LASIK Eye Surgery – Stockton, Modesto, Tracy, Merced, Manteca
Visante OCT Technical Information

Visante Anterior Segment Optical Coherence Tomography

Scan Speed: 8 frames / sec

Scan Sizes:

    Hi Res Mode: 10 x 3 mm – 512 scans

    Standard Mode: 16 x 6 mm – 256 scans

Scan Time:

    Hi Res Mode: 250 ms

    Standard Mode: 125 ms

OCT Scan Beam Wavelength: 1310nm

Resolution:

    Axial / Depth: 18 microns

    Lateral / Transverse: 60 microns

Optometer range (accommodation): -35 Diopters to +20 Diopters

Why 1310nm?

The 1310nm is the standard light used in the Visante OCT. Most other OCT's use the 820nm light. The 820nm has excellent penetration and little absorption by water. This is a great feature when trying to examine the retina. The 1310nm has greater absorption by water and significant more scattering. This causes a 20 times reduction in its exposure to the retina. Consequently, the signal can be amplified 20 times more and have similar retinal exposure. This 20 fold increase in the signal intensity allows for faster image processing. This results in significant reduction in motion artifact. Additionally, the 1310nm has the capacity to penetrate through turbid tissue such as sclera and opaque cornea.

 

The image on the right is an OCT obtained using an 820nm can. It can be noted that the angle structures are not visible. The image at the bottom using the 1310nm Visante clearly shows the angle.  This is also true for corneas that are opacified, where the 820nm scan has little penetration capacity.

 

The image on the right is an OCT obtained using an 820nm scan. The relative slow speed of obtaining the image creates great motion artifact. The slow speed may be fine for the smaller area scan of the retina, but not adequate for the anterior segment. The 1310nm image below of the anterior segment show minimal to no motion artifact.

The Visante OCT is the only anterior segment OCT imaging system that has a 16 mm wide span of scanning.  This is essential in proper evaluation of the angles as well as important review of the relationship of the anterior segment structures.  Most other systems are based on the 820nm light system and have a very small size view.  The above 2 limit their capacity to view the Angle properly or see through an opacified cornea as well as allow for proper determination of relationship of anterior segment structures.

The Pachymetric Map may be obtained in either 8 scans or 16 scans.  The 16 Scans is the standard that I always use.  The 8 scan was one that was initially installed on the Visante 1.0 system and has become largely replaced in clinical practice with the 16 Scan Global Pachymetric Map.  The Global Pachymap is acquired in 1.0 seconds with 16 scans of modified high resolution image that is 10mm by 3mm in size with 128 scan spots.  That translates to acquisition of 2048 pachymetric data points.

In the Visante 3.0 system, there is now a data link that had been created between the ATLAS Topographer and the Visante OCT.  This data link is maintained through an ethernet system using CAT-5 wires.  The data is imported from the ATLAS Topographer (compatible systems are the ATLAS 993, 995 and 9000)automatically at set intervals (I have mine set at 30 seconds).  The new combined system is called the Visante omni.

The Visante omni uses the Anterior Elevation Data from the ATLAS and the Pachymetric data to calculate the Posterior Elevation information.  This combined information provides a wealth of information in considering early corneal changes and is specially useful in evaluation of candidates for LASIK eye surgery.

 

Page written on 082409 – still under construction

In addition to performing LASIK, Dr. Ash offers advanced cataracts treatments. In fact, he is a leading Modesto and Stockton cataracts surgeon.