Previous estimates of scleral thickness were limited in various ways by the measurement technique used. OCT imaging also allows high-resolution repeatable, non-invasive measurement of scleral tissue in vivo. 14, 15Ī: A high resolution cross sectional image of the human cornea (an average of 30 B-Scans) and B: thickness maps of the total cornea and epithelium across the central 7 mm derived from the interpolation of 12 radial line scans Scleral thickness 12 Most commercial OCT instruments have automated corneal thickness segmentation incorporated within the manufacturer-provided software, which can assist with the identification and monitoring of corneal ectasia 13 and scleral lens-induced corneal oedema. Customised anterior segment OCT imaging systems can also provide an axial resolution of close to 1 μm in corneal tissue. The high resolution of current anterior segment OCT instruments (approximately 5–10 μm in corneal tissue) 11 enables reliable visualisation, segmentation and quantification of each corneal layer, particularly with the use of B-scan averaging to improve image quality (Figure 1). Since larger diameter scleral lenses are designed to vault the corneal apex and limbus, align with the underlying sclera within the haptic landing zone and induce minimal adverse changes to the superficial tissue layers (the conjunctiva, Tenon's capsule, and the episclera), high-resolution cross-sectional images of a scleral lens in situ provides valuable clinical information in addition to slitlamp biomicroscopy. Since the introduction of anterior segment OCT imaging in 1994, 10 the understanding of corneal, conjunctival and scleral morphometry has continued to grow, and in recent years commercial OCT systems have become valuable clinical tools which inform initial scleral lens selection and aid fitting assessment or troubleshooting. Anterior segment anatomy and morphometryĪ comprehensive understanding of the biometrics of the anterior segment is integral to both scleral contact lens design and fitting. This review examines the role of OCT imaging in modern scleral contact lens practice and potential research applications. At the present time, in addition to manufacturer fitting algorithms, practitioners routinely utilise corneoscleral topographical data and OCT imaging as part of an empirical fitting approach (which complements diagnostic lens fitting), to determine the most appropriate initial trial lens, to objectively assess the central and peripheral lens fit, and customise lens design. Scleral contact lenses have been successfully fitted for over 130 years using a diagnostic fitting approach that primarily relied upon impression moulding to estimate scleral topography, and practitioner observation and intuition interpreting sodium fluorescein patterns, or alterations in the conjunctival and superficial scleral vasculature (haptic compression). 7, 8 In modern contact lens practice, scleral lenses can also delay the need for corneal transplantation in keratoconus 9 and for a number of clinical scenarios are considered the contact lens correction of choice, particularly for complex ocular shapes. 2- 6 These unique clinical applications have remained largely unchanged since glass haptic shells and lenses were first described in the late 19 th century. 1 The benefits of scleral contact lenses have been described in detail elsewhere, including the correction of high ametropia, neutralising irregular anterior corneal optics, corneal protection, and therapeutic rehabilitation of the ocular surface. Over the past decade, scleral contact lens prescribing has increased globally, largely due to advances in contact lens manufacturing and ophthalmic instrumentation, in particular optical coherence tomography (OCT).
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