Last updated: September 2026
Electro-oculography (EOG) tests a completely different part of the visual system than the ERG does — it's the test to reach for specifically when Best disease is on your differential, since the ERG in that condition is often deceptively normal.
EOG records the standing electrical potential between the cornea and Bruch's membrane/RPE — not a light-evoked response like the ERG, but a resting potential that changes predictably with light and dark adaptation. Skin electrodes are placed near the outer and inner canthus of each eye, and the patient makes fixed-angle horizontal saccades between alternating lights; each eye movement produces a measurable deflection proportional to this standing potential.
The current international testing protocol is set by ISCEV (International Society for Clinical Electrophysiology of Vision); the 2017 standard formally renamed "Arden ratio" to "light peak:dark trough ratio," though "Arden ratio" remains the term most commonly used in everyday clinical conversation and older literature.
In Best vitelliform macular dystrophy, the full-field ERG is typically normal, while the EOG light rise is severely reduced or absent — this dissociation (normal ERG + abnormal EOG) is itself the diagnostic clue, and is what distinguishes Best disease from other autosomal dominant maculopathies with similar fundus appearance, including some cases of adult vitelliform dystrophy and pattern dystrophy.
Recent genotype-confirmed data adds an important nuance: EOG severity in Best disease is more variable than classically taught — in one large cohort of BEST1-confirmed patients, roughly 27% had a completely absent light rise, 65% had intermediate reduction, and a small minority (8%) had only mild reduction. The takeaway: a mildly reduced or borderline EOG does not exclude Best disease in a patient with a compatible phenotype.
A useful discriminating pattern: in autosomal recessive bestrophinopathy and adult-onset vitelliform disease, the ERG itself is often already abnormal, but the EOG is disproportionately more abnormal than the ERG reduction alone would predict — this relative dissociation, not just an isolated abnormal number, is what points toward RPE-specific pathology.
Key references: ISCEV Standard for Clinical Electro-oculography (2017 update). Doc Ophthalmol. | Electrooculogram, EyeWiki. | Genotype-phenotype variability of EOG in Best disease and ARB, UCL.
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