stimuli were generated by light-emitting diodes located in an image plane of the eye pupil. These diodes could uniformly illuminate a field as large as 501 at the fundus with a maximum luminance of 40 lux for each color; (B) focal contrast reversal checkerboards. These were displayed on the monitor of a pattern generating system (VGS series 5, Cambridge Research System, England) and focused at the subject’s retina through a dichroic mirror placed between the fundus camera objective and the eye of the subject and a spectacle lens with a dioptric power specific for the tested eye, as shown in Fig. 1 (Logean et al., 2005).

Reproducibility and habituation of RFonh

Defining RFonh as RFonh ¼ 100 ((Fonh,st Fonh,bl)/ Fonh,bl), where Fonh,bl is the average flow during baseline (no stimulus) and Fonh,st is the mean flow during the last 20 s of a 1 min stimulation, test–retest

coefficient of variation of RFonh data determined in five subjects under various conditions of stimulation ranged from 10 to 48% (average, 26%) (Falsini et al., 2002).

Habituation, an effect that may lead to a reduction of RFonh over time, was investigated in a volunteer using a 15 Hz luminance flicker applied for 1 min and repeated several times over periods of 12 and 20 min. Linear regressions across both series of data did not reveal any significant trend (Falsini et al., 2002), suggesting the absence of this phenomenon at the level of the optic nerve. Furthermore, 8 min recordings of Fonh from a temporal site of the disc during luminance flicker

showed no significant trend when a linear regression was determined for the period of flicker between 30 s and 8 min (Falsini et al., 2002).

Retinal neural activity as assessed from the electroretinogram (ERG)

The visually evoked neural retinal activity changes can be induced by diffuse flicker and pattern contrast reversal stimuli and assessed by means of the flicker and pattern ERG (F-ERG and P-ERG, respectively), which are now briefly reviewed.

F-ERG

The F-ERG has two major components: a linear component at the same temporal frequency as the stimulus (fundamental harmonic, 1F) and a nonlinear component at twice the stimulation frequency (second harmonic, 2F). The 2F may be dominant at low temporal frequencies (Baker and Hess, 1984). Many lines of evidence indicate that the 2F, unlike the 1F, component (which is probably of receptoral origin) reflects the activity of proximal retinal layers (Porciatti and Falsini, 1993). Current source density analysis in primate retinas disclosed several sources for the 2F, with at least one in the inner retina (Baker et al., 1988).

P-ERG

A steady-state P-ERG can be recorded in response to black–white pattern reversal modulation of