FOIB is a multidisciplinary team of engineers, scientists, clinicians, and students from different backgrounds that focuses on developing cutting-edge non-invasive cellular-level resolution imaging systems, including high-resolution optical coherence tomography/microscopy and fluorescence microscopy for imaging the living eye in humans and transgenic mice. We use a translational research approach to not only advance the understanding of disease mechanisms through transgenic mouse models but also facilitate the diagnosis and management of diseases in humans. The ultimate goal of our group is to enable longitudinal studies in transgenic mice and humans so that one can track the dynamics of cellular processes in vivo and follow up these processes over time in the same subject. The group is particularly interested in understanding the structural and physiological remodeling of the anterior segment of the eye in disease conditions such as keratoconus, Fuchs endothelial corneal dystrophy, and primary open-angle glaucoma, as well as the long-term effects of specialty contact lenses on corneal physiology.

The Cornea

The cornea is the first transparent window of the eye and is the primary area of interest in our lab

The cornea is a thin (~540 micrometers thick in humans and ~ 120 micrometers thick in mice) layer that provides 2/3 of the dioptric power of the eye and is made of five distinct layers, including the epithelium, Bowman’s membrane, the stroma, Descemet’s membrane, and the endothelium
The epithelium (~60 micrometers thick in humans and ~ 40 micrometers thick in mice) protects the eye from foreign materials and serves as a transporter of nutrients from the tear film to other layers of the cornea
Bowman’s membrane is a thin layer (~10 micrometers thick in humans and presumably non-existent in mice)
The stroma is the thickest layer of the cornea (~470 micrometers thick in humans and ~ 80 micrometers thick in mice) and is mainly made of collagen fibers, keratocytes, and water
Descemet’s membrane is a strong age-dependent thin film (~10 micrometers thick in adult humans and ~ 3 micrometers thick in adult mice) mainly made of collagen fibers serving as a basement membrane for endothelial cells
The endothelium is a monolayer of hexagonal cells (~5 micrometers thick) that maintains the cornea’s deturgescence state (i.e., the level of hydration).

The cornea is protected by a thin layer of fluid called Tear Film that keeps the cornea moist, ensuring an optically smooth corneal surface to effectively transmit light into the eye. The Tear Film also supplies nutrients to corneal tissues.

Any of these layers can be affected by a multitude of diseases, compromising its integrity and function

Optical Solutions to Enable New Discoveries in Biology

Optical imaging techniques such as optical coherence tomography (OCT) and fluorescence microscopy (FM) have enabled tremendous biological and clinical research opportunities. However, the need for enhancing technological innovations to allow a better understanding of biological processes (structural and physiological remodeling) involved in developmental and pathological conditions is still manifest.

Our research interest lies at the frontier of optics, engineering, and biology. It includes anterior segment imaging, light interaction with biological tissue, interferometry, optical metrology, optical coherence tomography, fluorescence microscopy, optical system design, and image processing.

In our research group, we strive to give trainees the opportunity to develop a multidisciplinary skills-set to help them better navigate their future career paths.

Optical Coherence Tomography/ Microscopy

Fluorescence Microscopy

Multimodal Imaging System

Transgenic Mouse Imaging

Evaluating structural and functional changes in the cornea of transgenic mouse models.

Today, scientists have powerful tools to induce genetic mutations in mouse models, enhancing our understanding of disease mechanisms. Transforming growth factor-beta (TGF-β) is crucial for corneal development, maintenance, and repair, ensuring the transparency necessary for normal vision. Disruptions in TGF-β2 pathways, studied using genetically modified animals, have been identified as significant contributors to various corneal diseases. Research in mice has demonstrated that complete deletion of TGF-β receptor type 2 (Tbr2) or downstream mediators like Smad4 results in early embryonic death and corneal thinning due to reduced keratocyte density and extracellular matrix (ECM) synthesis. Previous studies using optical coherence microscopy (OCM) in Smad4-deficient mice confirmed corneal stroma thinning and epithelial thickening, likely a compensatory response. However, the molecular mechanisms driving these changes were not fully understood. To investigate further, this study aimed to develop a multimodality optical imaging system to assess gene expression and structural changes in the corneas of transgenic mice.

The researchers integrated optical coherence microscopy (OCM) and dual-channel fluorescence microscopy (DCFM) to track the temporal and spatial distribution of gene expression in a triple transgenic mouse model (KeraRT; tet-O-Cre; RosamTmG). This model expresses red tdTomato in corneal keratocytes, which is progressively replaced by enhanced green fluorescent proteins (EGFP) upon doxycycline (Dox) treatment. Three mice were analyzed at different Dox treatment intervals (0, 9, and 47 days), showing successful EGFP activation in the corneal keratocytes of treated mice.

End results showed that the system achieved high-resolution imaging and concurrent co-registration of reflectance and fluorescence signals. Future studies will use this system to investigate TGFβ2 signaling pathways in corneal development and pathology using additional transgenic models, enabling longitudinal studies of cellular processes in the same animal.

Human Corneal Imaging

In vivo Imaging of Human Corneal Microstructures Using Self- Interference Optical Coherence Microscopy

In vivo imaging of human corneal microstructures at cellular resolution is crucial for diagnosing and managing corneal disorders. It also assists in assessing disease progression and monitoring the effectiveness of various treatments.

This study introduces the polarization-dependent optical coherence microscope (POCM) to non-invasively image the human cornea’s microstructures with high resolution and contrast. POCM leverages light polarization and self-interference between corneal layers, achieving volumetric imaging (500 x 500 x 2048 voxels) over a field of view of 0.5 x 0.5 mm², with a lateral resolution of ~2.2 μm and a volume rate of 1 Hz. It captures images at a volume rate of 1 Hz, minimizing motion artifacts. Current methods like in vivo confocal microscopy (IVCM) require contact with the eye, causing discomfort and potential alterations to corneal structure, while optical coherence tomography (OCT) has low lateral resolution. Although optical coherence microscopy (OCM) improves resolution, it faces challenges with speed and corneal curvature. In this research, POCM is used which overcomes these limitations, offering detailed, non-invasive imaging crucial for early diagnosis and treatment of corneal diseases.

As a result, our system attained an axial resolution of approximately 2.4 μm within the cornea using its standard reference arm. However, the self-interference technique improved the axial resolution to 1.4 μm, facilitated by the source and detector. This enhancement allows for high-contrast imaging of anterior corneal microstructures, eliminating issues caused by dispersion mismatch, eye movement, and corneal curvature.

Non-invasive in vivo imaging of human corneal microstructures with optical coherence microscopy

The cornea’s transparent and organized microstructures are crucial for its function and optical power. Various diseases and conditions, like keratoconus and Fuchs endothelial corneal dystrophy (FECD), can damage the cornea, leading to vision loss or blindness. Non-invasive imaging technologies at cellular resolution can detect early biomarkers of corneal diseases, aiding early intervention and monitoring.

In vivo confocal microscopy (IVCM) and optical coherence tomography (OCT) have improved our ability to visualize corneal pathologies. IVCM provides high-resolution images of corneal layers but requires contact with the eye, causing discomfort and potential structural disruption. OCT offers non-contact, three-dimensional images but has lower cellular detail and is prone to motion artifacts. Optical coherence microscopy (OCM) combines the high axial resolution of OCT with the high lateral resolution of IVCM using high numerical aperture lenses. Full-field OCM (FF-OCM) and spectral-domain OCM (SD-OCM) enhance the visualization of corneal microstructures but still face some limitations.

This study presents a non-contact polarization-dependent optical coherence microscope (POCM) for non-invasive, in vivo imaging of human corneal microstructures at a cellular level. Unlike previous techniques, POCM reduces strong reflections from the corneal surface, allowing high-contrast imaging of underlying structures like epithelial cells and the sub-basal nerve plexus. By integrating quarter-wave plates in the sample and reference arms of the interferometer, the system achieves deeper tissue penetration and reduces specular reflection from the corneal surface. A common-path approach is used to control polarization without needing a broadband polarization-maintained fiber. The POCM captures volumetric images (500 × 500 × 2048 voxels) of the cornea with a 0.5 × 0.5 mm² field of view, achieving a resolution of ∼2.2 μm at a volume rate of 1 Hz. It employs self-interference to reduce curvature and motion artifacts, enabling high-resolution imaging of various corneal microstructures, such as epithelial cells, sub-basal nerve plexus, and stromal keratocytes.

Primary Open-angle Glaucoma

Image Registration Results