Keratoconus

What is Keratoconus?

Keratoconus (keh-rah-toe-cone-us) is a weakness in the cornea (the clear dome-shaped window at the front of your eye). The normal curvature of the cornea helps to focus the image onto the light processing layer (retina) at the back of the eye. In keratoconus, your cornea becomes weaker and thinner. As a result of the thinning, the normal round shape of the cornea becomes distorted and a cone-shaped bulge develops due to the pressure inside the eye.

The cone curvature in keratoconus leads to a blurred image on the retina. This type of focusing problem is known as “irregular astigmatism”.

The word keratoconus comes from the Greek words ‘kerato’ for cornea and ‘konus’ meaning cone, describing the common cone shaped feature of the condition.

A little more information about the cornea

A healthy cornea is made up of a number of layers and is very strong, smooth and clear. The middle section of the cornea is called the stroma and consists of many regular shaped bundles of connective tissue (collagen) which are joined firmly together.

Your cornea is transparent and very sensitive with lots of nerve endings. This helps you detect when you have dirt or an eyelash on your surface of your eye. The transparent skin cell layer is the top layer to to cornea and is a protective barrier for your eye which helps prevent against infection and injury.

Your cornea bends and focuses light into your eye, which is then further focused by your eye’s lens onto the retina at the back of the eye. The retina converts the light into electrical signals which are sent to the brain and interpreted as the images that we call sight.

What are the symptoms of Keratoconus?

People who have keratoconus experience distortion of their vision including multiple images, sensitivity to light and ‘streaking’. Keratoconus can also cause your eyes to become more myopic (short sighted) which makes distant objects appear blurred and nearer objects clearer.

Symptoms include finding bright light uncomfortable and difficulty seeing things in bright light. This is because the distorted cornea scatters light more as it enters your eye. Some people see halos around lights especially at night time, making night driving difficult.

The amount of visual distortion varies between eyes as often one eye is usually more cone-shaped than the other.

What causes Keratoconus?

Keratoconus usually develops between the ages of 10 and 25 years and although the exact cause is unknown, there may be a genetic origin. About 15% of patients have a family member with the condition. About 1 in 2000 people have keratoconus but the incidence is higher in South Asian people affecting 1 in 450. We have a high prevalence of keratoconus in New Zealand compared with other countries. Excessive eye rubbing could be a contributing factor and people with allergies or eczema may be prone to developing keratoconus due to a high occurrence of rubbing their eyes, which is thought to make the cornea weaker. Keratoconus can appear or get worse at any age but tends to worsen more quickly the younger a person is. Keratoconus is not curable, but it often stabilises by the early 30s.

How do you diagnose Keratoconus?

Your optician or ophthalmologist will review your medical history and do a thorough eye exam to confirm if you have keratoconus and is also able to monitor the progression.

Tests they will do include:

Refraction - this checks the focus of your eyes and gives you your prescription for the strength of the lenses that you need to correct your vision

Keratometry - measures the curve of your cornea to determine the level of astigmatism. Your ophthalmologist will shine a circle of light onto your cornea and analyse its reflection to determine its basic shape

Computerised corneal mapping or topography - this takes images of your cornea to determine its shape and shows the areas which are most curved

Corneal pachymetry - to measure the corneal thickness

Slit-lamp exam - identifies any abnormalities of diseases of the eye. Your ophthalmologist will shine a high intensity beam of light onto your eye and use a low-powered microscope to look closely at it.

Intraocular pressure.

It is important to attend your regular appointments with your optometrist or ophthalmologist to monitor the progression of your keratoconus so the right treatment can be individualised for you at each stage of the condition.

What are corneal hydrops?

Corneal hydrops is a rare complication of keratoconus where the fluid from inside your eye enters your cornea through breaks in the membrane at the back of the cornea. This fluid causes your cornea to become swollen affecting your vision, making it blurry even with your contact lenses in. Your cornea will appear cloudy or milky and your eye may have pain, light sensitivity, become teary and red. The hydrops take around three months to heal and as your eye is recovering you will be advised not to wear your contact lenses. Your ophthalmologist can give you eye drops to help with the discomfort. As the breaks heal, scar tissue can form causing the cornea to change shape and flatten and you may therefore require a new contact lens prescription. Some people find contact lenses more comfortable and they stay in better after having hydrops. Sometimes the corneal scarring will require a corneal transplant to recover vision.

How do you treat Keratoconus?

Keratoconus cannot be treated with eye drops or other medications.

The first treatment option is to try and correct the vision problems caused by the irregular, cone-shaped cornea with glasses and soft contact lenses. If keratoconus worsens vision may only be able to be corrected by rigid gas permeable (hard) contact lenses. Because keratoconus makes the cornea progressively more thinner this means that your prescription glasses or contact lenses will need changed more frequently. There are many types of contact lenses options available which you can discuss with your optometrist (custom soft contact lenses, gas permeable contact lenses, piggybacking contact lenses, hybrid contact lenses, scleral and semi-scleral lenses).

If your keratoconus is progressing then Corneal Cross-linking is an option to treat the keratoconus and stop further change and progression.

When glasses are no longer correcting the vision or the cone shaped cornea can no longer tolerate the hard contact lenses, keraring corneal implant surgery may be of benefit, or corneal cross linking. Keraring corneal implants help improve vision and are designed to make it more comfortable to wear the rigid gas permeable (hard) contact lenses.

Corneal cross linking is a surgical treatment used to stop the progression of keratoconus.

Patients with advanced keratoconus that don’t respond to keraring corneal implants or corneal cross linking may require a corneal transplant.

Can Laser Eye Surgery treat Keratoconus?

Unfortunately Laser Eye Surgery such as PRK, LASIK, SMILE can make keratoconus worse.  When someone is being assessed for Laser Eye Surgery they always have corneal topography done to exclude any signs of early Keratoconus. Some people with keratoconus can benefit from a Staar ICL to reduce their need for glasses. People over 60 with keratoconus can also develop cataracts which can be treated successfully to improve their vision.

 

For more information about your keratoconus book an assessment at Bowen Eye Clinic on 0800 69 2020 to discuss management and treatment options.