Lens induced oedema has been somewhat reduced in response to adopting high oxygen permeable materials and improvement in lens design capabilities to minimise lens and fluid reservoir thickness, but still remains an issue that needs to be managed. ![]() The literature on risk of microbial keratitis infection in scleral lens wear is sparce, but suggests risk to be low, possibly as a result of the relatively slow but growing population of scleral lens wearers.Optical performance from scleral lenses is typically similar to rigid corneal lenses but suffers potential for decentration that can induce prism and flexure leading to residual astigmatism.Various challenges to successful scleral lens wear are outlined in the report: When it comes to assessing lens fit, the report summarises the latest research and clinical understanding on assessing optimal sagittal lens depth, back surface profile, fluid reservoir thickness, oxygen permeability, lens centration, movement and wettability. Impression lens fitting retains a place in clinical practice, particularly for highly irregular corneas that can result in inaccurate topographic measurements, with better fitting resulting from scanning the impression mold instead. ![]() ![]() Technology improvements are revealed in the report to have also influenced lens fitting, resulting in a shift away from using diagnostic lenses at initial fit towards the first lens on eye being designed empirically based on corneal topography measurement. Central lens thickness, typically 200-500µm, introduces a further consideration, balancing the needs of using a sufficiently thick lens to prevent warping and on-eye flexure, whilst ensuring adequate oxygen transmissibility is maintained. However, diurnal changes to ocular physiology as well as accommodation induced changes to ocular shape challenge the ability to achieve a perfect lens fit by introducing variability that a rigid lens design cannot overcome. Ability to now manufacturer complex scleral lens shapes that more closely conform with measured scleral surface topography has been shown to reduce lens decentration and flexure, post-lens debris and air-bubbles, conjunctival prolapse, localised vessel blanching and lens impingement. The scleral lens report details how ocular shape differs across populations, and that in most eyes the scleral elevation profile is not spherical. Complimenting advances in the manufacture of lenses, advances in ocular imaging using optical coherence tomography (OCT) and specular microscopy, have considerably improved the understanding of ocular shape and response to lens wear. 1 Modern scleral lens designs are divided into three distinct zones consisting of the optic transition and landing zones, each of which, in response to continual advances in manufacturing technology, can now be constructed in innumerable ways. The CLEAR Scleral Lens paper covers the history and evolution of scleral lenses from initial manufacture in glass, on to PMMA and then to modern gas permeable materials that overcome the oxygen limitations of the previous materials. ![]() He is a partner in private practice conducting clinical research on use of contact lenses and orthokeratology to control progression of myopia, and holds an Adjunct Senior Lecturer position at the School of Optometry and Vision Science, University of New South Wales, Sydney.īarnett M, Courey C, Fadel D, et al. Download PDF Dr Paul Gifford consults with the contact lens industry on development of contact lens designs and their implementation into clinical practice.
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