CL prescriptions and what they mean

[Lynn White]

Sweet, As far as I remember, you use a Night and Day lens which is actually silicon hydrogel. Although this is thin, it is much stiffer than normal a normal soft lens hydrogel and therefore holds its own shape better. The lens won't actually match your eye shape that well which is why i assume they don't want you to use the same toric.

A toric lens has curves that match your astigmatism, ie matches the way your eye curves in different directions. With the Focus lens this all changes... I can't say more than that as I don't know exactly what they are doing with your eye/lenses!!

[Sweet]

Ok thanks for that! If it is any consolation i honestly am not sure what they are up to either, but if i can see well (even if i do need two pieces of plastic to do it), then that is more than enough for me! LOL! Also it would be worrying to me if they really changed my RGP lens because what would happen if i ran out of soft lenses? Maybe i wouldn't be able to see as well with just the RGP one.

Yes it is a night and day as they still adamantly refuse to give me disposables. Aww dam cleaning lmao! Although with only wearing lenses in one eye i can use a lens case for both lenses! Neat!

Sweet X x X

[jayuk]

Lynn

Is it worth then mentioning the different levels of KC and the issues around the fitting? My understanding has been that there are 3 stages that we all go through with KC...and the level of advancement is based on the K reading .......i understadn that our fellow friends across the water have 4 levels which they adhere to.....when diagnosing the stage of KC..

1) Mild - less than 48.00 diopters in either corneal meridian

2) Moderate 48.00 to 54.00 diopters in either corneal meridian

3) Advanced >54.00 diopters in either corneal meridian

J

[jayuk]

Lynn

I agree that the KC cornea isnt average...and I think you made a really good point on the Soft lens and flattening; as I remember when having the fitting.....that if I kept the Kerasoft in for like 3+ housr and then tried the RGP again...the vision wasnt as clear........which kind of make sense based on what you say now.........I think before I took piggybacking as a "not a big issue" approach lol....but having gone though it.....it really does need a 1-3 day apporach in terms of even determining which lenses MAY be suitable and the combinations!

J

[Sweet]

Hhmm until now i didn't really understand the different combinations either.

I think though that i would rather have a soft lens that didn't change my eye shape and leave the RGP to do that just in case i ran out of soft lenses or only had my RGP.

The reason i gave for wanting to try piggy backing was to have something to put my RGP on as it was killing me to wear it on it's own. I would always have a red eye and it hurt so much i couldn't tolerate it for long hours. Not good when i work twelve hour shifts!

Now it is much better and i rarely get any redness piggy backing, except when i'm tired. Moorfields are keeping checks on it though as i have two dry areas that are not helped by wearing a soft lens but they are letting me carry on for now so long as i am careful and as i told them leave them out when not working. So for now i am keeping my fingers crossed but will know more on my first check up in June.

Sweet X x X

[John Smith]

This is an excellent thread. Thanks everyone (especially to Lynn).

On question though, Lynn: you mentioned that the BCOR value would not go below 7.00 in a non-KC eye. How dies this work with children? Even though a child's eyes are disproportionately large compared to the head, surely a child's eyes are smaller than an adults, so a smaller BCOR would result?

[Lynn White]

No .. children's eyes stay mainly the same size as they grow. And in any case, the radius of curvature of the eye is descriptive of its general shape - as in a gentle flattish curve. KC by definition is more cone shaped and the higher radii of curvature reflect that

Jay, we don't quite categorise KC in the same way in the UK and certainly, we don't change fitting techniques based purely on K readings. Basically, one fits whatever works best!

I do understand what you mean though and what you are asking really requires an article with pictures of fittings and corneae etc to be useful. I will work on this!!

Oh and you may be confusing matters for some people with your references to stages in dioptres. Just to explain, Americans measure the cornea in dioptres not radii of curvature. Its the same thing really, as power is a function of the curvature of a surface. So the higher the power the smaller the radius of curvature!

[Andrew MacLean]

You'd think that after all these years the United States would have fallen into line with UK useage of the language!

[Ali Akay]

John,
Adding to Lynn's comments, most babies are longsighted (hypermetropic) as the eyes are small and the corneal curvature fairly steep.But a very clever thing called "emmetropisation" happens in the first few years so that as the eye reaches its adult size the curvature follows to give optimum focus on the retina.This is believed to be initiated by a feedback ie blurred retinal image starts a cortical process that alters the curvature to maintain clear focus.Sometimes this mechanism doesnt work very well and the child ends up long or short sighted (a small degree of longsightedness is the norm for children).We often descibe this to the parents as children growing out of longsightedness as their eyes get bigger, and if the eyes keep growing they become shortsighted! However children who are highly hypermetropic at an early age tend not to change. Another interesting point is that a 1mm increase in the length of the eyeball equates to about 2.5D of change.

To give you an idea of how quickly the eye grows in infants, when we fit babies with contact lenses following congenital cataract removal,they typically need a contact lens with power of around +40, yes 40, but this rapidly drops to about half within 12-18 months.

I hope I havent confused everyone even more!

[rosemary johnson]

Lynn,
What you say makes perfect sense, to me at least.
But please could you say tht what you are describing are

**CORNEAL**

RGO lenses - as scleral lenses are also made of RGP materials and most certainly don't average 9mm in diameter! (Mine are about 24mm.)

as regards piggybacking - I'm piggybacking for comfort only - I can and have, and no doubt in the future willa gain be, wearing the RGP lens on its own without the soft lens under. Trouble is, I get 5 hours tolerance one day in three maximum. So the soft lens acts as a cushion, and gives a great increase in tolerance. Vision characteristics are slightly different but not much practical difference - ie. lots of ghost images and reading is hard work, with or without, but is just about possible.

BTW, I'm sort of assuming that prescriptions for scleral lenses - at least for the scleral rgp lenses these days - are quite a bit different, being based on fitting sets? - for that matter, i'd guess the old days of PMMA sclerals was also different, being typically based about eyeballs mouldings?

Rosemary