Recovery of the water content of hydrogel contact lenses after use

The aim of the present study is to determine the amount and time of water-content recovery of ionic contact lenses (Surevue and Acuvue) and non-ionic contact lenses (Soflens 38, Soflens 66 and Optima 38) when submerged in maintenance solution for 9 h. Using a hand-held refractometer, we measured the water content of the lenses upon removal from the eye, and after 15, 30, 45 min, 1, 2 and 9 h in soaking solution. Both ionic lenses presented pre-wear water content of 58%, while two of the non-ionic ones (Soflens 38 and Optima 38) registered 38.6% and the third (Soflens 66) had 66%. We found a significant increase (p < 0.05) in water content after submersion in the Opti-Free solution for all the time periods studied and for all lenses. The water-content recovery was faster in the non-ionic lenses (Soflens 38, Soflens 66 and Optima 38) than in the ionic ones (Surevue and Acuvue), especially at 15 min. After 9 h in the soaking solution, the Surevue Acuvue, Soflens 38, Soflens 66 and Optima 38 lenses reached water-content recovery values of 99.7%, 99.6%, 99.8%, 99.8% and 99.6%, respectively, without significant differences (p > 0.05) between ionic and non-ionic lenses, although the non-ionic lenses reached slightly higher water-content values at all the times studied. These results indicate that when the refractometer technique is used to measure water content, the lens types used in this study regain their initial water-content values after 9 h in soaking solution. These data indicate the time needed for hydrogel contact lenses to reach their maximum water content after removal from the eye and submersion in maintenance solution. By ensuring maximum water content and minimum reduction of oxygen for the cornea, the specialist can help avoid clinical signs and symptoms related to low water content in the lenses.