Gonioscopy in the diagnosis of glaucoma

Gonioscopy is a very important examination method for diagnosing and monitoring the treatment of patients with glaucoma. The main task of gonioscopy is the visualization of the configuration of the anterior camera angle.

Under normal conditions, the structures of the anterior chamber angle are not visible through the cornea due to the optical effect of total internal reflection. The essence of this optical-physical phenomenon lies in the fact that the light reflected from the anterior chamber angle is refracted inside the cornea at the cornea-air border. A gonioscopic lens (or gonioli) eliminates this effect because, by changing the angle of the lens-air boundary, it allows one to study the structures of the anterior chamber angle.

Gonioscopy can be direct or indirect, depending on the lens used, with an increase of 15-20 times.

[1], [2], [3], [4], [5], [6], [7], [8], [9], [10]

Direct gonioscopy

An example of a tool for direct gonioscopy is the Keppe (Koerre) lens. For research using this lens, you need a magnifying equipment (microscope) and an additional light source. The patient should be in the supine position.

Benefits:

• Direct gonioscopy is indicated for patients with nystagmus and altered cornea.
• Gonioscopy is used in children in the hospital with local anesthesia. Standard sedative therapy is possible if necessary. Lens Keppe allows you to explore both the angle of the anterior chamber and the posterior pole of the eye.
• Direct gonioscopy provides a panoramic angle estimate, allowing you to compare different sectors, as well as two eyes, if two lenses are installed at the same time.
• Retro-illumination is possible, which is very important for determining the nature of congenital or acquired pathology of the angle.

Disadvantages:

• With direct gonioscopy, it is necessary that the patient is in the supine position.
• The procedure is technically more complicated.
• An additional light source and magnifying equipment (microscope) are needed, but the optical quality of the image is worse than when examined with a slit lamp.

[11], [12], [13], [14]

Indirect gonioscopy

The angle is visualized with the help of a lens combined with one or several mirrors, which makes it possible to evaluate its structures opposite to the installed mirror. To evaluate the nasal quadrant, the mirror is placed temporally, but the upper and lower orientations of the image are preserved. The image is obtained using a slit lamp. Since the invention of the method of indirect gonioscopy Goldmann, which used a single-mirror gonio-lens, many types of lenses have been developed. Use lenses with two mirrors that allow you to examine all the quadrants when the lens rotates 90 °. Other lenses with four mirrors allow you to estimate the entire angle of the front camera, without rotating them. Goldmann lenses and the like have a contact surface with a large radius of curvature and diameter than the cornea, which requires the use of a viscous contact substance. When using Zeiss lenses (Zeiss) and the like, there is no need for a contact substance, since their radius of curvature coincides with that of the cornea. These lenses have a smaller contact surface diameter, and the space between the cornea and the lens is filled with a tear film.

Choosing the right gonio lens type is key to successful gonioscopy. To do this, consider a few points. Prior to the use of gonioliин, one can estimate the depth of the anterior chamber using the Van Herick-Schaffer method. If you assume a wide open angle, you can use any lens, since nothing will impede the visualization of the anterior chamber angle.

On the other hand, if it is assumed that the angle of the anterior chamber is narrow, it is preferable to use Goldman’s single or two mirror lenses or Zeiss lens. The mirrors in these lenses are located above and closer to the center, which allows visualization of structures that are otherwise not visible due to the frontal shift of the iridescentral lens diaphragm.

Imagine an observer standing at point A trying to see a house behind the hill. The hill in this example resembles the bulge of the iris. To solve this problem, the observer must move to a higher point - B, which will allow him to see the house, or move closer to the center (to the top of the mountain) - to point A 'or to point B', which is even better, since it will open a full view. House and its surrounding elements.

[15], [16], [17], [18], [19]

Method of gonioscopy

In each eye installs anesthetic, then conduct an examination using a slit lamp. Depending on the type of lens used, it may be necessary to have a viscous contact substance. Gonioles are carefully placed on the eye, trying to avoid deformation of the intraocular structures. To obtain a good image of the angle, the beam of light of the slit lamp should be perpendicular to the goniolimage mirror.

It is necessary to adjust the slit lamp during the examination process.

The patient is asked to look at the light source to assess the upper and lower corners.

The light source is tilted anteriorly, and the goniolize is slightly shifted downward, the patient is asked to look in the direction they want to be examined to assess the nasal and temporal angles.

These simple technical details are necessary to assess narrow angles and identify various angle structures, in particular the Schwalbe ring.

Elements of the anterior chamber angle

The structure of the angle of the front camera can be divided into two groups.

• The fixed part, consisting of the Schwalbe ring, trabecular meshwork and scleral spur.
• The movable part, which includes the anterior surface of the ciliary body and the place of attachment of the iris with its last fold.

The examiner should conduct a general examination to assess important aspects.

• The plane of the iris - the iris can be flat (wide angle) and very convex (narrow mil).
• The last fold of the iris and its distance from the Schwalbe ring are two elements for estimating the angle amplitude. The upper part of the corner is usually narrower than all the other parts.
• The root of the iris is the place of attachment of the iris to the ciliary body. This is the thinnest part, it is most easily shifted when the pressure in the back chamber rises. In myopia, the iris is larger and thinner, with a huge number of crypts, it is usually attached to the back of the ciliary body. On the other hand, in hypermetropia, the iris is thicker, attached anteriorly to the ciliary body, which creates a narrower angle configuration.
• Nodules, cysts, nevi and foreign bodies of the iris.

[20], [21], [22], [23], [24], [25]

Angle classification

During gonioscopy, the angle amplitude is determined, as well as the type of glaucoma, open-angle or angle-closure, each of which has its own epidemiology, pathophysiology, treatment and prevention. Schaffer's classification estimates the amplitude of the angle between the last fold of the iris and the trabecular Schwalbe ring network.

• Grade IV - 45 °.
• Grade III - 30 °.
• Grade II - 20 °, angle closing possible.
• Grade I - 10 °, probably a corner closure.
• Slit - angle less than 10 °, more likely the angle to close.
• Closed - the iris fits tightly to the cornea.

The Spaeth classification also takes into account details concerning the periphery of the iris, as well as the effect of depression on the angle configuration.

Uveitis When you take away, you can see the places of inhomogeneous pigment deposits, which gives a picture of the "dirty" angle.

Closed angle glaucoma. With closed angle glaucoma, the patchy areas of pigment deposition can be seen on any element of the anterior chamber angle, their presence indicates that the iris fits to this place, but there is no permanent attachment. Pigment spots and a narrow angle can be evidence of a postponed episode of acute closed angle glaucoma.

Usually in the area of the angle there is no vascularization. Sometimes you can see small branches of the arterial circle of the ciliary body. These branches are usually covered with a uveal network, form a circular sinuous structure or can converge radially to the iris sphincter. In the case of neovascular glaucoma, abnormal vessels cross the ciliary body and branch in the trabecular network. The contraction of fibroblast myofibrils accompanying abnormal vessels causes the formation of peripheral anterior synechiae and the closure of the angle.

[26], [27], [28], [29]

Use of gonioscopy for trauma

Contusion. When striking the cornea, a wave of liquid dramatically forms. This wave moves to an angle, since the irido-lens diaphragm serves as a valve, preventing the fluid from moving in the backward direction. This fluid movement can damage the angle structures, the severity of the damage depends on the force of the impact. Separation of the iris from the scleral spur at the site of attachment is iridodialysis.

Angle recession. The angle recession occurs when the ciliary body ruptures, its outer wall remains covered with the longitudinal part of the ciliary muscle.

Cyclodialysis Cyclodialysis - complete separation of the ciliary body from the sclera, as a result of which a message opens with the suprahoroid space. Cyclodialysis is often accompanied by hyphema.

Iridodialysis Iridodialysis occurs when the iris is torn off at its attachment to the scleral spur.

Causes of gonioscopy errors

When conducting gonioscopy, the researcher must remember that some actions distort the results of the study. Gonioscopic lens increases the amplitude of the angle (deepens it), too much pressure on the sclera causes the fluid to move to the corner.

Compression gonioscopy is invaluable in evaluating angle-closure glaucoma, especially for the differential diagnosis of iris overlay from true synechiae. For this type of gonioscopy it is recommended to use Zeiss gonioles. When compression gonioscopy mechanically affect the aqueous humor, which leads to a depression of the cornea, allowing the researcher to dynamically change the relative position of the iris. This procedure helps to distinguish a narrow angle from a closed one, as well as to determine the risk of its closure. Excessive pressure leads to the formation of folds on the Descemet's membrane, which makes it difficult to inspect the angle.

[30], [31], [32], [33], [34]