Optometry

A 70-year-old man presented to the emergency room complaining of progressive vision loss in the left eye over the last 2 weeks. He described a gradual decline with no aggravating or alleviating conditions known. The subjective vision loss was primarily in the inferior field of the left eye; he also had nonspecific pain around both eyes. The patient denied any temporal mandibular pain upon chewing or talking.

Further questioning revealed the patient had not taken his hypertension medication for 3 months. He took the following medications for blood pressure control: amlodipine 10 mg at bedtime, fosinopril 40 mg at bedtime, hydrochlorothiazide 25 mg daily, metoprolol tartrate 50 mg twice daily and clonidine HCl 0.1 mg twice daily. He also took aspirin 81 mg daily as a blood thinner, glipizide 5 mg twice daily and metformin HCl 1,000 mg twice daily for diabetes and omeprazole 20 mg daily for gastroesophageal reflux disease.

Figure 1. On dilated fundus examination, the retina and optic nerve appeared healthy in the right eye with a cup-to-disc ratio of 0.1; the left optic nerve head was hyperemic and edematous with no appreciable cupping. Images: Bockin D

On physical examination in the emergency room, his blood pressure was 240/100 mm Hg, oral temperature was 97.9° F (36.6° C), his chest was clear, heart sounds were regular without murmur, his abdomen was obese and soft, he had active bowel sounds and was non-tender to palpation, and his extremities had no significant edema or gross cyanosis or clubbing. His EKG showed sinus rhythm.

The patient was started on IV hydralazine for hypertension, which lowered his blood pressure to 171/90 mm Hg. Blood work showed normal platelet count and erythrocyte sedimentation rate and a glucose level of 143. In addition, a non-contrast head CT scan was performed to rule out stroke.

Figure 2. The field loss in the left eye was confirmed with automated Goldman perimetry using a size III 4E white target; the greatest restriction was inferior nasal, although the entire inferior field was constricted overall.

Figure 3. The imagery from the head CT performed earlier was available after the exam was completed. It was negative for stroke.

The ER sent the patient to the eye clinic for emergent examination for his vision loss after his blood pressure stabilized. His prior best corrected acuity from the medical chart was OD +0.75 +1.75 x 160 20/20 and OS +1.25 +0.25 x 015 20/20. On the day of my examination, his acuity was OD +0.75 +1.75 x 160 20/25 and OS +1.25 +0.25 x 015 20/70. There was no improvement with pinhole. In addition, the patient continued to tip his body forward to see chart.

The patient’s external eye examination was noted for full and smooth eye movements in all positions of gaze, clear corneas and nuclear sclerosis in both eyes that was not consistent with the field loss. Applanation tonometry was 30 mm Hg in both eyes. There was an abnormal pupillary response in the left eye, and pupillary testing revealed a mild relative afferent pupillary defect.

Gross confrontation visual fields showed constriction of the inferior field in the left eye and a full field in the right. The field loss in the left eye was confirmed with automated Goldmann perimetry (Zeiss-Humphrey) using a size III 4E white target; the greatest restriction was inferior nasal, although the entire inferior field was reduced overall. Goldmann kinetic visual field was performed because I did not feel the patient had the cognitive ability to respond to a standard HVF 24-2.

On dilated fundus examination, the retina and optic nerve appeared healthy in the right eye with a cup-to-disc ratio of 0.1; the left optic nerve head was hyperemic and edematous with no appreciable cupping.

The imagery from the head CT performed earlier was available after the exam was completed.

What is your diagnosis?

Differential diagnosis would include nonarteritic ischemic optic neuropathy, inflammatory optic neuritis, compressive optic nerve tumor, central retinal vein occlusion, central retinal artery occlusion, arteritic ischemic optic neuropathy (giant cell arteritis), pseudotumor cerebri and true papilledema. The diagnosis was anterior non-ischemic optic neuropathy.

The most urgent consideration among this list would be giant cell arteritis. This was ruled out with normal sedimentation rate and absence of concordant symptoms. Other vascular events were eliminated by fundus appearances. Also low on the differential list are the inflammatory optic nerve etiologies. The patient’s profile is most consistent with nonarteritic anterior ischemic optic neuropathy (AION).

Figure 4. Fundus exam revealed a normal optic nerve in the right eye with a sector optic atrophy in the left eye.

Figure 5. Hemorrhages and edema have cleared. Repeat visual fields were ordered and there was no appreciable change in visual field loss.

AION is attributed to ischemia at the optic nerve head due to structural crowding that may impair perfusion to the nerve and thereby cause edema. The condition is divided into two sub-categories: non-arteritic (NAION) and arteritic (AAION).

AAION is most commonly associated with temporal arteritis. Patient demographics for AION are typically older than 50 years; the median age group for NAION is older than 60, and with AAION the median age is 70 years old. There is a gender predilection for females, but only in cases of AAION. Incidence of AAION is 5% to 10% of cases of AION, while NAION accounts for 90% to 95%, according to Arnold.

Patients with either form of AION typically report a rapid onset of painless, unilateral vision loss manifested by decreased visual acuity, decreased visual field or both. Vision loss is more severe in AAION, typically worse than 20/200. The most common visual field defect with either form of AION is altitudinal, but it may also present as a general depression, an arcuate scotoma or a cecocentral defect.

A retrospective study using Goldmann perimetry suggested that the most common field loss was actually inferior nasal and, when combined with overall inferior field loss, it is highly indicative of NAION. The inferior nasal defect is explained by the location of the watershed zone of the posterior ciliary arteries, which is often temporal to the optic nerve head and the most susceptible to ischemia.

Figure 6. The left eye showed thinning from 240° to 110° and from 160° to 200°. This indicated more RNFL damage than the larger sector optic atrophy on physical exanimation.

Signs of an AION are a pale and hyperemic optic nerve head with edema (diffuse or segmental) in the acute phase and optic atrophy in later stages. The edema may be present several weeks to months before vision loss is reported. Arnold suggests that in AAION, the disc is more pallid than hyperemic, which is more common with NAION.

Flame hemorrhages and narrowed peripapillary arterioles are also associated with AION. Because the presentation is typically unilateral, a relative afferent pupillary defect is often expected. Systemic associations with the arteritic form are symptoms common with temporal arteritis (i.e., headache, jaw claudication and scalp tenderness). Vision loss in the arteritic form may be preceded by episodes of transient vision loss, which is also highly indicative of arteritis.

The patient presented in this case study appeared to have more factors associated with the non-arteritic form; therefore, the rest of this discussion will focus primarily on NAION.

No proven systemic associations

This form of AION has no proven systemic associations; however, according to Hayreh, studies suggest that a patient with arterial hypertension (including the malignant form), nocturnal arterial hypotension, diabetes mellitus, ischemic heart disease, migraines or sleep apnea are at higher risk for developing a NAION.

Nocturnal hypotension is thought to play a significant role, considering 73% of patients with NAION report vision loss upon awakening. This is especially true for patients who take their anti-hypertensive medications at night or some prostatic hypertrophy medications.

A study by Landau and colleagues that focused on 24-hour monitoring of blood pressure in both hypertensive and control patients found that patients on medication for high blood pressure tended to have a lower overall reading and tended to have a slower and unsteady rise to typical daytime levels. This evidence suggests that the causative factor in NAION is chronic hypoperfusion of the nerve rather than an isolated ischemic event.

The study also applied the J-curve hypothesis to the control of hypertension, indicating that there is an optimal level of blood pressure above which incidence of disease decreases as it approaches the ideal level and below which it increases.

Ocular risk factors

A crowded optic disc with a small or absent cup-to-disc ratio is considered a “disc at risk” for developing NAION. According to Hayreh, other ocular risk factors are the location of the watershed zone for the posterior ciliary arteries, vascular disorders in the arteries supplying the optic nerve head, optic disc drusen, cataract extraction and elevated intraocular pressure. Vision loss in cases of NAION can be “static” or “progressive,” indicating that the initial loss may stabilize or worsen over the course of several weeks to months after the primary event.

According to Arnold, the progressive form is found in 22% to 37% of patients with NAION. In some cases, a patient with NAION may also report periorbital pain. The risk of the fellow eye developing an NAION is 12% to 19% over the course of 5 years, Hayreh said.

Proposed treatments

Several treatments have been proposed for NAION; however, no statistical support has shown that any of the treatments are particularly effective. The current options include optic nerve sheath decompression, aspirin (to prevent occurrence in the fellow eye), levodopa, systemic corticosteroid therapy and intravitreal injections of bevacizumab.

Optic nerve sheath decompression was first proposed in 1989 for cases of progressive NAION; however, it has been implemented in all forms of NAION, and research shows it may be more harmful than helpful because 24% of patients who had the procedure had further visual loss compared to only 12% of untreated patients. This is especially hazardous considering 41% to 43% of cases show spontaneous improvement in visual acuity with no treatment, reported Hayreh.

The use of aspirin after the initial event has been suggested to help prevent occurrence in the second eye. Again, long-term studies have disproven this theory, considering aspirin has no effect on nocturnal hypotension, Hayreh said. Levodopa was another proposed drug therapy but there is not enough statistical support to show efficacy.

Hayreh reported that systemic corticosteroids have been used effectively in cases of arteritic AION, but research has shown that patients with NAION treated within the first 2 weeks of onset, with a visual acuity of 20/70 or worse, showed improvement in 70% of cases compared to 41% of untreated cases. Visual field defects also improved in 40% of patients treated with corticosteroids vs. 25% of the untreated cases.

Intravitreal injections of bevacizumab have been used to treat a variety of ocular diseases including macular edema and macular degeneration. This drug was first proposed for use in NAION in 2007 with the intention of reducing optic disc edema and therefore improving visual acuity. A few cases reports since then have shown some patients developed NAION after receiving the injection. However, as mentioned before, disc edema can precede visual loss by approximately 6 weeks and, therefore, the injections could have precipitated the NAION by increasing IOP that, in turn, decreases the perfusion pressure to the eye, reported Hayreh.

AION can be a devastating condition for the patient due to the sudden loss of vision. As eye care providers, it is vital to understand the mechanism of this disease and be able to provide support and understanding during the course of treatment. Though no clear solution is available for NAION, knowing the patient’s options can provide some clarity and hope for the future.

Patient management

The patient’s assessment at this visit was anterior non-ischemic optic neuropathy with elevated IOP, and he was instructed to use Alphagan P (brimonidine tartrate, Allergan) twice a day and consider adding Travatan Z (travoprost, Alcon) once at bedtime in each eye after the inflammation has subsided to help reduce the pressure. He was scheduled to return for a follow-up in 1 month to monitor IOP and vision in the left eye.

According to Hayreh, treatment of elevated IOP is controversial with NAION. Because of the patient’s reported systemic medication noncompliance and elevated IOP on exam, it was elected to treat with ocular hypertensive medications.

Follow-up visits

On his first follow-up, the patient had no new symptoms. As with his initial examination, the patient was still again out of systemic medications and only refilled his prescription that day. He stated he used the Alphagan P but did not re-fill or ask for more drops. He said he can see better than at the last visit. His systemic profile improved to an A1c of 6.3% and fasting glucose of 174 mg/dL.

Visual acuity did not improve with glasses; it was OD 20/25 and OS 20/70 with pinhole. He had to tip forward to see the chart; if he did not, his acuity was 20/400. Applanation tonometry was 20 mm Hg in each eye.

Fundus exam revealed a normal optic nerve in the right eye with a sector optic atrophy in the left eye. The hemorrhages and edema had cleared. Repeat visual fields showed no appreciable change in visual field loss.

The treatment plan was now to use only one bottle of drops. His IOP was still above normal. The patient continued to be noncompliant with both systemic medications as well as ocular. I felt some of the noncompliance was due to possible confusion from mild brain edema as a consequence of uncontrolled hypertension. I asked him to use brimonidine twice daily.

On the next follow-up exam, ocular coherence tomography showed normal retinal nerve fiber layer (RNFL) in the right eye and significant loss of RNFL in the left eye. With the TSNIT images that are overlaid on the age-related normative data background, the left eye showed thinning from 240° to 110° and from 160° to 200°. This indicated more RNFL damage than the larger sector optic atrophy on physical exanimation.

At this exam, applanation tonometry was OD 14 mm Hg and OS 16 mm Hg, and his cognitive abilities were much improved. I asked him to return, ordered a HVF 24-2 and considered discontinuing the brimonidine.

On the next follow-up examination the patient said he had been instilling his drops and taking his systemic medication. Once again he was down to 1 day of medication, and I got his physician and the pharmacy to renew all systemic medications.

His IOP was 18 mm Hg in both eyes. His threshold visual field showed the right eye as normal and the left eye with complete inferior homonymous hemianopsia. Once again, because of his history, I did not discontinue the brimonidine, but he will take a “drop vacation” 30 days prior to the next follow-up examination, which will be in 60 days.

References:

• Arnold, AC. Ischemic optic neuropathies. Ophthalmol Clinic North Am. 2001;14:83-98.
• Hayreh SS. Ischemic optic neuropathy. Prog Retin Eye Res. 2009;28(1):34-62.
• Hayreh SS. Management of non-arteritic anterior ischemic optic neuropathy. Graefes Arch Clin Exp Ophthalmol. 2009;247:1595-1600.
• Hayreh SS, Zimmerman B. Visual field abnormalities in nonarteritic anterior ischemic optic neuropathy: Their pattern and prevalence at initial examination. Arch Ophthalmol. 2005;123:1554-1562.
• Landau K, Winterkorn JS, Mailloux LU, et al. Twenty-four-hour blood pressure monitoring in patients with anterior ischemic optic neuropathy. Arch Ophthalmol. 1996;114:570-575.

• Donald G. Bockin, OD, can be reached at the Central Texas Veterans Health Care System, 1901 Memorial Drive, Temple, TX 76504; (254) 743-0733; donbockin@gmail.com.
• Edited by Leo P. Semes, OD, professor of optometry, University of Alabama at Birmingham and a member of the Primary Care Optometry News Editorial Board. He may be contacted at 1716 University Blvd., Birmingham, AL 35294-0010; (205) 934-6773; fax: (205) 934-6758; lsemes@uab.edu.