How can a 'bad' pre and post lens tear film lead to discomfort?

• A. Pre-lens instability leads to friction between lid and lens; post-lens instability leads to friction between lens and cornea/conjunctiva; Both
• B. Pre-lens instability leads to friction between lid and lens only
• C. Post-lens instability leads to friction between lens and cornea only
• D. Neither affects comfort

Answer: (C)

The key idea is that comfort from contact lens wear hinges on lubrication between the lens and the eye, especially on the back surface where the lens rests against the cornea and conjunctiva. If the tear film on the back of the lens (the post-lens tear film) is unstable, there isn’t consistent lubrication there. Each blink can then cause the lens to rub more firmly against the corneal and conjunctival surfaces, producing friction, micro-irritations, and a gritty or dry sensation that drives discomfort during wear.

A unstable tear film in front of the lens (pre-lens) would mainly affect how the lid slides over the lens and how tear fluid is distributed in front of the eye. That can influence lid movement comfort, edge effects, or front-surface sensation, but the most direct source of traction and irritation leading to the classic discomfort during wear comes from the back surface interaction when the post-lens tear film is not providing smooth lubrication.

So, the friction most responsible for the described discomfort is between the lens and the cornea/conjunctiva due to post-lens tear film instability.