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R.T. Tzekov, W.H. Ridder III, K.–M. Zhang, W. Orilla, J. Burke; Temporal frequency effects on the sweep VEP in primate acuity determination . Invest. Ophthalmol. Vis. Sci. 2004;45(13):3499.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Previous studies of sweep VEPs (sVEP) in primates have typically used stimuli with a temporal frequency of 6 – 7.5 Hz. There is no non–human primate sVEP data published that indicates that this is the optimal temporal frequency to obtain visual acuity estimates. The purpose of this study was to investigate the relationship between the stimulus temporal frequency and the obtained acuity threshold in anesthetized cynomologus monkeys. Methods: Sweep VEPs were obtained on five cynomologus monkeys (2.6 – 4.2 kg) that were anesthetized and paralyzed (ketamine, 10mg/kg; vercuronium bromide, 30 µg/kg). Cycloplegia was achieved with topical administration of cyclopentolate 0.5%. The stimuli were vertically oriented sinusoidal gratings (400 cd/m2, 80% contrast, 3 – 23 cpd) projected on the retina with a modified fundus camera stimulator (EDI, San Mateo, CA). The temporal frequencies investigated were: 1.04, 2.08, 4.17, 5.36, 7.50, 12.51 and 18.76 Hz. Stimulus generation, data collection and analysis were carried out with the Power Diva system (SKERI, San Francisco, CA). Results:The mean acuity at 2.08 Hz was significantly higher than at 7.5 Hz (12.9 cpd ± 2.7 vs. 9.6 ± 3.8 cpd, p < 0.05). In general, low temporal frequencies (1.04 and 2.08 Hz) produced better acuities than high temporal frequencies. No visual acuity threshold was recordable at 18.76 Hz. Conclusions: Our findings demonstrate that lower temporal frequencies (1 – 3 Hz) produce better acuity estimates than higher temporal frequencies (6 – 18.76 Hz) in anesthetized primates. This is in contrast to results obtained with steady–state VEPs in alert primates (Nakayama and Mackeben, Vis Res 1982, 22:1261–1271) and may reflect methodological differences between the two methods.
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