Walker Terry W, Mutti Donald O
The Ohio State University College of Optometry, Columbus 43210-1240, USA.
Optom Vis Sci. 2002 Jul;79(7):424-30. doi: 10.1097/00006324-200207000-00010.
Ocular shape is altered in myopia, and accommodation during nearwork is a proposed risk factor for myopia. Using relative peripheral refractive error (RPRE), ocular shape was assessed before, during, and after a period of sustained nearwork to determine whether accommodation affects ocular shape.
Measurements of RPRE at 30 degrees in the nasal visual field were obtained using the spherical equivalent calculated from Canon R-1 autorefraction. The RPRE of 41 young adults was measured on two separate occasions separated by at least 1 week to assess RPRE repeatability. Later, the RPRE of 22 young adults was measured at a 0 D accommodative stimulus and then at a 3 D stimulus level at 0, 1, and 2 h during which subjects performed sustained nearwork at 33 cm. After 2 h of nearwork, subjects had RPRE measured at prescribed time intervals over a 1-h period in which they looked in the distance (0 D stimulus).
The measurement of RPRE had adequate repeatability (mean difference +/- SD, -0.05 +/- 0.35 D) with +/- 0.68 D as the 95% limits of agreement. The onset of accommodation produced an immediate hyperopic shift of RPRE relative to baseline (+0.37 +/- 0.44 D; p = 0.0007), indicating that ocular shape had become more prolate. This shape remained unchanged after 1 h of sustained accommodation (RPRE difference from baseline, +0.25 +/- 0.55 D; p = 0.04) and then returned to baseline dimensions after 2h of accommodation (RPRE difference from baseline, +0.11 +/- 0.39 D; p = 0.21). At the 0 D stimulus level one minute after the period of nearwork, RPRE became more myopic relative to baseline (RPRE difference from baseline, -0.28 +/- 0.50 D; p = 0.016). Ocular shape returned to baseline dimensions after 45 min of accommodative relaxation.
Accommodation induced the ocular shape to become more prolate. The opposite occurred after accommodation was relaxed, namely a change toward a more oblate ocular shape. The transient nature of these changes suggests that tension on the choroid and choroidal hysteresis may play a role in influencing ocular shape.
近视患者眼部形状会发生改变，而近距离工作时的调节被认为是近视的一个风险因素。通过相对周边屈光不正（RPRE），在一段持续的近距离工作之前、期间和之后评估眼部形状，以确定调节是否会影响眼部形状。
使用佳能R-1自动验光仪计算出的球镜等效值来测量鼻侧视野30度处的RPRE。41名年轻成年人的RPRE在至少间隔1周的两个不同时间进行测量，以评估RPRE的可重复性。之后，22名年轻成年人的RPRE在0 D调节刺激下测量，然后在3 D刺激水平下于0、1和2小时测量，在此期间受试者在33 cm处进行持续的近距离工作。在2小时的近距离工作后，受试者在1小时内按照规定的时间间隔测量RPRE，在此期间他们看向远处（0 D刺激）。
RPRE的测量具有足够的可重复性（平均差异±标准差，-0.05±0.35 D），95%一致性界限为±0.68 D。调节开始时，RPRE相对于基线立即出现远视性偏移（+0.37±0.44 D；p = 0.0007），表明眼部形状变得更加扁平。在持续调节1小时后，这种形状保持不变（与基线的RPRE差异，+0.25±0.55 D；p = 0.04），然后在调节2小时后恢复到基线尺寸（与基线的RPRE差异，+0.11±0.39 D；p = 0.21）。在近距离工作结束后1分钟的0 D刺激水平下，RPRE相对于基线变得更加近视（与基线的RPRE差异，-0.28±0.50 D；p = 0.016）。在调节放松45分钟后，眼部形状恢复到基线尺寸。
调节使眼部形状变得更加扁平。调节放松后则出现相反情况，即眼部形状向更加球形转变。这些变化的短暂性表明脉络膜上的张力和脉络膜滞后可能在影响眼部形状方面发挥作用。
