Celeris Flash Stimulator
Celeris Flash Stimulators illuminate the entire visual field with flashes of light. They are equipped with Red, Green, and Blue LEDs. UV stimuli are also available upon request. These stimulators come in a variety of sizes and stimulus ranges. Sizes options include baby mouse (2mm), mouse (3mm), rat (5mm), and rabbit. Luminance ranges also vary from dim (5x10-7 - 0.1), standard (0.001 - 100), and (0.01 - 1,000) bright. Contact Support for help with choosing the appropriate stimulator for your experiments.
Here is an example video: Celeris Full-Field ERG and VEP Animal Setup
High-Quality Electrical Connection
Conductive Gel: A conductive gel is required to sustain an electrical connection between the eye and the electrode. For best results, use .3% Hypromellose gel. Simple saline solution dries too quickly and requires frequent reapplication. Meanwhile, 2.5% hypromellose gel is too thick to sufficiently hydrate the eye. To apply the gel, place a dollop directly onto the stimulator-electrode. Then bring the electrode into contact with the surface of the rodent’s eye.
Corneal Hydration: For optimal electrical conduction, the eye must remain sufficiently hydrated. The cupped shape of the stimulator covers the eye, and the conductive gel adds moisture. Together, the eye remains sufficiently hydrated over the course of testing. Go here for more about Eye Preparation.
Drying out of the eye could contribute to reversible cataract formation which would obscure light from reaching the retina. A dry cornea also yields lower electrical conductivity, resulting in decreased ERG response amplitudes.
Clean Stimulators: Dried hypromellose gel can become opaque and obscure the light source from reaching the retina. After use, clean the stimulators before the gel dries. Although it is not necessary to clean the stimulators completely between each use when running multiple tests in one session. For more details, read about Cleaning Technique.
Direct contact: The metal of the electrode must touch the cornea of the eyeball directly. If the electrode is hovering, suspended in the conductive gel, then amplitudes will be artificially low. Avoid placing the metal electrode against the eyelid, fur, and whiskers. This will dampen the signal strength of an ERG response.
For best results, try to visualize the top of the cornea from beneath the stimulator. If a piece of the cornea is visible from the top, then the electrode is certainly in full-contact with the eye.
If the animal's eyes are so small that it is impossible to make full, direct contact then consider using a smaller sized electrode. Diagnosys makes baby mouse (2mm), mouse (3mm), and rat (5mm) sized electrode-stimulators.
Impedance: Impedance is a quantitative measure of electrical connectivity. When the electrodes are applied to the eye, impedance readings that range between 5 and 15 kilo-ohms qualify as a good electrical connection. If impedances are too high, then remove the electrode and reapply it, adding more conductive gel.
When using a Touch/Touch protocol, without a ground electrode, all impedance readings will appear as an average of the two eyes. Therefore, adjusting one eye's electrode will change the impedance reading of both eyes.
Stimulator Position and Pressure
Pressure: For optimal results, the electrode will be making direct contact with the cornea without any downward force or pressure. Applied external pressure may elevate the intra-ocular pressure and reduce retinal blood flow, thus diminishing an ERG response.
Stimulator Angle: Incongruity in stimulator positioning can cause amplitude differences between left and right eye ERG responses. The angle of stimulator placement needs to be uniform. Ensure that both stimulators are positioned with the optical axis of the eye.
T-Bar: For lightly larger animals, it may be necessary to use the T-Bar to elevate the stimulator to the animal's eye. In such case, keep the stimulator attached to its magnet, then connect the magnet to the T-Bar.
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