GLAUCOMA
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The Gonioscopy

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).

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.





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).

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.

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