Patterns and Mechanisms of Formation of the Functional Angular Block in Angle-Closure Glaucoma

The dissertation is devoted to the study of the patterns and mechanisms of formation of the functional angular block (FAB) in angle-closure glaucoma. FAB is considered as a hidden (latent) stage of angle-closure glaucoma, characterized by a narrow anterior chamber angle, anterior displacement of the lens-iris diaphragm, deep posterior chamber, anterior position of the ciliary processes, impaired hydrodynamics, and hidden pre-trabecular retention. A comparative analysis of the structural and functional state of the visual system in patients with FAB, individuals in the control group, and patients with early stages of angle-closure glaucoma with intermittent and primarily chronic course was conducted.

The research was carried out at the State Budgetary Institution "East Siberian Scientific Center of the Siberian Branch of the Russian Academy of Medical Sciences" in Irkutsk. The work includes a literature review, a description of research methods, and clinical analysis. The pathogenetic mechanisms of FAB formation were identified, differential diagnostic criteria were developed based on discriminant analysis, and a conceptual scheme for the transition of functional angular block to the clinical stage of angle-closure glaucoma was constructed. The results were published in eight works.

Relevance of the study

It is known that approximately 67 million people worldwide suffer from glaucoma. In industrially developed countries, among individuals over 40 years of age, the prevalence of glaucoma reaches 1.7% of the total number of eye diseases. In the nosological structure of primary visual disability, glaucoma has taken first place in the world. Its prevalence in the Irkutsk region is 28 per 1,000 population (Shchuko A.G., Yuryeva T.N., Chekmareva L.T., Malyshev V.V., 2004).

One of the forms of this disease is angle-closure glaucoma (ACG), which accounts for up to 30% of all cases of primary glaucoma (Nesterov A.P., 1995).

According to modern concepts, up to 80-90% of ACG clinically follows an intermittent and primarily chronic course, and it is more frequently encountered among the Mongoloid population type, exceeding the prevalence of the disease among individuals of European nationality by tens of times (Egorova E.V., Bessarabov A.N., Faizieva U.S., 2003). Numerous studies associate the frequency of ACG with anatomical features of the eyeball structure, regarding them as predisposing factors to the development of the disease (Faizieva U.S., 2002). However, the informativeness of individual anatomical parameters or their combination in the development of ACG and its clinical course variants remains controversial, as does the interpretation of predisposing and provoking factors (Shilkin G.A., 1982; Lu D.R., 1986).

It is known that the most common type of obstruction of access to the filtering zone of the anterior chamber angle of the eye is its blockage by the iris root - the so-called angular form. The resulting angular block is initially functional, subsequently becoming organic (synechial) or combined. Attempts to separate pre-glaucoma or, according to the terminology of some authors, so-called prodromal, hidden, latent glaucoma (Volkov V.V., 1985) or functional angular block (Akopyan V.S., 1982) as an independent nosological form were undertaken long ago. However, even today, different viewpoints exist in the literature on this matter. The mechanisms of formation of the functional angular block (FAB), the patterns of changes in other eye structures under these conditions, are not fully understood. The criteria for diagnosis and differential diagnosis of FAB with early stages of ACG have not been determined.

All of this determined the main goal of the work: to reveal the patterns and mechanisms of formation of the functional angular block, which is a hidden form of angle-closure glaucoma, and to develop on this basis criteria for its differential diagnosis.

To achieve the stated goal, the following tasks were sequentially addressed in the work:

1. To conduct a comparative analysis of the structural and functional state of the visual system in patients with functional angular block and individuals in the control group.

2. To conduct a comparative analysis of the structural and functional state of the visual system in patients with functional angular block and patients with early-stage angle-closure glaucoma with intermittent course.

3. To conduct a comparative analysis of the structural and functional state of the visual system in patients with functional angular block and patients with early-stage angle-closure glaucoma with primarily chronic course.

4. To develop differential diagnostic criteria for functional angular block with early stages of angle-closure glaucoma with intermittent and primarily chronic course.

5. To develop a conceptual scheme for the inclusion of pathogenetic mechanisms of formation of the functional angular block and transition to the clinical stage of angle-closure glaucoma.

Scientific novelty

Pathognomonic patterns of structural and functional changes of the visual system for functional angular block were identified for the first time. New are the data that, in functional angular block, the characteristic structural features of the iridociliary zone include: anterior displacement of the lens-iris diaphragm with deepening of the posterior chamber, convex iris profile, anterior position of the ciliary processes, small distance between the iris root and the trabecular zone, which cause impairment of communication between the anterior and posterior chambers of the eye and deterioration of hydrodynamics.

It was established for the first time that in functional angular block there are high correlational dependencies between the structural elements of the eye and coordinated changes in the outflow facility of aqueous humor with the value of intraocular pressure after performing the Heimburg load test, as revealed by multifactor regression analysis, which may indicate the presence of hidden pre-trabecular retention.

Differential criteria for the structural and functional state of the visual system in normal conditions and in functional angular block were developed based on the application of discriminant analysis. These include anterior chamber depth, Lowe coefficient, intraocular pressure after the Heimburg test, Becker coefficient, electroretinographic threshold of the eye, optic disc excavation, refraction, visual field, and patient sex.

It was proven for the first time that the parameters of the anatomical structure of the eye and the indicators of visual system function in patients with functional angular block significantly differ from the indicators of patients with early-stage angle-closure glaucoma with intermittent course and primarily chronic course.

It was established that the differential criteria for the structural and functional state of the visual system in functional angular block and early-stage angle-closure glaucoma with intermittent course are: anterior chamber depth, degree of openness, profile, degree of pigmentation of the anterior chamber angle, Becker coefficient, minute volume of aqueous humor production, optic disc excavation, visual field, and presence of glaucoma in the fellow eye. In angle-closure glaucoma with primarily chronic course, these criteria are: true intraocular pressure, Becker coefficient, degree of openness, pigmentation of the anterior chamber angle, Forbes test, optic disc excavation, and visual acuity.

The parameters of linear discriminant equations that allow differential diagnosis between normal conditions, functional angular block, and early clinical stages of angle-closure glaucoma were determined for the first time. A graph of remoteness (closeness) was constructed between the visual system states of all four studied groups in an 11-dimensional feature space, enabling a quantitative representation of their differences.

Overall, it has been demonstrated that functional angular block is an independent pathological state of the visual system and represents a latent stage of angle-closure glaucoma.

The theoretical and practical significance of the work lies in the fact that the patterns of structural and functional changes of the visual system in functional angular block were established and the mechanisms of its formation were identified. It was proven that the parameters of the anatomical structure of the eye and the indicators of visual system function in patients with FAB significantly differ from those of the control group and patients with early-stage ACG with intermittent and primarily chronic course, which made it possible to identify FAB as an independent (latent) stage of ACG. Differential diagnostic criteria for functional angular block with early stages of ACG were developed. The created computer differential diagnostic program improved the accuracy and objectivity of diagnosing FAB and early stages of ACG, which made it possible to determine the pathogenetic direction of treatment.

Main provisions for defense:

1. Functional angular block is a latent stage of angle-closure glaucoma, characterized by a narrow anterior chamber angle, anterior displacement of the lens-iris diaphragm, deep posterior chamber, anterior position of the ciliary processes, hidden pre-trabecular retention, and impaired ocular hydrodynamics, at which laser iridectomy allows restoration of the relationship of the anatomical structures of the anterior segment of the eye, hydrodynamics, and prevention of further glaucoma progression.

2. Anterior chamber depth and closed angle, organic changes in the outflow pathways, pronounced disturbances of aqueous humor circulation, decreased minute volume of aqueous humor production, and glaucomatous optic disc excavation are differential diagnostic criteria for early stages of angle-closure glaucoma with intermittent and primarily chronic course, distinguishing them from functional angular block.

Practical significance of the work

The main provisions of the work were reported and discussed:

- At the scientific-practical conference "Fedorovsky Readings." Moscow - 2003.

- At the interregional conference of ophthalmologists dedicated to the 40th anniversary of the children's eye service of Krasnoyarsk Krai. Krasnoyarsk - 2003.

- At the II International Conference of Ophthalmologists of the Black Sea Region. Odessa - 2004.

- At the jubilee scientific-practical conference "Current Issues of Ophthalmology." Tomsk - 2004.

- At the jubilee scientific-practical conference. Tambov - 2005.

- At the VIII All-Russian Congress of Ophthalmologists. Moscow - 2005.

- At the expanded meeting of the scientific-methodological council of the Irkutsk branch of the MNTC "Microsurgery of the Eye" and the city society of pathophysiologists. Irkutsk - 2005.

- At the meeting of the expert commission of the dissertation council D 001.054.01 at the State Budgetary Institution "East Siberian Scientific Center of the Siberian Branch of the Russian Academy of Medical Sciences" (Irkutsk, 2006).

Publications

Eight works on the dissertation topic have been published.

Structure and volume of the dissertation

The work contains an introduction, a literature review, a description of research methods, and three chapters of original results. The reference list contains 299 sources, of which 154 are by Russian and 145 by foreign authors. The dissertation text is presented on 138 pages of typewritten text, illustrated with 19 figures and 12 tables.