What is the diagnosis and treatment for idiopathic blind spot (IBS) enlargement?

Idiopathic Blind Spot Enlargement Syndrome: Diagnosis and Management

Idiopathic blind spot enlargement syndrome (AIBSES) is a rare outer retinopathy characterized by unilateral visual field loss in the blind spot area that requires spectral domain optical coherence tomography (SD-OCT) for definitive diagnosis and typically resolves without specific treatment, though corticosteroids may be considered in severe or progressive cases.

Clinical Presentation

AIBSES predominantly affects young adults, with a notable predilection for women, and presents with:

• Acute onset photopsia (flashing lights or shimmering visual phenomena) 1
• Enlargement of the physiologic blind spot on visual field testing 1, 2
• Normal or near-normal visual acuity in most cases 2
• Few or no visible optic disc changes on funduscopic examination 1
• Possible dyschromatopsia and afferent pupillary defects 2

Diagnostic Approach

Key Diagnostic Tests

1. Spectral Domain OCT (SD-OCT) - Gold standard for diagnosis 1

   • Look for:
     • Peripapillary changes in the ellipsoid zone
     • Disruption or absence of the inner/outer segment (IS/OS) line
     • Changes in the middle cone outer segment tip line in the nasal macular area 3

2. Visual Field Testing

   • Characteristic enlarged blind spot of variable size and density 2
   • Critical for diagnosis and monitoring disease progression 3

3. Fundus Autofluorescence

   • Increased peripapillary autofluorescence 4
   • Can determine the range of lesions earlier in the disease course 3

4. Visual Evoked Potential (VEP)

   • Characteristically shows no P100 latency delay, helping to differentiate from optic neuritis 1

5. Additional Testing When Indicated

   • Fluorescein Angiography (FA): May show optic disc staining and retinal pigment epithelial lesions 2
   • Indocyanine Green Angiography (ICGA): May reveal diffuse, small hypofluorescent spots throughout the posterior pole 3
   • Electroretinogram (ERG): Full-field ERG typically normal, but focal ERG often abnormal 2

Differential Diagnosis

AIBSES is often misdiagnosed as optic neuritis due to low awareness 1. Important differentials include:

• Optic neuritis (distinguished by VEP showing normal P100 latency in AIBSES)
• Multiple evanescent white dot syndrome (MEWDS)
• Macular hole or epiretinal membrane causing visual disturbances 5
• Vitreomacular traction syndrome 5
• Retinal vasculitis (can coexist with AIBSES in rare cases) 6

Management Approach

1. Observation and Monitoring

   • Most cases show spontaneous improvement over time 1
   • Regular monitoring with visual field testing and OCT is essential 1, 4

2. Corticosteroid Therapy

   • Consider in cases with:
     • Rapid progression
     • Severe symptoms
     • Associated inflammatory signs like vasculitis 6
   • Weight-adapted oral prednisolone, gradually tapered over 6-8 weeks 1
   • May support outer retinal reorganization 1

3. Patient Education

   • Educate about the typically self-limiting nature of the condition
   • Instruct on regular monocular Amsler grid testing to monitor for changes 5
   • Explain the importance of follow-up appointments

Prognosis

• Photopsia typically decreases over time 2
• Visual field defects may persist in some patients despite treatment 2
• OCT may show restoration of the outer retinal layers 6-12 months after disease onset 1
• Recurrence is possible in approximately 22% of cases 2
• Full recovery of symptoms may occur at 6-7 months after onset in many patients 1

Clinical Pearls and Pitfalls

• Pearl: The striking predilection for the peripapillary retina distinguishes AIBSES from MEWDS 2
• Pearl: Serial OCT imaging can demonstrate anatomic evidence of ellipsoid zone recovery that correlates with functional visual field improvement 4
• Pitfall: Misdiagnosis as optic neuritis is common due to similar presentation but can lead to inappropriate management 1
• Pitfall: Failure to perform OCT may result in missed diagnosis, as funduscopic examination may appear relatively normal 1
• Pitfall: Discontinuation of corticosteroid treatment in cases with associated inflammation may lead to recurrence and worsening of symptoms 6

Follow-up Recommendations

• OCT imaging at 3,6, and 12 months to monitor outer retinal recovery 4
• Visual field testing at each follow-up visit to assess functional improvement
• Extended follow-up for at least 12 months to monitor for potential recurrence 2