Abstract
Purpose:
Functional imaging of the retina can be useful for studying retinal physiology and for accurate diagnosis of retinal diseases. A relatively new method in this regard is retinal intrinsic optical imaging, a technique that measures light reflectance changes following retinal stimulation. Prior to clinical use of this technique, detailed knowledge of the properties and the origin of intrinsic signals are required, and constitutes the aim of this study.
Methods:
Retinal intrinsic optical imaging was performed using a fundus camera capturing the reflected light from the retina, illuminated by near infrared light. Retina stimulation was consisted of a brief spot or a full-field illumination of green light. Experiments were performed on anesthetized and paralyzed rabbits in scotopic conditions. Electroretinograms were also recorded to monitor retinal physiology and confirm the effects of the various drug injections.
Results:
The activity-dependency of intrinsic responses was evaluated by observing the effects of stimulus intensity and duration on intrinsic responses amplitude. The cellular origin of retinal intrinsic signals was studied by inhibiting sequentially the activity of each of the retinal layers through intra-vitreous injections of pharmacological agents. TTX was used to inhibit ganglion cells, APB for ON bipolar cells, and PDA for OFF bipolar cells. Injections of saline were also performed as a control. A non-linear proportional relationship was observed between intrinsic signal amplitude and both the intensity and duration of the stimuli. Injection of TTX caused a decrease in intrinsic response amplitude (26 ± 2%, n=11), suggesting a partial role of ganglion cells activity in the genesis of intrinsic responses. The injection of APB after TTX further decreased intrinsic responses by 23 ± 4% (n= 6), whereas the injection of PDA caused a reduction of 14 ± 2% (n=6).
Conclusions:
Our results suggest that: 1) Retinal intrinsic responses reflect the general activity of retinal neurons. 2) Activity from cells in the outer and middle layers of the retina is partly responsible for the intrinsic signals observed in the retina. However, after inhibition of the latter, 42 % of the initial response amplitude remains, suggesting a major role for photoreceptors activity in the origin of retinal intrinsic signals.
Keywords: 552 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) •
688 retina