Identification of peripheral anterior synechia with anterior segment optical coherence tomography.

PURPOSE: To generate a model that evaluates the presence and extent of peripheral anterior synechia (PAS) based on anterior segment optical coherence tomography (AS-OCT). METHODS: The extent of PAS involvement in the eyes of patients with angle closure was assessed by indentation gonioscopy, and the part of non-PAS and PAS were assigned into two groups (NPAS and PAS). Anterior chamber angles were then imaged by AS-OCT with light-emitting diode (LED) irradiation directly into the pupils, leading to pupillary constriction and increasing anterior chamber angle width. Parameters including the angle opening distance at 750 µm anterior to the scleral spur (AOD750) and trabecular-iris space area at 750 µm anterior to the scleral spur (TISA750) were then obtained. The differences before and after LED irradiation of AOD750 and TISA750 were calculated and used to generate a PAS model based on binary logistic regression. Validation data were then tested. RESULTS: A total of 258 AS-OCT images in 14 eyes were assigned to the modeling data, and 120 were assigned to the validation data. There were no differences in AOD750 and TISA750 in the dark between NPAS and PAS (PAOD750 = 0.258, PTISA750 = 0.486), whereas after LED light exposure, TISA750light was larger in NPAS than in PAS (P = 0.047). The light-dark differences of both parameters showed significant differences between the two groups (PAOD750dif = 0.019, PTISA750dif < 0.001). The area under the curve of the model performance was 0.841, and the overall correct rate was 80.8% based on the validation data. CONCLUSIONS: The present study demonstrates that the AS-OCT-based PAS model could be useful in the identifying of the presence of synechial angle closure and evaluating the extent of PAS in a single eye.

Anterior Segment Biometry of the Accommodating Intraocular Lens and its Relationship With the Amplitude of Accommodation.

OBJECTIVES: To evaluate the anterior segment biometry of the Tetraflex accommodating intraocular lens (AIOL) and the contribution of forward movement to the amplitude of accommodation (AMP). METHODS: Patients who underwent phacoemulsification with implantation of Tetraflex AIOLs and control nonaccommodating intraocular lenses were imaged by custom-built, long scan depth spectral-domain optical coherence tomography at relaxed and maximal accommodative states. Anterior segment biometry was performed and correlated with the clinical manifestation including AMP. RESULTS: Patients in the Tetraflex group showed better distance-corrected near visual acuity (logMAR 0.43±0.10 vs. logMAR 0.51±0.10, P<0.05) and greater AMP (1.99±0.58 diopters [D] vs. 1.59±0.45 D, P<0.05) compared with the control group. The measurement of the postoperative anterior chamber depth (ACD) during accommodation showed a forward movement of the AIOLs in 16 eyes (69.6%). Compared with the control group, a greater proportion of cases in the Tetraflex group experienced forward movement (χ test, P<0.001). The AMP in the AIOL group negatively correlated with changes in postoperative ACD during accommodation (r=-0.47, P<0.05), whereas AMP in the control group negatively correlated with postoperative pupil diameter (r=-0.57, P<0.05). CONCLUSIONS: The Tetraflex AIOLs seemed to have a tendency for forward movement; however, the slight forward axial shifts of the Tetraflex AIOL during natural accommodation may not produce a clinically relevant change in optical power.

Real-Time Measurement of Dynamic Changes of Anterior Segment Biometry and Wavefront Aberrations During Accommodation.

OBJECTIVES: To analyze the dynamic relationship between ocular geometrical structure and high-order aberrations (HOAs) in teal-time during accommodation of human eye. METHODS: A custom-built spectral domain optical coherence tomography (OCT) system with high-speed and ultra-long scan depth was used to image the anterior segment, whereas a Shack-Hartmann wavefront sensor was used to detect the whole-eye aberration. A Badal optometer with switched visual targets was integrated with this system to induce 0 and 3.00 D accommodative stimuli. Three young adult subjects were measured and the structural parameters of anterior segment were measured from OCT images and accommodative response and HOAs were calculated and exponentially fitted in real time during the accommodation. RESULTS: The dynamic process from nonaccommodation to 3.00 D accommodation results in reduced pupil diameter, shallower anterior chamber depth, and increased crystalline lens thickness. After an accommodative active time, the RMS of the HOAs changes sharply when an accommodative stimulus is introduced and then tends to be stable. The accommodative response time and velocity are characterized by fitted parameters. The individual differences of changing in HOAs between subjects can be explained by the different sign and changing tendency of certain terms of aberration coefficients in form of Zernike polynomials during the accommodation. CONCLUSIONS: Based on the integrated ocular measurement platform including OCT system and wavefront sensor, our research demonstrated how the morphology of the human anterior segment affect the aberration in real time during accommodation. The dynamic relationship between them helps us to deeply understand the mechanism of accommodation.

Automatic biometry of the anterior segment during accommodation imaged by optical coherence tomography.

OBJECTIVE: To test accuracy and repeatability of a software algorithm that performs automatic biometry of the anterior segment of the human eye imaged with long scan depth optical coherence tomography (OCT). METHODS: The ocular anterior segment imaging was performed with custom-built long scan depth OCT. An automatic software algorithm including boundary segmentation, image registration, and optical correction was developed for fast and reliable biometric measurements based on the OCT images. The boundary segmentation algorithm mainly used the gradient information of images and applied the shortest path search based on the dynamic programming to optimize the edge finding. The automatic algorithm was validated by comparison of the biometric dimensions between automatic and manual measurements and repeatability study. RESULTS: Biometric dimensions of the anterior segment, including central corneal thickness, anterior chamber depth, pupil diameter, crystalline lens thickness, and radii of curvature of the anterior and posterior surfaces of lens, were obtained by the automatic algorithm successfully. There were no significant differences between the automatic and manual measurements for all biometric dimensions. The intraclass correlation coefficients (ICC) of agreement between automatic and manual measurements ranged from 0.85 to 0.98. The coefficients of repeatability and ICC for all automatic dimensions were satisfactory (1.1%-6.1% and 0.663-0.990, respectively). CONCLUSIONS: The high accuracy, good repeatability, and fast execution speed for automatic measurement of the anterior segment dimensions on the OCT images were demonstrated. The application of this automatic biometry is promising for investigating dynamic changes of human anterior segment during accommodation in real time.

Fully automated biometry of in situ intraocular lenses using long scan depth spectral-domain optical coherence tomography.

PURPOSE: Spectral-domain optical coherence tomography (SD-OCT) was used to automatically measure accommodative biometric changes in the anterior segment of eyes implanted with an intraocular lens (IOL). The repeatability and reliability of the automated measurements were also evaluated. METHODS: Long scan depth SD-OCT was used to image the anterior segment of eyes implanted with IOLs. A fully automated algorithm was used to detect the boundaries of the cornea and IOL and yielded the measurements. The results included anterior segment dimensions in IOL eyes and the deflection of the IOLs. Automated measurements were validated in vitro and compared with the manual results in vivo on 15 cross-sectional images from patients with IOLs. Five eyes with five different types of IOLs, respectively, were enrolled to test the repeatability of the automated measurements during accommodation. RESULTS: Intraocular lens central thickness and anterior and posterior curvature radii measured by long scan depth SD-OCT in vitro and in a model eye matched well with those determined by a micrometer caliper and interferometer. In vivo, there was good correlation of the biometric data determined by automated and manual segmentations (P<0.05, r-value range: 0.635-0.997). There were no significant differences for any variable between the two measurements at each accommodative state (P>0.05). Anterior chamber depth and pupil diameter showed significant changes between the nonaccommodative and 2.5-D accommodative states (P<0.05), whereas the shape of the IOLs did not change significantly (P>0.05). CONCLUSIONS: The long scan depth SD-OCT with the automated algorithm was verified to have a great potential in studying accommodative biometric changes of the anterior segment in eyes with IOLs and IOL deflections.

Corneal reshaping and wavefront aberrations during overnight orthokeratology.

PURPOSE: To investigate changes of corneal thickness at the vertical and horizontal meridians and of wavefront aberrations (WA) over a 30-day period of overnight myopia orthokeratology (OK) lens wear. METHODS: Sixteen subjects (11 women, 5 men, 26.3±3.2 years) were enrolled and fitted for OK lenses. Long scan depth optical coherence tomography was used to measure corneal thickness profiles at both horizontal and vertical meridians at baseline and on days 1, 7, and 30 days. Corneal and ocular WA of a 6-mm pupil were measured and the root-mean-square (RMS) of the astigmatism, coma, spherical aberration (SA), and total higher-order aberrations (HOAs) were determined. RESULTS: During the 30-day period, the central cornea thinned in the horizontal and vertical meridians, whereas corneal thickening occurred in the temporal, nasal, and inferior mid-peripheries. In contrast, the cornea thinned in the mid-peripheral superior. There were significant increases in RMS for astigmatism, SA, coma, and positive horizontal coma during the study period. After OK, there were significant positive correlations between the midperipheral-central thickness change difference and the changes in corneal and ocular RMS of total HOAs and SA (r range: 0.281 to 0.492, P<0.05). Only the change of corneal coma RMS was correlated with midperipheral-central thickness change difference (r=0.270, P<0.05). The change in corneal horizontal coma was correlated with the temporal-nasal thickness change difference (r=-0.289, P<0.05). CONCLUSIONS: Overnight OK caused unique changes in corneal thickness profiles at the vertical and horizontal meridians and increased corneal and ocular HOAs related to corneal reshaping.

Spatial mapping of corneal biomechanical properties using wave-based optical coherence elastography.

Quantifying the mechanical properties of the cornea can provide valuable insights into the occurrence and progression of keratoconus, as well as the effectiveness of corneal crosslinking surgery. This study presents a non-contact and non-invasive wave-based optical coherence elastography system that utilizes air-pulse stimulation to create a two-dimensional map of corneal elasticity. Homogeneous and dual concentration phantoms were measured with the sampling of 25 × 25 points over a 6.6 × 6.6 mm2 area, to verify the measurement capability for elastic mapping and the spatial resolution (0.91 mm). The velocity of elastic waves distribution of porcine corneas before and after corneal crosslinking surgery were further mapped, showing a significant change in biomechanics in crosslinked region. This system features non-invasiveness and high resolution, holding great potential for application in ophthalmic clinics.

Biomechanical and histological changes associated with riboflavin ultraviolet-A-induced CXL with different irradiances in young human corneal stroma.

Keratoconus (KC) is a degenerative condition affecting the cornea, characterized by progressive thinning and bulging, which can ultimately result in serious visual impairment. The onset and progression of KC are closely tied to the gradual weakening of the cornea's biomechanical properties. KC progression can be prevented with corneal cross-linking (CXL), but this treatment has shortcomings, and evaluating its tissue stiffening effect is important for determining its efficacy. In this field, the shortage of human corneas has made it necessary for most previous studies to rely on animal corneas, which have different microstructure and may be affected differently from human corneas. In this research, we have used the lenticules obtained through small incision lenticule extraction (SMILE) surgeries as a source of human tissue to assess CXL. And to further improve the results' reliability, we used inflation testing, personalized finite element modeling, numerical optimization and histology microstructure analysis. These methods enabled determining the biomechanical and histological effects of CXL protocols involving different irradiation intensities of 3, 9, 18, and 30 mW/cm2, all delivering the same total energy dose of 5.4 J/cm2. The results showed that the CXL effect did not vary significantly with protocols using 3-18 mW/cm2 irradiance, but there was a significant efficacy drop with 30 mW/cm2 irradiance. This study validated the updated algorithm and provided guidance for corneal lenticule reuse and the effects of different CXL protocols on the biomechanical properties of the human corneal stroma.

Entire thickness profiles of the epithelium and contact lens in vivo imaged with high-speed and high-resolution optical coherence tomography.

PURPOSE: To test the feasibility of measuring the entire thickness profiles of the epithelium and contact lens (CL) in vivo, using high-speed and high-resolution spectral-domain optical coherence tomography (SD-OCT). METHODS: A custom-built, long scan depth SD-OCT was developed based on a complementary metal oxide semiconductor (CMOS) camera, and the axial resolution was approximately 5.1 µm in tissue. Five eyes of five subjects were imaged twice across the horizontal meridian before and while wearing one CL. Semiautomatic measurement was done to yield the entire thickness profiles of the epithelium, total cornea, and CL after correcting for optical distortion. RESULTS: The full width and depth of the epithelium, ocular surface, and CL were clearly visualized. The epithelial thickness at the center was 51.9±3.5 µm; it remained at this thickness across the central 7 mm diameter and then increased at both temporal and nasal peripheries. The CL profile showed the thinnest point at the center with thickness of 100.3±4.9 µm. The thickness increased toward the midperiphery and then decreased at the edge. CONCLUSIONS: This pilot study demonstrated the feasibility of using high-speed CMOS-based OCT to evaluate the entire thickness profiles of the epithelium and CL in vivo. Further development will be needed to extend the scanning from 2D to 3D with a robust automatic image processing ability.

Anterior segment biometry during accommodation imaged with ultralong scan depth optical coherence tomography.

PURPOSE: To measure by ultralong scan depth optical coherence tomography (UL-OCT) dimensional changes in the anterior segment of human eyes during accommodation. DESIGN: Evaluation of diagnostic test or technology. PARTICIPANTS: Forty-one right eyes of healthy subjects with a mean age of 34 years (range, 22-41 years) and a mean refraction of -2.5 ± 2.6 diopters were imaged in 2 repeated measurements at minimal and maximal accommodations. METHODS: A specially adapted and designed UL-OCT instrument was used to image from the front surface of the cornea to the back surface of the crystalline lens. Custom software corrected the optical distortion of the images and yielded the biometric measurements. The coefficient of repeatability and the intraclass correlation coefficient were calculated to evaluate the repeatability and reliability. MAIN OUTCOME MEASURES: Anterior segment parameters and associated repeatability and reliability upon accommodation. The dimensional results included central corneal thickness (CCT), anterior chamber depth and width (ACD, ACW), pupil diameter (PD), lens thickness (LT), anterior segment length (ASL = ACD + LT), lens central position (LCP = ACD + 1/2LT), and horizontal radii of the lens anterior and posterior surface curvatures (LAC, LPC). RESULTS: Repeated measurements of each variable within each accommodative state did not differ significantly (P>0.05). The coefficients of repeatability (CORs) and intraclass correlation coefficients for CCT, ACW, ACD, LT, LCP, and ASL were excellent (1.2%- 3.59% and 0.998-0.877, respectively). They were higher for PD (18.90%-21.63% and 0.880-0.874, respectively) and moderate for LAC and LPC (34.86%-42.72% and 0.669-0.251, respectively) in the 2 accommodative states. Compared with minimal accommodation, PD, ACD, LAC, LPC, and LCP decreased and LT and ASL increased significantly at maximal accommodation (P<0.05), whereas CCT and ACW did not change (P>0.05). CONCLUSIONS: The UL-OCT measured changes in anterior segment dimensions during accommodation with good repeatability and reliability. During accommodation, the back surface of the lens became steeper as the lens moved forward. FINANCIAL DISCLOSURE(S): The authors have no proprietary or commercial interest in any of the materials discussed in this article.

Daytime variations of tear osmolarity and tear meniscus volume.

OBJECTIVES: The aim of this study was to determine the pattern of variations in tear osmolarity and tear meniscus volume in patients with dry eyes and in healthy control subjects over an 8-hr daytime period. METHODS: Ten normal subjects (5 men and 5 women with a mean age of 27±7 years) and 10 dry eye patients (4 men and 6 women with a mean age of 36±12 years) who had been diagnosed on the basis of having an ocular surface discomfort index >12 and a tear breakup time of <10 sec or Schirmer test score of <5 mm were included. The tear meniscus volumes of the participants were measured using ultrahigh resolution optical coherence tomography (OCT), and tear osmolarity was measured using the TearLab Osmolarity System. Both measurements protocols were conducted on the right eye of each participant every 2 hrs beginning at 8:30 AM and ending at 4:30 PM. The OCT imaging was performed first and was followed by osmolarity testing. RESULTS: The mean tear osmolarity of the dry eye patients was 304.0±10.8 mOsm/L, and the mean tear osmolarity of the normal subjects was 298.0±14.2 mOsm/L (P>0.05). Over the course of 8 hrs, the average measured osmolarities of the dry eye group varied by approximately 21.9±13.5 mOsm/L (range, 6-43 mOsm/L), and the average measured tear osmolarities of the normal group varied by approximately 21.0±9.2 mOsm/L (range, 8-35 mOsm/L). At 2:30 PM, the average volume of the tear menisci in the dry eye group was significantly lower than that of the subjects in the normal group (P<0.05). No correlations between the tear meniscus volumes and tear osmolarities of either group were observed. CONCLUSIONS: Variations in the tear osmolarities of individual dry eye patients and healthy normal control subjects were documented over the course of 8 daytime hours. No relationships between tear osmolarities and tear meniscus volumes were observed.

In situ assessment of lens elasticity with noncontact optical coherence elastography.

Lens biomechanics has great potential for application in clinical diagnostics and treatment monitoring of presbyopia and cataracts. However, current approaches to lens elastography do not meet the desired safety or sensitivity for clinical application. In this regard, we propose a noncontact optical coherence elastography (OCE) method to facilitate quantitative in situ imaging of lens elasticity. Elastic waves induced by air-pulse stimulation on the limbus propagate to the lens and are then imaged using custom-built swept-source optical coherence tomography to obtain the elastic wave velocity and Young's modulus. The proposed OCE method was first validated by comparing the results of in situ and in vitro measurements of porcine lenses. The results demonstrate that the Young's modulus measured in situ was highly consistent with that measured in vitro and had an intraclass correlation coefficient of 0.988. We further investigated the elastic changes induced by cold storage and microwave heating. During 36-hour cold storage, the mean Young's modulus gradually increased (from 5.62 ± 1.24 kPa to 11.40 ± 2.68 kPa, P < 0.0001, n = 9) along with the formation of nuclear opacities. 15-second microwave heating caused a greater increase in the mean Young's modulus (from 6.86 ± 1.21 kPa to 25.96 ± 8.64 kPa, P < 0.0025, n = 6) without apparent cataract formation. Accordingly, this study reports the first air-pulse OCE measurements of in situ lenses, which quantified the loss of lens elasticity during simulated cataract development with good repeatability and sensitivity, thus enhancing the potential for adoption of lens biomechanics in the clinic.

Identification of Peripheral Anterior Synechia by Corneal Deformation Using Air-Puff Dynamic Anterior Segment Optical Coherence Tomography.

Indentation gonioscopy is commonly used in the clinic to evaluate peripheral anterior synechia (PAS) of angle closure glaucoma (ACG). The examination requires contacting with the cornea, resulting in an uncomfortable feeling for patients, and it only provides qualitative outcomes which may be affected by subjective judgment of the clinicians. Previous studies had reported to identify the presence of PAS by measuring the changes of morphological parameters of the anterior chamber angle (ACA) under the pupillary light reflex, by anterior segment optical coherence tomography (AS-OCT). However, this method was invalid for some subjects who had low sensitiveness to light. This article describes an air-puff dynamic anterior segment optical coherence tomography (DAS-OCT) system that can evaluate the presence of PAS in a non-contact approach. The peripheral cornea is deformed by an air puff jetted from the DAS-OCT, causing a transfer of force to the ACA, just as how indentation gonioscopy works. The dynamic changes of the ACA before and after the air puff are recorded by OCT. Ten eyes of normal subjects were enrolled in this study to validate the repeatability and availability of the measurements. Then, ten samples of the ACA from five subjects with ACG were recruited and were assigned into two groups, the non PAS group (NPAS) and PAS group, according to the results of gonioscopy. The ACA structural parameters including the angle opening distance at 750 µm to the scleral spur (AOD750) and the trabecular-iris space area at 750 µm anterior to the scleral spur (TISA750) were then calculated automatically by a custom-written algorithm. The intraclass correlation coefficient (ICC) of measured parameters was all above 0.85 for normal subjects, exhibiting good repeatability. For patients, both parameters showed significant differences between the two groups after the air puff, while no differences were observed before the air puff. AOD750dif and TISA750dif between two groups showed more significant differences, indicating that they could be used as indicators to identify the presence of PAS. In conclusion, the DAS-OCT system proposed in this study is demonstrated effective to identify the presence of PAS by measuring the changes of the ACA via a noncontact approach. It shows great potential for applications in guidance for diagnosis of angle closure glaucoma.

In vivo non-contact measurement of human iris elasticity by optical coherence elastography.

Quantifying the mechanical properties of the iris can offer valuable insights into the pathophysiology of primary angle closure glaucoma. However, current techniques for iris elastography remain ex vivo with limited clinical applications. This article describes a proposition for a non-contact and non-invasive air-puff optical coherence elastography (OCE) system that can evaluate iris elasticity in vivo. Ten eyes recruited from seven subjects underwent OCE imaging acquisition under three different illumination conditions. The Young's modulus of each eye was detected and shown to be inversely proportional to the iris length, indicating a relationship between mechanical properties and morphology of the iris. With its noninvasive and high-resolution features, this air-puff system shows great potential for applications in clinical ophthalmology.

Diurnal variation of corneal elasticity in healthy young human using air-puff optical coherence elastography.

Due to the disruption of intraocular pressure (IOP) and central corneal thickness (CCT), diurnal variation in normal young human corneal elasticity is not clear. Using the custom-built air-puff optical coherence elastography, one eye of 21 normal subjects is enrolled randomly to measure the central corneal elasticity, IOP, and CCT in different time points within a day. Based on the multi-level model, the corneal elastic modulus is found to have a linear positive relation with IOP (P < .01) but not CCT (P = .175) and time point (P = .174-.686). A new indicator, corneal elasticity change rate, is proposed to present the magnitude of corneal elasticity change caused by 1 mmHg IOP, which can correct the interference effect of IOP. The results show that the corneal elasticity in the normal young human does not have the characteristics of diurnal variation under IOP control. Furthermore, IOP plays an important role in the corneal elasticity, and corneal elasticity change rate can increase the comparability of results between individuals.

Assessment of corneal viscoelasticity using elastic wave optical coherence elastography.

The corneal viscoelasticity have great clinical significance, such as the early diagnosis of keratoconus. In this work, an analysis method which utilized the elastic wave velocity, frequency and energy attenuation to assess the corneal viscoelasticity is presented. Using phase-resolved optical coherence tomography, the spatial-temporal displacement map is derived. The phase velocity dispersion curve and center frequency are obtained by transforming the displacement map into the wavenumber-frequency domain through the 2D fast Fourier transform (FFT). The shear modulus is calculated through Rayleigh wave equation using the phase velocity in the high frequency. The normalized energy distribution is plotted by transforming the displacement map into the spatial-frequency domain through the 1D FFT. The energy attenuation coefficient is derived by exponential fitting to calculate the viscous modulus. Different concentrations of tissue-mimicking phantoms and porcine corneas are imaged to validate this method, which demonstrates that the method has the capability to assess the corneal viscoelasticity.

Modeling of gonioscopic anterior chamber angle grades based on anterior segment optical coherence tomography.

BACKGROUND: To quantitatively assess anterior chamber angle (ACA) structure by anterior segment optical coherence tomography (AS-OCT) and develop a model to evaluate angle width as defined by gonioscopy. METHODS: The ACAs of each quadrant were evaluated by gonioscopy, classified by the Scheie grading system, and assigned into one of the three grades: small angle (SA), moderate angle (MA), and large angle (LA). The eyes were imaged by AS-OCT, and ACA structural parameters including angle opening distance at the scleral spur (AODSS) and at 750 µm anterior to the scleral spur (AOD750), trabecular-iris space area at 750 µm anterior to the scleral spur (TISA750), and a newly defined parameter "light intersection distance" (LID), were measured. The ACA structural data were used to construct an ordered logistic regression model for assignment of ACAs to one of the three angle grades. The validity of the model was then tested. RESULTS: A total of 169 quadrants from 53 subjects were included in the analysis, of which 111 quadrants were included in the modeling data and 58 in the testing data. In pairwise comparisons of SA, MA, and LA by ANOVA, the measured parameters were as follows: AOD750 (0.174 ± 0.060 vs. 0.249 ± 0.068 vs. 0.376 ± 0.114 mm; P < 0.001), TISA750 (0.075 ± 0.035 vs. 0.117 ± 0.036 vs. 0.181 ± 0.062 mm2; P < 0.001), and LID (- 0.300 ± 0.187 vs. -0.085 ± 0.170 vs. 0.122 ± 0.156 mm; P < 0.001). The ACA grading model based on LID showed a relatively high correction rate of 72.4%, and the model efficiency, calculated using the receiver operating characteristic, showed an area under the curve of 0.740. Weighted kappa statistics showed a good agreement for multiple ACA grades (0.772). CONCLUSIONS: The AS-OCT-based multiple ACA grades model was demonstrated as a non-contact approach for ACA assessment with high speed and high spatial resolution, providing guidance for diagnosis of angle closure.

In vivo noninvasive measurement of spatially resolved corneal elasticity in human eyes using Lamb wave optical coherence elastography.

Current elastography techniques are limited in application to accurately assess spatially resolved corneal elasticity in vivo for human eyes. The air-puff optical coherence elastography (OCE) with an eye motion artifacts correction algorithm is developed to distinguish the in vivo cornea vibration from the eye motion and visualize the Lamb wave propagation clearly in healthy subjects. Based on the Lamb wave model, the phase velocity dispersion curve in the high-frequency is calculated to obtain spatially resolved corneal elasticity accurately with high repeatability. It is found that the corneal elasticity has regional variations and is correlated with intraocular pressure, which suggests that the method has the potential to provide noninvasive measurement of spatially resolved corneal elasticity in clinical practice.

In vivo evaluation of corneal biomechanical properties by optical coherence elastography at different cross-linking irradiances.

Corneal collagen cross-linking (CXL) strengthens the biomechanical properties of damaged corneas. Quantifying the changes of stiffness due to different CXL protocols is difficult, especially in vivo. A noninvasive elastic wave-based optical coherence elastography system was developed to construct in vivo corneal elasticity maps by excitation of air puff. Biomechanical differences were compared for rabbit corneas given three different CXL protocols while keeping the total energy delivered constant. The Young's modulus was weaker in corneas treated with higher irradiance levels over shorter durations, and a slight increase of Young's modulus was present in all groups one week after the recovery process. Due to the noninvasive nature and minimal force to generate corneal elastic waves, this technique has the potential for early detection and treatment of corneal diseases in clinic.

Widely tunable reflection-type Fabry-Perot interferometer based on relaxor ferroelectric poly(vinylidenefluoride-chlorotrifluoroethylene-trifluoroethylene).

A reflection-type Fabry-Perot interferometer (FPI) with a large tunability has been demonstrated on relaxor ferroelectric poly(vinylidenefluoride-chlorotrifluoroethylene-trifluoroethylene) [P(VDFCTFE-TrFE)] 78.9/13.9/7.2 mol% with a thickness of 9.2 microm. The optical path length of the FPI is modulated by the electrostrictive strain of the terpolymer under electric field, where the low-loss distributed Bragg reflector and aluminium film are employed as the mirrors in the FPI. A positive strain of 20% has been achieved in the terpolymer film under a field of 30 MV/m, which leads to the FPI with a tunable range of more than 200 nm at wavelengths around 680 nm.