Keratoconus

Keratoconus causes the central area of the cornea to become weak and thinner, making the shape ‘bulge’ in an irregular manner. This results in a refractive error with the end result being distorted vision.

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. 

Although it can begin at any age, keratoconus often starts during puberty and progresses over time until it stabilises, many years later. However, for some patients keratoconus will progress to the point where vision is impaired such that glasses or contact lenses cannot improve the vision further. Although often only one eye is noticeably affected, it is common for both eyes to be affected.

It is estimated to affect 1 person in 2000. Therefore keratoconus is not uncommon.

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

Contact lenses

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. Many 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.

Piggyback or Hybrid lenses.

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

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.

Other options if Contact lenses are not suitable

Intacs

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. The insertion of Intacs is a surgical procedure.

Corneal graft surgery

For patients for whom other methods of correction are not suitable, corneal transplant can be the best option. This operation has been carried out for over 100 years. In recent years this technique has been greatly improved. The technique involves removing the misshapen corneal tissue and replacing it with healthy corneal tissue. It is a very successful technique with 90% of patients obtaining a great improvement in vision.

Although transplantation is very successful, it is a relatively invasive surgical procedure and as consequence carries a degree of risk. Corneal grafts are undertaken only if other methods of correction are unsuitable.

The absence of blood vessels in the cornea means that the healing process is slow and it may take up to 18 months before the shape of the transplanted cornea (and effectiveness as a focusing lens) has stabilised. During this time, vision in a transplanted eye would often be non functional.

Despite technically successful surgery, it is common for patients who undergo corneal transplants to require a contact lens to optimise the vision after surgery. It is best to exhaust all non-surgical options before undergoing corneal transplant surgery.

Beyond transplant

If the vision is still not clear after a corneal transplant do not give up hope of good vision. There are still many options available. The vision is often blurred due to long sight, short sight or astigmatism which can be regular or irregular. All these conditions can be corrected using all the techniques discussed previously. If glasses or contact lenses are unacceptable procedures such as INTACS, topographic guided laser treatment, Intraocular lens implants are all possible methods of further correcting vision.

Newer methods of treating Keratoconus 

Corneal Collagen Cross-Linking. (CXL)

Cross-linking is not a new technique and has long been used as a medical interventional technique in other areas such as dentistry. However, in recent years it has gained momentum in the treatment for stabilising keratoconus. First performed in 1997, it is now being used 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. The effect is similar to the change we commonly see when toasting bread. A fine slice of bread bends easily and has little strength but after toasting, the bread results in being stronger and slightly more compact.

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
few side effects reported. Additionally, retreatment is an option at a later date if required.

Cross-linking therapy is being used for a number of diseases of the cornea and is proving a useful treatment in conjunction with other surgical techniques such as Intacs and refractive laser surgery.

However Cross linking is not for everybody. The first requirement is to ensure that the thickness of the cornea is adequate for the treatment. Special non-invasive measuring devices are used by your specialist to accurately and quickly take these readings.

Below are 2 topography maps for a patient of ours who underwent cross linking for keratoconus.

The maps show the difference the cross linking has made to the topography. In both scans, map B is the pre CXL map and map A is the map taken after cross linking. The last column shows that there is a significant shrinkage of the ‘cone’ after cross linking. This patient experiences an improvement in vision, contact lens comfort, and reduced glare and haloes.

The Cross Linking Procedure

The procedure of Cross Linking itself takes just 60 minutes and may be either conducted in an Operating theatre or a special “clean” room. The eye is anaesthetized with drops and the surface cells are removed. Riboflavin eye drops are applied every two minutes for 30 minutes. At the end of these 30 minutes, application of the ultraviolet light is commenced for a further 30 minutes, with further application of the Riboflavin eye drops.

At the end of the procedure, the Consultant will wash the corneal surface with a special solution and a protective bandage contact lens is placed for a period of 1-2 weeks.

What are the risks of Cross Linking?

Risks of the procedure (to all structures of the eye) are minimal. Rigorous observation of the indications and contraindications has been conducted

After Cross Linking, patients often experience:

• Post-operative pain and sensation of foreign body in the eye for 24-48 hours after treatment until re-epithelialisation is complete
• Watering of the eye for 24-72 hours after treatment
• Transient corneal oedema with visual blurring for 30-60 days after treatment
• Corneal haze usually occurs but clears in the first 8 weeks. 

Topographic guided customised ablation laser surgery. (T-CAT)

Advanced Topographic Guided Laser Treatment (T-CAT) is one of the most precise methods of reducing higher order abberrations in patients with keratoconus. Following precise mapping of the cornea, the laser treatment is customised to follow the topography to gently remove up to 50 microns of corneal tissue in the most irregular areas. . The major irregularities caused by keratoconus can be reduced often improving vision , reducing discomfort with contact lenses and reducing the requirement to wear contact lenses.

The advent of cross linking has allowed the use of laser in an eye with keratoconus.

Below is an example of the changes that can be achieved with Laser and Cross linking. This patient underwent surgery at our clinic and the post surgical topography is much more regular than the pre operative map. This resulted in a significant improvement in the patient’s vision and comfort, and a reduction in glare and halo symptoms.

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