Scanning the retinae of the human eyes with a laser beam is an approved diagnosis method in ophthalmology; moreover
the retinal blood vessels form a biometric modality for identifying persons. Medical applied Scanning Laser
Ophthalmoscopes (SLOs) usually contain galvanometric mirror systems to move the laser spot with a defined speed
across the retina. Hence, the load of laser radiation is uniformly distributed and eye safety requirements can be easily
complied. Micro machined mirrors also known as Micro Electro Mechanical Systems (MEMS) are interesting
alternatives for designing retina scanning systems. In particular double-resonant MEMS are well suited for mass
fabrication at low cost. However, their Lissajous-shaped scanning figure requires a particular analysis and specific
measures to meet the requirements for a Class 1 laser device, i.e. eye-safe operation.
The scanning laser spot causes a non-uniform pulsing radiation load hitting the retinal elements within the field of view
(FoV). The relevant laser safety standards define a smallest considerable element for eye-related impacts to be a point
source that is visible with an angle of maximum 1.5 mrad. For non-uniform pulsing expositions onto retinal elements the
standard requires to consider all particular impacts, i.e. single pulses, pulse sequences in certain time intervals and
cumulated laser radiation loads. As it may be expected, a Lissajous scanning figure causes the most critical radiation
loads at its edges and borders. Depending on the applied power the laser has to be switched off here to avoid any retinal
Many applications could benefit from miniaturized systems to scan blood vessels behind the retina in the human eye, so
called „retina scanning“. This reaches from access control to sophisticated security applications and medical devices.
High volume systems for consumer applications require low cost and a user friendly operation. For example this
includes no need for removal of glasses and self-adjustment, in turn guidance of focus and point of attraction by
simultaneous projection for the user.
A new system has been designed based on the well-known resonantly driven 2-d scanner mirror of Fraunhofer IPMS. A
combined NIR and VIS laser system illuminates the eye through an eye piece designed for an operating distance
allowing the use of glasses and granting sufficient field of view. This usability feature was considered to be more
important than highest miniaturization. The modulated VIS laser facilitates the projection of an image directly onto the
retina. The backscattered light from the continuous NIR laser contains the information of the blood vessels and is
detected by a highly sensitive photo diode.
A demonstrational setup has been realized including readout and driving electronics. The laser power was adjusted to an
eye-secure level. Additional security features were integrated. Test measurements revealed promising results. In a first
demonstration application the detection of biometric pattern of the blood vessels was evaluated for issues authentication
There is an increasing need for reliable authentication for a number of applications such as e commerce. Common authentication methods based on ownership (ID card) or knowledge factors (password, PIN) are often prone to manipulations and may therefore be not safe enough. Various inherence factor based methods like fingerprint, retinal pattern or voice identifications are considered more secure. Retina scanning in particular offers both low false rejection rate (FRR) and low false acceptance rate (FAR) with about one in a million. Images of the retina with its characteristic pattern of blood vessels can be made with either a fundus camera or laser scanning methods. The present work describes the optical design of a new compact retina laser scanner which is based on MEMS (Micro Electric Mechanical System) technology. The use of a dual axis micro scanning mirror for laser beam deflection enables a more compact and robust design compared to classical systems. The scanner exhibits a full field of view of 10° which corresponds to an area of 4 mm2 on the retinal surface surrounding the optical disc. The system works in the near infrared and is designed for use under ambient light conditions, which implies a pupil diameter of 1.5 mm. Furthermore it features a long eye relief of 30 mm so that it can be conveniently used by persons wearing glasses. The optical design requirements and the optical performance are discussed in terms of spot diagrams and ray fan plots.