Contact lenses suddenly becoming weaker
I wear (monthly) contact lenses to correct for myopia and astigmatism, and recently I have noticed that, after a couple of weeks of use, the right contact lense suddenly becomes weaker and my visual acuity in that eye is substantially impaired. This has happened three times over the last month or so, with three different pairs of contact lenses. Initially, they're both fine, but after a while the right lense suddenly appears to become weaker by around the same degree. These incidents did not take place in similar circumstances, i.e. not after long periods of wear, and I've worn contacts for some years without ever experiencing this problem. I have not recently changed to a different brand or prescription.
Since all three pairs of contact lenses which caused this problem came from the same batch of three, I'm inclined to think that it may have simply been the result of a faulty set. I haven't experienced any other eye difficulties recently. However, I'd like to know if anyone has ever experienced the same problem, and if so what happened.