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Effect of nystagmus on VEP-based objective visual acuity estimates
Elisabeth V Quanz1, Juliane Kuske1, Francie H Stolle1
1Ophthalmic Department, Otto-Von-Guericke University Magdeburg, Magdeburg, Germany.
Scientific Reports
|July 22, 2024
Summary
Objective visual acuity (VA) estimates using VEP were slightly overestimated compared to subjective psychophysical VA in nystagmus patients. This overestimation correlated with the degree of fixation instability, providing a useful clinical estimation tool.
Area of Science:
- Ophthalmology
- Neuroscience
- Clinical Electrophysiology
Background:
- Nystagmus significantly impacts visual function and the reliability of visual acuity (VA) assessments.
- Discrepancies between subjective and objective VA measures are common in individuals with nystagmus.
- Accurate VA estimation is crucial for clinical management and research in nystagmus patients.
Purpose of the Study:
- To compare subjective visual acuity (VApsych) and objective visual acuity (VAVEP) estimates in individuals with nystagmus.
- To investigate the relationship between the degree of fixation instability and the difference between subjective and objective VA measures.
- To determine if objective VA estimates are systematically overestimated compared to subjective measures in nystagmus.
Main Methods:
- Recruited 20 participants with nystagmus from various causes (idiopathic infantile nystagmus, albinism, achiasma, acquired).
- Measured best-corrected visual acuity (BCVA) psychophysically (Freiburg visual acuity test - FrACT) and electrophysiologically (EP2000) following International Society of Clinical Electrophysiology of Vision (ISCEV) guidelines.
- Assessed fixation instability using a Nidek microperimeter (MP-1) on the eye with the greater instability.
Main Results:
- Objective VAVEP estimates were significantly better than subjective VApsych estimates (mean difference of 0.12 logMAR, P=0.017).
- A linear correlation was found between the difference in VA (∆VA) and the degree of fixation instability (r2 = 0.21, p = 0.048).
- On average, VAVEP overestimated VApsych by approximately one line, with a 50% reduction in fixation probability leading to a ~0.25 logMAR overestimation.
Conclusions:
- Objective VAVEP measurements tend to overestimate visual acuity compared to subjective VApsych in nystagmus patients.
- The magnitude of this overestimation is directly related to the degree of fixation instability.
- These findings highlight the importance of considering fixation instability when interpreting electrophysiological VA estimates in nystagmus.
