In order to maintain its optical clarity, the cornea has a complex and highly-specialized micromorphology of fibers, cells and nerves. A small malfunction in any part of this sophisticated system may lead to a range of degenerative, inherited or infectious blinding disorders. Taking into account that the largest corneal blindness burden falls on developing countries, cost-effective disease prevention through early diagnosis and treatment is preferable over surgical interventions.
Unfortunately, there are drawbacks with current scanning technologies for cornea diseases. Confocal microscopy (IVCM), the state-of-the-art tool for cellular-resolution imaging of the cornea, requires contact with the eye, preceded by ocular anesthesia. Moreover, IVCM provides only a limited field of view (FOV), well below 0.5 mm × 0.5 mm, which results in a long examination time as the clinician searches for the region of interest. Another method, conventional OCT, provides high axial resolution of corneal layers, but does not resolve cells, while UHR-OCT resolves cells, however the en face images suffer from eye movement artifacts during X–Y beam scanning.
To overcome these issues, a team at the Institut Langevin, Paris, France, recently developed in vivo full-field optical coherence tomography (FFOCT) and demonstrated its capability1 to capture images in real-time of the central human cornea, resolving features such as nerves, cells, and nuclei without touching the eye. This experimental technology leverages an Adimec CoaXPress camera linked with a BitFlow Cyton-CXP4 CoaXPress frame grabber to acquire high-resolution en face images directly without beam scanning artifacts, at a frame rate of 275 frames/s (0.6 billion pixels/s). Institut Langevin's system allows direct monitoring of blood flow dynamics, and enables creation of high-resolution velocity maps. Custom programs written in Labview 2014 and Thorlabs SpectralRadar SDK were used for FFOCT and SDOCT image acquisition and display, peak detection and motor control. Illumination is provided by an NIR 850 nm light-emitting diode (LED) source with light collected by an aspheric condenser lens.
Both the Adimec camera and the BitFlow frame grabber are designed for CoaXPress (CXP), the world’s leading standard for high-speed imaging in professional and industrial imaging applications. CoaXPress combines the traditional simplicity of coaxial cable with state of the art high-speed serial data technology. The combination of these two features – coaxial cable and “express” speed – provides a highly desirable solution for high-speed imaging and data transmission. The latest version delivers a downlink of up to 12.5 Gbps per cable for video, images and data, plus a lower speed uplink up to 42 Mbps for communications and control. Power is also available over the cable (“Power-over-Coax”).
"CoaXPress imaging allowed our team to demonstrate real-time, millimeter-field movies of central and peripheral in vivo corneas that consistently reveal cells and nerves, which can be quantified according to the existing medical protocols used for IVCM," explained Viacheslav Mazlin, a researcher with Institut Langevin. "We can have access to the same information as IVCM and view cornea blood flow with high contrast, with the examination taking only a fraction of a second."
Along with revealing the same micrometer corneal features as IVCM in a non-contact way, the newly developed system does not require use of any medication and is immune to beam scanning artifacts. These advancements improve patient comfort, removes risk of corneal damage and risk of infection, and opens up the possibility for high-resolution imaging in a risk-sensitive population such as young children and candidates for corneal transplant surgery with fragile corneas. It also provides images with three times larger field of view than IVCM, which makes it easier to locate the clinical area of interest and follow the same location over time. It also opens a door to quantitative diagnosis of dry eye condition by providing information about tear film velocity and stabilization time following a blink, the evaporation time of the liquid micro-droplets on the surface of the eye, and potentially the thickness of the tear film.
