What is keratoconus?
Keratoconus is a potentially blinding condition caused by gradual thinning and bulging forward of the cornea. Doctors often explain to the patient that the front of their eye is becoming shaped more like a rugby ball rather than a football.
Keratoconus always affects both eyes, although very commonly, one eye tends to be significantly worse than the other. Most cases of keratoconus are picked up on routine screening by opticians who may notice rapid changes in your glasses prescription and increasing astigmatism. As corneal bulging increases, patients typically become more short sighted and develop more astigmatism. Vision can be poor despite glasses.
Keratoconus tends to begin during teenage years and continues to progress up to the late 30's, after which it tends to slow down and remain stable. Rapid progression seems to occur during teenage and early 20's. Unfortunately, if the condition isn't treated early on with collagen cross linking, patients are left with an abnormal shaped cornea that requires a contact lens to see well.
Keratoconus is a very variable disease and can be very mild in one person and not progress very much, whilst being severe and rapidly progressive in other cases.
Why do people get keratoconus?
Our understanding of what causes keratoconus is still evolving. Whilst certain abnormal genes have been identified in patients with keratoconus and whilst keratoconus can occur in different members of the same family, the expression of keratoconus appears to be more complex. The risk of your children developing keratoconus if you have the condition is roughly 3% and is higher than children whose parents do not have the condition.
The current working theory for people develop keratoconus is called the 2 hit hypothesis. This proposes that keratoconus occurs in people due to multiple factors, one of which is a genetic propensity, whilst the others may be an environmental trigger such as allergic eye disease or eye rubbing. A combination of these factors may lead to keratoconus in patients with a predisposition to corneal weakness.
Why does keratoconus matter?
Keratoconus worsens your vision. The cornea is the main optical component of the eye. The cornea helps focus the world around you onto your retina at the back of the eye where it is perceived. As the cornea begins to bulge in keratoconus the regular optics of the cornea are distorted and hence it is difficult to focus a clear image onto the retina. This can result in distortion, ghosting and multiple image formation.
Unfortunately, as keratoconus progresses it becomes increasingly difficult for spectacles to correct vision. Most keratoconus patients achieve their best vision with a rigid contact lens which works by arching over the bulging cone of cornea and artificially creating a smooth spherical surface that is optically superior.
If keratoconus gets really bad, patients may require a corneal transplant. Without corneal crosslinking, this occurs in approximately 20% of patients.
How is keratoconus treated?
The aims of keratoconus treatment are twofold;
1. Correction of vision:
Vision correction in mild cases may simply be with glasses, as severity increases your eye surgeon may suggest various types of contact lenses including rigid gas permeable lenses, hybrid soft/hard lenses or scleral lenses.
In advanced cases corneal transplantation may be required.
2. Preventing progression of keratoconus:
Prevention is better than cure and Collagen Cross Linking (cxl) is now considered an effective treatment to stop the progression of Keratoconus. There is now a huge body of evidence in the medical literature validating its efficacy. This treatment is most beneficial when done early before the shape of the cornea becomes very abnormal. Mr Guerin performs collagen cross linking at the Mater Private Hospital.
NB CROSSLINKING DOES NOT MAKE KERATOCONUS BETTER – IT PREVENTS IT GETTING WORSE
The idea of this treatment is to strengthen the cornea so it doesn’t bend further out of shape due to keratoconus. The cornea consists of millions of collagen fibres in close contact with each other. Cross linking is a medical procedure that combines the use of ultra-violet light and Riboflavin eye drops to strengthen the bonds between these fibres and thus make the cornea stronger. In collagen cross-linking, Riboflavin (vitamin B2) is dripped onto the anaesthetised cornea, which is then exposed to ultra-violet light. The light causes the Riboflavin to fluoresce, which leads to the formation of bonds between collagen molecules or collagen cross-linking.
More about the crosslinking procedure
CXL is performed as a day-case procedure. Although the procedure takes less than an hour, there is usually some waiting time before treatment and some further time is required for discharge instruction. So be prepared to spend up to half a day in hospital.
The treatment is performed in an operating room, where you will be asked to lie flat on the treatment table. Anaesthetic drops are used to completely numb the surface of the eye before a small clip is placed to keep the eyelids open. The surface skin of the eye (epithelium) is gently brushed clear and riboflavin drops are applied every few minutes for 20 minutes. Following this, the ultraviolet light is shone at the eye for 4 minutes. A soft ‘bandage’ contact lens is placed on the eye at the end of procedure.
What happens after CXL?
You will be given eye drops to use after the procedure. The soft contact lens will remain in your eye until the surface has healed (usually 3 days). After the anaesthetic drops wear off later that day, the eye will be gritty, red and sensitive to light for several days afterwards. Everyone’s experience of pain is different, with some patients reporting very little discomfort and others describing the first few days as very uncomfortable. The eyes may be light sensitive and many patients find sunglasses helpful. Your vision will be quite blurred at first, but will clear gradually over the first few weeks.
You will be seen by Mr Guerin on day 1 and day 3 after the procedure, and then in a more spaced out manner.
Do I need to take time off work or studies?
Yes. You should allow approximately 3-5 days off work while most of the surface healing occurs. You will be putting eye drops in every hour for the first day, and then every 4 hours for the following days. Using the eye soon after surgery (e.g. reading, TV, computer) will not do any damage, but you may find it more comfortable to rest with the eyes closed early on.
What should I do, or not do, after CXL?
It is important to put the eye drops in regularly as prescribed. Wash and shower normally, but try to avoid getting water in your eyes. You may exercise but should not swim before the surface of the eye has healed. You may drive when you can read a number plate at 70 feet with both eyes open whilst wearing glasses or contact lenses as appropriate; we will check your vision in the clinic the following week to confirm if your vision is good enough to drive. It is normally safe to resume contact lens wear once the eye surface skin layer has healed. Typically this is around the end of week 2
Risks of treatment
In general, CXL is very safe, but like all operations the body needs time to heal and problems do occasionally occur. You need to weigh this up against the fact that without CXL treatment, at least 20% of all patients with keratoconus will eventually require a corneal transplant.
Loss of vision – scarring of the cornea can occur rarely and 3% of cases can result may lose some vision.
Corneal haze – this can cause ghosting and haloes from lights at night. This is temporary but can last up to 12 months and is common. You will be placed on steroid drops afterwards to help control this.
Corneal inflammation – crosslinking can cause sterile corneal inflammation in approximately 8% of patients. These usually settle with the steroid drops.
Corneal infection is rare but possible. You will be placed on antibiotic drops afterwards and monitored closely. Severe corneal infection is very rare but has been reported and may result in a corneal transplant
Need for Retreatment - remember crosslinking does not work in 3% of cases, so repeat treamtnet may be necessary
Risk to cornea endothelium - If the cornea is less than 400 um thick there is a potential reiak of damage by the UV light to the corneal endothelium cells which line the inner opart of the cornea. Hence we use hypotonic riboflavin drops on the cornea in some cases to make it thicker so it’s is not damaged by the UV light. There is also a potential risk to the lens and the retina from the UV light.
For further information please consult www.keratoconus-group.org.uk