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The classification of glaucoma relies heavily upon knowledge of the
anterior segment anatomy, particularly that of the anterior chamber
angle. Gonioscopy refers to the techniques used for viewing the
anterior chamber angle of the eye for evaluation, management and
classification of normal and abnormal angle structures. The anterior
chamber is commonly evaluated during slit lamp biomicroscopy,
but the chamber angle is hidden from ordinary view because of
total internal reflection of light rays emanating from the angle
structures. (Fig. 1).
Figure 1: The normally hidden anterior
chamber angle: The anterior chamber angle is not routinely seen
during slit lamp biomicroscopy because light rays emanating from
the chamber angle are refracted back into the eye (total
internal reflection of light rays). During slit lamp
examination, the anterior chamber may be described as 4+ deep,
but without gonioscopy, the additional diagnostic clues of
disease are forever hidden from ordinary view.
It requires additional effort, skill and patient
co-operation to view the normally concealed chamber angle by either
indirect (angle structures -- Fig. 2-- viewed through a mirror) or
direct (angle structures -- Fig. 3 -- viewed directly) gonioscopic
techniques. Without gonioscopy, it is impossible to classify the
glaucoma properly.
Figure 2: Indirect gonioscopy: A
special contact lens overcomes the problem of total internal
reflection of light rays from the chamber angle. The bending of
light rays back into the chamber angle at the cornea-air
interface is eliminated when a contact lens (gonioprism) is
placed on the cornea. With this method of indirect gonioscopy,
the light rays are reflected by a mirror in the gonioprism to
the observer and focused with the slit lamp biomicroscope. The
Goldmann and Zeiss lenses are examples of indirect goniolenses.
Figure 3: Direct gonioscopy: With
direct gonioscopy, the goniolens allows chamber-angle light rays
to be refracted directly through the cornea-contact lens
interface and a hand-held gonioscope is required for
magnification and illumination. The Koeppe lens is an example of
a direct goniolens with antireflective coating, and is best with
laser therapy (Fig. 4 and Table 1).
On a busy patient day, the Zeiss or equivalent
gonioprism (Posner, Sussman) is the most convenient contact lens for
rapidly evaluating any chamber angle, and the Goldmann or equivalent
gonioprism with antireflective coating is best for laser therapy
(Fig. 4 and Table 1).
Figure 4: The two most common contact
lenses for gonioscopy.
Table 1 (below): Contact Lenses Used
for Gonioscopy
| Contact Lens |
Type |
Advantage |
Disadvantage |
| Koeppe |
Direct |
Convenient for
examination under anesthesia (EUA), no angle distortion,
able to view fundus, easiest for angle photography,
excellent anatomic view, panoramic view. |
Patient must be
in supine position, laborious examination patient dislikes,
examiner must change position, gonioscope or operating
microscope required. |
| Barkan |
Direct |
Surgical
goniolens with blunted side allows access for goiotomy,
variable sizes. |
Same as Koeppe. |
| Goldman 3-Mirror |
Indirect |
Excellent
gonioprism for neophyte to learn anatomy, viscous bridge
creates suction effect stabilizing eye for examination and
laser therapy. |
Goniogel required
for best view which obscures patient's vision and may
compromise further same-day diagnostic tests, corneal
abrasion in compromised cornea, part of angle hidden in
narrow-angeled eyes, time consuming when necessary to
evaluate both eyes, artificial narrowing of the angle. |
| Zeiss 4-Mirror |
Indirect
|
Rapid evaluation
without goniogel, no corneal compromise with goniogel,
further same-day diagnostic tests not compromised,
indentation or compression gonioscopy allows expert
evaluation of narrow-angled eyes with hidden anatomy, patient
friendly, slit lamp friendly with minimal movement to see
360°,option for compression to perform indentation gonioscopy. |
Must first master
Goldmann gonioprism, more hand-eye co-ordination necessary
than for Goldmann gonioprism, Unger handle required, easy to
apply excessive force causing corneal folds with poor view
of angle. |
More technical information about gonioscopy is available
by clicking here. This PDF file will appear in a new browser
window; as the document contains many images, it might take short
while to fully load.
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