Purchase this article with an account.
Pengfei Zhang, Mayank Goswami, Robert J Zawadzki, Edward N Pugh; The Photosensitivity of Rhodopsin and the Spectral Reflectivity of the Mouse Fundus Measured in Vivo with Scanning Laser Ophthalmoscopy. Invest. Ophthalmol. Vis. Sci. 2016;57(12):3627.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
To measure in the mouse eye the reflectivity increase associated with rhodopsin bleaching, and to determine the absolute photosensitivity of rhodopsin bleaching in vivo.
The retina of albino (Balb/c) and pigmented (C57Bl/6J) mice were imaged with a custom SLO. A supercontinuum laser delivered either filtered monochromatic or broadband light. Back-reflected dual-band (501 nm; 690 nm) monochromatic light was measured in some experiments; in others, fundus spectral reflectivity for the broadband source was measured with a spectrum analyzer.
A Balb/c mouse experiment employing dual-band SLO is shown in Fig.1. A, B show images of 501 nm reflected light prior to and after 100 serial scans (1 μW) of the subregions identified by red squares, while C shows the result of subtracting image A from B. D, E plots the average intensity of 501 nm light reflected during each scan fitted with the formula I = I0 + ΔImax [1− (1−B0)N-1], with B0 the fractional increment per scan and N the scan #. F plots the normalized data of E as a function of cumulative energy density Q (photons μm-2) fitted by ΔI/ΔImax = 1− exp(-Q/Qe), where 1/Qe is the photosensitivity at 501 nm. The average value of log10 Qe was 7.83 ± 0.12 (mean ± s.d., n = 71 expts), for 7 Balb/c mice and 7.86 ± 0.21 (n = 21) for 5 C57Bl/6J mice. Broadband scanning yielded very similar values of Qe with energy density expressed in rhodopsin-equivalent units. Both the action spectrum of the incremental reflectance change obtained with narrowband light, and the reflectance difference spectra obtained with broadband light were consistent with the reflectance increase arising from rhodopsin bleaching.
The bleaching of rhodopsin in vivo in mice can be measured precisely with SLO. The photosensitivity 1/Qe is 2-fold higher than predicted by assuming that light reaching the mouse rod outer segment has the same energy density as that reaching the retinal surface. Based on published EM and rod counts, the total cross-sectional area of rod outer segments is ~ 50% of the total retinal surface area, whereas rod inner segments are densely packed. We conclude that light captured and guided by mouse rod inner segments increases the energy density impinging on rod outer segments, increasing the apparent photosensivity of rhodopsin bleaching ~ 2-fold.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
Fig.1 Experiment illustrating serial bleaching.
This PDF is available to Subscribers Only