Naked Science Forum

Life Sciences => Physiology & Medicine => Topic started by: anet on 25/01/2009 19:22:22

Title: Why are some contact lenses more comfortable than others?
Post by: anet on 25/01/2009 19:22:22

I've just bought my first lot of contact lenses. The right one is a normal, soft, monthly disposable lense and feels fine. The left one is a toric lense for astigmatism and its really uncomfortable. Its slightly blurry (I can see much clearer with my glasses) it feels heavy and it feels like there is a big glob of something on the bottom of my eye ball. And it is really difficult to take out. Has anyone else had this problem? Is it a problem with my prescription or do I just have to get used to it? Or maybe I'm just not suitable to wear lenses cos at the moment I can only keep them in for a couple of hours and then I get a headache.

Title: Re: Why are some contact lenses more comfortable than others?
Post by: RD on 26/01/2009 16:42:38

Quote from: anet on 25/01/2009 19:22:22

I've just bought my first lot of contact lenses. The right one is a normal, soft, monthly disposable lense and feels fine. The left one is a toric lense for astigmatism and its really uncomfortable. Its slightly blurry (I can see much clearer with my glasses) it feels heavy and it feels like there is a big glob of something on the bottom of my eye ball.

The toric lens, unlike your other (spherical) lens, has to be oriented in a particular way: it has a top and a bottom.
If you put it in rotated 90^o from its correct position your vision in that eye would get more blurry than without a lens.

Quote

All toric lenses have their own unique marking to allow us to assess lens rotation.
Many manufacturers put their markings at 6 o'clock, while others put them at 3 o'clock and 9 o'clock.

http://findarticles.com/p/articles/mi_qa3921/is_200409/ai_n9436353


The method used to maintain the correct orientation of your toric lens may be what is causing your discomfort ...

Quote

Regardless of modality, soft toric lenses require some means of keeping their cylinder axis properly aligned with that of the patient's refractive error. Most employ one of three methods, or a combination of these three:

1. Prism ballasting. This method of stabilization entails adding more lens material mass to the inferior portion of the lens, making that part of the lens thicker. Doing this helps prevent the lens from rotating and is one of the more common methods of lens stabilization, as it offers a good compromise between patient comfort and stability.

2. Lens truncation. This design involves cutting off the bottom portion of the lens, leaving it flat or truncated. The flat edge usually aligns with the lower lid, and the bottom "corners" help hold the lens in place. Lens truncation is an effective stabilization system, but it tends to make the lens less comfortable.

3. Thin zones. Also called "dynamic stabilization" and "double slab-off," this design involves removing lens material at both the apex (superior portion) and base (inferior portion) of the lens, creating thin zones at the top and bottom. These zones allow the eyelids to exert pressure on the lens and hinder its rotation. This design offers the greatest comfort of the three stabilization methods, but the the least resistance to rotation.

http://findarticles.com/p/articles/mi_qa3921/is_200409/ai_n9436353

Title: Re: Why are some contact lenses more comfortable than others?
Post by: Make it Lady on 26/01/2009 17:39:11

Could I be cheeky and ask a side question. I have dry eye syndrome but have noticed my eyesight is deteriorating. Would I be able to wear contacts without scratching my cornea?