Contact Lens Basics, Instruction, Oxygen permeability

contact lens articles

What is Contact Lens?

A contact lens is a small plastic wafer typically designed to rest on anterior surface of cornea or sclera (basically corneoscleral part) with the purpose to correct refractive errors and also used for cosmetic purpose to artificially change the color.
Types of Contact Lens fitting

1. Alignment Fit (Ideal):

  • Ideal fitting in which contact lens floats on precorneal tear film.
  • There is no pooling of dye (tears) anywhere.
  • Contact lens doesn’t touch the surface of the cornea.
  • With each blink movements of contact lens are sufficient for tear exchange.

2.Steep Fit (Tight):

  • Also known as TIGHT fitting.
  • Contact lens touches the cornea at periphery.
  • There is pooling of dye (tears) at the center of cornea.
  • With each link, there are little movements of contact lens causing inadequate tear exchange. This leads to corneal hypoxia (Lack of oxygen supply to cornea).
  • Initially, this type of fitting can be comfortable immediately after wearing contact lens but starts having problems after some time due to corneal hypoxia.

3.Flat Fit (Loose)

  • Also known as LOOSE fitting.
  • Contact lens touches the cornea ats center.
  • There is pooling of dye (tears) at the periphery.
  • With each blink, the movements of a contact lens on cornea are more than normal.
  • There is adequate tear exchange and no risk of corneal hypoxia.
  • Excessive movements of contact lens give foreign body sensation and patient feels uncomfortable and takes more time to adjust with the lens.

How does cornea get oxygen supply while using contact lens?

  • The vital source is the atmospheric oxygen dissolved in tears (precorneal tear film). When a person wears contact lens, the supply of oxygen is decreased.
  • The oxygen supply depends on various factors:
  • Contact lens material: The material may or may not allow oxygen to pass through it. This depends on Dk value of the material.
  • Higher Dk value = More oxygen permeability.
  • Movement of contact lens: With each blink, there is a movement of contact lens that results in tear exchange.
  • More blink rates = More tear exchange and more oxygen available to cornea
  • The water content of contact lens: High water content of contact lens also increases oxygen supply to cornea.
  • Perilimbal capillaries also supply oxygen to cornea.
  • Oxygen dissolved in aqueous humor: Supplies oxygen and nutrition to inner layers of cornea.

What happens if we sleep wearing contact lens?

  • During sleep, our eyes are closed i.e. NO BLINKING OF EYES = NO TEAR EXCHANGE. That remarkably decrease oxygen supply to cornea leading to corneal hypoxia. Cornea becomes edematous with microcysts. Eyes become red and may cause blurring of vision along with pain.
  • So, it is strongly recommended not to sleep wearing contact lens.
  • Instructions regarding the use of Contact Lens
  • Wash both hands and sanitize them before inserting or removing Contact Lens
  • Clean Contact Lens with a contact lens solution after removing and before inserting
  • Store them in a clean vial with adequate contact lens solution so that it doesn’t get dried up
  • Wear contact lens according to your wearing schedule
  • If you are using a prescribed powered contact lens then make sure to carry your specs and contact lens kit with you while traveling.
  • Cosmetics such as Kajal should be applied after wearing the contact lens. But I would suggest avoiding applying Kajal in any of the conditions because it is an effective cause for the punctum to block. As a result of which the aqueous drainage system will not function making your eyes to lacrimate.
  • Perfumes should be sprayed before putting contact lens because these are alcohol based chemicals and can remain in the air as aerosols for some time which will be absorbed by contact lens. And this will damage cornea.

What you should not do if you have a pair of contact lens…

  • Never wet your contact lens with your saliva
  • Never clean your contact lens with tissue paper of any piece of cloth
  • Never sleep with contact lens on
  • Never wash your contact lens in tap water.
  • Never put them in hot water thinking that it will disinfect it. Instead, it will damage your contact lens
  • Never insert your contact lens over a sink. Once you drop it off your hands it will be lost down the drain.
  • Never use it if you are having allergic reactions to it. And never use it if you are having an eye infection.
  • If any foreign body or dust particles get into your eyes never rub your eyes. Better is to take off your contact lens and wash your eyes with clean water.

About the author -  Ajay Shahi (Shakhil) Optometrist.