Non-arteritic ischemic optic neuropathy (NAION) is a common cause of acute, painless monocular vision loss in adults over 50 years of age. NAION is a diagnosis of exclusion established once arteritic disease and other etiologies of acute vision loss have been ruled out. Clinicians should distinguish NAION from arteritic ischemic optic neuropathy (AION) because failure to properly treat patients with AION results in a poorer prognosis. NAION is often associated with risk factors such as obstructive sleep apnea, atherosclerosis, diabetes mellitus, hypertension, hyperlipidemia, smoking, and phosphodiesterase-5 inhibitors. Clinicians should consider these risk factors to help prevent the development of NAION in their patients. Here we present the case of a 63-year-old Caucasian male who presented with acute, painless monocular vision loss.
Non-arteritic ischemic optic neuropathy (NAION) is a disease characterized by acute, painless monocular vision loss that represents one of the most common causes of optic neuropathy in adults over 50 years of age. . The exact pathophysiology of NAION is unclear, but it appears to be caused by decreased optic nerve perfusion [1,2]. It is essential to distinguish NAION from arteritic ischemic optic neuropathy (IONA). Although both conditions present with acute vision loss, AION has a much worse prognosis than NAION. Because AION has an extremely poor prognosis if not treated promptly and appropriately, clinicians should understand the clinical features of AION that distinguish it from AION . Here we present the case of a 63-year-old Caucasian male who presented with acute, painless monocular vision loss.
Presentation of the case
A 63-year-old Caucasian male presented with acute, painless vision loss affecting his right eye that occurred without any identifiable initiating event. He complained of isolated blurred vision in his right eye with no other neurological symptoms. The initial ophthalmological assessment suggested an ischemic optic neuropathy. The patient did not report jaw claudication, scalp tenderness, or temporal headache. Physical examination was positive for decreased right-sided visual acuity, visual field defect, 360 degree optic nerve edema and clouding of vessels, optic disc hemorrhage, and optic disc pallor 1 +. Corrected right eye visual acuity was reported as HM (hand motion) 2′ while corrected left eye visual acuity was reported as 20/20. There was no afferent pupillary abnormality in either eye. Magnetic resonance imaging (MRI) of the brain with and without contrast medium was unremarkable. Contrast-enhanced MRI of the orbits showed subtle and even enhancement of the left and right optic nerves immediately behind the globes (Figure 1).
The patient was started on high dose intravenous steroids and evaluated by ophthalmology, rheumatology and vascular surgery. Complete blood count and complete metabolic panel were unremarkable. Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), measured before steroid administration, were 28 mm/h and 0.3 mg/dL, respectively. The lipid panel was notable for high low density lipoprotein levels of 155 mg/dL, high total cholesterol of 314 mg/dL and high triglyceride level of 531 mg/dL. Hemoglobin A1c was 12.1%. Temporal artery ultrasound, performed prior to steroid administration, did not reveal giant cell arteritis (GCA). Temporal artery biopsy, performed after steroid administration, was also negative for GCA. Since a diagnosis of NAION was considered very likely, the steroids were stopped. After being discharged, the patient was seen in the rheumatology clinic. He underwent polysomnography, which revealed severe obstructive sleep apnea (OSA) with an apnea-hypopnea index (AHI) of 33.2 events per hour, thus requiring continuous positive airway pressure (CPAP) therapy. Although he denied using phosphodiesterase-5 (PDE-5) inhibitors prior to his admission to hospital, he had several other risk factors for NAION, including hypertension, hyperlipidemia, diabetes mellitus uncontrolled type 2 and untreated OSAS.
NAION is characterized by acute, painless monocular vision loss. No definitive treatment for NAION is available; therefore, identifying and controlling modifiable risk factors is critical to preventing this condition. NAION is thought to occur due to decreased optic nerve perfusion and has been associated with conditions that can lead to decreased optic nerve perfusion via microvascular occlusions, such as diabetes mellitus and hyperlipidemia . Additionally, NAION can arise due to impaired autoregulatory mechanisms of the optic nerve head by factors such as arteriosclerosis or chronic hypertension. [2,3]. Based on angiographic evidence, NAION is not associated with embolic or thrombotic events. NAION is a diagnosis of exclusion and is established after excluding arteritic disease and other etiologies of acute vision loss. It is essential to exclude AION, which presents similarly to NAION but has a much worse prognosis than NAION if not treated promptly and appropriately. An important feature distinguishing NAION from AION is the optic disc edema with hyperemia compared to the significant optic disc pallor seen in AION. It is important when taking a history of patients with acute, painless monocular vision loss to ask if they have had symptoms such as jaw claudication, temporal headache, tenderness of the scalp, weight loss, or fatigue, as these symptoms should alert clinicians to the most urgent diagnosis. from secondary AION to GCA.
Additionally, evaluation of these patients should include ESR and CRP, as elevation of these inflammatory markers is more indicative of the diagnosis of AION than NAION. . Finally, performing a temporal artery biopsy or a temporal artery ultrasound should be considered in these patients. Although negative results for GCA do not rule out AION, such results would place the diagnosis of AION much lower on the differential [1,4]. A summary of the clinical and laboratory features of GCA and the frequencies at which they occur are presented in Table 1 . Failure to distinguish AION from NAION and early initiation of treatment with high-dose steroids in patients with AION can lead to rapid blindness and poor vision recovery .
Although the prognosis for vision recovery in patients with NAION is poor, it is better than the prognosis for vision recovery in patients with AION. The Ischemic Optic Neuropathy Decompression Trial (IONDT) showed that 43% of patients with NAION regained at least three lines of visual acuity on the ocular Snellen chart within six months. In contrast, a study by Liu et al. showed that only 34% of patients with vision loss due to GCA experienced visual improvement [5,6]. Although there is a 5% risk of recurrent NAION in the same eye, there is a 15-20% risk of NAION in the other eye [2,3]. NAION is often associated with risk factors such as OSA, atherosclerosis, diabetes mellitus, hypertension, hyperlipidemia, smoking, and PDE-5 inhibitors, most of which were present in our patient. . Although there is no cure for NAION, controlling these risk factors is critical in the management of NAION and to reduce the risk of NAION occurring in the other eye. .
Obstructive sleep apnea, in particular, is strongly associated with NAION. Palombi et al. demonstrated that OSAS is the disorder most frequently associated with NAION. They found that 89% of newly diagnosed patients with NAION who underwent polysomnography had an AHI of more than 15 events per hour and that the relative risk of OSAS in patients with NAION compared to the general population was 4 ,9. . Several theories that OSA is supposed to contribute to the development of NAION have been proposed. One theory suggests that hypoxia caused by OSA leads to damage to the optic nerve. Another theory is that intermittent sympathetic surges caused by repeated apneic events result in impaired optic nerve autoregulation. Additionally, it is believed that elevated intracranial pressure during apneic events may damage the optic nerve directly or through circulatory compression. . OSA is often treated with CPAP therapy during sleep, and one study showed that treating OSA patients with CPAP therapy reduced their likelihood of developing NAION [9,10].
As noted above, clinicians should be able to distinguish NAION from AION. Additionally, clinicians should be aware of the risk factors associated with NAION, particularly OSA. By addressing these risk factors, clinicians can help prevent the development of NAION in their patients.