Portable Widefield Fundus Camera With Sequential HDR Imaging
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Solution Overview
Problem
Conventional fundus cameras have limited field of view (FOV) and image contrast, making it difficult to detect subtle abnormalities in eye diseases like diabetic retinopathy and age-related macular degeneration, especially in low-resource settings where bulky and expensive scanning laser ophthalmoscopes are not feasible.
Innovation Solution
A portable fundus camera with high dynamic range (HDR) imaging capability using miniaturized indirect ophthalmoscopy illumination and orthogonal polarization control, combined with sequential illumination power levels and HDR image fusion, to enhance image contrast and FOV without pharmacologic pupillary dilation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If conventional transpupillary illumination is used, then the device can provide widefield imaging, but the field of view is limited and image contrast is poor
Solution Approach 1:
The illumination is divided into multiple discrete points arranged in a pattern, rather than using a single large illumination source. This segmentation allows the system to achieve widefield imaging by capturing multiple illuminated regions, effectively expanding the field of view while maintaining a compact device structure.
Solution Approach 2:
The patent transitions from traditional two-dimensional transpupillary illumination to a three-dimensional configuration by positioning illumination sources at different locations and angles. This dimensional change enables the illumination to wrap around the eye, providing comprehensive widefield coverage without requiring a bulky device.
2Weight of moving object
If miniaturized indirect ophthalmoscopy illumination is used, then the device becomes portable, but illumination reflectance artifacts appear
Solution Approach 1:
The patent employs asymmetric illumination geometry where the illumination sources are positioned at specific off-axis angles relative to the optical axis. This asymmetric arrangement creates illumination paths that avoid direct reflection back to the sensor, eliminating reflectance artifacts while maintaining the portable indirect ophthalmoscopy configuration.
Solution Approach 2:
The patent introduces an intermediary optical element (such as a beam splitter or dichroic mirror) between the illumination path and the sensor path. This intermediary component redirects the illumination light away from the sensor while maintaining the compact portable design, effectively eliminating reflectance artifacts.
3Measurement precision
If sequential illumination at increasing power levels is used, then high dynamic range imaging is achieved, but the acquisition time must be within pupillary reflex time
Solution Approach 1:
The patent uses periodic pulsed illumination at sequentially increasing power levels, with each pulse lasting only a fraction of the pupillary reflex time. By using short-duration pulses rather than continuous illumination, the system can capture multiple exposure levels (LDR images) rapidly, achieving high dynamic range imaging while completing acquisition before the pupillary reflex occurs.
Solution Approach 2:
The patent maintains continuous illumination guidance using near-infrared light throughout the acquisition process, while superimposing the visible light pulsed illumination sequences. This continuous NIR illumination keeps the eye focused and the pupil stable, ensuring that the rapid sequential visible light pulses are captured within the pupillary reflex window without interruption to the imaging process.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The portable HDR fundus camera achieves a 101° eye-angle snapshot FOV and up to 190° eye-angle FOV with improved image contrast, effectively detecting pathological markers like microaneurysms and pigment clumping, comparable to ultra-widefield SLO imagers, suitable for telemedicine in resource-limited areas.
Implementation Method 1
an imaging sensor configured to capture a corresponding low dynamic range (LDR) image of output light reflected or backscattered by the retina
Implementation Method 2
a quarter waveplate positioned on a side of the ophthalmic lens opposite the camera lens, the quarter waveplate converting the linearly polarized input light to circularly polarized input light
Implementation Method 3
a linear polarizer disposed between the ophthalmic lens and the camera lens, the linear polarizer configured to receive depolarized output light reflected or backscattered by the retina and linearly polarized output light converted by the quarter waveplate from helically flipped output light reflected by the retina, and allow polarized output light with a polarization axis in a second direction that is aligned with the linear polarizer to reach the imaging sensor
Data Source
AI summary
Various examples are provided related to high dynamic range (HDR) imaging of a retina. In one example, a fundus camera includes an imaging sensor; an ophthalmic lens; and a source of input light. The source can illuminate the retina at sequentially increasing illumination power levels during a series of illumination periods within a pupillary reflex time of the eye. The imaging sensor can capture a corresponding low dynamic range (LDR) image of during each of the series of illumination periods, which can be combined to generate a HDR image of the retina. An external fixation target can be used to capture LDR images at different visual angles to generate HDR images, which can be combined to generate widefield HDR images.