Infrared photorefraction

Initially developed to refract chickens in the vertical pupil meridian (Schaeffel, Farkas, Howland 1986), it was later optimized also for humans (Schaeffel, Wilhelm, Zrenner 1993). With the help of Stefan Weiss and Florian Gekeler, it was further developed to also measure astigmatism. Later it merged into the first generation commerical photorefractors (at this time called PowerRefractor). Later generations are marketed by Plusoptix, Nuernberg (www.plusoptix.de).  The strength of photorefraction is that it can sample at high speed (current CMOS cameras make easily 80 Hz), both eyes at once, with binocular pupillography, direction of gaze and fast accommodation sampling. Furthermore, it works in virtually all vertebrate eyes – including tadpoles (Mathis et al 1988). Recently, it was marketed also for mice, rats, monkeys, guinea pigs and other through the STZ (link) – see also www.uak.medizin.uni-tuebingen.de/frank/peo1_schaeffel.html (any material can be taken from there as well). A demo movie shows how chickens can accommodate independently in both eyes (we can’t) – see “chick accommodation independent both eyes”

1. Scanning infrared photorefraction – photorefraction was further developed with the help of Juan Tabernero  to scan the refractive state in both horizontal and vertical meridian across the central 100 deg of the visual field. A short video to show the procedure can be seen here (make to link to a video showing the “scanning refractor”; ask Michelle whether she does not mind if this is online)
2. Various versions of eye trackers - monocular with high resolution (< 0.1 deg), binocular with about 0.5 deg resolution. The developed eye trackers have a simple automated calibration scheme and track the fixation axis at 87 (640x480 pix) or 180 Hz (320x240 pix; CMOS camera). They are currently used to study fixational eye movements. They are also used to study vertical heterophorias in subject with vertical prisms
3. Infrared photokeratometers – a ring with 8 IR LEDs is imaged on the cornea and the software fits a circle through the first Purkinje images to measure corneal radius of curvature. Calibration is done simply with a ball mearing with known radius of curvature. Used in mice, rats, chickens, snakes and others (see Poster, link)
4. Measurement of crystalline lens tilt and decentration. Using a single IR LED and a highly magnified video image of the eye, the positions of the first, third and fourth Purkine image can be measured for 3 different eye positions, and tilt and decentration are automatically determined by the software. A comparison to another Purkinje-Meter, developed by Juan Tabernero and Pablo Artal, was performed in fall 2011 at the Hanusch Eye Hospital in Vienna (Nino Hirnschall and Prof. O. Findl). The results (still unpublished) were satisfying. A short presentation explains the measurement principle (link: see attached PDF file “lens tilt”)
5. Lens scanner to measure intraocular lenses (including multifocal). This device determines automatically the contrast in a video image at different spatial frequencies while the focus was changed by a USB-controlled stepping motor from -8 to +8 D. It records contrast transfer on the screen, and detects multiple focal points (see pictures: lens scanner 1 and 2)
6. Automated evaluation of optomotor responses in chicks and mice (more details are on our previous webpage -http://www.uak.medizin.uni-tuebingen.de/frank/peo1_schaeffel.html#p5)