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Contacts lenses: Evaluating the types of lenses and their suitability to different groups of people.

Updated on October 2, 2014

A brief intro to contact lenses

Contact lenses is an alternative to traditional eye-glasses. difference between them is that the former is "invisible" since it is inserted into your cornea and the latter is stuck on the bridge of your nose.

So WHY are people wearing contact lenses, and why are contact lenses becoming increasingly popular nowadays?

There can be quite a lot of factors that prompts people to prefer contacts over traditional glasses. Some of the most common reasons that people give are:

1) Appearance factor: Some people simply thinks that power-glasses negatively affect their appearances; or that they are concerned by the fact that having pair of glasses can be seen as a type disability, and can affect how they are being judged or assessed in the society.

2) Activity factor: People who plays sports a lot are not suggested to wear eye-glasses as they can be quite inconvenient. Among the inconveniences are the high risk of breaking the glasses/frames and the sharp pieces may hurt you.

3) Profession factor: Some industry may prefer hiring employees who do not wear glasses. Flight attendants can be a prime example.

4) Vision quality factor: Regardless of whether you are wearing contact lenses or traditional glasses, FOCAL POINT is the most crucial part in both types of corrective lenses. Many people feel that contact lenses do give a wider and sharper vision to wearers. They are right. This is due to the fact that contact lenses are always "adhered" to your pupil, hence the focal points move along with your pupils all the time; traditional glasses, however, has a static focal point on the glass, and once your pupils are out of the bounds of the focal point, vision will not be as clear.

Which type of contact lenses are you currently wearing?

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Identifying the types of contact lenses

Contact lenses are generally categorized into "soft" and "hard" lenses.

Under the soft lens category, 2 of the most commonly used types of lenses are namely Hydrogel lenses, Silicone Hydrogel lenses and Toric lenses.

As for the hard lens category, Rigid Gas Permeable (RGP) Lenses is the most popular one.

Note that Toric Lenses can also be made from RGP material even though it is quite rare. Take that into account when deciding on your preferred type of lenses.

Evaluating Hydrogel Lenses

This is the most common type of contact lens, in fact, over 60% of contact lens wearers are wearing this type of lens. Many patients who have short and long sightedness prefer this type of lenses.

Hydrogel lenses are easy to get accustomed to due to its softness, you basically do not feel anything (low or no lens awareness) after they are inserted into your cornea. This is one of the reasons why hydrogel lenses are so widely used. Moreover, hydrogel lens wearers tend to have less frequent dry-eyes condition compared to hard lens wearers.

One of the downsides of hydrogel lenses is that it has lower gas-permeability therefore an increase risk of hypoxia (a condition of lacking oxygen) in the eyes. This is largely due to the larger size of the hydrogel lens as they covers a vaster area of your cornea, decreasing the chances of gas transitions. For the same reason, the recommended wearing period of hydrogel lens is only about 8 hours/day.

Evaluating Silicone Hydrogel Lenses

Yes you are right, "Silicone Hydrogel Lens" and "Hydrogel lens" are almost identical, but Silicone Hydrogel Lens is indeed the "revised" version of Hydrogel Lens.

The major issue that Silicone hydrogel lens addresses is the gas permeability and risk of hypoxia. Silicone Hydrogel Lens has a higher gas permeability than its "brother" Hydrogel Lens; hence wearing hour-wise, Silicone Hydrogel Lens can be worn for about 10-12 hours/day, compared to 8 hours/day of traditional Hydrogel Lenses. Many Hydrogel Lens wearers nowadays are gradually switching to Silicone Hydrogel Lens as it seems to be a better solution.

Evaluating Toric Lenses

Toric lenses are largely used for the purpose of correcting corneal and/or lenticular astigmatism.

Unlike other types of lenses, toric lenses can contain two powers in each lens, hence having an axis drawing across the lens to separate the two powers. That means, for the best visibility quality of vision, the lenses must maintain in one position once inserted into the cornea and cannot roll. This is why toric lenses are normally heavier at the lower half part of the lens - to minimize movements. Such uncommon structure of the lens can be quite hard to get accustomed to. The heavier part may exert constant pressure on patients' eyes hence lead to strong lens-awareness and feeling of discomfort.

Evaluating RGP Lenses

RGP lenses are among the least popular lenses worn by patients, owing to its unpleasant initial experiences. I am an RGP lens wearer and my near sightedness is about 15.00D per eye, which is an abnormally high power. Thereby saying, RGP lens can save those with high power near sightedness and as well as far sightedness from wearing glasses, but high power lenses, of course, will need to be custom made by selected brands (not all brands are capable of making high power RGP lenses, please seek advice from your doctor.), this type of lenses can be a very good alternative should you are not recommended or not willing to undergo LASIK surgery.

The rigidity or RGP lens causes patients to have an extremely strong lens-awareness, eye-dryness and even slight pain during the first few weeks of wear, making lubricant a necessity to combat these conditions. The feeling is in fact very similar to having sands in your eyes (Imagine having such experience for several weeks!).

Nevertheless, RGP lenses may last 2-3 years (quite economical in terms of costs), and can be worn 14-16 hours/day, the longest among all types contact lenses. The materials used to make RGP lenses do not allow protein to build up/contaminate as easily and readily as in other lenses, hence posing wearers to significantly lower risks of infection compared to wearers of other lenses.

Allergy reaction that may happen to new hard-lens wearers. It happens to me during my first two weeks on hard lenses.
Allergy reaction that may happen to new hard-lens wearers. It happens to me during my first two weeks on hard lenses. | Source

A bit more advice for RGP Lenses wearers

As I have mentioned above, the initial experience with hard lenses can be quite unpleasant. Slight allergy can happen to many wearers including myself, but a lot of us had mistaken allergic reaction as bacterial infection (for example, me!) and started to get panic hence ran all the way back to the clinic like nuts!

It is absolutely normal to see partial redness (as in the photo on the right) during your first few weeks with Gas permeable hard lenses. This is because your corneas have yet to adapt to the foreign yet hard objects that are being inserted (it can take up to a month before you are fully accustomed to them). Should wearers encounter similar conditions, they can basically rule out the possibility of bacterial infection IF there is no swelling/pain in the eyes, no abnormally large amount of tears discharging, and no blurry vision. Give it some time and slowly lengthen your wearing hours, and you will eventually find the allergy gone. Just don't panic!

Contact lenses' summary at a glance

Types
Rigidity
Durable for...
Recommended approximate wearing hours per day
Suitable groups of people
Hydrogel Lenses
Soft
1 to 1.5 YEARS
6 to 8 hours
Near or far sightedness
Silicone Hydrogel Lenses
Soft
1 to 1.5 YEARS
8 to 10 hours
Near or far sightedness
Toric Lenses
Soft (hard lenses are available although rare)
3 to 6 MONTHS
8 to 10 hours
Astigmatism
Rigid Gas Permeable Lenses
Hard
2 to 3 YEARS
14 to 16 hours
High-power near or far sightedness

© 2014 Thomas Chan

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