The relationship between stimulus intensity and response amplitude for the photopic negative response of the flash electroretinogram

The aim of this study was to investigate the relationship between stimulus intensity and response amplitude for the photopic negative response (PhNR) of the flash ERG. Specific aims were (i) to determine whether a generalized Naka-Rushton function provided a good fit to the intensity-response data and (ii) to determine the variability of the parameters of the best-fitting Naka-Rushton models. Electroretinograms were recorded in 18 participants, on two occasions, using both DTL fibre and skin active electrodes, in response to Ganzfeld red stimuli (Lee filter "terry red") ranging in stimulus strength from -1.30 to 0.53 log cd.s.m(-2) (0.28-2.11 log phot td.s) presented over a steady blue background (Schott glass filter BG28; 3.9 log scot td). PhNR amplitude was measured from b-wave peak and from pre-stimulus baseline. The Naka-Rushton function was fitted to all intensity-response data, and parameters, 'n', 'Vmax' and 'K' were obtained. Coefficients of variation (CoV), and inter-ocular and inter-session limits of agreement (LoA) were calculated for both Naka-Rushton parameters. A generalized Naka-Rushton function was found to provide a good fit to the intensity-response data, except at the highest stimulus intensity, where a reduction in amplitude occurred in many individuals. The 'Vmax' parameter was less variable than 'K' for all intensity-response data. Variability was lower for DTL than skin electrodes, and for peak-to-trough PhNR measurements, compared to baseline-to-trough. This study has demonstrated for the first time that the Naka-Rushton model provides a useful means of quantifying the intensity-response relationship of the PhNR

Morphological and Functional Changes in the Retina after Chronic Oxygen-Induced Retinopathy

The mouse model of oxygen-induced retinopathy (OIR) has been widely used for studies of retinopathy of prematurity (ROP). This disorder, characterized by abnormal vascularization of the retina, tends to occur in low birth weight neonates after exposure to high supplemental oxygen. Currently, the incidence of ROP is increasing because of increased survival of these infants due to medical progress. However, little is known about changes in the chronic phase after ROP. Therefore, in this study, we examined morphological and functional changes in the retina using a chronic OIR model. Both the a- and b-waves in the OIR model recovered in a time-dependent manner at 4 weeks (w), 6 w, and 8 w, but the oscillatory potential (OP) amplitudes remained depressed following a return to normoxic conditions. Furthermore, decrease in the thicknesses of the inner plexiform layer (IPL) and inner nuclear layer (INL) at postnatal day (P) 17, 4 w, and 8 w and hyperpermeability of blood vessels were observed in conjunction with the decrease in the expression of claudin-5 and occludin at 8 w. The chronic OIR model revealed the following: (1) a decrease in OP amplitudes, (2) morphological abnormalities in the retinal cells (limited to the IPL and INL) and blood vessels, and (3) an increase in retinal vascular permeability via the impairment of the tight junction proteins. These findings suggest that the experimental animal model used in this study is suitable for elucidating the pathogenesis of ROP and may lead to the development of potential therapeutic agents for ROP treatment

Characteristics of late negative ERG responses elicited by sawtooth flicker

BACKGROUND: This study aimed to determine whether the properties of the late negative responses (LNRs) of the electroretinogram (ERG) elicited by sawtooth flicker are consistent with the characteristics of the photopic negative response generated by a light pulse (PhNR(pulse)). METHODS: ERG recordings were obtained from 10 visually normal individuals and from 6 patients with optic atrophy (OA) in response to 8-Hz rapid-on and rapid-off sawtooth flicker and to brief (4 ms) light pulses. All stimuli were either long-wavelength (R), middle-wavelength (G), or a combination of equal luminances of long and middle-wavelengths (Y) presented on a short-wavelength, rod-saturating adapting field. Amplitudes of LNRs were obtained in response to rapid-on (LNR(on)) and rapid-off (LNR(off)) sawtooth flicker, and were also derived from the sum of the ERG waveforms to the two sawtooth phases (LNR(add)). RESULTS: For the control subjects, PhNR(pulse) amplitude varied with stimulus wavelength, being largest in response to a long-wavelength pulse, as expected. However, the amplitudes of LNR(on), LNR(off), and LNR(add) were not significantly different for R, Y, and G sawtooth flicker. Despite the absence of a chromatic effect, LNR(off) and LNR(add) amplitudes were significantly smaller in the OA patients than in the controls, similar to the results for the PhNR(pulse), implying an inner retinal origin for the LNR(off) and LNR(add). However, LNR(on) amplitudes did not differ significantly between the OA patients and controls, although there was a significant correlation between the LNR(on) and PhNR(pulse) for R stimuli. CONCLUSION: We conclude that LNR(off) and LNR(add) but not LNR(on) can be useful measures to assess the integrity of the inner retina that can complement the PhNR(pulse)

Inner segment ellipsoid band length is a prognostic factor in retinitis pigmentosa associated with EYS mutations: 5-year observation of retinal structure

[Purpose] To evaluate whether the length of the inner segment ellipsoid (ISe) band can be used as a prognostic factor for disease course in retinitis pigmentosa (RP) patients with EYS mutations by observation over a period of 5 years. [Methods] Twelve RP patients with EYS mutations were studied. The horizontal and vertical ISe length of the right eye was manually measured at five time points annually, using spectral domain optical coherence tomography. A regression line through the five points from baseline to the final measurement was drawn and the ratio of the length (%) at each point to the baseline length was calculated; the slope was defined as the rate of ISe shortening (%/year). The correlation between the rate of ISe shortening and age, visual acuity, and mean deviation (MD) value were evaluated. The intraclass correlation coefficient (ICC) for the measurements was calculated. [Results] The mean rate of ISe shortening was −4.65±2.89% per year and the decline was statistically significant. The rate of shortening was significantly negatively correlated with the baseline length (P=0.046, r=0.58), but not with the baseline age, visual acuity, and MD value. The ICC (2, 1) was 0.999. [Conclusions] ISe of all RP patients with EYS mutations shortened during the 5 years of annual observation. The measurement of the length of ISe is a simple and convenient method with high repeatability, and the length is a sensitive prognostic factor for the rate of ISe shortening in RP patients with EYS mutations