Characteristics of corneal staining in hydrogel contact lens wearers

Corneal fluorescein staining is widely used in clinical practice and research, but little information exists on the distribution of staining in a large group of asymptomatic contact lens wearers. This cross-sectional study took place at 3 centers, and investigated the pattern of corneal fluorescein staining in both eyes of 98 hydrogel contact lens wearers. We also investigated the strategies used by three experienced clinicians to grade corneal staining. Overall corneal staining was graded using a scale from 0 to 4 in one-half steps, and five corneal zones, superior, inferior, nasal, temporal, and central, were also graded. The average overall staining grade for both eyes of our subjects was 0.50, with an average of 0.57 for the right eye and 0.44 for the left. This difference between the eyes was statistically significant (p = 0.011). In addition, a comparison of the zones within each eye showed a significant difference (p = 0.0001) among the zones. Corneal staining between the two eyes was also positively and significantly correlated (r = 0.58; p = 0.0001). Grading strategies among clinical investigators were significantly different (p = 0.0001), indicating a potential source of bias in multi-centered studies. The difference in corneal staining between the eyes may represent a source of systematic bias, and could be due to grading the right eye before the left. The correlation in corneal staining between the eyes indicates that the two eyes of a subject cannot serve as independent data points. One-third of the subjects who participated in this study had notable corneal staining. This finding underlines the importance of regularly checking corneal staining in clinical practice.