I also learned how to check for retinal hemorrhage and retinal ulcers in dog eyes.
To check for a retinal hemorrhage, a light is shined through a special lens (sort of like a magnifying glass). If red is visible in the retina when looking through the lens, that means there could be a hemorrhage.
Left: Normal dog retina. Right: Retinal hemorrhage
To check for a corneal ulcer (the outer layer, the cornea, wears away and forms a dent), a special green fluorescent stain is used. If there is no ulcer, the liquid will slip right off the cornea. If there is an ulcer, the liquid will pass through the break in the cornea and enter the eye, causing it to fluoresce green. This allows the presence and location of an ulcer to be determined. It’s also easier to see an ulcer using this method when the room is darkened.
The green splotch at the bottom of this dog’s eye indicates that an ulcer is located there. The green liquid rimming the bottom eyelid is excess stain that has slipped off the cornea.