The clinical impact of contact lens wear on neural structure and function of the cornea

Contact lens (CL) use is growing rapidly, with a current estimate of over 100 million wearers worldwide. Vast improvements in materials and designs have occurred over the past decades with advancements in the understanding of ocular surface health with CL wear. However, the potential impact of CL on neural structures and function of the ocular surface, particularly in relation to the richly innervated cornea, remain poorly understood. Problems with sensation such as CL discomfort and conditions that may be associated with lens wear including dry eye disease also remain pervasive. This narrative review discusses the findings from studies involving soft or rigid CL wearers, assessed with c linical techniques designed for examining the neural integrity of the cornea, namely in vivo confocal microscopy and esthesiometry. While the collective findings remain equivocal in terms of the changes in corneal nerve morphology and function with conventional CL wear, more specialised CLs, namely orthokeratology lenses, which mechanically manipulates the structure of the cornea seem to produce more prominent changes in nerve distribution and sensitivity reduction. Given the intricate relationship between neural and immune mechanisms in maintaining balanced ocular surface health, the potential links between these structural and functional findings with parainflammation and neuroinflammation, as well as clinical issues including CL discomfort and dry eye disease, are also explored.