Gonioscopy is a diagnostic procedure in ophthalmology (eye care) and is used to inspect the so-called chamber angle. The chamber angle (angulus iridocornealis) is an anatomic structure of the eye located between the cornea (cornea) and iris (iris). It consists of the following components:
- Swallow line – delicate gray line at the boundary between corneal endothelium (corneal inner surface) and trabecular meshwork.
- Trabecular ligament – sieve-like meshwork in the chamber angle, the posterior part of which is usually pigmented
- Scleral spur – whitish line between trabecular meshwork and ciliary body band.
- Ciliary body band – brownish band to which the iris base is attached.
In the chamber angle is the so-called Schlemm canal through which the aqueous humor, which is a nutrient fluid that washes around the lens and the inner surface of the cornea, drains or is reabsorbed. If this circulation is disturbed, so that the aqueous humor cannot be reabsorbed, e.g., due to a too narrow chamber angle, an increase of the intraocular pressure occurs. This results in a clinical picture known as glaucoma. Glaucoma (or glaucoma) is characterized by ongoing damage to the optic nerve caused by compression of the nerve fibers at the papilla (exit point of the nerve from the eye) with excavation (hollowing, protrusion) of the same. Glaucoma is one of the most common causes of blindness. Gonioscopy should be performed when glaucoma is suspected and in glaucoma patients. The purpose of the examination is to visualize the angle of the ventricle, as it is not visible to the naked eye. This is due to total reflection of light by the cornea. The goal is to detect the pathomechanisms (processes underlying the development of disease) of glaucoma, and the examination is also used to classify the width of the chamber angle in order to assess the risk of angle-closure glaucoma.
Indications (areas of application)
- Glaucoma – primary glaucoma e.g. angle closure glaucoma or secondary glaucoma caused by another eye disease: Neovascularization glaucoma, pigmentary glaucoma, obstruction of the angle of the ventricle by neoplasms such as retinoblastoma (tumor).
- Developmental disorders of the eye – eg, congenital (congenital) glaucoma, hydrophthalmos.
- Foreign body in the chamber angle
- Pre-, intra- or postoperative eye surgery – e.g. goniotomy.
- Rubeosis iridis – chamber angle neovascularization.
- Suspected tumor
- Uveitis – Inflammation of the middle skin of the eye consisting of the choroid (choroid), corpus ciliare (ciliary body) and iris (iris). Depending on the localization, there is either an anterior (front), intermediate (middle located) or posterior (back) inflammation or, in the case of complete disease of all structures, panuveitis.
- Cysts in the area of the ventricular angle
The procedure
Before the actual examination, the eye is anesthetized (numbed). The ophthalmologist places the gonioscope directly on the eye, and the use of contact gel may be necessary (substance applied between the gonioscope and the cornea so that both surfaces lie optimally on each other). Gonioscopy can be divided into a direct and an indirect procedure. Direct gonioscopy is performed, for example, with the help of a Barkan gonioscope. The device is used in cases of hydrophthalmos (infantile glaucoma) or goniotomy (surgical method in the treatment of congenital glaucoma) to produce an upright image of the chamber angle. Indirect gonioscopy is mainly used for general diagnosis of pathological changes of the chamber angle and during laser goniotomy. The Goldmann or Zeiss gonioscope from a lens with a built-in mirror and produces a mirror image of the opposite chamber angle. A variant is the intendation gonioscopy or indentation gonioscopy. In this procedure, corneal indentation is performed in parallel with gonioscopy to determine whether a narrowed or occluded chamber angle (e.g., in angle-closure glaucoma) can be opened by the pressure of aqueous humor. During the examination of the chamber angle, attention is paid to the following pathologic changes, which are particularly important in suspected glaucoma:
- Neovascularization (new vessel formation) causes a so-called neovascularization glaucoma.
- Opening angle of the chamber angle, if it is too small, angle-closure glaucoma may develop
- Pigmentation of the trabecular meshwork, indicating pigmentary glaucoma.
- Adhesion of the angle of the ventricle, here is also the risk of angle-closure glaucoma.
Gonioscopy can detect pathological changes in the chamber angle of the eye. If necessary, the severity of the disease can be determined. Gonioscopy is a noninvasive diagnostic procedure in ophthalmology that can provide important diagnostic information, especially in cases of suspected glaucoma.
