Functional Visual Loss

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= Visual impairment not caused by an organic origin

Examination / Tests

  • Complete ophthalmological examination, including dilated fundus examination (to rule out organic causes)
  • Pupil examination (RAPD!)
  • Visual acuity testing:
    • “Bottom-up” examination: start with the smallest line
    • Monocular reduced visual loss:
      • Fogging of the better eye (e.g., with plus lenses)
      • Red-green test
    • Binocular no light perception (NLP):
      • OKN drum: in the presence of optokinetic nystagmus, visual acuity should be at least 0.05
      • Mirror test
      • Fingertip test: bringing together the fingertips of both index fingers, possible even in blindness, based on proprioception rather than visual abilities
    • Mojon chart 1 (optotypes get smaller, but the minimum resolution angle remains the same—when the largest optotype is recognized, the smallest optotype should also be recognized)
  • Stereopsis
  • Prism tests:
    • Base-out prism test: a 4dpt or 10dpt prism base-out in front of one eye usually leads to movement of both eyes toward the apex followed by a follow-up movement of the contralateral eye toward the center; in actual visual loss, no movement is triggered when holding the prism in front of the affected eye
    • Vertical prism test: a 4dpt prism base down in front of the good eye; with symmetrical vision from both eyes, the patient sees vertical double images (e.g., two optotypes on top of each other)
  • Visual field examination:
    • Check at different distances (the visual field should increase with greater distance)
    • Goldman perimetry: often a spiral-shaped visual field or concentric restriction
    • Automatic perimetry: frequently a cloverleaf-shaped visual field

Important Differential Diagnoses

  • Bilateral retrochiasmal pathology (e.g., occipital stroke)
  • Chiasma pathology without optic atrophy (e.g., craniopharyngioma)
  • Early-stage posterior subcapsular opacity
  • Early-stage keratoconus, irregular astigmatism
  • LHON (Leber’s hereditary optic neuropathy)
  • Maculopathies (CRCS, macular edema, epiretinal membrane)
  • Stargardt disease
  • Paraneoplastic retinopathy
  • Retinitis pigmentosa sine pigmento
  • Retrobulbar optic neuropathy
  • Syndromes with enlarged blind spot, AZOOR (Acute Zonal Occult Outer Retinopathy)
  • Cone-rod dystrophy

Management

  • Confrontation is usually not helpful
  • Simple reassurance of a normal eye exam
  • Explain to the patient that the symptoms will improve on their own and that the prognosis is very good
    • Providing a way out for the patient
    • Optionally offer lubricating eye drops or “eye exercises”
  • Offer 1-2 follow-up appointments; often, symptoms have disappeared by then
  • Sometimes an organic problem only manifests later in the course (see differential diagnoses)

Sources

  • EyeWiki Functional Visual Loss
  • Non-organic vision loss von Dr. Andrew G. Lee
  • The Wills Eye Manual: Office and Emergency Room Diagnosis and Treatment of Eye Disease; Nika Bagheri MD, Brynn Wajda MD, et al; Lippincott Williams&Wilkins; 7th Edition (2016)
  • Kanski’s Clinical Ophthalmology: A Systematic Approach; Jack J. Kanski MD, Brad Bowling MD; Saunders Ltd.; 8th Edition(2015)
  • American Academy of Ophthalmology; 2017-2018 Basic and Clinical Science Course (BCSC), Section 05: Neuro-Ophthalmology
  • 1 Mojon DS, Flueckiger P. A new optotype chart for detection of nonorganic visual loss. Ophthalmology. 2002 Apr;109(4):810-5. doi: 10.1016/s0161-6420(01)01050-8. PMID: 11927447.