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Can fixation instability improve text perception during eccentric fixation in patients with central scotomas?
A Déruaz1, M Matter, A R Whatham
1Neuro-ophthalmology Unit, Ophthalmology Clinic, Department of Clinical Neurosciences and Dermatology, Geneva University Hospitals, 22 Alcide Jentzer, 1211 Geneva 14, Switzerland. anouk.deruaz@hcuge.ch
The British Journal of Ophthalmology
|March 20, 2004
Summary
Ocular instability, or small eye movements, can surprisingly improve reading for individuals with central vision loss from conditions like age-related macular degeneration. This finding suggests incorporating fixation instability into visual rehabilitation strategies.
Area of Science:
- Ophthalmology
- Neuroscience
- Vision Science
Background:
- Investigated oculomotor behavior in 14 patients with central scotomas due to age-related macular degeneration (AMD) or Stargardt's disease.
- Observed that some patients needed to "move their eye" to maintain perception of text.
- Utilized a scanning laser ophthalmoscope (SLO) to project stimuli and assess fixation.
Purpose of the Study:
- To determine if purposeful changes in fixation position could enhance perception of eccentrically fixated text.
- To explore the functional advantage of ocular instability in individuals with central vision loss.
Main Methods:
- Twenty healthy subjects alternated fixation every 3-4 seconds between two dots 10 degrees apart.
- Subjects reported perception changes of a laterally located letter (1.5 degrees high, 7 degrees apart) equidistant between fixation spots.
Main Results:
- 19 subjects reported transient letter image "refreshment" immediately after saccades (eye movements).
- Improved perception lasted about one second.
- Persistent fixation led to rapid fading and reduced letter recognition.
Conclusions:
- Ocular instability during eccentric viewing may counteract Troxler's phenomenon, improving text perception.
- Saccades related to fixation instability could benefit individuals with central scotoma and eccentric fixation.
- Consideration of fixation instability is recommended for visual rehabilitation in these patients.