Signaling myopia

Clear vision requires that the cornea and the lens focus light onto the retina. If the shape of the eye produces a focal plane behind the retina, the eye is myopic, and the image appears blurred. In many developing animals, the sharpness of retinal images regulates the growth of the sclera (the outer connective tissue sheath of the eye), so that axial eye length is matched to the refractive power of the lens and cornea. In this issue (pages 706–712), Andy Fischer and colleagues suggest a candidate for this growth-regulating signal. They found that expression of the immediate-early gene ZENK (red) in a particular class of chick retinal amacrine cells (containing glucagon) was regulated by image defocus. ZENK expression was suppressed by several experimental conditions that enhance eye growth (such as a lens that blurs vision), but increased under conditions that suppress it, such as lens removal. This suggests that these amacrine cells could be involved in focus-induced changes in ocular growth and refraction.