Journal of Rehabilitation Research and Development
Vol. 38 No. 1, January/February 2001
Pages 123 – 128

SLO radiant power and brightness

Rolf W. Nygaard, PhD and Ronald A. Schuchard, PhD

Department of Ophthalmology, University of Missouri-KC, Kansas City, MO 64108; VA Rehab R&D Center and Emory University School of Medicine, Decatur, GA 30322



Available output in the Scanning Laser Ophthalmoscope (SLO) may be expressed as radiant power at the beam pivot (SLO exit pupil), in units of microwatts (mW). This power corresponds to dimensions of brightness (like luminance and retinal illuminance) and to a range of related measures (like cd/m2, lm/m2, and the troland value) in both free and Maxwellian views. We demonstrate that the conversion factor power/troland=1.26*10-3 mW and 3.15*10-4 mW for SLO nominal visual angles 40° and 20°, respectively. The factor permits measured SLO power to be expressed in units of brightness and (inversely) brightnesses of everyday objects to be expressed in units of SLO power. Examples of both conversions are given. Reference to the literature demonstrates the importance of expressing SLO power in brightness terms common to everyday activities and to visual function-testing instruments besides the SLO.

Key words: calibration, laser, ophthalmoscopy, SLO.

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