Pattern Stimulator Application

Celeris Pattern Stimulator

The Celeris Pattern Stimulator is capable of presenting black/white checkerboard, grating, and multifocal patterns. It can be used to stimulate both ERG and VEP responses. Application of the pattern stimulator requires more practice than its full-field counterpart. Consistency is the key to generating reliable and reproducible data. 

Here is an example video: Celeris Pattern ERG and VEP Animal Setup

Check for Cataracts

Pattern tests require the animal to distinguish between the black/white portions of the stimulus, thus vision-compromising cataracts will adversely affect the response. Some anesthetics may form reversible cataracts. Keeping the animal's body temperature stable decreases the likelihood of cataract formation. 

Conductive Gel 

Conductive gel is required to create an electrical connection and to hydrate the eye. Hypromellose 0.3% gel is most highly recommended. Apply a thin layer of hypromellose gel to the tip of the pattern stimulator. Too much gel will cause the image to blur and lead to diminished responses. 

Upon finishing a test, be sure to clean the gel off of the stimulators before it dries. Dried gel will become opaque and obscure the stimulus from view. If the gel does dry, use water to clean it. 

Electrical Connection

A maximum amount of the electrode's metal surface area must make direct contact with the animal's cornea to promote a good electrical connection.

Whiskers: Ensure that whiskers do not interfere between the metal and the cornea. Moving the whiskers out of the way is sufficient without cutting them. 

Visualize Top of Cornea: Place the stimulator so that the cornea is visible above the stimulator. The electrode needs to be in direct contact with the cornea, and not on top of the eyelid or fur. Notice the shiny sliver of cornea visible in the image below. 

Stimulator Position and Pressure

Pressure: When applying the stimulator, ensure that there is direct contact between the electrode and the eye. However, avoid excess pressure which would press the eyeball into the head. Applied pressure risks reducing blood flow to the retina, which could dampen ERG responses.

Angle: The stimulator must be perpendicular to the optical axis of the eye. The optical axis passes through the center of the cornea and lens. Therefore, position the pattern stimulator so that it perpendicularly touches the front-most part of the cornea. 

Check for Stimulus through Viewing Port

To check if the stimulator is presenting a pattern, look through the viewing port. If you do not see the stimulus pattern, neither will the mouse. Restart the program as necessary and be sure to select the appropriate protocol for testing. The Pattern Stimulator's HDMI cable must be securely plugged into the port on the side of the Celeris. 

Binocular Pattern Stimulator Setup 

A raised platform must be used in order to position two pattern stimulators on a mouse or small animal. The raised platform is made of highly-conductive metal which will transfer heat from the built-in heating pad to help maintain body temperature during testing. In this setup, both pattern stimulators must be rotated vertically 90 degrees. Diagnosys-provided protocols adjust for this change within the protocol settings.