A novel optical scanning method for an anterior segment optical coherence tomography (AS-OCT) system has been
described. This method has been designed for imaging the entire anterior segment of the eye (from cornea to posterior
surface of the crystalline lens) at a time. The ability to image the entire anterior segment is crucial in understanding the
mechanism of human accommodation and the efficacy of accommodative intraocular lenses.
In a conventional scanning system the beam is shined straight into the eye parallel to the optical axis. For anterior
segment imaging, large lateral scan area leads to an increase in the angle of incidence on each of the four ocular surfaces.
This causes significant reduction in signal reflected from regions further from the optical axis. This reduction combined
with loss in signal due to coherence makes it difficult to image the entire anterior segment of the eye, where optical
depth penetration of 10mm is required.
To overcome this limitation, we have designed a new OCT scanning system, which achieves close to normal incidences
across all the lateral locations on the ocular surfaces within a 6 mm clear aperture. This provides an increase in the
amount of light scattered back to the system resulting in higher signal-to-noise ratio (SNR). The scanning system
consists of two different custom designed lenses, one of them optimized for cornea and the anterior surface of the
crystalline lens, while the other for the posterior surface of the crystalline lens. Two semicircular halves of each lens
were glued together to form a single optical system.
To evaluate the performance of our design we constructed and imaged a model eye and compared it with images
obtained by conventional telecentric scanning method. SNR improvement by a factor of 3.71 was observed for the front
surface of the lens and 18.83 for the back surface of the lens.