What is a Contact Lens?
Types of Contact Lens fitting
Alignment Fit (Ideal)
- Ideal fitting in which contact lens floats on the precorneal tear film.
- There is no pooling of dye (tears) anywhere.
- The contact lens doesn’t touch the surface of the cornea.
- With each blink movements of the contact lens are sufficient for tear exchange.
Steep Fit (Tight)
- Also known as TIGHT fitting.
- Contact lens touches the cornea at the periphery.
- There is the pooling of dye (tears) at the centre of the cornea.
- With each link, there are few movements of the contact lens causing inadequate tear exchange. This leads to corneal hypoxia (Lack of oxygen supply to the cornea).
- Initially, this type of fitting can be comfortable immediately after wearing the contact lens but starts having problems after some time due to corneal hypoxia.
Flat Fit (Loose)
- Also known as LOOSE fitting.
- Contact lens touches the cornea ats centre.
- There is the pooling of dye (tears) at the periphery.
- With each blink, the movements of a contact lens on the cornea are more than normal.
- There are 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 the cornea get oxygen supply while using a contact lens?
- The vital source is the atmospheric oxygen dissolved in tears (precorneal tear film). When a person wears a 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 the Dk value of the material.
- Higher Dk value = More oxygen permeability.
- Movement of contact lens: With each blink, there is a movement of the contact lens that results in tear exchange.
- More blink rates = More tear exchange and more oxygen available to the cornea
- The water content of the contact lens: High water content of the contact lens also increases oxygen supply to the cornea.
- Perilimbal capillaries also supply oxygen to the cornea.
- Oxygen dissolved in aqueous humour: Supplies oxygen and nutrition to inner layers of the 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 the cornea leading to corneal hypoxia. The cornea becomes edematous with microsystems. 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 travelling.
- 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 lacrimate.
- Perfumes should be sprayed before putting on 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 the 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 of Ethical Eye Care & Opticals.