Specialist in bespoke cataract surgery, keratoconus, corneal transplantation and eye surface disease
Keratoconus is an uncommon condition that affects the cornea (the transparent dome at the front of the eye and its main focusing system).
It is characterised by thinning and bulging of the tissue.
This distortion of the corneal shape results in irregular astigmatism which causes a reduction in vision.
It typically presents in adolescence. Progression is variable, but without treatment 10-25% of cases need surgery.
The picture is of corneal tissue showing increased stiffness (top/temporarily stained yellow) immediately after undergoing cross linkage compared to non-cross-linked tissue (bottom).
Treatment depends of the degree of ectasia (corneal bulging) and the resultant irregular astigmatism. Mild cases can be treated with astigmatic spectacles and soft toric (astigmatism correcting) contact lenses. As the disease progresses rigid (hard) contact lenses become necessary to improve vision. In the majority of patients such lenses give good vision, but are not the solution in all cases. Discomfort may limit the use of rigid contact lens wear and in advanced cases fitting may be difficult. Severe bulging and corneal scarring in advanced keratoconus can limit the visual improvement with contact lenses.
Between 10-25% of patients require some form of surgery. The options include:
This is a relatively new way of treating the condition and the first one which may actually stabilise the cornea and stops keratoconus getting worse. It increases the mechanical stability of the cornea and its resistance to enzymatic digestion by inducing cross linkage between collagen fibres in the cornea.
The technique is performed under topical anaesthesia (eye drops). As riboflavin does not easily penetrate, the corneal skin or epithelium is painlessly removed using a blunt spatula
During the procedure riboflavin eye drops are applied to the eye surface every three to five minutes. Once enough has been absorbed (usually after about 30 minutes), ultraviolet light is shone at the eye for 10 minutes
After the treatment a bandage contact lens is placed in the eye and this is worn continuously until review in outpatients. A combination of a steroid and antibiotic drop is prescribed.
In most patients the diseases stops getting worse: clinical studies looking at results for up to 5 years after treatment have found that progression of the disease is halted in 90% of patients.
In addition, a significant proportion (between 20 and 70% in different studies) show improvement.
The majority of patients develop haze following the procedure. This is not a complication, but a part of the healing process that results in a stiffer cornea. The haze is maximal at about 4 weeks and can result in temporary cloudiness of vision. It clears slowly, but can take several months to go completely. In occasional cases (approximately 1 in 100) the hazy vision can last longer.
Generally Collagen Cross Linkage is a safe procedure, but there are some possible complications.
Cells in the corneal tissue (keratocytes) are killed off by the ultraviolet light, but are replaced by the body and this does not seem to cause any problems. The light could also damage the endothelial layer of cells on the back surface of the cornea, and for this reason people with very thin corneas (less than 0.4 mm) may not be suitable for treatment. There has been no evidence of damage to the endothelial cells in studies so far.
UV light is potentially damaging to the lens and retina, but the riboflavin drops stops the light penetrating to these deeper structures.
There is a risk of infection as well as other non-infective inflammatory problems after treatment. In 1-3 patients out of 100, these are severe enough to cause some loss of vision, even with treatment and even with new glasses or contact lenses. However, this risk has to be weighed against the risk of the keratoconus getting worse, possibly to a stage which requires transplantation; a procedure that carries substantially greater risks than cross-linkage.
Cross linkage is a relatively new treatment and all long term effects may not yet be known. Although the benefits seem to be permanent, it is possible that some patients may need repeat treatment at some point in the future.
If you undergo the procedure, the eye will be uncomfortable for a few days, with some haziness of vision and slight swelling of the lid.
Should you experience a worsening of pain, a sudden loss of vision, increased redness of the eye or increased swelling of the eyelids, you need to be examined urgently.
During normal working hours please contact Mr Prydal’s secretary on 0116 274 3718. At other times ring the hospital at which you had treatment.
Also, the ophthalmologists are on call at Leicester Royal Infirmary 24/7 and will be happy to see you. You can attend Eye Casualty there without an appointment.
The green stain clears quickly after the procedure.