Transporting and wearing contact lenses travelling is not always the most practical thing, but I decided that for my 4 month trip I could manage it. With only a 40 litre backpack (it's small enough to be carry-on) my main concern was the contact lens solution: I knew I couldn't carry a 4-month supply in my backpack.
Here are the things that I would consider before you pack your lens:
1. How much solution do you use and will you need for your trip?
Track how long it takes you to use a bottle of solution before you leave so you can plan accordingly. Allow yourself plenty of solution as the nature of travelling may mean that you take your contact lenses out more.
If you've run out of time to do this, generously fill your pot with solution to measure how much you use. Add about 10ml extra for cleaning the lens. Now divide this number by the ml in the bottle and you have an estimate of how many days each bottle will last you.
2. Do you know where you can buy more lenses or solution when required?
I had to really search online boards to understand where I would and wouldn't be able to purchase contact lens solution in Asia. If you're visiting Europe or America ask on message boards which stores stock contact lens solution and good brands to buy.
Countries that I found contact lens solution in/would guess you can find in large cities include: Japan, Thailand, Vietnam, Singapore, Malaysia and Indonesia (on the large touristy islands like Bali).
Countries where I would not expect to easily source items: Laos, Cambodia and Fiji.
NOTE: This is speculation. I bought solution in Thailand and instructed my friend and boyfriend, who met me during the trip, to bring supplies to ensure I had enough for the duration.
3. How will you ensure that your lenses remain sterile?
Be extra diligent when washing your hands. I would carry anti bacterial hand soap with you which is great when faced with horrible, dirty bars of soap at hostels or guesthouses.
4. Would a combination of lenses fit your needs?
I carried a limited number of disposable contact lens for use when partying or on night trains for when I wasn't convoked they would be taken care of properly, making sure my monthly lenses remained sterile. The optician will want to see you to assess your suitable for different types of lenses even if you've used them before, so make sure you leave plenty of time to stock up.
5. How will you ensure you have the correct lens prior to your trip?... and won't have a bundle stacked up upon your return
Inform your contact lens provider that you won't in the country and they may be able to give you an advance in lens, as they did for me. Ask if they can cancel/freeze the standing order while you're away.
6. Will airline regulations be a problem with regards to your contact lens solution?
If you are not planning to check in a bag contact lens solution, as with all liquids, must be in bottles below 100ml. Specsavers sends out their solution in 250ml bottles and it isn't easy to decant due to the specialised tip on the bottle. Why not try going in store and to see if you can swap the larger bottles for their sample 100ml size.
Alternatively, larger airports in the UK should stock 100ml bottles of solution in Boots. I would only wait til the airport if you're absolutely certain you want to use your bag as carry on and you've exhausted all other options.