Pathogenetic Rationale for Transpupillary Thermotherapy and Argon-Helium-Neon Laser Pleoptics in Anisometropic Amblyopia

This dissertation is devoted to the study of the pathogenetic mechanisms of anisometropic amblyopia formation in children. The author examines the structural-functional state of the visual system, including nerve impulse conduction along the papillomacular bundle, retinal reception, and regional haemodynamics in the ocular vessels, in patients with anisometropic amblyopia before and after treatment.

Based on the identified disorders, a combined treatment method is substantiated, combining transpupillary thermotherapy of the optic nerve head with argon-helium-neon laser pleoptics (laser stimulation of the macular area of the retina). The work includes an assessment of the clinical effectiveness of this method and an analysis of the mechanisms of its action on various links in the pathogenesis of the disease.

Relevance of the problem.

Amblyopia is one of the causes of low vision in children [3]. It accounts for one third of all existing ophthalmic pathology and is among the most severe diseases of the organ of vision in children [25, 132, 160-162, 225].

According to contemporary views, the principal role in the formation of different types of amblyopia belongs to sensory deprivation resulting from refractive disorders (including anisometropia), reduced transparency of the optical media, or strabismus with impaired binocular vision during the maturation of the visual system and the formation of visual perception as a complex integrative process [179, 211].

Anisometropia is one of the disorders of the refractive capacity of the eyes in which the difference between the refractive power of the two eyeballs exceeds 2 diopters. Patients with high-degree anisometropia constitute a serious medical and social group owing to the rapid development of deep amblyopia in the "worse" eye, strabismus, and impairment of binocular functions in the absence of timely adequate correction.

The prevalence of anisometropia in the population, according to various authors, ranges from 2.5 to 54.8 % [186, 195]. Refractive and anisometropic amblyopia occurs in 2.3 % of preschool and school-age children [11, 130].

Anisometropic amblyopia is understood as reduced vision, more often unilateral, without visible lesions explaining this reduction, in which refractive anomalies cause blurred images on the retina. At the same time, the normal neurophysiological development of the visual pathways and visual cortical centres is impaired [1, 82].

Most researchers hold that in amblyopia morphofunctional disorders occur mainly in the subcortical visual centres and the visual cortex of the brain, i.e., in the central part of the visual analyser. Consequently, methods of its treatment are based primarily on the use of stimuli (light or structured) adequate to the visual analyser in order to activate the functioning of the fovea-cortical pathway. An important place among such methods in ophthalmology has been taken by laser pleoptics [4, 115, 174]. At present, argon-helium-neon laser pleoptics combined with binometry is recognized as an effective method of treating amblyopia [87, 203].

To date, the effectiveness of treatment of anisometropic amblyopia does not exceed 50-70 %. This is largely due to the absence of a holistic understanding of the patterns and mechanisms of the formation of this pathology, in particular the relationship between regional blood circulation and the structural-functional parameters of the visual system.

In recent years, studies of blood flow in the vessels of the eye and orbit have been actively developing and gaining increasing popularity. Considerable attention is paid to circulatory disorders in this vascular basin; their presence and severity are associated with the genesis of visual disorders [99, 210]. Individual studies indicate a decrease in haemodynamic parameters in the vascular system of the eye in the refractive form of amblyopia [94, 145].

Although combined methods of treating amblyopia that improve the blood supply of the eye are now widely used, there are no clear ideas about the mechanisms underlying their pathogenetic rationale.

At the same time, on the basis of studies conducted at the Irkutsk Branch of the S. N. Fyodorov Federal State Institution IRA Eye Microsurgery Complex, it has been established that the method of transpupillary thermotherapy of the optic nerve head makes it possible to purposefully influence the mechanisms providing regional blood flow. It was also noted that the application of this method in retinal vein thrombosis and anterior ischaemic optic neuropathy contributes to an increase in visual acuity parameters [103, 129, 171, 204].

Accordingly, it was hypothesized that the combination of laser pleoptics with transpupillary thermotherapy could be an effective method of treating anisometropic amblyopia.

All of the above determined the aim of the work: to elucidate the pathogenetic mechanisms of the formation of anisometropic amblyopia and to develop a treatment method based on the combined use of transpupillary thermotherapy and argon-helium-neon laser pleoptics, its pathogenetic rationale, and an assessment of its clinical effectiveness.

To achieve the stated aim, the following tasks were addressed:

1. To assess the state of the visual system in children with anisometropic amblyopia in order to identify the most important links in the pathogenesis of this disease.

2. To establish changes in the structural-functional parameters of the visual system in children with anisometropic amblyopia under the influence of transpupillary thermotherapy of the optic nerve head.

3. To elucidate the patterns of structural-functional changes in the visual system in children with anisometropic amblyopia after argon-helium-neon laser stimulation of the macular area of the retina.

4. To reveal the patterns of changes in the structural-functional state of the visual system in children with anisometropic amblyopia under the influence of transpupillary thermotherapy combined with argon-helium-neon laser pleoptics, and to determine the clinical effectiveness of this treatment method.

Scientific novelty.

For the first time it has been established that decreased conduction of nerve impulses along the papillomacular bundle and reduced regional blood circulation are important links in the pathogenesis of anisometropic amblyopia.

New are the data that improved conduction of nerve impulses along the visual fibres is the leading sanogenetic mechanism of argon-helium-neon laser pleoptics in anisometropic amblyopia.

It has been proven that the principal therapeutic mechanisms of transpupillary thermotherapy of the optic nerve head are increased blood flow in the posterior short ciliary arteries and the central retinal artery, improved neuroreceptor interaction, and improved conduction of nerve impulses along the papillomacular bundle.

Priority data show that the sequential application of transpupillary thermotherapy of the optic nerve head and argon-helium-neon laser stimulation of the macular area of the retina promotes increased conduction along the papillomacular bundle, enhanced regional blood flow, and a stable improvement of visual functions.

Main propositions submitted for defence:

1. The leading links in the pathogenesis of anisometropic amblyopia are: impaired conduction along the papillomacular bundle; interocular asymmetry; impaired reception in ganglion cells, the cone system, and the outer layers of the retina; reduced blood flow in the posterior short ciliary arteries and the central retinal artery; increased resistance and an elevated pulsatility index of these vessels.

2. The application of transpupillary thermotherapy of the optic nerve head followed by argon-helium-neon laser stimulation of the central fovea of the retina in children with anisometropic amblyopia leads to improved neuroreceptor interaction and conduction along the optic nerve fibres and the papillomacular bundle, and to enhanced regional blood circulation. Transpupillary thermotherapy followed by argon-helium-neon laser stimulation is a pathogenetically substantiated and effective method of treating anisometropic amblyopia.

Theoretical and practical significance of the work.

On the basis of the mechanisms of structural-functional disorders of the visual system in children with anisometropic amblyopia identified in the study, a new combined treatment method has been proposed. It has been proven that the application of transpupillary thermotherapy and argon laser pleoptics is pathogenetically substantiated, since these methods sequentially act on different links in the pathogenesis of the disease. The results of the study have been introduced into the clinical practice of the Irkutsk Branch of the S. N. Fyodorov IRA Eye Microsurgery Complex Federal State Budgetary Institution of the Ministry of Health and Social Development of Russia, the ophthalmology department of the Irkutsk Regional Children's Clinical Hospital, and the teaching process of the Department of Eye Diseases of the Irkutsk State Postgraduate Medical Training Academy.

Approval of the work.

• Conference "All-Russian Round Table 'Topical Problems of Strabismus Treatment'" with internet broadcast (Novosibirsk, 2010);

• Interregional scientific-practical conference with international participation (Orenburg, 2010);

• International scientific-practical conference on ophthalmosurgery "East - West" (Ufa, Bashkortostan, 2010);

• All-Russian scientific-practical conference with international participation "Fyodorov Readings - 2011", S. N. Fyodorov Federal State Institution IRA Eye Microsurgery Complex of Rosmedtekhnologii (Moscow, 2011);

• Extended meeting of the scientific-medical council of the Irkutsk Branch of the S. N. Fyodorov Federal State Institution IRA Eye Microsurgery Complex (Irkutsk, 2011).

Publications.

Fifteen scientific papers on the topic of the dissertation have been published, including 6 in leading peer-reviewed journals recommended by the Higher Attestation Commission of the Ministry of Education and Science of the Russian Federation.

Volume and structure of the dissertation.

The dissertation is presented in 120 pages of typewritten text and contains an introduction, a literature review, a description of research and treatment methods, a clinical characterization of patients, two chapters of the author's own research results and their discussion, a conclusion, conclusions, and a bibliography (207 sources in Russian and 133 in foreign languages). The text of the dissertation is illustrated with 13 figures and 4 tables.