Optic Nerve Drusen

Optic Nerve Drusen
SYMPTOMS Typically asymptomatic
Less common symptoms include Transient vision loss that lasts for a few seconds, Flickering of lights, Decrease in peripheral vision especially if there is RNFL damage, Central vision loss if a CNVM develops
SIGNS Typically bilateral
The two types of optic nerve drusen are visible or buried
Optic nerve drusen itself: Refractile, Yellow-white deposits, Found in various sectors of the optic nerve (typically nasal), Small focal deposits or large clustered deposits
Optic nerve appearance with optic nerve drusen: Optic disc margins are indistinct or distorted, Appearance of thick/full rim tissue (rim tissue may actually be thin), Presence of a small optic disc cup or loss of an optic disc cup (cupping can be masked), Anomalous branching of blood vessels at the optic nerve, Increase in central retinal vein size due to an increase in venous pressure from compression of the retinal vein by the optic nerve drusen
Complications of optic nerve drusen: RNFL defects secondary to direct compression by surfacing and enlarging optic nerve drusen along with abnormal axoplasmic flow, Visual field defects due to RNFL damage (typically along the inferior visual field and does not necessarily correlate to the location of the optic nerve drusen), Compression and nicking of blood vessels can occur as the optic nerve drusen begins to surface and get larger (this can potentially cause splinter disc hemorrhages, non-AIONs, CRAOs, and CRVOs), Choroidal neovascular membranes
WORK-UP Pupils (typically normal but can present with a mild APD if optic nerve drusen is asymmetric), EOMs, Color vision (typically normal), Visual field (can present as an enlarged blind spot or arcuate defect), Slit lamp examination, Dilated retinal exam, Fundus photos, OCT, Fundus autofluorescence (increase in AF due to the presence of mitochondrial prophyrins which are fluorophores/may not show up as an increase in AF if the optic nerve drusen is buried or not calcified), B-scan ultrasound (highly reflective area near/at the optic nerve despite lowering gain associated with a significant spike on the overlying A-scan/may not be apparent if the optic nerve drusen is buried or not calcified), Fluorescein angiography (late nodular staining of the optic disc and late circumferential staining of the peripapillary region with no evidence of leakage/appears autofluorescent even if no dye is injected)
OCT (Optic nerve analysis with EDI and RNFL analysis): *Elevation of the neuroretinal rim thickness *"Lumpy bumpy" optic nerve contour *Elevation of the optic disc without involvement of the retinal nerve fiber layer with a jagged appearance *Flat or posterior displacement of the Bruch's/RPE complex especially near the Bruch's membrane opening *Presence of peripapillary hyper-reflective ovoid-mass like structures (PHOMS) which represent bulging optic nerve axons *Hyporeflective spaces with hyper-reflective borders within the disc which represent the actual optic nerve drusen *Hyper-reflective horizontal lines or spots within the optic disc may be an early indication of optic nerve drusen formation *Absence of subretinal fluid adjacent to Bruch's membrane opening *RNFL thickness is typically normal or thinner than normal
TREATMENT Normal visual field with normal RNFL/GCL and normal IOP: Monitor. No treatment needed
Normal visual field with normal RNFL/GCL and elevated IOP (>21mmHg): Strongly consider treatment
Normal visual field with RNFL/GCL thinning and normal or elevated IOP (>21mmHg): Strongly consider treatment especially if IOPs are elevated
Visual field loss with RNFL/GCL thinning and normal or elevated IOP (>21mmHg): Begin treatment
Higher IOP (>21 mmHg) increases risk of visual field loss in patients with optic nerve drusen by 91%
If beginning treatment, use a topical glaucoma medication (for example, a topical prostaglandin 1gtt QHS) in order to increase perfusion to the optic nerve and reduce further damage to the RNFL/GCL
FOLLOW-UP Normal visual field with normal RNFL/GCL and normal IOP: See patient back in 1 year
Normal visual field with normal RNFL/GCL and elevated IOP (>21mmHg): See patient back in 6 months
Normal visual field with RNFL/GCL thinning and normal or elevated IOP (>21mmHg): See patient back every 4-6 months
Visual field loss with RNFL/GCL thinning and normal or elevated IOP (>21mmHg): See patient back every 3-6 months
ETIOLOGY Autosomal dominant inheritance
Globules of mucopolysaccarides, mucoproteins, and mitochondria that develop due to axonal rupture from a combination of reduced axoplasmic flow and abnormal axonal metabolism (associated with abnormal optic nerve vasculature and a small scleral canal)
Development of optic nerve drusen is a dynamic process as they get larger, get more calcified, and begin to surface over time
DIFFERENTIAL DX Crowded optic disc, Ischemic optic neuropathy, Papilledema, Infiltrative optic neuropathy, Optic neuritis
NOTES Optic nerve drusen are found anterior to the lamina cribosa
On average, there is about 50 optic nerve drusen per eye that can be anywhere from 5 to 1000 microns in diameter
On average, optic nerve drusen are typically visualized at the age of 12 years old
Patients with optic nerve drusen tend to give the optic nerve a pseudo-edematous appearance (this is especially true if the optic nerve drusen are buried)
Retinitis pigmentosa, Pseudoxanthoma elasticum, and Angioid streaks can be associated with optic nerve drusen
Optic nerve drusen alone and glaucoma can cause the same pattern of visual field loss and RNFL/GCL loss. Both optic nerve drusen and glaucoma can show progression in both visual field loss and RNFL/GCL loss as a patient gets older (although patients with just optic nerve drusen tend to show more stabilization when getting older)
Optic nerve drusen obscures the ability of the clinician to make an accurate assessment regarding the optic nerve (masks cupping and rim tissue thinning). Despite all the new technology, it is still difficult to determine if RNFL/GCL/VF loss is secondary to glaucoma and/or optic nerve drusen
Optic Nerve Drusen: Fundus autofluorescence shows optic nerve drusen with increased autofluorescence https://imagebank.asrs.org/file/2928/optic-disc-drusen