Maculopathies can mimic an optic neuropathy (Table 4-1). They can produce decreased visual acuity and central visual field loss with variable color vision loss. However, unless there is extensive retinal abnormality, relative afferent pupillary defect (RAPD) in maculopathies is usually not present. Maculopathy tends to cause parallel losses in color discrimination and visual acuity, unlike optic nerve disease, which may cause a disproportionately greater loss in color vision than in visual acuity, particularly if the disease is inflammatory or compressive. The exception is cone dystrophy, in which there is relatively unimpaired central visual acuity in patients experiencing severe color impairment.
Table 4-1 Clinical Distinction Between Optic Neuropathy and Maculopathy
Visual field deficits in maculopathy tend to be focal and central, whereas deficits in optic neuropathies tend to be larger, often cecocentral, and part of a generalized depression of visual field sensitivity. Metamorphopsia almost always has a macular origin and is a symptom of optic neuropathies only in rare cases. In general, maculopathies produce visible fundus abnormalities that can aid correct diagnosis but that, when subtle, can be mistaken for optic neuropathy. Optical coherence tomography (OCT), autofluorescence imaging of the macula, fluorescein angiography, and multifocal electroretinography (ERG) may help detect an abnormality in retinal structure or function. (See Chapter 3 and BCSC Section 12, Retina and Vitreous, for further discussion of these imaging techniques.)
Common maculopathies and retinopathies that are often mistaken for optic nerve disease include acute idiopathic blind-spot enlargement (AIBSE) and acute zonal occult outer retinopathy (AZOOR), both of which overlap with multiple evanescent white dot syndrome (MEWDS), as well as cone dystrophy. Patients with these entities may present with normal funduscopic findings. Rarer entities include cancer-associated retinopathy and melanoma-associated retinopathy. Other retinal disorders that may be mistaken for optic neuropathies include central serous chorioretinopathy and cystoid macular edema (these disorders are discussed in detail in BCSC Section 12, Retina and Vitreous).
Acute Idiopathic Blind-Spot Enlargement, Acute Zonal Occult Outer Retinopathy, and Multiple Evanescent White Dot Syndrome
Traditionally, enlargement of the blind spot (Fig 4-1) on visual field testing is associated with changes of the optic nerve head (ONH) such as edema or tilting. However, the term AIBSE describes a clinical syndrome in which the prominent visual symptom is a monocular scotoma, often temporal in location and associated with photopsias. The main finding is an enlarged blind spot. The fundus may appear normal or show evidence of ONH edema, peripapillary retinal lesions, choroiditis, changes in the retinal pigment epithelium (RPE), or uveitis.
Figure 4-1 Enlargement of the blind spot in the left eye, as shown on Humphrey 24-2 perimetry. A 32-year-old woman presented with a 6-month history of continuously flashing lights to the left side in her left eye. Visual acuity was 20/15 bilaterally with a <0.3–log10 unit left afferent pupillary defect. Results of automated quantitative perimetry show enlargement of the physiologic blind spot. This temporal defect does not respect the vertical midline.
(Courtesy of Michael S. Lee, MD.)
The term AZOOR is used to describe a syndrome similar to AIBSE but with more extensive retinal changes. This variability has led to controversy over whether these entities are separate or a spectrum of 1 disorder. MEWDS exemplifies this controversy. Fundus examination may reveal characteristic small, deep retinal white spots in the posterior retina that usually last for weeks and resolve spontaneously. The transient nature of the lesions could explain the normal retinal appearance at first examination. Photopsias are a prominent symptom thought to reflect disease of the outer retina. Fluorescein angiography and indocyanine angiography are often abnormal. Multifocal ERG shows depression in the peripapillary region, whereas a full-field ERG response may demonstrate depressed a-waves or substantial intereye asymmetry. Spectral-domain OCT may reveal attenuation of the outer layers.
Although AIBSE, AZOOR, and MEWDS represent outer retinal disorders, patients with these conditions may have a small RAPD. In general, patients with these disorders have a good visual prognosis. (See BCSC Section 9, Uveitis and Ocular Inflammation, and Section 12, Retina and Vitreous, for further discussion.)
Gross NE, Yannuzzi LA, Freund KB, Spaide RF, Amato GP, Sigal R. Multiple evanescent white dot syndrome. Arch Ophthalmol. 2006;124(4):493–500.
Jampol LM, Wiredu A. MEWDS, MFC, PIC, AMN, AIBSE, and AZOOR: one disease or many? Retina. 1995;15(5):373–378.
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Volpe NJ, Rizzo JF III, Lessell S. Acute idiopathic blind spot enlargement syndrome. A review of 27 new cases. Arch Ophthalmol. 2001;119(1):59–63.
Excerpted from BCSC 2020-2021 series: Section 5 - Neuro-Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.