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J. S. Kroisamer, C. Simader, U. Schmidt-Erfurth; Microperimetric Fixation in Normal Individuals: Influence of Room Light Intensity, Shape and Size of Fixation Targets. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3202. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The aim of this comparative study was to evaluate if microperimetric fixation findings are affected by shape or size of the fixation target or by room light intensity.
Static threshold perimetry including fixation evaluation was performed six times during the same day using MP1 microperimetry (Nidek Technologies, software version 1.4.2) in 35 eyes of 20 healthy volunteers. During the first four examinations the influence of shape and size of the fixation target was evaluated. The chosen fixation targets were a 1° circle, a 5° circle, a 1° cross and a 6° cross. The examination setting did not vary, a standardized grid with 25 stimuli was used, and room light intensity was constant. The influence of room light intensity was evaluated during the subsequent two examinations. Chosen room light intensities were 0.16-0.25 lx and 3-4.5 lx, respectively. A standardized grid and a 1° red fixation circle were used for both examinations. The center of all measured fixation points was calculated. Average radius (r), measured in degree [°], as well as maximum r of all fixation points were evaluated as a measure of distribution of fixation. Fixation findings were analyzed by a conventional statistical software package (SPSS® version 11.5).
Concerning bright and dark room conditions, neither average r nor maximum r showed a statistically significant (p<0.05) difference. However, oneway-ANOVA analysis showed a statistically significant difference (p<0.05) between the fixation results (average r) of the four examinations with different fixation targets. Using the 5° circle as fixation target resulted in the most unstable fixation. Furthermore, a statistically significant correlation between average r and duration of the examination was found. Long examination time correlated well with bad fixation.
The results indicate a significant effect of shape and size of fixation targets on fixation evaluation using the Nidek MP1 system. Therefore, for follow-up examinations a constant fixation target is required in order to obtain comparable results.
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