A previous abrasion in the contralateral eye influences the cell kinetics during healing of a central corneal abrasion.

PURPOSE: To study the influence of a previous erosion in the fellow eye on the proliferative response during healing of a central corneal erosion. METHODS: A corneal abrasion was made on the right eye of 20 rats. After 1 week a corneal erosion was made in the left eye of the pre-treated animals and in 20 previously untreated animals. Cell kinetic methods were used to estimate the labelling index (LI) and the mitotic rate (MR) after 1, 2, 4, 6 and 12 days. RESULTS: After 24 hours the corneal erosions were covered by epithelial cells in 3 of 4 animals in both groups. The LI and the MR were significantly higher in the pre-treated group on the 2nd day after erosion. CONCLUSIONS: The proliferation measured by LI and MR was increased when an abrasion was made in the contralateral eye 1 week earlier. This might explain the faster healing rate of the second eye reported by other authors (Rask et al. 1996). The healing process in the cornea is modulated by systemic influence.

Apoptosis in shed human corneal cells.

PURPOSE: To determine whether shear forces applied to the corneal epithelium by the repeated insertion and removal of a hydrogel contact lens alter the size and number of cells removed and to determine the contribution of apoptosis to this process. METHODS; Human corneal cells were collected from eight healthy subjects by sequential contact lens cytology (20 lens insertions and removals). Collected cells were stained with acridine orange for counting and measurement of cell size. In a separate experiment, collected cells were fixed and stained with TdT-mediated dUTP nick-end labeling (TUNEL) or labeled immediately after collection using annexin V. Hoechst stain and propidium iodide (PI) were used as nuclear counterstains. The proportion of cells labeled with acridine orange, TUNEL, and annexin V was quantified by fluorescence microscopy. RESULTS; The number of cells increased in later collections, and cells were smaller. The mean number of positively stained cells using TUNEL was 57%. Annexin V labeling on unfixed fresh samples showed a mean of 64%, with an increase in later collections. Apoptotic bodies were observed in very few cells. In most cells the nucleus and cytoplasmic membrane were intact. Structures were observed in which nuclei were missing (Hoechst negative) but in which cytoplasm had the size and appearance of whole, nucleated cells. These structures (cell ghosts) increased in number along with the increase in nucleated cells in later collections. CONCLUSIONS: The sequential removal of a soft contact lens caused a progressive increase in the number of cells collected from the surface and a progressive decrease in their size. The majority of nucleated cells removed by a contact lens were apoptotic in the sense of being positively labeled by TUNEL and annexin V. Morphologically they differed from classically apoptotic cells, in that cells showed an intact nuclear structure and no discernible apoptotic bodies. They could represent a last stage in a pathway of cell differentiation in which frictional forces induced by the removal of the contact lens activate the apoptotic program and cause the cell to be shed. There is also a pathway in which cells lose their nuclei before leaving the epithelial surface.

UVB-induced formation of (6-4) photoproducts in the rat corneal epithelium.

The induction of DNA photoproducts in rat corneal epithelium was studied after in vivo exposure to different doses of ultraviolet B light at 297 nm. Affinity-purified antibodies with a major specificity against UV-induced (6-4) photoproducts were used. The results indicate a dose dependent formation of (6-4) photoproducts. Even a minimal erythema dose (25 mJ/cm2) produced (6-4) photoproducts, demonstrating that DNA damage occurs in corneal tissue following exposure to biologically relevant doses of UVB light.

Early cell kinetic effects of some drugs on the rat corneal and conjunctival epithelia.

The early cell kinetic response in the rat corneal and conjunctival epithelia was studied after a single topical application of dipivefrine, adrenaline and timolol with and without benzalkonium chloride. Benzalkonium chloride alone in different concentrations, 0.004%, 0.01%, 0.02% and 0.04%, respectively, was also evaluated. The stathmokinetic method and the tritiated thymidine technique were used to estimate the mitotic rate and the labelling index. Dipivefrine (Propine) gave a significant depression of the mitotic rate almost to the same extent as adrenaline in the corneal epithelium, whereas no changes were found in the limbal area and in the conjunctiva. Timolol (Oftan) with or without benzalkonium chloride, and benzalkonium chloride in different concentrations gave no obvious changes of the mitotic rate. No distinct drug effects on the labelling index were observed.