Optic disc drusen (ODD) refers to the presence of calcified hyaline bodies in the distal portions of the second cranial nerve, the optic nerve. This condition is congenital and may eventually interfere with vision. In most cases though, ODD is an incidental finding that doesn't pose any problem to the affected individual. Related terms are optic nerve head drusen and optic nerve drusen.
The vast majority of ODD patients is asymptomatic. If the condition does provoke any symptoms, those typically arise in youth or adulthood . The presence of calcified bodies within the optic disc may cause optic nerve dysfunction that, in turn, results in a mild loss of visual acuity and visual field defects. The more superficial those calcified bodies are located, the more likely they are to eventually interfere with vision. An assessment of the patient's visual field may reveal deficits in the inferior nasal section or in any other peripheral area. A general peripheral vision loss results in a concentric constriction. Also, an enlargement of the blind spot may be noted .
ODD most commonly affects both eyes and is more often seen in women than in men. Individuals with small, crowded optic discs may be predisposed for the development of ODD.
Calcified hyaline bodies may be located very close to the surface of the distal terminus of the optic nerve, the optic disc. In such cases, the ophthalmologist may observe characteristic anomalies while performing an examination of the ocular fundus : The calcified bodies may be seen directly; the optic disc may be raised or missing its central cup. The optic disc's edges may be blurred, and abnormal vascular structures may also be present. Very rarely, hemorrhages may be detected.
It may be challenging to distinguish superficial ODD from optic disc edema though , but the latter may be an indicator of more severe pathologies causing an increased intracranial pressure and should thus be ruled out. In order to differentiate both conditions, the ophthalmologist can make use of their distinct fluorescent behavior: ODD is associated with the presence of hyperautofluorescent particles, optic disc edema isn't. The main disadvantage of fundus autofluorescence is its low signal strength. It thus will only yield positive findings in ODD patients that carry calcified bodies in very close proximity to the retinal surface . Peak signals can be expected to be two orders of magnitude higher in fundus fluorescein angiography. Here, ODD may be identified upon the observation of a well-defined hyperfluorescence in the late phase . In contrast, diffuse leakage of the fluorescent dye is typical of optic disc edema.
Still, the maximum depth of tissue penetration is limited even in fundus fluorescein angiography. However, calcified bodies may in fact lie within deeper structures of the optic nerve and be thus not accessible using the aforedescribed techniques. In order to visualize these particles, imaging techniques like B-scan sonography, optical coherence tomography and computed tomography may be applied   .