Modifying a Rodenstock scanning laser ophthalmoscope for imaging densitometry

Abstract

The necessary modifications and technical requirements are described for using a commercially available scanning laser ophthalmoscope (Rodenstock Model 101 SLO) as an imaging densitometer to assess human photopigment distribution. The main requirements are a linear detector amplifier, fast shutters for the laser beams, and a trigger unit. Images must be compensated for varying laser intensity. Both rod and cone photopigments are measured with the 514-nm argon laser of the SLO. Discrimination is possible owing to the different spatial distribution. The cone pigment density peaks in the foveal center (D = 0.40) with a steep decrease with increasing eccentricity E (full width at half-maximum, 2.5 degrees ). Rod photopigment increases with increasing eccentricity (D = 0.23 for E = 11 degrees ). These values are in agreement with previous reported results obtained with scanning laser ophthalmoscopes specially designed for retinal densitometry and high stability.

Novel snapshot imaging of photoreceptor bleaching in macaque and human retinas

“…36 However, for mapping the distribution of the photopigments, the recording protocol is still too complicated, and the number of modifi cations that have to be made to the commercial instrument make it diffi cult to use in the clinic. 37 Recently, changes in the intensity of fundus autofl uorescence during bleaching have been used to assess photopigment distribution. However, the measured refl ectivity is strongly affected by absorption of macular pigments, limiting its use.…”

Variation in Sensitivity, Absorption and Density of the Central Rod Distribution with Eccentricity

“…However, it has been shown that it is possible to measure the pure cone photopigment distribution with scanning laser densitometry using 595-nm laser light [Elsner et al, 1993] or 633-nm laser light [van Norren et al, 1989]. 595-nm light has the advantage of higher absorption for cone photopigments compared to 633-nm light.…”

Investigating the light absorption in a single pass through the photoreceptor layer by means of the lipofuscin fluorescence

“…Both of these parameters are influenced by the wave-guiding properties of the cone photoreceptors, which increase the effective optical density for a fixed amount of photopigment and modify the effective cone apertures due to angular tuning. Retinal reflectometry and densitometry have successfully provided means for probing the combined influence of these parameters and for examining the physical properties of the photoreceptors, by providing in vivo estimates of the total photopigment in the eye (Elsner, Burns, Hughes, & Webb, 1992, 1993Kilbride, Read, Fishman, & Fishman, 1983;Marcos, Tornow, Elsner, & Navarro, 1997;Rushton, 1958;Tornow, Beuel, & Zrenner, 1997;van Norren & van de Kraats, 1989), and of cone directionality (Burns, Wu, Delori, & Elsner, 1995;DeLint, Berendschot, & van Norren, 1997;Gorrand & Delori,1995;He, Marcos, & Burns, 1999;van Blokland, 1986;Vohnsen, Iglesias, & Artal, 2004).…”