Fixation stability during Rarebit Fovea Test.
BACKGROUND
Unstable fixation has been reported to be a common cause of unreliable results in perimetry. The Rarebit Fovea Test (RFT) is a computerised foveal function test that evaluates the 4 x 3 degrees central visual field, using very small test stimuli. To minimise the test time, no fixation control is used. Instead, stable fixation is facilitated by the use of a dynamic fixation target. The aim of the current study was to evaluate fixation stability during a RFT examination by continuous recording of the eye movements.


METHODS
Twelve healthy subjects were enrolled in the study together with two amblyopic subjects. A three-dimensional eye tracker was used to measure eye movements during two test sessions. All subjects went through one session of fixation measurement with stimulus presentation and one session without stimulus presentation. Both sessions lasted approximately 90 seconds.


RESULTS
Mean hit rate (MHR) in the whole group was 89.7 per cent. Five out of 14 subjects had abnormal RFT results. There was no significant difference in fixation stability either between the test sessions with and without stimulus presentations (p = 0.79) or between the subjects with abnormal (n = 5) and normal (n = 11) MHR, (p = 0.55).


CONCLUSIONS
Fixation seems stable during RFT testing, thus the test design and fixation target used in the RFT could be considered adequate, at least in subjects with normal or near normal visual function. Further studies are needed to evaluate how different visual abnormalities will affect fixation stability during RFT testing.
Nilsson
Maria M
MM
Unit of Optometry, Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden. Maria.Nilsson@ste.ki.se
Stevenson
Scott B
SB
Kumar
Girish
G
Martin
Lene
L
Brautaset
Rune L
RL
D000328:Adult; D000550:Amblyopia / Q000175:diagnosis* / Q000503:physiopathology; D005260:Female; D005403:Fixation, Ocular / Q000502:physiology*; D005584:Fovea Centralis / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010775:Photic Stimulation; D015203:Reproducibility of Results; D014787:Vision Tests / Q000592:standards*; D014794:Visual Fields / Q000502:physiology; D055815:Young Adult