Abstract
Purpose :
There is an increasing trend towards ultra-wide-field fundus imaging and more compact devices. In this experimental study, we designed a confocal scanning laser optical system with a wide field of view using four-color lasers to optimize fundus image quality.
Methods :
The image optimization routine was performed using two methods:
1) Correction of chromatic variation of magnification
To reduce color fringing on the pupil surface and achieve high resolution for each color on the fundus, an optical system with aberration correction was designed, giving higher priority to aberrations that could not be corrected by image processing. Chromatic variation of magnification of the fundus that was not optimized in the optical system was corrected by mathematical processing after image acquisition.
2) Color tone correction
In the three-color (R, G, B) SLO imaging, the optimum color tone can vary based on the because the patient disease and individual fundus characteristics. For example, the reflectance at the fundus differs depending on patient ethnicity, and transmittance can decreased in the eye due to mild cataract. To address the need for imaging based on these variable conditions and to adjust the color tone pattern, the shape of the histogram for each color is adjusted.
Results :
The chromatic variation of magnification of the fundus conjugate to the designed optical system was calculated. Subsequently, using the IR wavelength for observation as the reference wavelength out of R, G, B, and IR, the relative chromatic variation of magnification of the other three wavelengths was calculated. As a result, color fringing was eliminated, and the expected optical resolution was achieved.
Color tone correction was achieved by initially determining several target histogram patterns for each wavelength. Next, the average value and the standard deviation of the histograms were adjusted with the captured image. Then, human eyes were measured and high resolution fundus images were achieved.
Conclusions :
This new fundus imaging device with an image optimization algorithm, significantly improves color balance in the objective lens optical system and with an ultra-wide-field adapter attached. This optical design also corrects for distortion and aberration of the fundus. High quality fundus images were obtained with this prototype optical design.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.