Osmolality of the tear fluid in the contralateral eye during monocular contact lens wear.

The effect of monocular hydrogel contact lens wear on the osmolality of the tear fluid in the ipsilateral and contralateral eyes was measured. The hydrogel contact lenses were of similar diameter and either 38% or 70% water content with thicknesses of 0.07 mm, 0.15 mm or 0.30 mm. The ipsilateral eye showed an initial 2 m.osm/kg decrease (hypo-osmotic) in tear fluid osmolality from baseline after lens insertion. After 5 min the osmolality increased (hyperosmotic) to 15 m.osm/kg greater than baseline, remaining around this level for the 60 min of lens wear. This hyperosmotic change was attributed to an increase in water evaporation due to disruption of the tear film by the contact lens. There was a similar pattern of change in the contralateral eye, but of smaller magnitude. All contact lenses produced a similar effect on tear fluid osmolality, except the combination of a 0.30 mm thick lens of 70% water content fitted with a flat bearing relationship which induced a greater hyperosmotic change after 5 min wear.