Issue link: https://optometricmanagementsupplements.epubxp.com/i/587112
S P E C I A L E D I T I O N 2 0 1 5 • O P T O M E T R I C M A N A G E M E N T . C O M 13 functional and complex in makeup. Te base layer of the tear flm is comprised of tear flm mucins, which extend from inside the epithelial cells, through the hydrophobic cell membrane, to the outside of the cell. Called the glycocalyx, these high molecu- lar weight mucins are bound to the cornea on one end but have hydrophilic tails that extend into and hold the aqueous to the cell surface (Figure 1, page 15). 1 Because cell membranes are largely hydrophobic, without the T EARS ARE vital to maintain a healthy ocular surface and an optically clear entrance to the eye. Without them, we would not have the sharp retinal image that allows us to see the world and each other clearly. Tears are rich and com- plex, and that richness is necessary for their efcacy. Water alone could not nourish and protect the delicate corneal and conjunctival epithelia, nor give us the clear, stable vision we experience daily. Te human tear flm is optimized to address a unique additional challenge: cre- ate a smooth, optically transparent, refractive interface between the hydrophilic environment of the eye and the hydrophobic external environment of the air. Tis interface is stabilized through synergistic interac- tions of hydrophilic, amphiphilic and lipophilic tear-flm components, including ocular mucins, proteins and lipids. Tese components work in concert to continuously lubri- cate, moisturize, smooth, oxygenate, eliminate waste and protect the ocular surface during and between blink cycles. A COMPLEX STRUCTURE Te old picture of the tear flm consisted of a simple three-layer — mucin, aqueous and lipid — structure. Re- cent research has revealed it to be much more complex, with more than 18 known mucins, 491 proteins (identifed so far) and at least 153 lipid types — all of which interact to provide structural integrity to the tear flm while also performing their individual functions. 1,2,3 And each of the three major components of the tear flm is itself multi- AN INNOVATIVE NEW CONTACT LENS DESIGNED TO WORK WITH THE TEAR FILM INSPIRED BY THE SCIENCE OF TEARS Bar t Johnson, Brian Pall, O.D., M.S., F.A.A.O., and Charles W. Scales, Ph.D. Functions of the Tear Film Mucins • Anchor and stabilize the tear flm • Protect ocular surface from abrasion through formation of the glycocalyx • Lubricate cell surfaces so corneal epithelium doesn't stick to tarsal conjunctiva • Reduce shear stress during blink Spotlight on Science FE ATURE OPTOME TRIC MANAGEMENT