| Optic Nerve Head Drusen  Signs and Symptoms
A condition involving retained hyaline bodies in the anterior optic nerve,
optic nerve head drusen (ONHD) has been referred to in the literature by many diverse and
confusing names. Among the descriptive terms are congenitally elevated or anomalous discs,
pseudopapilledema, pseudoneuritis, buried disc drusen, and disc hyaline bodies. ONHD is
encountered in approximately 1 percent of the general population, and is bilateral in 70
percent of cases. The condition occurs primarily in Caucasians and is believed to
demonstrate an autosomal dominant inheritance pattern with incomplete penetrance.
Typically, patients with ONHD remain asymptomatic, and the finding is discovered only on
routine ocular evaluation. In some instances, however, the condition can present with
mildly decreased visual acuity and visual field defects. An afferent pupillary defect may
be noted if the condition is both significant and asymmetric. Reports of recurrent,
transient visual obscurations associated with disc drusen have also been documented.
The classic appearance of ONHD involves bilaterally elevated optic discs
with irregular or "scalloped" margins, a small or nonexistent cup, and unusual
vascular branching patterns that arise from a central vessel core. Often there are small,
refractile hyaline deposits visible on the surface of the disc and/or in the peripapillary
area. ONHD most often manifests on the nasal disc margin, but can be found within any part
of the nerve head. In younger patients, the disc elevation tends to be more pronounced and
the drusen less calcific, making them less visible ophthalmoscopically, and hence offering
a more challenging diagnostic dilemma. Unlike true disc edema, ONHD very rarely presents
with juxtapapillary nerve fiber edema, exudate, or cotton-wool spots.
Pathophysiology
There is no histopathological correlation between drusen of the optic nerve
head and retinal drusen; the former represent acellular laminated concretions, often
partially calcified, possibly related to accumulation of axoplasmic derivatives of
degenerating retinal nerve fibers. As mentioned, ONHD tend to remain "buried" in
children, but slowly become visible as they enlarge toward the disc surface and as the
overlying retinal nerve fiber layer progressively thins. They are usually
ophthalmoscopically detectable by the early to mid-teens, although these authors have seen
patients in their mid-20s who continue to display "buried drusen". Within the
optic nerve, the hyaline bodies are confined anterior to the lamina cribosa and thus can
compress and compromise the nerve fibers and vascular supply, leading to visual field
defects and disc hemorrhages. Along with slowly developing optic atrophy in extreme cases,
disruption of the juxtapapillary tissue can result in choroidal neovascular membrane
formation leading to subretinal hemorrhage and disciform retinal scarring.
Management
Although ONHD is typically classified as a benign condition, it can lead to
modest visual compromise. First and foremost, ONHD must be clearly differentiated from
acquired disc edema, which warrants immediate neurologic evaluation and treatment.
Management of ONHD includes prompt and proper diagnosis, which is aided greatly by the use
of ocular ultrasonography. The high reflectivity of the calcified hyaline bodies is
dramatically evident on B-scan ultrasonography, even at particularly low gain levels.
Careful evaluation of optic nerve function is imperative, and should include standard
Snellen acuity, contrast sensitivity, color vision testing, and threshold visual fields.
Photodocumentation should be obtained for future monitoring. It is also important for
patients to self-monitor their vision periodically, particularly because of the risk of
choroidal neovascular membrane formation. Should these membranes be noted or suspected,
intravenous fluorescein angiography is recommended, followed by laser photocoagulation as
indicated. More routine cases should be monitored every six to 12 months.
Clinical Pearls
Some suggest that the vast majority of congenitally
anomalous, elevated optic discs are likely associated with nerve head drusen. Recognize
the clinical features associated with ONHD in comparison to those features indicative of
true optic disc edema. In ONHD, expect a typically "normal" pink to
pinkish-yellow color, rather than a pale waxy disc or a hyperemic disc. In addition, a
spontaneous venous pulsation is present in about 80 percent of patients with ONHD, but is
absent in cases of true disc edema. Most importantly, recognize that while the disc
margins may be irregular in ONHD, rarely are they blurred or obscured.
Ultrasonography is probably the single most important
ancillary test to perform in adults with ONHD. This procedure should be performed on all
adult patients presenting with elevated optic discs that are not definitively identifiable
as true optic disc edema based upon ophthalmoscopic observation or history. Keep in mind,
however, that optic disc drusen are generally not calcified in children and adolescents.
Hence, ultrasonography may prove to be of little help in diagnosing these cases.
While visual fields are an important method of
documenting and monitoring optic nerve compromise secondary to ONHD, they are neither
uniform nor diagnostic. The more common patterns encountered in ONHD include nasal step
defects, enlargement of the physiologic blindspot, arcuate scotomas, sectoral field loss,
and altitudinal defects.
Other reports in this section
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