Rod-Cone Dystrophy (Retinitis Pigmentosa or RP)

Although patients typically show a conspicuous degeneration of the retina, ERG changes can precede ophthalmoscopically visible fundus changes in all genetic patterns of the disease. In fact, the ERG is considered to be the definitive test for this disorder. Patients with the autosomal recessive or the X-linked recessive forms of the disease have undetectable or much reduced ERG responses from an early age.

The autosomal dominant forms of RP usually have a later onset of symptoms and a less rapid progression. ERGs may be recordable from these patients. In early stages of the disease, both rod and cone ERGs can be recorded. As the disease progresses, some cone function may still be recorded after the rod response is extinguished.

Even in RP patients with “extinguished” ERGs, it is usually possible to record some signal from the cones. Berson and colleagues used the ERG to establish that large doses of Vitamin A may retard the degenerative processes in RP. If you are planning to use Vitamin A to treat patients with RP, you should follow them using the ERG.

Leber’s congenital amaurosis is an inherited retinal disorder characterized by diffuse photoreceptor cell disease. This condition is not rare, and accounts for between 10% and 20% of all blindness in children. Once poor vision is suspected, an ERG showing markedly reduced amplitudes will indicate this disorder. This may spare the patient and family costly neurologic and radiologic examinations looking for a central visual disorder.

Related Tests

  • ERG
    • Dim Scotopic Flash
    • Moderate Scotopic Flash
    • Moderate Photopic Flash
  • Dark Adaptometry/Scotopic Sensitivity

Related Products

  • RETeval® Visual Electrodiagnostic Device
  • UTAS Visual Diagnostic System

Cone and Cone-Rod Dystrophies

These dystrophies are inherited through autosomal dominant, autosomal recessive, and X-linked recessive mechanisms. Patients usually manifest with loss of acuity, central scotomata, and defective color vision. In patients with cone dystrophy, cone ERG recordings are attenuated or extinguished, however rod ERG recordings may be minimally affected in the early stages of the disease.

Patients with cone-rod dystrophies will show markedly reduced or absent cone ERGs and reduced rod ERGs. The changes in both rod and cone ERG function will be determined by the disease type (cone vs. cone-rod) and the stage of the disease.

Related Tests

  • ERG
    • Dim Scotopic Flash
    • Moderate Scotopic Flash
    • Moderate Photopic Flash

Related Products

  • RETeval Visual Electrodiagnostic Device
  • UTAS Visual Diagnostic System

Stationary Night Blinding Disorders

In many forms of congenital stationary night blindness, the patient presents with poor night vision and is myopic. I n the X-linked form, visual acuity is usually between 20/40 and 20/200. However, some patients with both the autosomal recessive and X-linked forms do not exhibit myopia, and have normal visual acuity. Further, some patients do not complain of night blindness. In this case, a definitive diagnosis can only be made on the basis of the ERG.

In Oguchi’s disease, vision and peripheral fields are normal in daylight; however there is a manifest decrease in visual sensitivity in dim illumination. After typical dark adaptation, rod ERGs are reduced in amplitude. With prolonged dark adaptation (several hours), however, ERG amplitudes can return to near-normal levels.

Fundus albipunctatus is an autosomal recessive disorder characterized by early onset of nonprogressive poor night vision and yellowish-white spots scattered throughout the peripheral fundus. ERG and EOG values may reach normal values, but only after a prolonged (several hours) period of dark adaptation.

Related Tests

  • ERG
  • Dim Scotopic Flash
  • EOG
  • Dark Adaptometry/Scotopic Sensitivity

Related Products

  • RETeval Visual Electrodiagnostic Device
  • UTAS Visual Diagnostic System

Pigment Epithelial Dystrophies

Stargardt’s disease, or fundus flavimaculatus, is an autosomally recessive inherited disorder that typically presents in the first 10 – 20 years of life. It is characterized by a decrease in visual acuity and bilateral atrophic foveal lesions. Ultimately, visual acuity will reach 20/200 to 20/400. In general, cone ERG waveforms will be reduced in amplitude, and rod amplitudes may be as well. Generally, a somewhat prolonged period of dark adaptation (45 minutes) is necessary to record maximal rod amplitudes.

Related Tests

  • ERG
    • Dim Scotopic Flash
    • Moderate Photopic Flash

Related Products

  • RETeval Visual Electrodiagnostic Device
  • UTAS Visual Diagnostic System

Best’s Disease

Best’s vitelliform macular dystrophy, or Best’s Disease, is an autosomal dominant condition characterized by macular lesions that appear between the ages of 5 and 15 years. Most patients are visually asymptomatic or show only moderate visual loss until 40 to 50 years of age. In Best’s disease, the ERG will be normal or nearly normal, however the EOG will be profoundly affected making it the preferred method for diagnosis.

Related Tests

  • EOG

Related Products

  • UTAS Visual Diagnostic System

Chorioretinal Dystrophies

Choroidal atrophy most frequently results in a decrease in acuity and (in the diffuse form) poor night vision, starting at age 40 to 50. Generally, the amplitude of the ERG parallels the clinically apparent fundus involvement. If ERG amplitudes are lower than expected, cone dystrophy should be suspected.

Patients with gyrate atrophy generally present between 20 and 30 years of age with poor night vision. The ERG cone and rod amplitudes are markedly reduced or completely absent. Gyrate atrophy is one of the few progressive night-blinding disorders in which a metabolic defect has been implicated and for which therapeutic trials with a low protein diet are under investigation.

Related Tests

  • ERG
    • Dim Scotopic Flash
    • Moderate Scotopic Flash
    • Moderate Photopic Flash
  • Dark Adaptometry/Scotopic Sensitivity

Related Products

  • RETeval Visual Electrodiagnostic Device
  • UTAS Visual Diagnostic System

X-Linked Juvenile Retinoschisis

In this disease, patients have peripheral retinoschisis in about half of all cases, foveal microcystic changes in nearly all cases, and occasionally, macular lesions. Both rod and cone ERG amplitudes are reduced, reflecting damage within the inner retinal layers. The a-wave of the ERG is generally less impaired than the b-wave.

Related Tests

  • ERG
    • Dim Scotopic Flash
    • Moderate Scotopic Flash
    • Moderate Photopic Flash

Related Products

  • RETeval Visual Electrodiagnostic Device
  • UTAS Visual Diagnostic System