Optic Disk Ophthalmoscopy

The optic disk has a physiologic indentation known as the optic cup. In the presence of persistently elevated intraocular pressure, the optic cup becomes enlarged and can be evaluated by ophthalmoscopy.

Stereoscopic examination of the optic disk through a slit-lamp biomicroscope fitted with a contact lens provides a three-dimensional image. The optic cup may be examined stereoscopically with the pupil dilated.

H The optic nerve is the eye's "glaucoma memory." Evaluating this structure will tell the examiner whether damage from glaucoma is present and how far advanced it is.

Normal optic cup (Fig. 10.8): The normal anatomy can vary widely. Large normal optic cups are nearly always round and differ from the vertical elongation of the optic cup seen in eyes with glaucoma.

Documenting the optic disk: Recording findings in sketches is suitable for routine documentation and follow-up examination of the optic disk. Photographing the optic disk with a fundus camera permits longer-term follow-up. Stereoscopic photography also provides a three-dimensional image. Optic disk measurement and tomography can provide precise measurements of the optic nerve.

Optic disk measurement. The area of the optic disk, optic cup, and neuroreti-nal rim (vital optic disk tissue) can be measured by planimetry on two-dimensional photographs of the optic nerve.

Fig. 10.8 The optic disk is sharply demarcated. It is level with the retina, and its color indicates vital tissue. The small central optic cup (arrow) is discernible as brighter area.

Optic disk tomography. Modern laser scanning ophthalmoscopes permit three-dimensional documentation of the optic nerve (Fig. 10.9).

Glaucomatous changes in the optic nerve: Glaucoma produces typical changes in the shape of the optic cup. Progressive destruction of nerve fibers, fibrous and vascular tissue, and glial tissue will be observable. This tissue atrophy leads to an increase in the size of the optic cup and to pale discoloration of the optic disk (Fig. 10.10).

H Progressive glaucomatous changes in the optic disk are closely associated with increasing visual field defects (Figs. 10.11 a - d).

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