At the completion of this CPD activity, optometrists will have developed their knowledge of myopia management. Including:
- Recognise differentiating clinical features between NAION and unilateral glaucoma
- Review some of the symptoms and features of NAION in a presenting patient
- Understand the role that OCT-A has in the diagnosis of NAION
- Know the symptoms and features that distinguish NAION from Giant cell artertis (GCA)
NOTE: Optometry Australia members can enter their details at the bottom of this article to have it automatically added to their Learning Plan.
With glaucoma on the rise, clinicians are increasingly finding that even with the latest technology, true diagnosis remains stubbornly difficult. As the authors point out, the diagnosis gets even harder when other pathologies masquerade as glaucoma.
Dr Lewis Levitz
FRANZCO FRCSEd FCS(SA)Ophth MMed MBBCH
Vision Eye Institute, Melbourne
BOptom, PostGradDipAdvClinOptom, PostGradCertOcTher, FACO
Specsavers Knox, Melbourne
Australian College of Optometry, Melbourne
Co-authors: Z Kurtz (BOptom Specsavers Epping, Melbourne), D Levitz (Monash Medical School)
Differentiating visual field defects caused by non-arteritic anterior ischaemic optic neuropathy (NAION) from those caused by unilateral glaucoma can often be difficult in subtle and longstanding cases. The classical altitudinal field defect noted with NAION may be only partial, and therefore difficult to distinguish from an arcuate scotoma characteristic of glaucoma. Furthermore, patients may have overlapping background risk factors such as sleep apnoea or nocturnal hypotension.
Differentiating between NAION and unilateral glaucoma is important as the management is very different. Glaucoma often requires lifelong treatment and follow-up, which is costly, time consuming and sometimes associated with local and systemic side effects. On the other hand, there is no proven treatment for NAION.
This case report discusses the potential future benefit of the use of optical coherence tomography angiography (OCT-A) in the diagnosis of NAION. Also, it emphasises the importance of a visual field assessment on initial presentation to the optometrist or ophthalmologist.
A 62-year old Caucasian male was referred by his optometrist to the ophthalmologist in 2022 following the detection of a right superior visual field defect. The visual field exam was performed by his optometrist due to a suspicious optic nerve appearance on fundoscopy and corresponding abnormal OCT.
The referral stated that the patient had a right superior field defect, thinning of his right retinal nerve fibre layer and increased optic nerve cupping of 0.7 in the right eye. The patient’s intraocular pressures were measured at 17mm Hg in the right eye and 19mmHg in the left. There was initial clinical suspicion of unilateral glaucoma affecting his right eye.
On presentation to the ophthalmologist, the patient stated that he had no history of hypercholesterolaemia, hypertension or diabetes which are risk factors for a retinal vascular occlusion. He did remember seeing an ophthalmologist in 2015, but he could not recall the details of his previous visit.
Visual acuities were measured as 6/6 in each eye. His intraocular pressure measured 17mmHg in both eyes. His visual fields were repeated (Figures 1A and 1B) and OCT (Figure 2) and OCT-A (Figure 3 – top of article) exams were performed. A combined report was generated on the proprietary software (Figure 4).
Why unilateral glaucoma was suspected
OCT performed at the time showed thinning in the inferior retinal nerve fibre layer in the right eye. This was consistent with the visual field loss. Disc asymmetry was noted, with cup-disc ratios of 0.7 in the right eye and 0.6 in the left eye. In light of all of these findings, a diagnosis of glaucoma was considered.
Differentials in addition to unilateral glaucoma
At the time, other differential diagnosis included a previous NAION and possibly an old resolved branch retinal vein occlusion (BRVO) or branch retinal artery occlusion (BRAO).1,2 Other causes of pseudo-glaucomatous field loss such as a tilted disc, optic nerve coloboma, retinoschisis and retinal pigment epithelial hyperplasia were ruled out on dilated fundoscopy. OCT-A showed decreased perfusion inferiorly. This can be found in both normal tension glaucoma (NTG) and NAION.3,4
Fortunately for our patient, a diagnosis could be made once notes from his original referral were retrieved.
His previous notes showed that he was referred by an optometrist to another ophthalmologist seven years earlier in 2015 with a sudden one-week onset of superior visual disturbance in his right eye. This was described by the patient as ‘a shadow with a yellow stripe.’ The optometrist then suspected a right eye retinal detachment. Examination by the ophthalmologist at the time revealed vision of 6/6 in both eyes, no colour vision defect, IOP of 22mmHg both eyes and a right optic nerve which was ‘swollen’ inferiorly. A posterior vitreous detachment was noted in the right eye. OCT at the time showed an elevated right inferior nerve fibre layer (Figure 5).
This corresponded with the area of retinal nerve fibre layer loss noted seven years later with the resultant visual field defect (Figure 6).
The patient was diagnosed as having had a previous NAION seven years previously which led to the development of the superior visual field defect.
Distinguishing NAION from unilateral glaucoma
Differentiating unilateral glaucoma from a longstanding NAION can be challenging. Many of the risk factors are similar, including sleep apnoea and nocturnal hypotension and hypoxemia of the optic nerve.5,6
One of the main differentiating clinical features between NAION and glaucoma is that NAION presents with sudden onset of visual loss with a swollen optic nerve while glaucoma presents more insidiously with optic nerve cupping. A swollen nerve is not always found in NAION, as some patients present late when clinical findings relating to an acute insult to the optic nerve have already resolved. The visual field can also look similar with the arcuate scotoma of glaucoma resembling an incomplete altitudinal field loss of NAION.
Some of the features of NAION are:
- Sudden unilateral painless visual loss
- Relative afferent pupil defect
- Swollen optic nerve
- Crowded optic disc in fellow eye: ‘Disc at risk’
- Altitudinal visual field defect
- Colour vision loss in keeping with visual acuity
- Normal anterior eye examination
- Normal ocular motility
The prompt referral of the patient by the original optometrist in 2015 allowed for the visualisation of the swollen optic nerve. This information was critical in supporting the diagnosis in 2022, especially because the patient was unaware of their visual field defect.
Having the second optometrist re-refer the patient seven years later allowed the patient to have an OCT-A scan, which was not available in 2015. OCT-A showed mild decrease in retinal circumpapillary perfusion density3 which may have been more marked if he had suffered from glaucoma. The OCT-A findings strongly suggested a diagnosis of NAION.
The patient was referred to his GP for a full physical examination to exclude diabetes and sleep apnoea. NAION is not associated with arterial risk factors for ischaemic vessel disease or smoking, but these, as well as hypertension should be managed if present.1,7 Follow-up after an acute NAION is usually planned at two weeks to review the visual field. This may be done with either the co-managing optometrist or ophthalmologist to ensure no progression of further visual field loss. Vision and visual fields are assessed again at four months.
NAION is thought to be caused by ischaemic damage to the optic nerve. No treatment is currently considered effective, visual improvement is unimpressive and the pathophysiology is largely unknown.7 It usually presents with acute, painless visual loss accompanied by an afferent pupil defect (APD) and disc oedema. Certain risk factors are thought to be associated with NAION and these include diabetes and obstructive sleep apnoea.5
The majority of patients with NAION have small optic discs with small or absent cups. The affected eye presents with optic disc oedema which may be diffuse or localised. There may also be nerve fibre layer haemorrhages. Optic nerve swelling may appear weeks to days before the visual loss presents, which may suggest an aetiology other than an acute arterial event.
Distinguishing NAION from Giant Cell Arteritis
In NAION, the degree of colour vision impairment corresponds to the visual acuity deficit.5 The relative sparing of colour vision and the lack of pain on eye movement suggests a diagnosis of NAION rather than optic neuritis.
Arteritic ischaemic optic neuropathy (AION), also called Giant cell arteritis (GCA) or temporal arteritis, should also be excluded although the aetiology and clinical findings between AION and NAION differ. Giant cell arteritis may be associated with systemic features such as scalp tenderness, headaches, jaw claudication and polymyalgia rheumatica.8 The infarcted optic disc in GCA is usually elevated, pale and can be associated with cotton wool spots (Table 1).
While GCA is known to be due to arterial occlusion and infection of the prelaminar optic nerve, NAION may be due to obstruction of venules draining from the optic nerve into the central retinal vein. This would explain the hyperaemic appearance of the optic nerve that resolves to leave a relatively preserved disc structure.7,9 It would also explain why NAION occurs in patients with hypoperfusion states such as diabetes and possibly sleep apnoea.
Differentiating between normal tension glaucoma and a previous NAION is difficult. Patients with these two conditions may have overlapping risk factors as both are thought to be associated with optic nerve hypoperfusion. NAION may be caused by transient nonperfusion or hypoperfusion of the optic nerve head.10 The intraocular pressures may be in the same ‘normal’ range for both conditions. The field defects may be similar with a partial altitudinal scotoma of NAION being mistaken for an arcuate scotoma associated with glaucoma.
New technology might allow for the differentiation to be easier as our understanding of these two conditions evolve.
In a recent study OCT-A was used to compare the optic nerve morphology in patients with either NAION, NTG or normal subjects matched by age, axial length, and optic disc area.10 Certain parameters, such as lamina cribosa depth and lamina cribosa curvature index were noted to be larger in NTG than in NAION or in healthy optic nerves. Unfortunately, these measurements are not usually reported on OCT or OCT-A. The retinal nerve fibre thickness did not differ between NTG and NAION.
The study showed that optic nerve cupping is significantly larger in NTG than in NAION even though the retinal nerve fibre layer (RNFL) loss and visual fields are very similar. The authors postulated that the fundamental pathology between NAION and NTG is different. NAION was considered to be a condition of transient optic nerve head hypoperfusion eventually leading to optic nerve pallor whereas NTG seemed to be due to mechanical stress on the lamina cribosa resulting in optic nerve cupping.10
OCT-A is also being used to differentiate NAION from NTG. Early findings seem to suggest that both NTG and NAION have reduced peripapillary perfusion. The lower perfusion densities in NTG may indicate greater vascular changes in NTG.
Patients with NAION should have diabetes, hypertension and hypercholesterolaemia excluded. Patients younger than 40 years should be referred for homocysteine level assessment and to exclude a systemic vasculitis.8
The treatment of NAION is challenging. There are no class one studies showing benefit from either medical or surgical treatments.11 Therapies aimed at secondary prevention of fellow eye involvement in NAION remain of unproven benefit.11 Suggested treatment to try to ‘protect’ the other eye may include treating ocular hypertension and some patients may have aspirin prescribed although there is no evidence of benefit.8
A patient with NAION can be advised that the chance of a similar event occurring in the other eye is about 15%12 and the chance of the NAION recurring in the same eye is low (5%).13
Differentiation unilateral glaucoma from longstanding or subacute NAION may be challenging. For the best patient outcomes, it important that a comprehensive eye examination including colour vision testing, field testing and OCT be conducted on the initial presentation. In the future, there may be a role for OCT-A to distinguish between these two conditions.
- Hayreh SS, Jonas JB, Zimmerman MB. Nonarteritic Anterior Ischemic Optic Neuropathy and Tobacco Smoking. Ophthalmology. 2007;
- R.A. Covar; A Lee; A Kifley; P Mitchell. Pseudo–Glaucomatous Visual Field Defects in an Older Population: Blue Mountains Eye Study [Internet]. Investigative ophthalmology & visual science. [cited 2022 Apr 12]. Available from: https://iovs.arvojournals.org/article.aspx?articleid=2393271
- Mastropasqua R, Agnifili L, Borrelli E, Fasanella V, Brescia L, Di Antonio L, et al. Optical Coherence Tomography Angiography of the Peripapillary Retina in Normal-Tension Glaucoma and Chronic Nonarteritic Anterior Ischemic Optic Neuropathy. Curr Eye Res [Internet]. 2018 Jun 3 [cited 2022 Apr 14];43(6):778–84. Available from: https://pubmed.ncbi.nlm.nih.gov/29451992/
- Kim JA, Lee EJ, Kim TW, Yang HK, Hwang JM. Comparison of optic nerve head microvasculature between normal-tension glaucoma and nonarteritic anterior ischemic optic neuropathy. Investig Ophthalmol Vis Sci. 2021 Aug 1; 62 (10).
- Archer EL, Pepin S. Obstructive sleep apnea and nonarteritic anterior ischemic optic neuropathy: Evidence for an association. Journal of Clinical Sleep Medicine. 2013.
- Mojon DS, Hedges TR, Ehrenberg B, Karam EZ, Goldblum D, Abou-Chebl A, et al. Association between sleep apnea syndrome and nonarteritic anterior ischemic optic neuropathy. Arch Ophthalmol. 2002;
- Levin LA, Danesh-Meyer H V. Hypothesis: a venous etiology for nonarteritic anterior ischemic optic neuropathy. Arch Ophthalmol (Chicago, Ill 1960) [Internet]. 2008 Nov [cited 2022 Apr 12]; 126 (11): 1582–5. Available from: https://pubmed.ncbi.nlm.nih.gov/19001228/
- A Pane. M A Burdon. N R Miller. The Neuro-ophthalmology Survival Guide. First Edit. Mosby Elsevier; 2006.
- Danesh-Meyer H, Savino PJ, Spaeth GL, Gamble GD. Comparison of arteritis and nonarteritic anterior ischemic optic neuropathies with the Heidelberg Retina Tomograph. Ophthalmology [Internet]. 2005 Jun [cited 2022 Apr 12]; 112 (6): 1104–12. Available from: https://pubmed.ncbi.nlm.nih.gov/15885786/
- Kim JA, Lee EJ, Kim TW, Kim H, Girard MJA, Mari JM, et al. Differentiation of Nonarteritic Anterior Ischemic Optic Neuropathy from Normal Tension Glaucoma by Comparison of the Lamina Cribrosa. Invest Ophthalmol Vis Sci. 2020;
- Atkins EJ, Bruce BB, Newman NJ, Biousse V. Treatment of Nonarteritic Anterior Ischemic Optic Neuropathy. Surv Ophthalmol. 2010 Jan; 55 (1): 47–63.
- Newman NJ, Scherer R, Langenberg P, Kelman S, Feldon S, Kaufman D, et al. The fellow eye in NAION: report from the ischemic optic neuropathy decompression trial follow-up study. Am J Ophthalmol [Internet]. 2002 Sep [cited 2022 Apr 12]; 134 (3):317–28. Available from: https://pubmed.ncbi.nlm.nih.gov/12208242/
- Berry S, Lin W V., Sadaka A, Lee AG. Nonarteritic anterior ischemic optic neuropathy: Cause, effect, and management. Eye and Brain. 2017.