Simultaneous and Bilateral Non-Arteritic Anterior Ischaemic Optic Neuropathy and Acute Angle-Closure

ABSTRACT

Non-arteritic anterior ischaemic optic neuropathy (NAION) is the second most common cause of permanent optic nerve-related visual loss in adults after glaucoma. NAION is caused by complex mechanisms that lead to optic nerve head hypoperfusion and is frequently associated with cardiovascular risk factors like type 2 diabetes mellitus (DM2) and hypertension. An attack of acute angle-closure (AAC) occurs when the trabecular meshwork is blocked with peripheral iris that causes an abrupt rise in intraocular pressure, which can trigger a decrease in optic nerve head perfusion. We present a case with simultaneous and bilateral AAC and NAION in association with uncontrolled DM2.

Introduction

An attack of acute angle-closure (AAC) occurs when the trabecular meshwork is blocked with peripheral iris and leads to an abrupt rise in intraocular pressure (IOP).¹ Untreated, it may cause permanent vision loss.² Most AAC episodes are unilateral, but up to 10% of patients may have bilateral ACC.³ After the acute event the optic nerve might respond with minimal or no changes, typical glaucomatous cupping, or in some cases pallor and reduction in the retinal nerve fibre layer (RNFL) with minimal cupping.⁴

Non-arteritic anterior ischaemic optic neuropathy (NAION) is the second most common cause of permanent optic nerve-related visual loss in adults after glaucoma.⁵ It is part of the group of ischaemic optic neuropathies that are more common in older patients, with an annual incidence of 2.3 to 10.2 cases per 100,000 persons 50 years of age or older.⁶ It is commonly associated with arterial hypertension (50%), nocturnal hypotension, and diabetes mellitus (25%).⁶ Its pathogenesis is frequently related to hypoperfusion of the posterior ciliary arteries of the optic nerve head (ONH) that results in ischaemia.⁶ The optic nerve appearance after the resolution of this type of ischaemic damage is characterized by ONH pallor, reduced RNFL thickness, and minimal optic disc cupping.

Some patients with an AAC, after the resolution of the acute event, develop a pale optic disc with minimal cupping similar to optic nerves after NAION. These similarities that some patients develop after an AAC could be partially explained by the effect that IOP has on ocular perfusion. After an increase of around 50 mmHg of the IOP, the inner retinal capillary density decreases.⁷ The present case with simultaneous and bilateral AAC and NAION is an interesting example of the complex relationship between IOP and ocular perfusion.

Case report

A 55-year-old woman without previous ophthalmological problems but with long-standing uncontrolled type 2 diabetes mellitus (DM2) presented with a one-week history of frontal headache and nausea. Five days before presentation, she complained of vision deterioration in the left eye (OS) followed by the right eye (OD) the following day. The patient denied symptoms of giant cell arteritis (GCA) or the use of any new medication or eye drops over the previous days. The patient had not been previously evaluated in our Ophthalmology clinic.

On examination, the uncorrected visual acuity was counting fingers in both eyes (OU). Her eye movements were normal. Anterior segment slit-lamp examination revealed bilateral mild conjunctival hyperaemia, ciliary flush, corneal epithelial microcystic oedema, shallow anterior chambers, and fixed and dilated pupils OU. Posterior pole examination was difficult because of corneal oedema but revealed hyperaemic optic discs OU. Further details of the ONH were not possible to assess. The IOPs were 42 mmHg OD and 32 mmHg OS. Gonioscopy revealed closed angles.

She was diagnosed with bilateral AAC and treated with timolol 0.5%/dorzolamide 2%/brimonidine 0.2% (Krytantek®, Sophia®) and pilocarpine 0.5% drops. The IOP decreased to 20 mmHg OD and 22 mmHg OS over the following hours. The next day, the uncorrected visual acuity was 20/160 OU. The patient had dyschromatopsia but denied diplopia or pain during ocular movements. The ciliary flush and corneal oedema had disappeared and her pupils were fixed and small secondary to the pilocarpine. The IOP was 8 mmHg OU. Visualisation of the posterior pole improved and confirmed the presence of ONH oedema with the addition of peripapillary haemorrhages OU (Figure 1a and Figure 1b) as well as retinal haemorrhages and exudates compatible with diabetic retinopathy. ONH optical coherence tomography (OCT) (Cirrus HD-OCT^TM, Carl Zeiss Meditec AG, Jena, Germany) showed an increase in RNFL and neuroretinal rim thickness (Figure 2a).

Figure 1.

Colour fundus photography (FF450^plus with VISUPAC^TM, Carl Zeiss Meditec AG, Jena, Germany) of the right (A, C) and left (B, D) optic nerve heads (ONH). A and B: Swollen ONHs with scant peripapillary haemorrhages in both eyes on the 1^st day after acute angle-closure. C and D: Right and left ONHs one month later

Figure 2.

Optical coherence tomography (OCT) (Cirrus HD-OCT^TM, Carl Zeiss Meditec AG, Jena, Germany) optic disc cube 200 × 200 scan report of both eyes. A: The 1^st day after acute angle-closure, evidencing marked augmentation of the retinal nerve fibre layer thickness. B: Optic nerve head changes one month later

The neurological assessment was unremarkable. The erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) levels were normal. Brain and orbit magnetic resonance imaging were unremarkable.

The updated diagnosis was simultaneous and bilateral AAC and NAION. She underwent laser peripheral iridotomy the day after the initial presentation that reduced the IOP without the need for further anti-glaucomatous treatment.

One month later, she remained asymptomatic with pinhole visual acuity of 20/100 OU. The IOP was 15 mmHg OD and 12 mmHg OS and she had patent iridotomies. The ONH examination showed disc pallor, well-defined borders, lack of ‘disc-at-risk’ characteristics, and an asymmetric cup-to-disc ratio of 0.4 OD and 0.6 OS (Figure 1c and Figure 1d). Kinetic Goldmann visual fields were performed and showed generalised depression. ONH OCT showed complete resolution of the oedema (Figure 2b), although, in subsequent OCT examinations the RNFL thickness was reduced. The diabetic retinopathy had progressed from the first examination, and a sub-hyaloid haemorrhage was identified in OS. A fluorescein angiogram identified zones of retinal capillary non-perfusion and neovascularisation of the retina OU but the ONH did not show early staining or leakage. A macular OCT revealed changes associated with previous episodes of untreated diabetic macular oedema. A diagnosis of proliferative diabetic retinopathy was confirmed, and she was scheduled for pan-retinal photocoagulation.

Discussion

The vascular regulatory mechanism in diabetic microangiopathy in response to a sudden increase in intraocular pressure is presently unknown. Previous cases of AAC and NAION have been rarely described. In 2001 Slavin et al.⁸ reported one case of bilateral NAION in a patient with an AAC a month apart between eyes. Other cases of simultaneous AAC and NAION have been described unilaterally.^9–11 To our knowledge, simultaneous bilateral presentation has been only reported by Torricelli et al.¹² in a patient with iridoschisis.

In the present case, the NAION could have been precipitated by the acute IOP rise secondary to the AAC. She did not have the typical ‘disc-at-risk’ or crowded configuration but very likely had the microvascular and autonomic abnormalities found in patients with DM2.¹³ Diabetic patients have a diminished ability to respond to changes in perfusion pressure in the event of an IOP rise.¹⁴ This dysfunction seems to be further attenuated by hyperglycaemia.¹⁵ In the present case, both factors were present at the time of the first examination.

The relationship between IOP and ischaemic damage to the optic nerve has been extensively described in animal models.¹⁶ More recently, this relationship has been supported using OCT angiography. An IOP over 50 mmHg, which is common in AAC, affects the vessel density of the inner retinal vessels and could jeopardise the circulation of the optic nerve.⁷ In our case, the coexistence of uncontrolled DM2 could have also participated, reaching the level of disruption required to affect ONH perfusion.

An alternative hypothesis is that the NAION developed first and triggered an AAC in a patient with a susceptible occludable anterior chamber angle. An increase in choroidal thickness has been previously identified in patients with NAION¹⁷ and it could be the factor required to modify the anatomy of the ciliary body pushing it forward and occluding a previously predisposed narrow angle.

Irrespective of the primary factor that triggered the simultaneous damage to the optic nerves and the anterior segment it is important for clinicians to actively examine the optic nerves during an attack of AAC and the anterior chamber in patients with NAION.

Declaration of interest statement

No potential conflict of interest was reported by the authors. Informed consent was obtained prior publication of this case report.