Abstract
Purpose: :
Epithelial cells at the ocular surface are subject to significant shear forces (friction) generated during eyelid blinking as well as contact lens wear, especially in the presence of a compromised tear film. Given the recent discovery that ocular surface cells express mRNA of Lubricin, a cartilage boundary lubricant present in the knee, the purpose of this study was to assess the boundary lubricating ability of Lubricin at the cornea-eyelid biointerface.
Methods: :
Fresh human corneas and eyelids were mounted on a BOSE ELF3200 biomechanical testing machine with custom sample holders, forming a cornea-eyelid interface. Sample surfaces were articulated against each other at effective sliding velocities ranging from 0.3-30 mm/s under physiological loads of 15-20 kPa. Samples (n=6) were tested serially in lubricant baths of SterilePlus saline (Baush & Lomb), Aquify (CIBA Vision), and Lubricin purified from media conditioned by cartilage explants @ 300 ug/mL. Control samples (n=3) were tested in saline followed by bovine serum albumin (BSA) @ 300 ug/mL. Both static and kinetic friction coefficients were calculated.
Results: :
Lubricin functioned as an extremely effective friction-lowering boundary lubricant at the cornea-eyelid interface. At all sliding velocities, both static & kinetic frictions were greatest in saline, slightly decreased in Aquify, and lowest in Lubricin. Kinetic friction values were essentially invariant with sliding velocity, indicating a boundary mode of lubrication was operative, ranging from 0.28±0.02 (mean±sem) in saline to 0.23±0.02 in Aquify, to 0.15±0.02 in Lubricin. The friction lowering effect of Lubricin appeared specific, as BSA at 300 ug/mL did not reduce friction compared to saline.
Conclusions: :
These results indicate that Lubricin functions as an ocular surface boundary lubricant to reduce friction and wear, possibly better than currently available eye drops. These data support our hypothesis that Lubricin protects the ocular surface against significant shear forces generated during an eyelid blink and contact lens wear.
Keywords: cornea: tears/tear film/dry eye