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USER MANUAL
RETEVET™ PORTABLE ERG
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4. BEFORE PERFORMING AN ERG TEST
Anesthesia
An ERG can be obtained without anesthesia or sedation in dogs. In other animals, anesthesia may be needed in order to
complete the test. Anesthesia usually will affect the ERG, and the literature should be consulted for recommendations. Make
sure the eyes of anesthetized animal will not roll down, which may occur with certain pharmacological agents or by a physical
block. Typically, for research purposes animals (mice, rats, rabbits, dogs, pigs, NHP) can be anesthetized with a Ketamine / Xalazine
combination for ERG recordings. Tenneson and Vezina studied 6 different anesthetic agents in a 2017 ARVO poster, a copy of
which is
https://www.criver.com/sites/default/fi les/resource-fi les/SP-ARVO-17-effect-of- anesthetic-selection-for-ERG.pdf.
Monocular or Binocular Recording
Consider whether you would like to obtain an electroretinogram from one eye (monocular) or from both eyes (binocular).
Monocular recording is faster, and may be suffi cient when there is a strong possibility that the eyes are similar, for example:
in systemic exposure models in rats and mice in research or in toxicology safety evaluations in rabbits. With monocular
interventions, recording from both eyes enable the untreated eye to be a control if binocular recordings are made.
Preparing the Animal
Preform ERG testing before photography or indirect ophthalmoscopy if dark-adapted recordings are desired, because
60 minutes are needed for the rods to fully recover from bright light exposures (Tuntivanich et al. 2005).
Dilate the pupils using, for example, a combination of 0.5 % proparacaine and 1 % of tropicamide. Wait 20 – 30 minutes for
full dilation. Cautiously verify dilation, especially in black-eyed animals. Anesthetize the cornea around 5 minutes prior to the
recording.
Use goniosol or other methylcellulose solution to provide a conductive path between a contact lens electrode and the cornea.
If needed, plan ahead for the location and how the animal will be dark-adapted. Use dim red lights in the dark room because
rods are insensitive to red light.
Ensure normal body temperature is maintained if the animal is anesthetized. Electroretinograms are temperature-dependent.
Make sure you have all the electrodes and eye speculum if needed.
Electrode Choice
Choose the electrode based on the size of the animal to be tested. ERG-Jet and DTL electrodes are common in larger animals
(Mentzer et al. 2005) as well as the newer RM-canine electrode. For smaller animals such as mice and rats, DTL or contact lens
electrodes can be used. All these electrodes are available from EICKEMEYER®. While individual preferences vary, we
recommend ERG-Jet or RM-canine electrodes for the larger animals. Stainless-steel needle electrodes are used as reference
and ground electrodes and they are also available from EICKEMEYER®.
