This answer comes from H. Dwight Cavanagh, M.D., The W. Maxwell Thomas Chair, professor and vice chairman of ophthalmology at the University of Texas Southwestern Medical Center at Dallas.
Although it is widely believed that contact lenses exacerbate the potential damage to the eye from chemical exposure, recent scientific studies indicate that rigid (hard) and hydrogel (soft) contact lenses actually decrease the exposure of their wearer's eyes to toxic irritants in the environment.
Perhaps the best study of this issue was published in the January 1992 edition of the Journal of the Contact Lens Association of Ophthalmologists (CLAO Journal) by eye researchers who examined 128 cases of occupational eye injuries in individuals who were wearing contact lenses at the time. This study confirmed and extended previous findings that, overall, contact lenses partially protected and minimized--rather than worsened-- injuries.
Although the study also looked at a variety of injuries, including physical trauma, the data demonstrate that types of contact lenses can provide important protection by decreasing the exposure of the eyes to volatile or toxic solvents in the air.
In another study of hard contact lenses, researchers simulated chemical splash accidents in laboratory animals. They found that eyes fit with hard contact lenses experienced less corneal damage and that contact lenses essentially provided protection against strong acids. In this study, animal's eyes were exposed to acetic acid, n-butylamine, or acetone.
A similar study examined how well soft contact lenses absorb trichloroethylene (TCE) and xylene vapors. This study found that high water-content contact lenses increased the concentration of the vapors within the lenses. But the researchers also found that, although the uptake of the vapors by the contact lenses was considerable, the solvents were released primarily back into the air, not the eye. In other words, wearing contact lenses did not increase exposure of the cornea to potential damage from chemicals.
Image: Michigan State University
Sterile saline, which is a wetting agent used by many contact lens wearers, also appears to play a role in limiting the damage certain chemicals and vapors can do to the eye. One of the most recent studies, conducted at the University of Nebraska Medical Center, compared the absorption rate of saline solutions exposed directly to solvent vapors with the absorption rate of saline used with contact lenses. The introduction of saline alone did not appear to further disperse the chemicals or vapors over the eye's surface. And results from the test of the saline-contact lens combination further demonstrated that eye damage was decreased; most of the vapors absorbed by the contact lenses were released back into the air.
These observations have major relevance, especially for industrial and laboratory workers, who may be laboring under traditional workplace restrictions that bar them from using contact lenses while on duty. Such restrictions appear to be unnecessary in many instances.
But we must remember that the findings mentioned here do not apply to all chemicals and solvents, so great care and knowledge of various chemicals and their effects continue to be necessary. Also, ophthalmologists concur that additional safety precautions should be taken when working around concentrated chemicals that can cause severe occular irritation or surface damage to the cornea; a pair of well-made safety goggles should always be used in occupations that put employees at risk of exposure to severely toxic chemicals and vapors, such as concentrated acids or lye.