Gonioscopy is biomicroscopic examination of the anterior chamber angle of the eye, where aqueous humor gains access to Schlemm’s canal. It enables the glaucomas to be classified into two main groups, angle-closure glaucoma and open-angle glaucoma. Gonioscopy is helpful diagnostically, prognostically, and therapeutically in glaucoma.
METHODS OF GONIOSCOPY
Because of the curvature of the cornea and the difference in the index of refraction between the eye and the air, light rays coming from the far peripheral iris, the angle recess, and the trabecular meshwork undergo total internal reflection ( Fig. 6-1 ), which prevents the clinician from examining these structures without the use of a contact lens to eliminate the air–cornea interface. Three types of gonioscopic contact lenses are available: (1) those whose surface is slightly larger than the cornea and that require a gonioscopic coupling gel (e.g., Goldmann lens); (2) those whose surface is smaller than the cornea and that use the patient’s tear film as a coupling agent (e.g., Zeiss or Sussman four-mirror lens); and (3) those whose surface is quite large, that use saline or similar fluid as a coupling agent, and that necessitate that the patient lie supine (e.g., Koeppe lens) ( Fig. 6-2 ). Devices from the first two groupings are most popular because they can be used under standard examination circumstances, with the patient sitting at the slit lamp. Advantages and disadvantages of the direct and indirect methods are listed in Table 6-1 .
|Indirect gonioscopy||Equipment and examination posture are routine and familiar||Difficult to see laterally into narrow angles|
|Fast||Retroillumination is difficult|
|Facilitates indentation gonioscopy||Orientation initially confusing|
|Slit lamp gives controlled illumination and high magnification for detailed viewing||May require a special coupling agent|
|Direct gonioscopy||Greater patient comfort||Cumbersome and time-consuming|
|Binocular comparison possible||Special equipment required|
|Orientation simple||Less magnification, with loss of detail|
|Orientation relevant for surgical procedures (e.g., goniotomy, trabeculodialysis, goniosynechialysis)|
|Excellent for teaching|
|Can see over convex iris|
|Can assess dynamic effects of pupillary light response on angle configuration|
|Most comparable to ultrasonic biomicroscopy findings|
Goldmann and Zeiss lenses (indirect method)
The Goldmann and Zeiss types of lenses are termed indirect gonioscopic lenses because they have mirrors by which the angle is examined with reflected light ( Figs 6-3 and 6-4 ). The patient can be examined with the light and magnification of the slit lamp and corneal microscope. The magnification obtained depends on the power of the microscope and should be 16X to 20X.