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Sonography in optic disk drusen: imaging findings and role in diagnosis when funduscopic findings are normal.

OBJECTIVE
Optic disk drusen are relatively benign lesions of the eye but can cause visual symptoms and may occasionally mimic papilledema on funduscopy. We studied the range of sonographic findings and determined if sonography can be used to diagnose this condition in the absence of typical funduscopic findings.


SUBJECTS AND METHODS
Sonography of the eyes was performed in 12 patients with known or suspected optic disk drusen by using a 10-MHz transducer. Optic disk drusen were diagnosed clinically in 16 of the 24 eyes. The funduscopic appearance was typical in 11 eyes and atypical in five eyes. In these five patients, the diagnosis was made on the basis of an abnormal appearance of the disk and either a strong family history of drusen (four patients) or funduscopic findings that were typical of drusen in the opposite eye (one patient).


RESULTS
The head of the optic nerve was abnormal in 19 of 24 eyes on sonography and in 16 on funduscopy. In all cases with abnormal findings on sonograms, an ovoid echogenic lesion was evident at the junction of the retina and the optic nerve. The lesions varied in size from 1.5 to 4.0 mm in diameter and from 1 to 3 mm in thickness and projected posteriorly rather than into the vitreous body. Calcification was evident on sonograms in 16 cases. The degree of acoustic shadowing was proportional to the size of the echogenic focus. In the three cases in which funduscopic findings were normal, sonography showed small drusen deposits. In the five eyes that showed disk abnormality but were not typical of drusen on funduscopy, sonography showed lesions of varying size; cases with typical funduscopic appearances tended to show large lesions on sonography.


CONCLUSION
Optic disk drusen can be diagnosed on the basis of their typical sonographic appearance even in the absence of typical funduscopic findings. Optic disk drusen may be seen incidentally when sonograms are made for other conditions, and the finding should not be confused with more serious lesions of the optic nerve.