Becker R, Gräf M
Zentrum für Augenheilkunde, Justus-Liebig-Universität Giessen.
Klin Monbl Augenheilkd. 2006 Apr;223(4):294-6. doi: 10.1055/s-2005-859013.
The growing popularity of digital imaging leads to an increasing number of photos transferred by parents via E-mail to an ophthalmologist, showing a child with a displacement of corneal reflections. This must not necessarily lead to the diagnosis of manifest strabismus.
The displacement of the first Purkinje image is demonstrated by moving the flash of a digital camera sideways from the objective. Photographs were taken at a distance of 0.6 m while the healthy test subject was looking into the camera. Flashlight was displaced gradually up to 20 cm to the left side of the objective. The resulting displacement of the corneal reflections was measured after transferring the photos to a computer.
Displacement of the source of light by 10 cm resulted in a displacement of the first Purkinje image of about 1 mm, i. e., about 0.1 mm per degree.
Displacement of corneal reflection was 0.1 mm per degree. Asymmetry of corneal reflections is twice as much, since the corneal reflections are displaced in the same direction on both eyes. Lateral displacement of the flash from the objective of the camera by 2.5 cm results in an asymmetry of 0.5 mm, thus suggesting a squint angle of 6 degrees. Vice versa, a real strabismus can be masked. This bias can be avoided by using the camera with the flash above the objective in relation to the patient's interpupillar axis. Nevertheless, it is impossible to diagnose or to exclude a microstrabismus by this method itself, because an angle kappa, if it is different on both eyes, can also mimic or mask a manifest strabismus.
数字成像的日益普及导致家长通过电子邮件向眼科医生发送越来越多的照片，照片显示孩子角膜反射移位。但这不一定会导致明显斜视的诊断。
通过将数码相机的闪光灯从物镜侧向移动来演示第一普尔钦耶图像的移位。在健康受试者注视相机时，于0.6米的距离拍摄照片。闪光灯逐渐向物镜左侧移位达20厘米。将照片传输到计算机后，测量由此产生的角膜反射移位。
光源移位10厘米导致第一普尔钦耶图像移位约1毫米，即每度约0.1毫米。
角膜反射移位为每度0.1毫米。角膜反射不对称度是其两倍，因为双眼的角膜反射向同一方向移位。闪光灯相对于相机物镜横向移位2.5厘米会导致0.5毫米的不对称，由此提示斜视角度为6度。反之，真正的斜视可能会被掩盖。通过将闪光灯置于相对于患者瞳孔间轴在物镜上方的相机可避免这种偏差。然而，仅靠这种方法本身无法诊断或排除微小斜视，因为如果双眼的kappa角不同，也可能模拟或掩盖明显斜视。
