Keratoconus

The word Keratoconus (KC) comes from the Greek words 'kerato' meaning horn or cornea and 'konos' meaning cone and thus the word literally means a cornea (front surface of the eye) with a cone shape. Keratoconus is a degenerative, non-inflammatory disorder of the eye in which structural changes within the cornea causes it to thin and change to a more conical shape.

The symptoms of Keratoconus usually include severe distortion of vision, with multiple images, ghosting, halos, streaking and sensitivity to light. Keratoconus is the most common dystrophy of the cornea, affecting around one person in a thousand, and it seems to occur in populations throughout the world, although some ethnic groups experience a greater prevalence than others.

It occurs usually in both eyes although the severity can differ in each eye. The onset of keratoconus is usually at puberty (around age 16) and it tends to be progressive till the third and forth decade of life. It usually arrest at this stage, but may adopt a variable pattern of progression.

How did you get it?

The exact etiology of keratoconus is still unknown as there are many links to the condition. The role of heredity has been reported in 10% of cases. Associations with systemic disorders include

• Down syndrome
• Turner syndrome
• Ehlers-Danlos syndrome
• Marfan syndrome and other connective tissue disorders
• Atopic disease (hay fever, asthma, eczema and food allergies).

Ocular associations include:

• Vernal disease
• Blue sclera
• Retinitis pigmentosa
• Leber’s congenital amaurosis
• Retinopathy of prematurity (associated with premature birth)

Associations with hormone changes and over wear of non Gas Permeable PMMA contact lenses have also been made.

There is also a strong association (over 60%) between Keratoconus and rubbing the eyes. Keratoconic patients usually present with allergic inflammation in their eyes making the eyes feel chronically itchy. Vigorous rubbing of the eyes causes a mild pain sensation which distracts the mind from the itchiness and so appears to relieve the itchy sensation. Unfortunately the pain sensation causes the brain to initiate an inflammatory response in the eye which could lead to further thinning of the cornea.

Why can’t I see clearly with Keratoconus?

The eye has a normal constant internal pressure, which causes the cornea to protrude outwards, like a balloon affect, as the thinned cornea cannot keep the corneal structure intact.  This bulging process is know as corneal ectasia.

The irregular corneal shape causes incoming light rays to be scattered and the visual image can't focus sharp and crisply on the back of the eye, which contributes to a decrease in vision.

What does the shape of a Keratoconus cornea look like?

Using corneal topography it is possible to map the shape of a cornea and construct a 3D model of what a keratoconus cornea looks like.

The 3D topography map above shows a cornea with mild or stage 1 keratoconus and the map below shows a cornea with more severe or stage 3 keratoconus.  Looking at the contour of the map below it becomes clear where the name Keratoconus (coned shaped cornea) comes from.

What symptoms can I expect?

• Gradually decreasing vision
• Unable to attain good vision despite multiple changes in glasses or soft contact lenses
• Sensitivity to light (photophobia)
• Double vision in one or both eyes (monocular and binocular diplopia)
• Halo’s around lights
• Pain and decreased vision due to hydrops in advanced disease.
   

What treatment and management options are available?

This is a brief outline of the types of management options available for keratoconus.

Glasses

In the early stages vision can be corrected with glasses or regular soft contact lenses but as the Keratoconus progresses they are not able to correct the distortion caused by the irregular corneal surface and more complex contact lens designs are required.

Contact Lenses

There is no one “best” contact lens for keratoconus. The “best lens” is the one that fits your eye, corrects your vision and is comfortable to wear. Contact lens fitting for keratoconus is part science and part art. A great deal of patience and input is required both on the part of the fitter and the patient.

Since each lens design has its own unique characteristics, we need to carefully evaluate the needs of the individual situation to find the contact lens that offers the best combination of visual acuity, comfort and corneal health.

Soft Contact Lenses

The role of soft contact lenses in keratoconus is limited to the early stages of the disease. This is due to the low stiffness or rigidity factor (modulus value) of the materials the soft contact lenses are manufactured from. The low modulus of the soft contact lenses allows the lens to drape over the irregular corneal surface and in the process loose the natural shape of the contact lens.

The loss of shape of the refractive front surface of the soft contact lens makes the lens ineffective to focus the light rays correctly to the back of the eye. The result is still irregular, distortion filled images seen by the eye.

There are however some specially designed thicker soft contact lenses available which are useful for mild to moderate keratoconus fitting. The thicker soft contact lens retains more of its shape when fitted on the irregular Keratoconic cornea and thus provides sharper vision compared to a standard soft contact lens.

The negative of this lens however is that the oxygen supply to the cornea is compromised due to all the resistance the thick material offers to gas flow through the lens. Corneas fitted with these thick soft contact lenses are more prone to complications associated with oxygen deprivation and carbon dioxide build-up, like new blood vessels growing into the cornea (neo-vascularisation) and corneal edema. Patients fitted with these lenses should take care and have follow up visits done at least once a year to ensure optimal corneal health.

RGP Contact Lenses

Rigid Gas Permeable (RGP or GP) contact lenses are the primary option for correcting Keratoconus. The word 'Rigid' defines the type of lens indicating the high modulus value of the lens. The words ‘Gas Permeable' describes the lens material character of allowing high amounts of oxygen and carbon dioxide to move through the lens. The higher the gas permeability of the lens material, the better the cornea can 'breath' through the lens.

There are also many different Rigid Gas Permeable contact lens designs on the market. The RGP lenses have a rigid shape that is not affected by the irregular shape of the keratoconic cornea. When the RGP contact lens is correctly fitted on the Keratoconic cornea, the irregular space between the lens and the cornea is filled with the tear fluid.  This creates a smooth optical surface for the eye, thus preventing incoming light rays to be scattered, and allowing the visual image to be focused more sharp and crisp on the back of the eye.

Rigid Gas Permeable contact lenses also creates a supporting surface for the cornea, unlike soft contact lenses or glasses, that help to stabilise the cones and normally helps to slow down the progression of the cone. 

Piggy Back Method

The Piggy Back system is usually used when too much discomfort is experienced wearing the RGP lens on its own. The system consists of two pairs of lenses being worn simultaneously.

First a high gas permeable soft silicone lens is placed on the eye. The Keratonic RGP lens is then placed on top of the soft silicone contact lens. The soft contact lens acts as a cushion between the cornea and the RGP lens and ensures maximum comfort for the patient. The RGP contact lens in turn ensures maximum clear vision.

When fitted accurately and using the correct high gas permeable materials in both the soft and rigid contact lenses, the system provides a very effective, safe and healthy alternative to patients who experience discomfort wearing RGP lenses alone.

Hybrid Lenses

This is a special combination lens that has a rigid lens center surrounded by a soft lens skirt. It is normally a comfortable lens to wear but can seal of on the eye after a few hours of wear leading to complications if left unchecked.

Recently this lens type has become available in high gas permeable materials and is made by a USA based company called SynergEyes. The increased oxygen flow through the lens has improved the complication rate seen if the lens seals off on the cornea. The lens is a good alternative to conventional RGP fitting techniques, but being an imported lens, comes with a heftier price tag.

Scleral and Semi-scleral Contact Lenses

Scleral lenses look like RGP contact lenses but have a larger overall diameter. The focus of these lenses is to vault the central keratoconic cornea and allow the lens to rest on the white part of the eye, called the sclera.

The size can be a scary prospect for beginner wearers and takes some time to get use to, especially when learning to insert and remove the lens for the first time. Scleral lenses do offer some advantages. Because of their size, they tend not to fall out and dust or dirt particles cannot get in as easily.

Surgical Mangement

Keratoplasty

Advanced levels of keratoconus are normally associated with corneal hydrops. Hydrops is when the cornea gets so thin and the curvature of the cornea gets so steep that it causes a break in Decement’s membrane (a membrane between the middle and inner layer of the cornea). This creates edema (fluid swelling) in the inner layers of the cornea and the formation of scar tissue. The break can be associated with pain and the scarring acutely decreases vision.

In many of these cases a cornea transplant (Penetrating Keratoplasty) will be needed. The outcome of this surgery is normally very good and with modern medication less and less corneal rejections are seen.

The photo above shows a keratoconus cornea which required a Penetrating Keratoplasty or corneal graft. The white ring is scar tissue where the old cornea was cut and removed and the new donor cornea was grafted on.  The grafted cornea is kept in place with stitches (seen on the photo as the radial black lines) for almost a year before they are removed.

The picture above shows a 3D topography view of a grafted cornea.  The bow tie like shape seen in the centre of the map is the corneal astigmatism typically seen with corneal grafts.

It is important to note then that after the surgery most of the corneas are clear but still irregular in shape, especially after the stitches are removed. Due to the irregular corneal shape seen with corneal grafts, most patients will still require RGP contact lenses after the Penetrating Keratoplasty surgery to maintain clear and stable sight.

Corneal Collagen Crosslinking

Corneal Collagen Crosslinking or CxL for short, is a relatively new surgical procedure. The top corneal tissue, the epithelium, is scraped away and then bathed with custom made Riboflavin eye drops. The Riboflavin is then activated by exposing the eye to a special UV light. This procedure increases the crosslinking bonds between the collagen fibres of the cornea making the cornea stiffer and less likely to form the irregular keratoconic bulge (ectasia).

Corneal collagen crosslinking does not correct or cure the keratoconus. The primary use of the procedure is only to stabilises the disease and prevent it from progressing further. For the moment it appears if the procedure is only effective for about 5 years, where after the procedure needs to be repeated again. Not all patients are candidates for corneal collagen crosslinking as the thinnest portion of the cornea cannot be less than 400 micro millimetres.

Medication

Currently no know medication is available to cure Keratoconus. However secondary complications can occur with Keratoconus and for these certain medications can be beneficial.

Your Optometrist or Eye Care Provider will provide you with the correct medication depending on the signs and symptoms found. Most of the medications given will be in the form of topical eye drops and can include:

• Wetting or lubrication drops
• Anti histamine drops
• Mast cell stabiliser drops
• Corticosteroid or anti-inflammatory drops
• Anti-bacterial drops

Most of the common problems associated with Keratoconus and contact lens wear is due to chronic dryness and allergic conditions on the eye surface. For this special attention is also given to diet and dry eye supplements like Omega 3 oils (Fish and flaxseed oils), Evening primrose oil and Vit A & C.

What is my prognosis?

The prognosis with Rigid Gas Permeable contact lenses is generally good, with most patients able to attain good vision and no restriction in their life styles.

When too much scarring or thinning occurs in the cornea, a corneal transplant is indicated. The success rate of corneal transplantation (Penetrating Keratoplasty) in Keratoconus is generally high. Again good vision is normally achieved after the transplant with the use of RGP lenses.

How long will the fit take?

The duration of the contact lens fitting can vary and will typically involve multiple visits to the practice. It is also necessary to return to the practice on regular intervals after completion of the fit. The frequency of the follow up visits is case depended and will be discussed with you.

How much will it cost?

The costs consist out of the initial eye examination consultation fee, topography scanning, professional fit fees, instructional fee and the cost of the lenses.

Every Keratoconic contact lens fit is unique. With the first eye examination we will be able to fully access the Keratoconus and then provide you with a tailor made management plan and an accurate quote for all the services you will require.

Patient compliancy

Keratoconus with most people is a progressive disorder. A multi disciplinary relationship between optometrist and ophthalmologist and good compliance from the patient will result in optimum results.

Rigid contact lenses are custom designed to fit the cornea at the given stage and minor changes in corneal curvature can cause the lenses not to fit properly. This can lead to abrasions on the cornea creating an ideal condition for bacteria to cause infection and possible corneal scarring that can lead to a complete loss of vision in the affected eye.

It is therefore of high importance that Keratoconic patients return for regular visits (normally once a year) for their condition to be monitored.

I have Keratoconus, can you help me?

Yes. We have extensive experience in the management and fitting of Keratoconus. Charl has also lectured on the subject of RGP fitting and Keratoconus on numerous National and International congresses.

We look forward to working with you as your family eye care practice. Please contact us whenever you'd like to talk about anything you think may be affecting your eye’s health. It's our hope that we can have a relationship where the lines of communication are open and communication goes both ways. Let's work together to help you live the satisfying life that you deserve.

Written by :

Charl Laas