[Opportunities for confocal and laser biomicroscopy of corneal nerves in diabetic polyneuropathy]

[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.

[The effects of corneal collagen cross-linking on the corneal structure in keratoconus]

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.

[Changes in corneal nerve fibers after microinvasive cataract surgery (a preliminary report)]

INTRODUCTION

Potential changes in corneal nerve fibers (CNF) induced by cataract phacoemulsification remain insufficiently studied. The need for research in this direction is dictated by a number of circumstances: introduction of corneal confocal microscopy into clinical practice, the need for phaco surgery in the presence of corneal changes of various genesis, the possible negative impact of laser radiation during hybrid (femtosecond laser-assisted) phacoemulsification.

PURPOSE

To assess the changes in CNF after various methods of microinvasive cataract surgery.

MATERIAL AND METHODS

The studies were conducted in patients aged 50 to 60 years who underwent standard ultrasound and hybrid phacoemulsification; the patients were respectively divided into two groups (30 surgeries each). The algorithm for assessing the state of CNF involved laser confocal microscopy using original software. To quantify the state of the nerves, two coefficients were used: CNF orientation anisotropy (KΔL) and CNF orientation symmetry (K_sym).

RESULTS

Regardless of the surgery technique, tendencies were noted for the orientation anisotropy coefficient to decrease and the orientation symmetry coefficient to increase, which are conditionally comparable with previously identified age-related changes in CNF. After hybrid phacoemulsification, a decrease in the orientation anisotropy coefficient 2-2.5 months after the intervention turned out to be statistically less significant compared to the standard ultrasound technique.

CONCLUSION

Further research should be aimed at analyzing the long-term results of both microinvasive phacosurgery techniques and the «classical» extracapsular cataract extraction, which remains the method of choice in a number of clinical situations.

[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.

[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.

[Anatomical and functional features of corneal nerve fibers and methods of their evaluation]

Condition of the ocular surface greatly depends on functional integrity of corneal nerve fibers. Improving the methods used to study corneal nerve fibers allows their condition to be timely evaluated and adequately interpreted. The article reviews the structure, function, chemical composition of corneal nerve fibers, specifics of their innervation, as well as application of modern methods of their evaluation in diagnostics of various pathological conditions.

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.

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.