March 2019

COVER FEATURE

Refractive corrections
Obtaining earlier keratoconus diagnoses


by Rich Daly EyeWorld Contributing Writer



A suspect for keratoconus because high irregular astigmatism is truncated. The thickness maps suggest keratoconus, but this is probably a very central cone, which tricks the device’s artificial intelligence.

Belin/Ambrosio Enhanced Ectasia display, which is used to detect earlier keratoconic changes, shows the patient is relatively normal.

Anterior segment OCT thickness maps look normal, but the epithelial thickness map shows the epithelium has remodeled in order to hide the extremely central cone.
Source (all): John Kanellopoulos, MD

 

“In many cases it can be difficult to identify early keratoconus in patients who are interested in LASIK. Advances in imaging technologies help us evaluate the cornea and define keratoconus as early as possible.”
—William Trattler, MD


Surgeons identify keys to earlier diagnosis of keratoconus patients

A growing number of tools and a better understanding of keratoconus are helping physicians diagnose the progressive disease at earlier stages.
“Currently, the earliest stage that can be diagnosed with a reasonable degree of certainty would be what is called ‘subclinical keratoconus,’” said Michael Belin, MD, professor of ophthalmology and vision science, University of Arizona, Tucson, Arizona. “This is true disease and should not be confused with ‘suspect’ or ‘form fruste.’”
Subclinical keratoconus has abnormalities on the posterior corneal surface or changes in corneal thickness compatible with keratoconus, such as abnormal pachymetric progression. It remains subclinical because the anterior surface remains normal and the patient retains good visual acuity, Dr. Belin said.
Renato Ambrósio Jr., MD, adjunct professor of ophthalmology, Federal University of the State of Rio de Janeiro (UNIRIO), Brazil, said the terms “subclinical,” “fruste” and “mild” are confusing since the clinical literature applies them to different conditions.
“There is no easy agreement on these definitions,” Dr. Ambrósio said. “We have learned a lot from the very asymmetric ectasia (VAE) cases in which one eye presents with normal front surface topography. However, some of these VAE cases are truly unilateral. Interestingly, while keratoconus typically presents as an asymmetric disease, this is by definition bilateral. With advanced corneal imaging including the integrated tomography and biomechanical assessment, we can detect very mild disease in the majority of these cases.” Prospective studies are needed to clarify the issue, Dr. Ambrósio said.
A. John Kanellopoulos, MD, medical director, LaserVision Clinical and Research Eye Institute, Athens, Greece, and clinical professor of ophthalmology, New York University Medical School, New York, has published numerous studies on the issue and concluded that in its earliest stages the corneal epithelium will thicken overall. That could mean that a normally 50- to 52-micron epithelial thickness may increase up to an average of more than 58 microns prior to creating irregularities.
“Overall epithelial thickening may be an early sign of corneal biomechanical instability. If the ectasia progresses, and as it is almost always associated with vigorous eye rubbing, the epithelium remodels to eventually thin over the area of thinning and ‘bulging’ stroma and thickening around it as a means to keep the anterior cornea surface smooth and thus the optics of the eye at their best,” Dr. Kanellopoulos said.
In such early stages, topography and tomography cannot yet pick up any irregularity, especially if the ectasia is central. Instead, epithelium mapping provided by anterior segment OCT and/or high frequency ultrasound shows what is normal, what is epithelial distribution in dry eyes, and what is epithelial distribution in keratoconus.
“You would be surprised how many patients pass with flying colors the Placido disc topography and the Scheimpflug-based tomography to be flagged red with epithelium mapping, an easy capture by anterior segment OCT devices such as the Avanti [Optovue, Fremont, California],” Dr. Kanellopoulos said.

Available tools

Identifying keratoconus at an early stage is critical, since the condition can progress if a patient undergoes corneal refractive surgery, said William Trattler, MD, Center for Excellence in Eye Care, Miami.
“In many cases it can be difficult to identify early keratoconus in patients who are interested in LASIK. Advances in imaging technologies help us evaluate the cornea and define keratoconus as early as possible,” Dr. Trattler said. “Early keratoconus may not be obvious on a standard Placido disc topography, but there are some technologies we can use that will help us identify it at an early stage.”
Like many clinicians, Dr. Trattler uses tomography to examine the cornea for keratoconus in its very early stages. One pattern, called a truncated bow tie, can present with a normal topography without inferior steepening. The condition can be identified on the Percentage Thickness Increase (PTI) map on the Pentacam (Oculus, Wetzlar, Germany), which compares the relative thickness between the central cornea and the peripheral cornea. Another early keratoconus sign can be identified with epithelial thickness maps, which can highlight an area of epithelial thinning over the apex of an early cone with both OCT and high frequency ultrasound. Another diagnostic modality evaluates the dynamic strength (or weakness) of the cornea with a jet of air.
“Corneas with keratoconus are more flexible, and both the Corvis ST [Oculus] and Ocular Response Analyzer [Reichert Technologies, Depew, New York] use software to interpret the movements of the cornea after exposure to a jet of air to help identify early keratoconus,” Dr. Trattler said.
However, Dr. Kanellopoulos said he has found the air puff technology can provide a lot of false positives and false negatives for keratoconus.
Additionally, Dr. Kanellopoulos said Brillouin-based technology, which is light scattering microscopy, may provide another clinical tool to assess cornea biomechanics to obtain an earlier diagnosis “but in the stage we are now, it is quite early.”
Dr. Belin’s primary means for screening and diagnosing keratoconus is anterior segment tomography, especially Scheimpflug devices, which provide the best corneal coverage, are easy to use, and are in most corneal or refractive practices. Additionally, Dr. Belin uses the Belin/Ambrosio Enhanced Ectasia display on the Pentacam to detect earlier keratoconic changes.
Dr. Ambrósio said the integrated tomography and biomechanical assessment with the Ambrósio, Roberts & Vinciguerra display using artificial intelligence has enhanced the accuracy to detect abnormalities among cases with normal topography (front surface curvature) and tomography. This approach is available with the Pentacam and the Corvis ST.

Age detection

Although about 60% of keratoconus patients are male, all patients should be screened, Dr. Trattler said. That is especially true if they experience changes in refraction.
It can be difficult to test very young patients with topography and tomography, and the youngest Dr. Trattler is able to reliably test range from 7 to 9 years old.
Dr. Ambrósio urged screening patients beginning at 4 or 5 years old, depending on the cooperation of the child.
Improved treatments have changed the paradigm in keratoconus screening, Dr. Kanellopoulos said. The advent of corneal crosslinking, which can halt progression of the disease and even reverse some of its manifestations, has made screening patients pivotal to prevent young adults or teenagers suffering from severe visual debilitation related to keratoconus. The ideal screening age is 16 or 17 years old, especially for males, but Dr. Kanellopoulos images the cornea of every patient evaluated in the office for any reason.
Dr. Kanellopoulos also pursues scans for relatives of known patients with keratoconus.
Additionally, it is important to educate optometrists and ophthalmologists on the need for screening.
Dr. Ambrósio agreed on the need for enhanced corneal imaging technologies, especially for high-risk patients such as children who rub their eyes and family members of keratoconus patients.
“The clinician should do what is available, but ideally, every child should have corneal imaging tests done, and these should be stored in a database for future reference comparison,” Dr. Ambrósio said.

Patient education

Post-diagnosis, the first step in patient education for Dr. Trattler is to address eye rubbing, which is a known risk factor.
“I have them do what they can to avoid eye rubbing, although that’s difficult because eye rubbing is a habit that can be hard for some patients to modify or eliminate,” Dr. Trattler said.
Dr. Ambrósio also agreed with the importance of educating patients not to rub the eye so as not to cause nocturnal eye pressure.
Dr. Trattler also talks to patients with keratoconus about the importance of the crosslinking procedure to strengthen the cornea to prevent progression of their condition.
Dr. Kanellopoulos’ post-diagnosis approach is tailored to the patient’s age, the residual cornea thickness at the thinnest part of the cornea, and the level of patient functioning.
For instance, among patients 15 to 25 years old, Dr. Kanellopoulos focuses on not letting them slip through and progress rapidly. But he examines patients older than 35 years old every 1 or 2 years or more if their symptoms change.
“Under the same token, if the cornea thickness is less than 450 microns, I am much more aggressive and follow these patients closely, every 3 months, and recommend crosslinking with our Athens protocol, which appears to be the most effective and the most productive way to correct these eyes, even if the ablation is minimal,” Dr. Kanellopoulos said.
Patients who refract even to 20/25 but who are unable to drive comfortably and do their daily chores are candidates for treatment.

Moving to crosslinking

For Dr. Belin, moving to performing to crosslinking varies on the age of the patient and the severity of the disease.
“The younger the patient, typically the more aggressive the disease is, and there is a good argument to crosslink children when a definitive diagnosis is made,” Dr. Belin said. “On the other hand, in adults, we often monitor for disease progression.”
Monitoring requires tomographic evaluation, as many patients show progression despite appearing to have a stable anterior surface or Kmax, Dr. Belin said.
As a general rule, Dr. Kanellopoulos crosslinks diagnosed patients younger than 20 years old, even without documented progression. If the keratoconus is mild—stage 2 and under—he explores a refractive transepithelial or epithelium-on crosslinking with the advanced KXL System (Avedro, Waltham, Massachusetts) offering customized pattern ability.
If there is documented progression, Dr. Kanellopoulos crosslinks as soon as possible. A crucial point is to establish a parallel strategy to avoid eye rubbing, he said.

Editors’ note: Dr. Belin has financial interests with Oculus, Avedro, and CXL Ophthalmics (Sherborn, Massachusetts). Dr. Ambrósio has financial interests with Oculus, Alcon (Fort Worth, Texas), Carl Zeiss Meditec (Jena, Germany), Mediphacos (Belo Horizonte, Brazil), and Essilor (Charenton-le-Pont, France). Dr. Kanellopoulos has financial interests with AJKMD Events, Alcon, Avedro, ISP Surgical (Bangkok, Thailand), Tula Medical (Doylestown, Pennsylvania), and Carl Zeiss Meditec. Dr. Trattler has financial interests with ArcScan (Golden, Colorado), Avedro, Oculus, and CXL Ophthalmics.

Contact information

Ambrósio: dr.renatoambrosio@gmail.com
Belin: MWBelin@aol.com
Kanellopoulos: ajkmd@mac.com
Trattler: wtrattler@gmail.com

Obtaining earlier keratoconus diagnoses Obtaining earlier keratoconus diagnoses
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