October 08, 2020
6 min read
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Man presents with dark spot in peripheral vision

Automated perimetry testing showed a left homonymous inferior quadrantanopia.

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A 62-year-old man presented to the New England Eye Center comprehensive ophthalmology clinic for an urgent evaluation of a black shadow in the inferotemporal field of his left eye that started suddenly 4 days prior while he was sitting.

Christine Benador-Shen
Christine Benador-Shen
Malgorzata Dymerska Peterson
Malgorzata Dymerska Peterson

He did not have any pain, flashes, floaters, decrease in central vision, field loss in the right eye or injection. He otherwise felt well. The shadow moved slightly when he moved his head from left to center, and it was more prominent in brighter lighting. His ocular history included a right superotemporal operculated retinal hole with vitreous hemorrhage, for which he underwent laser retinopexy 6 years prior. He had not followed up for routine eye care since that time.

His medical history included mechanical mitral valve replacement after endocarditis for which he took warfarin and reported good compliance, history of opiate addiction for which he was on methadone, attention deficit disorder and anxiety, which was treated with clonazepam. He reported a 15-year history of smoking.

Examination

On examination, the patient’s best corrected visual acuities were 20/25-2 in the right eye and 20/25+2 in the left eye. Pupils were equal in size and reactive to light with no relative afferent pupillary defect. IOPs were 13 mm Hg bilaterally. Confrontation visual fields were full. Extraocular motility was full bilaterally. He correctly identified all of the Ishihara color plates in both eyes. Anterior segment exam was notable only for bilateral moderate nuclear sclerosis. On dilated funduscopic examination, both nerves were pink with sharp margins and small cup-to-disc ratios. A right superotemporal operculated retinal hole with good surrounding laser barricade was noted. There were no new retinal tears in either eye. The retinal vasculature was normal, and the vitreous was clear.

Ancillary testing

Automated perimetry testing (Humphrey visual field 30-2 SITA Fast) showed a left homonymous inferior quadrantanopia (Figure 1). OCTs of both the macula and the retinal nerve fiber layer were unremarkable.

Humphrey visual field
Figure 1. Humphrey visual field 30-2 of the left and right eyes, respectively, on initial testing. Testing was reliable in both eyes and demonstrated left inferior homonymous quadrantanopia that spared the macula. There were a few deficits superiorly, especially in the right eye, that were concerning for a left hemifield cut.

Source: Chelsea Gottschalk, MD, Melina Morkin, MD, Astrid Werner, MD, and Laurel N. Vuong, MD

What is your diagnosis?

See answer below.

Dark spot in peripheral vision

Given the unremarkable dilated examination and visual field testing showing a left homonymous visual field loss, there was concern for an intracranial process posterior to the optic chiasm on the right side. The differential diagnosis for this patient included ischemic or hemorrhagic cerebrovascular accident (CVA), tumor, arteriovenous malformation and trauma. The most common cause of a homonymous hemianopia in an adult is an ischemic stroke. Because our patient had a mechanical mitral heart valve and a history of opiate use disorder, there was concern that he could be embolizing from the valve either from a platelet thrombus or endocarditis vegetation. The patient’s significant other added that a few weeks prior, the patient had a 4-hour period in which he was acting confused, further adding to the suspicion that the patient may be actively embolizing from his mechanical valve to the brain.

Workup and management

The patient was sent directly to the emergency room at Tufts Medical Center for a stroke workup and neurology evaluation. CT of the head showed gray-white matter indistinction involving the medial right occipital lobe, concerning for a stroke. Because the onset of vision loss was 4 days prior, the patient was not a candidate for tissue plasminogen activator (tPA) treatment, which is typically given 3 to 4.5 hours after the onset of symptoms. He was admitted for further workup.

Subsequent MRI of the brain showed restricted diffusion of the medial right occipital lobe in the posterior cerebral artery (PCA) territory, compatible with an early subacute infarct (Figure 2). Additionally, there were several remote lacunar infarcts of the left cerebellar hemisphere as well as left inferior frontal gyrus encephalomalacia. CT angiography of the neck did not show any carotid or other large vessel stenosis, occlusion or dissection. An EKG showed normal sinus rhythm. HbA1c was 5.9% (in the prediabetic range), and low-density lipoprotein cholesterol was mildly elevated at 146. His international normalized ratio (INR) was 1.3, whereas the goal in the setting of a mechanical heart valve was 2.5 to 3.5. The patient was started on enoxaparin sodium injections until his INR was in the therapeutic range. A transthoracic echocardiogram did not show any vegetations or thrombus on the mechanical heart valve. Ultimately, it was thought the etiology of the strokes was most likely to be cardioembolic events from the patient’s mechanical valve in the setting of a subtherapeutic INR. The patient was discharged on a new warfarin regimen with close follow-up for INR monitoring. He was also started on a statin.

restricted diffusion in the medial right occipital lobe
Figure 2. MRI diffusion-weighted imaging sequence demonstrated restricted diffusion in the medial right occipital lobe in the posterior cerebral artery territory.

At follow-up in the neuro-ophthalmology clinic 4 weeks after discharge, the patient mentioned that the visual field loss appeared to be smaller. Repeat Humphrey visual field testing confirmed that the left homonymous inferior quadrantanopia had improved (Figure 3).

follow-up testing 4 weeks after initial exam
Figure 3. Humphrey visual field 30-2 of the left and right eyes, respectively, on follow-up testing 4 weeks after initial exam. Testing was reliable in both eyes and showed a more defined and slightly smaller left inferior homonymous quadrantanopia compared with initial testing.

Discussion

Ophthalmologists are uniquely positioned to diagnose CVAs from bilateral visual field loss in the absence of other neurologic symptoms. These patients often present to the ophthalmology clinic, not the emergency room, because they assume they have a primary ophthalmological problem instead of a neurological one. Additionally, while the majority of patients recognize their visual deficits as field loss, some only notice difficulty with reading or complain of blurred vision, many perceive the vision loss to be in one eye only, and a small percentage do not recognize any vision changes and the field loss is incidentally identified. Our patient perceived his vision loss to be only in the left eye rather than bilaterally. This case underlines the important role of automated perimetry in such evaluations and in helping to diagnose CVAs, as the ophthalmologist may be focused on finding a unilateral process instead of a bilateral cause of vision loss. While confrontation visual fields are a good initial examination technique, they can often miss more subtle field changes that are found on automated testing.

In our patient’s case, the pattern of visual field loss, the congruity between the two eyes and the lack of other neurologic symptoms highly suggested pathology in the occipital lobe. Other patterns commonly found with occipital lobe lesions include superior homonymous quadrantanopia, homonymous hemianopia, a monocular temporal crescent and a homonymous hemianopia sparing the temporal crescent contralateral to the lesion. Most of these visual field patterns demonstrate congruity compared with more anterior lesions, with the exception of the temporal crescent, which occurs in the anteromedial region of the occipital lobe as a result of a separation between crossed and uncrossed fibers. Additionally, infarcts of the posterior cerebral artery demonstrate macula sparing, as the central portion of the visual field is subserved by the tip of the occipital lobe, which receives its blood supply by both the PCA and middle cerebral artery. With our patient, the PCA was felt to be the only artery involved, which explains why the visual field demonstrates a macula-sparing quadrantanopia.

When patients present with acute or subacute homonymous field loss, an intracranial process is suspected, and it is important to send them to the emergency room for urgent workup, as a stroke can be high on the list of differential diagnoses, especially in patients like ours. If discovered within 3 to 4.5 hours after onset, these patients may benefit from tPA to increase the chance of recovery of the presenting deficits. Immediate evaluation and treatment will also prevent any additional events and debilitating symptoms.