Introduction:
Abnormal deposition of calcium and protein in the optic nerve is referred to as optic nerve drusen, and Muller first described it. It does not produce any symptoms and is usually undiagnosed. Optic nerve drusen occur in 1 to 2 % of the population.
What Is Optic Nerve Drusen?
The optic disc or optic nerve head is where the optic nerve connects to the retina. Optic nerve drusen are the abnormal accumulation of proteinaceous material in the optic disc that gets calcified overage. The deposition can occur on the surface or deep inside the optic nerve disc. It initiates during childhood and usually affects both eyes. In addition, it gives the raised and lumpy appearance of the optic nerve, which is usually found incidentally on eye examination and is also referred to as pseudo papilledema.
What Are the Symptoms Of Optic Nerve Drusen?
Individuals with optic nerve drusen are usually asymptomatic.
But a few symptoms can occur as follows:
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Mild visual field defects (blind areas within the visual field). It increases overage.
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Color vision remains normal.
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Rarely complete blindness occurs if complicated by other optic nerve disorders.
What Are the Clinical Signs of Optic Nerve Drusen?
On clinical examination, calcium deposition mainly occurs superficially (60 %). It looks like pale (white or yellow), rounded, minor, or large clusters on the surface of the optic disc. When calcium deposits deep inside the optic disc, it appears swollen. Localized elevation of the disc with irregular margins, occupied by unusual branching of vessels, is common to both. The disc swelling does not extend to the retina, and the optic nerve layer is not thickened.
How to Diagnose Optic Nerve Drusen?
The clinical signs of superficial calcium deposition are peculiar to optic nerve drusen, whereas the buried deposit requires various techniques to be differentiated from other optic nerve conditions.
They are listed below:
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Computed Tomography (CT) helps detect calcium depositions. But, the use of CT is limited as it increases radiation exposure and does not detect any non-calcified forms of optic nerve drusen.
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Ultrasonography is highly sensitive in detecting buried optic nerve drusen. Rarely in children, the optic nerve drusen can occur together with another optic disc edema which poses a significant challenge in diagnosis.
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Fluorescein Angiography involves injecting a special dye to visualize the circulation in the retina. It aids in differentiating the buried optic nerve drusen from papilloedema.
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Optical Coherence Tomography (OCT) has evolved significantly and helps in visualizing the deeper structures. It uses retinal nerve fiber thickness for differentiating optic nerve drusen from optic disc edema. The thickness of the retinal nerve fiber layer increases disc edema compared to optic nerve disc drusen.
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Visual Evoked Potential (VEP) measures the response from the brain to a color or picture shown on a screen (visual stimuli). The visual evolved potential increases in individuals with severe visual defects due to optic nerve drusen. But the potential measures did not change in the standard visual field.
What Is the Differential Diagnosis?
The diseases that correlate with optic nerve drusen are as follows:
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Glaucoma is a condition that damages the optic nerve, and on imaging, it shows cupping of the optic disc along with optic nerve drusen. The disease is characterized by increased intraocular pressure, loss of nerve fibers, and the visual field.
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Papilloedema is the optic disc swelling that occurs due to increased intraocular pressure. The intraocular pressure increases in patients with intracranial tumors and intracranial hypertension and are also manifested with optic nerve drusen.
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Retinitis pigmentosa is a genetic disorder that causes progressive loss of vision. On fundus examination, the presence of optic nerve drusen is high. The patients with optic nerve drusen also showed a higher prevalence of retinitis pigmentosa.
What Are the Complications of Optic Nerve Drusen?
Optic nerve drusen can rarely lead to the following complications:
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Ischaemic Optic Neuropathy is optic nerve damage that occurs due to arterial obstruction. The risk of patients with optic nerve drusen developing ischemic optic neuropathy is high. It is characterized by sudden vision loss, deteriorated optic nerve function, and optic disc edema. It is managed by treating the causes like diabetes, vasculitis, etc. Radial neurotomy surgical procedure is also done, but the recovery is slow.
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Retinal Hemorrhage is the bleeding from the retina that occurs due to damage of retinal capillaries. The optic nerve drusen occurring in a small optic disc rarely causes leakage of blood from capillaries.
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Retinal Vascular Obstruction blocks the retinal artery or vein associated with optic nerve disc drusen. It can affect young children and causes blindness.
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Choroidal Neovascularization is the formation of new vessels from the eye's choroid. The patients are usually asymptomatic, and it occurs in children with optic nerve drusen. Vision loss may occur if the newly formed vessels extend to the retina.
How Is Optic Nerve Drusen Treated?
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There is no specific treatment accepted for optic nerve drusen. Surgical removal of optic nerve drusen is found to worsen vision.
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Choroidal neovascularization is treated by photodynamic therapy.
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Intravitreal injection of antibodies against factors that cause neovascularization.
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Glaucoma is treated by decreasing the intraocular pressure if progressive vision loss occurs.
Conclusion:
Optic nerve drusen is a rare condition that does not cause significant symptoms. However, sometimes, it may lead to various complications. The regular visual field examination helps diagnose such conditions and prevent worsening of vision.
