Comparative in vivo high-resolution confocal microscopy of corneal epithelium, sub-basal nerves and stromal cells in mice with and without dry eye after photorefractive keratectomy.
BACKGROUND
The present study compares, using a new-generation high-resolution in vivo confocal microscope, the epithelial morphology, sub-basal nerves and stroma in two groups of mice: one exposed to normal conditions (NC) and the other to a desiccating environment (DE), following photorefractive keratectomy (PRK) with mechanical epithelial scraping.


METHODS
Twenty-four 4- to 8-week-old female Balb/C mice were used in this study. Twenty mice underwent bilateral corneal epithelial scraping using an electric brush prior to PRK. Then, the mice were divided in two groups: 10 mice were placed in NC. The other 10 mice were exposed to a DE for 2 weeks. Four mice served as controls. Corneas were analysed in vivo using the Rostock Cornea Module of the Heidelberg retina tomograph II. For all eyes, 20 confocal microscopic images of each layer, that is, the superficial and basal corneal epithelium, Bowman's layer, anterior and posterior stroma and the endothelium, were recorded. Epithelial and stromal cell densities and sub-basal and stromal nerves were measured and compared.


RESULTS
There was a higher density of superficial epithelial cells in the DE group (693 +/- 148 cells/mm(2) in NC group and 443 +/- 128 cells/mm(2) in DE group; Mann-Whitney U-test; P = 0.05). Higher number of basal cells were observed in the DE group. Its density was 986 +/- 198 cells/mm(2) in NC and 1598 +/- 280 cells/mm(2) in DE group (Mann-Whitney U-test; P < 0.05). Significantly higher number of reflective structures were noted within the stroma without clearly visible nuclei in the DE group compared with the NC eyes. Additionally, higher number of beads, nerve sprouts and higher tortuosity of sub-basal nerves were observed in the DE group. No difference was observed in the endothelial cell density between the groups.


CONCLUSIONS
Exposure of corneas to a DE after PRK with previous mechanical epithelial scraping increases epithelial turnover and is associated with a higher number of reflective structures in the stroma. Additionally increased nerve beading, nerve sprouts and tortuosity of sub-basal nerves were observed in the DE group, possibly directed to repair the alterations observed at the epithelial level.
Esquenazi
Salomon
S
LSU Eye Center and Neuroscience Center, LSU Health Sciences Center School of Medicine, New Orleans, Louisiana 70112, USA. sesque@lsuhsc.edu
He
Jiucheng
J
Li
Na
N
Bazan
Nicolas G
NG
Esquenazi
Isi
I
Bazan
Haydee E P
HE
D000818:Animals; D002452:Cell Count; D003315:Cornea / Q000294:innervation*; D003319:Corneal Stroma / Q000473:pathology*; D003890:Desiccation; D015352:Dry Eye Syndromes / Q000209:etiology / Q000473:pathology*; D019573:Epithelium, Corneal / Q000473:pathology*; D005260:Female; D005347:Fibroblasts / Q000473:pathology; D054018:Lasers, Excimer; D051379:Mice; D008807:Mice, Inbred BALB C; D018613:Microscopy, Confocal; D009882:Ophthalmic Nerve / Q000473:pathology*; D018903:Photorefractive Keratectomy; D011183:Postoperative Complications