Far-Red, High-Resolution, Reflection-Free Images of the Anterior Segment in Retro-Illumination

Examination of the anterior segment using retro-illumination is part of the routine clinical examination, but capturing images that can be used by the clinician remains a challenge because reflections are always present, resolution is insufficient, and the patient's glare often causes motion blur. Our aim was therefore to overcome these limitations.

We modified a slit lamp by using a far-red LED, a high-resolution camera, and by modifying the light path using polarizers and an obturator to suppress reflections while optimizing the light flux. We used this prototype to image various ocular conditions to illustrate its potential.

With the ×40 magnification of the slit lamp, the prototype provided images with a resolution of 6.2 µm, and a field of view of 9.7 mm. We obtained images without motion blur in all patients. The vast majority of images were reflection-free. Only the images of a few patients with pseudophakia showed persistent small reflection. The resolution was sufficient to highlight, for example, all the Descemetic excrescences (Guttae) constitutive of a Fuchs endothelial corneal dystrophy (FECD).

Our retro-illumination device prototype provides high-resolution images of the different structures of the anterior segment of the eye, easy to acquire mainly because they do not dazzle patients. We believe that these images have the potential to facilitate the diagnosis and monitoring of many different diseases both in routine use and in clinical trials where they could be used as objective endpoints.

Our prototype revisits retro-illumination with a potential to become a new imaging device.