Eye Oxygen and Lenses

• When contacts are worn every day of the week for extended periods of time (more than 16 hours a day) the eye can suffer from oxygen depletion as a result. Since contacts cling to the front of the eye, this pressure tends to cut off blood vessel circulation (and thus oxygen) in the cornea.
  
  When this occurs for extended periods of time each day, old blood vessels trying to supply oxygen to that part of the eye veer off, prompting new blood vessels to form, according to the online website Healing Daily.com.
  
  

New Blood Vessels

• This new blood vessel formation---a process known as angiogenesis, according to the University College Dublin---is a direct result of the original blood vessels' inability to reach the cornea with oxygen. However, new vessels are not regulated like the original vessels in growth or function, which can severely affect the cornea and sight if not addressed medically---or if contacts are worn too long during the day and/or at night.
  
  

Eye Infection from Contact Use

• In addition to depleting eye oxygen, long-term use of soft contacts (especially overnight) can create another potential eye-damaging problem: microbial keratitis, an eye infection. Microbial keratitis, while not generally a sight-threatening condition, does have the potential to do permanent eye damage to the cornea, which could result in partial or complete blindness.
  
  

Soft Vs. Hard Lenses

• When evaluating eye health, soft contact lenses versus hard lenses should be considered, but may not make a difference if precautions are taken. For example, research shows that hard contact lens wearers are less likely to get microbial keratitis (20 percent less in comparison to extended-wear soft contact users, and 3 percent less likely than daily-wear soft lens wearers). This is due to the fact that hard lenses are typically removed at bedtime; not left in overnight like soft lenses.
  
  

Significant

• So while contact lenses can potentially damage the eye, and even damage sight severely, this damage is normally only the result of extreme overuse.