Neuro - Orbit - Compressive Optic Neuropathy
The optic nerve (Cranial Nerve II) allows us to see. The nerve receives sensory input from images in the environment and transmits the signal to the occipital cortex of the brain. The nerve extends from the back of the eye, travels within the orbit, and through the optic canal (hole in the skull) to the brain (see image below)
Neuro means nerve and pathy means abnormal. In compressive optic neuropathy, the nerve does not work properly because it is being mashed by surrounding structures (for example, enlarged muscles and/or fat). Blood flow is not normal and nerve cells are injured. The optic nerve is most vulnerable to compression where it is adjacent to or surrounded by bone and is relatively immobile.
Signs of compressive optic neuropathy include the following:
- slowly progressive visual loss
- decreased color perception and brightness (red appears less red or light appears less bright in the affected eye
- relative afferent pupil defect (APD) (normally, light shined into one pupil causes both pupils to constrict, but with an APD, the compressed optic nerve does not work properly so it cannot pass along the signal for the pupil to constrict, so instead, the pupil in the affected eye dilates).
- Eye movement is NOT affected because the optic nerve does control eye movement.
General causes of compressive optic neuropathy include tumors, inflammation (such as in thyroid eye disease), and infection. Management depends on the underlying cause.
