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Diagnosing IRD

Retinal dystrophies can be categorised in several ways including if they are syndromic (those affecting other organ systems, e.g. Usher syndrome), or non-syndromic (those where the symptoms are solely vision-related) and by the subtype of cell that is predominantly affected.1,2

In conditions where rod cells are more severely affected, night time or low-light and peripheral vision will be affected before degeneration of the central macula and colour vision. In those where cone cells are primarily affected, the primary signs may be photophobia, central visual acuity and reduced colour and contrast sensitivity before further visual impairment becomes apparent.1

Flow chart

This video features a patient and her family discovering the symptoms and diagnosis of IRD. The family shares reasons for pursuing a genetic test and details their life after the diagnosis.

Signs and symptoms

Because of the number of diseases that are included in the term inherited retinal dystrophy, there are a wide range of different signs and symptoms that include loss of night vision, visual field, colour vision, and central acuity.1 Initial symptoms that may indicate a likelihood of an IRD include:

image of a smiling man, holding and looking down at a laughing baby

In babies and young children

  • Nystagmus (uncontrolled eye movements)3
  • Failure to fix and follow
  • Photophobia (sensitivity to light)4
  • Undetectable ERG recording3
  • Reduced visual field and/or reduced light sensitivity1
  • Problems with hearing and balance (associated with Usher syndrome)1

 

Image of a woman wearing headphones and speaking, gesticulating with her hands and holding a pencil.

In older children, teenagers and adults

  • Loss of visual acuity1,2
  • Nyctalopia (loss of night vision)1,2
  • Problems seeing in dim or low light1,2
  • Slow eye response when switching from bright to dim light

 

This video gives an idea of what it can be like to live with an IRD, to care for someone who has it and also highlights some of the symptoms

Clinical testing

Beyond standard visual field testing and retinal imaging, there are a number of testing options available to help confirm diagnosis of a specific IRD.1 Some of the more commonly used examples are outlined below.

Electroretinogram

Using a skin electrode in young children or contact lens electrodes with older children and adults.
Flash, pattern, and flicker light stimuli are used to detect photoreceptor response and function.1

 

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Fundus autofluorescence

Lipofuscin, a fluorophore, is stored in the retinal pigment epithelium and can act as a surrogate marker of photoreceptor activity that can be picked up by fundus autofluorescence. Different patterns of fluorescence can indicate particular diagnoses.1

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Optical coherence tomography (OCT)

OCT uses light reflection to visualise the structure of different layers of the retina in fine detail. It can be used to measure retinal thickening and to determine the level of progression of retinal dystrophies.1

 

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Genetic testing

Previously, diagnosis of IRD has relied heavily on clinical testing. This is partly due to the accessibility of genetic testing, but also the availability of clinical trials and approved therapies requiring a genetic diagnosis. With the development of new screening methods and with new research into treatments for specific gene mutations it is now more important for patients to receive a genetic diagnosis.

Deciding if your patient meets the criteria for genetic testing
Genetic testing is appropriate for most patients with presumed genetically caused retinal degeneration. Consider testing if:

Patient meets criteria for suspected IRD5
Patient displays symptoms including :

Vision icons

Has a diagnosis of an inherited retinal dystrophy, or a family history of IRD5

Once your patient is suspected of having an IRD, consider ordering a genetic test.

Genetic testing provides more information about your patient's IRD and is the only way of confirming which genes are affected. It refines the diagnosis and prognosis, allows for better disease management and can identify or confirm eligibility for natural history studies of clinical trials.5 Patients may benefit from access to a genetic counsellor when receiving a genetic diagnosis. The process for ordering a genetic test can differ from laboratory to laboratory, so please check with the relevant centre in your country (see below).

Where to refer a patient

You can refer your patient to centres for genetic testing within your country.

References
1. Henderson R. Paed Child Care 2020; 30: 19–27.

2. Fahim AT, et al. Nonyndromic Retinitis Pigmentosa Overview 2000 Aug 4 [Updated 2017 Jan 19] In: Adam MP, et al., editors.
GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993–2020.

3. Kumaran N, et al. Br J Ophthalmol 2017; 101: 1147–1154.

4. Gill JS, et al. Br J Ophthalmol 2019; 103: 711–720.

5. American Academy of Ophthalmology®, IRD Clinical Statement 2016.
Available at:https://www.aao.org/clinical-statement/recommendations-on-clinical-assessment-of-patients Accessed July 2020.

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