Psychophysical methods for studying intraocular pressure in glaucoma

In a broad sense, psychophysiological testing means a subjective evaluation of visual functions. From a clinical perspective for a patient with glaucoma, this term refers to the perimetry for evaluating the peripheral vision of the eye. Given the early onset of peripheral vision impairment in glaucoma compared to central vision, the evaluation of visual fields is useful from both diagnostic and therapeutic positions. It is important to note that the use of the term "peripheral vision" does not always imply a distant periphery. In fact, most of the visual field defects in glaucoma occur paracentrally (within 24 ° from the fixation point). The term "peripheral vision" should be understood as everything except the central fixation (ie, more than 5-10 ° from the center).

The presented information is aimed at demonstrating representative models of visual fields in glaucoma, and does not provide for a comprehensive discussion of perimetry. There is a literature devoted exclusively to a more detailed description of perimetry, as well as atlases of perimetric data.

[1], [2], [3], [4]

Diagnostics

Automated monochromatic examination of the visual fields as part of the initial assessment of the patient's condition with suspicion of glaucoma is important in the diagnosis of glaucomatous lesion of the optic nerve. Anomalies of the visual fields are important for the localization of lesions along the entire visual tract from the retina to the occipital lobes of the brain. Glaucomatous defects in the field of vision, as a rule, are associated with the lesion of the focal nerve.

It is very important to note that the so-called defects of the optic nerve fields (ie, defects as a result of damage to the optic nerve) do not in themselves serve as a diagnostic sign of glaucoma. They should be considered in conjunction with a characteristic type of optic nerve and anamnesis. Indices of intraocular pressure, gonioscopy results and anterior segment visualization data can help determine the specific type of glaucoma. All optical neuropathies (anterior ischemic optic neuropathies, compression optic neuropathies, etc.) lead to the formation of defects in the optic nerve fields.

It is also extremely important to note that the absence of defects in the optic nerve fields does not exclude the diagnosis of glaucoma. Despite the fact that in 2002 the automated achromatic static field study was recognized as the "gold standard" for evaluating the functions of the optic nerve, the sensitivity limit of this method in determining the loss of ganglion cells is still limited. Clinical and experimental data indicate that the earliest visual field defects detected by this method correspond to the loss of approximately 40% of ganglion cells.

[5], [6], [7], [8], [9]

Introduction

Automated achromatic static examination of the visual fields in parallel with the serial evaluation of the optic nerve state remains the "gold standard" of observation in glaucoma. To protect the optic nerve from the damaging effect of an elevated ophthalmic process, scientists are trying to reach the target level of intraocular pressure. The target level of intraocular pressure is an empirical concept, since its level must be determined by itself. Automated achromatic static examination of visual fields and serial evaluation of the optic nerve state - the ways by which it is determined whether the empirically achieved level of pressure is effective to protect the optic nerve.

Description

Perimetry is necessary to detect the limit of vision at a particular place in the field of vision. The limit of vision is defined as the minimum level of light perceived at a given field of view (retinal sensitivity). The limit of vision differs from the lowest level of light energy, which stimulates the photoreceptor cells of the retina. Perimetry is based on the patient's subjective perception of what he or she can see. Thus, the limit of vision is "psychophysical testing" - a certain level of cognitive and intra-retinal perception.

The highest limit of vision is typical for the central visual fossa, which is the center of the field of vision. As you move to the periphery, sensitivity decreases. The three-dimensional model of this phenomenon is often called the "hill of vision." The field of view for one eye is 60 ° up, 60 ° nasal, 75 ° down and 100 ° temporal.

There are two basic methods of perimetry: static and kinetic. Historically, various forms of kinetic perimetry were first developed, in general they are performed manually. The visual stimulus of known size and brightness is moved from the periphery from outside the vision to the center. At a certain moment, it passes the point when the subject begins to perceive it. This is the limit of vision in a given place. The study continues with various stimuli of different size and brightness, creating a topographic map of the "island of vision". Goldmann tried to create a map of the entire field of vision.

A static investigation of the field of vision is concluded in the representation of visual stimuli of various sizes and brightness at fixed points. Despite the fact that there are a lot of different methods for determining the limit of vision, most of them follow a basic principle. The researcher begins the perimetry with a presentation of high-brightness stimuli, at intervals, presents stimuli of lesser brightness until the patient ceases to see them. Then, as a rule, the test is repeated, representing stimuli with gradually increasing brightness and smaller intervals, until the patient again ceases to perceive the stimulus. The resulting brightness of light is the limit of vision in a given field of view. In general, the static investigation of the fields of view is automated, when it is performed, white stimuli are presented on a white background, and therefore the name of the method is an automated achromatic static field of vision study. There are many machines that carry out this research, among them Humphrey ( Allergan, Irvine, CA), Octopus (Octopus) and Dicon (Dicon). In our work, we prefer Humphrey.

Many research algorithms have been developed, such as the full vision limit, FASTPAC, STATPAC, the Swedish interactive vision limit (SITA) algorithm, etc. They differ in duration and insignificantly - with respect to the depth of the defect of the field of view.

Frequent defects in visual fields found in patients with glaucoma

With glaucoma, the defects are located in the optic nerve and focal in the trellis plate. In the study of visual fields, their defects have relatively specific manifestations, which is associated with the anatomy of the retinal layer of nerve fibers. This layer consists of axons of ganglion cells and is projected through the optic nerve to the lateral geniculate nucleus.

The axons of ganglion cells located nasally to the optic nerve disk go straight to the disc; lesions of the optic nerve, affecting fibers from this region, give a temporal wedge-shaped defect. Axons of ganglion cells located temporally to the optic nerve are bent in it. The line that crosses the central visual fossa and optic nerve is called a horizontal suture. Ganglion cells located above this seam are bent higher and direct the fibers to the supra-temporal area of the optic nerve. For fibers of ganglion cells located temporally to the optic nerve and below the horizontal seam, the opposite direction is characteristic.

Lesions of the optic nerve, affecting fibers from the region located temporally to the nerve, give both nasal steps and arcuate defects. Nasal stairs have their name not only because of nasal localization, but also because such defects are located in the horizontal meridian region. The horizontal seam is the anatomical basis of these defects. Arcuate defects received their name in appearance. Nasal step and arched defects are encountered much more often than temporal wedge defects. With the progression of glaucoma, multiple defects can be detected in one and the same eye.