Hamm Lisa M, Mistry Kishan, Black Joanna M, C Grant Cameron, Dakin Steven C
School of Optometry and Vision Science, The University of Auckland, Auckland, New Zealand.
New Zealand National Eye Centre, The University of Auckland, Auckland, New Zealand.
Transl Vis Sci Technol. 2019 Jan 30;8(1):16. doi: 10.1167/tvst.8.1.16. eCollection 2019 Jan.
Reliable estimation of visual acuity requires that observers maintain a constant distance from the target, but use of chin rests is not always feasible. Our aim was to quantify children's movement during community testing and its impact on near (40 cm) and intermediate (150 cm) acuity measures.
Thirty-three 7-year-old children performed several acuity tests run on a tablet computer, administered in the child's home by a trained lay screener. The tablet webcam was used to derive a continuous estimate of the child's position during testing. We estimated acuity using both the recommended viewing distance and using trial-by-trial estimates of the child's physical distance from the screen.
Although initial positioning in the 40-cm viewing distance condition was accurate, on 18% of trials children moved sufficiently to support a 0.1 logMAR improvement in acuity, leading 16% of staircases to overestimate acuity by more than one line. Initial positioning for the 150-cm condition was less accurate, but the longer viewing distance minimized the impact of children's movement on the visual angle of the target. Overall, at 150 cm 8% of staircases were overestimated by more than 0.1 logMAR.
Children move substantially during intermediate and near acuity tests despite assessors encouraging maintenance of the correct viewing distance.
Real-time estimates of the child's physical distance from the target are possible when assessments are conducted on camera-enabled devices. Correction for movement will likely lead to more accurate measures of near and intermediate visual acuity.
可靠地估计视力需要观察者与目标保持恒定距离，但使用颏托并不总是可行的。我们的目的是量化儿童在社区测试中的移动情况及其对近视力（40厘米）和中视力（150厘米）测量的影响。
33名7岁儿童在平板电脑上进行了多项视力测试，由一名经过培训的非专业筛查人员在儿童家中进行测试。在测试过程中，使用平板电脑的网络摄像头持续估计儿童的位置。我们既使用推荐的观察距离，也使用每次试验中儿童与屏幕实际距离的估计值来估计视力。
尽管在40厘米观察距离条件下的初始定位是准确的，但在18%的试验中，儿童移动得足够多，足以使视力提高0.1 logMAR，导致16%的视力阶梯高估视力超过一行。150厘米条件下的初始定位不太准确，但较长的观察距离将儿童移动对目标视角的影响降至最低。总体而言，在150厘米处，8%的视力阶梯被高估超过0.1 logMAR。
尽管评估人员鼓励保持正确的观察距离，但儿童在中视力和近视力测试中仍会大幅移动。
当在具有摄像头功能的设备上进行评估时，可以实时估计儿童与目标的实际距离。对移动进行校正可能会使近视力和中视力的测量更加准确。
