A ring applied to the surface of the tissue stabilizes the tissue to {HEAD ~ the optics} and localizes a portion of the tissue surface through an aperture in {TAIL ~ the ring} 
A ring applied to the surface of the tissue stabilizes the tissue to { HEAD ~ the optics } and localizes a portion of the tissue surface through an aperture in { TAIL ~ the ring }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL