Comparison of conventional ERG parameters and high-intensity A-wave analysis in a clinical setting

The molecular basis of human retinal and vitreoretinal diseases

During the last two to three decades, a large body of work has revealed the molecular basis of many human disorders, including retinal and vitreoretinal degenerations and dysfunctions. Although belonging to the group of orphan diseases, they affect probably more than two million people worldwide. Most excitingly, treatment of a particular form of congenital retinal degeneration is now possible. A major advantage for treatment is the unique structure and accessibility of the eye and its different components, including the vitreous and retina. Knowledge of the many different eye diseases affecting retinal structure and function (night and colour blindness, retinitis pigmentosa, cone and cone rod dystrophies, photoreceptor dysfunctions, as well as vitreoretinal traits) is critical for future therapeutic development. We have attempted to present a comprehensive picture of these disorders, including biological, clinical, genetic and molecular information. The structural organization of the review leads the reader through non-syndromic and syndromic forms of (i) rod dominated diseases, (ii) cone dominated diseases, (iii) generalized retinal degenerations and (iv) vitreoretinal disorders, caused by mutations in more than 165 genes. Clinical variability and genetic heterogeneity have an important impact on genetic testing and counselling of affected families. As phenotypes do not always correlate with the respective genotypes, it is of utmost importance that clinicians, geneticists, counsellors, diagnostic laboratories and basic researchers understand the relationships between phenotypic manifestations and specific genes, as well as mutations and pathophysiologic mechanisms. We discuss future perspectives.

Rod a-wave analysis using high intensity flashes adds information on rod system function in 25% of clinical ERG recordings

PURPOSE

To investigate whether rod a-wave analysis using high intensity flashes adds information above that obtained with standard ERG.

METHODS

A total of 2,396 eyes were recorded. Patient age was 2.4 months-84.6 years.

RESULTS

A-wave analysis of high intensity flashes provided additional information on rod system function in 25% of eyes recorded, most importantly in subjects with midretinal disease and artificially reduced rod responses. High intensity flashes also provided measurable responses for longitudinal monitoring in rod dystrophies with non-recordable rod ERGs.

CONCLUSIONS

Clinical ERG testing would benefit greatly from adding high intensity flashes to its standard testing conditions.

Intraocular triamcinolone acetonide for macular edema due to CRVO. A multifocal-ERG and OCT study

PURPOSE

To investigate the effectiveness of intravitreal triamcinolone acetonide in the treatment of cystoid macular edema due to central retinal vein occlusion (CRVO). A noncomparative, prospective, interventional case series.

METHODS

In this study 15 eyes of 15 patients (9 males and 6 females) with macular edema due to non-ischemic CRVO were treated with intravitreal injection of 4 mg triamcinolone acetonide and followed-up for 1 year. Examination included measurement of best-corrected visual acuity (BCVA) for distance, measurement of intraocular pressure (IOP), fluorescein angiography, foveal retinal thickness measurement by optical coherence tomography (OCT), and multifocal electroretinography recordings (MFERG) preoperatively 3, 6 and 12 months postoperatively.

RESULTS

The visual acuity increased to a significant degree at 3 months, to a smaller degree at 6 months but at 12 months there was no significant improvement. The OCT macula thickness improved to a significant level all the follow-up period but with less significance at 12 months. The MFERG recordings from the fovea showed significant improvement at 3 and 6 months. The MFERG from the parafovea area showed significant improvement at 3 and 6 and to a smaller degree at 12 months. The intraocular pressure increased at 3 and 6 months but returned to pretreatment level at 12 months.

CONCLUSION

Intravitreal injection of triamcinolone acetonide leads to a significant improvement of mean VA in patients with macular edema due to CRVO. However, this significant effect is not permanent and persists for a maximum of 3-6 months. Thereafter all the indexes tend to deteriorate.

Utility in clinical practice of standard vs. high-intensity ERG a-waves

PURPOSE

Standard ERG a-waves represent contributions from both photoreceptor and inner retinal cells, while the leading edge of the high-intensity a-wave is produced only by photoreceptors. This has raised questions about the value of the a-wave as an indicator of photoreceptor disease, and has led to suggestions for standardizing higher-intensity stimuli. Our objective was to compare the behavior of standard and high-intensity a-waves in clinical practice.

METHODS

Standard ISCEV (International Society for Clinical Electrophysiology of Vision) a-waves and high-intensity a-wave responses were recorded under scotopic and photopic conditions from normal subjects and from patients with photoreceptor dystrophies and other diseases.

RESULTS

The standard scotopic a-wave amplitude followed the high-intensity a-wave closely among patients with different diagnoses, and the results did not change significantly when cone a-waves were subtracted to isolate rod signals. The only exception was one patient with the enhanced S cone syndrome (ESCS) whose dark-adapted responses were cone-driven. Initial peak times clustered in a small range for both standard and high-intensity responses, and were not very sensitive to disease.

CONCLUSION

High-intensity a-waves can show photoreceptor characteristics directly, and may help analyze some rare disorders. However, in our study the amplitude of conventional scotopic a-waves mirrored that of the high-intensity responses quite closely over a wide range of patients. This suggests that for practical purposes even if it is not perfect, the standard ERG is an excellent indicator of photoreceptor disease.