The light flicker may be detected by its stroboscopic effect. Flicker with LED lights may be more noticeable due to the fact that LED lights flicker between less than 10% and 100%, where as fluorescent lights dim to about 35% and back to 100%). Most people cannot notice the flicker in fluorescent lights that have a flicker rate of 120 cycles per second (or 120 Hz).
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This happens because the response to the light stimulus lasts longer than the flash itself. At this frequency – the critical flicker frequency or flicker fusion threshold – the flashes appear to fuse into a steady, continuous source of light. When a light is flickering at a frequency greater than 50 or so Hertz, most people can no longer distinguish between the individual flickers. The actual critical flicker frequency increases as the light intensity increases up to a maximum value, after which it starts to decrease. People can see lights flashing on and off up to about 50 flashes per second (50 Hz) – they are most sensitive to time-varying illumination in the 10-25 Hz range.
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It depends on the frequency of the flicker. Essentially, the power is turning on and off 120 times a second (actually the voltage varies from +120 volts to -120 volts, 60 times or cycles a second and is at zero volts twice in one cycle). Lamps operating on AC electric systems (alternating current) produce light flickering at a frequency of 120 Hertz (Hz, cycles per second), twice the power line frequency of 60 Hz (50 Hz in many countries outside North America).
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The severity of the flicker depends on several factors such as: It is caused when the voltage supplied to a light source changes or when the power line voltage itself fluctuates. Combined consideration of RNFL thickness and results from one of these perimetric tests can increase the total number of detected patients.Light flicker refers to rapid or quick and, repeated changes in the brightness of light over time – light that appears to flutter and be unsteady. ConclusionįDF and FDT stimulations can be used to detect patients with early glaucoma. The correlation analysis between local RNFL thickness and corresponding visual defects revealed significant Spearman correlation coefficients for the arcuate bundles of the visual field (FDF-inferior: R = −0.65, FDF-superior: R = −0.74, FDT-inferior: R = −0.55, FDT-superior: R = −0.72). Sensitivity in this patient group was 65 % for FDF-MD, 60 % for FDT-MD, and 60 % for RNFL-thickness, all at a specificity of 95 %. In this cohort of early glaucoma patients, the MD values were 6.1 ± 5.0 dB (FDF) and 4.5 ± 4.1 dB (FDT). Mean defect data from FDT and FDF perimetry were strongly correlated (R = −0.85, P <0.001). Venn-diagrams show the number of patients with abnormal results in HEP, Matrix, SAP, and mean RNFL thickness.
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Statistical analyses included comparison of the standard indices and correlations between methods. Exclusion criteria were: mean defect (MD) in SAP > 6 dB, eye diseases other than glaucoma, or non-reliable FDF or FDT measurements. All patients underwent FDF perimetry (HEP), FDT perimetry (Matrix), standard automated perimetry (SAP, Octopus), and peripapillar measurements of the RNFL thickness (Spectralis OCT). The definition of glaucoma was solely based on optic disc appearance. Seventy-two experienced glaucoma patients and 50 healthy subjects of the Erlangen Glaucoma Registry participated in the study. To compare perimetric data based on the second-generation frequency doubling technology (FDT) and on flicker defined form (FDF) stimulation in early glaucoma patients.