IN THE PAST TWO DECADES, the field of scleral lens (SL) fitting has grown exponentially. SLs are custom fit based on the shape and power of an individual eye. The customization is traditionally achieved with diagnostic fitting sets; this method relies heavily on the practitioner’s subjective clinical judgment and can be labor- and time-intensive, requiring the use of multiple trial lenses (Harthan et al, 2019). In recent years, advances in technology have allowed for more sophisticated customization, showing promise for a streamlined fitting process and improved outcomes.
As an alternative to diagnostic fitting, empirical fitting involves selecting lens parameters based only on data and theoretical models (Michaud et al, 2009). The use of trial lenses is not necessary beyond obtaining an accurate over-refraction. Currently, empirical fitting of SLs is assisted by the impression technique or scleral topography (Rojas-Viñuela et al, 2023).
With the impression technique, a mold of the anterior segment is taken and sent to a specialized laboratory. 3D scanning of the mold is used to design a SL that closely follows the curvature of the entire ocular surface. The impression technique is especially useful in fitting ocular surfaces that have significant irregularity, such as in the presence of pinguecula or glaucoma filtering blebs (Walker et al, 2020). The mold provides information on the height, curvature, and diameter of the irregularity to enable customization in the SL design, which is difficult to achieve with diagnostic fitting (Fadel, 2018).
Studying the shape of the anterior segment using scleral topography has profoundly changed the way practitioners fit SLs. For example, using scleral topography, the Scleral Shape Study Group (SSSG) determined that out of 140 eyes, only 5.7% of scleras were spherical and 28.6% were toric; the rest of the eyes showed either scleral toricity not exactly 180º apart or irregular scleral topography (DeNaeyer et al, 2017). This finding has encouraged more practitioners to design SLs with quadrant-specific or more customized free-form periphery based on scleral topography, thinking beyond the spherical or toric periphery that is incorporated in most of the available diagnostic fitting sets (Barnett et al, 2020).
Combined with scleral topography, new tools and software can further promote lens parameter customization. Several SL laboratories have developed proprietary online calculators, so that busy practitioners may design SL parameters themselves without having to call laboratory consultants to place lens orders. Another computer-aided design-based custom software allows practitioners to design free-form SLs assisted by scleral topography. After uploading scleral topography scans, practitioners can adjust the sagittal height and width of individual SL zones in every quadrant or every one-eighth meridian. A range of advanced features are also available, such as decentered optics, multifocal with front-surface toric, and fenestrations.
These tools and software put the practitioners in full control of SL parameter design, producing highly customized SLs that meet patients’ complex needs, only limited by the knowledge and comfort of the practitioner. Overall, empirical fitting may lead to accurate lens parameter selection with the first lens, which may mean fewer lens revisions, reduced chair time, and increased patient satisfaction (Barnett et al, 2021).
As our knowledge on the anterior segment shape continues to grow and new technologies and tools continue to improve, empirical fitting may become the gold standard for SL fitting in the near future and aid both the practitioner and the patient. CLS
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