Differentiation Between Gram Negative And Gram Positive Bacteria Using Optical Coherence Tomography

To distinguish between gram positive and gram negative bacteria in infectious keratitis using anterior segment OCT

Department of Ophthalmology and Optometry, Kepler University Clinic, Linz, Austria 

Three different OCT devices were used to perform scans of the cornea: CASIA 2 (Tomey, Japan), Heidelberg Spectralis (Heidelberg, Germany) and MS-39 (CSO, Italy). The following parameters were analysed: central corneal thickness, infiltrate thickness, infiltrate diameter, infiltrate distance to the corneal apex, corneal thickness 180° opposite to the infiltrate (mm), ratio of tissue loss or tissue gain in the area of infiltrate compared to the healthy opposite side (same distance measured from corneal apex to healthy side of the cornea of the same eye and affection of the pupillary axis (yes/no). After imaging corneal scraping was performed to determine the pathogen with microbiological testing.

Median (mean; standard deviation) corneal thickness, infiltrate thickness and infiltrate diameter for all patients was 782µm (787µm; 139µm), 260µm (288µm; 110µm) and 1180µm (1587µm; 1096µm), respectively. Median (mean; standard deviation) tissue loss/gain and entropy was 1.18 (1.22; 0.20) and 3.95 (3.92; 0.95), respectively. Logistic regression was used to evaluate the influence of OCT findings on gram negative detection. Infiltrate thickness (p=0.009), infiltrate diameter (p=0.026) and tissue loss/gain (p=0.017) were found to be significant, whereas corneal thickness (p=0.740), distance to center (p=0.240) and entropy (p=0.317) were not.

Anterior segment imaging for infectious keratitis is a novel field of application. Based on our results, infiltrate thickness and diameter were found to be significantly larger in gram negative than gram positive bacteria. These results are in line with those of previous research, confirming that gram negative bacteria cause a larger surface area of infiltration.