CONTACT LENSES

   Contact lenses are thin plastic discs that rest directly on the cornea.

Advantages of contact lenses

	Better correction for certain eye conditions, such as keratoconus and irregular astigmatim.
	Thick glasses reduce the side vision in spectacles because the power is only at the center. The frame also reduces side vision. This problem is overcome by contact lenses.
	No fogging of vision from humidity and perspiration.
	Cosmetic approach to eye problems.
	Very comfortable for sportsmen.
	Use of optical instruments such as microscope and camera becomes easier.

Disadvantages of contact lenses

  Expensive.
  Cost ineffective due to damage & loss.
  Requires special care.
  With hard lenses wearing time gradually builds up so strong motivation is required for successful results.

Different Type of Lenses

  Rigid Lenses. 
  Soft Lenses. 

Rigid Lenses Variety:

  Hard
  Semisoft
  Oxycon lenses

All the above three are same except for amount of oxygen passing through it. This is minimum in hard lens and maximum in oxycon lens. Increased oxygen permeability of the lens increases comfort and wearing time.


Advantages of Rigid lenses over soft lenses

  Durable.
  Inexpensive.
  Easy to clean and maintain.
  Provides better vision than soft lenses (in some cases).

Disadvantages of Rigid lenses over soft lenses

  The wearer needs more time to get used to. 
  Increased number of visits to the optician.
  More likely to slip away from the cornea – so unsuitable for active sports.
  Dust and foreign bodies caught behind the lens can cause irritation and watering.
  Not suitable for part time wearer.

Soft Lenses

These are made of gel like plastic and absorbs water like a sponge, making lens more comfortable to wear.

Advantages

  More comfortable so fits easily.
  Can be worn part time.
  Does not pop out so better than hard lenses for active and sports related lifestyle.
  Remains centrally located in the eyes.
  Dust does not get trapped so comfortable even in dusty atmosphere.

Disadvantages

  Expensive.
  Requires frequent replacement – at least once in a year.
  Needs proper care and cleaning.
  Vision may not be as sharp as hard lenses especially with astigmatism. However these days toric soft lenses are
     available for astigmatism which are even more expensive.


Soft contact lenses deteriorate over time as they become worn, dirty and accumulate protein deposits that cannot be removed even by elaborate cleaning. This can affect visual acuity and increase discomfort. There are chances of infection of the lens leading to corneal ulcer. These ulcers are difficult to treat and may lead to blindness. Most common organism responsible for ulcer is acanthamoeba.


Disposable contact lenses

Disposable lenses are soft lenses, which are replaced frequently such as daily, weekly, monthly or quarterly.

Someone who wants the best for their eyes should consider the advantages of disposable lenses

  Frequent replacement of disposable lenses leads to less deposits and eye irritation and infection. It is very
     suitable for people suffering from ordinary lens related problems.
  People with sensitive eyes respond better to disposable lenses, as irritation is almost nil.
  Deposits also reduce oxygen permeability of soft lenses and increase the irritation because of insufficient oxygen flow.
  Chances of lens related corneal ulcer is minimized
  For People who tend to loose contact lenses, disposable lenses are better option as they are comparatively less
     expensive.
  For occasional contact lens wearer this is the best alternative because it is cost-effective.

Thus we see that disposable contact lenses are best option as they provide maximum oxygen to the cornea, keeping the eyes fresh and healthy all day long.

Special Contact Lenses

  Toric contact lenses. 
  Bifocal contact Lenses.
  Colored contact Lenses
  Extended wear contact lenses
  Bandage contact Lenses 


Toric contact lenses

These are soft contact lenses with cylindrical power. It is expensive and limited range is available.

Bifocal Contact Lenses

Useful for presbyopes who do not want to wear glasses. It has distance and near segment. When person looks straight his distance correction comes in optical axis and while reading and near work the reading portion comes in optical axis.


Colored Contact Lenses

These are of 2 types:

  With Clear pupillary area: Used by
       nomal persons for cosmetic use. Commonly used by film and drama artists.
       people with peripheral corneal opacities.
  With black pupillary area: Used for total or central corneal opacities.

Extended Wear Contact Lenses

These are soft lenses that can be used for a week to one month without removing.

Advantage:

  Less cumbersome.
  Have good vision throughout the day and night, specially good for high myopes who other wise feel miserable when get up from sleep.
  Save cost and botheration of cleaning the lens. 

Disadvantage:

  More likely to catch infection.

Bandage Contact lenses

These are extended wear contact lenses and are used as a bandage in different eye conditions 
which causes irritation such as:

  Corneal oedema and Bullous Keratopathy.
  Recurrent corneal ulcers.
  Filamentary Keratitis.
  In Small corneal perforations it is used with tissue glue to close perforation.
  After eye surgeries: To give relief from surgical discomfort as after Lasik.