Photo Credit: Ivan Balvan

Electrophysiology tests in inherited retinal dystrophies can inform diagnosis and prognosis and guide patient visits.

“The genetic and clinical heterogeneity of inherited retinal dystrophies (IRDs) can make diagnosis and prognosis challenging, requiring full ophthalmologic evaluation, genetic testing, and electrophysiological testing,” Minzhong Yu, PhD, MMed, and colleagues wrote in a study published in the Journal of Clinical Medicine. “Advances in imaging modalities such as optical coherence tomography (OCT) and fundus autofluorescence (FAF) have detected subtle changes on the fundus exams, allowing for characterizations of IRDs.”

Electrophysiological tests can also help. “They can provide valuable diagnostic information about the functional change in different levels of the retina and visual pathway, which provides unique information in addition to the morphological characteristics tested,” Dr. Yu says.

Electrophysiological tests include multifocal electroretinogram (mfERG), full-field ERG (ffERG), electrooculogram (EOG), pattern electroretinogram (PERG), and visual evoked potential (VEP), according to the study’s results. Dr. Yu and colleagues examined how electrophysiology tests could be clinically applied. They assessed the following IRDs:

• Retinitis pigmentosa (RP)
• Cone dystrophy
• Cone dystrophy with supernormal rod response (CDSRR)
• Enhanced S-cone syndrome
• Bradyopsia
• Bietti crystalline dystrophy (BCD)
• Late-onset retinal degeneration (L-ORD)
• Fundus albipunctatus (FA)
• Retinitis punctata albescens (RPA)

Results Beneficial for Determining Diagnosis & Prognosis

The study confirms that electrophysiological testing is a valuable tool for accurately diagnosing and assessing prognosis in inherited retinal dystrophies, according to Dr. Yu and colleagues (Table).

In RP, which is the most common IRD and a major cause of visual disability, ffERG can identify early photoreceptor degeneration, even before patients detect symptoms, the study authors noted. Further, mfERG and PERG objectively evaluate residual cone function, which can be useful in determining prognosis because it impacts progressive blindness and decreased vision-related QOL.

In cone dystrophies, ffERG can be especially useful in the early stages when patients do not experience symptoms and have a normal fundus exam. For patients with CDSRR, electrophysiology testing is the primary tool for diagnosing the condition because of its pathognomonic and characteristic findings. “To further work up this suspected diagnosis, genetic testing is necessary to confirm the mutations in either the KCNV2 or PDE6H genes,” Dr. Yu and colleagues wrote.

Electrophysiological testing is also valuable in diagnosing bradyopsia, as it can identify characteristic ERG findings. For patients with BCD and L-ORD, electrophysiological testing may not be as critical for diagnosis, but it can be useful in monitoring progression.

Finally, electrophysiology testing has applications in both FA and RPA. In FA, this testing—coupled with genetic testing—may be the most reliable tool for diagnosing the condition, according to Dr. Yu and colleagues. For patients with RPA, electrophysiology testing can help diagnose and distinguish the disease from FA.

Applicability of Electrophysiology Tests in Clinic Visits

According to Dr. Yu, electrophysiology tests can be useful for physicians as they help patients and caregivers adapt to years or a lifetime of vision loss or blindness.

“Electrophysiology in non-macular IRDs may have implications for patient management and counseling,” he notes. “It could help clinicians communicate prognosis, potential visual impairments, and the expected progression of the disease to patients and their families.”

Further, Dr. Yu says that knowledge about the electrophysiological characteristics of non-macular IRDs may influence treatment decisions.

In the future, electrophysiology may help identify new treatments for IRDs.

“The application of electrophysiology in non-macular IRDs could be relevant in the context of ongoing research and development of new therapeutic approaches,” Dr. Yu explains. “Understanding the electrophysiological profile of these diseases may guide the development of targeted interventions.”