Eye Rubbing and Corneal Structural Changes: Randomized Case-Control Trial
The role of eye rubbing (ER) in keratoconus is well established, however the effects of ER on the cornea in healthy eyes is uncertain. This study assessed primarily the changes in central (3mm), paracentral (4-5mm) and peripheral (6-7mm) cornea of healthy volunteers following ER. Tear film stability was also measured.
A prospective, single-centre randomized control study on 49 healthy participants (98 eyes) was performed (http://clinicaltrials.gov/show/NCT02131740). Exclusion criteria included history of contact lens wear, atopy or previous ocular surgery. A randomly chosen eye of each subject was rubbed by the same researcher (EDH) for 2 minutes using an index finger in a circular, clockwise motion over a closed eyelid with the eyes in primary position of gaze. The fellow eye (control) was undisturbed. Corneal parameters and tear film break-up time (TBUT) were measured (OCULUS Pentacam) before and immediately after rubbing. Data was analyzed using paired t-tests and Larry Thibos vector analysis.
Corneal astigmatism increased from 0.85D to 1.03D with ER (p=0.004). Kmax (44.19 vs 43.46 (p=0.223)), anterior Q-value (-0.31 vs -0.31 (p=0.822)) and posterior Q-value (-0.38 vs -0.39 (p=0.182)) did not change significantly after ER. TBUT decreased from 5.31s to 3.91s with ER (p=0.0001). Thibos vector analysis showed a significant negative change in the J0 component in the central zone of rubbed eyes only (-0.158D ± 0.262D vs -0.273D ± 0.327D (p=0.037)), demonstrating a tendency towards against-the-rule astigmatism after rubbing. No statistically significant oblique astigmatism (J45) changes were observed in any of the three regions (p-values: 0.49, 0.85 and 0.91, respectively).
ER on healthy corneas induces significant change in astigmatism and tear film behavior. The significant changes in the central cornea following ER for two minutes in healthy volunteers may explain the patterns of progression in keratoconus following excessive ER. These findings have implications in understanding of the pathophysiology of keratoconus.