People with mild dry eye who start wearing contact lenses for the first time may experience an increase in dendritic cells—indicating inflammation—in the first few weeks of wear and a decrease in corneal sub-basal nerve cells, a team of Chinese researchers report. Their study, published in Eye Contact Lens, also suggests the dendritic cells can start to decrease after about a month of wear, allowing the sub-basal nerve cells to regenerate, although the latter could be a slow process and not start until week 12.

The study enrolled 20 non-contact lens wearing participants with mild dry eye. Each person underwent ocular surface evaluations including an ocular surface disease index (OSDI) questionnaire, tear film break-up time (TBUT) and Schirmer I test at baseline and then at one, four, 12 and 24 weeks. In vivo confocal microscopy was used to examine the density, area, number of dendrites, total dendritic length and sub-basal nerve densities in the central and peripheral corneas. Only right eyes were included in the investigation.

After wearing contact lenses, corneal dendritic cells were activated and increased, indicating ocular surface inflammation, the researchers noted. They also observed the activation and peak of dendritic cells at week four, when inflammation may be greatest. The peripheral dendritic cell density started to increase the first week, but the central cells didn’t increase until week four. After four weeks, both peripheral and central cells began to decrease, but they were still higher than baseline at week 24.

The change at week four could be due to the adaptation related to psychological factors, such as participants’ discomfort when wearing contact lenses for the first time, the researchers noted.

Conversely, the central and peripheral corneal sub-basal nerve densities decreased early on, with the peripheral cells tending to increase starting at week 12. In the early weeks of the study, the sub-basal nerve cells were negatively correlated with dendritic cell parameters, since the latter increased while the sub-basal nerve cells decreased. But at four weeks, both showed declines.

The significant decrease in sub-basal nerve cells was different than the findings from previous studies. The researchers thought this could be due to the fact the participants in the current study had mild dry eye, while other investigations included healthy subjects or participants “without limits.”

Measurements of corneal dendritic cells and sub-basal nerve cells may be helpful for patients considering therapeutic interventions because the measures could directly evaluate treatment response and complications, the investigators said in their paper on the study.

Further studies are needed to demonstrate whether the change of sub-basal nerve cells is permanent or temporary and the exact mechanism of correlation between sub-basal nerve cells and dendritic cells, the investigators added.

Liu Q, Xu Z, Xu Y, et al. Changes in corneal dendritic cell and sub-basal nerve in long-term contact lens wearers with dry eye. Eye Contact Lens. February 25, 2020. [Epub ahead of print].