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Alfredo Ruggeri, Enea Poletti, Neil S Lagali; Clinical grading of corneal subbasal nerve tortuosity. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1963.
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© ARVO (1962-2015); The Authors (2016-present)
Corneal subbasal nerve tortuosity (CNT) estimated from confocal microscopy is becoming a widely used clinical measure. Since a standardized definition is still lacking, we investigated the clinical perception of CNT by measuring expert graders’ agreement when assessing several different images. Their average response may also represent a reliable ground-truth reference for clinically assessing CNT.
A set of 30 images with a wide range of perceived NT was assembled from images acquired at 7 research centers (Auckland, Boston, Linköping, Manchester, Oslo, Rostock, Sydney). 7 experienced graders were asked to sort the 30 images by increasing NT, using a computer-aided image comparison tool that uses the human grader assessment to order the set from lowest to highest NT. Graders agreement was assessed by the Spearman Rank Correlation Coefficient (SRCC) among their orderings.<br /> Experiment 1. No specific instruction about CNT was provided. Most of the graders reported that they found it difficult to comparatively assess many small-range directional changes vs. few long-range ones.<br /> Experiment 2. 4 specific definitions of CNT were proposed: average (T1) or maximum (T2) of short-range direction changes; average (T3) or maximum (T4) of long-range direction direction changes (see examples in Fig. 1). The 7 graders were asked to order again the 30 image using in turn each of the 4 definitions.
All results from experiment 2 are better than the one from experiment 1 (Tab. 1). For the same type of CNT definition (short-range or long-range), maximum (T2 and T4) scored better than average (T1 and T3).<br /> Average SRCCs between T1 and T2 and between T3 and T4 orderings were all >0.94, whilst between T1 and T3 and T2 and T4 were all <0.40, suggesting high correlation between average and maximum and high independence between short and long-range directional changes.
The clinical perception of CNT appears to have two distinct forms, characterized by either short or long-range directional changes. Both types of tortuosity need to be considered when assessing CNT. We now need to investigate to what degree different cornea pathologies exhibit one or the other form in their subbasal nerve patterns.
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