Abstract
Purpose :
To evaluate optical quality of images obtained with the High Magnification Module for the Spectralis SLO (Heidelberg Engineeering) and to compare these images to images obtained with a custom-made adaptive optics scanning laser ophthalmoscope (AOSLO). The premise of our study was to determine if imaging with the high magnification module lens allows acquisition of images that show the photoreceptor cone mosaic.
Methods :
The Heidelberg Engineering High Magnification Module for the Spectralis SLO is a special lens that images an area of 8° x 8° degrees. The normal imaging modes of high-speed and high-resolution are supported. Due to light safety considerations the lens works only with the infrared imaging mode and ICG angiography mode. Blue and green imaging are not supported. We imaged 10 subjects with and without glasses and and captured images at different pupil diameter. Different pupil diameters were achieved by illuminating the fellow eye with a flash light. By varying the brightness of the flash light and room lights were were able to vary the pupil diameter. Pupil diameter was estimated based on the iris dimensions.
Results :
We found under optimal conditions we were able to see a photoreceptor cone mosaic with the High Magnification Module in normal subjects. We found that in subjects with uncorrected astigmatic error the images of the photoreceptors were elongated and cylindrical in nature. When imaging through the subjects best corrected eye glasses the photoreceptors had a circular appearance. We found that the best image quality was obtained at a pupil diameter of 3 mm. At larger pupil diameter the image quality was worse. The photoreceptor density using the High Magnification Module was within 10% of the density as measured in the same region using the AOSLO.
Conclusions :
The performance of the High Magnification Module was encouraging. The High Magnification Module has some limitations. Since the module is a fixed optical element, the module can only correct for defocus. Astigmatism can be corrected with properly refraction. We found that using the subject's own prescription improved image quality if the subject had astigmatic error. The human eye can be considered diffraction-limited up to a pupil diameter of 3 mm. This was confirmed by our experiments. Increase the pupil diameter beyond 3 mm decreased image quality.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.