Purpose: Ocular dryness is a common complaint of contact lens wearers. Decreased tear volume leads to an increase in ocular dryness. Comparing the results of the Zone-Quick phenol red thread test on a patient with and without contact lenses may be useful in deciding which lens material allows the most residual tear volume to remain on the eye. This study compares the tear volume without lenses and while wearing high and low water hydrogel and silicone hydrogel (SiHy) lenses.
Methods: The Zone-Quick test was performed on both eyes without lenses. The test was repeated using low and high water SiHy lenses (Ciba Focus Night & Day lotrafilcon A, 24% and Acuvue Advance, galyfilcon A, 47%) and hydrogel lenses (Bausch & Lomb Soflens 38 polymacon, 38% and Acuvue 2 etafilcon A, 58%). 225 subjects were tested with both types of high and low water lenses. The age range was 22-32.
Results: The Zone-Quick measurement without lenses showed no difference in baseline (t=0.29, p>0.05). Low water baseline is 23.91mm while with the low water lens is 24.38mm. Baseline for high water is 24.06mm and high water lens average is 21.84mm. Data were combined for both types of high and low water content lenses. The Zone-Quick test results obtained while wearing one of the lenses was subtracted from the results obtained from the no lens condition. These differences for the low and high water content lenses were then compared with a mixed design ANOVA. Results indicated that water content had a significant impact on tear volume (F=14.21,p<0.05). High water content lenses yielded a lower residual tear volume than low water lenses.
Conclusions: This study indicates the tear volume is unchanged while wearing low water SiHy or hydrogel lenses. It is significantly reduced with both types of high water lenses. This supports the idea that patients with decreased aqueous production may be better fit with lower water content lenses since the tear volume will not be reduced.