Quantification of scleral changes during dynamic accommodation

The mechanics of accommodation is a complex process that involves multiple intraocular ocular structures. Recent studies suggest that there is deformation of the sclera during accommodation that may also play a role in accommodation, influencing ciliary muscle contraction and contributing to the accommodative response. However, the type and magnitude of the deformations measured varies significantly across studies. We present high-resolution synchronous OCT measurements of the anterior sclera contour and thickness and lens thickness acquired in real-time during accommodative responses to 4D step stimuli. The lens thickness was used as an assessment of objective accommodation. No changes in nasal and temporal anterior scleral contour and scleral thickness were found during accommodation within the precision of our measurements. Our results demonstrate that there are no significant scleral deformations during accommodation

Automated segmentation of the ciliary muscle in OCT images using fully convolutional networks

Quantifying shape changes in the ciliary muscle during accommodation is essential in understanding the potential role of the ciliary muscle in presbyopia. The ciliary muscle can be imaged in-vivo using OCT but quantifying the ciliary muscle shape from these images has been challenging both due to the low contrast of the images at the apex of the ciliary muscle and the tedious work of segmenting the ciliary muscle shape. We present an automatic-segmentation tool for OCT images of the ciliary muscle using fully convolutional networks. A study using a dataset of 1,039 images shows that the trained fully convolutional network can successfully segment ciliary muscle images and quantify ciliary muscle thickness changes during accommodation. The study also shows that EfficientNet outperforms other current backbones of the literature

Age-related changes to the three-dimensional full shape of the isolated human crystalline lens

11 pags., 4 figs., 4 tabs.PURPOSE. Studying the full shape crystalline lens geometry is important to understand the changes undergone by the crystalline lens leading to presbyopia, cataract, or failure of emmetropization, and to aid in the design and selection of intraocular lenses and new strategies for correction. We used custom-developed three-dimensional (3-D) quantitative optical coherence tomography (OCT) to study age-related changes in the full shape of the isolated human crystalline lens. METHODS. A total of 103 ex vivo human isolated lenses from 87 subjects (age range, 0-56 years) were imaged using a 3-D spectral-domain OCT system. Lens models, constructed after segmentation of the surfaces and distortion correction, were used to automatically quantify central geometric parameters (lens thickness, radii of curvatures, and asphericities of anterior and posterior surfaces) and full shape parameters (lens volume, surface area, diameter, and equatorial plane position). Age-dependencies of these parameters were studied. RESULTS. Most of the measured parameters showed a biphasic behavior, statistically significantly increasing (radii of curvature, lens volume, surface area, diameter) or decreasing (asphericities, lens thickness) very fast in the first two decades of life, followed by a slow but significant increase after age 20 years (for all the parameters except for the posterior surface asphericity and the equatorial plane position, that remained constant). CONCLUSIONS. Three-dimensional quantitative OCT allowed us to study the age-dependency of geometric parameters of the full isolated human crystalline lens. We found that most of the lens geometric parameters showed a biphasic behavior, changing rapidly before age 20 years and with a slower linear growth thereafter.Supported by the Ministerio de Educación y Ciencia, Spain (FIS2017- 84753-R), European Research Council (ERC-2011- AdG-294099), and IMCUSTOMEYE Ref. 779960 (H2020-ICT2017-1) (SM), and European Research Council under Euro pean Union’s Horizon 2020 research and innovation programme H2020-MSCA COFUND-2015 FP-713694, MULTIPLY (AdC), Consejo Superior de Investigaciones Científicas ICoop Program, National Eye Institute (Grants 2R01EY021834, P30EY14801) (Center Grant), the Hyderabad Eye Research Foundation, Florida Lions Eye Bank and the Beauty of Sight Foundation, and an unrestricted grant from Research to Prevent Blindnes

Optical Power of the Isolated Human Crystalline Lens

PURPOSE. To characterize the age dependence of isolated human crystalline lens power and quantify the contributions of the lens surfaces and refractive index gradient. METHODS. Experiments were performed on 100 eyes of 73 donors (average 2.8 Ϯ 1.6 days postmortem) with an age range of 6 to 94 years. Lens power was measured with a modified commercial lensmeter or with an optical system based on the Scheiner principle. The radius of curvature and asphericity of the isolated lens surfaces were measured by shadow photography. For each lens, the contributions of the surfaces and the refractive index gradient to the measured lens power were calculated by using optical ray-tracing software. The age dependency of these refractive powers was assessed. RESULTS. The total refractive power and surface refractive power both showed a biphasic age dependency. The total power decreased at a rate of Ϫ0.41 D/y between ages 6 and 58.1, and increased at a rate of 0.33D/y between ages 58.1 and 82. The surface contribution decreased at a rate of Ϫ0.13 D/y between ages 6 and 55.2 and increased at a rate of 0.04 D/y between ages 55.2 and 94. The relative contribution of the surfaces increased by 0.17% per year. The equivalent refractive index also showed a biphasic age dependency with a decrease at a rate of Ϫ3.9 ϫ 10 Ϫ4 per year from ages 6 to 60.4 followed by a plateau. CONCLUSIONS. The lens power decreases with age, due mainly to a decrease in the contribution of the gradient. The use of a constant equivalent refractive index value to calculate lens power with the lens maker formula will underestimate the power of young lenses and overestimate the power of older lenses. (Invest Ophthalmol Vis Sci. 2008;49:2541-2548) DOI: 10.1167/iovs.07-1385 T he optical power of the crystalline lens is determined by the surface curvatures, the refractive index differences at the aqueous lens and lens vitreous interfaces, and the refractive index gradient distribution within the lens. 1 Studying the optical properties of the lens (i.e., optical power, refractive index distribution, and the surface refractive contributions) in vivo is difficult because of the position of the lens behind the cornea and pupil, as well as the distortions of the posterior lens surface caused by the lens refractive index gradient. Two approaches have been used to measure the lens power in vivo. In the first approach the curvatures of the lens surface and lens thickness are measured by phakometry and ultrasonic or optical biometry. The lens power is then calculated assuming an equivalent uniform refractive index (typically, ϳ1.42). 2,3 In the second approach, the lens power is calculated from measurements of axial eye length, anterior chamber depth, corneal power, and refractive state of the eye. These parameters are input into an eye model to calculate the power required for the lens to produce an optical system that matches the measurements. 3-6 Both techniques derive the lens power from measurements of other ocular parameters. Even though recent studies have cross-validated in vivo lens biometry techniques 9 -15 A comparison of in vivo -21 The isolated lens power has been shown to decrease with age

Combined anterior segment OCT and wavefront-based autorefractor using a shared beam

We have combined an anterior segment (AS) optical coherence tomography (OCT) system and a wavefront-based aberrometer with an approach that senses ocular wavefront aberrations using the OCT beam. Temporal interlacing of the OCT and aberrometer channels allows for OCT images and refractive error measurements to be acquired continuously and in real-time. The system measures refractive error with accuracy and precision comparable to that of clinical autorefractors. The proposed approach provides a compact modular design that is suitable for integrating OCT and wavefront-based autorefraction within the optical head of the ophthalmic surgical microscope for guiding cataract surgery or table-top devices for simultaneous autorefraction and ocular biometry

Paraxial equivalent of the gradient-index lens of the human eye

The lens of the eye has a refractive index gradient that changes as the lens grows throughout life. These changes play a key role in the optics of the eye. Yet, the lens is generally simulated using a homogeneous model with an equivalent index that does not accurately represent the gradient. We present an analytical paraxial model of the gradient lens of the eye that gives the direct relation between refractive index distribution and paraxial characteristics. The model accurately simulates the changes in lens power with age and accommodation. It predicts that a decrease in equivalent index with age is associated with a flattening of the axial refractive index profile and that changes in lens power with accommodation are due primarily to changes in the axial variation of the iso-indicial curvature, consistent with Gullstrand’s intracapsular theory of accommodation. The iso-indicial curvature gradient causes a shift of the principal planes compared to the homogeneous equivalent model. This shift introduces a clinically significant error in eye models that implement a homogenous lens. Our gradient lens model can be used in eye models to better predict the optics of the eye and the changes with age and accommodation

Medical Imaging Teaching Software and Dynamic Assessment Tracking System for Biomedical Engineering Program

Medical Imaging Teaching Software and Dynamic Assessment Tracking System for Biomedical Engineering ProgramBiomedical engineering (BME) education has developed as an interdisciplinary engineeringtraining area in the last 30 years. As a key training component in Biomedical Engineeringprograms, medical imaging education involves different physics principles, mathematicalderivations, and engineering implementations for image generation, reconstruction, andinstrumentation. Medical imaging techniques become increasingly crucial not only for clinicalapplications but in research laboratory as well. Recognizing the broad impacts of medicalimaging education on BME students’ career opportunities, many institutions have establishedsuch a curriculum. However, owing to the complexity of medical imaging techniques, teachingefficiency is a major obstacle for delivering the knowledge to students.Supported by a series of NSF CCLI grants through stages of proof of concept, creation ofprototype and expansion of application, we have developed an Internet based, interactiveteaching system, entitled “Medical Imaging Teaching Software (MITS) and DynamicAssessment Tracking System (DATS)”. The MITS/DATS package provides background review,text description, figure illustration, interactive animation, dynamic simulation, and applicationdemonstration for teaching five commonly used medical imaging modalities (X-ray, CT, MRI,PET and Ultrasound). Our effort has been focused on the development of animations forphysics/chemistry principles and simulations for engineering implementations. Each imagingmodality is taught or learned through five to six modules (topics). Teaching or learning proceedson the module basis. The system is integrated by the open source MySQL database software thatmanages updating teaching materials and also tracks student’s learning gain through differentassessments (see Figure of next page). Instructor gets instant feedback on the topic deliveredthrough his/her lecture when students work on the system.We have applied this teaching/tracking system in small size classes on selected imagingmodalities in last few years. The assessment result (pre/post) shows impressive learning gains inthe applications (see Table of next page). The learning gains are especially significant in conceptunderstanding. Expansion development and application are currently conducted in threeinstitutions in this metropolitan area. We plan to complete all teaching modules and apply toother institutions for BME or other engineering students.The Figure below shows the configuration of MITS/DATS package. This system isusername/password protected and Internet accessible. The assessment of student performancecan be acquired by instructor through the online database.The following table shows results from one medical imaging class (Medical Imaging Systems)for students learning X-ray and computed tomography (CT). Students who enrolled the classwere senior undergraduates (60-70%) or graduate students. Students’ academic, and courserecords (mean±SD) of before (n=23, top row) and after (n=21, bottom row) are listed in tablebelow: GPA All Prob. Concept Prob. Projects 3.42±0.34 82±9% 76±5% 82±5% *1 *2 *3 *3 3.46±0.44 89±8% 91±6% 90±6%where problems (“Prob.” in the table) in the tests and exams were “standardized” questions.Assigned projects for X-ray and CT were the same for both years. Statistical comparison(ANOVA, Single factor) of students’ cumulative GPA shows no difference between two years(*1p≤0.7), indicating similar background for all before/after students. Statistical comparison ofstudents’ correct percent rate for all questions (“All Prob.”) shows no significant difference;however, the p-value (*2p≤0.1) implies a “trend” of increased understanding to all questions(conceptual and computational). Students’ understanding improved most in conceptual questions(“Concept Prob.”) and in their projects (*3p≤0.05)