Abstract
The retinal pigment epithelial (RPE) cells contain intrinsic fluorophores that can be visualized using infrared autofluorescence (IRAF). Although IRAF is routinely utilized in the clinic for visualizing retinal health and disease, currently, it is not possible to discern cellular details using IRAF due to limits in resolution. We demonstrate that the combination of adaptive optics (AO) with IRAF (AO-IRAF) enables higher-resolution imaging of the IRAF signal, revealing the RPE mosaic in the living human eye. Quantitative analysis of visualized RPE cells in 10 healthy subjects across various eccentricities demonstrates the possibility for in vivo density measurements of RPE cells, which range from 6505 to 5388 cells/mm2 for the areas measured (peaking at the fovea). We also identified cone photoreceptors in relation to underlying RPE cells, and found that RPE cells support on average up to 18.74 cone photoreceptors in the fovea down to an average of 1.03 cone photoreceptors per RPE cell at an eccentricity of 6 mm. Clinical application of AO-IRAF to a patient with retinitis pigmentosa illustrates the potential for AO-IRAF imaging to become a valuable complementary approach to the current landscape of high resolution imaging modalities.
Highlights
Infrared autofluorescence (IRAF) is an increasingly-utilized clinical modality for visualization and monitoring of the health of the retinal pigment epithelial (RPE) cells in a variety of different diseases that include age-related macular degeneration [1,2,3], central serous chorioretinopathy [4], retinitis pigmentosa [5], ABCA4-associated retinopathies [6], Best vitelliform macular dystrophy [7], and others
Since the Adaptive optics (AO)-IRAF signal is at least several-fold weaker than the AO-indocyanine green (ICG) signal [15], detection of fluorescent light in the 810830 nm band was further enhanced by redesigning our computer-controlled fixation system [20] to utilize a large dichroic, which transmits a higher percentage of light in the 810-830 nm band than the 90/10 pellicle beamsplitter that we previously utilized for our AO fixation system
The local similarity between AO-IRAF and IRAF in this paper is consistent with data shown in our previous report [16] and confirms that we are measuring the same signal with these two techniques
Summary
Infrared autofluorescence (IRAF) is an increasingly-utilized clinical modality for visualization and monitoring of the health of the retinal pigment epithelial (RPE) cells in a variety of different diseases that include age-related macular degeneration [1,2,3], central serous chorioretinopathy [4], retinitis pigmentosa [5], ABCA4-associated retinopathies [6], Best vitelliform macular dystrophy [7], and others. Its clinical value is derived from the fact that it provides a complementary picture of retinal lesions, which from a macroscopic perspective appears to be similar to those visualized using other modalities (most typically compared to short-wavelength autofluorescence) but at a finer scale is often slightly or entirely distinct from other modalities [1,3,5,6,7]. Unraveling these microscopic nuances could reveal new insights about the mechanisms of disease. We and others have independently reported that the integration of AO with IRAF can be used to resolve individual RPE cells [16,17]
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