Gonioscopy

The anatomical structure which form the cornea ( cornea) and the iris in the anterior chamber of the eye is called the anterior chamber angle ( Angulus iridocornealis ). Through him, the aqueous humor flows out. Is he pathologically altered, it may cause a drain fault with intraocular pressure increase and the formation of glaucoma. Degenerative diseases of the chamber angle is the pathological correlate of chronic open-angle glaucoma and are therefore among the most common causes of blindness.

  • 3.1 implementation

Anatomy

It can be ( front to back ), the following structures are different (see figure):

  • Schwalbe line: it lies closest to the front and appears as a delicate gray line; it is the boundary between the corneal endothelium and trabecular meshwork.
  • Trabecular meshwork: A distinction is a front unpigmented share following the Schwalbe line with an off-white color and a functional rear, usually pigmented share. In the rear portion of the aqueous humor outflow via Schlemm's canal is done.
  • Scleral spur: the foremost portion of the sclera; he appears as a prominent, white line between functional trabecular meshwork and Ziliarkörperband, unless the structure is superimposed by a strong pigmentation.
  • Ziliarkörperband: Part of the ciliary muscle from the scleral spur and iris base; it appears gray to dark brown.

Clinical Significance

Investigation techniques

With the slit lamp of the chamber angle is not directly visible by the total reflection of the cornea, but only an indirect assessment of the anterior chamber angle width ( see below) by estimating the distance between the corneal surface and the iris (method according to van Herick ) possible. With the help of a contact glass is also a direct inspection of the chamber angle with the slit lamp possible ( gonioscopy, see below ).

As imaging techniques for morphological assessment of the angle the ultrasound biomicroscopy and Scheimpflug camera are available.

Width of the chamber angle

The width of the chamber angle is of clinical importance, since a close chamber angle is associated with an increased risk for the development of an acute glaucoma attack or chronic angle-closure glaucoma.

At higher hyperopia, cataract and in Asians of the chamber angle is often close.

Several systems have been proposed for the classification of chamber angle width, with the classification according to Shaffer has prevailed:

  • 0 degrees (0 °): closed chamber angle ( irido - corneal contact).
  • Grade I (10 °): very narrow chamber angle ( only Schwalbe line visible), shutter very likely.
  • Grade II (20 °): moderately tight chamber angle ( trabecular meshwork visible), closure possible.
  • Grade III (20-35 °): open chamber angle ( up to the scleral spur privacy), closure unlikely.
  • Grade IV ( 35-45 °): very broad chamber angle ( Ziliarkörperband visible), closure impossible.

A similar alternative classification is according to Scheie. Target these classifications it is essentially to estimate the risk of glaucoma attack by angle block.

Diseases

  • Embryonic development disorders: a prominent Schwalbe's line ( posterior embryotoxon ) may be associated with malformations ( Axenfeld -Rieger anomaly ) and a congenital glaucoma.
  • Degenerative changes of the trabecular meshwork be regarded as the cause of chronic open-angle glaucoma.
  • Pigment deposits in the chamber angle, which are usually located in the lower quadrant, a reference to a pigment dispersion glaucoma, or seizures may be made ​​angle block.
  • Abnormal vessels of the anterior chamber angle are typically branched out tender, extend in any direction. They are an indication of disease ( neovascular glaucoma, uveitis, Fuchs' heterochromic ).
  • Tumors of the anterior uvea ( ciliary body, iris )
  • Cysts of the iris
  • Foreign body in the anterior chamber angle

Operations of the chamber angle

Selective laser trabeculoplasty is a procedure on chamber angle to reduce intraocular pressure. The fistulating pressure lowering surgical procedures involve structures of the chamber angle. The chamber angle can also serve the maintenance of intraocular artificial lenses.

Gonioscopy

Gonioscopy is the most common ophthalmic procedures for the investigation of the chamber angle.

For optical and anatomical reasons, it is light that falls in the direction of the chamber angle, reflected from the corneal surface, so that the region faces a direct observation is not accessible. Therefore, the examination of the chamber angle with an additional optical aid, the contact glass (or gonioscope ) possible.

Implementation

Gonioscopy is performed with a contact glass, which is referred to in this context as gonioscope. A distinction is made between direct and indirect gonioscopy. Glasses for indirect gonioscopy (eg Goldmann three mirror glass, Zeiss four- mirror glass) are the most common.

  • The Goldmann three mirror contact glass has 3 levels: 2 levels for the study of retinal periphery and another for the study of the chamber angle ( tilt angle of 59 °). The examination is performed at the slit lamp to the surface anesthesia, with a viscous substance between the cornea and contact lens is required. By rotating the three-mirror contact glass 360 ° of the anterior chamber angle can be viewed circular.
  • The Zeiss glass mirror 4 has an inclination angle of 64 °. There is no rotation of the glass in the investigation is necessary. Due to the flatter curvature radius a viscous substance is not necessary. By applying pressure to the cornea can be achieved with the Zeiss glass a liquid redistribution in the anterior chamber so that the chamber angle is widened. Thus, an acute-angled, not observable chamber angles are widened so far that Goniosynechien can be viewed. Through this so-called Eindellgonioskopie an acute angle -closure glaucoma without Goniosynechien can be distinguished from a chronic angle closure glaucoma with Goniosynechien.

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