Anterior Ischemic Optic Neuropathy (AION) is a potentially visually devastating disease that occurs in the middle aged and the elderly. It is often referred to as a stroke of the optic nerve. AION begins suddenly in one eye and with little warning. It frequently progresses to the other eye over time.
Our Neuro-Ophthalmology experts can diagnose and manage the symptoms of ischemic visual loss.
Dr Luke Chen consults in Fitzroy, Box Hill and St Kilda Rd.
Vision loss often includes both the loss of visual field and visual acuity which can vary from being nearly normal to severely impaired. The unexpected sudden visual acuity and visual field loss makes AION a particularly overwhelming disease for many patients.The optic nerve contains approximately 1.2 million nerve fibers. All visual images we see are transmitted through the optic nerve to our brain. A stroke of the optic nerve is caused by a blockage in the blood supply to the front or anterior portion of the optic nerve. Without nutrients and oxygen being supplied in adequate amounts, a portion of the nerve will be lost.
Optic nerve stroke is unrelated to a stroke in the brain and therefore it is not accompanied by any weakness or paralysis.
Visual Field Loss
Field testing is essential in evaluating patients with anterior ischemic optic neuropathy. Visual field loss is variable and depends on the extent of the blood flow to the optic nerve involved. Patients experience loss of peripheral vision, usually first in the lower field of view. In severe cases, tunnel vision may result. These losses in vision can be severe. A ‘relative loss’ means that motion is still perceptible, and an ‘absolute loss’ is where light cannot be perceived at all. Visual field defects may cause loss of confidence walking cauing to tripping or bumping into objects. Stair walking becomes very difficult.
Loss of ‘Contrast Sensitivity’
Contrast sensitivity is the ability of the eye to detect subtle changes in shades. Our world is not all black and white, but rather it is one of infinite shades. We depend on our ability to see contrast changes to read, and to even judge depth. After an AION, patients often can no longer decipher the subtle changes in vision. The use of increased task lighting and amber filters can aid contrast loss.
Recent studies have suggested that 40% of patients may experience some degree of improvement in central vision or visual acuity weeks to months after the vision or visual field loss. In some, the loss of side vision may not improve, but patients learn to adapt to the field loss and become less aware of the loss over time.
Source: Vision Enhancement Journal
International Foundation of Optic Nerve Disease