A topographical method to quantify scleral contact lens decentration

Purpose: To describe a simple method to quantify scleral contact lens decentration using over-topography captured with a Placido ring videokeratoscope, and its repeatability. Methods: Scleral lens over-topography (E300 videokeratoscope, Medmont) was measured on 10 healthy participants following 15 min of lens settling (16.5 mm total diameter ICD miniscleral, Capricornia). Horizontal and vertical lens decentration was quantified from the translation of the front optic zone relative to the pupil centre derived from ellipses manually fitted to tangential power over-topography maps using both a standard and normalised dioptric scale. Intrasession (different maps captured within the same measurement session), intraobserver (identical maps analysed by the same observer), and intertechqniue (standard or normalised tangential power scales) repeatability were calculated. Results: The mean lens decentration was 0.62 ± 0.18 mm temporally and 0.91 ± 0.33 mm inferiorly. Lens decentration derived from tangential topography maps with a standard power scale were more repeatable (95% limits of agreement for intraobserver repeatability ± 0.07 mm and intrasession repeatability ± 0.15 mm) than measurements derived from normalised maps (95% limits of agreement for intraobserver repeatability ± 0.11 mm and intrasession repeatability ± 0.20 mm). Conclusions: Scleral lens decentration can be reliably quantified using tangential power maps with a standard (fixed) scale captured during over-topography without the need for customised instrumentation or image analysis software. This method has a range of potential applications in research and clinical practice.