Danilo Andrade De Jesus

Using ultrasound backscattering signals and Nakagami statistical distribution to assess regional cataract hardness.

This study aims to analyze the protein aggregates spatial distribution for different cataract degrees, and correlate this information with the lens acoustical parameters and by this way, assess the cataract regional hardness. Different cataract degrees were induced ex vivo in porcine lenses. A 25 MHz ultrasonic transducer was used to obtain the acoustical parameters (velocity, attenuation, and backscattering signals). B-scan and Nakagami images were constructed. Also, lenses with different cataract degrees were sliced in two regions (nucleus and cortex), for fibers and collagen detection. A significant increase with cataract formation was found for the velocity, attenuation, and brightness intensity of the B-scan images and Nakagami m parameter (p <; 0.01). The acoustical parameters showed a good to moderate correlation with the m parameter for the different stages of cataract formation. A strong correlation was found between the protein aggregates in the cortex and the m parameter. Lenses without cataract are characterized using a classification and regression tree, by a mean brightness intensity ≤0.351, a variance of the B-scan brightness intensity ≤0.070, a velocity ≤1625 m/s, and an attenuation ≤0.415 dB/mm·MHz (sensitivity: 100% and specificity: 72.6%). To characterize different cataract degrees, the m parameter should be considered. Initial stages of cataract are characterized by a mean brightness intensity >0.351 and a variance of the m parameter >0.110. Advanced stages of cataract are characterized by a mean brightness intensity >0.351, a variance of the m parameter ≤0.110, and a mean m parameter >0.374. For initial and advanced stages of cataract, a sensitivity of 78.4% and a specificity of 86.5% are obtained.

Optical projection tomography as a tool for 3D imaging of hydrogels

An Optical Projection Tomography (OPT) system was developed and optimized to image 3D tissue engineered products based in hydrogels. We develop pre-reconstruction algorithms to get the best result from the reconstruction procedure, which include correction of the illumination and determination of sample center of rotation (CoR). Existing methods for CoR determination based on the detection of the maximum variance of reconstructed slices failed, so we develop a new CoR search method based in the detection of the variance sharpest local maximum. We show the capabilities of the system to give quantitative information of different types of hydrogels that may be useful in its characterization.

Assessment of corneal properties based on statistical modeling of OCT speckle

A new approach to assess the properties of the corneal micro-structure in vivo based on the statistical modeling of speckle obtained from Optical Coherence Tomography (OCT) is presented. A number of statistical models were proposed to fit the corneal speckle data obtained from OCT raw image. Short-term changes in corneal properties were studied by inducing corneal swelling whereas age-related changes were observed analyzing data of sixty-five subjects aged between twenty-four and seventy-three years. Generalized Gamma distribution has shown to be the best model, in terms of the Akaikes Information Criterion, to fit the OCT corneal speckle. Its parameters have shown statistically significant differences (Kruskal-Wallis, p < 0.001) for short and age-related corneal changes. In addition, it was observed that age-related changes influence the corneal biomechanical behaviour when corneal swelling is induced. This study shows that Generalized Gamma distribution can be utilized to modeling corneal speckle in OCT in vivo providing complementary quantified information where micro-structure of corneal tissue is of essence.

Precise measurement of scleral radius using anterior eye profilometry

PURPOSE To develop a new and precise methodology to measure the scleral radius based on anterior eye surface. METHODS Eye Surface Profiler (ESP, Eaglet-Eye, Netherlands) was used to acquire the anterior eye surface of 23 emmetropic subjects aged 28.1±6.6years (mean±standard deviation) ranging from 20 to 45. Scleral radius was obtained based on the approximation of the topographical scleral data to a sphere using least squares fitting and considering the axial length as a reference point. To better understand the role of scleral radius in ocular biometry, measurements of corneal radius, central corneal thickness, anterior chamber depth and white-to-white corneal diameter were acquired with IOLMaster 700 (Carl Zeiss Meditec AG, Jena, Germany). RESULTS The estimated scleral radius (11.2±0.3mm) was shown to be highly precise with a coefficient of variation of 0.4%. A statistically significant correlation between axial length and scleral radius (R2=0.957, p<0.001) was observed. Moreover, corneal radius (R2=0.420, p<0.001), anterior chamber depth (R2=0.141, p=0.039) and white-to-white corneal diameter (R2=0.146, p=0.036) have also shown statistically significant correlations with the scleral radius. Lastly, no correlation was observed comparing scleral radius to the central corneal thickness (R2=0.047, p=0.161). CONCLUSIONS Three-dimensional topography of anterior eye acquired with Eye Surface Profiler together with a given estimate of the axial length, can be used to calculate the scleral radius with high precision.

Age-related changes of the corneal speckle by Optical Coherence Tomography.

Ageing of the population has several consequences for the human visual system. The corneal tissue which is responsible for two thirds of the total optical power is not an exception, suffering structural and anatomical changes with the age. In this study, we have explored the usefulness of Optical Coherence Tomography (OCT) speckle to study the age-related changes in corneal stroma. The Generalized Gamma distribution has been suggested as a model for OCT corneal speckle and was used here to investigate OCT envelope statistics in three different age groups (65 subjects in total). The scaling and the two shape parameters have shown significant statistical differences (p <; 0.05) among the age groups, showing the possibility to track the corneal changes using envelope statistics. This study shows that Generalized Gamma distribution has a great potential to fit the corneal speckle and could be a helpful complement to evaluate the structure and elastic properties of the cornea in vivo.

Simplifying numerical ray tracing for two-dimensional non circularly symmetric models of the human eye.

Ray tracing is a powerful technique to understand the light behavior through an intricate optical system such as that of a human eye. The prediction of visual acuity can be achieved through characteristics of an optical system such as the geometrical point spread function. In general, its precision depends on the number of discrete rays and the accurate surface representation of each eyes components. Recently, a method that simplifies calculation of the geometrical point spread function has been proposed for circularly symmetric systems [Appl. Opt.53, 4784 (2014)]. An extension of this method to 2D noncircularly symmetric systems is proposed. In this method, a two-dimensional ray tracing procedure for an arbitrary number of surfaces and arbitrary surface shapes has been developed where surfaces, rays, and refractive indices are all represented in functional forms being approximated by Chebyshev polynomials. The Liou and Brennan anatomically accurate eye model has been adapted and used for evaluating the method. Further, real measurements of the anterior corneal surface of normal, astigmatic, and keratoconic eyes were substituted for the first surface in the model. The results have shown that performing ray tracing, utilizing the two-dimensional Chebyshev function approximation, is possible for noncircularly symmetric models, and that such calculation can be performed with a newly created Chebfun toolbox.

Characterization of scatterers concentration in cataractous lens using Nakagami distribution by ultrasounds

Cataract affects more than 20 million people in the world. Its formation is associated with the increase of protein aggregation in the eye lens. In the early stages the protein aggregates act as light scatterers and in the advanced stages these aggregates increase in size preventing the light propagation through the eye. This work aims to analyze the protein aggregates and its spatial distribution, for different stages of cataract formation. Cataract was induced in porcine lenses by immersion in an ethanol:2-propanol:formalin solution. Slices of 50 μm in thickness were obtained from the nucleus and the cortex, to locally analyze the frequency dependent attenuation and the Nakagami m parameter. The slices were stained and imaged with an inverted microscope. With cataract formation a significant increase was found for the ultrasound velocity (p>0.001), the frequency dependent attenuation (p<;0.001), the backscattering signals intensity - B-Scan images and the Nakagami m parameter (p<;0.001). The increase of the Nakagami m parameter in the cortex was in agreement with the increasing of the protein aggregates observed in the slices in this region, for different stages of cataract formation. The same was not observed for the nucleus, due to the higher compaction of the fibers in the nucleus in the advanced stages of the cataract, leading to weak backscattering signals. The results suggest that the interpretation of backscattering signals by the Nakagami distribution, when combined with the knowledge of the physical scatter properties are challenging for obtaining a distribution map of cataract hardness by a noninvasive method.

Using of the ultrasound frequency dependent attenuation and Nakagami distribution for cataract evaluation

Cataract is a clouding or opacity of the normally transparent crystalline lens of the eye. The cataract formation is associated with the increase of both inner fiber compaction and protein aggregation, which can be characterized by ultrasound backscattering. In this study, the tissue scatterers changing with cataract formation was investigated, and their influence in the frequency dependent attenuation such as in the Nakagami distribution was analyzed. For this purpose, cataracts were induced in twenty porcine lenses. A 25 MHz focused transducer was used to estimate the ultrasound attenuation considering the spectral ratio between echo signals from a reflector with and without lenses inserted. A power-law frequency dependence model was used to study the frequency dependent attenuation. The analyzed signals showed high backscattering and also a variation of the Nakagami parameter with cataract formation, indicating a scatter size increase. This conclusion could be important to assess the cataract hardness and to provide the correct information about its type and severity.

Ultrasound techniques for lens hardness characterization: A comparison study

Cataract affects more than 20 million people worldwide and is the leading cause of vision loss. Currently, the phacoemulsification is the most used procedure to extract cataract and recover visual acuity. Optimal phacoemulsification energy is demanded for safety cataract removal. It is well established that the energy value is determined by the cataract hardness. In this study twenty porcine eyes were used as experimental samples. Cataract was induced by an ethanol:2-propanol:formalin solution. A 25 MHz focused transducer has been used to estimate the ultrasound velocity and attenuation. Statistical analysis was performed to compare the different used methodologies and to correlate the different ultrasound parameters with different stages of cataract formation (lens hardness).

Quantitative automated circumpapillary microvascular density measurements: a new angioOCT-based methodology

PurposeTo develop a new methodology to detect glaucoma damage based on circumpapillary microvascular density (cpmVD) as measured by optical coherence tomography angiography (angioOCT).MethodsAngioOCT scans from a random eye of 40 healthy subjects (aged 63 ± 14 years) and 82 glaucoma patients (aged 66 ± 9 years with an average visual field loss of −7.8 ± 6.5 dB) were used to develop a new angioOCT evaluation methodology. Optic disc-centred 3 × 3 mm images were collected (Angioplex®, Zeiss Cirrus 5000 HD-OCT). An annular area with an inner radius of 1.16 mm and outer radius of 1.44 mm was chosen as the region of interest (ROI), with cpmVD calculated through lower envelope modulation avoiding the influence of the major retinal vessels. Additionally, the cpmVD and the microvascular density (mVD), stratified by sectors, were compared with the respective retinal nerve fibre layer (RNFL) thickness.ResultsA significantly lower cpmVD was observed in the glaucoma group, for all visual field sectors (p < 0.001), when comparing to the healthy group. The inferior and superior mVD sectors showed the largest differences between groups. Moreover, glaucoma was linked to a reduction of cpmVD variation when compared to the healthy group. Lastly, a comparison between two healthy subgroups showed that the method is not biased by the presence of slight movement artefacts, optic disc dimensions and vessel crowding (p > 0.05).ConclusionsThe presented open-source methodology provides a robust quantitative analysis of the 360˚ mVD. It shows that cpmVD, and mVD sectors measured by angioOCT, can be used in everyday glaucoma practice.