What causes a scotoma in the periphery?

Causes of Peripheral Scotomas

Peripheral scotomas are most commonly caused by retinal diseases, glaucoma, neurological conditions, or iatrogenic factors following ocular procedures. Understanding the specific etiology is crucial for appropriate management and prevention of vision loss.

Common Causes of Peripheral Scotomas

Retinal Disorders

• Macular Diseases with Eccentric Fixation

  • When central macular disease causes patients to develop eccentric fixation, what appears as a peripheral scotoma may actually be a central scotoma that is displaced due to the patient's use of a preferred retinal locus (PRL) 1
  • This is common in conditions like age-related macular degeneration (AMD) where patients develop a PRL to compensate for central vision loss

• Epiretinal Membrane and Vitreomacular Traction

  • Can cause distortion and scotomas in the peripheral visual field
  • May be associated with metamorphopsia (distortion) that can be identified on Amsler grid testing 1
  • Surgical intervention (vitrectomy) may improve or worsen scotomas in these patients

Glaucoma

• Normal-Tension Glaucoma
  • Produces characteristic peripheral visual field defects that often begin as paracentral or arcuate scotomas 2
  • Risk factors for specific patterns include:
    • Paracentral defects: more common in women and patients with disc hemorrhage
    • Arcuate scotomas: associated with hypertension but less common with disc hemorrhage or migraine
    • Hemispheric defects: associated with notching of the optic nerve rim

Iatrogenic Causes

• Post-Vitrectomy Scotomas

  • Occurs in approximately 6.4% of patients following pars plana vitrectomy for rhegmatogenous retinal detachment 3
  • Typically located in the inferotemporal visual field
  • May be caused by trauma from air flow during air-gas exchange directed toward the superior nasal paracentral retina
  • Multimodal imaging shows corresponding focal superior nasal ganglion cell loss on OCT

• Post-Macular Hole Surgery

  • Up to 70.1% of patients develop peripheral scotomas after vitrectomy with gas tamponade for macular holes 4
  • Most commonly affects the temporal and lower periphery of the visual field
  • Likely caused by persistent pressure of the gas bubble on the peripheral retina

Neurological Causes

• Cytomegalovirus (CMV) Retinitis

  • In immunocompromised patients, particularly those with CD4+ T lymphocyte counts <50 cells/μL 1
  • Peripheral retinitis may present with floaters, scotomata, or peripheral visual field defects
  • Characterized by perivascular fluffy yellow-white retinal infiltrates

• Migrainous Visual Phenomena

  • Can cause scintillating scotomas in the peripheral visual field 5
  • May be related to retinal spreading depression or mechanical deformation of the posterior segment of the eye

Diagnostic Approach

Visual Field Testing

• Tangent Screen Examination

  • Simple, portable method for detecting paracentral defects 6
  • Allows direct observation of patient fixation

• Automated Perimetry

  • Standard for quantitative assessment of visual field defects
  • May be less accurate in patients with unstable or nonfoveal fixation 1

• Microperimetry

  • More accurate for detecting both fixation patterns and scotomas in patients with macular disease
  • Uses eye-tracking technology to ensure stimuli are presented to the correct retinal position 1

Special Tests for Macular Disease

• Lights On/Off Test

  • Pathognomonic for dragged-fovea diplopia syndrome
  • When peripheral fusion cues are eliminated by darkening the room, central fusion allows a test letter to be seen singly 1

• Optotype-Frame Test

  • Alternative when peripheral cues cannot be eliminated
  • Patient fixates on an isolated Snellen optotype and reports whether the letter and monitor frame are single or double 1

Management Considerations

For Retinal Causes

• Treat underlying retinal disease
• Consider surgical intervention for epiretinal membranes if symptoms are severe
• Be aware that membrane peeling may improve scotomas in some patients but cause new scotomas in others 1

For Glaucoma

• Control intraocular pressure
• Regular monitoring of visual fields to detect progression

For Post-Surgical Scotomas

• Surgeons should take precautions during vitrectomy procedures:
  • Slow injection of gas after air-gas exchange
  • Careful positioning of infusion cannula to avoid direct air flow to vulnerable retinal areas 3

For Neurological Causes

• Treat underlying condition (e.g., immunosuppressive therapy for CMV retinitis in HIV patients) 1

Important Clinical Pearls

• What appears as a peripheral scotoma may actually be a central scotoma displaced by eccentric fixation in patients with macular disease
• Fixation is a dynamic process; patients may use multiple PRLs and fixation can change with different tasks, print sizes, or illumination conditions
• Traditional automated field tests may map scotomas in the wrong location in patients with eccentric fixation
• Consider both monocular and binocular testing, as some tests can only detect monocular scotomas while others can assess binocular function

Understanding the specific cause of peripheral scotomas is essential for appropriate management and prevention of further vision loss.