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Michael Tappin Consultant Ophthalmologist

Surrey Eye Clinic

Keratoconus

What is Keratoconus?

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The surface of the eye is called the cornea. The cornea is the transparent dome-
shaped front part of the eye and it is responsible for 80% of the eyes' ability to focus. To function properly it must be smooth and appropriately shaped. Keratoconus causes the central area of the cornea to become weak and thinner and will create a refractive error, i.e. vision becomes distorted. Keratoconus is usually first diagnosed in the form of an
astigmatism where the cornea is seen to bulge slightly, which in turn, will impair the
eyes’ ability to focus.

When keratoconus presents, it is usually in the second decade, however it can develop at any age. It is estimated to affect 1 person in 2000. Therefore keratoconus is not uncommon.

For many patients the disease does not progress and they will continue to have good
functional vision with glasses.

However, for some patients keratoconus will progress to the point where vision is
impaired and can no longer be improved with glasses. Although often only one eye is
involved it is not uncommon for both eyes to be affected however the disease usually
stabilises after 30 years or so.

What are the options when glasses no longer provide functional vision?

Rigid (hard) gas-permeable (RGP) contact lenses can greatly improve vision when
glasses are no longer effective. These are the most common method of improving the vision for patients with keratoconus. Supported by the natural tears in the eye, the irregular surface of the cornea is reshaped allowing for better vision.

The development of special keratoconus RGP contact lens designs has increased the
usage of RGP lenses over the years. However, RGP contact lenses cannot be worn by
everyone. Some people will experience unacceptable discomfort. Therefore they are
only partially successful, especially for patients with low production of tears, as an
adequate supply of tears is needed to provide adequate lubrication to buffer the RGP
lens.

If RGP contact lenses are not tolerated, piggyback lenses are sometimes used, where the hard lens is placed on top of a soft contact lens making wear more comfortable.

Contact Lenses

Piggyback or Hybrid Lenses

This is when a soft contact lenses is placed under the RGP lenses. This superimposed method, although more awkward, may sometimes be better tolerated than an RGP contact lens alone. Another option is the use of a hybrid lens (hard centre and soft edge), which is rarely satisfactory as a long-term solution.

Newer Methods for Treating Keratoconus

Cross Linking

Cross-linking is not a new technique and has long been used as a medical interventional technique. Commonly used to modify other substances e.g. drugs, chemicals - in dentistry to harden fillings and has been used for a number of years in ophthalmology by a number of prominent ophthalmic surgeons here in Europe.

It is a non-surgical method utilising a UVA light source, which is delivered onto the cornea together with a chemical mix largely made up of riboflavin for strengthening the collagen fibres within the corneal structure. The combination of the UVA light
and the riboflavin creates a joining or bonding of the chemical structures within the cornea. (Riboflavin is commonly found in our food and also known as vitamin B2, which is an easily absorbed micronutrient with a key role in maintaining health in both humans and animals).

This comparatively simple procedure has been shown in laboratory and clinical studies to increase the amount of collagen cross-linking in the cornea and subsequently strengthen the cornea. There are published European studies, to show that this cross linking procedure has been proven safe and effective in patients with no side effects reported. Additionally, retreatment is an option at a later date if required.

For further details about the cross linking procedure click HERE.

There is a significant improvement in the rigidity of the treated cornea (top) compared to untreated cornea (below).

Topographic Guided Laser Surgery

As an addition to collagen cross linking, Laser treatment can be applied to the cornea. This treatment can be customised using the latest technology for each individual cornea. The major irregularities caused by keratoconus can be reduced often improving vision and reducing the requirement to wear contact lenses.

Intacs.

The insertion of Intacs is a surgical procedure. Intacs are clear small, semicircular plastic rings of various thicknesses, which are inserted inside the cornea at its outer edges. The insertion of Intacs or rings flattens the central area of the cornea and corrects myopic refractive errors. A major advantage of Intacs is that no tissue is removed and there is no ablation or incision across the visual axsis. Intacs have proven to stop or slow down the progression of keratoconus, although often glasses or contact lenses will be required.

A Traditional or Full Thickness Corneal Graft

DALK

This is a deep anterior lamellar keratoplasty. It is a partial thickness corneal graft. It is a technique that removes only the diseased part of the cornea leaving the healthy part of the cornea intact.

This has the great advantage of reducing the frequency of graft rejection episodes and is associated with less post operative astigmatism and faster visual rehabilitation.

Full Thickness Corneal Graft.

This is called a penetrating keratoplasty. It is the traditional graft technique and is still an option for patients with keratoconus.