Journal article

Publication year: 2006

Pages: 294-296

Journal: Klinische Monatsblätter für Augenheilkunde

Volume number: 223

Issue number: 4

ISSN: 0023-2165

DOI Link: https://doi.org/10.1055/s-2005-859013

Publisher: Georg Thieme Verlag

Abstract: 
Background: 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. Materials and Methods: 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. Results: Displacement of the source of light by 10 cm resulted in a displacement of the first Purkinje image of about I mm, i.e., about 0.1 mm per degree. Conclusions: 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.

Harvard Citation style: Becker, R. and Gräf, M. (2006) Systemic bias in the photographic assessment of the 1st Purkinje image, Klinische Monatsblätter für Augenheilkunde, 223(4), pp. 294-296. https://doi.org/10.1055/s-2005-859013

APA Citation style: Becker, R., & Gräf, M. (2006). Systemic bias in the photographic assessment of the 1st Purkinje image. Klinische Monatsblätter für Augenheilkunde. 223(4), 294-296. https://doi.org/10.1055/s-2005-859013