From phakic IOLs to SILK and ray tracing, experts discussed the latest offerings and the ever-changing paradigm in refractive surgery during the recently held 35th Annual Meeting of the Asia-Pacific Association of Cataract and Refractive Surgeons (APACRS 2023).
At the 35th APACRS held in Singapore, eye specialists discussed options for moderate myopes such as phakic intraocular lenses (IOLs) and laser vision correction procedures. They also shared other innovative lenticular techniques, including the ray tracing approach for improving refractive predictability, the Smooth Incision Lenticule KeratomileusisTM (SILK) procedure, and the SmartSight protocol.
The best procedures for the moderate myope
When it comes to myopia correction, Dr. Michael Knorz from Germany, believed that the moderately myopic patient can opt for either phakic intraocular lenses (IOLs) or laser vision correction procedures, which include surface ablation, Femto- LASIK and small incision lenticule extraction (SMILE).
According to him, surface ablation has a good safety profile and allows for customized treatments (e.g., topography-guided). “However, these procedures can cause a lot of pain and discomfort, slow visual rehabilitation, significant dry eyes for several months and some optical side effects. They are also irreversible,” he said.
Meanwhile, laser lenticule extraction has a good safety profile, fast visual rehabilitation period, and fewer dry eye symptoms than LASIK or Femto- LASIK. He also noted that there are some optical side effects and the procedure is also not reversible. Also, since corneal aberrations limit vision, especially at night, corneal laser vision correction should be limited to moderate myopia due to potential losses in vision quality.
On the other hand, phakic IOLs provide better improvement in contrast sensitivity compared to LASIK or Femto-LASIK. “Visian ICL [a phakic IOL] has a good safety profile, provides faster visual recovery, no dry eye symptoms, as well as fewer optical aberrations resulting in
significantly better night vision than corneal laser surgery. It is also fully reversible and future procedures are not compromised,” Dr. Knorz said.
“So, to me, the first choice for treating the -5 D myope is the phakic IOL due to the vision quality it brings and its reversibility. Second is laser lenticule extraction because it causes less dry eyes than LASIK. Third is Femto-LASIK as it provides higher patient comfort than surface ablation, which is the last option. These four procedures are effective, reasonably safe, and are suitable for those less than 40,” he concluded.
The ray tracing approach
For decades, the focus of refractive surgery has beento reshape the cornea so that light that enters the eye can focus on the fovea. Nevertheless, Dr. Chandra Bala (Australia) thinksthat there should be a paradigm shift in refractive surgery.
“The purpose of refractive surgery is not to remove a thin lens from the cornea, but to change the angle of incidence at the front surface of the eye, which would correct the pathway of the light so that it will end at the fovea,” Dr. Bala shared. “In order to do that, we need to know what’s happening behind the cornea, and that requires us to know the journey of the light from the fovea to the front surface of the eye and from the infinity to the front surface of the eye. This is the concept behind Alcon’s Innoveyes ray tracing algorithm,” he added.
The ray tracing algorithm involves measuring all the elements of the eye — namely, the anterior and posterior cornea, anterior chamber depth, corneal thickness, lens thickness and axial length, noted Dr. Bala. By considering all optical surfaces of the eye, ray tracing offers the highest possible accuracy to improve the refractive predictability of corneal procedures.
“I believe that ray tracing technology is a new era in our thinking and ability to correct refractive error. We now recognize the need for an individual eye model — an ‘eyevatar’ for creating a personalized treatment plan,” he said.
Innovative procedures in lenticular surgery
As lenticular surgery becomes increasingly popular throughout the world, we are seeing more advancements in procedures and lasers. More recent varieties include the Smooth Incision Lenticule KeratomileusisTM (SILK) procedure (Johnson&Johnson Vision, California, USA) and the SmartSight protocol (SCHWIND, Kleinostheim, Germany), presented by Dr. Mahipal Sachdev from India and Dr. Thomas Kohnen from Germany, respectively.
Sharing his experience, Dr. Sachdev noted that the SILK procedure provides outstanding patient outcomes and highly accurate flap thickness with smooth stroll beds and easy lifts. This is largely due to the J&J Vision’s ELITATM femtosecond laser used in the procedure, which delivers low-energy treatment through a combination of ultrashort pulse frequency (10 Mhz) and small focus spot size (1.3 micron), creating fast and smooth cuts and inducing minimal tissue disruption in the stroma.
“My personal impression of this regime, which we started during the pandemic, is that it lives up to the name of smooth incision leticule extraction. There are minor or no tissue adhesions,” he shared. “All cases had a complete lenticular removal — none had cold spots, uncut areas, or bridges. None of the cases had any difficulty with the entry cut, and plane identification is relatively easy. Corneal biomicroscopy was unremarkable in all Day-1 and Week-1 postoperative visits, and visual recovery was fast. Patient satisfaction is great,” he added, noting that the procedure provides accurate refractive correction with tight outcomes and tight standard deviation for sphere and cylinder.
He also provided tips and pearls for best outcomes, which include having a good centration of the suction ring and a good approach in identifying the anterior plane, identifying the right type of patients, proper positioning of the patient head, as well as the use of proper instruments.
Meanwhile, the SmartSight procedure utilizes the SCHWIND ATOS® femtosecond laser and features intelligent eye tracking with pupil recognition and cyclotorsion compensation, providing a precise and gentle treatment method.
“The possible optical zone diameter of 5.5 mm to 7.5 mm creates a transition zone. The anterior cut has a diameter between 6 mm and 9 mm and a selectable cap thickness from 100 micrometers to 160 micrometers. Edge cut has an angle between 45º and 135º, and an arc length between 2 mm and 5 mm,” said Dr. Kohnen.
He shared Dr. Kishore Pradhan’s (Nepal) experience with the SCHWIND ATOS device after 12 months of follow-up, in which there was only one event of suction loss. According to Dr. Kishore, dissection was easy even in the presence of opaque bubble layers (OBLs), the bed cut was smooth, optical zones seemed larger than planned, and there was no immediate post-op wrinkling.
Also, Dr. Kohnen and his colleagues performed a study on 60 fresh pig eyes using the SmartSight procedure and found that the SCHWIND ATOS laser provides accurate and predictable cap thickness (CT), slight deviations in cap diameter (CD), and lenticular thickness (LT).
“Results are comparable with already established systems and procedures. However, provided settings seem to be challenging even with semiautomated algorithms, which could be due to the experimental setting of the trial. Overall, we found very good outcomes with this experimental setting,” he said.
Editor’s Note
- The 35th Asia-Pacific Association of Cataract and Refractive Surgeons (APACRS) annual meeting was held on June 8 to 10, 2023. Reporting for this story took place during the event.
- A version of this article was first published in CAKE Magazine Issue 19.
