<Keratoconus>

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Keratoconus

Keratoconus, often abbreviated to "KC", literally means "conical or cone-shaped cornea" it is a non-inflammatory eye condition in which the normally round dome-shaped cornea progressively becomes stretched and thin near its centre causing a cone-like bulge to develop. This makes the eye more myopic (shortsighted) and astigmatic and results in significant visual distortion. As the cornea is the clear window over the front of the eye it is responsible for focussing most of the light coming into the eye. Therefore, abnormalities of the cornea severely affect the way we see the world making simple tasks, like driving, watching TV or reading a book difficult.

In its earliest stages, keratoconus causes slight blurring and distortion of vision and increased sensitivity to glare and light. These symptoms usually first appear in the late teens and early twenties. The stretching of the cornea tends to progress but the rate varies. Keratoconus may progress for 10-20 years and then slow or stabilize. Each eye may be affected differently. Sometimes one eye may be badly affected while the other eye may show very little sign of the condition.

It is not a common eye disease, but it is by no means rare affecting between 1 in 3,000 and 1 in 10,000 people depending on where they live. It usually affects both eyes, although one eye is normally affected before the other. It is found in all parts of the United Kingdom and the rest of the world. It has no known significant geographic, cultural or social pattern.

The cause of keratoconus is unknown. However, it may be associated with allergy or possibly have a genetic component. Keratoconus rarely appears in an individual until puberty or beyond. Although no one can be sure how far keratoconus will develop in an individual, the condition does not cause blindness. With the current treatment available most people should be able to lead a normal lifestyle as a result of the condition.

However good vision may be difficult to maintain at times as the condition progresses and contact lens tolerance varies. Spectacles or soft contact lenses may be used to correct the mild shortsightedness and astigmatism caused in the early stages of keratoconus. As the disorder progresses and the cornea continues to thin and change shape, rigid gas permeable contact lenses are generally prescribed to correct vision more adequately. The contact lenses must be carefully fitted, and frequent checkups and lens changes may be needed to achieve and maintain good vision.

There is a small risk when wearing contact lenses and it is important to follow your contact lens practitioners advice on cleaning, handling and wearing times. Contact lenses do not, unfortunately, slow down the rate of progression of the cone, but they do give good vision during that period which could not otherwise be achieved. Drops, ointment, dietary changes and eye exercises also don't help but the condition does eventually stabilise, although it may take many years before that happens.

In about 10% to 20% of keratoconus patients the cornea may become extremely steep, thin and irregular or the vision cannot be improved sufficiently with contact lenses. The cornea may then need to be replaced surgically with a corneal transplant or graft. Visual recovery after a transplant takes a long time - sometimes as long as eighteen months - to settle down and there is a strong possibility that the eye will still need to be fitted with a contact lens afterwards in order to see properly. Surgery is therefore not a shortcut to perfect vision nor a way of avoiding contact lens wear.

There is also a risk of the transplant rejecting afterwards although over 90% of corneal transplants that are done for keratoconus are successful. For patients of St. James's University Hospital: if at any time your eye is uncomfortable or you think something is not right, do discuss it with your ophthalmologiost or contact lens practitioner when you come to the clinic. If necessary make an earlier appointment to attend the hospital or in an emergency the Accident and Emergency (Casualty) Department is open 24 hours. Patients of the Contact Lens Service can be seen in the department from 9am to 5pm Monday to Friday.

There are links to more information on the options for the management of keratoconus below (Please note this list of options is not exhaustive. Everyone with Keratoconus is individual and options will vary depending on your individual circumstances).

Spectacles
Soft contact lenses
Rigid Gas Permeable (RGP) corneal contact lenses
Soft/Hard combination contact lenses (hybrid)
Piggy back contact lenses
Scleral contact lenses
Corneal Collagen Cross-linking with Riboflavin (C3R)
Intacs
Mini-ARK (refractive surgery)
Corneal graft (transplant)

Spectacles

Spectacles may be used to correct the mild shortsightedness and astigmatism caused in the early stages of keratoconus but the quality of visual acuity decreases as the cornea becomes increasingly distorted. Spectacles may still be useful in severe keratoconus to give some improvement in visual acuity when contact lenses are not being worn.

Soft contact lenses

The role of soft lenses in keratoconus is limited because the soft lens drapes over the irregular corneal surface and the front surface of the lens assumes the same irregular surface as the cornea without trapping a fluid reservoir so the effective refracting surface is no improvement over the original corneal surface. However soft contact lenses made of hydrogel or silicone hydrogel materials may be used to correct the mild shortsightedness and astigmatism caused in the early stages of keratoconus but the quality of visual acuity usually decreases as the cornea becomes increasingly distorted.

Soft toric lenses that correct astigmatism and special "thicker" keratoconic soft lenses that mask some of the distortion may be helpful in early cases or where poor tolerance of rigid lenses occurs. Unfortunately they rarely give the same quality of visual acuity as a rigid gas permeable contact lens.

Rigid Gas Permeable (RGP) corneal contact lenses

These rigid contact lenses provide the optimal visual correction, the rigid lens masks the underlying irregular cornea and functions as the new refractive surface of the eye, with the tear film filling in the space between the back of the contact lens and the front of the eye. “Rigid” defines the type of lens. “Gas Permeable” describes the lens material. There are many different RGP lens designs. However some patients find them difficult to adapt to because of the lid sensation associated with their wear.

Soft/Hard combination contact lenses (hybrid)

A contact lens with a rigid centre surrounded by a soft skirt can be used to minimise lid sensation. However due to the low oxygen transmission of these lenses long wearing times should be avoided.

Piggy back contact lenses

Piggy-backing is the term used to describe wearing two lenses at once in the same eye, usually an RGP lens worn on top of a soft lens. If a rigid corneal lens is very uncomfortable to wear, a soft hydrogel or silicone hydrogel lens (with no or a very small prescription) can be used underneath to act as a cushion. This is an attempt to minimise corneal rubbing with the rigid lens and to enable it to be worn comfortably. The RGP lens provides crisp vision and the soft lens acts as a cushion providing comfort. Many people manage to successfully increase their wearing time with this management or can use it as a temporary measure when needed. Both lenses need to be cleaned thoroughly and handled differently. Regular contact lens appointments need to be kept to check the fitting and ensure that enough oxygen penetrates through both lenses.

Scleral contact lenses

These are large diameter lenses that rest on the white part of the eye, called the sclera, and vaults over the cornea. The size can be intimidating for some, but scleral lenses have many advantages. Because of their size, they do not fall out, dust or dirt particles cannot get behind them during wear. They are surprisingly comfortable to wear because the edges of the lens rests above and below the eye lid margins so there is no lens awareness. The introduction of rigid gas permeable (RGP) materials has made this design more readily available.

Corneal Collagen Cross-linking with Riboflavin (C3-R)

Collagen crosslinking using UV radiation combined with riboflavin is an experimental procedure currently being performed in Europe. It is not FDA approved for clinical use in the United States. The goal of collagen crosslinking is to strengthen and stiffen the corneal fibers in order to decrease the progression of keratoconus. It is thought that this method works by increasing collagen cross-linking, which are the natural "anchors" within the cornea. These anchors are responsible for preventing the cornea from bulging out and becoming steep and irregular (which is the cause of keratoconus). The safety and efficacy of crosslinking, as yet, is unclear.


The figures above show the parallel corneal layers (white) and the collagen cross-linking (red) which are increased after C3-R treatment.

Intacs

INTACS is the trademark name for micro-thin prescription inserts which were previously used as a form of refractive surgery in the treatment of low levels of myopia or nearsightedness, but has recently received approval for keratoconus in the USA.

Intacs are thin plastic, semi-circular rings inserted into the mid layer of the cornea. When inserted in the keratoconus cornea they flatten the cornea, changing the shape and location of the cone. The placement of Intacs remodels and reinforces the cornea, eliminating some or all of the irregularities caused by keratoconus in order to provide improved vision. This can improve uncorrected vision, however, depending on the severity of the KC, spectacles or contact lenses may still be needed for functional vision.