OPTIC DISC DRUSEN

Signs and Symptoms

Optic disc drusen (ODD) represent a condition involving retained hyaline bodies (products of degenerated retinal ganglion cell axoplasmic transport, also known colloid bodies) in the anterior, prelaminar portion of the optic nerve.

ODD and the clinical presentation they create have been referred to in the literature by many diverse and confusing names, including congenitally elevated or anomalous discs, pseudopapilledema, pseudoneuritis, buried disc drusen and disc hyaline bodies.1-7 ODD are relatively uncommon, occurring in less than 2% of the general population.1 As an entity, it has also been described as occurring exclusively in Caucasians; however, these authors have occasionally encountered ODD in patients of color. 2

Typically, patients with ODD present and remain without symptoms, with the finding disclosed only upon routine ocular evaluation. In some instances, the condition can present with mildly decreased visual acuity and visual field defects.2-5 An afferent pupillary defect may be noted if the condition is both significant and unilateral or asymmetric.2 Reports of recurrent, transient visual obscurations associated with disc drusen have also been documented.6,7

The classic appearance of ODD involves unilateral or bilaterally elevated optic discs with irregular or “scalloped” margins, a small or nonexistent cup and unusual vascular branching patterns (i.e., marked bifurcations and trifurcations) 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. ODD 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 calcified and discrete, making them less visible ophthalmoscopically and hence offering a more challenging diagnostic dilemma. Unlike true disc edema, ODD does not present with juxtapapillary nerve fiber edema, exudates or cotton-wool spots.

One report on 100 eyes with ODD noted the following ophthalmoscopic features: visible drusen (52%), blurred edges (84%), raised optic disc (74%), absence of optic disc cupping (69%), absence of venous pulse (54%), abnormal vascular branching (81%), presence of cilioretinal vessels (42%), peripapillary atrophy (56%) and hemorrhages (2%).8

Pathophysiology

ODD are bilateral in 70-80% of cases. They have been purported to demonstrate an autosomal dominant inheritance pattern with incomplete penetrance.2,9,10 Clinicians should realize that 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.

ODD are “buried” in children, but slowly become visible as they enlarge toward the disc surface and as the overlying retinal nerve fiber layer progressively thins.10,11 They are usually ophthalmoscopically detectable by the early to mid-teens, although these authors have seen patients in their mid-twenties who continue to display “buried drusen.” Within the optic nerve, the hyaline bodies are confined anterior to the lamina cribrosa and thus can compress and compromise the nerve fibers and vascular supply, leading to visual field defects and disc hemorrhages.2,4,7,12,13

Along with slowly developing optic atrophy in extreme cases and possible venous occlusion, disruption of the juxtapapillary tissue can result in choroidal neovascular membrane formation, leading to subretinal hemorrhage with its attendant complications.14-17

Management

While ODD is typically considered a benign condition, it can lead to modest visual compromise and in rare instances, devastating vision loss.18-20 First and foremost, ODD must be clearly differentiated from acquired disc edema, a situation that warrants prompt neurologic investigation and treatment. This is facilitated by careful evaluation of optic nerve, observing for a spontaneous venous pulse and the absence of vascular obscuration by an edematous nerve fiber layer. Nerve function must likewise be assessed, with particular attention to visual acuity assessment, contrast sensitivity, color vision testing, brightness testing and threshold perimetry.

While visual fields are an important method of documenting and monitoring optic nerve compromise secondary to ODD, they are neither uniform nor diagnostic. The more common patterns encountered include nasal step defects, enlargement of the physiologic blind spot, arcuate scotomas, sectoral field loss, and altitudinal defects.4,5,9-11 Photodocumentation should be obtained for future monitoring. Uncomplicated cases should be monitored every six to 12 months.

In indeterminate or ambiguous cases, the diagnosis of ODD may be aided by the use of several ancillary procedures. These include: (1) red-free ophthalmoscopic evaluation, which reveals autofluorescence of visible hyaline bodies; (2) confocal scanning laser ophthalmoscopy, which can demonstrate focal elevations and associated, focal nerve fiber thinning, (3) computed tomography of the orbits, which can identify calcified drusen within the optic nerves, and (4) ocular ultrasound testing.21,22 Ultrasonography is one of the most productive and least invasive in-office procedures that can be used to identify ODD. The high reflectivity of the calcified hyaline bodies is dramatically evident on B-scan testing, even with deeply buried drusen.21,23

Monochromatic fundus photography also assists in the differentiation of ODD from optic disc edema with good sensitivity and very high specificity. The best results are obtained when using autofluorescence and red filters.24

Optical coherence tomography (OCT) can be used to differentiate ODD from optic disc edema.25-28 Both ODD and optic disc edema will show an elevated optic disc with a hyporeflective area beneath the elevated topography of the disc. In cases of optic disc edema, there will be a smooth inner contour of this hyporeflective area within the disc. In contradistinction, there will be irregularity of the internal contour in ODD, demonstrating a ‘lumpy-bumpy’ appearance. Additionally, there is a hyporeflective space located between the sensory retina and the retinal pigment epithelium and choriocapillaris complex in cases of optic disc edema. This hyporeflective subretinal space will extend beyond the edge of the optic disc and have what is termed a recumbent ‘lazy V’ pattern. In contrast, there is very little hyporeflective space beyond the edge of the optic disc in ODD. Finally, nasal retinal nerve fiber layer thickness greater than 86 microns is more diagnostic of optic disc edema than ODD.

Qualitative criteria for optic disc edema include an elevated optic nerve head with smooth internal contour and subretinal hyporeflective space extending beyond the edge of the disc. Optic nerve head drusen displays a ‘lumpy-bumpy’ internal optic nerve contour and a rapid decline in subretinal hyporeflective space beyond the edge of the optic disc.26

While many patients with ODD remain asymptomatic throughout life, all individuals with this diagnosis should continue to periodically self-monitor their vision. Although the condition is typically very slow to advance, there is a risk of progressive vision loss or visual field loss over time. Also, abrupt visual changes can be associated with choroidal neovascular membrane formation and/or subretinal hemorrhage. In cases where neovascularization is noted or suspected, fluorescein angiography is typically employed to assess the location and size of the subretinal net, and determine if the neovascularization is classic (well defined) or occult (poorly defined). Treatment for choroidal neovascularization associated with ODD includes a variety of techniques, such as focal laser photocoagulation, photodynamic therapy and treatment with intravitreal injection of anti-VEGF medications.16,29-32

It has been reported that eyes with ODD and concurrent ocular hypertension are at greater risk of visual field loss. However, it is unknown if lowering IOP in these cases reduces the risk of progression of visual field loss. Should any eye with significant ODD develop elevated intraocular pressure (IOP), then prophylactic pressure reduction should be strongly considered and perhaps offered to the patient. In the absence of elevated IOP, there is no evidence that IOP reduction will have any effects on preventing visual morbidity.18

Clinical Pearls

It has been suggested that the vast majority of congenitally anomalous, elevated optic discs are likely associated with ODD. Often, younger patients who are diagnosed in this capacity will be found to have disc drusen later in life.

It is important to recognize the clinical features associated with ODD in comparison to those features indicative of true optic disc edema. In ODD, one can 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% of patients with ODD, but is absent in cases of true disc edema. Most importantly, while the disc margins may be irregular in ODD, rarely are they blurred or obscured.

B-scan ultrasonography and OCT analysis are probably the most important ancillary tests to perform when evaluating suspected ODD. It is recommended that these procedures be conducted on all adult patients presenting with elevated optic discs that are not definitively identifiable as ODD based upon ophthalmoscopic observation. 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 diagnosis.

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2. Rosenberg MA, Savino PJ, Glaser JS. A clinical analysis of pseudopapilledema: I, population, laterality, acuity, refractive error, ophthalmoscopic characteristics, and coincident disese. Arch Ophthalmol. 1979; 97(1):65-70.

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18. Grippo TM, Shihadeh WA, Schargus M, et al. Optic nerve head drusen and visual field loss in normotensive and hypertensive eyes. J Glaucoma. 2008;17(2):100-4.

19. Gili Manzanaro P, Yangüela Rodilla J, Rodríguez Caravaca G,et al. Decreased visual acuity from optic disc drusen. Arch Soc Esp Oftalmol. 2010;85(2):64-9.

20. Morris RW, Ellerbrock JM, Hamp AM, et al. Advanced visual field loss secondary to optic nerve head drusen: case report and literature review. Optometry. 2009;80(2):83-100.

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23. McNicholas MM, Power WJ, Griffin JF. Sonography in optic disk drusen: imaging findings and role in diagnosis when funduscopic findings are normal. AJR Am J Roentgenol. 1994;162(1):161-3.

24. Gili P, Flores-Rodríguez P, Yangüela J, et al. Sensitivity and specificity of monochromatic photography of the ocular fundus in differentiating optic nerve head drusen and optic disc oedema: Optic disc drusen and oedema. Graefes Arch Clin Exp Ophthalmol. 2012. [Epub ahead of print]

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29. Delyfer MN, Rougier MB, Fourmaux E, et al. Laser photocoagulation for choroidal neovascular membrane associated with optic disc drusen. Acta Ophthalmol Scand 2004;82(2):236-8.

30. Chaudhry NA, Lavaque AJ, Shah A, Liggett PE. Photodynamic therapy for choroidal neovascular membrane secondary to optic nerve drusen. Ophthalmic Surg Lasers Imaging. 2005;36(1):70-2.

31. Knape RM, Zavaleta EM, Clark CL 3rd, et al. Intravitreal bevacizumab treatment of bilateral peripapillary choroidal neovascularization from optic nerve head drusen. J AAPOS. 2011;15(1):87-90.

32. Gregory-Evans K, Rai P, Patterson J. Successful Treatment of Subretinal Neovascularization with Intravitreal Ranibizumab in a Child with Optic Nerve Head Drusen. J Pediatr Ophthalmol Strabismus. 2009. Epub 2009 Aug 21.