Functional imaging of photoreceptors in the retina by rhodopsin mapping
The subject invention provides novel apparatuses and methods for assessing the structure and function of photoreceptors in retina. In a specific embodiment, the assessment is accomplished by imaging rhodopsin, pigmented protein responsible for initiating vision acquisition of the eye, in living subjects. Advantageously, the technologies provided herein can be used for clinical evaluation of retinal photoreceptors for diagnosis, disease staging and follow-up, and outcome measurement for clinical trials of retinal degenerative disorders, including, for example, hereditary retinal degeneration and age-related macular degeneration.
1. An apparatus for evaluating the function of the retina of a subject based on an optical coherence tomography (OCT) technology, comprising a first source providing light in a near-infrared (NIR) wavelength, and a second broadband source providing light having wavelengths in a visible (VIS) spectrum; and the visible wavelengths being within the optical absorption spectrum of rhodopsin in the retina, the NIR light source is used for guiding the image alignment process before imaging with the VIS light source for rhodopsin absorption, and the apparatus further comprising an optical filter for separating the VIS light into a plurality of wavelength bands with center wavelengths in accordance with the wavelengths of distinct optical absorption coefficients characteristic to rhodopsin.
2. The apparatus according to claim 1 , further comprising a scanning laser ophthalmoscope (SLO) integrated with the OCT apparatus.
3. The apparatus according to claim 2 , wherein the SLO comprises a plurality of parallel optical fibers by which the laser source is split, the optical fibers illuminating pulsed laser spots onto the retina.
4. The apparatus according to claim 3 , wherein the imaging speed of the SLO increases by a multiplication factor equivalent to the number of parallel optical fibers provided.
5. The apparatus according to claim 3 , wherein the time delay between adjacent laser pulses is controlled by a difference in lengths between the optical fibers from which the pulses are delivered.
6. The apparatus according to claim 5 , wherein the time delay between adjacent laser pulses is less than about 1 μs.
7. The apparatus according to claim 6 , wherein the time delay between adjacent laser pulses allows the detection of the reflection of these pulses from the retina with a single detector.
8. The apparatus according to claim 1 , the optical filter for separating the VIS light source into a plurality of wavelength bands comprising three distinct band-pass filters, or a single, three-band filter.
9. The apparatus according to claim 8 , having three separate bands within the absorption spectrum of rhodopsin, and which is able to acquire three VIS-OCT images of the retina simultaneously.
10. The apparatus according to claim 1 , the plurality of wavelength bands with center wavelengths being 520 nm, 550 nm, and 580 nm.
11. A method of examining the function of the retina of a human, comprising:
collecting three-dimensional images of the retina in a dark and a bright environment, respectively, using a visible-light optical coherence tomography (VIS-OCT) apparatus equipped with a visible (VIS) light source and a near-infrared (NIR) light source, the wavelength of the VIS light source being within the optical absorption spectrum of rhodospsin, and the NIR light source being used only for guiding the image alignment process before imaging with the VIS light source for rhodopsin absorption, and the VIS light source being separated by an optical filter into a plurality of wavelength bands with center wavelengths in accordance with the wavelengths of distinct optical absorption coefficients characteristic to rhodopsin;
quantifying the optical absorption of the retina in the dark and the bright environment, respectively, based on the intensity of the VIS-OCT images collected under each condition;
using an appropriate model of fundus reflection to correlate the difference in intensity of the images between the dark and the bright environments with the optical density of rhodopsin present in the retina; and
providing an assessment of the function of the retina based on the optical density of rhodopsin.
12. The method according to claim 11 , wherein the method of using the VIS-OCT apparatus to collect three-dimensional retinal images comprises:
allowing the subject to adapt to a dark environment;
capturing a first series of cross-sectional images with the VIS light source in the dark environment;
allowing the subject to adapt to a bright environment;
capturing another series of cross-sectional images with the VIS light source in the bright environment; and
reconstructing a three-dimensional differential image of the retina for the dark and the bright environment, respectively.
13. The method according to claim 12 , wherein the three-dimensional retinal image comprises the spatial distribution of the rhodopsin whose optical absorption is quantified by the intensity of the images.
14. The method, according to claim 11 , further comprising the use of a scanning laser ophthalmoscope (SLO) integrated with the VIS-OCT apparatus, and wherein, by utilizing a combination of the VIS-OCT and the SLO images, a quantification of the rhodopsin concentration is achieved such that the VIS-OCT image provides absorption information along a depth.
15. The method, according to claim 14 , wherein quantitative rhodopsin distribution is calculated from three VIS-OCT images of dark-adapted retina simultaneously acquired, the three VIS-OCT images being in different wavelength bands determined by the optical filter used for separating the VIS light source.