Portable retinal imaging system
Preterm babies have a high risk of retinopathy. Doctors conduct fundus fluorescein angiography to determine the state of the blood vessels in their retinas. Disclosed is a system ( 100 ) for conducting fundus fluorescein angiography configured for light weight, small size, and providing a sharp, high contrast angiograph. The disclosed system uses a moulded annular light source, blue and white LEDs ( 120 ) for providing the illumination, an planar annular emission filter ( 125 ) for filtering the blue light, and imaging optics ( 130 ) configured for reducing aberration. The imaging optics ( 130 ) comprises a mechanical iris ( 136 ) to control the amount of light reaching an image sensor ( 150 ), a tuneable liquid lens ( 141 ) for focusing the image, a green barrier filter ( 146 ) that may be removed from the path of the light—for conducting fundus photography. The white LEDs and the mechanical iris ( 136 ) may be used for conducting fundus photography.
1. An imaging system ( 100 ) configured for carrying out dual functions of fundus fluorescein angiography on a preterm baby subject and fundus imaging on a subject's eye ( 105 ), the system ( 100 ) characterized by: an injection molded light guide ( 115 ) based annular light source; a source of light for the light guide, the source of light comprising a plurality of LEDs ( 120 ), the plurality of LEDs ( 120 ) being arranged in a circle—wherein, alternate LEDs are blue light emitting LEDs and white light emitting LEDs; a planar annular emission filter ( 125 ) positioned between the light guide ( 115 ) and the plurality of LEDs ( 120 ) for filtering the light emitted by the blue light emitting LEDs to reach the light guide ( 115 ) and for allowing light emitted by the white light emitting LEDs to reach the light guide ( 115 ) unfiltered; a green barrier filter ( 146 ), for filtering light reflected by the fundus of the subject's eye, before the light reaching an image sensor ( 150 ), and wherein the position of the green barrier filter ( 146 ) is motor controlled for inserting and removing the green barrier filter ( 146 ) from the optical axis of the imaging optics ( 130 ); an aperture unit ( 136 ) for controlling an amount of light reaching the image sensor ( 150 ); a liquid lens ( 141 ), a focal length of which may be varied by applying one or more voltages to electrodes of the liquid lens ( 141 ), for focusing an image on the image sensor ( 150 ); an imaging optics ( 130 ) comprising a plurality of lenses ( 581 to 586 ) configured for focusing an image of the fundus of the subject's eye ( 105 ), wherein the lenses ( 581 to 586 ) are lenses that bend light rays equally at either surface of each lens for producing a low distortion image on the image sensor ( 150 ); and a control unit ( 175 ) configured at least for receiving user inputs for selecting one of white light emitting LEDs and blue light emitting LEDs from the plurality of LEDs ( 120 ), focusing the image on the image sensor ( 150 ) through controlling the liquid lens ( 141 ), and inserting or removing the green barrier filter from the optical axis of the imaging optics ( 130 ).
2. The system ( 100 ) as claimed in claim 1 , wherein the planar annular emission filter ( 125 ) for filtering blue light has a low pass characteristic.
3. The system ( 100 ) as claimed in claim 1 , wherein the planar annular emission filter ( 125 ) for filtering blue light has a low pass characteristic suppressing light of wavelengths above 500 nm.
4. The system ( 100 ) as claimed in claim 1 , wherein the green barrier filter ( 146 ) has high pass characteristics.
5. The system ( 100 ) as claimed in claim 1 , wherein the green barrier filter ( 146 ) has high pass characteristics suppressing all wavelengths below 515 nm.
6. The system ( 100 ) as claimed in claim 1 , comprises a control unit ( 175 ) for receiving user inputs and executing one more functions selected from a list of functions comprising, but not limited to, energising blue light emitting LEDs only or white light emitting LEDs only from plurality of LEDs ( 120 ), raising or lowering the aperture of the mechanical iris ( 136 , 536 ), raising or lowering the focal length of a liquid lens ( 141 , 541 ), inserting or removing a green barrier filter ( 146 , 546 ) from the optical axis of the imaging optics ( 130 , 530 ).