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Marta Jiménez-García, Sorcha Ní Dhubhghail, Alejandra Consejo, Sarah Hershko, Carina Koppen, Jos J Rozema; A novel method to visualize keratoconus based on Scheimpflug densitometry. Invest. Ophthalmol. Vis. Sci. 2020;61(7):3335.
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© ARVO (1962-2015); The Authors (2016-present)
Keratoconus (KC) is frequently described using curvature, elevation and pachymetry. In this retrospective observational study, we report a new visualization method for KC based on densitometry maps, obtained with a Scheimpflug tomographer, that delimits the corneal region affected.
Ethics approval was granted from the Institutional Review Board. The study included 20 controls (N group) and 20 KC patients (KC group), divided into mild (KC2, n=10) and moderate (KC3, n=10) stages based on the Topographical Keratoconus Classification (TKC). Densitometry was analyzed using two methods: ‘one-layer scan’, that shows the densitometry at a selected depth (Figure 1) and ‘two-layers scan’, that averages densitometry between two corneal depths chosen at a depth of 120 µm and at the endothelium. Repeated same-day scans and longitudinal series were also evaluated to verify whether the findings evolved over time.
Analyzing the two-layers scans, 19/20 KC cases showed a bright decentred area that appeared to demarcate the cone (Figure 2). This phenomenon varied in clarity from a vague dark arc to a crisply delineated mark, and its shape, location and extent were consistent in exams taken on the same day. No similar marks were found in any of the normal subjects. The marks’ brightness, contrast, decentration and the number of octants delimited by a dark arc, expressed as numeric values, showed significant differences between N and KC groups for all four features (Mann-Whitney U, p<0.05). The mark was brighter and more contrasted in more advanced KC cases, but the differences between KC2 and KC3 groups were not significant. Densitometry changes over time were seen in progressive KC, but also in KC eyes considered clinically stable.
Densitometry maps rely only on the light’s transmission properties, an advantage over the classical map set. The delimited area, not found in normal corneas, appears to correspond with the area affected by KC and can be a supplementary documentation tool. Using TKC as classifier, no significant difference was found between KC2 and KC3. This might be due to the different features that TKC and densitometry are evaluating, corneal geometry and corneal transparency respectively, that might also explain why changes in densitometry were found in eyes considered clinically stable according to geometric criteria.
This is a 2020 ARVO Annual Meeting abstract.
One-layer Scan. Moderate KC
Two-layers Scan. Normal vs Mild and Moderate KC
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