Keratoconus

Overview
Clinicians
Clinicians

Keratoconus is an inherited eye condition that affects the cornea. It leads to reduced vision even when wearing glasses or contact lenses.

On this page, you can find the following information:

What causes keratoconus?
What are the symptoms of keratoconus?
When to seek urgent medical help
How is keratoconus diagnosed?
How is keratoconus treated?

Key points

Keratoconus is an inherited eye condition that affects the cornea. The cornea is the clear tissue that covers the front of your eye.
The normally round cornea becomes thinned, distorted and irregular. This leads to reduced vision.
Initial symptoms can be slight blurring or distortion of vision even when wearing glasses or contact lenses. Other symptoms include increased sensitivity to glare and light and as it progresses vision may become more distorted.
Treatment depends on the severity of the condition and ranges from glasses or contacts through to surgery.

What causes keratoconus?

The cause is unknown but keratoconus is seen to have a genetic component, which means you inherit it from a parent.

The cornea is the transparent front surface of the eye. In keratoconus, the cornea becomes thinned, distorted and irregular (cone shaped). This abnormal shape prevents the light entering your eye from being focused correctly on the retina and causes distortion of vision.

It also has a link to allergic conditions such as atopic eczema and eye rubbing. The condition usually happens in the late teens to early twenties, however, it can be present at any age. It is a progressive disorder and can happen rapidly or take years to develop. It commonly affects both eyes, although sometimes only one eye is affected.

image of a normal eye and cornea compared to an eye with keratoconus
Image: 123rf

What are the symptoms of keratoconus?

Symptoms include:

nearsightednes
astigmatis
blurred vision - even when wearing glasses or contact lenses
glare at night
eye rubbing
light sensitivity
frequent prescription changes in glasses and contact lenses.

When to seek urgent medical help

See a doctor immediately if you have any of these symptoms or signs:

blurred vision
eye pain when seeing lights
redness of your eyes
nausea or vomiting
pain in your eye.

How is keratoconus diagnosed?

If you are concerned that you might have keratoconus, it is important to see your GP or local optometrist for an eye examination. They will do some initial tests and can help work out what is causing your vision to be blurry.

After these initial tests, you are likely to need more detailed testing by an optometrist and/or an eye surgeon (ophthalmologist). These tests may include the following:

An eye test

You will be asked to read letters from different rows of a chart. This measures how well you see at certain distances.

An examination of the inside of your eye

In this test, drops are put in your eye to make the hole in the centre of your eye (your pupil) wider. This is called dilating your pupils. A special magnifying lens is used to look inside your eye to find out the cause of your blurred vision.

A slit lamp test

In this test, your external eye structures, such as your cornea, eyelids and conjunctiva, are examined using a microscope along with a slit lamp to detect any abnormalities. Before the test, fluorescein drops are put in your eye to make the abnormalities more prominent and obvious. This test checks for eye problems such as keratoconus, injury to the cornea and uveitis.

A corneal topography test

This is a computerised test that creates a map of the curve of your cornea. It is able to detect corneal abnormalities such as swelling or scarring.

Topography of the cornea

A tonometry test

In this test, an instrument is used to measure the pressure inside your eye. This test checks for other eye problems, such as glaucoma.

How is keratoconus treated?

Treatment of keratoconus depends on its severity. Generally, the management and treatment options for keratoconus can be divided into three categories:

Glasses or contact lenses

In mild cases, vision can be corrected using glasses or contact lenses. There are different types of contact lenses that your eye surgeon or ophthalmologist will be able to recommend to you. A government subsidy may be available to help with the costs of contact lens wear.

Intacs

Intacs are small plastic rings that are inserted into your cornea to improve the shape of your cornea and reduce visual distortion. They can be used alone or in conjunction with glasses or contact lenses.

Surgery

In severe cases when vision does not improve with glasses or contact lenses, surgery may be recommended. The surgery for treatment of keratoconus for many years was a corneal transplant surgery. In recent years, a new treatment called corneal collagen cross-linking is now available. This treatment works by stabilising your cornea and preventing progression. Your eye surgeon or ophthalmologist will be able to recommend the best procedure for you.

Learn more

Keratoconus MedlinePlus, US
Keratoconus Auckland Eye, NZ

Credits: Adapted with permission from The Auckland Eye Manual.. Reviewed By: Dr Janine Bycroft Page last updated: 21 Jul 2022

Information for healthcare providers on keratoconus

The content on this page will be of most use to clinicians, such as nurses, doctors, pharmacists, specialists and other healthcare providers.

The following information has been adapted with permission from The Auckland Eye Manual.

General description

This is a relatively common disorder with progressive conical distortion of the cornea due to ectasia (thinning). This results in increasing myopia (short-sightedness) and astigmatism. The aetiology is unclear although there is a tendency for keratoconus to run in families, and a definite link to eye rubbing has been established. It is believed to be more common in atopic patients. Presentation is usually in teens or early adulthood, during which time the condition may progress. Most cases are stable and non-progressive by the time the patients are in their mid-30s, although there are exceptions to this rule. The condition is usually bilateral but may be markedly asymmetric.

Symptoms

Increasing blurring of visual acuity, often starting in teenage years. This becomes increasingly hard to correct with glasses.
Severe cases may develop hydrops where Descemet’s membrane splits and the cornea becomes very oedematous.
This causes a rapid profound drop in vision, a visibly cloudy cornea and variable discomfort.

Signs

Significant ectasia and cone shape may be visible to the naked eye.
Central (or “apical”) corneal scarring may be visible.
Munson’s sign can be present in moderate keratoconus. This is where, on downward gaze, the lower lid contour is distorted from its normal regular curved shape into a triangular shape.
“Oil droplet” shadow in the red reflex on ophthalmolscopy.
“Scissoring” of the reflex in retinoscopy may be seen – this is a test done to check a patient’s refractive error, usually only by optometrists or ophthalmologists.

Slit lamp signs

• Thinning and cone shape of cornea may be visible in moderate keratoconus.
• Central (or “apical”) corneal scarring may be visible.
• Vogt’s striae – vertical lines or wrinkles in the posterior corneal stroma, which disappear when pressing on the eyeball.

Ultimately the diagnosis (especially in early or mild cases) is made by corneal topography machines such as the Orbscan.

Management

Mild keratoconus with good unaided vision:
• Monitoring by ophthalmologist or optometrist.

Mild to moderate keratoconus with reduced unaided vision:
• Glasses help some cases, but most patients need contact lenses. These may be soft “toric” contact lenses (CLs) that correct astigmatism, but more usually patients require hard contact lenses (or RGPs – rigid gas permeable lenses). Sometimes hard and soft lenses may be worn simultaneously (piggyback lenses) and sometimes special lenses such as semiscleral lenses are required.

Mild to moderate keratoconus in patients who are contact lens intolerant:
• Intrastromal corneal rings (plastic semicircle segments inserted into the tissue of the cornea) may be used to improve the shape of the cornea, to improve contact lens tolerance, or to make glasses an alternative option to contact lenses. These include Intacs and Kerarings. Moderate to severe keratoconus in patients in whom contact lenses don’t improve vision, or who are CLs intolerant:
• Corneal transplantation, either full thickness, or partial thickness (lamellar, or deep anterior
lamellar keratoplasty – DALK).

A new treatment called corneal collagen cross-linking is now available. This treatment involves the creation of cross-links between individual corneal fibres in order to stabilise the condition and prevent progression. It is therefore advisable to regularly monitor patients with topography up to age of around 30, and if progression is noted, treatment is advisable. This monitoring can be done by either the ophthalmologist or optometrist.

Referral guidelines

All newly diagnosed keratoconic patients should be referred to an ophthalmologist non-urgently for counselling and assessment of the need for collagen cross-linking.
Patients suffering acute loss of vision or a painful red eye (especially if a contact lens wearer) should be referred urgently within 24 hours.
All patients with an existing corneal transplant who develop any new symptoms of reduced vision, redness or discomfort should be referred urgently within 24 hours to exclude graft rejection.

Regional HealthPathways NZ

Access to the following regional pathways is localised for each region and access is limited to health providers. If you do not know the login details, contact your DHB or PHO for more information: