22 Aug RP Diagnosis: Electroretinogram (ERG) and Genetic Testing Explained
Medically reviewed by Dr. Prashant Tyagi (Stem Cell Biotechnology Specialist, 10+ years) and Dr. Pallavee Senior Consultant | Ophthalmologist & Eye Surgeon 22+ Years Experience
A confirmed retinitis pigmentosa (RP) diagnosis typically relies on two key tools working together – electroretinogram (ERG) testing and genetic testing. Patients often understand that these tests are part of the diagnostic process without fully understanding what each one actually reveals. Here’s a clear explanation of both.
What Electroretinogram (ERG) Testing Measures
ERG measures the electrical response of the retina’s photoreceptor cells – rods and cones – to light stimulation, providing an objective measure of how well these cells are actually functioning, beyond what can be assessed through visual examination alone. In RP, ERG typically shows reduced or delayed rod response earlier in the disease course, consistent with the rod-predominant pattern of cell loss characteristic of the condition, with cone response often becoming affected as the disease progresses further.
Why ERG Matters for RP Diagnosis Specifically
ERG is particularly valuable in RP diagnosis because functional changes in rod and cone response can sometimes be detected before significant structural changes are visible on standard eye examination or even on retinal imaging. This makes ERG a meaningful tool for earlier diagnosis, and for objectively tracking disease progression over time through repeated testing, rather than relying solely on a patient’s subjective description of symptoms.
What Genetic Testing Adds
While ERG confirms that rod and cone function is impaired in a pattern consistent with RP, it doesn’t identify the specific underlying genetic cause. Genetic testing analyses a patient’s DNA for mutations in any of the more than 80 genes currently associated with RP, providing definitive confirmation of the specific type of RP involved and clarifying the inheritance pattern – autosomal recessive, autosomal dominant, X-linked, or otherwise.
Why Both Tests Matter Together
ERG and genetic testing serve complementary purposes: ERG confirms functional impairment consistent with RP and helps track progression, while genetic testing confirms the specific molecular cause and carries direct implications for family counselling and, increasingly, eligibility for gene-specific treatment approaches currently in development. Relying on either test alone provides an incomplete picture compared to using both together.
What These Results Mean for Family Members
Because RP is inherited, a confirmed genetic diagnosis has direct implications for other family members – clarifying who may be at risk, informing family planning decisions, and in some cases enabling relatives to pursue their own testing before symptoms even appear. This kind of informed family counselling generally isn’t possible with ERG results alone, since ERG doesn’t reveal inheritance pattern.
Questions Worth Asking Your Doctor
- What did my ERG results specifically show about rod and cone function, and how does that align with a typical RP progression?
- Has genetic testing identified the specific gene involved in my case, and what does that suggest about my type of RP?
- What does my confirmed inheritance pattern mean for my children or siblings?
- How often should ERG testing be repeated to monitor progression going forward?
What This Means in Practice
For most patients receiving an RP diagnosis, both ERG and genetic testing together provide the most complete and clinically useful picture – functional confirmation alongside molecular and inheritance clarity. This combined approach also positions patients to understand whether emerging gene-specific treatments may eventually be relevant to their exact genetic subtype.
Government & Regulatory References
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- National Programme for Control of Blindness and Visual Impairment (NPCBVI) – Ministry of Health and Family Welfare, Government of India – India’s national programme for eye care infrastructure, which sets standards for diagnostic services – including OCT and related retinal and optic nerve imaging – at government eye care facilities across the country.
- All India Institute of Medical Sciences (AIIMS), New Delhi – Department of Ophthalmology (RP Centre) – a leading government referral centre for advanced optic nerve and neuro-ophthalmic diagnostic evaluation, including VEP and imaging-based assessment, relevant to patients seeking a specialist-level diagnostic workup in India
Related Links
Retinitis Pigmentosa Explained: Causes, Genetics & Early Symptoms
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