Hydrogel and overnight orthokeratology (OK) contact lens (CL) wear can increase tear film osmolarity, a new study finds. Researchers observed osmolarity values in non-CL wearers and those who have worn hydrogel and overnight OK lenses for at least three years, and found osmolarity was within normal limits in all groups, although it was significantly lower in non-CL wearers compared with hydrogel and OK lens wearers. Osmolarity returns to baseline one month after discontinuation of CL wear.