A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

Amplitude decorrelation measurement is sensitive to transverse flow and immune to phase noise in comparison to Doppler and other phase-based approaches. However, the high axial resolution of OCT makes it very sensitive to the pulsatile bulk motion noise in the axial direction. To overcome this limitation, we developed split-spectrum amplitude-decorrelation angiography (SSADA) to improve the signal-to-noise ratio (SNR) of flow detection. The full OCT spectrum was split into several narrower bands. Inter-B-scan decorrelation was computed using the spectral bands separately and then averaged. The SSADA algorithm was tested on in vivo images of the human macula and optic nerve head. It significantly improved both SNR for flow detection and connectivity of microvascular network when compared to other amplitude-decorrelation algorithms.

/pdf/split-spectrum-amplitude-decorrelation-angiography-with-5066x1kwi2.pdf

Split-spectrum amplitude-decorrelation angiography with optical coherence tomography

The diffraction tomography theorem is adapted to one-dimensional length measurement. The resulting spectral interferometry technique is described and the first length measurements using this technique on a model eye and on a human eye in vivo are presented.

Measurement of intraocular distances by backscattering spectral interferometry

We demonstrate a new technique for frequency-swept laser operation--Fourier domain mode locking (FDML)--and its application for swept-source optical coherence tomography (OCT) imaging. FDML is analogous to active laser mode locking for short pulse generation, except that the spectrum rather than the amplitude of the light field is modulated. High-speed, narrowband optical frequency sweeps are generated with a repetition period equal to the fundamental or a harmonic of cavity round-trip time. An FDML laser is constructed using a long fiber ring cavity, a semiconductor optical amplifier, and a tunable fiber Fabry-Perot filter. Effective sweep rates of up to 290 kHz are demonstrated with a 105 nm tuning range at 1300 nm center wavelength. The average output power is 3mW directly from the laser and 20 mW after post-amplification. Using the FDML laser for swept-source OCT, sensitivities of 108 dB are achieved and dynamic linewidths are narrow enough to enable imaging over a 7 mm depth with only a 7.5 dB decrease in sensitivity. We demonstrate swept-source OCT imaging with acquisition rates of up to 232,000 axial scans per second. This corresponds to 906 frames/second with 256 transverse pixel images, and 3.5 volumes/second with a 256x128x256 voxel element 3-DOCT data set. The FDML laser is ideal for swept-source OCT imaging, thus enabling high imaging speeds and large imaging depths.

Fourier Domain Mode Locking (FDML): A new laser operating regime and applications for optical coherence tomography.

A two- and three-dimensional swept source optical coherence tomography (SS-OCT) system, which uses a ready-to-ship scanning light source, is demonstrated. The light source has a center wavelength of 1.31 mum, -3 dB wavelength range of 110 nm, scanning rate of 20 KHz, and high linearity in frequency scanning. This paper presents a simple calibration method using a fringe analysis technique for spectral rescaling. This SS-OCT system is capable of realtime display of two-dimensional OCT and can obtain three-dimensional OCT with a measurement time of 2 s. In vivo human anterior eye segments are investigated two- and three-dimensionally. The system sensitivity is experimentally determined to be 114 dB. The three-dimensional OCT volumes reveal the structures of the anterior eye segments, which are difficult to observe in two-dimensional OCT images.

Three-dimensional and high-speed swept-source optical coherence tomography for in vivo investigation of human anterior eye segments

PURPOSE. To study the choroidal thickness in healthy subjects by swept-source optical coherence tomography (SS-OCT) at longer wavelength. METHODS. The macular area of 31 eyes (31 healthy volunteers) was studied with an SS-OCT prototype system, which uses a tunable laser as a light source operated at 100,000 Hz A scan repetition rate in the 1-m wavelength region. Three-dimensional volumetric measurement comprised of 512 128 A scans was acquired in 0.8 second. From a series of OCT images, a chroidal thickness map of the macular area was created by manual segmentation. To evaluate interoperator reproducibility, the choroidal thickness in each section from 10 subjects was determined independently by two observers. RESULTS. SS-OCT at the 1-m wavelength region allowed visualization of the fine structure of the choroid as well as that of the retina. Mean choroidal thickness and volume in the macula area were, respectively, 191.5 74.2 m and 5.411 2.097 mm 3 . The mean choroidal thickness of the outer nasal area was significantly thinner than that of all other areas (P 0.05). The measurements by the two independent observers were significantly identical; the intraclass correlation coefficient in mean choroidal thickness was between 0.945 and 0.980 in each area. The macular choroidal thickness was significantly correlated with axial length after adjustment for age (P 0.001), and with age after adjustment for axial length (P 0.001). CONCLUSIONS. SS-OCT system at 1 m provides macular choroidal thickness maps and allows one to evaluate the choroidal thickness more accurately. (Invest Ophthalmol Vis Sci. 2011; 52:4971‐4978) DOI:10.1167/iovs.11-7729

https://www.topcon-medical.it/files/Local_TES/Estudios_clinicos/15Macular_choroidal_thickness_and_volume_in_normal_subjects_measured_by_SS_OCT.pdf

Macular choroidal thickness and volume in normal subjects measured by swept-source optical coherence tomography.

Retinal, choroidal and scleral imaging by using swept-source optical coherence tomography (SS-OCT) with a 1-microm band probe light, and high-contrast and three-dimensional (3D) imaging of the choroidal vasculature are presented. This SS-OCT has a measurement speed of 28,000 A-lines/s, a depth resolution of 10.4 microm in tissue, and a sensitivity of 99.3 dB. Owing to the high penetration of the 1-microm probe light and the high sensitivity of the system, the in vivo sclera of a healthy volunteer can be observed. A software-based algorithm of scattering optical coherence angiography (S-OCA) is developed for the high-contrast and 3D imaging of the choroidal vessels. The S-OCA is used to visualize the 3D choroidal vasculature of the in vivo human macula and the optic nerve head. Comparisons of S-OCA with several other angiography techniques including Doppler OCA, Doppler OCT, fluorescein angiography, and indocyanine green angiography are also presented.

In vivo high-contrast imaging of deep posterior eye by 1-microm swept source optical coherence tomography and scattering optical coherence angiography.

PURPOSE To investigate circadian changes in subfoveal choroidal thickness (SFCT) and the relation to systemic factors in healthy subjects. METHODS Thirty-eight eyes of 19 healthy volunteers were enrolled. SFCT was measured by using prototype high-penetration optical coherence tomography. Intraocular pressure (IOP), systolic blood pressure (SBP), diastolic blood pressures (DBP), and heart rate (HR) were measured every 3 hours over a 24-hour period. Circadian changes in the mean arterial pressure (MAP) and mean ocular perfusion pressure (MOPP) were calculated. The difference between the maximal and minimal SFCTs was analyzed, and correlations between the SFCT and other systemic factors were evaluated. RESULTS There was a significant circadian variation in SFCT (P < 0.0001). The total mean SFCT was 280.3 ± 106.1 μm. At 6 PM, the mean SFCT (271.9 ± 103.5 μm) was the thinnest and at 3 AM it was the thickest (290.8 ± 110.8 μm). The SFCTs in 32 of 38 eyes were thickest between 3 and 9 AM and in 27 of 38 eyes, thinnest between 3 and 9 PM. The mean SFCT was significantly negatively correlated with the mean SBP (R(2) = 0.59, P = 0.02) in all eyes. There were no significant correlations between the mean SFCT and the mean DBP, MAP, HR, IOP, and MOPP in all eyes. CONCLUSIONS We investigated the circadian change of choroidal thickness using high-penetration optical coherence tomography in healthy volunteers. The significant diurnal change was found and the choroid was thicker at night and thinner in daytime. Fluctuations in the choroidal thickness may be related to SBP.

Circadian changes in subfoveal choroidal thickness and the relationship with circulatory factors in healthy subjects.

An optical image measuring apparatus forming an image expressing functional information on a living tissue. The optical image measuring apparatus includes a light emitting portion (2) outputting light (B1 and B2(B)) having different wavelengths intensity-modulating the light periodically, a polarizing plate (3) converting a light (B) to linearly polarized light, a half mirror (6) dividing the light (B) into signal light (S) and reference light (R), a wavelength plate (7) converting a polarization characteristic of the reference light (R), a frequency shifter (8) shifting a frequency of the reference light (R), the half mirror (6) superimposing the signal light (S) and the reference light (R) on each other to produce interference light (L), a polarization beam splitter (11) extracting a polarized light from the interference light (L), CCDs (21 and 22) detecting the extracted polarized interference light (L), and a signal processing portion (20) forming an image of an object to be measured (O) based on the polarized interference light (L) related to each of the light (B1 and B2), detected by the CCDs (21 and 22).

Masahiro Akiba

Papers

Three-dimensional and high-speed swept-source optical coherence tomography for in vivo investigation of human anterior eye segments

Macular choroidal thickness and volume in normal subjects measured by swept-source optical coherence tomography.

In vivo high-contrast imaging of deep posterior eye by 1-microm swept source optical coherence tomography and scattering optical coherence angiography.

Circadian changes in subfoveal choroidal thickness and the relationship with circulatory factors in healthy subjects.

Optical image measuring apparatus