Correlation of inflammatory cells and corneal nerve damage in fungal keratitis on in vivo confocal microscopy

Abstract

Objective: To investigate the relationship between inflammatory cell infiltration and nerve damage in patients with fungal keratitis at different degrees of severity. Methods: Retrospective study. A total of 44 consecutive patients (44 eyes) with fungal keratitis in Beijing Tongren Hospital Affiliated to Capital Medical University from January 2017 to December 2019 were selected as the patient group, including 30 males and 14 females, with an age of (58.3±11.5) years old. Twenty healthy people (20 eyes) were included as control group. Slit-lamp microscopy was performed to observe the corneal ulcer. According to the diameter of corneal ulcer, patients were divided into mild, moderate and severe groups. With in vivo confocal microscopic ,the images were obtained from the epithelial layer to the endothelial layer in the central cornea and superior, inferior, nasal and temporal peripheral cornea. Parameters of the maximum density of fungal hyphae, the maximum depth of hyphal infiltration, the density, area and length of dendritic cells (DCs), the nerve density, and the number and curvature of nerve trunks were collected. The Kruskal-Wallis test, Wilcoxon test, and Spearman correlation analysis were used for analyses. Results: On confocal microscopy, many uniform, highly reflective, segment-like structures in parallel or staggered rows were detected in the cornea, with a certain degree of physiological curvature and branching. Quantitative analysis of hyphal density found that the median rating of hyphal density was 2.6 (2.0, 3.0), mainly with medium to large amounts of hyphae. Most hyphae were 100-150 μm in depth (18 cases, 40.9%), and the maximum depth of hyphae in 95.5% (42 cases) of patients was within 300 μm. The hyphal invasion depth in the mild group was 89.4 (50.5, 106.8) μm, in the moderate group was 133 (122, 203) μm, and in the severe group was 135 (74, 151) μm. As the severity of the disease increased, the depth of hyphal invasion increased (F=4.248, P=0.001). Compared with the control group, the DC density [166 (81.3, 212.5) vs. 24.0 (20.8, 32.3) cells/μm2], area [441.3 (291.9, 529.5) vs. 63.7 (47.7, 70.3) μm2] and length [68.3 (39.4, 91.0) vs. 9.2 (7.0, 11.3) μm] increased in patients (W=493.5, 500.0, 500.0; P<0.01). The nerve density [5 398.3 (3 202.7, 6 828.3) vs. 19 171.8 (17 558.8, 21 550.4) μm/mm2; t=-14.448, P<0.01] and the length [692.7 (402.0, 925.1) vs.2 138.4 (1 940.4, 2 597.2) μm; t=-11.930, P<0.01] and number [2.9 (2.0,3.0) vs. 6.0 (5.5,7.0); t=-8.282, P<0.01] of nerve trunks in patients decreased. There were strong negative correlations between the nerve density, the number of nerve trunks, and the DC density (r=-0.555, -0.466; P<0.01). Conclusions: The depth of fungal hypha invasion in patients with fungal keratitis is mainly concentrated in the epithelial layer and superficial stroma layer. The density of mature dendritic cells in the lesion area was negatively correlated with the density and number of subbasal nerves. The density of subbasal nerves decreased as the increase of the severity of the lesion. (Chin J Ophthalmol, 2021, 57: 580-588).