| Background and objectiveMyopia is one of the most common ocular abnormalities.In the United States,25% of the adult population were found to be myopic, whereas the prevalence rates were reported to be as high as 80% in Asian populations.China's 1995 national census in the two hundred million people, the prevalence of myopia in university students range from 60% to 70%. In 2000 The Ministries of Education and Health made a survey ,which showed that the prevalence of myopia in Chinese students seem ranks second in the world.Myopia can be classified as physiological or pathologic. Physiological myopia is a normal variation in the refractive error resulting from excessive convergent power caused by the cornea or the lens. Pathologic myopia is usually associated with an elongated globe and a refractive error of at least -6.00 D and/or an axial length of >25.5 mm. The tissue alterations in high myopia affect the sclera, choroid, and retina, which can result in a number of ocular findings and potential complicationsMany complications of myopia can be serious threat to patient's visual function, in which retinal detachment is a very noteworthy complications. The risk factors of retinal detachment include myopia, vitreous detachment, retinal degeneration and hole there.In 1993, A large case-control study's results showed that myopia is a clearly relevant factor of rhegmatogenous retinal detachment . -1.00～-3.00D myopic would increase the incidence of retinal detachment four times ,>-3.00D myopic would increase the incidence of retinal detachment by 10 times. High myopia would increase the incidence of retinal detachment 15 times. Lattice degeneration as a risk factor may increase every refractive grading of retinal detachment's incidence of 10 times. The incidence of RD in high myopia associated with lattice degeneration was about 200 times of which is emmetropic without lattice degeneration .Earlier data about the correlation between axial length and peripheral retinal changes were inconsistent and sometimes conflicting. Based on reading previous literature ,it can be found that there were intrinsic limitations about these previous studies because the data were collected retrospectively, and recruited subjects were institution-based with a sample bias toward symptomatic individuals.A university-based study asymptomatic patients with myopia avoids many of the predispositions introduced by these previous studies. The purpose of this study was to study the prevalence and the characteristics of peripheral retinal findings in Chinese undergraduates with myopia (spherical equivalent <-0.50D) and to investigate the relationship among the severity of myopia , axial length or the depth of vitreous and the retinal lesions in myopia. The results will help determine the necessity and type of ocular screening and disease prevention programs to be used in similar populations.Methods:A Cross-sectional prevalence and charicteristics survey screening was conducted in Chinese undergraduates with refractions equal to or less than -0.50D. The examinations included: keratometry, cycloplegic refraction, intraocular pressure measurement, A and B scan ultrasonography, and retinal examinations by indirect ophthalmoscopy with scleral indentation and Goldmann three-mirror contact lens examination. Then recorded results in full.Result1 Three hundreds and thirty four eyes in 178 myopia with a mean refraction of -3.75±2.90D(range=-0.50～20.25D) were examined. The mean age was 21.30±1.57years(range=17～25years),The mean axial length was 25.04±1.24mm(range=21.00～31.21mm). The prevalence of high ocular pressure in Chinese undergraduates with high myopia was 2.82%(2 in 71 eyes).2 The refraction of myopia was positive correlated with axial length in Chinese undergraduates with myopia(r=0.92, P =0.000).3 The most common peripheral retinal findings was white without pressure (83 eyes), The prevalence was 24.85%; followed by frost-like degeneration in 11.68% and lattice degeneration in 8.98% of eyes. The prevalence of retinal holes was 3.59%;pigmentary degeneration 1.98%; The prevalence of retinal detachment was 0.30%. The depth of vitreous in eyes with peripheral retinal degeneration was significantly longer than eyes without peripheral retinal degeneration( P<0.05).4 A positive correlation was noted between axial length and the lesions of lattice degeneration , retinal hole and retinal detachment(P<0.05).5 The characteristics of lattice degeneration in Chinese undergraduates with myopia was: Most are located in the areas between equatorial region and ora serrata .always presented as oval-shaped or long belt-shaped , paralleled to the cornea margin, yellow-white spot-sediments can be seen within the region, typical fishbone-like grid was rare seen . The prevalence of retinal hole was 3.59%. In upper temporal quadrant (65.79%) the prevalence of Lattice degeneration was highest.Conclusion:1 In young undergraduates with myopia, diopter and the axial length was significantly correlated, diopter and cornea curvrture was uncorrelated .2 A high prevalence of peripheral retinal degenerations was found in Chinese undergraduates with myopia. The prevalence of peripheral retinal degeneration and myopia diopter was significantly correlated. The depth of vitreous in eyes with peripheral retinal degeneration was significantly longer than eyes without peripheral retinal degeneration (P<0.05).3 The presence of lattice degeneration , retinal holes and retinal detachment was positively correlated with axial length elongation.4 The prevalence of lattice degeneration was 8.98% of eyes in young undergraduates with myopia, the characteristics of most lattice degeneration were located in the areas between equatorial region and ora serrata. always presented as oval-shaped or long belt-shaped , paralleled to the corneascleral margin, yellow-white spot-sediments can be seen within the region, typical fishbone-like grid was rare seen. The prevalence of retinal hole was low(3.59%).
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