Optical coherence tomography of the human retina with dynamic focus

Despite the great advantages of spectral domain (SD) OCT in terms of sensitivity and imaging speed, the technology has still a drawback: the instantaneous recording of an entire A-scan prevents dynamic focusing and therefore high transversal resolution throughout a larger imaging depth. Time domain (TD) OCT, on the other hand, records its data only from a single depth at one instant, thus allowing to match the depth position of focal point and coherence gate by synchronous movement over the entire image depth. Transversal TD scanning patterns are especially suited for dynamic focus tracking because the rather slow progression of the coherence gate alleviates the mechanical demands on precise synchronous focus movement. We have implemented a dynamic focus tracking into our previously reported transversal TD retinal OCT system. A lens in the scanning optics is moved synchronously with the coherence gate with a predetermined velocity profile. B-scan and C-scan images of the retina are recorded in 0.5 to 1 sec. We demonstrate the method by imaging a USAF test resolution target in a model eye and a retina of a healthy volunteer in vivo. High transverse resolution and signal intensity are demonstrated throughout an imaging depth of 1 - 2 mm.