Refraction and eye growth are regulated by visual processing in the retina. Here, both the amount and the sign of imposed defocus are recognized and determine the sign of growth changes of the underlying sclera [1]. So far, little is known about the messengers that are released from the retina to induce these changes. Recently, it was shown that the immediate-early gene product ZENK, which is expressed in glucagon amacrine cells, is increased in these cells if chicks were treated with positive lenses and decreased if negative lenses or diffusers were worn [2,3]. There is also evidence for a potential role of glucagon itself as a stop signal in eye growth [4]. Gene expression in the retina, choroid, and sclera was investigated in recent studies. In tree shrews, the mRNA expression of scleral enzymes, such as matrix metalloproteinases (MMP) and tissue inhibitors of MMP (TIMP), were quanti-