Abstract
Purpose :
There is great interest in non-contact, cellular-scale corneal imaging for diagnostics and disease monitoring. Existing techniques derive image contrast from reflected light and therefore require a high degree of optical sectioning in order to reject much stronger reflections originating at other surfaces, such as the air-cornea interface. Here we present an alternative approach based on obliquely transmitted light, which produces phase-gradient contrast images of the cornea across a 1-mm field of view.
Methods :
Like the slit lamp technique known as retroillumination, our method uses reflected light from the fundus to transilluminate the cornea. However, our method differs in two important aspects: 1) we use a single long working distance objective lens for both illumination and imaging. This design enables the use of much larger numerical aperture (tantamount to higher resolving power). 2) We tailor the illumination pattern on the fundus to emphasize features of interest. For instance, in our prototype system (Fig. 1), we use an asymmetric illumination pattern to reveal phase-gradient contrast. To demonstrate the principle, we imaged the posterior corneal surface of a realistic model eye (Ocular Instruments OEMI-7).
Results :
With asymmetric transillumination, we can visualize the posterior surface of the model eye cornea. Specifically, we saw small scratches at the cornea-aqueous interface (see Fig. 2). When the illumination pattern was altered to be symmetric, no such scratches could be detected in single frames.
Conclusions :
We have introduced a new technique for corneal microscopy based on fundus reflection. Unlike other reflection-based corneal microscopy techniques, our method uses transmitted light. Transmission and reflection imaging geometries are known to produce qualitatively different image contrast. Future work should establish which corneal structures the method is sensitive to and compare sensitivity to reflection techniques.
This is a 2020 ARVO Annual Meeting abstract.