Ultrahigh Resolution Polarization Sensitive Optical Coherence Tomography of the Human Cornea with Conical Scanning Pattern and Variable Dispersion Compensation  
[PERSON]  
1 Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, 1090 Vienna, Austria; [EMAIL_ADDRESS] (F.B. ); [PERSON](B.B. ); [PERSON].) 2 Institute of Applied Physics, Vienna University of Technology, 1040 Vienna, Austria 2  
[PERSON]  
3 Narayana Nehrtalaya Foundation, Bengaluru 560099, India; [EMAIL_ADDRESS] (R.P.P); [EMAIL_ADDRESS] (A.S.-R.)  
[PERSON]  
3 Narayana Nehrtalaya Foundation, Bengaluru 560099, India; [EMAIL_ADDRESS] (R.P.P); [EMAIL_ADDRESS] (A.S.-R.)  
[PERSON]  
1 Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, 1090 Vienna, Austria; [EMAIL_ADDRESS] (F.B. ); [PERSON](B.B. ); [PERSON].) [PERSON]  
1 Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, 1090 Vienna, Austria; [EMAIL_ADDRESS] (F.B. ); [PERSON](B.B. ); [PERSON].) [PERSON]  
[PERSON].) [PERSON]  
1 Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, 1090 Vienna, Austria; [EMAIL_ADDRESS] (F.B. ); [PERSON](B.B. ); [PERSON].) parallel arranged and densely packed collagen fibrils of 25-35 nm thickness [2]. Thus, each lamella consists of 8-100 fibrils. The regular arrangement of these fibrils introduces form birefringence, an optical effect that can be measured using polarization sensitive methods, such as polarimetry [3] or polarization sensitive optical coherence tomography (PS-OCT) [4; 5; 6]. Descemet's membrane, a layer with approximately 10 \(\upmu\)m thickness, separates the stroma from the endothelium which appears as a honeycomb like mono cellular layer [1]. All corneal layers in the healthy eye are highly transparent which sets high demands on optical methods investigating the cornea in terms of system sensitivity. A variety of methods are available for imaging corneal structures and alterations thereof such as ultrasound imaging [7], confocal microscopy [8] and optical coherence tomography (OCT) [9]. Specifically, OCT can be regarded as a routine clinical tool as the technology provides contact free and non-invasively high axial resolution images of the cornea with a large field of view [10; 11]. As the shape of the cornea is approximately spherical with an extension of 11 mm (lateral) \(\times\) 5 mm (axial), there are some challenges for OCT imaging, specifically in the case of high axial resolution (ultrahigh resolution) imaging. Outside the central corneal area of 2-3 mm diameter, the probing beam has a large inclination with respect to the corneal surface. As a consequence, a lower OCT signal is detected from these areas because back reflected light is not captured by the system and only a weak backscattered portion of the light remains for detection. In addition, the sharpness of corneal interfaces is lost because of the finite lateral spot size of the imaging beam. Within this spot size, an interface has different axial depth positions. This leads to an axial blurring of the image in this region. Finally, the transverse resolution of such systems is limited by the low numerical aperture of the imaging beam that is needed in order to provide a sufficiently large depth of focus that covers the entire depth and lateral extension of the cornea. To overcome these issues, we recently developed a conical scanning scheme that achieves nearly perpendicular incidence of the imaging beam on the surface of the cornea [12]. This ensures a high signal quality from the corneal tissue throughout the entire field of view (from corneal limbus to limbus). This initial system was operated with swept source OCT at 1050 nm and achieved an axial resolution of 6.3 \(\upmu\)m (in tissue), limited by the sweep range of the used light source. However, highly reproducible and accurate thickness maps of epithelium, Bowman's layer and stroma in healthy volunteers could be provided with this system [13; 14].