Enhanced Refractive Screening with Scheimpflug Imaging: Getting the Whole Picture

Getting optical imaging right has always been one of the most important challenges in ophthalmology. Now, we’re blessed with the most advanced tools the world has ever seen. The OCULUS Pentacam® (Wetzlar, Germany) is an ophthalmic miracle, and allows for imaging abilities that our ancestors could have only dreamed of. When used in conjunction with the OCULUS Corvis® ST, ophthalmologists have access to biometric data, including tomography and topography, that can be paired with new AI systems to help detect eye defects before they begin. 

Three speakers led us through this fascinating discussion: Prof. Renato Ambrosio, who manages his own clinic in Rio de Janeiro and is professor at the Federal University of the State of Rio De Janeiro; Prof. Rohit Shetty, vice chairman at Narayana Nethralaya, Bangalore, and Dr. Riccardo Vinciguerra, of the Humanitas San Pio X Hospital in Milan, Italy. 

Together, these doctors led us through some fascinating cases of enhanced refractive screening techniques, and showed us that what appears to be readily apparent isn’t what’s always true. 

Diagnostics for refractive surgery

Prof. Ambrosio first led us through enhanced diagnostic methods for ectasia — which, while rare, certainly is still an issue. A large part of his talk focused on ectasia susceptibility, which he helps diagnose with the OCULUS Pentacam®. 

For reference, the Pentacam® provides a very appealing user interface and allows for significant customizability. It certainly has helped Dr. Ambrosio make advances in determining the risk factors for ectasia. 

The pathophysiology of ectasia depends on biomechanical decompensation of the cornea. This comes from innate corneal resistance and impact from the environment, including laser vision correction (LVC) procedures and eye rubbing. 

Eye rubbing, you say? Yes, surprisingly. Eye rubbing came up multiple times during this discussion — eye rubbing leads to a greater incidence of ectasia and keratoconus than, well, not eye rubbing. A study presented later on the topic even compared two identical twins, one of whom had developed keratoconus — attributed to eye rubbing. Sometimes, in medicine, the simple answer is the correct one. 

The OCULUS tools used provide biometric, topographic and tomographic data. Together, these doctors rely on all three measurements to determine potential cases for ectasia and keratoconus. In many cases, a patient may be susceptible to ectasia despite apparent normality — and biometric data gathered can help determine the risk factor. 

New metrics: The CBI-LVC Index

Dr. Riccardo Vinciguerra has developed a new, valuable index to help determine risk cases for ectasia: the Corvis Biometric Index-Laser Vision Correction (CBI-LVC) index. This can be found in the updated version of the OCULUS Corvis® ST, and helps doctors make rapid decisions as to who might be a risk factor for ectasia. 

It’s pretty amazing how the data for the algorithm was created. Dr. Vinciguerra had to find 685 stable post-LVC patients and 51 post-LVC patients with ectasia — and then measure the differences. The results may appear subtle, but they stand out to the algorithm like a red flag. 

A semi-automatic approach using the technology can help a doctor combine their own observations with the algorithm’s insights; the fully-automatic version requires only biometrics, and not tomography. 

Biomechanics and collagen

Prof. Shetty led us through a discussion of collagen and biometrics — and how biometrics can come to the rescue. As he described it, he’s attempting to decode confusion in biometrics — there’re multiple blind men trying to describe an elephant by feeling its parts, but no one is getting the full picture. 

The biometrics are getting closer, however, and biomechanics may have the full picture indeed. As he described it, the truth of a patient’s situation lies at the crux of biomechanics, topography, and polarized-sensitive optical coherence tomography (PSOCT). This gives a full view of not just the topographic or the tomographic structure of the eye, but the collagen structure that binds it all together as well. In some cases, what looks like a problem may not be — and vice versa. 

All in all, the data and value provided by the two OCULUS tools is indisputable, and we heap the highest kudos on these physicians for their explanations of its uses. This is a whiff of what’s to come, and we can’t wait for more. 

Editor’s Note: A version of this article was first published in Issue 3 of CAKE & PIE POST, C&PE 2021 Edition. The CAKE & PIE Expo 2021 was LIVE on June 18-19. All sessions are available on demand until July 19 at expo.mediamice.com upon login.