Electrophysiology and Multimodal Imaging to the Rescue
By Rachel Patel, MD; Albert T. Vitale, MD; Donnell J. Creel, PhD; and Kathleen B. Digre, MD
A 67-year-old woman was referred to neuro-ophthalmology for visual disturbances that she had noticed for the last five years.
She reported continuous movement like a ceiling fan in her peripheral vision. Sometimes she would see smoke swirling around her, lights seemed to flicker, and she had prominent floaters. She had progressive difficulty with adaptation to dim-light conditions. She rarely had headaches. She had been seen by several ophthalmologists and neurologists and had received the diagnosis of visual snow, migraine with aura, or migraine symptoms.
Testing and a New Diagnosis
Her examination showed a normal visual acuity and normal visual fields to confrontation.
Her slit lamp examination showed old vitreous cells. Her neurological examination was normal. Her visual field showed peripheral losses in both eyes (Figure 1), and her optical coherence tomography (OCT) showed bilateral granular disruption of the ellipsoid zone that spared the fovea (Figure 2).
Because of the problem with poor dark adaptation, we obtained a full-field electroretinogram (ffERG) (Figure 3), which demonstrated evidence of poor rod function but normal cone function. The ffERG abnormalities in combination with her vitreous and retinal findings prompted a referral to our uveitis colleagues. Her dilated examination revealed subtle creamy yellow spots in the superior macula and periphery bilaterally, most prominently nasal to the optic discs (Figure 4). Indocyanine green angiography (ICG) showed numerous hypofluorescent spots in the mid- and farperipheral retina (Figure 4).
Based on her clinical appearance and multimodal imaging, a diagnosis of birdshot chorioretinopathy was made. This diagnosis was further suggested by HLA-A29 positivity, and by a normal basic laboratory workup and chest X-ray to exclude alternative conditions such as sarcoidosis and lymphoma.
Birdshot Chorioretinopathy Symptoms and Treatment
Birdshot chorioretinopathy is an uncommon chronic bilateral posterior uveitis, named for the characteristic cream-colored retinal spots scattered in a “birdshot” pattern. While nearly all patients with birdshot chorioretinopathy are HLA-A29 positive, routine testing is not fruitful as the haplotype is present in approximately 7 percent of the general population.
Birdshot chorioretinopathy can be treated with immunosuppression. Monitoring for disease activity and initiating appropriate therapy is paramount; without treatment, disease progression may be insidious and result in irreversible vision loss.
Visual snow is a syndrome of positive visual phenomena in the visual field. While many such patients have had migraine, the constant presence of the visual disturbances differentiates it from migraine aura. The cause of visual snow is thought to be a visual processing disorder in the brain. It is considered a benign condition, and treatments are generally not successful. Most people, after learning of the diagnosis, develop the ability to ignore their symptoms.
As in patients with visual snow, patients with birdshot chorioretinopathy can have visual disturbances despite excellent visual acuity. However, there are differentiating features of birdshot chorioretinopathy that distinguish it from visual snow, including older age of onset, delay in dark adaptation (in contrast to nyctalopia alone), and absence of constant tiny flickering dots in the visual field. Birdshot chorioretinopathy tends to be a slowly progressive disease that can result in visual field loss and eventual loss of central visual acuity (often due to macular edema); therefore, recognition of the signs that distinguish birdshot chorioretinopathy from more benign etiologies of visual phenomena is critical.
While visual symptoms such as floaters and headaches are very common, not all visual symptoms are attributable to migraine or visual snow. Signs that may indicate that a uveitic or retinal pathology may be contributing include vitritis, focal visual field losses, and particularly electrophysiologic abnormalities. Patients with atypical symptoms or presentation may benefit from a multimodal imaging approach to determine the underlying etiology.
About the Authors
Dr. Digre specializes in neuro-ophthalmology and evaluates and treats complex visual complaints, which can be due to the optic nerve or brain disease.
Dr. Vitale directs Moran’s Uveitis Division and is one of the few ophthalmologists in the Mountain West specializing in the diagnosis and treatment of uveitis and other infections and inflammatory diseases of the eye.
Dr. Creel directs electrophysiology at the Moran Eye Center.
Dr. Patel is a second-year resident at the Moran Eye Center.