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Background Illumination (background + illumination)
Selected AbstractsAge-related lens yellowing per se contributes little to the increase in Farnsworth-Munsell 100 hue error scores with ageOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 1 2008Raymond O. Beirne Purpose:, To investigate the effects of real and simulated age-related changes in crystalline lens yellowing on Farnsworth,Munsell (FM) 100 hue total and partial error scores. Methods:, FM 100 hue total and partial error scores were measured in a group of younger (n = 10, mean age 22.2 ± 2.65 years) and a group of older (n = 10, mean age = 54.5 ± 2.64 years) normal observers along with psychophysical estimates of crystalline lens optical density and pupil size measurements. Three younger observers underwent repeated FM 100 hue testing using a variety of simulated age-related lens yellowing conditions, using filters with well-defined absorption properties which mimicked the real age-related lens yellowing changes of the older group. FM 100 hue scores were also measured under different levels of background illumination and pupil size in the 3 younger observers. Results:, FM 100 hue total and partial error scores were significantly higher in the older age group compared to the younger group (p <0.01). Lens density measures were significantly higher in the older age group compared to the young group (p<0.01), but showed less scatter with age than FM 100 hue error scores. Pupil size was significantly larger in the younger group compared to the older group (p<0.01). Simulated lens yellowing in the three younger observers, equivalent to the level of that of the older observers, did not affect any of their FM 100 hue total or partial error scores. Reductions in pupil size and illumination significantly affected the younger observers' performance, with increases in error score equivalent to the observed age-related decline between the younger and older group. Conclusions:, Lens yellowing per se makes little contribution to the increase in Farnsworth,Munsell 100 hue error score with increasing age. Retinal illumination levels and pupil size can significantly affect the error score and should be considered when interpreting FM 100 hue error scores in older subjects. Clinicians should also consider iris colour and macular pigment density when interpreting FM 100 hue error scores. [source] Ganzfeld changes in short wavelength automated perimetryOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 6 2002S. Sukumar Purpose:, The change in perception of background illumination known as Ganzfeld changes occurs while performing perimetry test. It occurs under higher background illumination and whilst covering the non-tested eye with a black patch. We investigated the occurrence of Ganzfeld changes in Short Wavelength Automated Perimetry (SWAP) and assessed the performance while covering the non-tested eye with a standard black patch and with a translucent occluder. Methods:, Twenty-eight volunteers of age 22 ± 3 years participated in the study. A custom made 16-point test was used to analyse the sensitivity with a standard black patch and with the translucent occluder. The number and duration of Ganzfeld changes in each condition were detected by subjective responses. The visual comfort of the subjects under each patching condition was assessed using a comfort scale (0,5) and subject's preference. Results:, Ganzfeld changes occurred when a standard black patch was used and appears to influence the ability to see the test targets. With a standard black patch 5 Ganzfeld changes were observed per minute and it varied between 2 and 8 s. The duration and occurrence increased towards the end of the test. Using a translucent occluder almost eliminates the occurrence of Ganzfeld changes and improved the sensitivity (p = 0.001). Of the 28 subjects, 22 preferred translucent occluder to black patch. Conclusion:, Use of a translucent spectacle occluder over the non-tested eye significantly reduces the Ganzfeld changes and improves the performance in SWAP. [source] Contribution of voltage-gated sodium channels to the b-wave of the mammalian flash electroretinogramTHE JOURNAL OF PHYSIOLOGY, Issue 10 2008Deb Kumar Mojumder Voltage-gated sodium channels (Nav channels) in retinal neurons are known to contribute to the mammalian flash electroretinogram (ERG) via activity of third-order retinal neurons, i.e. amacrine and ganglion cells. This study investigated the effects of tetrodotoxin (TTX) blockade of Nav channels on the b-wave, an ERG wave that originates mainly from activity of second-order retinal neurons. ERGs were recorded from anaesthetized Brown Norway rats in response to brief full-field flashes presented over a range of stimulus energies, under dark-adapted conditions and in the presence of steady mesopic and photopic backgrounds. Recordings were made before and after intravitreal injection of TTX (,3 ,m) alone, 3,6 weeks after optic nerve transection (ONTx) to induce ganglion cell degeneration, or in combination with an ionotropic glutamate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 200 ,m) to block light-evoked activity of inner retinal, horizontal and OFF bipolar cells, or with the glutamate agonist N -methyl- d -aspartate (NMDA, 100,200 ,m) to reduce light-evoked inner retinal activity. TTX reduced ERG amplitudes measured at fixed times corresponding to b-wave time to peak. Effects of TTX were seen under all background conditions, but were greatest for mesopic backgrounds. In dark-adapted retina, b-wave amplitudes were reduced only when very low stimulus energies affecting the inner retina, or very high stimulus energies were used. Loss of ganglion cells following ONTx did not affect b-wave amplitudes, and injection of TTX in eyes with ONTx reduced b-wave amplitudes by the same amount for each background condition as occurred when ganglion cells were intact, thereby eliminating a ganglion cell role in the TTX effects. Isolation of cone-driven responses by presenting test flashes after cessation of a rod-saturating conditioning flash indicated that the TTX effects were primarily on cone circuits contributing to the mixed rod,cone ERG. NMDA significantly reduced only the additional effects of TTX on the mixed rod,cone ERG observed under mesopic conditions, implicating inner retinal involvement in those effects. After pharmacological blockade with CNQX, TTX still reduced b-wave amplitudes in cone-isolated ERGs indicating Nav channels in ON cone bipolar cells themselves augment b-wave amplitude and sensitivity. This augmentation was largest under dark-adapted conditions, and decreased with increasing background illumination, indicating effects of background illumination on Nav channel function. These findings indicate that activation of Nav channels in ON cone bipolar cells affects the b-wave of the rat ERG and must be considered when analysing results of ERG studies of retinal function. [source] Neuronal adaptation in the human retina: a study of the single oscillatory response in dark adaptation and mesopic background illuminationACTA OPHTHALMOLOGICA, Issue 7 2007Anna-Lena Lundström Abstract. Purpose:, The single oscillatory response in complete dark adaptation (DA) and the effect of mesopic illumination were studied in order to investigate the behaviour of the neuronal adaptation system as reflected in the oscillatory potentials (OPs) of the electroretinogram (ERG). Methods:, The rapid oscillatory and slow components (a- and b-waves) of single ERGs were simultaneously recorded in nine healthy, young subjects in response to first flash after both DA of 45 mins and light adaptation to a steady background light (BGL) of low mesopic intensity. Results:, Two low-amplitude oscillatory peaks were present in the single response to the first flash recorded in DA. There was no increase in the summed amplitudes of the OPs (SOP) when recorded in the single response to the first flash in mesopic BGL. However, the morphology of the oscillatory response altered. The first OP was reduced and a third oscillatory peak appeared. Conclusions:, We conclude that early, scotopically related OPs may indeed be activated in the single response to the first flash in DA (i.e. without using conditioning flashes). Secondly, on its own, adaptation to mesopic BGL does not seem to trigger enhancement of the overall oscillatory response. The altered single oscillatory response to the first flash apparent in the mesopic BGL comprises a third cone-associated OP and seems to reflect a reorganization of the retinal microcircuitry from a predominantly rod-activated system to one of mixed rod/cone neuronal activity in the inner part of the retina at the level at which individual OPs have their respective origins. [source] | ||||||||||