What is a key characteristic of good tear exchange in GP lenses?

The key characteristic of good tear exchange in gas permeable (GP) lenses is that they are designed to have a fitting relationship that allows for adequate movement on the eye. A lens that fits loosely helps create space beneath the lens where tears can flow in and out. This movement is essential because it promotes the exchange of tears that helps to maintain corneal health by providing nutrients and washing away debris and waste products that might accumulate.

When a GP lens fits tightly, it can restrict tear exchange and lead to discomfort or reduced ocular health. Proper movement of the lens encourages the fresh tear film to flow beneath it, allowing for hydration of the cornea and maintaining a healthy ocular surface. This characteristic ensures that the lens is not only stable during normal functional activities but also allows for optimal tear exchange for the wearer's comfort and eye health.