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Margherita Casciano, Enrica Convento, Evelyn Longhin, Stela Vujosevic, Edoardo Midena; The Impact Of Stimulus Duration In Mesopic Microperimetry. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2201.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate if different light stimuli duration may modify final sensibility thresholds during microperimetry (MP) examination.
Twenty healthy subjects (20 eyes) were enrolled in this study. Two consecutive microperimetry examinations (MAIA; CenterVue, Padova, Italy) were performed 30 minutes apart from each other, with following parameters: 37-stimuli grid covering central 24° of the macula, 4-2 threshold strategy, fixation target: red circle of 1° diameter, stimulus size Goldmann III, background luminance set at 4 asb, stimulus dynamic range 36 dB. Duration of light stimulus was set at 200 msec or 40 msec. The sequence of exams with the 2 different stimuli duration was randomly performed. Fixation stability was determined for each examination. Stable fixation was indicated when more than 75% of the fixation points were located within a predetermined circle area of 2° (P1), regardless of the position of the foveal center. Relatively unstable fixation was indicated if less than 75% of the fixation points were located within a 2° circle, but if more than 75% of the fixation points were located within a 4° circle area (P2). Unstable fixation was indicated if less than 75% were located within a 4° circle.
Mean age of included subjects was 27.5±3.9 years. Mean light thresholds were significantly reduced with 40 msec-MP (24.7±1.1 dB) versus 200 msec-MP (28.1±1.0 dB) examination, (p=0.0001). Mean duration of 40 msec exams was 4.7±0.3 min, versus 4.7±0.5 min of 200 msec, (p>0.1). Fixation was stable in all subjects with 40 and 200 msec stimuli duration. The number of fixation points in P1 and P2 areas did not show any difference between 40 msec-MP and 200 msec-MP examination, (p>0.1).
Short stimuli duration decreases mean retinal thresholds during microperimetry examination in normals. Fixation stability seems not to be dependent on stimuli duration in normals. This finding should be taken into account in planning clinical trials.
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