Abstract
Purpose: :
In-spite of its widespread use, the significance of sodium fluorescein (SFL) staining on the ocular surface is not yet known. The purpose of this study was to determine if SFL staining of the superficial corneal surface is associated with corneal epithelial cell damage using an ex-vivo model.
Methods: :
Rabbit eyes with no pre-existing corneal staining, excised within 3h postmortem, were exposed to various damaging stimuli; including ophthalmic preservatives (PHMB), hypertonic or hypotonic saline, and abrasion by filter paper disk. The corneas were subsequently stained with 1% SFL and evaluated using a slit lamp bio-microscope. Corneas were further stained with Propidium iodide (PI), Hoechst 33342(HO) and Annexin-V (AN-V) to indentify dead, live and apoptotic cells, respectively and examined using confocal fluorescent microscopy (CFM). Untreated eyes were used as controls.
Results: :
Slit lamp observation confirmed the clinical appearance of superficial punctate SFL staining after exposure to all stimuli. Fluorescent cells observed with the slit-lamp could be seen to display hyper-fluorescence and early apoptotic membrane changes (AN-V +ve) on CFM evaluation. Controls had no apparent SFL staining on slit-lamp observation, but showed a uniform low level of fluorescence with CFM. These cells were judged to be healthy, with no AN-V or PI staining of the membrane or nucleus. Necrotic cells (PI +ve and AN-V -ve) showed significantly lower SFL staining than normal healthy cells and were not visible during slit lamp observation.
Conclusions: :
Superficial punctate SFL staining of the corneal epithelium visualized with the slit lamp bio-microscope corresponds to the presence of damaged epithelial cells. Neither healthy cells with intact membranes nor necrotic cells with disrupted membranes are visible in these circumstances.
Keywords: contact lens • cornea: epithelium • imaging/image analysis: clinical