Nidek ConfoScan 4 (z-ring) measurements over soft contact lenses

The aim was to compare the thickness of each corneal sublayer and the visualization of superficial epithelial cells measured with the ConfoScan 4 (CS4) z-ring with and without the use of a soft contact lens and to evaluate the recovery rate of corneal staining after measurement with the CS4 (z-ring) with and without the application of artificial tears (ATs).

Twenty-eight subjects aged 18 to 35 years were recruited to have measurements with the CS4 (z-ring) on 2 different days. The measurements were performed over soft contact lenses (hydrogel lens or silicone hydrogel lens) on the first day and on the naked cornea on the second day. The recovery rates of the corneal staining induced by the measurements at the second visit were monitored for 5 hrs after measurements, one eye with the application of ATs and one eye without.

No significant differences were found in the thicknesses of the central cornea and the sublayers measured with or without soft contact lenses. The intensity of epithelial cell images was improved with measurement made over hydrogel lenses, and on average, grade 3 (coverage) staining was observed in the corneas immediately after measurements without contact lenses. The recovery rate of the corneal staining did not improve with the application of ATs.

Thickness measurements with the CS4 (z-ring) were not affected if made over soft contact lenses. The use of a soft lens to buffer the cornea during measurements was effective in eliminating corneal dehydration, preventing staining induced by the z-ring without affecting the corneal thickness measurement. It also enhanced epithelial image brightness, which may improve the accuracy in pachymetry.