Otto Joanna M, Bach Michael, Kommerell Guntram
Universitäts-Augenklinik, Freiburg, Germany.
Strabismus. 2009 Oct-Dec;17(4):143-7. doi: 10.3109/09273970903295405.
We determined the vergence position of rest (horizontal component) in two sessions, 1 to 6 weeks apart. Each session contained 8 trials. Twenty observers with normal eyes looked through Risley prisms that allowed a continuous modulation of their strength. We asked the observers to look at a fully fusionable picture, and to adjust the prisms such that viewing appeared most relaxing. The viewing distances were 400 cm and 50 cm.
The standard deviation among the 8 trials of each session, averaged over the two sessions, the viewing distances of 400 cm and 50 cm, and the 20 observers, was + or -1.4 prism dioptres (cm/m). From the first session to the second, many observers changed the preferred prism significantly. At a viewing distance of 400 cm, 10 of 20 observers changed their preferred prism by more than 1.0 prism diopter, up to 3.3 prism diopters. At a viewing distance of 50 cm, 11 of 20 observers changed their preferred prism by more than 1.0 prism diopter, up to 5.1 prism diopters.
The prismatic strength estimated as being most relaxing can be very variable. Before considering a prescription, the practitioner should determine whether the preferred prismatic strength remains reasonably stable. To ascertain this consistency, more than one session seems to be necessary.
我们在两个相隔1至6周的时间段内测定了静息时的聚散位置（水平分量）。每个时间段包含8次试验。20名视力正常的观察者通过里斯利棱镜进行观察，该棱镜可使棱镜度数连续变化。我们要求观察者注视一幅完全可融合的图像，并调整棱镜，以使观察看起来最轻松。观察距离分别为400厘米和50厘米。
在两个时间段、400厘米和50厘米的观察距离以及20名观察者的条件下，每个时间段8次试验的标准差平均为±1.4棱镜度（厘米/米）。从第一个时间段到第二个时间段，许多观察者显著改变了其偏好的棱镜度数。在400厘米的观察距离下，20名观察者中有10名改变了其偏好的棱镜度数超过1.0棱镜度，最高达到3.3棱镜度。在50厘米的观察距离下，20名观察者中有11名改变了其偏好的棱镜度数超过1.0棱镜度，最高达到5.1棱镜度。
估计为最轻松的棱镜度数可能变化很大。在考虑配镜处方之前，从业者应确定偏好的棱镜度数是否保持合理稳定。为确定这种一致性，似乎需要不止一个时间段的测量。
