VISANTE OCT: ANTERIOR SEGMENT IMAGING AND BIOMETRY

OCT Gets Customized For the Anterior Segment

A proven technology for posterior segment imaging and analysis has been optimized for the front of the eye.

By Roger F. Steinert, M.D.

Given its micron resolution, millimeter depth penetration and cross-sectional imaging capabilities, optical coherence tomography (OCT) is a technology particularly useful for ophthalmic applications. Already, vitreoretinal specialists consider it an indispensable diagnostic and management tool. Now, the same technological expertise that brought posterior segment physicians the Stratus OCT system has been used to create a high-resolution, noncontact OCT system customized for the anterior segment.

The new Visante OCT is a versatile tool that:

■ Provides detailed images of the anterior chamber, including the cornea, iris, angle and lens

■ Measures anterior-chamber depth, anterior-chamber angles and anterior-chamber diameter (angleto-angle distance)

■ Produces high-resolution images of the cornea and stroma

■ Rapidly acquires pachymetry data to create accurate and repeatable thickness maps

■ Images, measures and documents corneal flap thickness and residual stromal thickness after LASIK.

These capabilities support ocular health evaluation, surgical planning and postoperative care for a wide range of applications, including corneal refractive surgery, phakic and pseudophakic IOL implantation and glaucoma.

The Importance of Wavelength

Both the Stratus OCT and the Visante OCT use interferometry to measure the time it takes for light to be reflected back from ocular tissue compared with the time it takes for light to be reflected back from a reference mirror. Multiple A-scans are combined to form two-dimensional images of ocular structures. The process is similar to B-scan ultrasound, but light is used instead of sound, contact with the eye is not necessary, and the resulting images are higher resolution.

The Stratus OCT operates at the 820-nm wavelength, which is optimal for retinal imaging. The Visante OCT, on the other hand, operates at the 1310-nm wavelength. The longer wavelength decreases retinal exposure so more energy can be delivered safely and much faster at the same signal-to-noise ratio, which minimizes patient motion artifact. The Visante OCT performs 2,000 A-scans per second versus 400 with the Stratus OCT. Also, reduced scattering with the 1,310-nm wavelength improves penetration into turbid sclera, iris and angle tissue.

Imaging the anterior segment at the 820-nm wavelength had been tried, but poor penetration through the sclera obscured the details of the angle. Furthermore, motion error from the slower scanning speed created a wavy surface appearance.

Scan Profiles and Resolution

The scan profiles of the Visante OCT and the Stratus OCT also differ. Vistante OCT scans are larger — 16 × 6 mm or 10 × 3 mm rather than 4 or 6 mm × 2 mm — so that high-resolution/high-magnification imaging of the cornea alone and imaging of the entire anterior segment can be accomplished. Finally, the Visante OCT has an axial resolution of 18 μm and a transverse (center) resolution of 60 μm.

Higher axial resolution and other enhancements to the Visante OCT system are under development and will further improve the utility of this exciting technology for practices providing anterior-segment care. OM