Cacho Isabel, Dickinson Christine M, Reeves Barnaby C, Harper Robert A
Faculty of Life Sciences, Moffat Building, The University of Manchester, Manchester, UK.
Optom Vis Sci. 2007 Jun;84(6):487-95. doi: 10.1097/OPX.0b013e318073c2f2.
To compare "single letter" (SL) acuity, "crowded letter" (CL) acuity, and "repeated letter" (RL) acuity for patients with age-related macular degeneration (AMD) and investigate if differences between these visual acuities are associated with fixation characteristics.
A total of 243 patients with AMD had their best-corrected visual acuity measured on an ETDRS chart. SL, CL, and RL acuities were measured using Landolt C targets on a monitor. Fifty-degree-field red-free fundus photographs were taken and a static target was used to calculate the Preferred Retinal Locus (PRL) distance and direction from the fovea. Quality of fixation (consistency and oculomotor response) was also assessed using a fundus camera and a dynamic target.
RL acuity was almost always better than CL acuity and SL acuity was almost always better than CL acuity. The mean (+/-SD) RL-CL and SL-CL acuity differences were -0.13 (+/-0.15) logMAR and -0.11 (+/-0.13) logMAR respectively. The median PRL distance was 3.73 degrees and the preferred retinal areas for the location of the PRL were the left (left quadrant of visual field; 39.5% of cases) and superior (inferior quadrant of visual field; 25.4%). Visual acuity was significantly associated with PRL distance but PRL distance only explained 10% of the variation in visual acuity. PRL distance was found to be a significant but weak predictor of the SL-CL acuity difference but fixation quality was not a good predictor of the RL-CL acuity difference.
Although the acuity measured under different stimulus conditions varies, the absolute differences are small. This suggests that these techniques would not be helpful in determining fixation characteristics, or predicting the outcome of rehabilitation in individual patients with AMD.
比较年龄相关性黄斑变性（AMD）患者的“单字母”（SL）视力、“拥挤字母”（CL）视力和“重复字母”（RL）视力，并研究这些视力之间的差异是否与注视特征相关。
共243例AMD患者在ETDRS视力表上测量其最佳矫正视力。使用显示器上的Landolt C视标测量SL、CL和RL视力。拍摄50度视野无赤眼底照片，并使用静态视标计算从中央凹到 Preferred Retinal Locus（PRL）的距离和方向。还使用眼底相机和动态视标评估注视质量（一致性和动眼反应）。
RL视力几乎总是优于CL视力，SL视力几乎总是优于CL视力。RL-CL和SL-CL视力差异的平均值（±标准差）分别为-0.13（±0.15）logMAR和-0.11（±0.13）logMAR。PRL的中位数距离为3.73度，PRL位置的首选视网膜区域是左侧（视野左象限；39.5%的病例）和上方（视野下象限；25.4%）。视力与PRL距离显著相关，但PRL距离仅解释了视力变化的10%。发现PRL距离是SL-CL视力差异的显著但较弱的预测指标，但注视质量不是RL-CL视力差异的良好预测指标。
尽管在不同刺激条件下测量的视力有所不同，但绝对差异很小。这表明这些技术无助于确定注视特征，或预测个体AMD患者的康复结果。
