Image supplied by Andrew Arnell, Specsavers Taylors Lakes, VIC
Optic nerve head drusen can be observed upon optic nerve assessment with funduscopy, retinal imaging and OCT. They tend not to be as apparent in young patients, becoming more visible with age. They appear as defined elevations, sometimes described as a ‘rice-grain’ or scalloped appearance of the optic nerve in adults (as pictured above). In most cases the drusen occur bilaterally, however appearance may be asymmetric between nerves.
Optic nerve head drusen are present in approximately 1% of the population and are thought to be congenital. Incidence increases to 3-4% for those with a positive family history of the condition, and males and females are affected equally.
Patients are almost always asymptomatic and as such, the finding of optic nerve head drusen is usually incidental at a routine eye examination. However, there are sinister differentials that must be excluded before a diagnosis of optic nerve head drusen is made.
It is thought that optic nerve head drusen develop as a result of abnormal axoplasmic metabolism causing protein and calcium salt build-up in the extra-cellular space surrounding ganglion cells in the optic nerve.
These deposits begin buried within the nerve and gradually enlarge and rise to the surface of the optic nerve, becoming more apparent from the age of 10 years.
Before a diagnosis of optic drusen can be made, it is important to differentiate this presentation with papilloedema and exclude papilloedema as a diagnosis.
As the drusen remain buried within the nerve during childhood, they can give the appearance of a swollen or elevated optic nerve in a child, without the classic characteristics of optic nerve head drusen.
True papilloedema will often present with significant blurring of the nerve margins, obscuration of blood vessels at the nerve rim, and haemorrhaging or exudation. However, it is important to be aware that early-stage papilloedema may not exhibit these signs. As such, it is important to conduct a full work-up, including appropriate functional tests, and to refer if unsure.
For adults, it is usually easier to differentiate the two due to the scalloped appearance of the drusen at the optic nerve head. Further confirmation can be obtained through other testing such as visual fields, colour vision, pupil testing, intraocular pressures and OCT.
Management & Prognosis
Optic nerve head drusen tend not to affect central vision, and there is no treatment that has been proven to alter the clinical course of the condition.
There are some notable associated symptoms and sequelae for people with optic nerve head drusen:
- Transient visual obscuration (uncommon)
- Slow progressing visual field defects caused by compression of the optic nerve and / or vascular supply (enlarged blind spot or constriction of field)
- Ischemic optic neuropathy (also caused by compression of the vascular supply to the nerve).
Therefore, patients should be monitored regularly for full ocular health assessments and visual field tests.