January 2019

REFRACTIVE

Refractive editor’s corner of the world
Early cataract diagnosis technology


by Michelle Stephenson EyeWorld Contributing Writer



HD Analyzer exam. Right eye has stage 2 dysfunctional lens syndrome with an OSI reading of 2.1, and there is scatter on the point spread function. The left eye has had an IOL and the optics are good with the OSI reading of 0.8 and the tight point spread function.
Source: Daniel Durrie, MD

 

The diagnosis of early cataracts as a source of blur can be challenging based on the slit lamp exam. History is extremely important, especially in low light situations. I call night time image quality with the best possible pair of glasses the “poor man’s wavefront analyzer”; with an otherwise healthy eye and an accurate spectacle correction, if night time image quality is reduced early lens changes should be a part of the differential diagnosis. Slit lamp examination can be quite difficult to decipher between an aging change in the lens that is visually significant versus an aging change that is not visually significant. Measuring optical scatter through technologies like the HD Analyzer and iTrace can be helpful. Measuring lenticular density with the Pentacam can also be helpful. In this “Refractive editor’s corner of the world,” Daniel Durrie, MD, and Lance Kugler, MD, share their thoughts on how these technologies supplement the patient history and slit lamp exam to help them diagnose visually significant changes due to early cataracts.  
Knowing that the lens is the culprit can be helpful in making sure that we don’t perform LASIK on patients with these early lens changes and also can help explain why they’re not getting the image they’re looking for with glasses or contact lenses. These changes may be too early for the patient to want to proceed with a lens replacement surgery, but it brings them inner peace when they know the source of their reduced image quality in low light situations.  
Thank you to Dr. Durrie and Dr. Kugler for enhancing our knowledge in this important arena.  

Vance Thompson, MD,
Refractive editor


Changes in the lens can now be identified long before a full-blown cataract develops

Cataracts can be diagnosed early in their development by tracking changes in patients’ lenses. The HD Analyzer (Visiometrics, Costa Mesa, California) and the iTrace (Tracey Technologies, Houston) are employed to quantify optical scatter, while the Pentacam (Oculus, Wetzlar, Germany) is used to quantify lens density.
“I use the HD Analyzer and Pentacam on every patient,” said Daniel Durrie, MD, Overland Park, Kansas. “There is a lot of interest in early cataract diagnosis technology because we recognize that changes are going on in the lens before people get a full-on cataract. Ophthalmologists are interested in being able to tell the patient where he or she is in the development of a cataract long before there is loss of best corrected visual acuity. Traditionally, we diagnose a cataract when two things happen. First, the patient’s best corrected vision drops to 20/40 or worse, which is the legal driving area. Additionally, we look for functional loss, such as using BAT [Brightness Acuity Tester, Marco, Jacksonville, Florida] to look at how patients function under certain lighting situations. Now, we are getting into looking objectively at the scatter in the lens. These three technologies are commonly used to do different things, so it’s nice to sort out how they will fit into practice at this point in time.”
Lance Kugler, MD, Omaha, Nebraska, agreed. “I consider those three devices to be indispensable for modern refractive surgery practice. A Scheimpflug topographer like the Pentacam provides the ability to view the anterior and posterior corneal surface. It uses advanced software analytics to look at the cornea and patterns that might be missed by the ophthalmologist. This provides a more sophisticated analysis, which I think is important. The Pentacam does a good job identifying appropriate candidates for surgical procedures and identifying people who have subclinical keratoconus or other issues. It is also useful for determining the distribution of corneal power in eyes that have had previous refractive surgery,” he said.

HD Analyzer

The iTrace and the HD Analyzer are diagnostic equipment that help ophthalmologists evaluate the scatter of the image quality as it goes through the lens.
“The HD Analyzer is the simplest to understand because it takes a low-energy laser ray, bounces it off the retina, and reads it on the way back,” Dr. Durrie said. “It knows what should come back through a normal eye that has no degradation in the optics. It measures the point spread function, the modulation transfer function, the cell ratio, and contrast loss scientifically. All of those provide an objective measurement of the amount of light that is scattered or lost as it goes through the lens. This device also will pick up abnormalities in the tear film or any corneal opacity or keratoconus.”
It is used to assess the quality of the optics, according to Dr. Durrie. “It even provides a simulated visual acuity estimate of a patient’s best corrected vision. If a patient’s optics are great, I know in this part of the exam that I don’t have to worry about a cataract, severe dry eyes, a cloudy cornea, or keratoconus. I can then proceed with my exam, and if a patient has a vision problem, I know it’s not in the optical degradation of the tear film, cornea, or the lens. Also, for a refractive surgery patient, I want to make sure he or she has good optics before elective refractive surgery on the cornea or implantation of a phakic IOL,” he explained.
Dr. Durrie said that he expects all patients over the age of 45 to have some degradation in their optics, but he wants to make sure it’s in the normal range. “The HD Analyzer provides a green, yellow, or red evaluation at the bottom of the screen or printout. If they are in the green, they are good. If they are moving toward yellow, they are starting to have some degradation. People in their late 40s and early 50s typically demonstrate degradation of their lens quality using the HD Analyzer. It is the simplest device to understand because it only does one thing. It looks for optical scatter or degradation of the image,” he said.

iTrace

According to Dr. Kugler, the iTrace is a combination wavefront analyzer/Placido disc topographer. Its job is to help the ophthalmologist determine which part of the eye is causing the visual distortions that the patient is seeing. “It can help determine the irregularity that’s coming from the cornea and from inside the eye. It doesn’t directly measure the image on the retina, but it does measure how the light is affected by the anterior cornea. It also measures the entire optical system in a wavefront map. Then you can subtract the cornea from the wavefront map, and that tells you what’s coming from the inside of the eye. It’s useful in patients who have higher-order aberrations and unusual visual symptoms because it can analyze what’s going on optically. It also has a lot of nice views that you can show patients, so they have a clearer understanding of what’s going on with their eyes,” he said.
Dr. Durrie explained that the iTrace has a dysfunctional lens syndrome index. “It provides a metric number depicting the lens scatter that is measured through the device. It’s a more broad-based device, which is an advantage and a disadvantage. It’s a little more complicated to explain to patients what it means,” he said.

Pentacam

This is a Scheimpflug device that provides an image of the eye so that surgeons can see the cornea in cross-section. “You can see the lens and look for lens density changes,” Dr. Durrie said. “I use the Pentacam to explain changes in the lens to patients. The graphics are helpful. I can point to their cornea and show them where their contact lenses are and where laser surgery is done. It also provides a side view of the lens, so I can show them the density of their lens. I can show them the difference between their lens and a full-blown cataract.”
Dr. Kugler said that there is a device similar to the iTrace called the OPD-Scan III (Nidek, Gamagori, Japan), and there are devices similar to the Pentacam, such as the Galilei device (Ziemer Ophthalmic Systems, Port, Switzerland), which has similar functionality. He noted that the HD Analyzer is unique.
“Of course, a good quality slit lamp exam is essential. Let’s not forget that the red reflex we can use from a direct ophthalmoscope can also give us a lot of information about the visual system,” Dr. Kugler said.

Editor’s notes: Dr. Durrie has financial interests with Visiometrics and Tracey Technologies. Dr. Kugler has no financial interests related to his comments.

Contact information

Durrie
: ddurrie@durrievision.com
Kugler: lkugler@kuglervision.com

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