2 隐斜与近视眼
隐斜视是能被融合反射控制的潜在性眼位偏斜,其中内隐斜为打破融合反射后,双眼呈内斜状态。如今,被广泛认可的Morgan标准值指出,视远隐斜为-1±2△,视近隐斜为-3±5△(负号为外隐斜,正号为内隐斜)。
Brown等[25]发现,在高加索人群中25%的近视眼儿童存在视近内隐斜。Walline等[26]以遮盖试验收集大样本儿童的隐斜资料,发现在屈光不正完全矫正下97%的儿童存在远点正位;幼儿园至五年级儿童的视近外隐斜度从31.8%降至21.0%,内隐斜度从6.7%增至12.2%。Goss等[27]测量33名年龄5.8~21岁、平均为-2.2 D近视眼者的隐斜状态,发现视远隐斜为正位或内隐斜(M=+3.2△),视近隐斜均值接近0(M =-0.3△),其中12%患者处于-1~+1△,9%高于+12△。这些研究均表明,屈光不正儿童在眼位上存在波动。
Tassinari[28]的研究表明,合并内隐斜的近视眼儿童会存在更大的调节滞后。他们对平均年龄10.9岁的近视眼儿童注视40 cm视标时,用Canon R-1自动验光仪测量调节反应和von Grafe法测量近隐斜。他们解释,在内隐斜较高者中调节滞后较大是为维持双眼单视而减少了调节性集合。由于双眼视下集合与调节的联系,内隐斜减少调节反应,这就使内隐斜近视眼儿童的调节滞后更大。调节反应降低所致的调节滞后减少了以AC/A相联的内隐斜的幅度,这样将降低融像性集合的需要。而且,集合性调节刺激了负相对调节以克服内隐斜的融像性集合,所以负相对调节可能表明调节滞后的增加。内隐斜近视眼可能利用他们更高的AC/A比和0.25~0.50 D的调节滞后来减少内隐斜的幅度,由此减少负融像性集合的需求。
由于渐变镜延缓视近内隐斜儿童近视眼进展效果显著,且随着渐变镜视近下加的变化,视近调节滞后减小,同时视近隐斜状态亦改变,故推测眼位呈内隐斜状态的近视眼患者的发病机制有别于其他眼位的近视眼患者。所以深入探讨内隐斜患者的近视眼发病机制以及眼动参数就显得尤为重要。
既然渐变镜的视近下加会在减少视近调节滞后时出现眼位呈外隐斜增大趋势,那么联合视近BI(base-in)的棱镜和视近下加的渐变镜就能在减少视近调节滞后同时减少视近外隐斜状态,从而降低渐变镜配戴所致眼动参数的不平衡。+2.52 D的视近下加联合6△的BI棱镜可以减少视近调节滞后至-0.33 D和视近隐斜至-2.4△[29],但是这种新式的渐变镜能否达到延缓近视眼进展目的还需进行纵向研究。另外,Jiang等[30]也通过对五种不同下加的调节滞后和隐斜度的分析提出渐变镜验配的最优化下加公式,为实现渐变镜的个体化配戴提供一定依据,为提高渐变镜延缓青少年近视眼进展的作用提供了新思路。
综上所述,调节滞后和隐斜状态在诸多近视眼研究中被证实是与近视眼的发生、进展相关的重要参数,进一步深入探讨调节滞后以及隐斜在近视眼发病中的作用,将为近视眼的防治提供更为有效的新手段和新方法。
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