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Tor Paaske Utheim, Otto Fricke, Neil S Lagali; Distinct ‘microdot’ structures accumulate in the cornea with age. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4857.
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To establish and quantify the prevalence of central corneal microdots the healthy cornea.
103 healthy, non contact lens-wearing subjects, aged 15 - 88 years, underwent laser-scanning in vivo confocal microscopy examination (IVCM) of the cornea using the volume scan mode. The three most anterior stromal IVCM images, just under Bowman’s layer, were analyzed from each eye. Masked and randomized with respect to age, these images were analyzed with a grading scale ranging from 0 to 5. Specifically, the number of point-like, reflective microdots within each 400 x 400 um image was graded as follows: Grade 0: < 5 dots, grade 1: 5-10 dots, grade 2: 10-25 dots, grade 3: 25-50 dots, grade 4: 50-75 dots and grade 5: > 75 dots. The grading criteria were determined from 3 observers for 15 subjects (75 images) to confirm general agreement with the counting method. Final grading was performed by one observer (618 images). Images with overlapping structures and Fiji software were applied to set the most suitable criteria for counting in order to reliably distinguish microdots from parts of keratocytes. The structures of interest were defined based on three criteria: size, level of reflection, and degree of circularity.
We found a strong correlation of microdot grade with age in right (Spearman Rank Order Correlation, rho = 0.69, P < 0.0001) and left (rho = 0.66, P < 0.0001) eyes independently. Microdot grade in both eyes of the same subject was highly correlated (rho = 0.89, P < 0.0001). No subjects under 60 years had a grade of 5, while no subjects over 60 years had a grade of 0 or 1. Median grade in subjects under 40 years was 1.8 while those over 60 years had a median grade of 4.0. The difference between these two age groups was highly significant (Mann-Whitney, P < 0.001).
To our knowledge, the present study is the first attempt to quantify microdots in the anterior stroma of the cornea in a healthy population. This work will help in establishing a baseline for future studies in various diseased populations. The strong correlation with age is noteworthy and warrants further studies to reveal the origin and nature of these structures.
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