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H. Dunbar, M. D. Crossland, G. S. Rubin; Fixation Stability Assessment: A Comparison Between the Nidek MP1 and the Rodenstock Scanning Laser Ophthalmoscope. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4736.
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© ARVO (1962-2015); The Authors (2016-present)
Fixation stability is impaired in many eye diseases and this impairment is known to be associated with reduced reading speed. Therefore an awareness of a patient’s ability to fixate is important when considering their functional vision. Traditionally fixation has been assessed using the Scanning Laser Ophthalmoscope (Rodenstock, Germany) an instrument that is no longer commercially available. The arrival of the MP1 Microperimeter (Nidek, Italy) now provides another option for the assessment of fixation. Here we compare fixation stability measured on each instrument in normally sighted eyes.
16 participants with normal vision were tested, 10 female and 6 males. Fixation stability was monocularly recorded on both the MP1 and the SLO in a counterbalanced order for 10 seconds whilst participants fixated a 1° red cross. Fixation data collected from each instrument was used to calculate the bivariate contour ellipse area (BCEA) that encompassed 68% of all fixation points. A log transform was applied to normalise BCEA values.
Mean BCEA for MP1 was 2.51 log minarc2 (SD 0.32) and for the SLO was 2.83 log minarc2 (SD 0.44). On average BCEA values from the MP1 were significantly smaller by 0.32 log minarc2 (p = 0.02), approximately a factor of 2. BCEA values between the two instruments were weakly linearly correlated (r = 0.33).
On average BCEA values were lower when measured on the MP1 as compared to the SLO. Our results do not allow us to suggest a standard correction factor by which one could convert between BCEA values from the MP1 and SLO. A weak linear relationship exists between these two measurements. This may reflect the small range of measurements looked at, or our small sample size. A stronger relationship may be evident over a larger range of values, as in people with eye disease.
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