It is unfortunate that your friend had to undergo an emergency eye surgery but it may not have been related to wearing contact lenses and it would not be right to associate the two in the absence of other parameters.
All the precautions and instructions must strictly be followed while wearing contact lens without which they can result in a multitude of problems.
Contact lens is primarily used in conditions like Myopia (near sightedness), Hypermetropia (far sightedness) and Astigmatism in place of the regular glasses. They are not only used for cosmetic reasons but also because of the convenience.
Some contact lens can be worn intermittently. Such soft lenses should be discarded after the occasional wear. This is a very convenience option as it eliminates the need for cleaning and disinfecting the lenses.
All other soft lenses are usually worn for the entire day and then removed to clean and disinfect every night. Even these have to be replaced weekly, monthly, quarterly or yearly as the case may be. Soft extended wear lenses can be worn overnight for 1 to 2 weeks depending upon the type. Some lenses called RGP (Rigid Gas Permeable) can last for years with proper care and precautions. Under no circumstances should contact lenses be worn beyond their replacement time schedule as it could cause many problems.
Wearing lenses overnight is generally not recommended as the amount of oxygen available to the eye is much less and the chances of infection to the eye are much more. It is safer to remove them at night.
Most of the problems and infections arising from wearing contact lenses can be prevented by proper fitting, following instructions and taking care and maintenance.
The most common side effects of wearing contact lenses continuously are irritation of the eyes, redness or blurred vision. Some of the common causes for these are poorly fitted lenses, wearing out of lenses, poor care of the lenses, and change in the power of eyes or sensitivity or allergy to cleaning solutions.
If these minor conditions are not looked into then it may result in greater infections or even corneal ulcers.
Use only the recommended cleaning solution as some solutions can be incompatible with certain lenses or may contain chemicals which can cause eye allergies in some persons.
If anyone experiences redness of the eyes accompanied by pain or blurred vision along with light sensitivity then this could be due to corneal ulcer or infection.
The surface of the cornea sometimes gets minor abrasions (scratches) due to either dirt or foreign particles getting under the lens or wearing the lens for longer durations of time.
Such conditions can lead to further complications. Proper cleaning and disinfection of the lenses is a must to avoid this.
Allergy due to cleaning solutions can easily be treating by washing the eyes with plenty of water and putting some anti allergic eye drops.
Sometimes small amounts of cosmetics get under the lens and cause a greasy coating on the lens. This must be cleaned immediately. It can also be done by polishing by the optician or else lenses must be changed.
In spite of taking all precautions and following all the cleaning instructions carefully if you still experience any of the above mentioned symptoms then it may actually have to do nothing with wearing contact lenses. It could be due to some other eye conditions like Cataract, Glaucoma , Diabetes or severe infection which seems like the case in your friend's case.. Get your eyes examined by an ophthalmologist for a clearer evaluation.
Whether the condition is suspected to be because of wearing contact lenses it must be diagnosed and treated to avoid further complications and no generalized hypothesis should be made.