What is keratoconus?
Keratoconus is an eye condition affecting the cornea (the front surface) of the eye. It results in an irregular cornea causing distorted (blurred) vision. Generally keratoconus develops in the teenage years but may begin before the age of ten or not until adulthood.
The word keratoconus is derived from latin words, kerato- "cornea" and -conus meaning "cone shaped". This describes the normally round shaped cornea becoming cone-shaped with the progression of the condition. The keratoconic cornea also tends to thin with progression of the condition. Generally keratoconus is a painless condition although it can cause some ocular irritation in more advanced cases.
The severity of keratoconus varies widely between individuals, some may manage with spectacles alone, others may require special contact lenses and a small minority go on to require surgery. Although keratoconus is considered a progressive condition (one that worsens over time) it is common for keratoconus to eventually stabilise (often around the age of 30).
Keratoconus is considered to be a genetic condition, and it is common to find more than one family member (or relative) with the condition.
Conditions such as allergy (hayfever), eczema and asthma are common in people with keratoconus.
How is keratoconus diagnosed?
Although the understanding of keratoconus is steadily growing among optometrists, unfortunately it is not uncommon for keratoconic patients to be misdiagnosed (particularly in mild cases). Early diagnosis of most ocular conditions (including keratoconus) is important for the best management of the patient.
Experience and technology play an important role in diagnosing early keratoconus. Any person with a family history of keratoconus should undergo testing, as their chance of developing the condition is much higher than average. Children of keratoconus patients especially should be examined regularly.
What is corneal topography?
Corneal topography (also known as corneal mapping) is performed using a computerised instrument that captures an image of the corneal surface and after analysis, displays that information as a kind of "map" of the cornea. This information is presented much like the topographical map of a mountain range, showing the peaks and valleys of the irregular cornea. The sensitivity of these instruments makes them a incredibly valuable tool in the early diagnosis of keratoconus and the ongoing management of the condition.
What are the treatment options for keratoconus?
In general, spectacles do not provide the best level of vision compared to specialised contact lenses as they do not completely neutralise the corneal distortion. However, in early keratoconus spectacles may be a reasonable option. In more more advanced keratoconus spectacles tend to be reserved as a back-up option.
If you have keratoconus, your optometrist can test you eyes for glasses and show you the level of vision they will provide.
Contact lenses are generally considered to be the main-stay of keratoconus management. The main types are soft and RGP (rigid gas permeable) lenses. There are many variations of both soft and RGP lenses, some more suitable for early keratoconus and others for advanced keratoconus.
Due to the complicated nature of the keratoconic eye, it pays to check your optometrist is experienced in fitting contact lenses for keratoconus.
The initial fitting and follow-up process usually takes a number of visits
The fitting and followup process
Generally a new patient will have a general eye examination before the fitting process commences. This is important to establish a number of things, including general health and medications (particularly how they relate to the eyes and/or contact lens wear). Also is helps establish the severity of the keratoconus and whether any other eye conditions are also present. Should the patient suffer from ocular allergy (hayfever in the eyes) this should be treated before contact lens wear is started.
The general examination is usually followed by corneal topography to establish the exact shape of the cornea and severity of the keratoconus.
Should contact lenses be considered to be the best option a fitting appointment is made. Lenses are fitted to the eye and assessed with a microscope and to determine the correct shape. Many parameters have to be considered and this process is more technically demanding ( and often time consuming) compared to fitting contact lenses for non-keratoconic eyes.
Once all the parameters (measurements) of the initial lenses has been calculated the lenses will be ordered from the laboratory. Most (but not all) contact lenses for keratoconus will be custom-made for the individual.
On receiving the lenses, the optometrist will check the initial fit and vision and have a contact lens assistant teach the process of insertion and removal to the patient.
After a period of adapting to the lenses (often about 2-3 weeks), the fit and vision with the lenses is evaluated and alterations made if required.
Regular followup examinations are required on an ongoing basis as the keratoconus often progresses. These reviews will usually take place about every 6 months.
Types of Contact Lenses for Keratoconus Soft Lenses
Soft contact lenses are sometimes a viable option especially for mild keratoconus. As the cornea is irregular (misshapen) in patients with keratoconus soft lenses do not usually provide vision as clear or as stable as with RGP lenses (see below). Many patients with keratoconus will not be suitable for soft lenses as they may not provide adequate vision. Soft lenses come in many different designs and materials and may be disposable or custom made. The major advantage of soft lenses is that they are (generally) easier to fit and patients usually adapt to them quickly.Rigid Gas Permeable (RGP) Lenses
RGP are the mainstay of keratoconus management. As the lenses are rigid they don't conform to the irregular keratoconic cornea, thereby creating an regular front surface for the light entering the eye. This provides (in most cases) a far superior level of vision when compared to soft lenses.
RGP lenses are available in different designs and can vary greatly in size. The decision of what design, size and shape to use is dependant on the degree and type of keratoconus (and whether the patient has had surgery). RGP lenses require a greater level of skill and experience to fit (especially for keratoconus), so it is important your optometrist has expertise in RGP lens fitting.
Although keratoconus patients enjoy the excellent vision provided by RGP lenses, they do take longer for the eye to adapt to wearing them. It is normal to be very aware of the lenses for the first few weeks and it may take several months to be completely adapted to them.Semi-scleral lenses
These are a type of RGP lens designed to fit out onto the sclera (the white of the eye). The diameter of these ranges from about 13 to 16mm. The large diameter of these designs usually provide good comfort and stability as the lens tucks under the eyelids and lens movement is slight. Typically these lenses are reserved for more advanced forms of keratoconus as oxygen and tear exchange is reduced compared to standard (corneal) RGP lenses for keratoconus, and this requires careful monitoring. Combination systems
Combining soft and RGP lenses (know as "piggy-backing") is increasingly used in the management of keratoconus. It is used for 2 main reasons. The first is to improve tolerance (and speed up adaptation) to RGP lenses. In cases where despite the RGP lenses fitting correctly, the patient may still not gain sufficient tolerance to wear the lenses for the required length of time during the day. Refitting with a soft disposable lens underneath usually gives significant improvement in tolerance in these cases. This may be a temporary or permanent solution. The use of piggybacks also can be useful for those working in dusty environments.
It is important to ensure that the system provides adequate oxygen to the eye, this is usually achieved by manufacturing both lenses in materials highly permeable to oxygen (so the eye can "breathe").
Also known as "corneal grafting" this procedure involves replacing your own irregular cornea with a donor cornea. There are several variations, most commonly penetrating keratoplasty (PK) and deep lamellar keratoplasty (DLK).
PK involves removing a full-thickness "button" of cornea about 8mm in diameter. The donor cornea is then sewn into place.
With DLK, the thin back layer of the cornea (called the endothelium) is left in place (so the incision does not quite go through all the layers) and the donor cornea is sewn into place on top of this.
As the donor cornea in foreign to the body, it is possible that the eye may try to reject the donor cornea. While this can usually be managed with medications (typically corticosteriod eye drops), is is probably the most significant reason for graft to "fail".
As DLK leaves the original endothelium intact, there is significantly less chance of rejection when compared to PK. However the visual outcomes (clarity) of PK tend to be better. Generally, which method of keratoplasty is performed is a decision made in conjunction with the ophthalmologist (eye surgeon).
One main reason for considering keratoplasty includes failure to able to maintain a lens on the eye. This is normally due to the keratoconus being so advanced that physically keeping a lens on the eye becomes impossible or risks damage to the eye. The other common reason for surgery is due to corneal scar tissue caused by the keratoconus reducing the vision significantly. Essentially, the cornea "stretchs" and develops scar tissue over the apex (peak) of the cornea. This creates a clouding of vision that contact lenses may not be able to correct effectively.
Keratoplasty is generally considered to be a last resort of patients with keratoconus. It is (almost) certain the a patient will still require either spectacles or contact lenses to correct the vision following keratoplasty.
Collagen Cross Linking (CCL)
CCL is a recently developed procedure designed to halt the progression of keratoconus. This is achieved by increasing the rigidity (stiffness) of the cornea preventing it from continuing to distort. The procedure involves removing the thin surface layers of the cornea (epithelium), saturating the cornea with riboflavin (vitamin B2) dye, then treating the area with UV light. The UV reacts with the riboflavin to increase the bonding between the collagen fibres that make up the cornea. The effect is a greatly increased rigidity and resistance to progression of the keratoconus. It does not cure the keratoconus but prevents it getting worse. Collagen cross linking is an exciting procedure that should reduce the numbers of patients requiring keratoplasty (corneal grafting).
CCL is best performed before the keratoconus gets too advanced, therefore it is recommended all keratoconic patients with children have them tested for keratoconus (with corneal topography) from the age of 8. This will ensure that if keratoconus develops it is diagnosed early.
These are small semi-circular plastic rings that are implanted into the cornea. The idea is to "stretch" the central cornea, causing it to flatten and reduce the visual distortion. The results tend to be variable and although they may improve the vision to some degree in mild cases, they do not usually eliminate the the need for contact lenses. They are seldom of benefit in more advanced cases of keratoconus. However, they can be removed should the need arise.
Can keratoconus cause me to go blind?
It is extremely rare for someone with keratoconus to go blind. Modern management both with contact lenses and/or surgery means the vast majority of keratoconus patients will lead a normal life. However, it is extremely important that the patient plays their part in looking after their eyes. This means keeping contact lenses in good condition, attending regular appointments and following the advice of their eye care professional.
Does keratoconus affect both eyes?
Over 95% of people with keratoconus will have the condition in both eyes. Reasonably often (especially in early keratoconus) only one eye will appear to be affected but corneal topography will confirm the condition in both eyes. For this reason both eyes are always imaged with the corneal topographer at regular intervals.
Do contact lenses hurt?
There are many different types of contact lenses used for keratoconus. Generally speaking RGP (hard) lenses are less comfortable when first fitted but give superior vision to soft lenses. Most keratoconus patients will adapt to their hard lenses, however if reasonable comfort is not achieved then there is several different options to improve comfort. If you tried contact lenses some time ago and didn't succeed, chances are that there are new options that will suit.
Will contact lenses fix (or worsen) my keratoconus?
No. Contact lenses for keratoconus are designed to provide a good standard of vision while worn. They will not reverse the condition.Can I have laser surgery to correct my keratoconus?
As long as the lenses are well fitted and cared for they will not worsen the condition. However, it is extremely important to have regular checks because dirty or ill-fitting lenses do have the potential to cause corneal scarring or infection.
No. Laser refractive surgery (eg: PRK, LASIK etc) reshapes the cornea by removing (ablating) corneal tissue resulting in a thinner cornea. This corneal thinning carries an extremely high risk of causing the keratoconus to rapidly worsen. Keratoconus is a contra-indication to laser refractive surgery.
I have been told I have astigmatism. Does this mean I have keratoconus?
Probably not. Astigmatism is induced when the front of the eye (cornea) is a different curve vertically versus horizontally, somewhat like a rugby ball. Regular astigmatism is normal and can be easily corrected with spectacles or soft contact lenses. Irregular astigmatism is caused by distortion of the cornea from injury, scarring, infection or conditions such as keratoconus or pellucid marginal degeneration. This irregular astigmatism is the main reason spectacles often don't work well for keratoconic patients as the astigmatism changes across the surface of the cornea.
"With-the-rule" astigmatism is when the cornea is flattest in the horizontal direction. "Against-the-rule" astigmatism is when the cornea is flattest vertically.
What is graft failure?
Graft failure (or rejection) is when the donor cornea is rejected by the eye it has been attached to. This can happen at any time but is more common when the graft is new. Symptoms include redness, glare, reduced vision and sometimes ache or pain. Rejection came usually be reversed with prompt intensive steriod therapy (eye drops) but treatment must be intiated with urgency.
What is corneal hydrops?
Corneal hydrops is an acute clouding of the cornea caused by a small break in the back layer of the cornea allowing fluid to enter. The cornea rapidly turns white causing a dramatic drop in vision. This break usually heals up and the fluid eventually gets "pumped" back out, resulting in a clearing of the cornea. However this can take months and often the eye is left with secondary scarring that may require keratoplasty to correct. Hydrops is usually treated with steriod eye drops and sometimes other ocular medications if secondary problems develop.