The effect of tear film break-up on symptoms, optical quality, and visual quality in normal, dry eye, and contact lens patients

The tear film is a layer of fluid that coats the surface of the eye, and is often, therefore, referred to as the "pre-corneal tear film." One of its primary functions is to provide the eye with a smooth optical surface. This uniform optical surface is essential for the maintenance of high-quality retinal images and vision. During periods between blinks, the tear film is not stable and does not remain uniform on the surface of the eye. Instead it appears to disrupt locally, a phenomenon called tear film break-up. Irregularities in tear film thickness can produce optical aberrations or light scatter, which alone or in combination, can decrease optical quality of the eye and potentially compromise visual function. My thesis research examined the spatial and temporal characteristics of tear film break-up and monitored the optical, visual, and discomfort consequences of tear film break-up. To this end, clinical methods such as sodium fluorescein and retroillumination were utilized to measure tear film stability, while Shack-Hartmann wavefront sensing was used to quantify the changes in optical aberrations and light scatter of the eye resulting from break-up of the tear film. Normal, dry eye and contact lens wearing subjects showed tear break-up with extended blink suppression. Tear break-up was also observed during the reduced blinking that accompanies attention demanding visual tasks such as computer use, during which subjects experienced associated increases in dry eye symptoms including visual complaints. Increases in optical aberrations and light scatter corresponded temporally and spatially with areas of tear break-up resulting in reduced optical quality of the eye. Decreased visual acuity was correlated to decreased optical quality. These results provide an explanation for visual complaints often reported by dry eye and contact lens patients.