Quote:
Originally Posted by guitarhero
Hello I am planning on ordering RGP lenses and I am using my regular contact prescription for everything other than the diameter. I currently have a 14mm diameter but I know GP lenses have a smaller diameter. Could anyone give me what would be the appropriate diameter for changing to RGP lenses or any other way of figuring what mine would be?
Also, can you wear any kind of RGP lenses at night or do they have to be a specific kind?
Thank you very much
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Hello guitarhero
Welcome to the forum. I'm sure you will find lots of helpful advice and hopefully you will be able to give us some advice by way of your experiences.
I gather that you are an experienced soft lens wearer (based on the 14mm dia lens). First (screening) question is, why do you want to switch to a RGP lens? They generally are not as comfortable as a good soft lens and the modern silicone hydrogel soft lenses are very oxygen permeable and approach the oxygen permeability of the better RGP lenses.
I will give you my experiences of RGP lenses, having been a long term wearer (30+ years) of soft lenses (and before that, hard lenses). I used to wear CooperVision/Hydron Omniflex lenses with a water content of 70%. I was advised to switch to the newer technology silicone hydrogel lenses and started wearing CooperVision
Biofinity lenses. These were very comfortable monthly lenses with very high oxygen permeability (Dk 128, Dk/t 160 based on a -3.0D lens).
However, I do have minor astigmatism (-0.5D and -0.75D in my left & right eyes respectively). I like to have very sharp long distance vision and a non toric RGP lens can partially correct astigmatism up to about -0.5D.
I saw my new optician and she asked me why I wanted them and what my expectations of RGP lenses were. She recommended two brands and I selected a high tech and expensive brand with very high oxygen permeability (Dk 189) - Menicon Z Alpha - which I had heard about on this forum. They are 9.6mm diameter, but this is a starting figure that my optician uses. You can have smaller or larger diameter.
Be aware that the RGP lenses are (for most people) not as comfortable as a standard soft lens and they may take up to 6 weeks to get used to them. So you need to be motivated to get used to them. But vision is usually superior to that with soft lenses.
Fitting a RGP lens is, I think, much harder than fitting a soft lens. My eyes were measured for base curve in the vertical and horizontal directions and then averaged. I have extremely flat corneas, but can still wear a standard run of the mill soft lens. However, RGP lenses are specified to the nearest 0.05mm base curve. It is normal for the optician to have to try 2 or maybe 3 fittings to get the correct RGP lens prescription for your eyes over a few weeks.
The Menicon Z Alpha lenses are one of the very few lenses actually certified for continuous/overnight wear. i.e. you can wear them for seven days continuous and then take them out to give a thorough clean and your eyes a rest.
You would need to check with your eye care specialist, as to what RGP lenses you could actually wear on a continuous basis. Every one is different and it will depend on the health of your eyes.
So, basically, if you have a good reason for switching to RGP lenses, then by all means go ahead, but you MUST do this through a
contact lens Specialist to ensure that the base curve, etc. is correct for your eyes.
The other thing, which I should mention is that the tear film between the RGP lens and your cornea plays quite an important part in the power of the lens. I normally need a -4.00D power in a soft lens, but my RGP lenses are -3.50D and the optician wanted to reduce that by another -0.25D, though I wanted both lenses to be the same power and it was a marginal change in my case.
I wish you luck and hope you let us know how you get on. But please don't try and self prescribe these RGP lenses, as the fitting is quite critical compared to soft lenses and you have very little chance of guessing the correct prescription without an eye care specialist's help.
If you have any further questions (I'm sure you will
), please ask.
knotlob
Welcome to the Contact Lenses Forum - Lens 101 forums. 
04-09-2010, 02:30 PM
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