Inner Retinal Function in Hereditary Retinal Dystrophies

Abstract

Hereditary retinal dystrophies are most often disorders of photoreceptors and/or the retinal pigment epithelium. Structures secondary to the photoreceptor layer such as bipolar, horizontal, amacrine and ganglion cells are secondarily involved. In later stages of the disease a mild to moderate loss of inner retina occurs, but the second and third neurons remain surprisingly viable even in late and severe stages of retinal dystrophies. The function of the inner retina in patients suffering from hereditary retinal dystrophies is not easy to determine because it depends on the input of photoreceptors. The electroretinogram (ERG) offers several possibilities in this respect: b-wave, off-response (off-ERG), oscillatory potentials, scotopic threshold response of the flash ERG and the pattern ERG (PERG). We looked at two ERG tests: the PERG and the off-ERG. The PERG is an indicator of ganglion cell function. Its amplitude is related to the photoreceptor input determined by the flash ERG and visual field testing. But in cases of an undetectable flash ERG response the PERG can be recorded in some patients, but not in others. This may be an indication of a different effect on inner retinal function in different groups of patients. On- and off-responses are related to the function of depolarizing and hyperpolarizing bipolar cells. Evaluation of 301 patients with various retinal dystrophies revealed that most hereditary disorders primarily affect the photoreceptors or the pigment epithelium. In some patients, alterations of the on- and off-response amplitudes or implicit times were indicative of inner retinal disorders and different pathophysiologic mechanisms. However, interpretation has to be made carefully, as on- and off-responses may be influenced by dysfunction of photoreceptor synapses to bipolar cells, bipolar cells, Müller cells and intercellular matrix.

ON- and OFF-response of the photopic electroretinogram in relation to stimulus characteristics

“…In previous ON-and OFF-response studies variable stimulus durations were used [1,2,[9][10][11][17][18][19][20] and optimal duration has not been established yet. Sieving [1] adopted 150 ms as optimal stimulus duration, due to the highest d-wave amplitude.…”

“…ON-and OFF-responses have been studied in various retinal dystrophies [1,2,[9][10][11][12][13][14][15] where they might be important indicators of inner retinal dysfunction, not necessarily recognized by the conventional cone ERG. Although several electrophysiological laboratories use long duration flash ERG (Table 1), stimulus parameters have not been standardised yet.…”

“…Although several electrophysiological laboratories use long duration flash ERG (Table 1), stimulus parameters have not been standardised yet. There are only a few studies, concerning the influence of stimulus duration [1,9,[18][19][20], stimulus intensity [1,9,17,18,21] and stimulus wavelength [8,22] on the characteristic of the ON-and OFF-response. The aim of this study was to investigate the effect of several stimulus parameters on the waveform and amplitude of a-, b-and d-waves, in order to contribute to the standardization of the ON-and OFF-response as a routine test in clinical visual electrophysiology.…”

Dysfunction of transmission in the inner retina: incidence and clinical causes of negative electroretinogram

“…ON-and OFF-ERGs were recorded with long duration stimuli with green LEDs as described previously [21]. Following brief flash ERG recording, ON-and OFF-responses were obtained with an LED-stimulator (Roland Consult, Brandenburg, Germany) using green LEDs (3 cd /sm 2 ) and flashes of long duration (200 ms) presented on background illumination.…”

Electroretinographic Changes in Eyes of Patients with BRCA1 Gene Mutation

“…ERG abnormalities have already been observed in carriers of several retinal diseases such as rod-cone dystrophy (retinitis pigmentosa in different genetic patterns) and cone-rod dystrophy [7,8].…”