What is Keratoconus?
Keratoconus is a disease of the cornea, the clear window at the front of the eye. It is responsible for 75% of the focusing power of the eye, which makes its shape very important. In keratoconus the cornea bulges, thins and warps, losing its natural shape and becoming more like a rugby ball in shape than a soccer ball. As this happens, focus is lost and vision becomes more blurry. A patient with keratoconus may notice their glasses prescription requiring regular changes, with increasing amounts of astigmatism. The onset of the disease can vary but most patients with keratoconus begin to notice blurry vision in their teens or twenties. The disease is almost always in both eyes to some extent, but is very often worse on one side. It is important to stress that the vast majority of patients are able to function normally with keratoconus, it is a “blurring not a blinding” disease.
Why does it happen?
Although genetics likely predispose a patient to getting keratoconus, it is not purely a genetically inherited disease. The cornea is composed primarily of collagen, the same protein that is found in your ligaments and tendons. We know that ligaments and tendons respond to mechanical force, and are capable of becoming softer and more pliable with repeated stretching. They also soften under hormonal influences, as happens during pregnancy to soften pelvic ligaments. It is probably not surprising therefore that the cornea can also soften and become more pliable with mechanical force or hormonal change. It is vital that the first message you absorb as a patient is to cease all rubbing of the eye which we feel is the most important environmental trigger for keratoconus. If this is difficult due to allergy and itch, it is our job to help treat this. Some patients report worsening of their vision during pregnancy, for women it is important to let us know if this is true in your case and what your future family plans are.
How is it treated?
Most corneal specialists now agree that there are two main goals in the treatment of keratoconus.
First- stabilise the bulging process. We achieve this by:
- Ceasing all eye rubbing
- Managing allergy if required
- Identifying and treating other sources of corneal pressure that might occur during sleep
- Using the collagen cross linking procedure (see below)
Second- improve the vision if required. We achieve this by:
- Visiting your optometrist for glasses or a specialty contact lens
- Newer surgical treatments such as topography guided PRK, ring implants or implantable contact lenses
- In extreme cases a corneal transplant may be required, this is referred to as a DALK or PK. (see lamellar corneal surgery section).
It is important to individualise these options. In doing this we have to first consider what the best choice is for you medically and, as a second priority, what best suits your work or lifestyle. For each patient there are two people making these decisions in partnership. Your ophthalmologist and your optometrist.
Collagen cross linking
Collagen cross linking employs a natural aging phenomenon as a treatment. As the collagen in our body ages, it becomes more “stiff”. At a cellular level this occurs due to the formation of “cross links” or bonds between collagen layers. Through this process, most patients with keratoconus will begin to stabilise in their mid to late thirties. As a treatment, corneal collagen cross linking aims to accelerate and emphasise this natural process, allowing us to stabilise the disease in almost all cases regardless of age. It is important to note several things about the treatment:
- Although it is very effective at halting progression of disease, it does not predictably improve corneal shape or vision (although some improvement can be seen).
- It is therefore best employed in people who we know are getting worse, but still have functional vision, in effect “freezing” the cornea in a relatively good shape.
- It is a photochemical reaction that takes 6 months to come to completion, during this time some fluctuation in vision and light sensitivity is expected.
- Its short and medium term side effects are well understood and complications from the procedure are very rare. As it has only been practised worldwide for the last 12 years, the long term side effects are unknown
Topography Guided PRK with Simultaneous Collagen Cross Linking
In some patients the disease may have already progressed to the point that useful vision has been lost. Because collagen cross linking alone cannot be relied upon to improve vision, many efforts have been directed towards finding techniques that can meet this need, rehabilitating vision once the disease has been stabilised. One such technique is topography guided PRK (TG PRK). TG PRK employs a laser to restore the cornea from a rugby ball back into a soccer ball shape, the cornea is then cross linked to “lock in” this profile.
The technique is dependent on the laser and the surgeon, and requires a great deal of planning. There are many published variations. Doctor Moloney trained in this technique with Dr. David Lin and Dr. Simon Holland at the Pacific Laser Eye Centre (PLEC) in Vancouver, Canada, a pioneering centre in this work. At PLEC there is experience in treating nearly 1000 keratoconic eyes over almost ten years with TGPRK. This has created a database from which future treatments can be calculated for greater accuracy. The treatment method developed allows for regularisation of corneal shape and improvement of vision. Depending on the severity of your disease the goal of TGPRK may be to allow a better contact lens fit, a transition from contact lenses back into glasses, or remove the need for glasses and contact lenses altogether.
This treatment option is a strong area of interest and expertise for Dr Moloney, who has published and given talks on the topic at national and international meetings. Read more about the treatment:
- Clinical Results of Topography-based Customized Ablations
- Topography-guided laser refractive surgery
- Topography-Guided Photorefractive Keratectomy (TGPRK)
A video presentation of this work was recently awarded first prize in the American Society of Cataract and Refractive Surgery film festival. This video may be viewed at:
Implantable contact lenses:
Some patients with keratoconus may have such a high prescription that to reduce glasses or contact lens dependence, the above techniques are not enough. In these rare cases, a contact lens may be implanted into the front chamber of the eye to correct the refractive error internally. This option carries the risks of intraocular surgery and is not taken lightly.