Keratoconus (literally meaning "conical cornea") is a thinning of the central zone of the cornea – the clear, front surface of the eye that is usually shaped like a dome. The normal pressure within the eye makes the thinner area of the cornea bulge forward slightly into a cone shape, resulting in visual impairment.
Keratoconus causes distortion that results in the image focusing at multiple points instead of a single point, leading to blurred, flared, or doubled vision. It can also cause sensitivity to light and glare. The condition usually affects both eyes, though it often affects one eye more than the other.
Image Source: Shutterstock
Keratoconus usually becomes apparent between the ages of 10 and 25. It can have a significant impact on a person's education, work, social, and family life if not treated correctly. In most cases, the condition gradually stabilises by the age of 35.
Causes of Keratoconus
Keratoconus is an eye disorder that is probably caused by genetic and environmental factors. It is traditionally thought to occur in about one in 2000 people, however, a 2020 Australian study of young adults found prevalence to be much higher, about 1 in 84 people. The difference in data is most likely due to improved screening, awareness, and understanding of this condition.
Keratoconus affects people world-wide, and the prevalence is different among different ethnic groups. For example, keratoconus is more prevalent among the Māori population within New Zealand, compared to the general population.
It is sometimes associated with atopic conditions such as hay fever, eczema, and asthma. Other genetic diseases associated with keratoconus, include Down's Syndrome, Marfan's Syndrome, and Ehlers-Danlos Syndrome.
In some cases, frequent and vigorous eye rubbing or ‘ knuckling’ can also increase your chance of developing keratoconus.
Symptoms of Keratoconus
The initial symptom of keratoconus is blurred distorted vision, which is caused by mild short-sightedness and irregular astigmatism. These symptoms usually occur in late teens or early adulthood. These issues are triggered by the cornea changing shape as it bulges forward. Other signs include:
- A need for frequent updates in glasses prescriptions
- Increased sensitivity to bright light and glare, which can cause problems with night driving
- Frequent, vigorous ‘knuckling’ eye rubbing
Keratoconus can be difficult to diagnose in the early stages, as the initial symptoms can be associated with other eye conditions. A telltale sign as the disease advances is frequent changes in glasses prescriptions and increasing complaints from a patient about their corrected vision.
Using a retinoscope (a hand-held torch-like instrument), your optometrist may be able to screen for keratoconus. This technique only takes a few seconds. A corneal topographer is the most accurate instrument for detecting early keratoconus. This machine creates a computer-generated colored topographical map of the cornea that highlights the development of a cone. Measurements of corneal thickness are also useful for diagnosis. A corneal ultrasound can accurately measure the corneal thickness and can detect thinning that occurs in keratoconus. Normal corneal thickness is approximately 0.55mm (or about the thickness of a bank card).
Corneal tomography is another method of measuring corneal shape and corneal thickness. This technique measures the front corneal surface and the inside corneal surface and so provides a comprehensive measure of corneal thickness across the whole surface.
All these methods are painless and simple procedures to carry out at the optometrist or ophthalmologist’s office.
Because keratoconus is genetic, it cannot be cured, however at the early stages spectacles and contact lenses can give good vision, allowing a person to live a relatively normal life with the condition. The contact lenses are usually rigid, like a rigid gas permeable lens (RGP), hybrid lens (combination of a soft and hard lens), or a mini-scleral lens. All these special contact lenses provide a new, regular front surface for the eye, eliminating the distortions caused by keratoconus.
Because the cornea continues to change shape, it is important for people with keratoconus to have regular eye examinations to ensure that their contact lenses fit correctly. A poorly-fitting contact lens can cause abrasions and scarring, which could make the condition worse.
Keratoconus is strongly associated with vigorous eye rubbing. Eye rubbing should be avoided as it can cause further weakening to already weak corneas. If you have keratoconus, you may not even be conscious of the habit. The frequent rubbing may be related to allergies, lid hygiene, or dry eye, so talk to your optometrist about ways to control these conditions, such as with anti-allergy eye drops or lid hygiene techniques. Download information flyer on eye rubbing and how to prevent it.
In about 15 per cent of cases, surgery in the form of a corneal graft may be required. In this procedure, the thinned area of the cornea is removed and replaced by normal tissue transplanted from a donor cornea. Corneal grafting is used only when all other methods for correcting vision have failed to provide good vision. Fortunately, the success rate for corneal grafts is extremely high, although most people will still need to wear glasses or contact lenses.
Another available treatment, called collagen cross-linking, is a therapy that uses administration of vitamin B12 and UV light to strengthen the structure of the cornea. Ophthalmologists (eye surgeons) may carry out this procedure to slow the progression of keratoconus. Your optometrist can refer you to an ophthalmologist to discuss this option.
Commonly asked Keratoconus questions
Can keratoconus cause blindness?
No, keratoconus cannot cause blindness. It can lead to partial blindness or significant visual impairment including blurred sight and sensitivity to light and glare, but if caught early, the condition can be managed.
Is there a way to prevent keratoconus?
As keratoconus is genetic, unfortunately most cases are not preventable. You may be able to reduce your chance of getting the condition by protecting your eyes from the sun’s UV rays with sunglasses, not rubbing your eyes and making sure your contact lenses fit properly.
Is keratoconus serious?
If detected early, most patients with keratoconus can manage the condition with glasses or contact lenses, which provide good vision. In the vast majority of cases, patients live a normal life with keratoconus. Some cases are more serious and may require surgery or other more invasive treatments.
What type of contact lenses are recommended for keratoconus?
Rigid gas permeable (RGP) or mini-scleral contact lenses are the most common contact lenses prescribed for keratoconus. These hard contact plastic contact lenses are better at retaining their shape and position in the eye than soft contact lenses. If you have keratoconus, an optometrist will advise you on the best contact lenses for your circumstances.
Where can I go for more advice on keratoconus?
Visit Keratoconus Australia for more information. If you think you might have keratoconus, we recommend making an appointment with an optometrist for a comprehensive eye examination. Comprehensive eye examinations, at regular intervals starting from childhood, ensure that most eye conditions can be identified. Eye examinations can also be an important tool for determining your overall health.
Published date: 10 November 2022
Author: Sophie Koh, National Professional Services Adviser at Optometry Australia
Bio: Sophie Koh is an experienced optometrist who started her career in the Northern Territory. She has broad experience working in public health and corporate settings across metropolitan, rural and outback Australia. She has extensive experience working in ophthalmology teams and training nurses in East Timor, Papua New Guinea and Solomon Islands. Sophie studied her undergraduate degree at the University of Melbourne and was amongst the first cohort of graduates to achieve the ACO Certificate in Ocular Therapeutics. She is currently the National Professional Services Adviser at Optometry Australia. She is passionate about public health and Indigenous eye health. She is devoted to empowering students and colleagues to improve their knowledge and skills so they can play a wider role in improving the health and wellbeing of our underprivileged communities locally and overseas.
Disclaimer: No information provided on the Good vision for life website is intended to constitute or substitute advice from visiting an optometrist. Many factors unknown to us may affect the applicability of any information on this website. You should seek appropriate personalised advice from a qualified optometrist about any eye health and vision conditions.