Hi Lydia
Wearing contact lenses can be much better than glasses for 2 groups of people in particular-those with very high spectacle powers, and those with a big difference in spectacle power between the 2 eyes. In these groups of people, wearing glasses can cause an uneasy feeling or even sometimes headaches.
In the context of long duration contact lens wear each day, you need to differentiate between the different kinds of contact lenses.
Those with high spectacle powers (especially myopes-shortsighted people) and wear soft lenses for very prolonged periods each day run a higher risk of developing problems. These can range from dry eyes (since the thick contact lens material can act like a sponge and soak up some proportion of your tears, simplistically), to 'contact lens overwear' - a situation where people develop small 'spots' or erosions on the corneal surface due to a combination of dryness and lack of oxygen. This lack of oxygen can sometimes cause blood vessels to grow into the cornea.
This doesn't mean that every soft contact lens wearer will develop these problems. Still, it is important that these patients get regular eye check ups, so that if problems develop, they can be addressed at an early stage and alternative methods explored.
Besides soft lenses, there are also rigid gas permeable (RGP) contact lenses. These cause much less problems even with prolonged wearing, because firstly they tend not to dry the eyes out so much, but even more importantly they allow much better oxygen transmission through to the cornea. Being smaller than the cornea, these lenses do not cover the all important limbus, and so do not affect the corneal limbal stem cells. If you wear RGPs, and wear them for 16 hours/day, but have regular eye check ups and have been doing well so far, there may not be too much to worry about.
For those who are not familiar with RGPs, before you rush out and demand a pair from your friendly optometrist, bear in mind that it takes a while to get used to these lenses. At the beginning, many beginner wearers feel a constant foreign body sensation like an eyelash in the eye. A number of people give up before they actually get used to these lenses. But for those who can get used to them, they are a great option, especially for correcting high degrees of spectacle power.
