1. Focal electroretinograms (ERGs) were recorded in response to sinusoidal homogeneous flicker (F-ERG) and counterphase-modulated sinusoidal gratings of 1.7 c/deg (P-ERG) in 26 normal subjects and in 35 age-matched patients with different retinal dysfunctions. 2. F-ERGs and P-ERGs were elicited with stimuli of the same field size (9 x 9 deg), temporal frequency (2.7-32 Hz), modulation depth (95%) and mean luminance (84 cd/m2). Steady-state analysis of responses was used in order to isolate the F-ERG 1st and 2nd harmonic component (1F and 2F respectively) and the P-ERG 2nd harmonic component (2P). 3. In normal subjects, 1F, 2F and 2P differed in their amplitude and phase characteristics as a function of temporal frequency. 4. Patients were grouped into two major categories on the basis of their presumed retinal dysfunction site. Group A: maculopathies with photoreceptor involvement; and group B: post-receptoral disorders. Group B patients were further divided into three subgroups. B1: postreceptoral dysfunctions of the posterior pole; B2: optic nerve head dysfunctions with clinical signs of retinal involvement; B3: descending optic atrophies without any clinical evidence of retinal involvement. 5. Statistical analyses performed upon F-ERGs and P-ERGs of normal subjects (N) and patient groups (A, B1, B2, B3) revealed the following significant (>95%) differences: 1F amplitude: N > A; 2F amplitude: N > A, B1, B2; B3 > A,B2; 2P amplitude: N > A, B1, B2, B3. 6. The present results indicate that the main harmonic components of the steady-state focal ERG in response to sinusoidal flicker or counterphase modulation of sinusoidal gratings (1F, 2F, 2P) can be dissociated on the basis of their response characteristics and different vulnerability in disease. 7. The relationship between ERG components and presumed retinal dysfunction site suggests that the linear 1F component is of receptoral origin, whereas the 2F and 2P components represent different subsets of even non-linearities in the inner retina.
|Original language||English (US)|
|Number of pages||10|
|Journal||Clinical Vision Sciences|
|State||Published - Jan 1 1989|
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