review presents an analysis of morphological, experimental and clinical studies of the cornea in patients with diabetes mellitus - full articles, reviews and monographs of Russian and foreign authors, mostly those published in the recent years. Among the considered topics are modern methods of examining conjunctiva and cornea, clinical and morphological changes in these tissues, and the early diabetic changes in all their structural layers. The review also describes the importance of diabetes-related changes in the conjunctival vessels and corneal nerve fibers and shows the correlation between the densities of corneal nerve fibers and epidermal nerve fibers.

A systematic review on the impact of diabetes mellitus on the ocular surface

Diabetes mellitus is associated with extensive morbidity and mortality in any human community. It is well understood that the burden of diabetes is attributed to chronic progressive damage in major end-organs, but it is underappreciated that the most superficial and transparent organ affected by diabetes is the cornea. Different corneal components (epithelium, nerves, immune cells and endothelium) underpin specific systemic complications of diabetes. Just as diabetic retinopathy is a marker of more generalized microvascular disease, corneal nerve changes can predict peripheral and autonomic neuropathy, providing a window of opportunity for early treatment. In addition, alterations of immune cells in corneas suggest an inflammatory component in diabetic complications. Furthermore, impaired corneal epithelial wound healing may also imply more widespread disease. The non-invasiveness and improvement in imaging technology facilitates the emergence of new screening tools. Systemic control of diabetes can improve ocular surface health, possibly aided by anti-inflammatory and vasoprotective agents.

[Clinical features and diagnosis of diabetic polyneuropathy]

Diabetic polyneuropathy (DPN) is a serious complication of diabetes that leads to early disability in patients if late diagnosed. There has been a lot of research into pathophysiological mechanisms of nerve fiber damage and risk factors for neurological complications of diabetes. Early diagnosis of the latter is quite a challenge and, thus, the problem of finding more reliable diagnostic modalities is rather pressing. In this review, an interdisciplinary approach to the said problem, high-end diagnostic methods, and clinical features of DPN are described.

Cornea and its changes in diabetes mellitus: the review

Diabetes mellitus (DM) is the most common endocrine disease, which makes it a priority among health and social problems. Ocular manifestations in diabetes often lead to patient disability. This review presents an analysis of morphological, experimental and clinical studies of the cornea in patients with diabetes mellitus, including original research, reviews and monographs of Russian and foreign authors from recent years. In addition, modern methods of corneal disease diagnosis are reviewed. Clinical and morphological changes in the diabetic cornea are discussed and early diabetic changes in all structural layers are indicated. The importance of changes to nerve fibres in diabetes is discussed and the correlation between the density of nerve fibres in the cornea and the density of epidermal nerve fibres is shown.