Mutti Donald O, Mitchell G Lynn, Sinnott Loraine T, Jones-Jordan Lisa A, Moeschberger Melvin L, Cotter Susan A, Kleinstein Robert N, Manny Ruth E, Twelker J Daniel, Zadnik Karla
The Ohio State University College of Optometry, Columbus, Ohio 43210-1240, USA.
Optom Vis Sci. 2012 Mar;89(3):251-62. doi: 10.1097/OPX.0b013e3182418213.
To describe corneal and crystalline lens dimensions before, during, and after myopia onset compared with age-matched emmetropic values.
Subjects were 732 children aged 6 to 14 years who became myopic and 596 emmetropic children participating between 1989 and 2007 in the Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error Study. Refractive error was measured using cycloplegic autorefraction, corneal power using a hand-held autokeratometer, crystalline lens parameters using video-based phakometry, and vitreous chamber depth (VCD) using A-scan ultrasonography. Corneal and crystalline lens parameters in children who became myopic were compared with age-, gender-, and ethnicity-matched model estimates of emmetrope values annually from 5 years before through 5 years after the onset of myopia. The comparison was made without and then with statistical adjustment of emmetrope component values to compensate for the effects of longer VCDs in children who became myopic.
Before myopia onset, the crystalline lens thinned, flattened, and lost power at similar rates for emmetropes and children who became myopic. The crystalline lens stopped thinning, flattening, and losing power within ±1 year of onset in children who became myopic compared with emmetropes statistically adjusted to match the longer VCDs of children who became myopic. In contrast, the cornea was only slightly steeper in children who became myopic compared with emmetropes (<0.25 D) and underwent little change across visits.
Myopia onset is characterized by an abrupt loss of compensatory changes in the crystalline lens that continue in emmetropes throughout childhood axial elongation. The mechanism responsible for this decoupling remains speculative but might include restricted equatorial growth from internal mechanical factors.
描述近视发生前、发生期间及发生后角膜和晶状体的尺寸，并与年龄匹配的正视眼值进行比较。
研究对象为732名6至14岁的近视儿童以及596名正视眼儿童，他们于1989年至2007年参与了种族与屈光不正研究的协作纵向评估。使用睫状肌麻痹验光测量屈光不正，手持自动角膜曲率计测量角膜屈光力，基于视频的晶状体测量法测量晶状体参数，A超超声检查测量玻璃体腔深度（VCD）。将近视儿童的角膜和晶状体参数与年龄、性别和种族匹配的正视眼值模型估计值进行比较，从近视发生前5年至发生后5年每年进行一次。比较时先不进行正视眼成分值的统计调整，然后进行调整以补偿近视儿童较长VCD的影响。
在近视发生前，正视眼儿童和近视儿童的晶状体变薄、变平以及屈光力下降的速率相似。与经统计调整以匹配近视儿童较长VCD的正视眼儿童相比，近视儿童的晶状体在近视发生后±1年内停止变薄、变平以及屈光力下降。相比之下，近视儿童的角膜仅比正视眼儿童稍陡（<0.25 D），且在各次检查中变化不大。
近视发生的特征是晶状体代偿性变化突然消失，而正视眼儿童在整个儿童期眼轴伸长过程中这种变化仍在持续。导致这种解耦的机制仍属推测，但可能包括内部机械因素导致的赤道生长受限。
