All you need to know about corneal dystrophies

Medically reviewed by Tina Patel on 09 February 2023.

In this article, we’re covering the following points:

• What are corneal dystrophies?
• What are the symptoms of corneal dystrophies?
• Types of corneal dystrophies
• What causes corneal dystrophies?
• How are corneal dystrophies diagnosed?
• How is this condition treated?

What are corneal dystrophies?

Corneal dystrophies are a group of diseases that affect the cornea. The cornea is the front transparent part of the eye that covers the iris (the coloured part of the eye) and pupil (the opening at the centre of the eye) and allows light to enter the eyes. This condition is genetic and shows slow progression, which can get worse with time. Some might experience vision disruptions such as blurred vision, or vision loss, while others might have no symptoms at all. This condition will usually affect both eyes; however, one eye can be worse than the other.

What are the symptoms of corneal dystrophies?

As mentioned above, not everyone will experience the symptoms and the symptoms will also depend on the type of corneal dystrophy the person is experiencing. Some might go through:

• Blurry vision
• Watery eyes
• Dry eyes
• Photophobia or sensitivity towards light
• Discomfort such as pain in the eye, aching eyes
• Corneal erosions – this is when the outer layer of the cornea, epithelium starts to loosen from the other layers. Some may notice their eyelids can be stuck to the cornea or their eyes are difficult to open on waking, this can cause disruption to the epithelium and the cells can pull away.

Types of corneal dystrophies

To understand the types of corneal dystrophies, first, it is important to understand the purpose and structure of the cornea. The two main functions of the cornea are to protect the eyes from infection/injury and to refract and focus light to reach the back of the eyes.

The cornea is made up of five layers, each layer functions differently to maintain a healthy cornea. Each dystrophy will start by affecting a particular layer of cornea, meaning, different dystrophies will depend on the layer of the cornea being affected.

The five layers of the cornea are (going from the outer part of the cornea to the inner part):

• Epithelium – the outermost layer of the cornea, it is like a barrier, protecting the cornea from foreign bodies, such as grit and infections.
• Bowman’s membrane – helps in maintaining the shape of the cornea.
• Stroma – this is the thickest layer of cornea made from water, collagen fibres and other connective tissues, making the cornea flexible and clear (this layer makes up 90% of the cornea’s thickness).
• Descemet’s membrane – the inner protective layer.
• Endothelium – this is the innermost layer that helps pump excess water out of the cornea.

There are more than 20 types of corneal dystrophies. They are grouped into three categories based on which layer is affected:

Anterior or superficial corneal dystrophies

These dystrophies affect the epithelium and bowman’s membrane (outer two layers of the cornea). Some of the dystrophies that fall under this category include epithelial basement membrane dystrophy, lisch corneal dystrophy etc. If your epithelium is affected, you will feel as if you have something stuck in your eyes, such as an eyelash; your eyes will feel uncomfortable. Many of these dystrophies begin before the age of 20 and progress slowly over time.

Stromal corneal dystrophies

This dystrophy occurs when the stroma (middle layer of the cornea) is affected. This may also progress into other layers. The dystrophies that fall under this category will start when you’re a child or a teenager.

Posterior corneal dystrophies

The innermost parts of the cornea are affected in posterior corneal dystrophies, i.e., Descemet’s membrane and endothelium. The most common posterior corneal dystrophies are Fuchs’ dystrophy. In Fuchs’ dystrophy, water is accumulated in the cornea, this condition is usually hereditary. Most of the dystrophies that fall under this category starts appearing early in life, sometimes at birth.

What causes corneal dystrophies?

Corneal dystrophies are caused due to the build-up of foreign material in one or more corneal layer. These are usually genetically passed, but it is not always the case. There are two ways in which corneal dystrophies can be inherited:

Autosomal dominant inheritance

One parent will have this condition. This means there is a 50% chance that the child will inherit this condition.

Autosomal recessive inheritance

This means that the parents do not have this condition, but they are the ‘carriers’. If two carriers have children, there is a 25% chance that the child will inherit this condition.

How are corneal dystrophies diagnosed?

They are diagnosed during an eye exam. Your optometrist will use a special tool called a slit lamp microscope. This test lets them see the abnormal deposits on the cornea. Please remember that if you have a family history of this condition, be sure to mention it to your optometrist.

How is this condition treated?

If you’re not showing any symptoms of corneal dystrophies, it is essential to go for regular eye tests, to keep a track of your eye health. If you have slight problems with your vison, or you think the symptoms are becoming prominent with time, you might be recommended some eye drops and/or ointments.

Tina Patel, the Contact Lens Optician at Feel Good Contacts states that, “Corneal dystrophies can be picked up during a routine eye test, that’s why it’s important to visit your optician at least every two years or sooner if you suspect something doesn’t feel right or are advised to do so by your optician”.

If your vision is bad or deteriorating, your doctor might suggest a corneal transplant; when eye drops or lenses can no longer help the patient, a corneal transplant is recommended. In this process, the doctor will remove all or a few layers of your cornea (depending on the dystrophy you have) and replace it with healthy tissue from a donor.