[Technical and optical aspects of smartphone-based fundus photography : Possibilities and limitations in practice].

Background: Smartphone-based adapters for fundus photography offer a cost-effective alternative to traditional fundus cameras. The various offers vary widely in design, size, purchasing costs, user-friendliness, and image quality when compared to each other and to traditional fundus cameras.

Objective: The aim is to enable the reader to understand the technical and optical aspects of fundus photography and therefore to evaluate the various offers of traditional fundus cameras and adaptors for smartphone-based fundus photography with respect to their personal requirements.

Material and methods: The technical and optical principles and aspects of fundus photography are explained and the various approaches to illumination, imaging, image capture and alignment are discussed. The association between field of view, pupil size, mydriasis and image quality are discussed as well as the challenges and difficulties of aligning the fundus camera relative to the patient's eye.

Results: The most important technical aspects of a fundus camera are the avoidance of disturbing reflections when taking photographs, an acceptable field of view angle, the user-friendliness during alignment, success rate of imaging and the question whether mydriasis is necessary.

Conclusion: The development of adapters for smartphone-based fundus photography has resulted in interesting offers, which make fundus photography available to a wider user spectrum at low purchase costs. The offers on the market vary widely. It is therefore difficult to reach a definitive evaluation; however, smartphone-based adapters mostly have limitations with respect to user-friendliness, the size of the field of view and image quality.