The Oxford nomenclature was developed to distinguish the type of cataract based on the optical signal discontinuity (OSD) zones. The OSD zones were used to distinguish sections within the crystalline lens in our study using OCT images. A swept-source OCT was used to observe in-vivo age-related changes in the crystalline lens from the 50 healthy eyes with the age range of 9 to 78 years. The C3 layer (from oxford nomenclature) of the cortex was identified as the section of the crystalline that contributes highly to the age-related changes. We compared age-related degradation of the optical quality of the crystalline lens measurements using commercial VAO and OQAS systems with a custom-built SS-OCT system.
The focusing power of the human eye is provided by the cornea and the crystalline lens (CL). The latter provides the capacity to alter its shape and provide fine focus adjustment during the accommodation process. We extended standard structural OCT analysis to precisely follow dynamically subtle OCT signal phase changes within the human CL during accommodation. Imaging was performed using the SS-OCT system equipped with the Badal system to provide accommodation demand. The presented phase-sensitive analysis allows for distinct motion extraction such as lens wobbling, bulging, or any other deformation that can be significant for crystalline lens accommodation-associated biomechanics.
A high speed motion detection technique using SS-OCT system is demonstrated. Acquired OCT signal from high speed reflector result in producing artifacts like axial position shifts and broadening of the OCT signal in final processed images. A methodology using forward and backward wavelength sweeps of swept source laser to correct these artifacts is proposed. Analysis of phase changes of interferograms recorded with bi-directional laser sweeps at high sweep rates can be used to determine the true trajectory of the fast moving object. This technique also helps in monitoring velocity of the object exceeding the velocity range set by the acquisition speed of the OCT system.
Swept source OCT was used to image crystalline lens of 100 eyes (age range: 9-78 years) and 3-dimensional lens suture structure was visualized in vivo for the first time. Lens suture patterns were extracted using average intensity projections (AIP) or cortical layers of crystalline lens. Our imaging system has capacity to extract complex star-sutures from cortical layers of lens and simple Y-sutures from fetal nucleus of crystalline lens. Age-related changes in lens and lens sutures were observed and were characterized quantitatively. The developed imaging system can be used to study growth of crystalline lens and its age-related diseases like cataract, presbyopia.
Transparency of ocular structures affects contrast in the retinal image and has an impact on visual quality. Vitreous constitutes the largest volumetric component of the human eye, thus it contributes to the intraocular scattering. The vitreous can contain subtle opacifications causing an increase in scattering and a reduction in vision. We report three-dimensional enhanced depth imaging of the anterior vitreous with SS-OCT. We show visualization of anterior vitreous opacities (floaters). We also demonstrate the quantification of vitreal opacities with respect to the age of the subjects.
Photothermal optical coherence tomography (PT-OCT) employs a secondary intensity-modulated photothermal laser to create modulated thermal strains that cause variations of the refractive index in the proximity of absorbing chromophores. These variations are directly detected with phase-sensitive OCT and offer insight to the molecular composition and thermo-elastic properties of the sample. Here, we define optimal PT laser modulation parameters by investigating the effect of PT laser power and modulation frequency on the ensuing thermal waves and thermal waves’ impact on the spatial resolution of PT-OCT imaging based on numerical simulations of PT-OCT and samples containing point absorbers.
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