Postnatal eye growth is definitely controlled by visual signs. defocus than in reducing hyperopia caused by myopic defocus; (1b) when the eye experiences alternating myopic and hyperopic defocus the eye is more sensitive to myopic defocus than to hyperopic defocus and tends to develop hyperopia actually if the period of hyperopic defocus is much longer than the period of myopic defocus; (2) when the eye experiences brief repeated episodes of defocus by wearing either positive or bad lenses lens payment depends on the rate of recurrence and period of individual episodes of lens put on not just the total daily period of lens put on; and (3) further analysis of the time constants for the hypothesized internal emmetropization signals show that LIG4 while it takes approximately the same amount HQL-79 of time for the signals to rise and saturate during lens-wearing episodes the decline of the signals between episodes depends strongly on the sign of defocus and the ocular component. Although most extensively analyzed in chicks the nonlinear temporal integration of visual signals has been found in additional animal models. These findings may help clarify the complex etiology of myopia in school-aged children and suggest ways to slow down myopia progression. Keywords: Myopia hyperopia axial size choroid emmetropization temporal integration After decades of studies on myopia carried out on various animals including tree shrews (Sherman et al. 1977; Norton and Rada 1995) rhesus monkeys (Wiesel and Raviola 1977; HQL-79 von Noorden and Crawford HQL-79 1978; Hung et al. 1995) chicks (Schaeffel et al. 1988; Irving et al. 1992) marmosets (Troilo and Judge 1993; Whatham and Judge 2001) guinea pigs (McFadden et al. 2004) and mice (Tejedor and de la Villa 2003; Schaeffel et al. 2004) it has become clear the growth of the eye like the growth of additional organs in our person is under homeostatic control and that the homeostatic control mechanism depends at least in part on visual signals that exert strong control over the axial length of the eye (Wallman and Winawer 2004). To see far objects clearly the focal length of the eye needs to match its physical size so the images will be focused on the photoreceptors in the retina a state known as emmetropia. When presented with defocus (i.e. when an image is not focused on the photoreceptors) the eye has a short term focusing mechanism (accommodation) and a long-term focusing mechanism (emmetropization). Emmetropization is the capacity to compensate for defocus by changing both the rate of ocular elongation and the thickness of the choroid (a vascular coating lying between the retinal pigment epithelium and sclera) to bring the retina closer to the focal aircraft. When the image is focused in front of the retina (so called “myopic defocus” since the eye is now functionally myopic) by wearing a positive lens the eye reduces its rate of ocular elongation and raises choroidal thickness to move the retina ahead to meet the focal aircraft (Number 1). Given enough time the eye will restore emmetropia with the positive lens in place and will therefore appear hyperopic without the lens. The opposite happens when wearing a negative lens that focuses images behind the retina (“hyperopic defocus” Number 1). Number 1 Schematics of ocular payment for defocus of reverse signs. (A) shows an emmetropic attention having a schematic representation of the myopic and hyperopic defocus produced by wearing a positive and negative spectacle lens respectively. (B) shows ocular … HQL-79 Among the varieties used in myopia study chicks are the most commonly used mostly because compared with other varieties chicks have been shown to be able to compensate for the widest range of defocus within a relatively short period of time (Irving et al. 1992). Indeed young chick eyes possess two distinguishing qualities facilitating payment: Their eyes (which grow at a relatively steady rate when measured until at least 42 days older (Gottlieb et al. 1987) switch their rate of growth within a day time or two to compensate for both myopic and hyperopic defocus and their choroids display large changes in thickness to compensate for both myopic and hyperopic defocus (Wallman et al. 1995). Indeed compensatory changes in choroidal thickness have been found in tree shrews (Siegwart and Norton 1998) marmosets (Troilo et al..