ABSTRACT
A Swept Source Polarization-Sensitive Optical Coherence Tomography (SS-PS-OCT) instrument has been designed, constructed, and verified to provide high sensitivity depth-resolved birefringence and phase retardation measurements of the retinal nerve fiber layer. The swept-source laser had a center wavelength of 1059 nm, a full-width-half-max spectral bandwidth of 58 nm and an A-line scan rate of 34 KHz. Power incident on the cornea was 440 µW and measured axial resolution was 17 µm in air. A multiple polarization state nonlinear fitting algorithm was used to measure retinal birefringence with low uncertainty. Maps of RNFL phase retardation in a subject measured with SS-PS-OCT compare well with those generated using a commercial scanning laser polarimetry instrument. Peak-to-valley variation of RNFL birefringence given here is less than values previously reported at 840nm.
Subject(s)
Cornea/pathology , Optic Nerve/pathology , Optics and Photonics/methods , Retinal Vessels/pathology , Tomography, Optical Coherence/methods , Algorithms , Birefringence , Equipment Design , Fourier Analysis , Models, Theoretical , Nerve Fibers , Optic Disk , Retina , Scanning Laser Polarimetry , Sensitivity and Specificity , Tomography, Optical Coherence/instrumentationABSTRACT
The long-pulse (200-350 micros) Holmium: YAG (Ho: YAG) laser (lambda = 2.12 microm) is used extensively in urology for laser lithotripsy. The long-pulse Erbium: YAG (Er: YAG) laser (lambda = 2.94 microm) fragments urinary calculi up to 5 times more efficiently than the Ho: YAG laser, however, no optical fibers are available to transmit efficiently 2.94 microm laser light for laser lithotripsy. We report results of a study evaluating a fluoride glass fiber to transmit Er: YAG laser light for laser lithotripsy and compare to a sapphire fiber that provides good transmission of Er: YAG light at low irradiance. The fluoride fiber provides superior light transmission efficiency over the sapphire fiber at an Er: YAG wavelength (2.94 microm). The sapphire fiber provides a more durable and robust delivery waveguide than the fluoride fiber when ablating urinary calculi in contact mode. Results of our study suggest that further development to improve performance of fluoride fibers for laser lithotripsy is warranted.
Subject(s)
Aluminum Oxide , Fluorides , Lasers, Solid-State , Lithotripsy, Laser/instrumentation , Optical Fibers , Air , Equipment Failure Analysis , Humans , In Vitro Techniques , Lasers, Solid-State/therapeutic use , Light , Lithotripsy, Laser/methods , Urinary Calculi/therapyABSTRACT
Retinal nerve fiber layer (RNFL) thickness, a measure of glaucoma progression, can be measured in images acquired by spectral domain optical coherence tomography (OCT). The accuracy of RNFL thickness estimation, however, is affected by the quality of the OCT images. In this paper, a new parameter, signal deviation (SD), which is based on the standard deviation of the intensities in OCT images, is introduced for objective assessment of OCT image quality. Two other objective assessment parameters, signal to noise ratio (SNR) and signal strength (SS), are also calculated for each OCT image. The results of the objective assessment are compared with subjective assessment. In the subjective assessment, one OCT expert graded the image quality according to a three-level scale (good, fair, and poor). The OCT B-scan images of the retina from six subjects are evaluated by both objective and subjective assessment. From the comparison, we demonstrate that the objective assessment successfully differentiates between the acceptable quality images (good and fair images) and poor quality OCT images as graded by OCT experts. We evaluate the performance of the objective assessment under different quality assessment parameters and demonstrate that SD is the best at distinguishing between fair and good quality images. The accuracy of RNFL thickness estimation is improved significantly after poor quality OCT images are rejected by automated objective assessment using the SD, SNR, and SS.
