Optic disc drusen
Optic disc drusen (ODD) are also known as hyaline bodies and are a relatively common entity. They are usually found incidentally on CT or on follow-up of abnormal fundoscopy.
Optic disc drusen are identified radiographically in up to 0.3-3.7% of the population and are frequently bilateral 1,4-5. They are typically seen in patients with age-related macular degeneration 7. They can also be familial and inherited as a dominant trait 1,4. In general, they are more common in Caucasians than African-Americans 4.
Most cases of drusen are asymptomatic, although patients may report episodic visual loss. The blind spot may also be enlarged, but this is subtle and is only usually found following formal visual field mapping 4.
Fundoscopic findings depend on how deeply the drusen is located in the optic disc. Superficial deposits exhibit characteristic autofluorescence making the diagnosis in such cases obvious. Deeper deposits have less-specific appearances with swelling of the optic disc that mimics papilloedema (pseudopapilloedema) 1,4,9.
A number of entities have been described associated with optic disc drusen. They include 3-5:
Optic disc drusen are small collections of hyaline material located within the head of the optic nerve (CN II) at variable depths 1-3. The earliest signs of drusen formation histologically are small globular or plaque-like deposits in Bruch membrane of hyaline material, present in the majority of individuals, and perhaps congenital in nature 3.
Small hard drusen (< 63 micrometres), visible on graded fundus photography are seen in a high proportion of individuals. They are not thought to be a risk factor for the development of age related maculopathy, and their prevalence is not age dependent 2. They are not visible on imaging.
Over time in some individuals, multiple micro-drusen (< 25 micrometres) coalesce 2-3. These larger deposits increase in prevalence with age and are associated with age related maculopathy 2. As they mineralise, it is these drusen that are visible radiographically.
Optic disc drusen vary in size from less than 1mm to up to 4mm in diameter and 3mm in thickness 1.
Ocular ultrasound demonstrates an echogenic focus within or on the surface of the optic nerve head. Posterior acoustic shadowing may be present with larger lesions 1.
Although drusen can be identified in childhood, they are small and non-mineralised. As such drusen are rarely identified in the paediatric patient, although a region of slight increased density and swelling may be evident on thin section scans 3.
Treatment and prognosis
In the vast majority of cases, no therapy is required 5. Occasionally, especially when drusen are large, vascular complications may occur, e.g. non-anterior ischaemic optic neuropathy (NAION), central retinal artery occlusion (CRAO), central retinal vein occlusion (CRVO) 5.
Optic pressure lowering agents may be of benefit if pressures are elevated, although whether elevated pressures represent glaucoma superimposed on drusen, or a direct complication of drusen cannot be distinguished 5.
When there are typical appearances, the differential is small. In general, the differential includes other causes of calcification of the globe including:
- usually a mass with calcification
- protruding into the vitreous body
- usually not located at the optic disc
- astrocytic hamartomas
- choroidal osteoma
- 1. 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. AJR Am J Roentgenol (abstract) [pubmed citation]
- 2. Sarks SH, Arnold JJ, Killingsworth MC et-al. Early drusen formation in the normal and aging eye and their relation to age related maculopathy: a clinicopathological study. Br J Ophthalmol. 1999;83 (3): 358-68. Br J Ophthalmol (link) [free text at pubmed] [pubmed citation]
- 3. Imaging of the Head and Neck. Mahmood F. Mafee, Galdino E. Valbasson, Minerva Becker, J. S. Lewin, S. G. Nour (Contributor), A. L. Weber (Contributor), M. Becker (Contributor). Thieme Medical Publishers ISBN:1588900096 (find it at amazon.com)
- 4. Neurology in clinical practice. [edited by] Walter G. Bradley. [et al.]; with 120 contributing authors. Philadelphia, PA : Butterworth-Heinemann, c2004. ISBN:9997625889 (find it at amazon.com)
- 5. Pediatric Ophthalmology, Neuro-Ophthalmology, Genetics. Birgit Lorenz (Editor), Francois-Xavier Borruat (Editor). Springer ISBN:3540336788 (find it at amazon.com)
- 6. Optic nerve disorders. Jane W. Chan. New York : Springer, c2007. ISBN:0387689788 (find it at amazon.com)
- 7. Lebedis CA, Sakai O. Nontraumatic orbital conditions: diagnosis with CT and MR imaging in the emergent setting. Radiographics. 2008;28 (6): 1741-53. doi:10.1148/rg.286085515 - Pubmed citation
- 8. Ramirez H, Blatt ES, Hibri NS. Computed tomographic identification of calcified optic nerve drusen. Radiology. 1983;148 (1): 137-9. Radiology (citation) - Pubmed citation
- 9. Bec P, Adam P, Mathis A et-al. Optic nerve head drusen. High-resolution computed tomographic approach. Arch. Ophthalmol. 1984;102 (5): 680-2. Arch. Ophthalmol. (link) - Pubmed citation