Originally Posted by Spongebob
What's so special about monthly contacts like Night and Day that allows them to be worn continuously for a month? How is it that these contacts can be worn for so long, yet some have to be thrown away after only one wear?
The daily disposables are made of the old style HEMA hydrogel materials & concequently do not pass as much oxygen as the newer silicone hydrogels. They also are very very thin & rip easily which makes repeated use a problem. Silicone hydrogels on the other hand have much better transmission of oxygen at any normal lense thickness & are less likely to be damaged by cleaning than the HEMA type lenses of any type. Silicone hydrogels do not dry out as readily as the older types of soft contacts. Silicone hydrogels are less likely to crumble even if they do dry out than standard hydrogels as they tend to retain some flexability not that it is wise to use them though once the do dry out even if they appear to be recovered from the dry spell.
What makes it possible to wear them continuously for a month?
There are a few factors at play here. One is the high oxygen transmission, anouther is low deposit attraction. The specific nature of the deposits that are attracted to the lense as some types of deposits are actually beneficial name specific lipids (fatty acids) as some actually attract water and keep the lense moist & comfortable with little need for rewetting drops. This type of deposit takes a while to form & reach peak effectiveness so consequently I found the Air Optix night & Day not fully comfortable for about a week but very comfortable after that. Even more so than without conacts in fact. When I say not fully comfortable I mean that there are periods of appearant drying. This seems to go away after 1 week continuous wear. This will not likely happen if used as daily wear.