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Stephanie Campbell, J. M Woodhouse, Keith M Meek; Detecting early keratoconus in Down's syndrome. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4203. doi: https://doi.org/.
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Keratoconus is significantly more prevalent in young people with Down's syndrome (DS) than in the typical aged-matched population. However, patients who have DS are unlikely to report early changes in vision both because of their communicative limitations, and because the DS visual system is inherently less sensitive than that in typically developing young people. As a result, presenting disease is commonly moderate to advanced, creating challenges for contact lens fitting and corneal grafting. Early diagnosis is a priority for young people with DS, so that they can benefit from interventions such as corneal cross-linking, but this diagnosis is difficult owing to a naturally steeper, thinner cornea, which is present even in healthy individuals with DS. The current study evaluates corneal and visual norms of young people with DS and suggests indicators which should raise suspicion of keratoconus during screening in this population.
A case-control study was conducted involving 56 eyes of 31 subjects (17 male, 14 female) with DS. The age range was 7 to 26 years (mean±SD 18.19±5.12). The subjects underwent corneal examination including slit lamp biomicroscopy, corneal tomography analysis using Pentacam (Oculus GmbH, Wetzlar, Germany) and biomechanical evaluation using Ocular Response Analyzer (Reichert, Buffalo, NY). Optometric data including best corrected spectacle visual acuity, contrast sensitivity, binocular status and spectacle refraction were obtained. Subjects were classified using a modified Amsler-Krumeich approach prior to statistical analysis.
The current cohort of young people with DS have a lower corneal resistance factor (mean±SD 8.7±2.2) than has been noted in typical subjects of a similar age in other published studies. In the non-keratoconic eyes examined, a minimum corneal thickness of as little as 378μm was noted (range 378μm to 575μm), whilst the maximum corneal power was 47.7D (range 42.6D to 27.7D). The range of regular corneal astigmatism was 0.1D to 1.6D. Corneal astigmatism >1.60D and corneal power >50D are each significant risk factors for keratoconus in DS.
Young people with DS, even without keratoconus, display an altered biomechanical status. Standard topographical and pachymetric indices for the identification of keratoconus in DS, are on their own, inappropriate, and this carries implications for monitoring and diagnosis in primary and secondary care.
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