Refractive
April 2023
by Liz Hillman
Editorial Co-Director
Image quality (IQ) is an “emerging area of interest” in the field of ophthalmology, said George Waring IV, MD, and it all starts with what the patient’s image quality is at the outset. “With the required specialized diagnostics and interpretation of these diagnostics to understand the sources of optical dysfunction, that’s part of the excitement of this. Now we’re building a foundation in the peer-reviewed literature to support the clinical impact, the optical impact on potential sources of optical dysfunction,” he said. “We now have ways to bring this into the office more readily, and it’s slowly making its way into the normal conversation and helping us understand the best way to provide the best outcomes.”
The construct of visual acuity in objective terms dates back to the mid-1800s with Snellen visual acuity, Dr. Waring explained, but lens and corneal refractive surgeons have learned there is more to vision than Snellen visual acuity.
“The qualitative aspects of visual acuity are often as important as the quantitative aspects of visual acuity, and technologies are emerging where we’re now able to have more quantitative aspects of quality of vision with the use of advanced diagnostics,” he said.
These include understanding the impact at the preop stage of static and dynamic factors of the tear film, of corneal shape of both the anterior and posterior surfaces, the optical quality of the cornea, the static and dynamic functions of the lens including various forms of opacity, the role of vitreous and vitreous opacities, and the role of the posterior capsule.
“To understand how we’re going to push the limits both in objective and subjective aspects of people’s visual acuity, we have to be able to understand what we need to address and screen preoperatively to customize and plan. This might involve work on the tear film, the cornea, the lens and potentially the vitreous in certain patient populations,” he said.
In his practice, Dr. Waring said an in-depth, customized vision analysis is conducted based on what the patient is being referred in for, with a different workup for laser vision correction patients vs. middle aged to older patients who are on the dysfunctional lens spectrum and will be evaluated for a surgical lens-based solution.
A LASIK referral, for example, will have more focus on the corneal aspects of the patient’s preoperative visual quality with high-resolution aberrometers, such as the iDESIGN system (Johnson & Johnson Vision), Dr. Waring said, in addition to high-resolution tomography to assess corneal curvature, shape, and optical quality. The tear film and tear performance are also assessed. Dr. Waring noted the paper published by Gouvea et al. in 2019 that demonstrated the role of the tear film on optical quality.1
A patient who is deemed to be in the second stage of optical maturity with dysfunctional lens syndrome will get the same workup as above, but attention is also paid to internal light scatter and reduced contrast sensitivity, as well as the loss of accommodation.
“We use Scheimpflug densitometry to assess the impact of lens density from the dysfunctional lens on optical quality, and now the Pentacam AXL Wave [Oculus] has a built-in aberrometer that separates internal from external aberrations and allows us to understand the impact of lens density from the dysfunctional lens on optical quality,” Dr. Waring said. “With ray tracing technology, we help validate the dysfunctional lens index with iTrace [Tracey Technologies], which helps separate the internal lens from the anterior cornea to understand internal optical dysfunction. This helps us determine the source and the opportunities for improvement. Use of advanced diagnostics helps us decide whether a patient may be best served with a lens-based procedure or a corneal-based procedure.”
Finally, there is the assessment of image quality preoperatively for the cataract patient. Dr. Waring said all of the above applies, but the cataract patient, “is more easily understood because we know they’ve gotten to the third stage of ocular maturity where internal optics have become so poor that it’s objectively and subjectively affecting quality of life.” He said the role of the anterior surface of the cornea is still important for image quality, and this is where high-resolution tomography comes into play.
“If we see irregular astigmatism, for example, we need to understand its root cause, including but not limited to dry eye and EBMD. If we identify EBMD, more times than not we recommend a staged procedure with a superficial keratectomy first … letting the cornea resurface, which often regularizes the previous irregular astigmatism,” Dr. Waring said.
Dr. Waring further explained the role of the vitreous on optical dysfunction, crediting the work of Jerry Sebag, MD, on this front. He said that more attention is being paid to this objectively and subjectively so patients can be counseled appropriately. For example, if the patient had vitreous opacities preoperatively but didn’t know about them, they might blame the procedure on poor visual quality when it was an existing condition.
Advanced preoperative image quality diagnostics, Dr. Waring continued, can help the surgeon determine where the patient falls in their stage of ocular maturity. We may have a 50-year-old with complaints of glare referred for cataract, Dr. Waring said, but with advanced diagnostics, the source of the glare could be found to be keratoconus, not to be confused with a patient who may only be at the first stage of dysfunctional lens syndrome.
“Not only do we get a better understanding of their image quality preop, but we gain a better understanding of their source of optical dysfunction to make better decisions about their care and to educate them better.”
Julie Schallhorn, MD, said in an email to EyeWorld that her preop IQ testing includes a combination of standard exam maneuvers, paying particular attention to the ocular surface and eyelids, as well as imaging of the shape of the cornea and of the tear film.
“Every preop cataract patient gets a full exam and Placido disc topography and Scheimpflug tomography, and every preop refractive surgery patient also gets an anterior segment OCT with epithelial thickness mapping,” she said. “Refractive patients with any evidence of lens changes on exam or those older than 45 also undergo combined Placido disc/ray tracing imaging (iTrace) to determine the relative impact of lenticular changes on visual quality. In cataract patients with irregular corneas, I will also obtain an iTrace to help determine the relative contribution of the corneal shape abnormalities vs. the lens opacity to visual quality.”
If she finds these measurements/images are normal, that’s the entirety of her preop workup. Cataract patients who have an unstable tear film will receive an automated tear breakup measurement with the Oculus Keratograph and an anterior segment OCT device to image the epithelium, Dr. Schallhorn said. “This can help determine the source of the irregularities seen on Placido disc imaging or exam,” she explained.
Dr. Schallhorn said maintaining a stable tear film is key to achieving the best possible image quality. “For the vast majority of patients, this is the major modifiable factor in image quality. Paying attention to tear film stability and managing lid health is of utmost importance. Many patients can have an unstable tear film but not report dry eye symptoms, so paying attention to the exam findings is the only way to detect this.”
Dr. Waring said he considers all of these technologies that have enabled and improved assessment of image quality important to the staged approach of assessing current image quality and image quality potential from the front to back of the eye.
“What may have been thought of as nice to have 10 years ago can be a need to have 10 years later,” he said. “It depends on the practice pattern of the surgeon and the goals of the surgeon and the patient.”
Dr. Schallhorn said her most vital measurements for cataract surgery are a thorough exam and Placido disc topography. “This will tell you most of what you need to know,” she said. The other important contributor to image quality is the retina. Routine preoperative macular OCT should be performed in any patient considering an advanced-technology IOL, as even subtle findings can affect the outcome of surgery.
In patients with abnormal topography, combined ray tracing/Placido disc imaging is nice to have to sort out the relative contribution of the cornea and lens to image quality, Dr. Schallhorn said, noting that this technology is essential for the 45- to 60-year-old age group deciding between lens vs. corneal surgery. For patients with irregular topography and early cataracts, knowing the relative contribution of each to the image quality can be helpful in preoperative patient counseling and setting expectations.
“As the diagnostic capabilities of our imaging devices continue to advance, we can start to move the conversation and the goal of surgery beyond a simple acuity number and into an era of optimizing image quality,” she said.
About the physicians
Julie Schallhorn, MD
Rose B. Williams Endowed Chair in Corneal Research
University of California, San Francisco
San Francisco, California
George Waring IV, MD
Waring Vision Institute
Mt. Pleasant, South Carolina
Reference
- Gouvea L, et al. Objective assessment of optical quality in dry eye disease using a double-pass imaging system. Clin Ophthalmol. 2019;13:1991–1996.
Relevant disclosures
Schallhorn: Carl Zeiss Meditec, Novus Vision
Waring: Johnson & Johnson Vision, Oculus, Tracey Technologies, Visiometrics
Contact
Schallhorn: jschallhorn@gmail.com
Waring: georgewaringiv@gmail.com
