Acute Idiopathic Blind Spot Enlargement (AIBSE) Syndrome
Acute idiopathic blind spot enlargement (AIBSE) syndrome is occult peripapillary retinopathy first described by Fletcher et al. in 1988. The report includes 7 cases presenting with a steep edged scotoma centered on the blind spot with photopsia and a normal fundus exam.
AIBSE syndrome has since been postulated to present either as an isolated finding or as an entity among a spectrum of primary inflammatory choriocapillaropathies (PICCP) with circumscribed loss of outer retinal function. This spectrum of chorioretinopathies includes acute zonal occult outer retinopathy (AZOOR), multiple evanescent white dot syndrome (MEWDS), acute macular neuroretinopathy (AMN), punctate inner choroidopathy (PIC), presumed ocular histoplasmosis syndrome (POHS), and multifocal choroiditis and panuveitis (MCP). 
Patients with AIBSE syndrome are generally young to middle-aged (average in the third decade of life) with a range of age- onset between 10 and 57 years old. There is a female predominance for AIBSE but males can be affected There is a higher incidence of AIBSES in Caucasian patients and patients with high to moderate myopia.
The pathogenesis of AIBSES remains elusive. However, a viral illness (e.g., influenza) or vaccination (e.g., measles, mumps, and rubella (MMR)) may act as an immunological trigger. Some authors have speculated that AIBSE is induced by choriocapillaris lesions causing a functional barrier within the outer retinal layer. Liu et al. hypothesized a model of the pathogenesis to be the following:
1. An acute inflammatory phase, where peripapillary choriocapillaris inflammation induces mild fundus changes within 2 weeks.
2. An involuting inflammatory phase, where the acute choriocapillaris inflammation gradually attenuates.
3. A chronic phase, where lesions can form.
Optical coherence tomography (OCT) and multifocal electroretinography (mERG) can be helpful in making the diagnosis of AIBSES. OCT can demonstrate microstructural alterations in the outer retina and mERG can demonstrate functional abnormalities even in the absence of structural lesion on the exam or OCT. Formal automated visual field testing demonstrates the unilateral or bilateral enlargement of the blind spot. Indocyanine green angiography (ICGA) and fundus fluorescein angiography (FFA) may also demonstrate abnormalities in AIBSES.” 
AIBSES is typically characterized by acute, unilateral onset of a scotoma centered on an enlarged blind spot, positive visual phenomena (i.e., photopsia), and a loss of vision in the absence of optic disc edema. Photopsia is the most prevalent positive visual phenomena. However, swirling, movement within the scotoma, colored lights, and after “flash bulb” sensations can also be identified in some patients. In addition, loss of vision symptoms commonly manifests as blurring, awareness of darkened areas or missing vision, spots in vision and, /or “looking through film” sensations.
Exam Findings & Testing
Ocular exam findings include enlargement of blind spot on visual field testing, dyschromatopsia, a variable relative afferent pupillary defect and, a normal fundus and optic disc. Patients may complain of typically mild decreased visual acuity or contrast sensitivity. Although most cases have a normal fundus exam, mild optic disc abnormalities (e.g., mild optic disc swelling or hyperemia) or subtle abnormalities on FFA (e.g., disc hyperfluorescence) can occur. Furthermore, intraocular inflammation, nonspecific retinal pigment epithelial changes or peripapillary “subretinal grayish discoloration”, and peripapillary vascular changes are sometimes observed. 
Visual Field Testing
Automated visual field testing typically demonstrates the blind spot enlargement. 
Fundus Fluorescein Angiography (FFA)
Indocyanine Green Angiography (ICGA)
Results from ICGA have been reported much less frequently. Some reports however, do identify abnormalities such as multiple hypofluorescent spots around the optic disc and arcades. There is speculation that the observed spots may indicate occluded choriocapillaris lobules as a result of inflammation. 
Optical Coherence Tomography (OCT)
During the acute phase of the disease, loss of regularity of the ellipsoid zone (EZ) or interdigitation zone (IZ) may be observed. Additionally, detection of transient discontinuity to the external limiting membrane (ELM) corresponds to diffuse outer retinal layer damage in the macula. 
Multifocal Electroretinography (mERG)
Fundus Autofluorescence (FAF)
Peripapillary autofluorescence enhancement may be observed. 
Magnetic Resonance Imaging (MRI)
Negative findings on MRI. 
Adaptive Optics Scanning Laser Ophthalmoscopy (AO-SLO)
Depletion of cone reflectivity with subsequent partial cone profile recovery has been observed.
AIBSES has been speculated as a late manifestation of MEWDS without the dots, although the penchant for the peripapillary retina dysfunction suggests a local etiologic factor and differentiates AIBSE from MEWDS and other PICCPs.
- Acute posterior multifocal placoid pigment epitheliopathy
- Serpiginous choroiditis
- Birdshot retinochoroidopathy
Treatment remains unclear.
However, OCT findings indicate AIBSE syndrome to be a self-limited, widespread pathology of the outer retina.
After 4 weeks, the majority of symptoms including the positive visual symptoms and the peripapillary scotoma typically resolve. Furthermore, improvement of the continuity of the ELM and EZ with marked visual field improvement is usually observed after approximately 3-4 months.  However, the enlargement of the blind spot usually does not return to normal and peripapillary scars may be observed. Moreover, residual photopsia and visual defects can occur in some patients.
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- Wong M, Campos-Baniak M, Colleaux K. Acute idiopathic blind spot enlargement syndrome following measles, mumps and rubella vaccination. Can J Ophthalmol. 2018.
- Doan A, Lee A, Boldt H. Acute Zonal Occult Outer Retinopathy (AZOOR) and Acute Idiopathic Blind Spot Enlargement Syndrome (AIBSE): 34-year-old female awoke with painless loss of vision OS 3 weeks prior to presentation. EyeRounds.org 2005.
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- Piri N, Kaplan H, Sigford D, Tezel T. High-definition Optical Coherence Tomography Findings in Acute Idiopathic Blind Spot Enlargement (AIBSE) Syndrome. Ocular Immunology and Inflammation 2014;22(6):494-496.
- Fletcher W, Imes R. Acute Idiopathic Blind Spot Enlargement and Acute Zonal Occult Outer Retinopathy: Potential Mimics of Neuro-Ophthalmic Disease. Journal of Neuro-Ophthalmology 2020;40(1):S43-S50.