Keratoconus is a non-inflammatory, degenerative eye condition caused by the thinning of the cornea. This results in the front surface of the eye protruding into a 'cone' shape. Patients experience distorted, blurry vision and often require specialised rigid contact lenses to obtain reasonable vision.
Keratoconus is a condition that involves progressive thinning of the cornea (the front surface of the eye), causing the surface to protrude forward - this is often termed the ‘cone.’ With increased severity, the amount of protrusion increases and so too does the irregularity of the otherwise smooth and regular cornea. Due to the progressive nature of keratoconus, early detection is important to ensure the appropriate management is undertaken.
Early in the course of this disorder, resulting visual changes can present like any other form of refractive error including short-sightedness, long-sightedness or astigmatism. Very early keratoconus may be corrected with spectacles or soft contact lenses. As the disease progresses the cornea becomes more distorted, leading to poor vision even with these corrections. Corneal rigid gas-permeable (RGP) lenses or scleral lenses are useful at this stage as the strong polymer the lenses are made from does not drape over the irregular corneal shape but instead holds its form, thus creating a new and regular front surface of the eye. This will provide the best vision for someone with keratoconus. Visit our contact lens pages for more information on RGPs and Scleral lenses.
CAPTION: An well fitted Corneal RGP contact lens on a keratoconic eye. In order to fit the patient's cornea better there is a steeper part of the lens at 6 o'clock shown by the 'MUD' inscription.
In Australia, keratoconus affects about 1 in 2000 people. It generally presents during pre-teenage years and progresses through the second and third decades of life. Most studies indicate no preference to gender. Differences in severity in either eye are commonly found. The condition is more prominent among patients with a personal history of allergy or eye rubbing or a family history of the condition. Often your optometrist will recommend certain anti-allergy eye drops to decrease symptoms of itchiness which cause keratoconics to rub their eyes and worsen their condition.
At Innovative Eye Care we use the latest technologies to diagnose the condition at its earliest stages and to monitor any changes in progression.
Microscopy of the front surface of the eye conveys the shape and thickness of the corneal surface.
CAPTION: Slit Lamp Biomicroscopy of normal cornea and keratoconic cornea
The above images show a normal, regular cornea on the left and a keratoconic cornea on the right. Note the forward protrusion of the cornea in the keratoconic eye, with a notable thinning of the cornea compared to the normal eye.
As well as corneal shape and thickness, there are a number of other findings visible under microscopy. These include the presence of prominent corneal nerves, Fleischer's iron ring and Vogt’s striae (corneal stress lines).
Corneal topography is a non-invasive way to measure the contours and shape of the cornea. It is the 'gold standard' in diagnosing and assessing keratoconus. Topographers work by shining concentric rings of light on the cornea and assessing what is reflected back. If the cornea is even and regular, the rings are reflected back evenly as well.
CAPTION: Corneal Topography of normal cornea
The above images are topographical results of a relatively normal cornea. Note the regular rings on the left image and the fairly concentric and uniform coloured contour maps on the right image. Areas of yellow represent areas that are more curved on the eye. These images portray a regular cornea with no distortions or irregularities.
CAPTION: Corneal topography of keratoconic cornea
In contrast, these images are results from a topography taken of a significantly keratoconic eye. Note the distorted and compressed rings on the image on the left. The coloured contour maps of the same eye show a much darker red area over the centre of the eye, conveying the protrusion or ‘cone’ of the cornea. This is significant to vision quality as the distorted surface is within the pupil zone (the black circle).
The OCT is an invaluable tool that allows practitioners to assess different layers of the eye as high-definition cross-sectional scans. This device was initially used to diagnose and manage macular degeneration and glaucoma at the back of the eye. More recent advancements in technology have enabled us to utilise the precision of these scans for assessment of the front portion of the eye: the cornea and contact lenses fitted on the eye.
CAPTION: OCT of keratoconus with a scleral contact lens above. Normal corneal thickness is 550 microns. This cornea is singificantly thinner at 291 microns.
Due to the highly detailed images taken with an OCT, the different layers of the cornea are visible, as well as their configuration as the cornea protrudes forward (as shown above). As keratoconic eyes exhibit an overall thinning of the cornea at and around the cone, these layers are able to be measured and quantified to better monitor disease progression.
CAPTION: OCT of Keratoconus with a Scleral Contact Lens.
The OCT also helps us assess the relationship between any specialised contact lenses and the eye, to achieve the most ideal, comfortable and safe fitting contact lens. The above example of a custom scleral lens on the eye conveys adequate clearance over the cone and a nice smooth landing of the edge of the lens on the white part of the eye to ensure maximum comfort.
As mentioned, keratoconus generally progresses from the pre-teenage years through the second and third decades of life. Unfortunately, being a multifactorial disease, the onset and progression is extremely variable between different people, and even between different eyes of the same person. Keratoconus is very unpredictable and can progress rapidly over a short period of time, before stabilising for months or years, then progressing again.
In rare situations someone with severe keratoconus can develop corneal hydrops, a condition where the posterior membrane of the cornea ruptures causing extreme corneal swelling, pain and ultimately scarring. Patient's who have corneal hydrops often require a corneal graft due to the residual scarring.
CAPTION: Corneal hydrops in a keratoconic patient of ours. The picture on the right is 6 months after the initial episode showing the residual corneal scar.
If keratoconus is diagnosed early enough, a new surgical technique called collagen cross-linking (CXL) is often recommended. For this procedure, riboflavin (Vitamin B2) is soaked into a keratoconic cornea and activated by UV light. This promotes cross-linking of the collagen fibrils in the cornea, leading to a strengthening of the tissue. Collagen cross-linking will not cure someone of keratoconus and it may not improve the vision, but should stabilise the cornea, decreasing the chance of further thinning and damage. If your cornea has become too thin (~400um) then CXL is too unsafe to be carried out, so early referral is important.
If the cornea becomes too thin or scars excessively over time, not even a perfect fitting contact lens may provide clear enough vision. In these instances a corneal graft may be required. The longer this can be delayed with contact lens wear and careful management the better, as grafts have a risk of rejection, require long courses of steroid drops, and often require spectacles or contact lenses to be used after the surgery to see to the best level.
It is important for keratoconic patients to be assessed and fitted by a keratoconus specialist. Our optometrists Lachlan Scott-Hoy, Karl Evans and Joanna Rohrlach have an interest in speciality contact lens fitting and have had years of experience fitting irregular cornea including keratoconus. Poorly fitting contact lenses have been shown to promote the progression of the disease in some individuals, due to an increase in inflammatory factors released into the tear fluid. Poorly fitting contact lenses can also cause permanent vision loss by scarring the cornea.
CAPTION: An example of a very poorly fitting RGP lens in a patient that was referred to us for management. This patient's lenses caused permanent corneal scarring (bottom right image) and needed a prompt refit into a scleral lens to rehabilitate the cornea.