Optic disc drusen

Presentation

Anatomy

The optic nerve is a cable connection that transmits images from the retina to the brain. It consists of over one million retinal ganglion cell axons. The optic nerve head, or optic disc is the anterior end of the nerve that is in the eye and hence is visible with an ophthalmoscope. It is located nasally and slightly inferior to the macula of the eye. There is a blind spot at the optic disc because there are no rods or cones beneath it to detect light. The central retinal artery and vein can be seen in the middle of the disc as it exits the scleral canal with the optic nerve to supply the retina. The vessels send branches out in all directions to supply the retina.

Pathophysiology

In children, optic disc drusen are usually buried and undetectable by fundoscopy except for a mild or moderate elevation of the optic disc. With age, the overlying axons become atrophied and the drusen become exposed and more visible. They may become apparent with an ophthalmoscope and some visual field loss at the end of adolescence. ODD can compress and eventually compromise the vasculature and retinal nerve fibers. Rarely, choroidal neovascularization may develop as the juxtapapillary nerve fibers are disrupted, with subsequent subretinal hemorrhage and retinal scarring.

Diagnosis

Differential diagnosis

In most patients, optic disc drusen are an incidental finding. It is important to differentiate them from other conditions that present with optic disc elevation, especially papilledema, which could imply raised intracranial pressure or tumors. True papilledema may present with exudates or cotton-wool spots, unlike ODD. The optic disc margins are characteristically irregular in ODD but not blurred as there is no swelling of the retinal nerve fibers. Spontaneous venous pulsations are present in about 80 percent of patients with ODD, but absent in cases of true disc edema. Disorders associated with disc elevation include: Alagille syndrome, Down syndrome, Kenny-Caffey syndrome, Leber Hereditary Optic Neuropathy and linear nevus sebaceous syndrome.

Management

Patients with optic disc drusen should be monitored periodically via ophthalmoscopy, Snellen acuity, contrast sensitivity, color vision, intraocular pressure and threshold visual fields. Associated conditions such as angioid streaks and retinitis pigmentosa should be screened for. Both the severity of optic disc drusen and the degree of intraocular pressure elevation have been associated with visual field loss. There is no widely accepted treatment for ODD, although some clinicians will prescribe eye drops designed to decrease the intra-ocular pressure and theoretically relieve mechanical stress on fibers of the optic disc. Rarely choroidal neovascular membranes may develop adjacent to the optic disc threatening bleeding and retinal scarring. Laser treatment or photodynamic therapy or other evolving therapies may prevent this complication.

Prognosis

Optic nerve damage is progressive and insidious. Some of patients will develop some peripheral field defects. These can include nasal step defects, enlarged blind spots, arcuate scotomas, sectoral field loss and altitudinal defects. Central vision loss is a rare complication of bleeding from peripapillar choroidal neovascular membranes. Anterior ischemic optic neuropathy (AION) is a potential complication.

Epidemiology

Optic disc drusen are found clinically in about 1% of the population but this increases to 3.4% in individuals with a family history of ODD. About two thirds to three quarters of clinical cases are bilateral. Males and females are affected at equal rates. Caucasians are the most susceptible ethnic group. Certain conditions have been associated with disc drusen such as retinitis pigmentosa, angioid streaks, Usher syndrome, Noonan syndrome and Alagille syndrome. Optic disc drusen are not related to Bruch membrane drusen of the retina which have been associated with age-related macular degeneration.

References

Further reading

References

1. Golnik, K. (2006). Congenital anomalies and acquired abnormalities of the optic nerve, (Version 14.3). UptoDate (On-Line Serial)
2. (April 1975). "Drusen of the optic disc. A histopathological study". Trans Ophthalmol Soc U K.
3. (November 2005). "[Optic disc drusen and acute vision loss]". Harefuah.
4. Tso MO. (October 1981). "Pathology and pathogenesis of drusen of the optic nervehead". Ophthalmology.
5. (January 2008). "Histologic findings after surgical excision of optic nerve head drusen". Retina.
6. (2001). "Handbook of Ocular Disease Management". Jobson Publishing L.L.C..
7. (December 2004). "Progression from anomalous optic discs to visible optic disc drusen". J Neuroophthalmol.
8. Horton, J.. (2005). "Harrison's principles of internal medicine". McGraw-Hill Medical Publishing Division.
9. {{OMIM. 127000. Kenny-Caffey Syndrome type 2
10. {{OMIM. 163200. Schimmelpenning-Feuerstein-MIMS Syndrome
11. (March 2008). "Optic nerve head drusen and visual field loss in normotensive and hypertensive eyes". J. Glaucoma.
12. (April 2004). "Laser photocoagulation for choroidal neovascular membrane associated with optic disc drusen". Acta Ophthalmol Scand.
13. (2015). "Laser treatment of drusen to prevent progression to advanced age-related macular degeneration". Cochrane Database Syst Rev.
14. (2005). "Photodynamic therapy for choroidal neovascular membrane secondary to optic nerve drusen". Ophthalmic Surg Lasers Imaging.
15. (April 2008). "Choroidal neovascularisation in children". Br J Ophthalmol.
16. (January 2004). "Anterior ischemic optic neuropathy in eyes with optic disc drusen". Arch. Ophthalmol..
17. (2021). "Anterior ischemic optic neuropathy secondary to optic nerve head drusen - A case report and review of literature". Indian Journal of Ophthalmology: Case Reports.
18. (July 1999). "Are optic disc drusen inherited?". Ophthalmology.
19. (2004). "Vaughan & Asbury's general ophthalmology". Lange Medical Books/McGraw-Hill.
20. {{OMIM. 163950. Noonan syndrome