UK Keratoconus Self Help and Support Association
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This presentation is to demonstrate the application of corneal and scleral lenses in keratoconus. Hydrogel (soft) lenses have a small role in keratoconus, for example with 'piggy back' lenses where a rigid corneal lens is worn over a hydrogel lens to improve comfort, or 'hybrid' type lenses, which have a rigid central portion and a soft peripheral skirt, as Professor Buckley previously described. Occasionally with low grade keratoconus it might be possible to give some visual improvement, or perhaps to correct the myopic element with soft lenses and then to correct the astigmatic element with spectacles worn in conjunction with contact lens wear.
Generally speaking, rigid lenses work quite well because they retain their shape when worn and trap a reservoir of fluid between the back surface of the lens and the cornea. The refractive indices of the tear pool and the cornea are similar, so there is not much refraction (bending) of the light as it passes through the cornea when a rigid lens is worn. Hydrogel lenses do not provide this function. They drape over the surface of the cornea, so do not trap a tear pool. The main refracting surface is the front surface of the hydrogel lens, which is not much less regular than the keratoconic cornea. So although rigid corneal lenses have their problems: they can be uncomfortable to wear or they can fall out, but they remain the mainstream method of correcting keratoconus.
The shape of keratoconus profiles is a myriad variety, most bearing little resemblance to a cone, so why we call the condition keratoconus, which means conical cornea, I'm not quite sure.
Slides of various keratoconus corneal shapes, some with a central apex, some where the apex is elevated upwards, others flat, another with a 'pot-bellied business man' shape, and the most common 'droopy' shape.
A more appropriate definition would be primary corneal ectasia, this means a thinning of the cornea with a protrusion over the thin zone. We think this would be a more appropriate title for the condition and would embrace all the different shapes we encounter. They all benefit form contact lens correction because of the irregular surface which is not neutralised well, if at all with spectacles, but is neutralised very well with a contact lens, or rather, with the fluid pool.
There's sadly no evidence to support the theory that wearing contact lenses retards the progress of keratoconus, - this was a theory which was popular and hopeful 20 or 30 years ago but has never been substantiated. So keratoconus sufferers wear lenses to correct the vision in the short term, without any long term therapeutic application.
Slides showing examples of contact lens fitting in keratoconus compared to fitting in mild short sightedness (myopia).
We use fluorescein which is excited by blue or UV light and can look at areas where the lens is in contact with the cornea and areas of clearance. Typically with a non keratoconic eye we'd be looking at a pool of fluorescein underneath the apex, a contact zone at mid periphery and a clearance zone at the edge of the lens. This is so some tear exchange is allowed behind the lens to enable corneal oxygenation and to take away debris from the metabolic processes. Since a keratoconic cornea has a typically protrusive profile, it's very unusual that we can achieve the clearance which is desirable under a normal contact lens fitting. More typically we see apical contact. The lens pivots over the cone apex, which is why lenses doesn't always stay in place.
Slide showing an example of the problem that occurs with corneal lenses not centering very well and very likely to fall out.
The person featured in this example was an obvious candidate for a scleral lens and we fitted him with one 20 yrs ago. He adapted to it within a few days. This was before we switched over to using mainly gas permeable materials for scleral lenses, so it was a success in the old style and proof that sometimes there is an old way of doing things as well as a new way.
Another problem is possible abrasions caused by heavy contact area of a lens on the cornea resulting in an abrasion. It can sometimes be very difficult to eradicate this problem because the cornea and the lenses are not good matches for shape.
People often come to our contact lens clinics asking if the modern laser treatments are right for them, but sadly we have to discourage this. The success rate seems to reasonably high for normal non keratoconic eyes, but there are occasional mishaps, and the long term effects are not known even for normal eyes. It also runs the risk of leaving scarring or a hazy central cornea. It is possible that the technology may be developed for keratoconus in the future, who knows, but the prospect cannot be good because the treatment further thins an already thin cornea.
Ninety five percent of keratoconus is dealt with by the hospital eye service in the UK at the present time. Since only about 5% of all new contact lens fittings are for rigid gas permeable fittings, (95% are for hydrogel lenses), fitting rigid lenses is something of a dying art and people who are interested in dealing with keratoconus tend to gravitate to the hospital service. If dealing with keratoconus was more available in the community, lots of practitioners would be fitting just a few people with keratoconus. There are advantages in this as more practitioners would gain some experience, but some disadvantages in developing the skills and an understanding of the problem areas in greater depth. There can be other problems which crop up with keratoconus apart from just the contact lens fitting so you need medical cover to deal with these if they occur. I visited the US once and was impressed by their local ophthalmic units. These dealt with all sort of things, albeit in a commercial way, but that's the norm in the States.
Scleral lenses have always had a role to play in management of keratoconus, but are used infrequently compared to rigid corneal lenses. They are perceived as cumbersome, uncomfortable, and the cause of hypoxic change. I wouldn't necessarily disagree, but nevertheless we are moving things along. If you show a new patient a scleral lens the response may well be "You are not being serious!". so I usually put one in my eye to show them there's nothing to be afraid of, and that wins over a certain number of people to my side. The size of the lens can be intimidating, people think it just won't go into the eye so it is necessary to dispel this feeling. Another problem is that some practitioners are also intimidated by scleral lenses, so it is not surprising that they transmit this feeling to the patients.
A slide showing vascular changes, blood vessels growing in.
Sometimes practitioners are faced with the question of whether or not this is acceptable when you know that this is induced by the contact lens. In this example, it occurred after more than 40 years of scleral lens wear. It is not sight threatening, but is a significant problem because a bed of corneal blood vessels may increase the risk of a future corneal transplant rejection. So we mustn't be complacent, but on the other hand this lens has provided this person with 40 years of normal vision without surgery. If it extends, as it has done sometimes, across the visual axis, then that is a different matter. Certainly we have to do something to prevent that from happening and the major development in scleral lens practice is the introduction of gas permeable materials which has made a big difference.
But I wouldn't want you to think there are only disadvantages to scleral lens wear. The advantages are not very well appreciated by the public, or it would appear, by practitioners. Virtually any kind of corneal topography can be fitted with some kind of scleral lens. There are various different types, much more variation than with other types of lenses. Because of their size the lenses are not subject to movement, and they are surprisingly comfortable to wear because the lids are nowhere near the edge of the lens so you have no lid sensation. There is a feeling of bulk, but I can wear them for 6 hours without any trouble. They are robust, and maintenance is easy.
More than half of all scleral lenses are used for patients with keratoconus. There has been a huge increase since 1984, mostly because of the gas permeable development. In 1984 sclerals were only being offered when all the other contact lens options had failed. Now we are looking at sclerals a lot earlier, sometimes alternating sclerals with corneals. The old style sclerals were ventilated with a slot or a small hole (fenestration) to allow tear exchange. The modern gas permeable lenses do not often need to be ventilated - enough oxygen is being transmitted through the lens. Slide of a cornea with a corneal 'pip' or nebula which with a corneal lens would be abraded by a corneal lens where a contact zone is unavoidable. With a scleral lens you can fit clear of the cornea so that the lens is not touching the pip.
Certainly gas permeable material has transformed scleral lens practice. Firstly by improved oxygenation, but also using non thermo-plastic material has made a big difference. In the old days, we used PMMA which is thermoplastic. We would take an impression of the eye, make a cast and heat a sheet of PMMA, press it over the cast and sculpture it to clear the cornea. You can't do that with gas permeable materials because if you heat them they disintegrate. But improved oxygenation has allowed us to move away from complex fitting using eye impressions, and use simple fitting sets in most cases.
It's fairly easy to fit gas permeable scleral lenses giving full corneal clearance. This is just as well because we have found that people can't tolerate the contact of gas permeable scleral lenses on the cornea when they could tolerate PMMA. Sometimes the result is a reduced visual acuity compared to the 'old days' when PMMA sclerals almost always made a fairly heavy contact. But if a corneal lens is on the floor half the time it's no good saying "I can see better with the corneal lens"! Sometimes we also fit a PMMA lens which gives them better visual acuity. We have about 600-700 scleral lens patients at Moorfields. Most of them are doing well enough to call it successful, but it is not without it own crop of new problems, which I'm beginning to find are taking over my life.
So, in summary, can scleral lenses reduce the need for a corneal transplant? With lenses you have an end point straightaway. You put a lens on and can demonstrate the visual gain immediately, or at least after the lens has settled down. If the underlying indication for a transplant is keratoconus, the success rate is quite good. However, a transplant requires an 18 month recovery period. It's also surgical a leap into the dark and as with all surgical procedures, there are a few that don't turn out so well. There is just as much topography variation post operatively, perhaps even more than pre-op keratoconus.
But if we maintain that lenses can avoid the need for a transplant, we also have to ask if using a scleral lens could jeopardise a future transplant in some way. If we generate a bed of blood vessels then that poses a considerable risk to the survival of a future transplant. Fortunately gas permeable materials have largely circumvented growth of blood vessels into the cornea - although we still have to be diligent.
Another question we must ask is whether or not early surgery improve the chances of a long term outcome. To put it another way, could delaying surgery affect the outcome if for example surgery becomes technically more difficult if the condition becomes more advanced? I acknowledge it is a reasonable point to raise and address that question to Professor Buckley.
Professor Buckley's reply: A lot of surgeons say to patients if we don't do it now, it will be more difficult later - I don't think there is any evidence for that at all, just a misconception. A slide showing the effect of hydrops - one might say this is an indication for a transplant, but this man is doing well with a scleral lens in that eye even though he has had a hydrops which has now largely resolved.
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