What diagnostic tool is primarily used to identify progressive retinal atrophy?

Electroretinography (ERG) is the most effective diagnostic tool for identifying progressive retinal atrophy (PRA), as it measures the electrical responses of the retina's photoreceptor cells to light stimulation. This condition is characterized by the gradual degeneration of photoreceptors, primarily rods and cones, leading to diminished or absent electrical activity in the retina, which can be detected through ERG testing. By assessing the function of these cells, veterinarians can confirm the presence of PRA even in its early stages, before any significant clinical signs become evident.

In contrast, ocular ultrasound is primarily used for imaging the structure of the eye rather than evaluating retinal function, making it less suitable for diagnosing functional retinal diseases. Fundoscopy allows for the direct visualization of the retina and can reveal some changes associated with PRA; however, it does not assess the electrical activity or functional integrity of the photoreceptors, making it less definitive for diagnosing this specific condition. The pupil light reflex (PLR) evaluates the response of the pupils to light but does not provide information about the specific health or function of the retina itself, which is crucial for diagnosing progressive retinal atrophy. Thus, ERG stands out as the primary tool for diagnosing this retinal degenerative disease.