MAPPING THE IRREGULAR CORNEA AND ANTERIOR SEGMENT

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Evolving systems let us do a better job managing patients with corneal disease and difficult-to-fit contact lens patients.

Each day we see patients who have irregular corneas, but thanks to evolving topography systems, we can improve diagnosing and managing corneal disease and fitting otherwise difficult-to-fit contact lens patients.

There are three types of technologies for assessing the shape of the cornea and general anterior segment, especially when prescribing contact lenses for patients with corneal irregularity: Placido-based topography, anterior segment tomography and corneo-scleral profile measurements.

Placido-Based Topography
This technology has been available for decades, and the systems are somewhat affordable.

Also, there are Placido-based topography systems that integrate other functions, such as aberrometry and dry eye diagnostic software. For example, the Oculus Keratograph 5M features a built-in color camera for external imaging. For dry eye patients, you can use the Keratograph 5M to assess the tear film, scan the meibomian glands and view morphological changes, evaluate the lipid layer and measure tear film break-up time and tear meniscus height.

Another system, the OPD-Scan III Wavefront Aberrometer from Marco not only features corneal topography, but it also includes an autorefractor, keratometer, pupillometer and an integrated wavefront aberrometer.

Keep in mind, that Placido-based topography systems measure a limited area of the cornea, and not all provide elevation data, so their usefulness is sometimes limited when fitting scleral and hybrid lenses. Also, they don’t provide information about corneal thickness, which we need for diagnosing corneal ectasia.

SCHEIMPFLUG TOMOGRAPHY

The Oculus Pentacam offers corneal thickness measurements and elevation data for evaluating patients, such as this one, who have keratoconus.

Anterior segment tomography falls into two categories: Scheimpflug imaging systems and anterior segment optical coherence tomography (ASOCT).

Examples of the Scheimpflug tomography systems are the Oculus Pentacam and the GALILEI G4 from Ziemer Ophthalmology, Scheimpflug imaging systems can measure across the entire cornea and onto the scleral surface as well as from the corneal surface to the crystalline lens of the eye.  These systems offer true elevation data and allow us to obtain global corneal thickness measurements. This is especially helpful for evaluating patients with corneal disease as well as for obtaining information about the anterior chamber angle and the configuration of the iris and pupil. Using this system, we can also evaluate the crystalline lens as cataracts develop. So, these systems are useful not only for evaluating patients with irregular corneas but also for evaluating glaucoma patients and performing calculations for cataract surgery.

The main disadvantage is cost because these systems tend to cost significantly more than Placido-based systems.

Anterior segment OCT allows us to assess the fit of this scleral lens in a patient with keratoconus.

ANTERIOR SEGMENT OCT
Anterior segment OCT is becoming much more common in optometric practice.  These multifunctional systems have very high corneal and anterior chamber resolution. They can give you the global thickness of the cornea, and they are able to analyze sclera. They’re especially useful because they allow us to see how scleral and hybrid contact lenses vault over the cornea and land on the sclera. We can assess and modify fits based upon the very high-resolution images. So that’s a great advantage for the assessment when fitting vaulting, scleral and hybrid contact lenses.

Additionally, the high-resolution anterior segment OCT images allow the clinician to document a variety of anterior segment anomalies, and newly introduced software in some systems (such as Optovue OCT) allow for measurement of corneal epithelial thickness, which is thought to show abnormalities, in keratoconus and dry eye at very early stages of the diseases.

CORNEO-SCIERAL PROFILE MEASUREMENTS
New technology is available to measure the shape of the anterior segment across the cornea and onto sclera. Examples of these corneo-scleral profiling devices include the sMap3D from Visionary Optics and the Eye Surface Profiler from Eaglet Eye.

These systems measure four quadrants and offer us the ability to simulate the design of a scleral lens that fits the contour of the eye, determine how much will vault over the cornea and how it will land on the sclera. So it creates a customized fit that is obviously advantageous since we’ve learned over the years that the scleral surface is asymmetrically astigmatic or toric.

This represents a change from the past, when we could only put a diagnostic lens on the eye and evaluate it with fluorescein staining at the slit lamp, making these systems helpful for the patient as well as the practice. OO

S. Barry Eiden, OD, FAAO, is the president and medical director of North Suburban Vision Consultant, Ltd., in Deerfield and Park Ridge, IL, and Keratoconus Specialists of Illinois. He is an adjunct faculty member at the University of Illinois, Chicago, Department of Ophthalmology, Cornea and Contact Lens Service, and at the Indiana, Illinois, SUNY, UMSL and Salus Colleges of Optometry

 

WHERE TO FIND IT:
Eaglet Eye

31.6.23.941.643 | Eaglet-Eye.com
MARCO
800.874.5274 | Marco.com
Oculus, Inc.

425.670.9977 | OculusUSA.com
Optovue
866.344.89448 | Optovue.com
Visionary Optics
877.533.1509 | Visionary.Optics.com
Ziemer
USA
866.708.4490 | ZiemerGroup.com

 

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