Experimental Study Of IGF-Ⅰ,IGF-Ⅱ In The Development Of Form Deprivation Myopia

Myopia is a leading cause of ametropia throughout the world. The investigation of epidemiology showes that, myopia has became a medical and community problem in the whole world , the happening of myopia in Asia is highest than that in other areas, therefore, the investigation about myopia in various fields is concerned extraordinarily. The mechanism of myopia is not understood, a basically confirmed conclusion at the moment is that myopia is the result of the environment elements and the hereditary elements affected together , During the early development phase after the animal was born, if disturbed the vision-depedent emmetropilization feed-back by form deprivation, would cause the axial length of eye prolong and coming into being myopia, that is form deprivation myopia. The local retina controls theory argues that form deprivation myopia is the result of the local retinal message factors regulate and control the growth of the sclera fibroblast cells, leading remodification of the sclera, and prolongation of the axial length.Insulin-like growth factor is discovered more than 40 years. The gene of IGF-Ⅰ , IGF-Ⅱ is widely expressed in neuroepithlium of retina , retinapigment epithelium , choroid and sclera . In 2000, Kusakari discovered that the immuni- activation of IGF-Ⅱ is significantly higher than the control group in occluded posterior sclera, he proposed that IGF- II probablly participated in the regular and control relationship between retinal and sclera during the development of form deprivation myopia. We established the model of experimental form deprivation myopia in guinea pig , to evaluate the expression of IGF in retina, choroid and sclera in the level of transcription and determine the role of IGF in the development of form deprivation myopia.Material and Method30 one-day-old guinea pigs were selected , all left eyes underwent form deprivation with transplant goggles, and the right eyes were used as control. Before experiment 4th week and 8th week refractive status was respectively determined by means of steak retinascopy and axial length was measured by type A ultrasound . After the left eyes were occluded for 8 weeks, randomly selected 5 occluded eyes and control eyes respectively, after routine fixation, dehydration, paraffin embedding, 5μm paraffin sections were taken. Routine hematoxylin-eosin(HE) staining, detected the morphological changes in form deprived guinea pig retina, choroids, sclera under light microscope. Another 10 occluded eyes and control eyes were collected respectively, and total RNA in the posterior retina, choroids, sclera was extracted traditionally using TRIZOL reagent and expression levels of IGF-Ⅰ and IGF-Ⅱ mRNA were analyzed via single step reverse transcription-polymerase chain reaction.Result1 Form deprivation could lead to development of myopia: the axial length had significant different between the occluded eyes and the control eyes (p< 0. 05) . The long the eyes were occluded, the more serious the degree of myopia was, and there was significant difference at different time.There was a linear correlation between the refractive state and the axiallength in the occluded eyes (r=-0.878 p=0.000) .2 HE staining showed that the occluded retina and choroid became thinner, the posterior fibrous sclera was thinner than the control, the collagen fiber changed into slender, ranged in chaos , and the gap between the fiber became larger , appeared obvious break.3 RT-PCR showed that regional expression of IGF gene existed in the guinea pig eyes. The highest abundance was in the retina, the higher for choroid and to a less degree for sclera. The levels of IGF mRNA expression in occluded retina and choroid was significantly higher than that in thecontrol, but lower in posterior sclera than that of the control (p<0.05) .Conclusion1 Monocular deprivation for 4 weeks lead to obvious myopia in occluded eyes of guinea pigs, the longer the eyes were occluded, the more significant the difference was. Guinea pig could be used as an effective and economical model of mammal in form deprived myopia study.2 Form deprivation in guinea pigs caused the posterior fibrous sclerathinner and feeble , the sclera was passively stretched , the eyeball was expanded and prolongated, resulted in myopia .The key of control the increasing axial length lies in strengthen the resistant power of sclera in mammals, rather than control the growth of sclera.3 The retina, choroid, sclera can express IGF mRNA by autocrine/ paracrine mechanism in guinea pig. The levels of IGF mRNA expression in occluded retina and choroids was significantly higher than that in the control, and lower in posterior sclera than that of the control. The results suggested that IGF participated in the development of form deprived myopia.4 If offer exogenous IGF during the critical period of visual development, it is likely to lessen the damaged vision by form deprivation.