TECHNOLOGY FOR ASSESSING CORNEAL HEALTH

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Heidelberg’s Spectralis Anterior Segment Module provides high-resolution images of cornea, anterior chamber angle, and sclera.

The rise of anterior segment technology provides many benefits when it comes to evaluating various corneal conditions.

Today’s optometric practices are finding a place for both anterior segment optical coherence tomography (AS-OCT) and corneal topography technologies to evaluate the anterior segment of the eye. Here’s why.

AS-OCT

Optometrists are familiar with OCT as an important technology for analyzing the retina and optic nerve. In recent years, it has become a valuable tool for evaluating the anterior segment as well. Anterior segment OCT (AS-OCT) can image the cornea, anterior chamber, crystalline lens, and iris, providing many clinical applications. Doctors who embrace this technology can find it beneficial for managing glaucoma and anterior segment disease, as well as refractive surgery patients.

Many doctors use AS-OCT to assess angle structure in glaucoma patients with narrow or suspicious angles. When angles are narrow, the cross-sectional views obtained without having to perform gonioscopy are very useful. If the doctor is suspicious of a narrow or occludable angle, an AS-OCT in both light and dark illumination can reveal the structural changes that occur in darkness. This offers information that cannot be seen in the slit lamp using gonioscopy, which requires some illumination.

Practitioners will find that AS-OCT can also be helpful with patient education. It’s easier for patients to understand how the angle can be blocked when they can see an image that shows the trabecular meshwork and a narrow angle. Explaining why an iridotomy is necessary and how it works can be easier when patients are looking at scans of their own eye rather than an eye model.

Additionally, AS-OCT is a valuable instrument for LASIK surgeons and doctors both before and after surgery. Pachymetry maps showing corneal thickness measurements can be very helpful in detecting abnormal corneas. With the ability to detect focal steepening and early focal corneal thinning, patients with forme fruste keratoconus can be eliminated as LASIK candidates. This technology is also helpful when a LASIK patient needs an enhancement. Both flap thickness and residual stromal thickness can be measured to confirm that an ablation would be safe. It also helps confirm there is not ectasia following LASIK.

The Visante® OCT 3.0 from Carl Zeiss Meditec, Inc. includes a corneal flap tool that documents flap thickness and residual bed thickness along the entire ablation zone. The latest update to this time domain system is the Visante omni anterior segment evaluation—making it one of the first systems to combine OCT and Placido disk technologies. Integrating proven anterior topography from the company’s ATLAS Corneal Topographer with precision OCT pachymetry, Visante omni provides comprehensive anterior and posterior topography with pachymetry analysis for improved patient care. The Visante OCT uses a non-contact technique to provide sharp, highly detailed images and precise biometrics of the anterior segment, including corneal shape and angle information.

The anterior segment imaging in Optovue’s iVue provides angle visualization, tear film
analysis, contact lens analysis, and pachymetry.

 
The iVue® Spectral-Domain OCT (SD-OCT) from Optovue Inc. offers retina, glaucoma, and anterior segment scanning. This is one of the smallest, most compact SD-OCTs in the world. The Anterior Segment imaging capabilities are non-contact and include angle visualization and measurement, contact lens evaluation, and a full 6mm diameter color-coded Pachymetry Map with minimum thickness marker. In addition to Pachymetry Mapping, a user-defined corneal point thickness allows documentation of the flap and residual bed thickness along the ablation zone.

The U.S. FDA recently granted clearance for Heidelberg Engineering, Inc.’s new Spectralis® Anterior Segment Module (ASM). The ASM provides high-resolution images of cornea, anterior chamber angle and sclera utilizing unique Heidelberg Noise Reduction™ technology for enhanced detail. Practitioners can assess both chamber angles at the same time using 16mm-wide angle-to-angle OCT scan.

TOPOGRAPHY
Corneal topography has become common in eyecare for corneal measurements. By assisting in diagnosis of corneal irregularities, contact lenses fittings and pre- and post-operative refractive surgery, it has an important place in every practitioner’s office.

There are two types of topography systems on the market— reflection-based and projection-based systems.

Reflection-based systems assume the cornea behaves as a mirror. A Placido disc reflects rings off the corneal surface and the distance between the reflected rings is recorded.

HIGH-RES BIOMETRY Anterior segment optical coherence tomography has become the best tool for high-resolution biometry. Uses include mapping of corneal thickness and keratoconus evaluation; measurement of LASIK flap and stromal bed thickness; visualization and measurement of anterior chamber angle and diagnosis of narrow angle glaucoma; measuring the dimensions of the anterior chamber and assessing the fit of intraocular lens implants; and visualizing and measuring the results of corneal implants and lamellar procedures.

Projection-based systems are a good choice for larger anterior segment practices. These systems measure elevation by locating actual points in space through triangulation. In addition to front surface curvature values and elevations, projection-based systems also measure the posterior cornea. These systems can also calculate pachymetry values, angle measurements, epithelium, and LASIK flap measurements.

The following are examples of some corneal topographers available.

Introduced at Vision Expo West, the new OCULUS Keratograph 5M is an advanced corneal topographer with a built-in real keratometer and a color camera optimized for external imaging. Unique capabilities include examining the meibomian glands, non-invasive tear film break-up time, and tear meniscus height measurement, and also assessing the lipid layer and automatic bulbar redness classification.

The new OCULUS Keratograph 5M corneal topographer features a built-in keratometer and color camera optimized for external imaging.

The OCULUS Pentacam® provides the topography and elevation maps for the front and back surface of the cornea as well as non-contact pachymetry data. Additional software modules provide anterior chamber depth, chamber angles and volume information, early keratoconus detection capability, and more.

The OPD-Scan III from Marco collects autorefraction, keratometry, pupillometry, corneal topography, and wavefront aberrometry measurments. Blue light, 33 ring, placido disc topography is easier for patients to tolerate.

Topcon Medical Systems, Inc.’s five-in-one1 KR-1W Wavefront Analyzer boasts the combined technologies of wavefront aberration, corneal topography, autorefraction, keratometry, and pupillometry. The system features full auto-alignment, wavefront image sequence, and simulated visual acuity assessment.

NIDEK Inc.’s Magellan Mapper (MM-1) corneal topographer is ergonomically designed to offer easy camera alignment and reduced examination time. Klyce Corneal Navigator™ screens nine different corneal conditions, including pellucid marginal degeneration and keratoconus.

The many applications of AS-OCT and topography can make a significant difference in diagnosing, monitoring progression, and clinical decision-making. In the ever-changing world of eyecare, integrating anterior segment technology will help both your patients and your practice when it comes to evaluating corneal health.


Eric L. Bran, Professional Editor for Optometric Office, is in a private group practice in Ridgefield, CT.


WHERE TO FIND IT:

Carl Zeiss Meditec, Inc. • 800-929-1431 ext. 1009 • meditec.zeiss.com/usa
Heidelberg Engineering, Inc. • 800-929-1431 ext. 1042
heidelbergengineering.com
OCULUS, Inc. • 800-929-1431 ext. 1027 • oculususa.com
Optovue Inc. • 800-929-1431 ext. 1028 • optovue.com
Marco • 800-929-1431 ext. 1021 • marco.com
NIDEK Inc. • 800-929-1431 ext. 1026 • usa.nidek.com
Topcon Medical Systems, Inc. • 800-929-1431 ext. 1041topconmedical.com


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