ESCRS 2024: OCT Imaging from Research to Clinical Practice
Speaker: Sorcha Ni Dhubhghaill
The transition from time-domain to spectral-domain optical coherence tomography (OCT) has markedly enhanced the quality and efficiency of OCT imaging in ophthalmology. Initiated in 1996 with the advent of larger-scale devices, the technological evolution has broadened OCT's applications to various medical fields, including ophthalmology, cardiology, dermatology, and gastroenterology. Advances in mathematical techniques for analyzing interference patterns have facilitated faster and more precise imaging results. OCT is now routinely employed for various diagnostic purposes, including corneal pachymetry mapping, corneal power mapping, segment biometry evaluation, high-resolution cross-sectional imaging, and retinal nerve fiber layer assessment. It is instrumental in detecting glaucomatous damage before its visibility on perimetry tests. Specifically, anterior chamber OCT plays a crucial role in anterior chamber biometry, aiding in the assessment of intracapsular lens (ICL) vaulting and establishing the safety parameters for ICL placement. Additionally, anterior chamber OCT and ICL assessments are critical for evaluating iris morphology issues that might contraindicate using an ICL, particularly in the presence of a cyst. Incorporating OCT technology into clinical practice has led to more precise ocular evaluations, resulting in improved patient outcomes and a deeper understanding of ocular anatomy.
The intraocular lens (IOL) Master 500, a basic interferometer, has been succeeded by the more advanced IOL Master 700, which utilizes OCT to provide highly accurate axial length measurements. Axial length is the most critical parameter for IOL calculations, making the precision of OCT-based measurements crucial. Incorporating OCT-based IOL formulas into clinical practice has enhanced the ability to measure both the anterior and posterior cornea and the true corneal power. Beyond numerical measurements, OCT offers valuable insights into anatomical features. It can identify issues such as divided lamellae in lens swelling, signs of open capsular bags, and anterior capsular fibrosis. These findings are instrumental in preparing for procedures such as capsular rexus and mitigating potential complications. During an Yttrium-Aluminum-Garnet (YAG) capsulotomy, OCT provides a clear view of any turbid fluid behind the lens, aiding in the relief of capsular bag distension. The capability is especially beneficial for patients with capsular block syndrome, who may present with a turbid fluid-filled bag behind the lens.
Corneal imaging and OCT have become invaluable tools in various ophthalmic procedures, particularly for corneal hydrops, scarring, and Fuchs' dystrophy. OCT imaging enhances suture planning by providing detailed epithelium mapping, a capability that traditional ShymeFlug imaging lacks. As OCT technology advances, it is expected to surpass Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) in screening for ectasia, offering superior diagnostic precision. OCT's ability to map the corneal epithelium allows for more accurate localization of epithelial abnormalities. Despite these advantages, OCT has limitations, including challenges in creating comprehensive full-globe OCT images, which can be addressed using digital editing tools like Photoshop. Integrating OCT with microscopes may further enhance its utility in clinical practice.
The utilization of OCT in the operating room has undergone significant advancements, particularly with integrated systems offering high-definition imaging capabilities. These systems are highly beneficial for obtaining detailed intraoperative images, although they occasionally produce ghost artifacts. A major challenge associated with OCT remains its cost, which its procedural efficiency and speed must justify. Despite its advantages in providing real-time imaging, the high expense of intraoperative OCT often makes it difficult to rationalize. OCT proves its value in cataract surgery by enhancing the visualization of critical structures. For instance, during the anterior capsulorhexis, OCT can capture detailed images of the capsular bag and anterior hyaloid, offering a clearer view of the surgical field. Post-implantation, the lens capsule may exhibit flaccidity, but it eventually stabilizes around the lens. Additionally, OCT can reveal the space behind the lens, where particles may traverse through the zonules and reach the posterior capsule, providing insights into the anterior hyaloid and the posterior capsule.
Intraoperative OCT enhances surgical safety by guiding depth measurements and hydro delineation, reducing the risk of capsular rupture during procedures. Thirteen studies have demonstrated the utility of intraoperative OCT for visualizing capsular structures, yet its cost remains a significant hurdle, complicating efforts to justify its integration into routine surgical practice. In the field of corneal imaging, recent innovations such as the Oculus Pentacam Cornea Zoom have set new standards by providing unprecedented detail in corneal scans. The advanced technology enables nearly anatomical-level imaging, which is particularly valuable for assessing the thickness of the epithelium and Bowman's layer, especially in patients with ecstatic conditions like keratoconus. Despite these advancements, OCT is not without its limitations. High-quality scans are not always achievable, and the cost remains a critical concern. Intraoperative OCT can be instrumental in identifying Salzmann nodules, characterized by a cleavage plane over Bowman's layer. Techniques initially described by Marc Morel have been shown to facilitate faster healing and improved visual outcomes.
Corneal transplant surgery can be significantly improved using OCT and techniques such as Descemet Stripping Automated Endothelial Keratoplasty (DSAEK). OCT facilitates the detection of persistent fluid at the interface, indicating when additional procedures may be necessary. During Descemet's Membrane Endothelial Keratoplasty (DMEK), OCT provides valuable guidance without requiring a cannula. The process begins with scanning inside the tube to ensure proper graft alignment, followed by the OCT motsuris technique to confirm the graft's curling direction. Despite these advantages, the cost-effectiveness of OCT in DMEK has been scrutinized. A study on cost-effectiveness found that OCT impacted decision-making in 40% of cases and contributed to faster surgeries. However, the benefit does not necessarily translate into substantial financial savings. To justify the investment in OCT, it is essential to collaborate with specialists in retina, cornea, and cataract surgery to build a compelling case for its use.
OCT is the primary imaging modality for evaluating the anterior segment of the eye. However, its effectiveness can be limited by the presence of the pigment layer, which can obstruct the signal and prevent visualization of certain anatomical structures, such as the ciliary sulcus and ciliary body. Despite these limitations, OCT enhances safety and efficiency in DMEK by providing a more precise view of the ciliary body, thereby improving procedural accuracy and outcomes.
Spectral Domain Optical Coherence Tomography, or Fourier Domain OCT, was developed before Time Domain OCT, a technology that emerged from Vienna's innovations. As optical imaging technologies continue to evolve, recent advancements have combined existing technologies to push the boundaries of imaging capabilities. One such integration is combining OCT with confocal microscopy principles, offering high-resolution imaging with depth information characteristic of OCT while maintaining the non-contact nature of the confocal microscope. The combination enhances the ability to observe fine cellular structures in detail without physical contact, facilitating more versatile and comprehensive imaging applications. The advancement highlights the ongoing trend of merging different technological strengths to overcome the limitations of individual systems, paving the way for future innovations in the field.
42nd Congress of the European Society of Cataract and Refractive Surgeons, 6 – 10 September 2024, Fira de Barcelona, Spain.
