IGF1 and cytomegalovirus retinitis: The initial application of ASO therapy for ocular conditions involved injecting the IGF-I ASO during conditioned eye-blink learning in rats, which resulted in the normalization of cerebellar IGF-I levels following treatment.541 The delivery of ASOs to the retina has also been explored.542 Fomivirsen is a 21-mer ASO modified with a PS backbone, designed to target and inhibit the viral IE-2 protein.543 As the first approved ASO-based drug, fomivirsen treats cytomegalovirus retinitis in patients with acquired immunodeficiency syndrome (AIDS) through intravitreal (IVT) administration.