Fundus Camera Autofluorescence Imaging with Interference Filters
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Solution Overview
Problem
Current autofluorescence imaging techniques in ophthalmology face challenges such as low contrast images due to overlapping fluorescence from the crystalline lens, limited field of view, and inability to accurately image the central macula, especially in patients with nuclear sclerosis or those who have undergone fluorescein angiography.
Innovation Solution
A fundus camera system utilizing high-quality thin film optical interference filters with an excitation filter range of 535-585 nm and a barrier filter range of 605-715 nm, designed to reject lens autofluorescence and provide a wider field of view, allowing for improved signal-to-noise ratio and accurate imaging of lipofuscin in the retina.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional autofluorescence imaging is used with standard excitation and barrier filters, then fluorescein angiography can be performed, but the crystalline lens autofluorescence overlaps with the fundus fluorescence causing washed out images with low contrast
Solution Approach 1:
The patent changes the wavelength parameters of the optical filters to resolve the spectral overlap between lens and fundus fluorescence. The excitation filter is set to 535-585 nm and the barrier filter to 605-715 nm, which shifts the detection window to a region where lens autofluorescence is minimal while fundus lipofuscin fluorescence remains strong, thereby improving image contrast
Solution Approach 2:
The patent extracts and eliminates the harmful lens autofluorescence signal by using a barrier filter with a sharp cut-on at 605 nm. This filter configuration blocks the shorter wavelength lens fluorescence while transmitting the longer wavelength fundus fluorescence, effectively separating the desired signal from the interference
2Measurement precision
If scanning laser ophthalmoscope is used to reject lens autofluorescence, then autofluorescence images can be obtained, but the field of view is limited and images require noise reduction through averaging multiple images
Solution Approach 1:
The patent replaces the complex scanning laser ophthalmoscope system with a simpler wide-field fundus camera system. By using advanced thin-film interference filters with high optical density blocking characteristics, the system achieves effective lens autofluorescence rejection without requiring mechanical scanning or complex confocal optics, thereby simplifying the device while maintaining signal quality
Solution Approach 2:
The patent changes the optical filter parameters to achieve both wide field of view and high signal-to-noise ratio simultaneously. The excitation filter (535-585 nm) and barrier filter (605-715 nm) are designed with specific bandwidths and optical densities that enable wide-angle imaging while maintaining effective rejection of lens autofluorescence, eliminating the need for multiple image averaging
3Measurement precision
If fluorescein dye is used for angiography, then vascular anatomy can be visualized, but the lens autofluorescence adds to the fluorescence from the fundus producing images with low contrast
Solution Approach 1:
The patent changes the wavelength parameters of both the excitation and barrier filters to a configuration that eliminates lens autofluorescence interference in fluorescein angiography. The excitation filter centered at 535-585 nm and barrier filter at 605-715 nm create a spectral window that blocks lens fluorescence while transmitting both fluorescein and lipofuscin signals, thereby improving vascular image contrast
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 system achieves high-quality autofluorescence images with increased brightness and contrast, enabling wider-angle imaging of the ocular fundus, accurate assessment of macular pigment, and improved diagnostic capabilities for retinal diseases without the need for post-processing, using a non-cooled CCD camera and reduced patient discomfort.
Implementation Method 1
high quality thin film optical interference filters
Implementation Method 2
high quality thin film optical interference filters
Implementation Method 3
high quality thin film optical interference filters
Implementation Method 4
high quality thin film optical interference filters
Implementation Method 5
Lipofuscin can be made to fluoresce and has a broad emission band (105 in Figure 1) ranging from about 500 to beyond 750 nm
Data Source
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AI summary
Methods and apparatus for taking autofluorescence images with a fundus camera capable of a field of view of at least 30 degrees and preferably 50 degrees or more using high quality thin film optical interference filters In one embodiment, a fil set (404, 410) is disclosed for achieving this functionality Using these methods and/or apparatus, a practitioner can take high-quality autofluorescence images of the fundus using a CCD camera (421) that does not have to be cooled, take such images without exciting damaging photochemical reactions in the retina, detect accumulation of fluorophores in the retina prior to the significant accumulation of fluorophores in the retinal pigment epithelium, and topographically localize and quantitate retinal abnormalities and retinal pigment epithelium abnormalities.