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J. R. Etter, M. Walsh, E. Schmeisser; Focal Electroretinogram (fERG) and Chaos Theory in the Detection of Glaucoma. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2223. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
A chaotic system is that in which future events are occur in response to initial conditions and events. It is thought that healthy tissues display more chaotic behavior than unhealthy tissues. Furthermore, focal ERG (fERG) is thought to be affected in glaucomatous eyes. The purpose of this study was to determine whether the fERG patterns of normal patients will display more chaotic variability than those with glaucoma.
Ten normal patients and 10 patients with glaucoma were recruited from the Duke Eye Center for the study. After informed consent, fERG was performed on each patient. Administration of the fERG involved applying 1 set of DTL electrodes (Diagnosys, Lowell, MA) toeach eye and a central electrode on the patient's forehead. The patient was then given the handheld MaculoScope (Doran Instruments, Littelton, MA) and told to look at the center of a flickering disc of 4.2 degrees in diameter which delivered a stimulus at 33 Hz directly to the macula.Surrounding the central disc there was an annulus of 10 degrees which delivered a much brighter stimulus to surrounding tissue in order to dampen the response of peripheral retina. Two runs of fERG were performed on each eye: one run recorded an averaged fERG curve over 2 minutes in a 120 millisecond stimulus synchronized window while the other recorded all responses recorded from the eye over 30 seconds in a single sweep. All fERG data was recorded and collected into a database.Initially, the average fERGs were analyzed and average amplitude and implicit time data was determined for normal patients and patients with glaucoma. The second (single sweep) runs for all eyes were then analyzed by calculating the Hurst exponent to determine their level of chaoticbehavior. The single sweep runs for all eyes are currently undergoing additional analysis to help further determine their level of chaotic behavior.
Average fERG amplitude and implicit time in normal patients were 1342 nV and 55 milliseconds respectively, while those in glaucomatous patients were 3787 nV and 53 milliseconds. The Hurst exponent trended lower in glaucomatous patients (median = 1.8) compared to normal patients (1.9) (p=0.15). Additional analysis is pending.
Preliminary results indicate that the fERG of glaucomatous patients appeared to exhibit less chaotic behavior, which corresponds with the hypothesis that healty tissues act more like chaotic systems; however, the difference was not statistically significant. Additional analysis of the data is pending.
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