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PubMed This is a summary of 24 peer-reviewed journal articles Updated
Ophthalmology

Understanding Your Child's Diagnostic Tests

At a Glance

Diagnosing Leber Congenital Amaurosis (LCA) requires functional tests like an ERG, which often shows "nonrecordable" electrical signals in the retina. Doctors also use Handheld OCT to check retinal structure and genetic testing to pinpoint the exact mutated gene causing the vision loss.

Confirming a diagnosis of Leber Congenital Amaurosis (LCA) involves looking at both how the eye looks (structure) and how it works (function). Because infants cannot describe what they see, doctors use specialized technology to measure the electrical signals in the eye and the physical health of the retinal layers.

The Electroretinogram (ERG)

The Electroretinogram (ERG) is often the most important functional test for a child with suspected LCA [1]. Think of it like an EKG for the eye; just as an EKG measures the electrical activity of the heart, an ERG measures the electrical response of the retina (the light-sensitive tissue at the back of the eye) when it is stimulated by light [1][2].

What to Expect During the Test

Performing an ERG on an infant requires patience and specialized tools.

  • Preparation: The eyes are typically dilated with drops. Because the test measures responses to different light levels, your child may spend time in a darkened room first (dark adaptation) [3].
  • Electrodes: Doctors use tiny sensors to pick up electrical signals. In infants, these are often skin electrodes (small sensor strips placed on the skin under the eye) or DTL electrodes (a thin, thread-like fiber that rests on the eye surface), which are much more comfortable than the older contact-lens style electrodes [4][5][6].
  • Environment: To get a clear reading without the child moving, the test may be performed under light sedation or general anesthesia, or sometimes while the infant is naturally sleeping [1][7].

Understanding “Nonrecordable”

If your child’s report says the ERG was severely attenuated or nonrecordable, it means the retina is producing very little to no electrical signal in response to light [8][9]. In LCA, this is a classic finding that indicates the photoreceptors (the cells that catch light) are not functioning correctly from birth [8].

Differentiation: Is it LCA?

Doctors use testing to distinguish LCA from other conditions that look similar in infancy:

  • Cortical Visual Impairment (CVI): Unlike LCA, children with CVI have a normal ERG [10]. Their vision loss is caused by the brain’s inability to process visual information, not a problem with the eyes themselves [10][11].
  • Achromatopsia or CSNB: These are other retinal conditions where children have poor vision from birth. While their symptoms overlap with LCA, genetic testing is the definitive way to tell them apart, as different genes are responsible for each [12][13].

Advanced Monitoring Tools

Beyond the ERG, two other tools help doctors monitor your child’s eye health:

  1. Handheld OCT (HH-OCT): This is a high-resolution scanner that takes cross-sectional pictures of the retina’s layers [14]. Unlike traditional machines, handheld versions allow doctors to scan an infant’s eye while they are lying down or awake [15][16]. Surprisingly, some children with LCA have very healthy-looking retinal structures on OCT, even if their ERG is nonrecordable, which can be a positive sign for future treatments [17][18].
  2. Full-field Stimulus Testing (FST): If a child’s ERG is “nonrecordable,” it doesn’t always mean they have zero vision. FST is a more sensitive test that can measure very low levels of light perception that a standard ERG might miss [19][20]. It is often used to track progress in clinical trials [19].

The Diagnostic Report Checklist

A complete diagnostic report is your child’s medical ID card. It should include:

  • The Gene Name: (e.g., RPE65, CEP290, GUCY2D) [21].
  • The Mutation Type: It should specify if the variants are pathogenic (disease-causing) or variants of uncertain significance (VUS) [22][23].
  • Functional Summary: A clear description of the ERG results and any structural findings from the OCT [24][20].

Common questions in this guide

What does a "nonrecordable" ERG mean for my child?
A nonrecordable or severely attenuated ERG means the light-sensing cells in the retina are producing very little to no electrical signal. In Leber Congenital Amaurosis, this indicates that the photoreceptors are not functioning correctly.
How is an ERG performed on an infant?
Infant ERGs are done using tiny, comfortable sensors like skin or DTL electrodes placed near the eye. To ensure the infant remains still for accurate readings, the test may be done while the child is naturally sleeping, or under light sedation or anesthesia.
How can doctors tell the difference between LCA and CVI?
While both conditions cause poor vision in infancy, children with Cortical Visual Impairment (CVI) have a normal ERG because the issue is with how the brain processes vision. Children with LCA will have an abnormal ERG because the problem is in the retina itself.
What is Handheld OCT used for in diagnosing LCA?
Handheld OCT is a high-resolution scanner that takes pictures of the retina's layers while a child is lying down or awake. It helps doctors see if the physical structure of the retina is healthy, even if the electrical signals measured by an ERG are low.
What information should be in my child's genetic diagnostic report?
A complete genetic report should include the specific gene name, such as RPE65 or CEP290. It should also state whether the genetic variants found are known to cause disease (pathogenic) or are variants of uncertain significance.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Were skin electrodes or corneal electrodes used for my child's ERG, and how does that choice affect the results?
  2. 2.Was the ERG performed under sedation or while my child was awake?
  3. 3.What did the ERG show regarding rod versus cone function, and is it 'nonrecordable' or just 'severely attenuated'?
  4. 4.Can you perform handheld OCT to check if my child's retinal structure is still intact despite the low ERG signals?
  5. 5.How does my child's FST (Full-field Stimulus Testing) result compare to their ERG—is there any light sensitivity that the ERG didn't pick up?
  6. 6.Does the genetic report clearly identify two pathogenic mutations, or are there 'Variants of Uncertain Significance' (VUS) that we need to investigate further?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

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This page explains diagnostic testing for Leber Congenital Amaurosis for educational purposes. Always consult your pediatric ophthalmologist or geneticist for specific interpretation of your child's test results.

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