Tear Lipid Layer and Contact Lens Comfort
Tear Lipid Layer and Contact Lens Comfort
This review describes the impact of contact lens wear on the tear film lipid layer and how changes in the lipid layer might modulate contact lens-related discomfort. Relevant clinical, functional, and biochemical aspects of the tear film lipid layer are reviewed. Contact lens wear modulates these aspects of the lipid layer, specifically the prelens lipid layer thickness is reduced; tear evaporation rate is increased; tear breakup time is reduced; and the concentration of lipid components such as cholesterol esters, wax esters, and phospholipids varies. The full implications of these changes are unclear; however, there is some evidence that contact lens-related discomfort is associated with a thinner prelens lipid layer, increased lipid degradation, and greater secretory phospholipase A2 activity. Certain fatty acids appear to be associated with maintaining the structural stability of the tear film but their role in retarding tear evaporation and modulating contact lens-related discomfort remains to be elucidated.
Worldwide, approximately 140 million people use contact lenses for vision correction, with 85% wearing hydrogel or silicone hydrogel soft lenses. Despite the popularity of lenses, more than 50% of lens wearers experience lens-related discomfort and dryness, leading to a significant proportion to discontinue lens wear. These comfort-related issues make it critical for researchers to examine the causative factors of contact lens wear discomfort and dryness and to design ways to overcome a range of troublesome symptoms among lens wearers.
The stability of the tear film structure likely plays an important role in contributing to contact lens wear discomfort. The tear film is a thin (3 μm) fluid layer that covers the cornea and the anterior ocular surface. Apart from nourishing the avascular corneal surface by transferring atmospheric oxygen and other nutrients, it protects the ocular surface against invasions by pathogens or other foreign substances. The tear film also provides a quality optical surface and lubricates the ocular surface. A three-layered structure of the tear film was initially described by Wolff, comprising an inner mucoid layer (0.02–0.04 μm) covering the corneal epithelium, an intermediate aqueous layer (2.7 μm), and a superficial oily layer called the lipid layer (0.08 μm). The thicknesses of the tear film layers given above are based on the reflection spectra from the cornea, observed by King-Smith et al.
This review highlights the important role of the lipid layer in contact lens wear as this layer undergoes significant change during lens wear. In addition, variations in different aspects of the lipid layer in relation to contact lens wear and ocular comfort are reviewed.
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Abstract and Introduction
Abstract
This review describes the impact of contact lens wear on the tear film lipid layer and how changes in the lipid layer might modulate contact lens-related discomfort. Relevant clinical, functional, and biochemical aspects of the tear film lipid layer are reviewed. Contact lens wear modulates these aspects of the lipid layer, specifically the prelens lipid layer thickness is reduced; tear evaporation rate is increased; tear breakup time is reduced; and the concentration of lipid components such as cholesterol esters, wax esters, and phospholipids varies. The full implications of these changes are unclear; however, there is some evidence that contact lens-related discomfort is associated with a thinner prelens lipid layer, increased lipid degradation, and greater secretory phospholipase A2 activity. Certain fatty acids appear to be associated with maintaining the structural stability of the tear film but their role in retarding tear evaporation and modulating contact lens-related discomfort remains to be elucidated.
Introduction
Worldwide, approximately 140 million people use contact lenses for vision correction, with 85% wearing hydrogel or silicone hydrogel soft lenses. Despite the popularity of lenses, more than 50% of lens wearers experience lens-related discomfort and dryness, leading to a significant proportion to discontinue lens wear. These comfort-related issues make it critical for researchers to examine the causative factors of contact lens wear discomfort and dryness and to design ways to overcome a range of troublesome symptoms among lens wearers.
The stability of the tear film structure likely plays an important role in contributing to contact lens wear discomfort. The tear film is a thin (3 μm) fluid layer that covers the cornea and the anterior ocular surface. Apart from nourishing the avascular corneal surface by transferring atmospheric oxygen and other nutrients, it protects the ocular surface against invasions by pathogens or other foreign substances. The tear film also provides a quality optical surface and lubricates the ocular surface. A three-layered structure of the tear film was initially described by Wolff, comprising an inner mucoid layer (0.02–0.04 μm) covering the corneal epithelium, an intermediate aqueous layer (2.7 μm), and a superficial oily layer called the lipid layer (0.08 μm). The thicknesses of the tear film layers given above are based on the reflection spectra from the cornea, observed by King-Smith et al.
This review highlights the important role of the lipid layer in contact lens wear as this layer undergoes significant change during lens wear. In addition, variations in different aspects of the lipid layer in relation to contact lens wear and ocular comfort are reviewed.
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