Human eye sclera detection and tracking using a modified time-adaptive self-organizing map

This paper investigates the use of time-adaptive self-organizing map (TASOM)-based active contour models (ACMs) for detecting the boundaries of the human eye sclera and tracking its movements in a sequence of images. The task begins with extracting the head boundary based on a skin-color model. Then the eye strip is located with an acceptable accuracy using a morphological method. Eye features such as the iris center or eye corners are detected through the iris edge information. TASOM-based ACM is used to extract the inner boundary of the eye. Finally, by tracking the changes in the neighborhood characteristics of the eye-boundary estimating neurons, the eyes are tracked effectively. The original TASOM algorithm is found to have some weaknesses in this application. These include formation of undesired twists in the neuron chain and holes in the boundary, lengthy chain of neurons, and low speed of the algorithm. These weaknesses are overcome by introducing a new method for finding the winning neuron, a new definition for unused neurons, and a new method of feature selection and application to the network. Experimental results show a very good performance for the proposed method in general and a better performance than that of the gradient vector field (GVF) snake-based method.     

飞秒激光对离体兔巩膜的光离解作用

为探索飞秒激光在兔眼巩膜上产生光离解作用的可行性,并寻找适当的激光切割方式及相关参数,将不同脉冲能量的飞秒激光(800nm/50fs)聚焦后作用于离体兔眼巩膜。通过计算机控制的三维平台的定向移动,飞秒激光能够在兔眼巩膜上完成打孔、蛇形扫描和线性切割三种方式的光离解作用。应用光学显微镜和扫描电镜(SEM)观察激光作用后巩膜的形态学变化,并用Nd∶YAG激光作为对比。实验结果表明,飞秒激光经过显微物镜(NA0.2)聚焦后,当其功率密度达到或超过9.55×1014W/cm2,脉冲能量在37.5~125μJ变化时,激光以0.1mm/s的速度线性扫描巩膜能形成深度为30~70μm的沟道;当激光的功率密度减小至7.96×1014W/cm2,脉冲能量小于31.25μJ/pulse时,在相同条件下却不能产生光离解作用。与Nd∶YAG激光相比,飞秒激光在兔眼巩膜上切割瘘道的内壁更加光滑整齐,对周围的组织损伤更小。飞秒激光对离体兔眼巩膜高精度和微创伤的光离解作用,预示了它在未来青光眼治疗中有潜在的应用价值。     

Residual deformations in ocular tissues

Residual deformations strongly influence the local biomechanical environment in a number of connective tissues. The sclera is known to be biomechanically important in healthy and diseased eyes, such as in glaucoma. Here, we study the residual deformations of the sclera, as well as the adjacent choroid and retina. Using freshly harvested porcine eyes, we developed two approaches of quantifying residual deformations in the spherically shaped tissues of interest. The first consisted of punching discs from the posterior wall of the eye and quantifying the changes in the area and eccentricity of these samples. The second consisted of cutting a ring from the equatorial sclera and making stress-relieving cuts in it. Measurements of curvature were made before and after the stress-relieving cuts. Using the first approach, we observed a 42% areal contraction of the choroid, but only modest contractions of the sclera and retina. The observed contractions were asymmetric. In the second approach, we observed an opening of the scleral rings (approx. 10% decrease in curvature). We conclude that residual bending deformations are present in the sclera, which we speculate may be due to radially heterogeneous growth and remodelling of the tissue during normal development. Further, residual areal deformations present in the choroid may be due to the network of elastic fibres in this tissue and residual deformations in the constituent vascular bed. Future studies of ocular biomechanics should attempt to include effects of these residual deformations into mechanical models in order to gain a better understanding of the biomechanics of the ocular wall.     

Creep of the eye sclera

 Irreversible stretching (creep) of the eye sclera, considered as a cause of the high myopia, has been studied experimentally. Both dramatic acceleration and significant deceleration of the sclera creep have been observed in the presence of some enzymes. Creep of various connective tissues caused by static and cyclic mechanical stresses (gravity, blood pressure, etc.) can manifest in many age and pathological changes in human body. Authors express the hope that investigations in this area and finding appropriate inhibitors may replace surgery (eye, cosmetic) by prophylactic therapy. Received: 21 July 1998 / Accepted: 28 August 1998     

Two‐photon microscopy of deep intravital tissues and its merits in clinical research

Multiphoton excitation laser scanning microscopy, relying on the simultaneous absorption of two or more photons by a molecule, is one of the most exciting recent developments in biomedical imaging. Thanks to its superior imaging capability of deeper tissue penetration and efficient light detection, this system becomes more and more an inspiring tool for intravital bulk tissue imaging. Two‐photon excitation microscopy including 2‐photon fluorescence and second harmonic generated signal microscopy is the most common multiphoton microscopic application. In the present review we take diverse ocular tissues as intravital samples to demonstrate the advantages of this approach. Experiments with registration of intracellular 2‐photon fluorescence and extracellular collagen second harmonic generated signal microscopy in native ocular tissues are focused. Data show that the in‐tandem combination of 2‐photon fluorescence and second harmonic generated signal microscopy as two‐modality microscopy allows for in situ co‐localization imaging of various microstructural components in the whole‐mount deep intravital tissues. New applications and recent developments of this high technology in clinical studies such as 2‐photon‐controlled drug release, in vivo drug screening and administration in skin and kidney, as well as its uses in tumourous tissues such as melanoma and glioma, in diseased lung, brain and heart are additionally reviewed. Intrinsic emission two‐modal 2‐photon microscopy/tomography, acting as an efficient and sensitive non‐injurious imaging approach featured by high contrast and subcellular spatial resolution, has been proved to be a promising tool for intravital deep tissue imaging and clinical studies. Given the level of its performance, we believe that the non‐linear optical imaging technique has tremendous potentials to find more applications in biomedical fundamental and clinical research in the near future.     

Biomechanics of the optic nerve head and peripapillary sclera in a mouse model of glaucoma

The deformation of the mouse astrocytic lamina (AL) and adjacent peripapillary sclera (PPS) was measured in response to elevated intraocular pressure. We subjected explanted mouse eyes to inflation testing, comparing control eyes to those 3 days and 6 weeks after induction of ocular hypertension (OHT) via ocular microbead injection. Laser scanning microscopy was used with second harmonic generation to image the collagenous PPS and two-photon fluorescence to image transgenic fluorescent astrocytes in the AL. Digital volume correlation was applied to calculate strains in the PPS and AL. The specimen-averaged strains were biaxial in the AL and PPS, with greater strain overall in the x- than y-direction in the AL and greater strain in the θ- than the r-direction in the PPS. Strains increased after 3-day OHT, with greater strain overall in the 3-day AL than control AL, and greater circumferential strain in the 3-day PPS than control PPS. In the 6-week OHT eyes, AL and PPS strains were similar overall to controls. This experimental glaucoma model demonstrated a dynamic change in the mechanical behaviour of the AL and PPS over time at the site of neuronal injury and remodelling in glaucoma.     

Detection of eye strain through blink rate and sclera area using raspberry-pi

In this paper, a unique approach is proposed to determine eye strain in children caused due to the prolonged exposure to LCD and PDP screens. Blink rate and area of eye sclera are the two efficient metrics relied upon to determine eye strain. Initially, blink rate is computed by monitoring state transitions from open to closed eyes. To segment the sclera region of the eye Otsu’s thresholding and colour tracking, were implemented. These approaches had limitations due to illumination and skin tone. To overcome this, Modified Otsu using Colour Tracking is proposed in this paper. The occurrence of eye strain is determined by comparing the values of the metrics derived in real time with a threshold. The proposed algorithm detects eye strain with an accuracy of 83%. After detection of fatigue an alert message is sent to caretakers.     

基于高斯眼白模型的疲劳驾驶检测

目的 为解决疲劳驾驶检测中人眼状态识别的难点,提出一种基于眼白分割的疲劳检测方法。方法 首先对获取图像进行人脸检测,利用眼白在Cb-Cr上良好的聚类性,基于YCbCr颜色空间建立高斯眼白分割模型;然后在人脸区域图像内做眼白分割,计算眼白面积;最后将眼白面积作为人眼开度指标,结合PERCLOS（percentage of eyelid closure over the pupil over time）判定人的疲劳状态。结果 选取10个短视频进行采帧分析,实验结果表明,高斯眼白分割模型能有效分离眼白,并识别人眼开合状态,准确率可达96.77%。结论 在良好光线条件下,本文方法能取得不错的分割效果;本文所提出的以眼白面积作为判定人眼开度的指标,能准确地判定人的疲劳状态。实验结果证明了该方法的有效性,值得今后做更深入的研究。     

Anterior eye shape in emmetropes,low to moderate myopes,and high myopes

PurposeMyopia prevalence has increased in recent years, including the levels of high myopia. While myopia has been associated with scleral remodelling and changes in posterior scleral shape, there has been little research examining how myopia affects in-vivo anterior sclera shape. We compared anterior scleral shape in emmetropes, low to moderate myopes, and high myopes.MethodsIn this prospective study, the Eye Surface Profiler instrument was used to quantify anterior eye surface shapes of forty-five young adult participants (58 % females) aged between 18 and 35 years, including 15 emmetropes, 15 low to moderate myopes, and 15 high myopes. Sagittal height and axial radius of curvature of regions over the nasal and temporal corneal periphery and anterior sclera were exported and analysed.ResultsAfter quality control of the data, 39 and 43 subjects had data analysed from the nasal and temporal sides, respectively. The nasal sides of the surfaces of the corneal periphery and anterior sclera had greater sagittal height in high myopes than in emmetropes across all regions (mean sagittal heights 2.44 ± 0.07 and 2.21 ± 0.04 mm, respectively, p = 0.02), but no significant differences were found between low to moderate myopes with emmetropes or with high myopes. No significant refractive group differences occurred for temporal anterior eye surface height. High myopes’ nasal-temporal asymmetry of sagittal height was less than of emmetropes (means 0.20 ± 0.07 and 0.46 ± 0.06 mm, respectively, p = 0.02). High myopes also exhibited less nasal-temporal axial radius of curvature asymmetry than emmetropes (mean 0.35 ± 0.08 and 0.71 ± 0.08 mm, respectively, p = 0.01) across all regions.ConclusionsHigh myopes exhibited a different anterior eye surface shape than emmetropes, having greater sagittal height in the nasal corneal periphery and anterior sclera. There was less nasal-temporal asymmetry of sagittal height and axial radius of curvature in high myopes than in emmetropes. Asymmetric growth of the eye associated with myopia development may be the underlying reason. These findings have implications for design of contact lenses, particularly soft and larger rigid lenses such as mini-sclerals.     

Experimental evaluation of the viscoelasticity of porcine vitreous

This study aims to estimate the material properties of the porcine vitreous while testing it in close to its natural physiological conditions. Eighteen porcine eyes were tested within 48 h post-mortem. A custom-built computer-controlled test rig was designed to support, load and monitor the behaviour of eye globes while being subjected to dynamic rotation cycles mimicking saccade eye movement. Specimens were glued to the base of a container, surrounded by gelatin, frozen and cut in half to expose the vitreous. After thawing, the container was subjected to concentric dynamic rotations of up to 5°, 10° or 15°, while taking 50 MP photos of the specimen every 2 ms. The images were analysed by a digital image correlation algorithm to trace the movement of marked points on the vitreous surface with different radii from the centre of the posterior chamber. The initial camera image was used in building a finite-element model of the test set-up, which was used in an inverse analysis exercise to estimate the material properties of the vitreous. Angular displacements of the monitored points were up to 3.3°, 4.1° and 3.9° in response to eye rotations of 5°, 10° and 15°, respectively. With the experimental relationships between eye rotation and angular displacements used as target behaviour, the inverse analysis exercise estimated the initial shear modulus, the long-term shear modulus and the viscoelastic decay constant of the porcine vitreous as 2.10 ± 0.15 Pa, 0.50 ± 0.04 Pa and 1.20 ± 0.09 s⁻¹, respectively. Consideration of the viscoelasticity of the vitreous was essential to represent its experimental behaviour. Testing the vitreous in close to its normal physiological conditions produced estimations of the initial shear modulus and long-term shear modulus that were, respectively, smaller and larger than reported values (Zimberlin et al. 2010 Soft Matter 6, 3632–3635. (doi:10.1039/b925407b), Liu et al. 2013 J. Biomech. 46, 1321–7. (doi:10.1016/j.jbiomech.2013.02.006), Rossi et al. 2011 Invest. Ophthalmol. Vis. Sci. 52, 3994–4002. (doi:10.1167/iovs.10-6477)).