There is no one lens type or design that is ‘best.’ The best contact lens is the one that works best for you at any particular time.

BY ANDREW SMITH MSc FCOptom DipCLP FBCLA.

As your cornea changes over time so may the type and design of lens that is most suitable. In addition to the stage of your keratoconus there are other features of your eyes, eyelids that will affect way a particular lens works. Also, as individuals we all react differently to the sensations of a lens on the eye.

Fitting contact lenses to a keratoconic eye is not a simple task, each eye is individual in its shape so the lens has to be tailored to shape. It is a process that will, unless you are very lucky, take several visits and adjustments to the lens to optimise the fit. You must find a practitioner (Optometrist, Contact Lens Optician or Ophthalmologist) with a special interest in and experience of contact lenses for keratoconus and irregular cornea.

The other important factor in your success as a contact lens wearer is how you care for your eyes and contact lenses. Always follow the directions of the person who fitted you with contact lenses. Get in to a routine, always wash your hands thoroughly and dry them completely before handling anything to do with your contact lenses, use the care solutions that you are advised and in the way that you are shown. Change your lens case at least every three months, rinse it out daily with saline, wipe it with a clean tissue and either leave it with the lids on or open face down.

The first lens that your contact lens practitioner will fit you with will depend on several factors:

• Your previous contact lenses or spectacles
• How early in the keratoconus journey you are
• Your personal visual needs
• Your personal preferences
• Your practitioner’s preference and recommendations based on the measurements that have been taken

After discussing the options and recommendations there will be a diagnostic lens fitting where the contact lens practitioner will try several lenses on the eye to see which gives the best result. Following this a first pair of lenses will be ordered. These are made individually to the prescription found from the diagnostic lenses. Depending on the lens and the manufacturer this may take several weeks. When you collect these lenses you will be advised how to handle the lenses, how to look after them and how long you should wear them each day during the build up period.

Occasionally, when the fit of the lenses is assessed it may be found that they are not suitable for you to take away and a second lens will need to be ordered. Once you take away your first pair of lenses there will be a few days or weeks of adaptation as your eyes get used to the sensation of the lenses. Even if your eyes feel comfortable it is important not to wear them longer than you have been advised.

You will need to return for progress checks from time to time and it may be that in the first few months adjustments will need to be made to either the fit or the focus of the lenses.

It is important to realise that contact lenses do not stop the progression of keratoconus or, indeed speed it up.

So, what are the options:

If you are still getting good vision through your glasses there is a chance that you might be suitable for regular soft toric contact lenses replaced either daily, two weekly or monthly. However, it is likely that you may still experience shadowing and as your cornea becomes steeper the fit of the lenses will become poor. At this point you will need a more customised design. As a general rule rigid contact lenses will give a crisper image than a soft lens but they do take a little more time to adapt to.

There are many manufacturers and ‘brands’ of contact lenses available with new ones arriving on a regular basis. Also, manufacturers are constantly working to improve existing lenses so if you have tried a particular type in the past and been unsuccessful then it is always worth asking about new developments.

Custom soft contact lenses:

There are an increasing number of soft contact lenses tailor made for keratoconus and many practitioners are now using them as the first option to try. They are intended for mild to moderate keratoconus. The soft nature of the material means that they will attract deposits from the tears which can trigger allergic type reactions. To reduce the risk of this the lenses need to be replaced every three to six months depending on the material and each individual’s reaction. Soft lenses are easier to get used to than corneal gas permeable lenses but might not give such a crisp image.

Corneal gas permeable lenses:

Traditionally the ‘go to’ lens for keratoconus. They float on a pool of tears over the cornea. The front surface of the contact lens corrects the focus of your eyes while the tears between the back of the lens and the cornea fill in the irregular curves of the cornea. This results in crisp vision for most people. Corneal lenses are smaller than other lenses and because they float on the tears and move when you blink the edges of the lenses can be felt on blinking and when the eyes move. The first few times the lenses are worn it will feel like you have something in the eye for a minute or so then the sensation will reduce to a tickling and finally you will forget they are there. This may take up to four weeks if you are particularly sensitive. The important thing to keep in mind is that every day you wear the lenses they should be more comfortable than the day before and stay comfortable for longer. Take care on windy days as dust can blow in the eye and get under the lens. This can be uncomfortable for a few blinks until it washes away.

“Piggybacking’ contact lenses:

Some contact lens practitioners will advise piggybacking one type of lens on top of another usually to improve comfort. The most common combination is a corneal gas permeable worn over the top of a soft lens. This prevents the corneal lens rubbing against the cornea and reduces the amount of movement so there is less awareness of the lens from the lids. Because you are wearing two lenses both need to let maximum oxygen through to the cornea which with modern lenses should not be too much of a worry. If you are prescribed a reusable (monthly or two weekly) soft lens then you will need to be careful which solutions you use as not many are suitable for both soft and gas permeable materials. To get over this problem single use daily disposable soft lenses are increasingly used.

Hybrid contact lenses:

These are lens which have a rigid centre (like a corneal lens) bonded to a soft ‘skirt.’ They are about the same size as a custom soft lens. The advantage is that they give the same vision quality as a corneal lens but move less so that the comfort is more like that of a soft lens. There are an increasing number of this type of lens on the market each with its own unique features. Because the skirt is soft it will attract deposits in the same way as any other soft material so they need regular replacement.

Scleral contact lenses:

Are larger than other types but are possibly the most comfortable lens to wear. All other lenses rest to some extent on the sensitive cornea or the edges move against the eyelids. Scleral lenses rest on the insensitive white of the eye and are separated from the corneal by a thin layer of tears. The lenses do not move so don’t rub on the lids.

Historically, scleral lenses were only used as a last resort but over the last few years a new generation of ‘mini-scleral’ lenses have become available. They are smaller than traditional scleral lenses but a little larger than custom soft lenses. There are now many designs available, some with very sophisticated refinements to improve comfort and vision. The key to success with a scleral lens is the skill of the fitter and ensuring that the correct solutions are used. The lenses must be applied to the eye full of sterile, preservative free saline and without a bubble. This can be quite a challenge at first but once mastered is relatively straightforward. Most people find the vision with scleral lenses excellent but there are a minority who find they get more ghosting with a scleral than with a corneal lens. Scleral lenses can be helpful if you suffer from contact lens related dry eye.

The Scleral Lens Education Society (SLS) video “Scleral Contact Lens Insertion, Removal, Troubleshooting, and Lens Care”
http://www.sclerallens.org/how-use-scleral-lenses is a useful resource for both practitioners and patients alike

This is intended as an overview of the different types of contact lenses that can be used in keratoconus. Trade names, brand names and specific manufacturers have not been mentioned – just as no one type of lens is best neither is one brand or design. Most experienced fitters will have access to a range of designs from a range of manufacturers.

Remember, each keratoconic eye is unique so finding the right lens for you is not a question of picking a lens off the shelf. Your lifestyle, allergies, other medical issues as well as the stage of your keratoconus will need to be taken in to account. When you go for fitting or for aftercare appointments make sure you discuss your concerns or any issues you may be having with your contact lens practitioner. Don’t worry about asking a daft question or mentioning something that you are putting up with because you think that’s just how contact lenses are. Even in a busy NHS clinic your practitioner will make time available to discuss these things. It may require a return visit but might make your life so much better.

Finally, remember that contact lens fitting is a process not a one off occurrence. When you are first fitted or the fit is altered after an number of months or years it is highly likely that the lens fit and vision will need to be fine tuned over the first weeks (or even months). Unless instructed otherwise always attend your contact lens appointment having worn your contact lenses for as long as possible on that day and bring your case and solutions with you.

LOOK AFTER YOUR LENSES

Whatever lens you wear It is important to clean your contact lenses daily to maintain the highest standards of comfort and visual clarity. Each day after you remove your lenses, you must clean them prior to overnight storage.

Always use the correct solution, never use tap water. Change your contact lens case regularly as bacteria will happily live in the little damp case, that could damage your eyes and cause infections.

Try not to overwear your lens especially in the early days of getting used to them. If they hurt – take them out and clean them, and let your eyes rest. Try to avoid aircon and get fresh air to your eyes when you can. There are various rewetting and comfort drops available from pharmacies and your doctor. Always check that they’re suitable to use with your type of contact lens.