On- and off-response ERGs elicited by sawtooth stimuli in normal subjects and glaucoma patients

Abstract

The aim of this study is to measure the on- and off-responses and their response asymmetries elicited by sawtooth stimuli in normal subjects and glaucoma patients. Furthermore, the correlation between the ERGs and other functional and structural parameters are investigated. Full-field stimuli were produced using a Ganzfeld bowl with Light Emitting Diodes (LEDs) as light sources. On- and off-response ERGs were recorded from 17 healthy subjects, 12 pre-perimetric and 15 perimetric glaucoma patients using 4-Hz luminance rapid-on and rapid-off sawtooth stimuli (white light; mean luminance 55 cd/m(2)) at 100% contrast. The on- and off-responses were added to study response asymmetries. In addition, flash ERGs were elicited by red stimuli (200 cd/m(2)) on a blue background (10 cd/m(2)). The mean deviations (MD) of the visual field defects were obtained by standard automated perimetry. The retinal nerve fibre layer thickness (RNFLT) was measured with Spectral Domain Optical Coherence Tomography (SOCT). We studied the correlation between ERG response amplitudes, visual field mean deviation (MDs) and RNFLT values. The on-responses showed an initial negative (N-on) followed by a positive (P-on), a late positive (LP-on) and a late negative responses (LN-on). The off-responses showed an initial positive (P-off) a late positive (LP-off) and a late negative response (LN-off). The addition of on- and off-responses revealed an initial positive (P-add) and a late negative response (LN-add). The on-response components (N-on, P-on and LN-on) in the glaucoma patients were relatively similar to those of the control subjects. However, the LP-on was significantly elevated (p = 0.03) in perimetric patients. The LP-off was significantly elevated (p < 0.001), and the amplitude of LN-off was significantly reduced in perimetric patients (p = 0.02). The LN-add amplitude was significantly reduced (p < 0.001) and delayed (p = 0.03) in perimetric patients. The amplitudes of the LN-off and LN-add ERG components were significantly correlated with the PhNR in the flash ERG (LN-off: p = 0.01; LN-add: p < 0.001) and with RNFLT (LN-off: p = 0.006; LN-add: p = 0.001). On- and off-response ERGs and their response asymmetries, elicited by sawtooth stimuli, are altered in the glaucoma patients. The late components are affected. Changes in the late negative components are correlated with structural and other functional changes.

Human flicker electroretinography using different temporal modulations at mesopic and photopic luminance levels

“…Most electroretinographic studies in the literature focus on specific luminance ranges, in which the results agree well with our findings [3,6,[11][12][13][14]. However, these studies in general do not include or do not specifically investigate the luminance range where the transition from rod-to cone-driven responses can be found.…”

“…It was One cycle of the response is displayed. The transition between the mesopic and photopic responses is observable around 7 cd/m 2 previously proposed that these are two independent components with distinct frequency and contrast characteristics [14]. Furthermore, the responses at high and low luminances have different phases.…”

“…Early works to analyze luminance tracking in the ERG response [7,8] have applied flash stimuli that clearly elicit different ERG responses when compared to flicker type stimulation [6,9]. While also standard ISCEV protocols are based on flashed stimuli [2], several research groups [3,6,[9][10][11][12][13][14] used different temporal flicker modulations to stimulate the retina and the visual system.…”

Full-field electroretinogram response to increment and decrement stimuli

“…In contrast, a sawtooth stimulus has been used by a number of investigators to elicit increment and decrement responses from the retina [17,18,[25][26][27][28][29]. The sawtooth waveform has both transient and ramp components, and by changing the polarity of these components the sawtooth can be used to mimic the increment and decrement transients found in long duration flashes.…”

“…Conditions in which the ERG d-wave is more reduced than the b-wave have been reported in few cases, but which had uncertain underlying etiology [33,41]. And while b-wave amplitude is typically unaffected in patients with glaucoma, the d-wave and the Photopic Negative Response (PhNR) [14] to increment and decrement stimuli are somewhat reduced [13,42,43]. In summary, analysis of the b-wave and d-wave responses can provide insight to the retinal pathways that are affected by a particular disease.…”