What's start of the art with Gas Permeables?

[russell s]

Hi All,

Long while since I last posted, but regular follower of the posts here.

Wonder if others can help...

I'm looking for some feedback on what are the most popular GP lenses for KC at the moment?

I've suffered with moderate KC for 20 + years and though I started out with GP lenses for the last 10 years or so I've been wearing Kerasoft #2s. These have been ok, but not great and I'm now looking to get back to my optician and revisit gas permeable.

From the internet it would seem that Rose K2 lenses are popular for KC, but are there any other brands that are worth checking out? I fully accept that with lenses KC suffers are all unique and as such I'm not looking for a specific recommendation, rather a ball park list of the popular brands to discuss with my optician.

Many thanks,

Russ

[longhoc]

Hi Russ

Yes, RoseK is considered to be the standard for RGP and Keratoconus, although usually in NHS eye units, they'll try to start off with a stock lens. Only if they can't get a technically acceptable fit will they look at the RoseK range.

I've seen a study which was interesting in that it found a statistically significant patient-claimed improvement from RoseK users but the study authors could not identify why this was. Nor could they find much in the way of improvements in Best Corrected Visual Aquity. The material used in the manufacture is identical to a stock RGP lens with regards to oxygen permeability. The flexibility given to optometrists to specify geometry is though much wider and -- this might be the reason why patient feedback is better -- the fitting sets are very comprehensive so it's easier for the optometrist to go through possibilities.

There's not alas been any wonder breakthrough in rigid lenses -- you're still trying to do something inherently contradictory i.e. fit an irregular shaped cornea with what is basically a regularly shaped lens. You can tweak the parameters, but only so far. What has improved hugely is corneal topography which does take a bit of the guesswork out of prescribing a lens. That said, it still requires an experienced optometrist and -- I sometimes suspect -- a bit of luck ! Sticking my neck out a bit further, I'd also hazard a guess that it sometimes needs a fair bit of chair-time (which I wonder if it isn't always possible in a potentially constrained NHS environment to give) and a co-operative Keratoconus patient.

One development I've heard of, but not had direct experience of, is SoClear which is a brand name for a lens design which is now available. To quote the manufacturer's marketing:

When properly fitted, SoClear lenses provide visual performance consistent with rigid designs and lens comfort and stability approaching Hydrogel designs

... to which my initial concern is around the "... when properly fitted..." wording. Hmm... thereby will hang the tricky bit

I too am going to find out a bit more about current thinking in lenses once I get fitted for a lens in my grafted eye so will report back in a few months time. If anyone has any real world experience, I'd be eager myself to hear about it !

Sclerals and semi-sclerals will probably not have changed that much since the introduction of improved materials a good 10 years ago, so there might not be anything new in that line, but again, if anyone knows better, hopefully they'll put me right on that one.

Good luck, let us know how you get on if you can.

Best wishes

Chris

[russell s]

Hi Chris,

And many thanks for such a comprehensive reply. Sounds like you have done a fair amount of research.

I'm intrigued by your comments re topography - I have had the scans, but as far as I'm aware the results have never been used by my optician to optimise the fit. Would seem to make a lot of sense to use the topography results.

Like many on this forum, blurred vision is only one part of the story, ghosting is also a big problem. The Rose k2 marketing info refers to 'Aberration Control' to reduce ghosting and also 'Asymmetric Corneal Technology ("ACT")' - lens asymmetry to improve the fit. Sounds very convincing, but as you mention totally reliant on the skill of the optician and the diagnostic kit available.

Couple of questions for the experts here; can contact lenses be customised - dialled in - to minimise ghosting? Do topography scans or similar pinpoint the source of the ghosting problem?

I'll be very interested to hear how you get on with your search for lenses and from others too. I'll certainly hope to evaluate both the latest GPs and the SoClear hybrids.

Fortunately my KC is not severe enough to require a graft, but I have read the moderate KC is often the most difficult to fit with lenses. I've not escaped surgery mind you.

'Sods law' as my ophthalmologist put it has also blessed me in the last 18 months with 'map dot fingerprint dystrophy' in both eyes - right across the visual field in my stronger eye! This exhibits similar symptoms to KC and I'm awaiting a debridement (chemically stripping the top surface of the cornea) procedure on the NHS to my stronger eye. Not a complicated procedure, but extremely painful for 2-3 days after as the top layer grows back.

Assuming this procedure is successful, I'll then be ready to resume my lens quest.

All the best,

Russ

[GarethB]

Kerasoft 2 is relatively old technology when it comes to soft lenses for KC and I never got on with them either, infact I complained quite bitterly about them on this web site and the manufacturers invited me to their offices to see for thmselves why they weren't working. This was while they were developing Kerasoft 3 and they changed the design that week in part because of what they observed.

Kerasoft 3 worked prefectly for me and far better than any RGP, I am now on the Kerasoft IC which is even better still, wear them all day every day with no variation in vision and are the best lenses I have ever had.

For you it might just be a case of changing to the latest version of Kerasoft lenses.

Scans to optomise a fit can be very misleading as the equipment used is designed to scan a normal shaped eye and the data can be misleading, it certainly is for my eyes and MUST BE USED in conjunction with obeservation as the scan helps with the central part of theye eye but does nothing for anything on the edge of the optical zone where the lens edges touch the cornea.

The Kerasoft IC can be dialled in to reduce ghosting and halos by getting abetter fit. When fitting an RGP lens optoms aim for what they call a three point touch which means the lens touches the cornea at three points but to do this you get pooling of tears which can exagerate ghosting, halos etc. The way the optical correction applied to the Kerasoft IC is very different to that of the older Kerasoft lenses and I have found ghosting is non-existant, halos are less than when I could get away with glasses years ago, I get 6/5 in both eyes which is better than my RGP lenses and average 16 hours lens wear and comfort wise, I can't feel the lenses in my eyes, even after too much use of the PC, my eyes aren't drying out.

[russell s]

Gareth,

Were your lenses fitted by the NHS or privately? I tried the ICs a couple of years back - they gave me good vision, but did nothing for the ghosting apart from sharpening it up. They we also not stable in my eyes, 5 mins good next 25 mins variable etc. My optician concluded that my eyelids were disturbing the lens hence they were not suitable for me. Must admit I was not totally convinced and did wonder at the time if a private practitioner would have persevered more with the fitting.

[GarethB]

My IC's have been fitted by both the NHS and private. From what you describe the lenses, from what I have learnt with the soft lenses is that they weren't fitted properly if you had variable vision after 25 minutes plus if your eyelids were moving the lens. The lenses are silicone hydrogel, so thinner than the older Kersosoft lenses plus as with other soft lenses are larger diameter than RGP lenses so the lens edge is covered by the eye lids. So if eye lids are moving the lenses is correct, I can see you haveing problems with RGP's that would have the eye lids pushing the lens and potentially popping it out when you blinked which was one of the issues I had that lead me to the soft lenses.

Before over refraction, it is important to obseve the lenses immediatly after insertion for

Movement - the lens should move if I recall correctly about the same as an RGP lens, a few mm's, are there ari bubbles and are they moving or just getting smaller?
Rotation - the laser mark should be pointing straight down and anything over 10 degrees either side and swinging side to side when you blink means long term you won't get good vision and the fit needs adjusting.
Comfort - this is also important.

All these need to be looked at again after the lens has had time to settle for 5 minutes of so and if everything is in the same place over refraction in most cases I am aware of gives excellent results.

Plus the lens design and material composition have been improved further over the past couple of years as part of the manufacturers continued comitment to product improvement which I am sure other manufacturers do.

At the workshops that I have attended optoms often go straight for a complex fit, (especially when they see my topographies which show a graft and irgeularities in the host cornea) when following a few simple rules and being guided by what they see at the cornea margin and the topography gives you plenty of information to fit a more simple lens that that works perfectly and doesn't take that long to fit.

[russell s]

With the kerasoft #3s and ICs, do you get good vision pretty much as soon as you put them in? I currently wear a Kerasoft #2 in my weaker eye and a #3 in my stronger eye.

The #2 delivers its best performance straight away (about 4 lines on the eye chart for me)and remains consistent, but the #3 takes about 30 mins to settle down and sharpen up which to me is an indication that something is not right.

[GarethB]

For me it is pretty much immediate that I get excellent vision with the IC and I think it the same with the 3's, but it is yeas since I wore one of those.

Kerasoft 2's would take about 30 minutes before I got stable vision but after 8 - 10 hours I would get fogging due to the cornea being unable to breathe properly which is why yhe material for the Kerasoft 3 which lead the the Kerasoft IC was developed. If I recall correctly, the Kerasoft 3 and IC's have a comparable gas permeability to an RGP lens.

[Ali Akay]

Hi Russ, coming back to your original question about different types of gas permeables, I tend to use Acuity AK lenses made by Acuity Contact Lenses more than anything else. I find the main problem with Rose K is that its a very small lens (standard diameter is 8.70mm) and the size of the optic zone varies with the base curve and is rather small for steep lenses which causes extra problems with haloes etc especially with night driving. Acuity lens is 9.50 mm and usually works well even for very steep corneas. If your practitioner hasnt heard about them I am sure they can supply them with a fitting set. (I have no financial interest in this product).