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Anterior segment dysgenesis (ASD): for patients

Overview

The anterior segment describes the structures in the front portion of the eye, which encompasses the sclera, cornea, iris, trabecular meshwork and the lens. Each component of the anterior segment has an important role, and therefore malformation (dysgenesis) of any component can potentially affect the normal function of the eye, and therefore impact on vision.

This is a three dimensional illustration of the eye. The structures are listed from front to back. The anterior segment, highlighted in a blue box consists of the sclera, cornea, pupil, iris and lens. The posterior segment, highlighted by a green box consists of the retina, macula, optic disc and the optic nerve.
The anterior and posterior segments of the eye

ASD is an umbrella term that describes eye conditions that are caused by malformation of any of the above structures, which are mostly due to changes (mutations) in any one of the number of genes involved in the normal development of the anterior segment. Patients may only have one of the structures affected, or more commonly a number of the structures are affected. Sometimes, it can also be associated with other developmental eye conditions such as microphthalmia. As some of the genes involved in eye development also play a part in the development of other organs, some patients with ASD may also have symptoms affecting other parts of the body (systemic involvement).  

Although ASD is a fairly general term, some clinical conditions that are classified under ASD are well described, these include:

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The condition

Symptoms

A variety of symptoms can occur in ASD depending on the structures affected. Broadly speaking these may include:

  • Blurred vision
  • Gradual loss of vision
  • Glare
  • Painful eyes
  • Watery eyes, grittiness, discomfort

The severity of ASD differs significantly among patients. Therefore, some patients may only have very mild symptoms, or not symptoms at all while others can be greatly affected. Importantly, patients affected by certain types of ASD are at increased risk of developing glaucoma, which can cause significant visual disability (due to damage to the optic nerve) if not detected and treated early.

How is it diagnosed?

ASD is usually diagnosed by an ophthalmologist. However, some patients may be found to have noticeable anterior segment malformations at birth, which is identified by the paediatrician, and may warrant further investigations as some ASD conditions are associated with conditions that affect other parts of the body or linked to specific syndromes.

Findings which may be picked up at birth includes abnormal corneal deposits, a hazy cornea, enlarged eyeball (also known as buphthalmos—usually associated with primary congenital glaucoma, nystagmus (involuntary movement of the eyes), missing iris (usually associated with aniridia), or that the pupil may appear white on photographs/when light is shone in the eye instead of red (may be associated with congenital cataracts). 

The right eye of an infant is enlarged due to primary congenital glaucoma
A child affected by primary congenital glaucoma presenting with buphthalmos

Credit: Prof Sir PT Khaw, consultant ophthalmologist, Moorfields Eye Hospital, London
The pupil appears white due to an opaque lens.
A case of congenital cataract

Credit: Prof Chris Lloyd, consultant paediatric ophthalmologist, Great Ormond Street Hospital for Children (GOSH), London

During the eye clinic appointment, you may undergo further tests and investigations which will help the ophthalmologist to obtain a more accurate diagnosis. 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 also ask to examine first degree relatives as identification of other affected family members can help in diagnosing a particular type of ASD and understanding how the condition runs in the family.

Genetic testing can be undertaken to help identify the gene responsible so that the clinical team can refer you to other specialists (e.g if the particular gene identified is associated with conditions affecting other parts of the body), and families can have a better-informed genetic counselling session and more accurate advice on prognosis. It is important to note that the gene responsible may not always be identifiable in patients with ASD despite using modern testing techniques.[1,2]

How is it inherited?

ASD can be inherited in a variety of manner depending on the gene responsible (causative gene). These include autosomal dominant, autosomal recessive or X-linked patterns.  In some cases, the mutation in the causative gene may arise sporadically (“by chance”), meaning the affected individual is the first in the family to have that particular mutation. The mutation can then be subsequently passed on to future generations in any of the above manner, depending on the gene involved.

As ASD is an inherited condition, 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?

Given the significant variability in clinical severity and therefore symptoms, treatment can also be highly variable. Although there is no treatment at present that can correct the genetic changes causing ASD, a number of measures can be taken to preserve, or sometimes even improve vision. These can range from supportive treatment such as prescribing glasses or treating a “lazy” eye by patching the better seeing eye, to eye drops and surgery. Sometimes, a combination of all three may be required. It is therefore difficult for us to state a particular treatment for ASD in this article as it is such a broad term. Please visit the respective condition pages detailed in the “Overview” section to find out more.

It is important to note that some ASD conditions are associated with a higher risk of glaucoma development. Hence, regular monitoring (either by an ophthalmologist or an optometrist) may be required, and treatment commenced once it is detected. Monitoring is usually lifelong. Glaucoma can be treated by either eye drops, surgery or a combination of both. The treatment options depend on the type of glaucoma and the severity.

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Current research in ASD

Human eye development during pregnancy is a complex process. We have not yet identified all the genes involved in this process and their role in various conditions. Research currently focuses on identifying the remaining genes and understanding how mutations in these genes result in ASD and other birth anomalies of the eye.

Once the full range of genes is known, researchers can then study each gene closely to identify potential targets for intervention and develop new treatments. The genes involved can be investigated using animal models to assess their role in eye development.[3] Furthermore, advances in glaucoma therapies can also improve the visual prognosis of ASD patients affected by glaucoma.

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Practical advice

Living with ASD

The visual function of patients affected by ASDs is highly variable depending on the condition. Some patients may have no symptoms for majority of their lives, whilst others may have poor vision from birth.

For patients with visual impairment, they are still able to lead an independent life through maximising and preserving their available vision, and having access to social support. Here are some ideas:

  • Regular monitoring with an ophthalmologist or an optometrist if the ASD condition is associated with glaucoma development
  • Attending the low vision clinic which provides access to low vision specialists, Eye Clinic Liaison Officers (ECLOs), visual aids and visual rehabilitation services
  • Utilising assistive technologies  to improve quality of life and aid independence
  • 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

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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.  Patel A, Hayward JD, Tailor V, et al. The Oculome Panel Test: Next-Generation Sequencing to Diagnose a Diverse Range of Genetic Developmental Eye Disorders. Ophthalmology. Jun 2019;126(6):888-907
  2.  Jackson D, Malka S, Harding P, Palma J, Dunbar H, Moosajee M. Molecular diagnostic challenges for non-retinal developmental eye disorders in the United Kingdom. Am J Med Genet C Semin Med Genet. Sep 2020;184(3):578-589
  3.  Hjalt TA, Semina EV. Current molecular understanding of Axenfeld-Rieger syndrome. Expert Rev Mol Med. Nov 8 2005;7(25):1-17

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Updated on November 30, 2020
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