In early cases of Retinitis pigmentosa, which ERG is usually more abnormal?

In early cases of Retinitis Pigmentosa (RP), the scotopic electroretinogram (ERG) is typically more abnormal due to the progressive degeneration of the rod photoreceptors that precede cone photoreceptor dysfunction. Retinitis pigmentosa primarily affects the rod pathways initially, leading to night blindness and peripheral vision loss, which are symptoms related to rod function.

The scotopic ERG assesses the function of the rod photoreceptors in low light conditions. Because rod cells are the first to be impacted in RP, this ERG will demonstrate reduced amplitude or delayed values indicative of rod dysfunction. As the disease progresses and cone photoreceptor involvement becomes more significant, you may then see changes in the photopic ERG, which measures cone function.

In summary, the scotopic ERG being more abnormal in early RP is directly correlated with the degeneration of rod photoreceptors and their pivotal role in night vision and peripheral sight. This reflects the typical disease progression of RP, where cone cell involvement occurs later.