The duration of normal visual exposure necessary to prevent form deprivation myopia in chicks

Abstract

The aim of this study was to determine the minimum daily period of exposure to normal visual stimulation required to prevent occlusion induced myopia in chicks. Chicks were treated with monocular translucent occlusion in a 12 hr light/12 hr dark cycle. Occluders were removed for 0 (constant occlusion), 15, 20, 30, 40, 60, 75, 90, 120, 150, 240 or 720 (no occlusion) minutes each day for either 2 or 3 weeks. Fellow eyes and the eyes of normal chicks (bilaterally unoccluded) were used as controls. Occlusion-induced myopia and axial elongation were found to decrease significantly (P < 0.01) with increasing daily exposure to normal visual stimulation. Application of a time series equation to the data estimates that 30 and 130 min of normal visual exposure per day reduces myopia by 50 and 95% respectively. This study demonstrated that the regulation of ocular growth is affected strongly by short periods of normal visual stimulation in the presence of long periods of abnormal stimulation.

Pirenzepine Affects Scleral Metabolic Changes in Myopia through a Non-toxic Mechanism

“…Although the site(s) at which pirenzepine treatment or unoccluded vision exert their inhibitory effects on myopia development are uncertain, the present study demonstrates that the end effect on scleral metabolism is similar, namely a transient reduction of elevated glycosaminoglycan synthesis. Given that myopia development was inhibited by both pirenzepine treatment and the provision of unoccluded vision (Nickla et al, 1989;Napper et al, 1995) and both of these treatments were found to induce similar transient, and reversible, changes in glycosaminoglycan synthesis, these ®ndings further support a non-toxic and physiological role for pirenzepine in myopia prevention.…”

“…Previous studies have demonstrated that other methods of interrupting the signal for ocular growth, such as providing unoccluded vision during deprivation, for short periods are also effective at preventing myopia development (Nickla et al, 1989;Napper et al, 1995). As the provision of unoccluded vision must be considered a non-invasive and, therefore, physiological means of ocular growth regulation, scleral glycosaminoglycan synthesis was examined in animals allowed 3 hr of unoccluded vision each day to provide an unequivocally`non-toxic' comparison to the pirenzepine treatment.…”

“…Speci®cally, daily periods of 2±3 hr of unoccluded vision have been shown to reduce the amount of myopia inducible in chicks by up to 90 % (Napper et al, 1995).…”

Long-term visual prognosis of infantile-onset high myopia

“…We thought that this slight increase in axial length would likely be the normal growth rate of an eyeball during an individual's development. Therefore, we suspected that full correction of refractive errors at early life may elicit a clear image for the individual, and that this might halt the progression of myopia due to the inhibition of the normal growth of the eyeball, 26 as well, the results of several animal studies using species such as chicks, [27][28][29] tree shrews, 30,31 and monkeys 32 also indicated that form-deprivation myopia may be counterbalanced by the application of relatively short daily periods of unrestricted vision. However, the comprehension of the mechanism of myopic regression clearly needs to be explored by further study.…”

Vitamin D in Dry Eye and Myopia

“…Schmid and Wildsoet (2004) reported myopia inhibitory effects of apomorphine (non-selective dopamine agonist) in both LIM and FDM in chicks, however animal model using guinea pig demonstrated only the inhibitory effects in FDM and both the levels of dopamine and dopamine metabolites were lower in FDM but such reduction was not observed in LIM (Dong et al, 2011b), indicating dopaminergic pathway is of higher relevance to FDM. In addition, less myopic shifts were observed with normal vision intervention in both FDM and LIM of chicks (Napper et al, 1995;Schmid & Wildsoet, 1996). Spiperone, a D2 dopamine antagonist, should therefore subdue myopia inhibitory effects of normal vision intervention.…”