Purchase this article with an account.
Benjamin D. Masella, Jennifer J. Hunter, David R. Williams; Spatially-resolved Adaptive Optics Photopigment Densitometry for Assessing Photoreceptor Function. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5677.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
The addition of adaptive optics to retinal imaging has enabled sub-cellular structural resolution in the living eye. However, high resolution structural imaging provides limited functional information. This study used photopigment densitometry in an adaptive optics scanning laser ophthalmoscope (AOSLO) to measure the kinetics of pigment regeneration with high spatial precision in non-human primates. With this technique, we can non-invasively quantify the health of the photoreceptor-retinal pigment epithelium (RPE) complex.
Macaque monkeys were anesthetized and dark adapted for one hour. The photoreceptors were then imaged using an AOSLO equipped to record two simultaneous reflectance videos (794 nm and 514 nm). Measurements made with the 514 nm channel were limited to dim flashes lasting 0.125 seconds to minimize the effect on pigment density. Images were recorded with a 2 degree square field of view, centered roughly 15 degrees from the fovea. After capturing an image to measure the dark adapted state, a half degree square area at the center of the imaging field was fully bleached. The 514 nm reflectance within this sub-area was measured immediately after the bleach and every five minutes thereafter for 35 minutes. Changes in 514 nm reflectance not related to pigment density were removed by normalizing to the surrounding unbleached region. To demonstrate the utility of this method, we measured photopigment kinetics before and after potentially-damaging, focal light exposures.
In locations with small photochemical lesions, we observed a loss of photopigment regeneration. We also measured and compared pre-lesion rhodopsin kinetics between subjects and found consistent differences in regeneration rate, which may be indicative of the relative health of the photoreceptor-RPE complex. We confirmed previous reports of systematic changes in infrared reflectance following visible stimulation, which precluded the use of the commonplace method of infrared normalization.
Infrared reflectance from photoreceptors varies after photopigment bleach. This may be indicative of a functionally relevant process such as migration of transducin between photoreceptor compartments. Adaptive optics photopigment densitometry can be used to assess the functional health of the photoreceptors and RPE with high spatial precision. Although we have demonstrated this method in monkeys, it has the potential to add a valuable spatially-resolved functional measure to the study of human retinal degenerations.
This PDF is available to Subscribers Only