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Keratoconus - Frequently asked Questions: ICR Implants




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Intra-Corneal Ring Implants FAQ
Produced Exclusively for KC Global

 

What are they?

Perspex ring implants placed in the cornea to flatten, stiffen and make more regular the shape of a keratoconic or ectatic cornea.

 

How many types are there?

There are three: Intacs, Ferrara and Bisantis.

 

How do they differ?

By their size and shape. All are made in segments of Perspex (originally a full 360 degree ring when first developed).The differences are in diameter and shape. Intacs are the largest in diameter, Ferrara in between and Bisantis the smallest.

Intacs are hexagonal in cross-section, Ferrara  rings are triangular and Bisantis are oval.

 

How safe is Perspex?

It first went into eyes inadvertently in 1940, in the Battle of Britain when the cockpit canopies of fighter pilots shattered. The fact that it caused no inflammation led Harold Ridley use it in eyes as lens replacements for cloudy natural lenses (cataracts) in 1949, and over 300 million have been implanted with no problems of rejection or inflammation in all that time. The same has been true for intracorneal rings.

 

How do they work?

If material is added to the edge of the cornea it is flattened in the centre. To correct an asymmetric cone requires rings of different sizes to be placed opposite each other. The smaller the ring, the more effect there should be. However, smaller rings are less predictable.

 

What are they used for?

Lower level myopia (their first use  was for up to about -4.00D), keratoconus, post-LASIK ectasia, other keratectatic disorders such as Pellucid Marginal Degeneration, and post-LASIK regression. .

 

Who is suitable and who is not?

Those with clear central corneas (although some reports of benefits in eyes with small scars), corneal thickness of 0.45mm or more at the insertion site, those with corneas flatter than 57D (best about 53D with a relatively low level of short sight) for Intacs, although the new SK type is designed for levels above this (including over 60D). In cases of early keratoconus and low myopia it is a good alternative to laser surgery.

Poorly controlled diabetes, severe eczema, excessively thin corneas (below 0.40 at the insertion site), a history of herpes simplex or herpes zoster of the eye, severe central scarring of the cornea, cataract (cloudy lens).

 

Are there age limits for the surgery?

Yes, 18 years of age is the usual lower limit, although in Egypt they have been used in people as young as 15y. Younger patients have larger pupils and so may suffer more from glare and halos. On the other hand many will put up with this to improve the astigmatism.

 

How are rings implanted?

A) Intacs. The procedure takes about 20 minutes, but less with the laser. The cornea is marked for the ring position (centered on the iris or pupil, depending on whether it is the Standard or SK model), a 1.2mm incision is made using a triple-edged diamond knife with a guard which limits depth at the implantation site to about 50-75% corneal thickness at the site. Then tunnels are made mechanically using suction and a probe, which separate the layers of the cornea like pages of a book, or a femtosecond laser which cuts a tunnel. Some surgeons prefer the former method as it does not cut any more fibers in an already damaged cornea and if the rings have to be removed the corneal tunnels return to normal. It also makes rings easier to implant than the laser which leaves fibers that need to be broken when the ring is inserted. Others prefer the laser because it is quicker, needs no suction and cuts very accurate tunnels although the flattening required for treatment may decenter the implant positions.

Once the channels are made the implants are then slid into place and a single suture is used to close the incision. This is removed several weeks later.

B) Ferrara and Bisantis are implanted similarly but using a manual technique and no suction with centering on the visual axis (line of sight).Ferrara was the first to suggest intracorneal rings to correct keratoconus. Initially he used it for higher levels of short sight (up to -20.0D).

 

What are the results?

A) In keratoconus 5 year results from Professor Colin show an improvement of best possible vision from 6/18 to 6/12 on average, but some did much better with up to an 8 line improvement. Ibrahim showed about 88% improved in unaided vision in the largest study with an average reduction in K values of 4.48D. About 4.5% of patients in the Colin study had a reduction in vision. Short sight reduced by 3.65D on average. As more has been learned these figures are improving and the new SK rings will help more advanced keratoconus. The larger the K readings the more the effect there is, up to a certain point. 

In the US myopia study of 452 eyes 93% were within 1.00D in a treatment range of 1.00-3.50D and 76% were 6/6 or better. In a European study of159 eyes 90% were within 1.00D in a treatment range of -1.00 to -6.00D and all were 6/7.5 or better. They have also been used to this treatment longer.

B) Ferrara rings show about 85% improvement in unaided vision with about 6% getting worse similar to Intacs. Siganos showed an improvement of short sight o f5.80D, but Kwitko only had a 1.53D improvement.

C) Bisantis: No published results available on Medline.

All 3 show marked variations and some have had to be removed for various reasons such as glare or corneal thinning.

 

What are the possible complications?

As with all surgery there are many, but most are rare or very rare.

Discomfort/ pain up to 48hrs which can be treated with medication, blurred or fluctuating vision and tearing with light sensitivity and dryness. There may be over or under effect which can be corrected sometimes by ring exchange. The rings may shift and need repositioning. Deposits of inert, lipid material can develop in the tunnels, but seem to have no effect and disappear if a ring is removed. Infection is very rare (1 in 500 ie much less than dying in a car crash!). Problems with insertion can occur (ring could be removed and repositioned at a later date). Some may have to be removed over the years (5.0% to 10.0%) and the eye should return fully to how it was before surgery, which was its main attraction in surgery for short sight.

.

How is size decided?

It is decided by the amount of overall short sight (spherical equivalent) and astigmatism. Intacs range from 0.25 to 0.45mm thickness and 6.77mm (standard) or 6.00mm (SK) inner diameter. Rings may be different in size of the keratoconus is asymmetric or even just a single ring may be implanted Ferrara rings are 4.40mm and 5.40mm inner diameter. Bisantis rings are made up of 4 parts with diameters of 3.50mm, 4.00mm and 5.00mm.

 

Can anything be done for remaining short sight or astigmatism?

Yes. Laser eye surgery is not generally recommended for ‘at risk’ corneas (although some are doing it after corneal collagen crosslinking (CXL), but phakic lens implants, which sit in front of the natural lens, or new lenses implanted in exchange for the natural lens can be used. Neither is likely to make vision perfect as strength calculation is difficult, but can improve it drastically.

 

Does it stop Keratoconus progressing?

It can in some cases, but the condition tends to slow down and stop by the 40s. However, it does not treat the underlying problem so the position may be improved, but the eye is not ‘cured’ and may continue to progress (about 5.00%).

 

Is there any other treatment available to stop progression of keratoconus?

Yes, corneal collagen crosslinking (CXL) which stiffens the cornea and is the first treatment that works on the underlying problem of keratoconus/ ectasia. The 2 treatments together may be a very powerful solution for the problem of keratoconus/ ectasia.

 

How is the eye frozen for surgery?

Usually this is done with local anesthetic drops. This prevents pain, but not the sensation of pressure. Surgery can be done under general anesthetic, but most is done with drops because it carries much less risk to health.

 

Does it hurt?

If it is truly painful the patient is unable to keep still so surgery is impossible. This means that it is in the surgeon’s interest to make it as pain free as possible. Normally there is a feeling of pressure when the channels are being made.

 

Are they easy to remove if necessary?

Intacs have tiny holes at either end which allow the segment to be removed using a blunt hook. Usually they slide out fairly easily up to 7 years later, but sometimes they are more difficult to remove.

 

Can the size be modified if the effect is wrong or can it be increased at a later date if needed?

Yes, this is possible.

 

Can I wear contact lenses afterwards?

Yes. One of the major benefits is being able to wear a simpler lens eg soft toric if anything is required at all.

 

Can I return to contact lenses if removal is necessary?

Yes. The cornea will return to its pre-operative shape, but this may take a few weeks.

 

Are there any limitations in what I can do in the short and long term after surgery?

Avoid washing the eye and swimming, heavy lifting, and eye make up in the first few weeks. Always avoid rubbing the eye vigorously. It is possible to cause damage and to move the rings in their channels.

 

Can they be seen?

Sometimes; a bit like a contact lens, especially if the pupil is large  (more than 7.0mm).

 

How many have been done?

Many thousands if you include short sight, keratoconus and all other uses.

 

When were they first used?

Ferrara in 1986 with a single ring and two ring segments in 1996, and Gene Reynolds developed the idea of intracorneal rings which progressed into Intacs in 1978, with the first human implant in 1991.

 

Are they fully approved?

Yes, both by the FDA in the US, and CE in Europe with studies lasting more than 10 years.

 

Can you feel them after they are implanted?

No, although there can be a temporary feeling of ‘stiffness’ associated with nerve damage at insertion. The nerve damage will heal over a period of several weeks.

 

If both eyes are being treated can they be done at the same time?

Technically yes. However, most surgeons would prefer to see how the first eye goes before doing the second, but both at the same time is not unreasonable.

 

Could it affect my eye for other treatments in future eg a corneal graft?

It could make things a bit more difficult especially if a ring segment is hard to remove, but the graft is normally larger in diameter than the Intacs or Ferrara ring segments and due to this can be removed smoothly.

 

Written Exclusively for KC Global by :

Dr. David Jory MBBS FRCOphth
Consultant Ophthalmologist

Keratoconus Clinic
ASC, Unit 6, The Technology Park
Colindeep Lane
London
NW9 6BX

Tel: +44 (0)207 099 0970
Fax: +44 (0)207 580 9020

www.davidjory.co.uk
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Produced by Dr David Jory for KC Global Exclusively on the 31st of July 2007 
 

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