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Corneal Dystrophies: for patients


Overview

The cornea is the clear tissue at the front of the eye which helps to focus light onto the retina to form an image. The cornea must remain clear and transparent in order to get the clearest vision.

Corneal dystrophies are a group of inherited eye conditions in which abnormal material builds up within the cornea. This can cause the cornea to lose its transparency and become cloudy. Whilst some corneal dystrophies do not cause any symptoms, others can cause symptoms such as pain, grittiness or discomfort, dryness, sensitivity to light and blurry vision.

The age of onset, symptoms experienced, and severity of these symptoms varies depending on the type of corneal dystrophy, though many have similar characteristics. Corneal dystrophies usually affect both eyes, progress slowly over years/decades and tend to run in families. Other organs of the body are usually unaffected. There is no cure for the underlying causes of corneal dystrophies currently, but successful treatments such as corneal transplants can improve symptoms and vision.

The cornea is composed of five different layers. Corneal dystrophies can affect one or more of these layers and have been classified according to which layers that are mainly affected. The most common corneal dystrophy is Fuchs endothelial corneal dystrophy.

The three main layers of the cornea. The thick stromal layer is sandwiched in between the superficial epithelium and the deep endothelial layer.
Different layers of the cornea

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The condition

Symptoms

1) Visual

A variety of symptoms can occur in corneal dystrophy, which include:

  • A gritty or ‘foreign body’ sensation in the eye (feeling like there is something in the eye)
  • A red and painful eye due to recurrent breakdowns of the epithelial layer of the cornea (recurrent corneal erosions)
  • Abnormal sensitivity to light (photophobia)
  • Glare symptoms
  • Blurred vision or reduced sharpness of vision (visual acuity) which may be improved by glasses/contact lens wear
  • Progressive visual decline

As the corneal epithelium (the most superficial layer) is filled with tiny nerve endings that is very sensitive to touch, corneal dystrophies affecting the epithelium tend to cause grittiness, discomfort and sometimes even a really sore eye from recurrent corneal erosions. Corneal dystrophies affecting the deeper layers such as the stroma and endothelium do not usually cause such symptoms.

How is it diagnosed?

Corneal dystrophies are usually diagnosed with an eye examination by an ophthalmologist

During the eye clinic appointment, you may undergo further tests using specialised cameras and microscopes to help better characterise the type of corneal dystrophy and therefore, help the ophthalmologist to provide you with a more accurate diagnosis and prognosis. You may also encounter other healthcare professionals such as an optometrist (previously known as opticians) that will perform tests to see if glasses/contact lenses are needed to help you see better.  

Sometimes, the ophthalmologist may ask to examine first degree relatives as identification of other affected family members can help in diagnosing a particular type of corneal dystrophy and understanding how the condition runs in the family. Genetic testing can also be undertaken to help identify the gene responsible so that families can have a more informed genetic counselling session.

How is it inherited?

Corneal dystrophies are inherited in various ways depending on the condition and the responsible gene.

1) Autosomal dominant (AD) inheritance

Most corneal dystrophy cases are inherited in this manner. Only one copy of the faulty gene (inherited from either parent) is required to cause disease. This means that each new-born of the patient has a 50% chance of inheriting the condition regardless of gender.

The faulty gene copy is present in the father while the mother is not affected. Each newborn of this couple has a 50% chance to be affected by the condition.
Autosomal dominant inheritance

2) Autosomal recessive (AR) inheritance

In this type of inheritance two faulty copies of a gene are required to have the condition. Both parents are usually unaffected carriers (who only carry one faulty copy of the gene) while the patient has two faulty gene copies (one faulty copy inherited from each parent). This means that every child of two unaffected carriers has the following risks regardless of gender:

  • 25% chance of being affected by corneal dystrophy
  • 25% chance of being unaffected
  • 50% chance of being a carrier with no symptoms
If the mother has 1 copy of the faulty gene in her X chromosome (a carrier) while the father is unaffected, there is 50% chance that a daughter is a carrier and a 50% chance that a son is affected by the condition.
Autosomal recessive inheritance

3) X-linked inheritance

In this type of inheritance, the faulty gene is located on the X-chromosome, which is only inherited from mothers in males. Males have only one X-chromosome, whilst females have two. If a male inherits a faulty gene in the X-chromosome from the mother, he will be affected by the condition (as he only has one copy of the X-chromosome containing the gene). As females have a second functioning X-chromosome, they are usually not affected by the condition.

If a mother has 1 copy of the faulty gene in her X chromosome (a carrier) while the father is unaffected, there is 50% chance that a daughter is a carrier and a 50% chance that a son is affected by the condition.
X-linked recessive inheritance

As corneal dystrophies are inherited conditions, families may choose to see a genetic counsellor to obtain more information and advice on inheritance and family planning options.

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Treatment

Is there any treatment?

1) Supportive treatment

In the early stages of corneal dystrophy, patients are usually managed conservatively without surgery. This may involve:

  • Using glasses or contact lenses to improve vision
  • Regular monitoring of vision in children to prevent the development of a “lazy eye” (amblyopia)
  • Lubricating eye drops and specialised contact lenses called bandage contact lens to help with flare-ups of recurrent corneal erosions; Antibiotic eye drops may be prescribed as well during an acute flare-up to prevent infections of the cornea
  • Saline eye drops can help to reduce corneal cloudiness in Fuchs endothelial corneal dystrophies 
  • Monitoring for other eye conditions such as glaucoma in children with posterior polymorphous corneal dystrophy

Some patients may not require any treatment at all if they do not have any symptoms but will be monitored for any disease progression.

2) Surgery

Most patients are relatively comfortable and able to achieve good vision using the above stated measures. However, surgery may be required in the following circumstances:

  • Risk of amblyopia (lazy eye) development in children
  • Significant and permanent visual limitation resulting from the corneal dystrophy
  • Pain from recurrent corneal erosions

The type of surgical procedure depends on the corneal layer involved. These procedures include:

  • Alcohol epitheliectomy with mechanical debridement – scraping off the deposits in the most superficial layer of the cornea (epithelium)
  • Excimer laser superficial phototherapeutic keratectomy (PTK)— a mild laser procedure used to remove deeper deposits up to the stromal layer and thus delay the need for corneal transplantation
  • Cornea transplant

Corneal transplant is a major eye surgery that involves replacing the affected cornea with a healthy cornea from a deceased donor. The donor cornea (graft) can be transplanted in two different ways with comparable visual outcomes:

  • Partial thickness (lamellar keratoplasty) — only the affected layer(s) are replaced; there are multiple types of partial thickness grafts but generally they have less risk of tissue rejection and faster recovery time but are technically more challenging to perform
  • Full thickness (penetrating keratoplasty) — all layers of the cornea are replaced and therefore are suitable for all types of corneal dystrophies; higher risk of rejection and longer recovery time but technically easier to perform than partial thickness grafts

A graft rejection occurs when the immune system in your body recognises the transplanted cornea as foreign and try to mount an inflammatory response to fight it, which could result in failure of the graft. The inflammatory response can normally be controlled with steroid eye drops but sometimes transplant surgery may need to be repeated with a new graft if there are repeated rejection issues with the current graft.

Some corneal dystrophies may recur after successful corneal transplant surgery but the timing to recurrence is highly variable. You should have a thorough discussion with your ophthalmologist about the potential risks and complications associated with each procedure when considering surgery for your condition.

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Current research in corneal dystrophies

1) Gene-based therapy

As scientists start to learn more about the genes responsible for various corneal dystrophies, research into potential therapies that can correct the associated genetic mutation(s) has also accelerated consequently. Several gene-based therapies are currently under investigation such as:

  • Gene editing using CRISPR/Cas9 technology
  • Small molecular therapies (small molecules genetically engineered to correct a disease-causing mutation) for Fuchs endothelial corneal dystrophy

2) Stem cells

The lack of suitable donor corneal grafts with healthy endothelium has made tissue-engineered endothelial grafts an attractive solution. The grafts can be cultured from stem cells, or reprogrammed from fully developed corneal cells. However, the development of a reliable protocol to culture such grafts that are suitable for human transplantation and the search for an optimum technique to deliver the cultured grafts into the human eye remain challenges that need to be overcome before tissue engineering therapy can be implemented.[1,2]

3) Neuroprotection

Neuroprotective agents encompass a broad range of therapies that aim to promote cell survival and preserve function. Toxic free radicals generated from oxygen consumption by corneal cells have been implicated as the underlying disease mechanisms of Fuchs endothelial corneal dystrophy.[3-5] A few medications have been identified as potential treatments for Fuchs endothelial corneal dystrophy but further studies are required to confirm these findings. The potential medications are:

Related links

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Practical advice

Living with corneal dystrophies

The visual function of patients affected by corneal dystrophies is highly variable and most achieve good vision with a combination of supportive measures and/or surgery; some may even not have any symptoms for majority of their lives. For patients with permanent reduced vision, they are still able to lead a relatively independent life through maximising their available vision and having access to social support. Here are some ideas:

  • Attending the low vision clinic which provides access to low vision specialists, Eye Clinic Liaison Officers (ECLOs), visual aids and visual rehabilitation services
  • Getting in touch with the local education authority for access to qualified teachers for children with visual impairment (QTVI) and special educational needs co-ordinator (SENCO)
  • Registering your child as sight impaired (SI) or severely sight impaired (SSI) if eligible for access to social support and financial concessions
  • Getting in touch with national or local charities for advice and peer support

Related links

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Referral to a specialist centre

If you are based in the UK and would like to be seen in the nearest specialist centre for your eye condition, either to receive a more comprehensive genetic management or just to find out more about current research, you can approach your GP to make a referral or alternatively arrange for a private appointment. 

More information can be found in our “How to see a genetic eye specialist?” page.

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Further information and support

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References

  1.  Okumura N, Kinoshita S, Koizumi N. Cell-Based Approach for Treatment of Corneal Endothelial Dysfunction. Cornea. 2014;33:S37-S41. doi:10.1097/ico.0000000000000229
  2.  Chen S, Zhu Q, Sun H, et al. Advances in culture, expansion and mechanistic studies of corneal endothelial cells: a systematic review. Journal of Biomedical Science. 2019/01/04 2019;26(1):2. doi:10.1186/s12929-018-0492-7
  3.  Jurkunas UV, Bitar MS, Funaki T, Azizi B. Evidence of oxidative stress in the pathogenesis of fuchs endothelial corneal dystrophy. Am J Pathol. Nov 2010;177(5):2278-89. doi:10.2353/ajpath.2010.100279
  4.  Engler C, Kelliher C, Spitze AR, Speck CL, Eberhart CG, Jun AS. Unfolded protein response in fuchs endothelial corneal dystrophy: a unifying pathogenic pathway? Am J Ophthalmol. Feb 2010;149(2):194-202.e2. doi:10.1016/j.ajo.2009.09.009
  5.  Borderie VM, Baudrimont M, Vallée A, Ereau TL, Gray F, Laroche L. Corneal endothelial cell apoptosis in patients with Fuchs’ dystrophy. Invest Ophthalmol Vis Sci. Aug 2000;41(9):2501-5

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Updated on January 24, 2021
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