Since its inception in SMILE, lenticule extraction-based laser vision correction (LVC) has experienced tremendous growth in recent years. Correspondingly, the demand for understanding the impact of this newcomer to LVC on the eye has surged. At APAO 2024 in Bali, Dr. Rohit Shetty delved into his research in this area. He explained why he places his trust in the Corvis® ST (OCULUS Optikgeräte GmbH, Wetzlar, Germany) for assessing corneal biomechanics in both laboratory and clinical settings to optimize surgical outcomes in modern LVC.
Lenticule extraction procedures have truly flourished in modern laser vision correction. However, despite the technology’s rapid success, questions persist regarding the precise effects of these surgeries on the treated ocular structures.
Enter Dr. Rohit Shetty (India), who has directed his research efforts toward unravelling the biomechanical effects of SMILE and its derivative procedures. During an OCULUS lunch symposium at the 39th Congress of the Asia-Pacific Academy of Ophthalmology (APAO 2024), Dr. Shetty elucidated why the latest advancements in biomechanics are crucial in lenticule extraction procedures—and why the OCULUS Corvis® ST is the tool of choice for this purpose.
Advancing understanding
Dr. Shetty has long recognized that there are gaps in our knowledge of the biomechanical implications of lenticule extraction surgery. His belief that such knowledge is imperative for achieving optimal patient outcomes underpinned his groundbreaking 2017 study on the topic .*
“We realized that surgical outcomes, both intraoperative and postoperative, are heavily influenced by the dynamics of corneal tissue,” Dr. Shetty explained. And understanding these dynamics is now the driving force behind a significant portion of the research coming out of his lab.
Dr. Shetty saw that a more precise, biomechanics-driven approach to corneal tissue dynamics was necessary to advance this understanding. This is due to the inherent variability associated with the subjective, qualitative judgments required in lenticule extraction procedures.
“It’s a completely new dimension of laser surgery, where a lot depends on tactile sensation and the performance of laser spots,” Dr. Shetty explained. “This is why we believe that integrating biomechanics in this era of extensive lenticule-based procedures is crucial. We need the ability to anticipate what is occurring.
Corvis® ST key to early discoveries
The core focus of both Dr. Shetty’s 2017 study and his ongoing research presented at APAO 2024 is to thus harness the power of predictive modelling based on biomechanical insights.
So how can surgeons better comprehend the biomechanical changes during lenticule extraction to facilitate such predictions? The answer involves scrutinizing the relevant biomechanical variables using an appropriate device. For Dr. Shetty, the OCULUS Corvis® ST has emerged as the ideal tool for biomechanical assessments.
In the 2017 study, OCT imaging was utilized to identify biomarkers such as his team’s proprietary Bowman’s roughness index (BRI) and corneal speckle distribution. However, it was the Corvis® ST, with its corneal stiffness measurement capabilities and more, which played a pivotal role in both the 2017 study and his team’s current endeavours.
“We opted for the Corvis® because of its integration with topography,” he elaborated. “It offers multiple parameters, not just a singular value. It provides stiffness parameters, an aqueous stress index, and elasticity modulus. And I have the flexibility to select the parameters I require.”
In the 2017 study, Dr. Shetty and his team shed light on the current possibilities in making the measurements they needed. “Current in vivo biomechanical assessment options are the Corvis® ST (OCULUS Optikgeräte GmbH, Wetzlar, Germany) and the Ocular Response Analyzer® (ORA) (Reichert Ophthalmic Instruments, Buffalo, NY, USA),” the study authors write.
Crucially, the authors noted that such in vivo measurements were only feasible with the Corvis® ST. “However, correlation between ORA indices and mechanical corneal stiffness is unknown. Using Corvis® ST, we can derive corneal stiffness,specific to the in vivo corneal deformation amplitude waveform.”*
Ultimately, the Corvis® ST’s unique capability to quantify mechanical corneal stiffness unveiled one of the most compelling findings of the 2017 study: corneal deformation at certain force levels indicated a swifter recovery of biomechanical strength in eyes that underwent lenticule extraction.* But this was just the beginning.
The predictive potential of Corvis® ST
Building upon these initial insights, Dr. Shetty’s current research aims to formulate a predictive model for patient outcomes in lenticule extraction. “The primary inquiries were: How does dissection ease correlate with visual quality? And can we forecast this using biomechanical robustness?” he remarked.
Leveraging preoperative biomechanical data from the Corvis® ST—such as corneal stiffness, Corvis Biomechanical Index, thinnest corneal thickness, stiffness parameter A1, and Belin/Ambrosio Enhanced Ectasia Display—Dr. Shetty’s team is now developing a random forest artificial intelligence model to predict the nature of the opaque bubble layer (OBL).
According to ongoing investigations, OBL density demonstrates a positive correlation with dissection difficulty. Consequently, with the aid of the Corvis® ST, it now appears possible to anticipate the characteristics of a given lenticule extraction surgery before it occurs.
“When we fed this small sample into our AI model, it accurately predicted—nearly 80% of the time—the outcomes anticipated by biomechanical analysis,” he noted.
Ultimately, Dr. Shetty contends that the Corvis® ST has been instrumental in realizing the tangible impact of his research on the lives of patients undergoing lenticule extraction. “Without the Corvis® ST, this would have remained a theoretical model—not a practical tool for real patients, which we now possess thanks to the data.”
For Dr. Shetty, the Corvis® ST’s potential goes way beyond the research laboratory. Despite the specialized role of the Corvis® ST in his groundbreaking work on lenticule extraction, he perceives the device as universally beneficial for all surgeons seeking to immediately enhance their surgical practices.
“We must dispel the notion that [Corvis® ST] is solely for highly specialized individuals,” he asserted. “It is immensely beneficial for beginners. It is reliable.”
“It was incredibly straightforward to integrate into practice,” he continued. “It accelerates processes, integrates seamlessly with topography, and furnishes invaluable data that I cannot do without. It enhances my proficiency as a surgeon and augments predictability.”
Ultimately, the Corvis® ST has emerged as the versatile solution Dr. Shetty has sought for his dynamic needs—both in the clinic and for his pivotal research shaping the future of patient outcomes in lenticule extraction-based laser vision correction. Before heading off to deliver his presentation to a packed symposium room at APAO 2024 in Bali, Dr. Shetty had one final thought on the Corvis® ST.
“Familiarize yourself with it. Engage in discussions about it. Its potential exceeds imagination.”
Editor’s Note: The 39th Congress of the Asia-Pacific Academy of Ophthalmology (APAO 2024) took place on February 22 to 25, 2024, in Bali, Indonesia. Reporting for this story took place during the event.
Reference
- Shetty R, Francis M, Shroff R, et al. Corneal Biomechanical Changes and Tissue Remodeling After SMILE and LASIK. Invest Ophthalmol Vis Sci. 2017;58(13):5703-5712.
