Daily and monthly contact lenses are not the same types of lenses. Although they look and in some cases feel the same the lenses are optimized to be used as a lens that gets replaced every day or cleaned and then reused.
With the use of a month the contact lens must withstand the daily cleaning process, this is why they are usually slightly thicker as dailies and oftentimes produce a slightly more dominant foreign body sensation.
But despite the thickness of both contact lenses the contact with the tear-film usually leads to deposits on the contact lens surface. In such a case the contact lens which is used for 30 days needs to have another lens surface to stay as fresh as possible over an extended amount of time.
For example, manufacturers of contact lenses nowadays apply plasma coatings to the lens surface like with the Focus night and day contacts which can work great with a tear film that shows more lipids in it. With dailies in most cases, this will not be an issue because the lens gets replaced anyway.
So as a chemist designing the lens material you would change the different aspects to fine tune the lens to meet the expectation of the wearer optimally. This is what happens for example with the brand Cooper vision which is one of the biggest manufactures for daly and monthly contact lenses.
Unfortunately, when I went to the consumer page on their website the information presented there was extremely comparable for the prowler 1-day lens as well as for the monthly lens which is also marketed under the prowler brand.
The daließ are made of the material called omafilcon A which has a water content of 60%. On the contrary, the monthly lens is made out of omafilcon B with a water content of 62%. Those are not the only differences you can see differences in the level of oxygen permeability as well as in the thickness. Both of them work great but although they are very similar they are not the same.
But of course, this is just one lens I picked and I can not speak for the whole industry here and check every manufacturer. But maybe the manufacturers themselves could highlight the differences better so both lenses were less likely to appear pretty much the same in the eyes of the consumers.
Monthly contact lenses are usually available in a bigger variety of prescriptions compared to daily contacts. This has more to do with economical factors for the company producing them compared to the manufacturing process or the materials.
One of the things that could make a difference rather from the technical aspects of the lenses or the comfort is the smaller likelihood of an severe infection with daily contact lenses compared to monthly ones as this study here says.
frankly spoken I believe it is good to double-check and in the past, there were some cases that got the situation a little heated for the manufactures of contact lenses in the example you can read below the manufacturer Bausch and Lomb get mentioned if you want to follow through the link as well as Johnson and Johnson in the second part.
Why Do Consumers Still Believe Monthly and Daily Contact Lenses Are the Same?
During the 1990 and 2000 contact lens manufacturers were under pressure due to their misleading marketing. In short, the same contact lens type was used for monthly wear as well as daily. If you want to read the more extensive information on this topic I have a link for you here ready.
But this is not all if you want to read on more about those cases I have another article excerpt from the Washington post from 2001 were the following is written:
Johnson & Johnson has agreed to pay as much as $860 million to settle lawsuits accusing the company of misleading consumers into prematurely throwing away disposable Acuvue contact lenses.
The suits contended that the company drove up sales of its 1-Day Acuvue soft lenses by advising consumers to use them just once, even though the product is identical to regular Acuvue lenses, which may be worn as long as two weeks.
NY Times
So here you have your answer. The monthly and daly lenses are not the same. One thing you should take with you is to not extend the wear with one of the contact lens types by your own. Usually for you nothing changes but your eye care professional will detect the changes in your eyes after a few months. So make sure no matter what you decide to buy, replace them as they should replaced.
Although daly contact lenses are usually double the price compared to monthly lenses the minimized risk factor for eye infections are the point I would decide on what to buy. I hope you found the information you wear looking for.
I wish you a great day.