The purpose of the study is to use new diagnostic methods (OCT and OCT-A) to shed light on risk factors for the development of NA-AION. The risk factors we are focusing on are comorbidities along with anatomical and vascular characteristics of the optic nerve.

Non-arteritic anterior ischemic optic neuropathy (NA-AION) is the most common acute optic neuropathy in the middle-aged and elderly population and can also occur in children and young adults. NA-AION leads to irreversible vision loss, and there is currently no effective treatment. In recent years, acellular calcified deposits in the optic nerve head called optic disc drusen (ODD) have been investigated as an important risk factor for NA-AION in patients under the age of 50.

The purpose of the study is to use new diagnostic methods optical coherence tomography (OCT) and OCT-angiography (OCTA) to shed light on risk factors for the development of NA-AION. We will perform two sub-studies:

1. Characteristics of the optic nerve head anatomy including the presence of ODD as risk factors for the development of NA-AION.
2. Vascular comorbidities and in vivo vasculature as a risk factor for developing NA-AION.

The study is an international prospective multicenter study including 20 sites in 9 different countries. The study population is patients diagnosed with NA-AION in a 1.5-year inclusion period. Each included patient gets 1-2 follow up visits during a 3-month follow up time.

Included patients will be examined as per standard clinical care for that site including OCT and OCT-A. Standard clinical care includes at least: obtaining medical history, measurement of visual acuity, slit lamp examination, and automated perimetry.

Characteristics and risk factors in NA-AION patients with ODD (ODD-AION) will be compared with NA-AOIN patients without ODD (nODD-AION).

Inclusion Criteria:

1. Diagnosis of first episode of NA-AION in study eye with symptom onset within 1 month prior

2. Subject age: Age >10

3. NA-AION diagnosis requires:

   • disc edema seen by site PI or by referring doctor
   • visual field defect in the study eye consistent with NA-AION and mean deviation worse than 3.0 dB using the study visual field examination protocol
   • relative afferent pupillary defect (unless the fellow eye had previous NA-AION or other optic nerve or retinal disease that is not exclusionary)

Exclusion Criteria:

1. Previous episode of NA-AION in the study eye only
2. Intraocular pressure of >21 mm Hg in the study eye
3. Clinical or pathological evidence of giant cell arteritis
4. Diseases that may affect the optic nerve: glaucoma, multiple sclerosis, Alzheimer disease, and Parkinson disease. Evidence of optic disc drusen and optic nerve hypoplasia are not exclusion criteria given they are important parts of the study. We will not exclude significant retinal diseases, since they may be related to underlying etiologies giving rise to ODD, such as macular degeneration, retinal dystrophies, but eyes with significant retinal diseases will be analyzed separately.

The study population is patients diagnosed with NA-AION in a 1.5-year inclusion period.