Non-mydriatic hyperspectral ocular fundus camera
Described herein is an ocular fundus imaging apparatus ( 11 ) including and an illumination module ( 140 ) and an imaging module ( 141 ). The illumination module ( 140 ) includes light sources ( 103, 104 ) configured to generate light at wavelengths within a desired spectral range. A first optical assembly is provided to shape and direct the light onto an eye ( 102 ) of a subject. A tuneable bandpass filter ( 109 ) selects a wavelength sub-interval within the desired spectral range. The imaging module ( 141 ) includes a second optical assembly to collect light returned from the eye ( 102 ) of the subject and to project the returned light from the eye ( 102 ) onto an image sensor ( 113 ). The second optical assembly includes one or more optical elements capable of compensating for ocular variation. The image sensor ( 113 ) is configured to image the returned light to generate an image of the ocular fundus at the wavelength sub-interval.
1. A non-mydriatic ocular fundus imaging apparatus including:
an illumination module having:
one or more light sources configured to generate light at wavelengths within a desired spectral range;
a first optical assembly to shape and direct the light onto an eye of a subject; and
a tuneable bandpass filter to select a wavelength sub-interval within the desired spectral range;
an imaging module having:
a second optical assembly to collect light returned from the eye of the subject and to project the returned light from the eye onto an image sensor, the second optical assembly including one or more optical elements capable of compensating for ocular variation; and
an image sensor configured to image the returned light to generate a non-mydriatic image of the ocular fundus at the wavelength sub-interval; and
one or more controllers configured to:
tune the tuneable bandpass filter between a plurality of wavelength sub-intervals within the desired spectral range;
control the image sensor to generate a plurality of non-mydriatic images of the ocular fundus at each of the plurality of wavelength sub-intervals; and
dynamically control the power of the one or more light sources to provide a respective predefined power level for each of the plurality of wavelength sub-intervals;
wherein the tuneable bandpass filter and the image sensor are synchronized by the one or more controllers so as to capture images at different wavelength sub-intervals within the desired spectral range; and
wherein the plurality of non-mydriatic images of the ocular fundus is captured within a time of 300 milliseconds.
2. The apparatus of claim 1 wherein the tuneable bandpass filter is tuneable between the infrared wavelength range and the blue wavelength range.
3. The apparatus of claim 2 wherein the tuneable bandpass filter is configured to be tuned from the infrared wavelength range to the blue wavelength range such that the image sensor captures one or more first images in the infrared wavelength range and subsequently captures one or more second images in the visible wavelength range.
4. The apparatus of claim 2 wherein the tuneable bandpass filter is configured to be tuned with predefined steps at a predefined speed.
5. The apparatus of claim 1 wherein the respective predefined power levels for each of the spectral sub-intervals are selected to compensate for spectral non-flatness arising from one or more of the illumination module and/or imaging module.
6. The apparatus of claim 1 wherein the power of the one or more light sources is controlled to achieve a threshold signal-to-noise ratio for the tissue being imaged.
7. The apparatus of claim 1 wherein the power of the one or more light sources is controlled to obtain a target digital count value on the image sensor for a reference surface.
8. The apparatus of claim 7 wherein the reference surface is derived from a retinal reflectivity of a sample population.
9. The apparatus of claim 1 wherein the power of the one or more light sources is controlled to compensate for an optical absorption by the illumination and/or imaging modules.
10. The apparatus of claim 1 wherein the power of the one or more light sources is controlled based on a sensitivity of the imaging sensor.
11. The apparatus of claim 1 wherein the second optical assembly includes a focusing lens sub-system having one or more focusing lenses moveable in position along an optical axis, and wherein the axial movement of the one or more focusing lenses is synchronized with a wavelength filter movement of the tuneable bandpass filter to give an improved focusing at the image sensor for each of a plurality of spectral sub-intervals to compensate for chromatic aberrations.
12. The apparatus of claim 1 wherein the focusing lens movement is nonlinear with respect to the wavelength tuning of the tuneable bandpass filter.
13. The apparatus of claim 1 wherein the focusing lens movement is quadratic with respect to the wavelength tuning of the tuneable bandpass filters.
14. The apparatus of claim 1 wherein the tuneable bandpass filter has a spectral bandwidth that is larger than the steps between the wavelength sub-intervals.
15. The apparatus of claim 1 wherein the tuneable bandpass filter is a linearly variable bandpass filter.
16. The apparatus of claim 1 wherein the illumination module includes an annulus disposed after the tuneable bandpass filter for shaping the light at a pupil plane of the eye of the subject.
17. The apparatus of claim 16 including an optical diffuser disposed between the tuneable bandpass filter and annulus.
18. The apparatus of claim 17 including a homogenizing rod disposed between the tuneable bandpass filter and annulus.
19. The apparatus of claim 18 wherein the optical diffuser is integral with or attached to the homogenizing rod.
20. The apparatus of claim 1 wherein the one or more light sources have a spectral bandwidth covering at least the range from 450 nm to 720 nm and include a first LED having output power in the infrared wavelength range and a second LED having output power in the visible range.