Non-Mydriatic Fundus Camera With Tunable Hyperspectral Filtering
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Solution Overview
Problem
Conventional fundus cameras struggle to capture high-quality, non-mydriatic hyperspectral images of the eye due to challenges in compensating for chromatic aberrations and internal reflections, while maintaining high spatial and spectral resolution, especially with rapid eye movements and limited illumination power.
Innovation Solution
An apparatus using a linearly variable bandpass filter synchronized with illumination and image acquisition, combined with gaze alignment and dynamic power compensation, to achieve high SNR hyperspectral imaging within 300 milliseconds, employing low-cost components like LEDs and variable bandpass filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional fundus cameras use broad spectrum white light illumination, then the imaging process is simple and fast, but chromatic aberrations and internal reflections degrade image quality
Solution Approach 1:
The broad spectrum white light is segmented into multiple narrow wavelength bands using a tunable bandpass filter. The imaging system acquires separate images at different wavelengths and combines them to form a hyperspectral image, thereby eliminating chromatic aberrations and internal reflections while maintaining imaging speed through efficient spectral sampling.
Solution Approach 2:
The tunable bandpass filter is tuned periodically across different wavelength bands, acquiring images at each wavelength step. This periodic spectral sampling allows the system to capture high-quality hyperspectral data within the pupillary light reflex time frame by optimizing the tuning speed and spectral resolution.
2Measurement precision
If hyperspectral imaging is performed with narrow wavelength bands, then spectral resolution is improved, but the imaging time increases beyond the pupillary light reflex duration
Solution Approach 1:
Instead of uniformly sampling the entire visible spectrum, the system uses a priori knowledge of retinal reflectance characteristics to identify and prioritize sampling at wavelengths where diagnostic information is most abundant. This partial spectral sampling achieves high spectral resolution for critical wavelengths while reducing total imaging time within the 300-500ms pupillary light reflex window.
Solution Approach 2:
The system dynamically adjusts the bandpass filter tuning speed and spectral sampling density based on the specific imaging conditions and diagnostic requirements. By optimizing these parameters, the system achieves sufficient spectral resolution for detecting retinal pathologies while completing the hyperspectral acquisition within the available time frame.
3Measurement precision
If illumination power is increased to improve image quality, then signal-to-noise ratio is improved, but pupil constriction occurs due to pupillary light reflex
Solution Approach 1:
The illumination is delivered in a periodic pulsed sequence synchronized with the bandpass filter tuning. Each pulse provides sufficient illumination for one spectral band acquisition, and the total illumination energy is distributed across multiple pulses within the pupillary light reflex time frame, preventing pupil constriction while maintaining adequate signal-to-noise ratio.
Solution Approach 2:
The system pre-calibrates the illumination power and exposure time for each wavelength band based on expected retinal reflectance characteristics. This preliminary optimization ensures that the total light energy delivered remains below the threshold that triggers pupillary light reflex, while each individual spectral measurement achieves sufficient signal-to-noise ratio.
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 apparatus captures high-quality, non-mydriatic hyperspectral images with improved spectral and spatial resolution, compensating for chromatic aberrations and internal reflections, enabling efficient imaging within the required time frame.
Implementation Method 1
a tuneable bandpass filter to select a wavelength sub-interval within a desired spectral range
Implementation Method 2
an image sensor configured to image the returned light to generate an image of the ocular fundus
Implementation Method 3
an illumination optical assembly to project light from a spectrally tuneable light source onto the fundus... and an imaging optical assembly to project the light returned from the fundus onto the camera sensor
Data Source
AI summary
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.