Dark Adaptation Time Research Articles

Short-term regulation and alternative pathways of photosynthetic electron transport in Hibiscus rosa-sinensis leaves

In this work, using the EPR and PAM-fluorometry methods, we have studied induction events of photosynthetic electron transport in Hibiscus rosa-sinensis leaves. The methods used are complementary, providing efficient tools for in situ monitoring of P700 redox transients and photochemical activity of photosystem II (PSII). The induction of P700+ in dark-adapted leaves is characterized by the multiphase kinetics with a lag-phase, which duration elongates with the dark-adaptation time. Analyzing effects of the uncoupler monensin and artificial electron carrier methylviologen (MV) on photooxidation of P700 and slow induction of chlorophyll a fluorescence (SIF), we could ascribe different phases of transient kinetics of electron transport processes in dark-adapted leaves to the following regulatory mechanisms: (i) acceleration of electron transfer on the acceptor side of PSI, (ii) pH-dependent modulation of the intersystem electron flow, and (iii) re-distribution of electron fluxes between alternative (linear, cyclic, and pseudocyclic) pathways. Monensin significantly decreases a level of P700+ and inhibits SIF. MV, which mediates electron flow from PSI to O2 with consequent formation of H2O2, promotes a rapid photooxidation of P700 without any lag-phase peculiar to untreated leaves. MV-mediated water–water cycle (H2O→PSII→PSI→MV→O2→H2O2→H2O) is accompanied by generation of ascorbate free radicals. This suggests that the ascorbate peroxidase system of defense against reactive oxygen species is active in chloroplasts of H. rosa-sinensis leaves. In DCMU-treated chloroplasts with inhibited PSII, the contribution of cyclic electron flow is insignificant as compared to linear electron flow. For analysis of induction events, we have simulated electron transport processes within the framework of our generalized mathematical model of oxygenic photosynthesis, which takes into account pH-dependent mechanisms of electron transport control and re-distribution of electron fluxes between alternative pathways. The model adequately describes the main peculiarities of P700+ induction and dynamics of the intersystem electron transport.

Dark adaptation time in canine electroretinography using a contact lens electrode with a built-in light source.

The purpose of this study was to evaluate the dark adaptation time in canine electroretinography (ERG) using a contact lens electrode with a built-in LED. Twelve eyes of six normal laboratory beagle dogs were used and exposed to steady room light at 500 lux for 30 min for light adaption. ERG was recorded at different time points during dark adaptation in sedated and light-adapted beagles. The stimulus intensity was 0.0096 cd/m2/sec. The b-wave amplitude increased significantly until 25 min of dark adaptation, whereas no significant changes in amplitudes were observed after 30 min. Dark adaptation for more than 25 min would be necessary for accurate ERG in canine ERG using a contact lens electrode with a built-in LED.

Differential changes in retina function with normal aging in humans

We evaluated the full field electroretinogram (ERG) to assess age-related changes in retina function in humans. ERG recordings were performed on healthy subjects with normal fundus appearance, lack of cataract and 20/20 acuity, aged 20-39 years (n = 27; mean age 25 ± 5, standard deviation), 40-59 years (n = 20; mean 53 ± 5), and 60-82 years (n = 18; mean 69 ± 5). Multiple ERG tests were applied, including light and dark-adapted stimulus-response function, dark adaptation and dynamic of recovery from a single bright flash under dark-adapted conditions. Changes in ERG properties were found in the oldest age group when compared with the two younger age groups. (1) The photopic hill effect was less pronounced. (2) Both photopic a-wave and b-wave amplitudes and implicit times were increased at high stimulus strengths. (3) Dark adaptation time was delayed for pure rod and L/M cone-driven responses, respectively. (4) Dark-adapted a-wave but not b-wave amplitudes were reduced, yielding higher B/A ratios. (5) Dark-adapted a- and b-waves implicit times were prolonged: there was a direct proportional correlation between minimal a-wave implicit times and age. (6) The dynamic of dark current recovery from a bright flash, under dark-adapted conditions, was transiently faster at intervals between 0.9 and 2 s. These results denote that aging of the healthy retina is accompanied by specific functional changes, which must be taken into account to optimally diagnose potential pathologies.

Intrasession variability of the full-field ERG

(1) To document variability of the full-field ERG within single recording sessions under ISCEV standards. (2) To identify clinical factors contributing to the observed variability. Nine volunteer subjects were studied, aged 19-32 with no history of retinal disease. ISCEV standard ERGs were recorded. Dark-adapted "standard combined" and light-adapted "cone" b-wave amplitudes and implicit times were measured. Multiple flashes were presented at different interflash intervals and after different periods of dark and light adaptation. The stability of the stimulus flash was measured with a photometer. The statistical coefficient of variability was roughly 2.5% for the standard combined b-wave amplitude and 4.5% for the cone b-wave. B-wave implicit times showed a coefficient of variability of 2% for standard combined responses and 1.25% for cone responses. Variation in interflash interval, dark and light adaptation times, and sporadic unusual waveforms influenced measured b-wave amplitudes. Intrasession variability is much lower than previously reported values for intersession variability. Nonetheless, it represents a baseline of variability that will affect results and that may be minimized by recognition and control of contributing factors.

The determination of dark adaptation time using electroretinography in conscious Miniature Schnauzer dogs

The optimal dark adaptation time of electroretinograms (ERG's) performed on conscious dogs were determined using a commercially available ERG unit with a contact lens electrode and a built-in light source (LED-electrode). The ERG recordings were performed on nine healthy Miniature Schnauzer dogs. The bilateral ERG's at seven different dark adaptation times at an intensity of 2.5 cd·s/m2 was performed. Signal averaging (4 flashes of light stimuli) was adopted to reduce electrophysiologic noise. As the dark adaptation time increased, a significant increase in the mean a-wave amplitudes was observed in comparison to base-line levels up to 10 min (p < 0.05). Thereafter, no significant differences in amplitude occured over the dark adaptation time. Moreover, at this time the mean amplitude was 60.30 ± 18.47 µV. However, no significant changes were observed for the implicit times of the a-wave. The implicit times and amplitude of the b-wave increased significantly up to 20 min of dark adaptation (p < 0.05). Beyond this time, the mean b-wave amplitudes was 132.92 ± 17.79 µV. The results of the present study demonstrate that, the optimal dark adaptation time when performing ERG's, should be at least 20 min in conscious Miniature Schnauzer dogs.

Visual function and dysfunction in early and late age-related maculopathy

Late age-related maculopathy (ARM) is responsible for the majority of blind registrations in the Western world among persons over 50 years of age. It has devastating effects on quality of life and independence and is becoming a major public health concern. Current treatment options are limited and most aim to slow progression rather than restore vision; therefore, early detection to identify those patients most suitable for these interventions is essential. In this work, we review the literature encompassing the investigation of visual function in ARM in order to highlight those visual function parameters which are affected very early in the disease process. We pay particular attention to measures of acuity, contrast sensitivity (CS), cone function, electrophysiology, visual adaptation, central visual field sensitivity and metamorphopsia. We also consider the impact of bilateral late ARM on visual function as well as the relationship between measures of vision function and self-reported visual functioning. Much interest has centred on the identification of functional changes which may predict progression to neovascular disease; therefore, we outline the longitudinal studies, which to date have reported dark-adaptation time, short-wavelength cone sensitivity, colour-match area effect, dark-adapted foveal sensitivity, foveal flicker sensitivity, slow recovery from glare and slower foveal electroretinogram implicit time as functional risk factors for the development of neovascular disease. Despite progress in this area, we emphasise the need for longitudinal studies designed in light of developments in disease classification and retinal imaging, which would ensure the correct classification of cases and controls, and provide increased understanding of the natural course and progression of the disease and further elucidate the structure-function relationships in this devastating disorder.

Effect of sediment type on microphytobenthos vertical distribution: Modelling the productive biomass and improving ground truth measurements

Intertidal flats are frequently colonised by microphytobenthos (MPB) assemblages that form transient biofilms at the sediment surface which are responsible for large fractions of estuarine primary production. The large spatio-temporal variability in MPB biomass distribution in concert with the fact that tidal flats can cover many km 2 makes the use of remote sensing particularly useful in assessing MPB distribution. Water content, sediment type and MPB vertical migration are variables that affect the relationship between ground truth measurements and remote sensing of benthic chlorophyll. The effect of chlorophyll depth distribution (top 2 mm) on the relationship between benthic chlorophyll and several remote sensing indices (NDVI, PI, R562/R647, derivative indices and PAM fluorescence) was investigated over a 2 year sampling period at 6 sites (Tagus estuary, Portugal). Additionally, the effect of the dark adaptation time required to measure the minimum fluorescence parameter ( F 0) was also tested. Sediment type strongly affected MPB depth distribution with muddy sites showing a strong negative exponential decay in chlorophyll with distance from the surface while sandy sites had a homogenous distribution over the same scale (2 mm). Chlorophyll content (mass per unit mass, μg g − 1 ) in the top 2 mm was better correlated with remote sensing indices than concentration (mass per unit volume, mg m − 3 ), both for NDVI (0.72 vs. 0.45) and for PAM fluorescence (0.70 vs. 0.55). Separating the data by transect increased the correlation values in all situations. A fitted model of chlorophyll depth distribution showed that the effect of asymmetrical chlorophyll depth distribution was stronger on the correlations between chlorophyll concentration and NDVI than on chlorophyll content and NDVI (0.46–2 mm vs. 0.74–125 μm, muddy site) the same was valid for fluorescence (0.66–2 mm vs. 0.92–125 μm, muddy site). Dark adapting the samples for more than 5 min did not result in any significant difference in the relationship between F 0 and chlorophyll a. The residuals from the regression of chlorophyll content on NDVI were positively correlated (0.7) with the mass per unit of mass of sediment < 63 μm and negatively (− 0.6) with chlorophyll concentration, this indicates that if no correction is performed to account for chlorophyll depth distribution both units will be strongly affected by the mass of < 63 μm particles. The results demonstrate that although expressing chlorophyll a as concentration is generally a better option for ground truth measurements care should be taken to account for chlorophyll depth distribution since strong asymmetries within the sampling depth can introduce large errors.

Assessment of the dark-adaptation time required for recovery of electroretinographic responses in dogs after fundus photography and indirect ophthalmoscopy

To investigate the duration of dark-adaptation time required for recovery of electroretinographic responses after fundus photography or indirect ophthalmoscopy in dogs. 6 dogs. Initially, scotopic-intensity series of electroretinograms (ERGs) were recorded after 20 minutes of dark adaptation. The fundus of the left eye of each dog was photographed (n = 10) or examined via indirect ophthalmoscopy for 5 minutes with moderate- (117 candela [cd]/m2) or bright-intensity (1,693 cd/m2) light; ERGs were repeated after a further 20 or 60 minutes of dark adaptation (6 procedures/dog). Following 20 minutes of dark adaptation after fundus photography, the b- and a-wave amplitudes were reduced in response to brighter stimuli, compared with pretest ERGs; after 60 minutes of dark adaptation, ERG amplitudes had recovered. Following 20 minutes of dark adaptation after indirect ophthalmoscopy (moderate-intensity light), significantly lower b-wave amplitudes were recorded in response to 2 of the brighter flash stimuli, compared with pretest ERGs; after 60 minutes of dark adaptation, ERG amplitudes had recovered. Following 20 minutes of dark adaptation after indirect ophthalmoscopy (bright-intensity light), all ERG amplitudes were significantly decreased and implicit times were significantly decreased at several flash intensities, compared with pretest ERGs; after 60 minutes of dark adaptation, ERG amplitudes and implicit times had returned to initial values, except for b-wave amplitudes recorded in response to dimmer stimuli. Results suggest that at least 60 minutes of dark adaptation should be allowed before ERGs are performed in dogs after fundus photography or indirect ophthalmoscopy.

The mechanism of the ozone-induced changes in thermoluminescence glow curves of barley leaves

The changes in thermoluminescence (TL) signals induced by short-term ozone exposure of leaves are characterized by a down-shift of the peak-temperature of the TLB-band and an increase of a TL band at 55°C. We investigated the relationship of these changes to photosystem 2 (PS2) photochemistry. The changes were not only detectable in the presence of ozone, but also after irradiation of dark-adapted leaves and after aging of irradiated detached leaf segments. The opposite effect on TL, an up-shift of the peak-temperature of the B-band and the decrease of the intensity of the band at 55°C were found after infiltration of leaves with nigericin, antimycin A, and diphenyleneiodonium chloride (DPI). Propyl gallate down-shifted the peak-temperature of the B-band. 2,5-dimethyl-1,4-benzoquinone up-shifted the peak-temperature of the B-band and decreased the intensity of the 55°C band. The intensity of the 55°C band did not change significantly in the presence of oxygen in comparison to that in nitrogen atmosphere. It decreased with time of dark adaptation (50% intensity was observed after 3 h of dark adaptation at room temperature), however, it was reactivated to its initial value (at 5 min of dark adaptation) after 1 single-turnover flash. The 55°C band was not significantly changed in the presence of DCMU. Thus the ozone-induced band at 55°C is assigned to charge recombination in PS2. Changes in the electron transport chain at the acceptor side of PS2, probably related to the cyclic electron transport around photosystem 1 and/or chlororespiration, could play an important role in the increase of the 55°C band and the down-shift of the B-band. The changes at the acceptor side indicated by TL can be an ex pression of a physiological regulatory mechanism functional under stress conditions.

Monitoring Migration and Measuring Biomass in Benthic Biofilms: The Effects of Dark/far-red Adaptation and Vertical Migration on Fluorescence Measurements

Pulse modulated fluorescence has increasingly been used as an ecological tool to examine changes in the vertical distribution of microphytobenthic cells within the upper layers of estuarine sediments (most often using the minimum fluorescence yield F(o)) as well as to indicate the health of the community (using the maximum PS II quantum efficiency F(v)/F(m)). However, the practicalities of in situ measurements, often dictates that short dark adaptation periods must be used ( approximately 15 min). The use of far-red light as an alternative to dark adaptation was investigated in natural migratory microphytobenthic biofilms and artificial non-migratory biofilms. Prolonged periods of darkness ( approximately 24 h) were not adequate to achieve 'true' measurements of F(o) and F(v)/F(m), which require complete oxidation of Q(A) and full reversal of non-photochemical quenching (NPQ). In some instances, stable values were only achieved using far-red light. Prolonged exposure to dark/far-red light led to a downwards migration of cells in natural assemblages, as seen by a reduction in both F(o) and the maximum fluorescence yield (F(m)). In non-migratory biofilms, F(m) increased in the dark and far-red treatments, indicating a reversal of NPQ, whereas F(o) decreased in far-red light but increased in the dark. It is suggested that far-red light and darkness differentially affected the balance between NPQ reversal and Q(A) oxidation that lead to the measured F(o) yield. The use of far-red light as an alternative to dark adaptation is discussed and the implications of short (e.g., 15 min) dark adaptation times used in situ are discussed with reference to the vertical migration of cells within sediment biofilms.

Availability of 11-cis retinal and opsins without chromophore as revealed by small bleaches of rhodopsin in excised albino mouse eyes

Small bleaches were used to study the rhodopsin regeneration process. At bleaches from 5.2% to 24.7%, the rhodopsin regenerations were consistent with a one-for-one recovery of bleached molecules. At response saturation rod photoreceptors exhibit a bleach level of only 5%. Major increases in rhodopsin regeneration were observed at bleach levels between 1.3% and 5.2%. The rhodopsin regenerations exhibited a linear relationship that was 4-times the bleach (dark adaptations of 0.75 and 1.5 h). The data show that the bleach initiates the availability, and possibly production, of 11-cis retinal in amounts that are 4-times the number of bleached molecules within the functional range of the rod photoreceptors. Rhodopsin regeneration also requires the presence of opsins without chromophore. Regenerations beyond the bleach indicate the presence of such opsins prior to the bleach. The opsin amounts were 8.1%, 8.6%, 3.1% and 0% of the total visual pigment at dark adaptation times of 0.75, 1.5, 24 and 48 h, respectively. Those opsins, as well as the ones produced by the bleach, may be regenerated to rhodopsin following a small bleach or with additional time in the dark.

Dark adaptation pattern of pregnant women as an indicator of functional disturbance at acceptable serum vitamin A levels

As a result of lack of precise guidelines, nutritional surveys on adults and high-risk groups are using diverse reference values as a dividing line between normal and deficient vitamin A status. To investigate whether pregnant women at marginally normal serum retinol status exhibit functional alteration that are characteristic of a deficiency state. Antenatal clinic, Gondar teaching hospital. Ninety-six healthy pregnant women were recruited for the study at the antenatal clinic. The dark adaptation time was tested in 48 pregnant women with marginal serum retinol level. The time lapse to see successive light stimuli of diminishing luminescence grade and change in retinal sensitivity pattern was measured using dark adaptometer. Results were compared with the results of a control group of women of similar age, parity and gestational period but with serum retinol values above 35 microg/dl. The mean serum retinol levels of cases and controls were 23.35 microg/dl and 40.47 microg/dl respectively (P<0.008). Cases have a lower dark adaptation than their controls, shown by their remarkably reduced sensitivity to light. For instance at mean final light threshold was -2.20+/-0.11 log cd/m(2) in cases as compared to -2.88+/-0.1 log cd/m(2) in the normal group (P<0.001). During pregnancy, dark adaptation was strongly associated with serum retinol concentration and women with marginal vitamin A concentration had lower dark adaptation. Hence marginally normal serum retinol levels should be categorized as a deficiency state, at least in pregnant women.

The reproducibility and sensitivity of visual evoked potential testing in rabbits

To examine the reproducibility and sensitivity of flash visual evoked potential (VEP) testing in rabbits, we recorded the VEPs elicited by light stimuli in conscious rabbits from an active electrode placed on the primary visual cortex. We analyzed flash VEPs of rab-bits by detecting the first negative peak, which was designated N 1.We evaluated the effects of dark adaptation time (from 5 to 30 min) on the latency and amplitude of N 1, and the coefficient of variation (CV) of these parameters. Then, the intensity of photopic stimulation was varied using a neutral density (ND) filter from the standard 0.6 J to its -1.8 log unit energy level at 0.3 log unit decrements. The N 1 latency and amplitude were measured at each recording. There was no significant change in VEP latency or amplitude when the dark adaptation time was varied from 5 to 30 min (n = 7, P > 0.05, ANOVA). The CV of the N1 latency was 0.4% and that of the N1 amplitude was 4.2% (n = 6). The N1 peak latency was prolonged and its amplitude decreased sig-nificantly with the decrease in the stimulus intensity; the changes in latency and amplitude relative to the standard were significant (n =11, p < 0.001, ANOVA) and were strongly correlated with the reduction in the stimulus intensity (r = 0.90 and -0.80, respectively, Pearson's test). Also, the latencies and amplitudes were significantly different between all adjacent 0.3 and 0.6 log unit pairs of stimulus intensity, respectively. These results indicated that rabbit VEPs showed good reproducibility and a high sensitivity to light difference intensities, and that they may be useful not only to evaluate functional damage, but also to investi-gate the neuroprotective effect of drugs or cytokines.

Ignoring Sparse Chromatic Context

The apparent colour of a target depends to some extent on the colour of the background. Jennes and Shevell have recently shown that a red background scattered with white or green dots has a different influence on the apparent colour of a target than a uniform background with the same space-averaged chromaticity and luminance (1995 Vision Research35 797 – 805). This could have important implications for our understanding of colour vision. However, it appears to be a very fragile effect. We were only successful in reproducing it when we used the same long dark-adaptation and pre-adaptation times as those used by Jennes and Shevell. One could argue that with shorter adaptation the effect was masked by gradual changes such as shifts in receptor sensitivity. However, when we interleaved trials with and without white dots for well over 20 min there was still no systematic difference between the two kinds of background. Moreover, when we repeated their experiment with a green rather than a red background, adding white dots had no effect. The long adaptation times that are required to produce the effect and the fact that we only found it for a long-wavelength background suggests that the effect may have to do with differences in the extent of rod adaptation. Although it remains an interesting phenomenon, this would probably make it irrelevant for normal colour vision.

Characterization of the photosynthetic system by measuring the laser-induced chlorophyll fluorescence in the msec range from medium distances

A continuous He-Ne laser with an acousto-optical modulator as a high-speed optical shutter generates a pulse with a length of 2 msec and a maximum power density of 600 W/m 2. According to the chlorophyll fluorescence-induction kinetics, the fluorescence intensity of plants reaches its initial value (F 0) and continues to rise during the excitation pulse. This increase can be described by an exponential function and a linear term, which depend on the power density at the laser spot, on the grade of inhibition of photosynthetic activity by herbicides or environmental stress, and on the duration of the dark adaptation time. A single measurement with the msec pulse method requires only a short time because the period of dark adaptation, necessary for the induction kinetics, can be reduced to several 100 msec. A modification of the device allows measurements at distances between 0.5 m and 3 m.

An electroretinogram protocol for toxicological screening in the canine model

A five-step electroretinogram protocol was developed for the dog to be used as a painless screening test for ocular effects of drugs or pesticides. Standard conditions of frequency band width, stimulus intensity, dark adaptation time and non-confounding anesthesia method were selected to allow analysis of wave components. The protocol demonstrated an acceptable level of inter-subject variability for compiling an age appropriate database, and for the detection of possible retinal component toxicities in chronic dog studies. This electrophysiologic procedure may serve to corroborate biochemical, clinical and pathology data, in establishing a compound's no-observable-effect-level (NOEL).

Use of fluorescence induction kinetics of Lemna minor as a tool for chemical stress evaluation

Slow fluorescence induction kinetics have been studied for Lemna minor under exposure to toxic chemicals. The first objective of the study was to find optimal values for condition measurements (dark adaptation time, light intensity, temperature, biomass and CO 2 concentration) to obtain only fluorescence induction due to chemical stress. The second end point was to test three chemical compounds, pentachlorophenol (PCP), simazin wand potassium bichromate. Results of toxicity were expressed as an index derivated from the Lichtentaler Vitality Index. A log-type dose-response curve was obtained for the three chemicals with an I 50 of 1.7 mg·1 −1 for PCP, 2.7 mg·1 −1 for simazin and 45 mg· −1 for potassium bichromate. This index is correlated to the inhibition of growth. The studied signal seems to be a good marker of pertubation of photosynthesis of aquatic plants in respect of the low variability (1–10%), the time scale of the response (1–2 min) and its easiness.

Three components in the light-induced current of the Limulus ventral photoreceptor.

1. Light-induced currents were measured in Limulus ventral nerve photoreceptors using a two-electrode voltage clamp. Three kinetically distinct components in the light-induced current could be distinguished by varying the light adaptation state of the photoreceptor and the intensity of the stimulus light. 2. The components could be partly separated by choosing appropriate stimulus intensities and dark adaptation time. Thus the properties of the components could be separately studied. The first component is the first to recover after a light adaptation, appears temporally first in the light-induced response, has the lowest activation threshold and is the smallest. The second component needs a longer time to recover after an adapting illumination and its kinetics differ from that of the other components. Applying a bright stimulus to a dark-adapted cell a third component can be observed late in the response. 3. The time to peak of the first and the third components depended on the stimulus intensity, but not on the dark adaptation time. The time to peak of the second component became shorter the longer the dark adaptation time. For a constant adaptation state the time to the maximum of component 2 was independent, but those of components 1 and 3 were dependent on the membrane voltage. 4. To exclude the possibility of the contribution of voltage-gated currents, light-activated currents were measured at clamp potentials more negative than -50 mV after adding 4-aminopyridine into the bath solution or injecting tetraethyl-ammonium chloride into the cell. The properties of the three components remained unchanged under these conditions. 5. The I-V curve of the first component was flat at negative membrane potentials and had a strong outward rectification at positive membrane potentials. The I-V curve of component 3 showed a negative resistance at potentials more negative than about -30 mV. In contrast, the I-V curve for the second component was always nearly linear. 6. No membrane potential was found where the light-induced current was zero. Instead, current traces close to the reversal potential showed a complex waveform indicating different reversal potentials for the three components. 7. The results indicate that the current components are caused by three different populations of light-sensitive channels. The different activations, deactivations and recovery kinetics of the components suggest that the three types of channels are activated by distinct intracellular transmitters.

Modulation of connexon densities in gap junctions of horizontal cell perikarya and axon terminals in fish retina: effects of light/dark cycles, interruption of the optic nerve and application of dopamine.

In the fish retina, connexon densities of gap junctions in the outer horizontal cells are modulated in response to different light or dark adaptation times and wavelengths. We have examined whether the connexon density is a suitable parameter of gap junction coupling under in situ conditions. Short-term light adaptation evoked low connexon densities, regardless of whether white or red light was used. Short-term dark adaptation evoked high connexon densities; this was more pronounced in the axon terminal than in perikaryal gap junctions. Under a 12 h red light/12 h dark cycle, a significant difference in connexon densities between the light and the dark period could be established in the gap junctions of the perikarya and axon terminals. Under a white light/dark cycle, only the gap junctions of axon terminals showed a significant difference. Crushing of the optic nerve resulted in an increase in connexon densities; this was more pronounced in axon terminals than in perikarya. Dopamine injected into the right eye of white-light-adapted animals had no effect. However, dopamine prevented the effect of optic-nerve crushing on connexon density. The reaction of axon-terminal gap junctions to different conditions thus resembles that of perikaryal gap junctions, but is more intense. Axon terminals are therefore thought to play an important role in the adaptation process.

On the relation between glare and straylight

An overview is given of the basic phenomena that may lead to glare complaints in patients. Prominent among them is increased intraocular straylight; this can be measured. Other causes may include: increased sensitivity to normal straylight, the length of (increased) light and dark adaptation times, (small angle) neuronal lateral interaction. Distinction must be made between disability glare and discomfort glare. Tests have been proposed to determine glare-induced loss of various visual functions. Often the test results are thought to be directly related to straylight but this may be untrue.