Keratoconus
Keratoconus is a disease of the cornea, the clear front window of the eye, which is also the most important optical element of the eye. In keratoconus, the cornea becomes progressively steeper, more irregular and thins. Usually, this leads to increasing myopia (short‐sightedness) and irregular astigmatism, causing blur and doubling of images. In mild cases, the irregularity in the corneal shape is best seen with specialised equipment called a topographer. In more advanced cases, there is often a characteristic bulge or cone‐like shape in the cornea, which can even be visible to the naked eye.
Keratoconus typically starts to produce symptoms in teenagers and young adults, but the onset may be in childhood, and the rate of progression is variable. Keratoconus typically affects one eye more than the other. Keratoconus is often associated with allergic conditions, such as allergic conjunctivitis, hayfever, asthma and eczema. Allergic eye disease produces ocular itch, and a tendency to want to rub the eyes. Some patients rub their eyes habitually, even without recognising it, and this can be unrelated to ocular itch. Repeated mechanical pressure on the weak cornea by eye rubbing produces further bulging and thinning of the cornea.
Traditional treatment for keratoconus centred on rehabilitating the vision with spectacles, hard contact lenses and corneal transplantation, depending on the severity of the keratoconus. If the cornea becomes very thin and steep, the back layer of the cornea (Descemet’s membrane) can split, which leads to a sudden onset of swelling in the cornea (hydrops), which will often resolve with residual scarring.
Until recently, there has been no treatment available to stop the progression of keratoconus, which often meant a gradual worsening of the condition, with some patients eventually requiring a corneal transplantation (corneal graft) in order to improve vision. If hydrops occurs, residual scarring often will produce a need for corneal transplantation.
Management of keratoconus has changed from the traditional model, as there are now more treatment options available. There are now two main priorities in treatment:
1) Slow or halt disease progression, and
2) Rehabilitate the vision
Corneal collagen cross-linking (CXL) has provided the first treatment which can slow or halt the progression of keratoconus. If keratoconus can be detected in the very early stages, corneal collagen cross-linking may offer the opportunity to stabilise the disease, when spectacle-corrected vision is excellent.
If specialty contact lenses become poorly tolerated, surgical options to improve vision can be considered. Implantation of intrastromal ring segments (such as Kerarings) is an option to correct significant irregularity in the cornea, with the aim of improving best vision with spectacles. Topographic-guided laser surface ablation can also be used to correct irregularity in the cornea. For high residual refractive error (high myopia and astigmatism) toric phakic implantable lenses (implantable contact lenses) may be used to improve functional vision.
For further medical information about combined treatments, see:
Editorial by Dr BJ Dupps “Combined collagen crosslinking treatments for keratoconus”
Journal of Cataract & Refractive Surgery. Vol 39:5, pp 663-664, May 2013
http://www.jcrsjournal.org/article/S0886-3350(13)00354-4/fulltext
This editorial discusses Dr Daya Sharma’s publication on combined treatment for progressive keratoconus with Keraring implantation, followed by corneal collagen cross-linking (CXL), followed by toric Implantable Collamer Lens (ICL).
Coşkunseven E, Sharma DP, Jankov MR 2nd, Kymionis GD, Richoz O, Hafezi F. Collagen copolymer toric phakic intraocular lens for residual myopic astigmatism after intrastromal corneal ring segment implantation and corneal collagen crosslinking in a 3-stage procedure for keratoconus. J Cataract Refract Surg. May 2013; 39(5):722-9.
http://www.jcrsjournal.org/article/S0886-3350(13)00003-5/abstract
What is the aim of treatment with Corneal Collagen Cross-linking (CXL)?
The aim of treatment with Corneal Collagen Cross-linking (CXL) is to slow or halt the progression of keratoconus or other corneal ectatic diseases. In the vast majority of cases, CXL is successful in this regard. CXL is performed to prevent further disease progression and deterioration in vision, particularly to avoid progression of keratoconus, which may require a corneal transplant. Progression of disease after CXL is unusual, and is more likely to happen in children who were initially progressing rapidly. However, CXL can be repeated if there is any evidence of further progression.
CXL is not a cure for keratoconus. Even when the procedure is successful, there may be no significant change in the vision or significant flattening of the cornea. This is why it is generally not used for patients who do not have evidence of disease progression. CXL is the only treatment which can slow or halt the disease progression. Spectacles or contact lenses are likely to still be required after the procedure. CXL is sometimes done after other procedures (such as implantation of Kerarings, or surface laser treatment) which do aim to improve the vision.
How does Corneal Collagen Cross-linking (CXL) work?
With increasing age, there is a natural, gradual process of increasing stiffness in the cornea, due to the formation of greater cross‐links between the collagen fibres. Keratoconus does not usually progress in people 50 years of age and over, because of this stiffening process. CXL is basically a way of prematurely making the cornea much stiffer, so that it won’t continue to bulge even further. Collagen cross-linking involves using a combination of riboflavin (vitamin B2), given as eye drops, and UV light. This produces a reaction in the cornea, resulting in the formation of more cross‐links between collagen fibres, and hence a significant strengthening of the cornea.
What are the benefits of Corneal Collagen Cross-linking (CXL)?
The vast majority of patients have stabilisation of their disease compared with the progression prior to treatment. The longer term effects are still being studied, however, we expect that the cornea in most patients with keratoconus would gradually stiffen with age in any case, meaning that significant worsening should be unlikely. Compared to untreated eyes, which continue to become steeper, eyes treated with CXL become slightly less steep at 12 months. The long‐term results of CXL beyond 10 years are not yet known, however, we do know that without treatment, many eyes would continue to progress, in some cases, requiring a corneal transplant.
About half of all eyes receiving CXL do get an improvement in their best possible vision, i.e. in up to 60% of patients, an improvement in best spectacle corrected vision (at least 1 line) can be observed. In the remaining patients, no improvement in vision is experienced, and it is important to reiterate that the treatment is not performed with visual improvement as the goal.
CXL is also useful for ectasia of the cornea following LASIK, and for pellucid marginal degeneration and other corneal ectatic disorders. People with disabilities who would not be able to wear contact lenses are likely to benefit from CXL to stabilise their keratoconus, while the vision is still correctable with glasses.
Intrastromal ring segments (such as Kerarings) are used primarily to rehabilitate the vision in patients who have poor vision with their best spectacle correction, due to irregular astigmatism in the cornea. It is best reserved as a procedure for patients who are unable to wear hard contact lenses or hybrid lenses. Patients in this situation may have been treated with a corneal transplant in the past. Ring segment implantation is an alternative to this which preserves the patient’s own cornea.
Ring segments are made of a specialised biocompatible material (PMMA), which has a long history of safety and efficacy for intraocular implantation, having been used for over 50 years in the manufacture of intraocular lenses that are implanted during cataract surgery.
Ring segment implantation is primarily used to reshape the cornea, to improve the best-spectacle corrected vision. By itself, the procedure cannot stabilise the cornea enough to prevent progression of keratoconus, so ring segments will often be combined with corneal collagen cross-linking if there is any evidence of progressive disease. Ring segment implantation can also be combined with other procedures to rehabilitate the vision, such as topographic-guided laser ablation and toric phakic intraocular lens implantation.
The Keraring procedure has the following objectives:
• Regularize the corneal surface, reducing distortions and improving the quality of vision.
• Flatten the cornea, reducing its cone-like shape.
• Reduce myopia and irregular astigmatism caused by keratoconus and other ectatic diseases, to improve the best spectacle-corrected vision after the procedure
Dr Daya Sharma uses the femtosecond laser to create channels for the ring segment placement. The femtosecond laser creates the channel rapidly and precisely, and reduces the risks of the procedure.
Dr Daya Sharma, is a Corneal and Refractive surgeon with a keen interest in managing patients with keratoconus, particularly in modern methods of treatment to improve the vision without needing a corneal transplant. To make an appointment to see Dr Daya Sharma in our Bondi Junction office (02 9387 5300) or our Miranda office (02 9531 5300).
For further medical information about combined treatments using Keraring implantation, see:
Editorial by Dr BJ Dupps “Combined collagen crosslinking treatments for keratoconus”
Journal of Cataract & Refractive Surgery. Vol 39:5, pp 663-664, May 2013
http://www.jcrsjournal.org/article/S0886-3350(13)00354-4/fulltext
This editorial discusses Dr Daya Sharma’s publication on combined treatment for progressive keratoconus with Keraring implantation, followed by corneal collagen cross-linking (CXL), followed by toric Implantable Collamer Lens (ICL).
Coşkunseven E, Sharma DP, Jankov MR 2nd, Kymionis GD, Richoz O, Hafezi F. Collagen copolymer toric phakic intraocular lens for residual myopic astigmatism after intrastromal corneal ring segment implantation and corneal collagen crosslinking in a 3-stage procedure for keratoconus. J Cataract Refract Surg. May 2013; 39(5):722-9.
http://www.jcrsjournal.org/article/S0886-3350(13)00003-5/abstract