Effect of target luminance on microfluctuations of accommodation

It is feasible that small temporal variations in steady-state accommodation may provide feedback to the accommodation control system through changes in retinal image contrast and that this feedback may be used to maintain an optimal accommodation response. The complex waveform of microfluctuations is dominated by two distinct regions of activity; a low frequency component (LFC< 0.6 Hz) and a high frequency component (1.0 ≤ HFC ≤ 2.3 Hz). Whereas the HFCs appear to be correlated with some intraocular manifestation of arterial pulse the contribution of the LFCs to the control of steady-state accommodation is unclear. The present study investigates the effect of target, luminance on the waveform of accommodative microfiuctuations. Three young emmetropic observers viewed monocularly a high contrast (90%) Maltese cross target placed at a vergence equal to their dark-focus level of accommodation in a Badal stimulus system. The luminance of the target was varied from 0.002 to 11.63cd m⁻² in nine equal logarithmic steps. Five continuous accommodation signals were collected for each viewing condition at a sampling rate of 102.4 Hz, and average power spectra subsequently calculated with a frequency resolution of O.1 Hz. One-way ANOVA revealed a significant variation in the root-mean-square (r.m.s.) value of the microfluctuations (F = 19.795. d.f. 124, P =0.0001) which could be attributed mainly to increases in the r.m.s. value for the two lowest luminances (0.002 and 0.004 cd m⁻²). Power spectrum analysis revealed that these changes in the microfluctuations could be attributed lo increases of power in the LFC. No systematic variation of the HFC could be observed with changing luminance level. The increase in power of the LFC as retinal-image quality is degraded suggests that it is this component which is used in the control of blur-driven accommodation responses.     

Refractive group differences in accommodation microfluctuations with changing accommodation stimulus

PURPOSE: Microfluctuations of accommodation are known to increase in magnitude with increasing accommodation stimulus. Reduced sensitivity to blur in myopic subjects could also lead to increases in the magnitude of the microfluctuations. The aim of this study is to examine the effect of variations in accommodation stimulus upon the microfluctuations in different refractive groups. METHODS: Thirty-six subjects were divided into three groups depending upon their refractive error and age of onset of their myopia; 12 emmetropes (EMMs), 12 early onset myopes (EOMs) and 12 late-onset myopes (LOMs). Steady-state accommodation responses were recorded continuously for 2 min using the Shin-Nippon SRW-5000 autorefractor at a sampling rate of 52 Hz while viewing targets at accommodation stimuli levels of 0, 1, 2, 3 and 4 D in a Badal (+5 D) optical system. RESULTS: The EMMs and EOMs showed systematic increases in the root mean square (r.m.s.) value of the microfluctuations with increasing accommodation stimulus. In contrast, no systematic variation with accommodation stimulus was found for the LOMs. Power spectrum analysis demonstrated that increases in the size of the microfluctuations were mediated by increases in the power of the low frequency components of the accommodation response. CONCLUSIONS: The magnitude of the microfluctuations in the EMMs and EOMs may be influenced primarily by accommodation response-induced zonular relaxation effects or to changes in the physical properties of the accommodation plant with increasing accommodation response. The LOMs may have an increased baseline neural blur threshold, which appears to modulate the magnitude of the accommodative microfluctuations for low accommodation levels. At higher accommodation demands, the changes in the physical properties of the accommodation plant or the zonular relaxation effects appear to exceed the blur threshold, and the known association between microfluctuations and accommodation stimulus level is restored.     

Can we do without mydriasis in multifocal ERG recordings?

The purpose of this study is to determine whether mfERG recordings with natural pupils approximate recordings obtained in mydriasis if the stimulus luminance is adjusted. If so, a bright monitor could obviate pupil dilation, rendering clinical management considerably easier. In 11 eyes of six subjects, we took four mfERG recordings with a resolution of 61 scaled hexagons per eye, two with natural pupils and two in mydriasis with a luminance of 150 cd/m² and 500 cd/m², respectively. Conditions will be abbreviated as “LoNat, HiNat, LoDil, and HiDil,” where Lo/Hi stands for low vs. high luminance and Nat/Dil stands for natural vs. dilated pupils. Response densities and peak times were averaged for the central seven and the remaining 54 hexagons. An ANOVA found highly significant effects for both amplitude and peak time between the four recording conditions (P always <0.001). However, for the two “middle” conditions, HiNat and LoDil, amplitudes and peak times did not differ markedly. Retinal illuminances of the conditions LoNat and HiNat each differed from the conditions LoDil and HiDil, respectively, by a factor of 5.4. Amplitudes increased and peak times decreased in the order of conditions LoNat, HiNat, LoDil, HiDil. When data were corrected for the Stiles–Crawford effect, there was an inversion of effective retinal illuminances of the recordings HiNat and LoDil. The mfERG guidelines correspond to the condition LoDil; for all practical purposes, the amplitudes and peak times are the same when the HiNat condition is used. Thus, when clinical constraints render pupil dilation undesirable, the mfERG can be recorded with natural pupils when monitor luminance is increased by five times (if available).     

Measurement of temporal summation of visual acuity with use of modified tachistoscope

Visual acuity was measured in 18 normal eyes of 10 subjects ranging in age from 20 to 30 years, using a modified tachistoscope. We changed the exposure duration of the target (1–1000 msec) or background luminance (0.1–200 cd/m²). Visual acuity improved with increasing duration of exposure. At background luminance over 10 cd/m², critical duration time was approximately 500 msec. At low luminances below 10 cd/m², however, critical duration was prolonged. This tendency was also seen when pupil diameter was fixed at 3 mm using an artificial pupil. Visual acuity also could be determined as the product of background luminance and exposure duration. We concluded that these findings follow the Bloch-Bunsen Roscoe law.     

The influence of luminance on the multifocal ERG

Purpose To assess the efficacy of high luminance in increasing the amplitude of the multifocal electroretinogram (mfERG). We examined 5 male and 5 female volunteers in the age of 22–52 years (median 28 years). Three different stimulus luminance levels were applied: the bright areas of the stimulus pattern were set to 150, 300 and 500 cd/m². We recorded the potentials via DTL electrodes using the VERIS Science 4.4 system with 61 hexagons, pupils were dilated. Analysis was based on the 5 ring averages.Results Across all hexagons and subjects, the response density (∼amplitude) rose by 20% when increasing the luminance by a factor of 3.3. The peak times decreased slightly with higher luminance, by less then 1.5 ms.Conclusions Combining the present results with those from two previous studies, the gain (= relative amplitude increase for relative luminance increase) is close to 0.4 over a range of 56–700 cd/m². The stimulus luminance range suggested in the mfERG guidelines seems well chosen.     

Stimulus luminance and the spatial acuity of domestic fowl (Gallus g. domesticus)

The luminance dependence of spatial acuity in domestic fowl was measured directly over stimulus luminances ranging from 0.06 to 57.35 cd m⁻². At the highest luminance, acuity was around 6.5 c deg⁻¹, in agreement with previous studies in this species. As stimulus luminance decreased, acuity fell with increasing rate to 3.2 c deg⁻¹ at 0.06 cd m⁻², following the same shape as acuity functions for other mammalian and avian species. These findings suggest that the rod-cone transition for domestic fowl is between 0.45 and 1.79 cd m⁻². Over the photopic range from 1.79 to 57.35 cd m⁻² the change of acuity for fowl was 1%, compared with 32% for humans. For domestic fowl, the Rovamo-Barten MTF model of contrast sensitivity accounted for the behaviour of acuity as a function of luminance down to mesopic levels.     

Effect of luminance and contrast on stereoscopic acuity

The threshold of binocular depth perception was measured in 11 healthy volunteers. A three-rod arrangement was employed in which both the luminance of the rods and that of the adapting field could be adjusted independently. This allowed fixing the contrast when the effect of luminance was studied or fixing the luminance when the effect of contrast was investigated. The observation distance was 400 mm. Thresholds were expressed as angular disparities and were based on 75% correct responses. Points of subjective equality were also determined. Lowest thresholds (2.85 ± 0.67 s of arc) were found for a moderate contrast of 0.5 whereas low (0.05) and high (0.95) contrast both produced significantly higher thresholds (luminance 250 cd/m²). Altering the field luminance (50, 250, 1600 cd/m²) under constant contrast conditions (0.95) did not measurably influence stereoscopic acuity.     

Evaluation of pupil responses and anterior chamber parameters in overactive bladder syndrome before and after antimuscarinic treatment

PurposeTo evaluate the static and dynamic pupillometric responses and anterior chamber parameters in overactive bladder (OAB) patients before and after solifenacin succinate treatment and to compare these results with those of healthy control subjects.Materials and methodsForty OAB patients who were planned to be treated with solifenacin succinate and 40 control subjects without any systemic or ocular diseases were included in the study. Following detailed ophthalmological examination, Pentacam imaging in order to detect anterior chamber angle, depth and volume; and static and dynamic pupillometry measurement in order to detect high-photopic (100 cd/m²), low-photopic (10 cd/m²), mesopic (1 cd/m²) and scotopic (0.1 cd/m²) pupil diameters, amplitude of pupil contraction, latency of pupil contraction, duration of pupil contraction, velocity of pupil contraction, latency of pupil dilation, duration of pupil dilation and velocity of pupil dilation were performed at baseline and at the first month of treatment. Data from the right eyes of the participants were used for statistical analysis.ResultsBaseline low- and high-photopic pupil diameters, duration of pupil contraction, latency of pupil dilatation and velocity of pupil dilatation values were significantly higher; and velocity of pupil contraction and duration of pupil dilation values were lower in the OAB group compared to the control group (P < 0.05 for all). One-month treatment with oral solifenacin succinate revealed higher scotopic and mesopic pupil diameters (P = 0.042, P = 0.031, respectively). Also, latency of pupil contraction was found to be increased and velocity of pupil dilatation was found to be decreased compared to pretreatment (P = 0.003, P < 0.001, respectively). We did not find any significant change in anterior chamber angle, depth and volume measured with Pentacam HR compared to pretreatment.ConclusionsPatients with OAB also have pupil abnormalities which probably reflect an underlying autonomic disorder that affects the bladder and pupils. One-month treatment of solifenacin succinate may lead to enlargement of pupil diameters under low illumination conditions and may lead to changes in dynamic pupillometric responses compatible with antimuscarinic treatment. Systemic antimuscarinic therapy has no effect on anterior chamber depth and intraocular pressure.Subject terms: Medical research, Health occupations, Pathogenesis     

Measuring and modelling the spatial contrast sensitivity of the chicken (Gallus g. domesticus)

The spatial contrast sensitivity (CSF) of the chicken has been measured using a behavioural technique. The results obtained show that spatial vision in this species is relatively poor compared with the human observer. For a visual stimulus luminance of 16 cd m⁻², the upper frequency limit of spatial vision in the chicken (acuity) was found to be about 7.0 c deg⁻¹, with peak spatial vision occurring at around 1.0 c deg⁻¹. Under equivalent stimulus conditions, the acuity of the human is around 50 c deg⁻¹ with a peak in spatial vision at about 3.0 c deg⁻¹. Peak spatial contrast sensitivity in the chicken was also found to be only about 2% that for the human. At a lower stimulus luminance of 0.1 cd m⁻², the chicken CSF reduced in overall magnitude and indicated an acuity level of about 5.0 c deg⁻¹. These experimental results were successfully modelled using modulation transfer (MTF) theory. This theoretical treatment enabled important neural mechanisms underlying spatial vision in the chicken to be revealed. The role played by spatial vision in the chicken’s ability to recognise detailed shapes in its visual environment was also examined by deploying the CSF as a visual weighting function with the Fourier series of a chicken comb.     

快速序列视觉呈现方式与其他类型视标实时调节反应的差异

目的：分析受检者在阅读快速序列视觉呈现方式（RSVP）与其他不同类型视标进行实时调节反应及调节微波动测量差异。方法：前瞻性研究。收集2019年4─10月期间在温州医科大学附属眼视光医院就诊的近视患者33例，年龄15～28（22.1±4.8）岁，等效球镜度（SE）为（-3.81±1.67）D。试验视标分为以下4类：RSVP、随机字符RSVP、马耳他视标和文本窗。每组视标试验时间为5 min，使用Grand Seiko WAM-5500红外验光仪进行实时的调节反应、调节微波动的测量。使用单因素方差分析比较受检者阅读或者注视不同视标时调节参数的差异，使用配对t检验比较试验初期10 s内与5 min内平均调节反应值的差异。结果：5 min试验显示，与RSVP、随机字符RSVP和文本窗比较，马耳他视标调节反应最低，差异均有统计学意义（t=2.45，P=0.016；t=2.57，P=0.011；t=3.85，P<0.001）；注视马耳他视标时，调节变异度大于阅读RSVP和文本窗，差异均有统计学意义（t=4.32，P<0.001；t=2.93，P=0.04）。调节微波动能量分析显示，与RSVP相比，注视马耳他视标时低频区能量明显增高（t=30.32，P<0.001）；与RSVP相比，阅读文本窗时中频及高频区能量明显增高（t=32.41，P<0.001；t=38.26，P<0.001）。RSVP、随机字符RSVP及马耳他视标在最初10 s的调节反应均高于5 min内调节反应的均值（t=2.30，P=0.028；t=2.45，P=0.020；t=3.71，P=0.001）。结论：阅读或注视不同类型的视标时，人眼的调节反应及调节微波动存在差异。阅读或注视持续一段时间后，调节反应会随着时间发生变化，最初的测量结果无法完全代表持续阅读或者注视时的调节反应。     

Photopic and scotopic VEPs in patients with congenital stationary night-blindness

Extended set of visual evoked potentials (VEPs) using pattern-reversal (PREPs), linear motion-onset and radial (expansion) motion-onset stimuli (M-VEPs) (detailed specification at http:0 //www.lfhk.cuni.cz/elf) was used to verify congenital stationary night-blindness (CSNB) characteristics in 7 patients (compared to 7 age matched controls) in photopic conditions (luminance of 17 cd/m²). No differences were found in any of the M-VEPs, whilst PREPs displayed prolonged latencies in 3 of 7 CSNB patients. Additionally, the PREPs and M-VEPs were tested in 3 normal and 3 CSNB subjects (the only available ones from the original group) over large range of scotopic, mesopic and photopic luminances (from 0.0001 to 65.4 cd/m²). Both types of low luminance VEPs had distinctly increased luminance threshold needed for reliable VEPs eliciting in CSNB patients (0.06 cd/m²) when compared with controls (0.003 cd/m²); the VEP appearance threshold was almost identical with the perceptual threshold in both groups. Thus, our pilot study proved that CSNB can be objectively detected also via scotopic VEP examination. Since the prolonged PREP latencies at 17 cd/m²normalised with luminance increase, it indicates that the lower luminance stimuli (compared to the standard recommended by ISCEV) can be more sensitive for some visual disorders detection.     

Contrast visual acuity after multifocal intraocular lens implantation:aspheric versus spherical design

AIM: To evaluate contrast visual acuity (CVA) after implantation of an aspheric apodized diffractive intraocular lens (IOL) or a spherical apodized diffractive IOL in cataract surgery. METHOD: This prospective randomized controlled study with a 12-month follow-up compared the results of cataract surgery with implantation of an aspheric AcrySof ReSTOR SN6AD3 IOL (30 eyes) and a spherical AcrySof ReSTOR SN60D3 IOL (30 eyes). CVA with best distance correction was measured at 4 contrast levels (100%, 25%, 10% and 5%) under 3 levels of chart luminance [250, 85 and 25 candelas per square meter (cd/m²)] using a multi-functional visual acuity tester (MFVA-100)． RESULTS:At 12 months after surgery, there were no statistically significant differences in 100% CVA and 25% CVA under 250cd/m² (P100%=0.875 and P25%=0.057) and 85cd/m² (P100%=0.198 and P25%=0.193) between the aspheric group and the spherical group. However, the 10% CVA and 5% CVA were significant better in aspheric group than spherical group under 250cd/m² (P10%=0.042 and P5%=0.007) and 85cd/m² (P10%=0.002 and P5%=0.039). Under the luminance level of 25cd/m², no significant differences was found in the 100% CVA between the 2 group (P100%=0.245), while aspheric group had better visual acuity in the remaining 3 contracts (P25%=0.023, P10%=0.026 and P5%=0.002, respectively). CONCULSION:The aspheric AcrySof ReSTOR SN6AD3 IOL provided patients with better low-contrast visual acuity than the spherical AcrySof ReSTOR SN60D3 IOL.     

Investigating structural and biochemical correlates of ganglion cell dysfunction in streptozotocin-induced diabetic rats

The aim of this study was to determine whether inner retinal dysfunction in diabetic rats is correlated with structural and/or biochemical changes in the retina and optic nerve. Using the electroretinogram (ERG; −5.83 to 1.28 log cd.s.m⁻²) retinal function (photoreceptor, bipolar, amacrine and ganglion cell components) was measured in control (n = 13; citrate buffer) and diabetic (n = 13; streptozotocin, STZ, 50 mg kg⁻¹) rats, 12 weeks following treatment. Retinae and optic nerves were analyzed for structural changes and retinae were assessed for alterations in growth factor/cytokine expression using quantitative real-time PCR. We found that phototransduction efficiency was reduced 12 weeks after STZ-induced diabetes (−30%), leading to reduced amplitude of ON-bipolar (−18%) and amacrine cell (−29%) dominated responses; ganglion cell dysfunction (−84%) was more profound. In the optic nerve, nerve fascicle area and myelin sheath thickness were reduced (p < 0.05), whereas the ratio of blood vessels and connective tissue to total nerve cross-sectional area was increased (p < 0.05) in diabetic compared to control rats. In the retina, connective tissue growth factor (CTGF), transforming growth factor beta, type 2 receptor (TGFβ-r2) mRNA and platelet-derived growth factor B (PDGF-B) mRNA were increased (p < 0.035). Reduced ganglion cell function was correlated with increased CTGF and TGFβ-r2, but not PDGF-B mRNA. In summary, the ganglion cell component exhibited the greatest level of dysfunction within the ERG components examined after 12 weeks of STZ-induced diabetes; the level correlated with increased CTGF and TGFβ-r2 mRNA, but not with gross morphological changes in the retina or optic nerve.     

Effects of inhibition of neuronal nitric oxide synthase on basal retinal blood flow regulation

Nitric oxide (NO) has been observed to regulate blood flow under basal and stimulated conditions in the retina. Recent evidence suggests that NO produced by neuronal nitric oxide synthase (nNOS) may regulate blood flow in addition to that produced by endothelial nitric oxide synthase (eNOS). The objective of the current study was to investigate the contribution of NO produced by nNOS in the regulation of basal retinal blood flow. A non-specific NOS inhibitor N (G)-nitro-l-arginine methyl ester (l-NAME) and the specific nNOS inhibitors 1-(2-trifluoromethylphenyl) imidazole (TRIM) and (4S)-N-(4-amino-5 [aminoethyl] aminopentyl)-N-nitroguanidine (AAAN) were injected into the vitreous (intravitreal) of Long-Evans rats. Vessel diameters, velocities and volumetric blood flow rates (VBF) in the retinal circulation were determined prior to and in 30-min intervals for 4-4.5 h after injection. In addition, the basal amount of nNOS in the rat retina was quantified using a specific enzyme linked immunoassay (ELISA). Treatment with l-NAME and TRIM significantly decreased diameters and VBF. Compared with saline, treatment with l-NAME and TRIM produced a significant (p < 0.001) decrease of ∼12-17% in vessel diameters. Treatment with AAAN significantly decreased vessel diameters and venous VBF. Compared with saline AAAN produced a significant decrease of ∼7% in arterial (p < 0.001) and 5% in venous (p = 0.011) diameters, respectively. The amount of nNOS in the rat retina was 0.17 ± 0.0147 pmol mg⁻¹ of dry retina. The results suggest that though inhibition of nNOS decreases basal diameters, constant VBF is maintained in the retinal circulation.     

Quantitative and functional influence of surround luminance on the letter contrast sensitivity function

Aim: To determine the influence of surround luminance on the letter contrast sensitivity function. Method: The binocular contrast sensitivities of 31 young and ocularly healthy individuals were measured with letters of sizes calculated to obtain the targeted fundamental frequencies of 3, 10, 20, and 30 c deg^?1, respectively; with surround luminances from 1 to 1000 cd m^?2, always with a test chart background luminance of 200 cd m^?2. Results: The letter contrast sensitivity increased with surround luminance up to 100 cd m^?2 and decreased when surround luminance increased from 100 to 1000 cd m^?2. These increments are larger for higher fundamental spatial frequencies, while decrements are similar for all frequencies. To analyse pupil size influence, results were compared with theoretical predictions obtained by combining different ocular MTFs with a typical neural function, where pupil size decrease leads to letter contrast sensitivity increments and veiling luminance causes the observed decrements. Other possible optical or neural factors that influence these values have also been considered. Conclusions: Letter contrast sensitivity function depends on surround luminance and this influence should be considered in future standardized directives.     

Unbiased estimation of refractive state of aberrated eyes

We seek unbiased methods for estimating the target vergence required to maximize visual acuity based on wavefront aberration measurements. Experiments were designed to minimize the impact of confounding factors that have hampered previous research. Objective wavefront refractions and subjective acuity refractions were obtained for the same monochromatic wavelength. Accommodation and pupil fluctuations were eliminated by cycloplegia. Unbiased subjective refractions that maximize visual acuity for high contrast letters were performed with a computer controlled forced choice staircase procedure, using 0.125 diopter steps of defocus. All experiments were performed for two pupil diameters (3 mm and 6 mm). As reported in the literature, subjective refractive error does not change appreciably when the pupil dilates. For 3 mm pupils most metrics yielded objective refractions that were about 0.1 D more hyperopic than subjective acuity refractions. When pupil diameter increased to 6 mm, this bias changed in the myopic direction and the variability between metrics also increased. These inaccuracies were small compared to the precision of the measurements, which implies that most metrics provided unbiased estimates of refractive state for medium and large pupils. Thus a variety of image quality metrics may be used to determine ocular refractive state for monochromatic (635 nm) light, thereby achieving accurate results without the need for empirical correction factors.     

Constant luminance (cd·s/m<Superscript>2</Superscript>) versus constant retinal illuminance (Td·s) stimulation in flicker ERGs

Purpose

To compare the effect of variable pupil size on the flicker electroretinogram (ERG) between a stimulus having constant luminance and a stimulus having constant retinal illuminance (constant Troland) that compensates for pupil size.

Methods

Subjects (n = 18) were tested with 12 pairs of the stimuli. The stimulus pair consisted of the ISCEV standard constant luminance stimulus (3 cd·s/m² with a 30 cd/m² background) and a constant retinal illuminance stimulus (32 Td·s with a 320 Td background) selected to provide the same stimulus and background when the pupil diameter is 3.7 mm. Half the subjects were artificially dilated, and their response was measured before and during the dilation. The natural pupil group was used to assess intra- and inter-subject variability. The artificially dilated group was used to measure the flicker ERG’s dependence on pupil size.

Results

With natural pupils, intra-subject variability was lower with the constant Troland stimulus, while inter-subject variability was similar between stimuli. During pupil dilation, the constant Troland stimulus did not have a dependence on pupil size up to 6.3 mm and had slightly larger amplitudes with longer implicit times for fully dilated pupils. For the constant luminance stimulus, waveform amplitudes varied by 22% per mm change in pupil diameter, or by 48% over the 2.2 mm diameter range measured in dilated pupil size. There was no difference in inter-subject variability between constant Troland natural pupils and the same subjects with a constant luminance stimulus when dilated (i.e., the ISCEV standard condition).

Conclusions

These results suggest that a constant Troland flicker ERG test with natural pupils may be advantageous in clinical testing. Because of its insensitivity to pupil size, constant Troland stimuli should produce smaller reference ranges, which in turn should improve the sensitivity for detection of abnormalities and for monitoring changes. In addition, the test can be administered more efficiently as it does not require artificial dilation.

Clinical Trial registration number

This trial is registered at ClinicalTrials.gov (NCT02466607).

     

Trophic factors GDNF and BDNF improve function of retinal sheet transplants

The aim of this study was to compare glial-derived neurotrophic factor (GDNF) treatment with brain-derived neurotrophic factor (BDNF) treatment of retinal transplants on restoration of visual responses in the superior colliculus (SC) of the S334ter line 3 rat model of rapid retinal degeneration (RD). RD rats (age 4-6 weeks) received subretinal transplants of intact sheets of fetal retina expressing the marker human placental alkaline phosphatase (hPAP). Experimental groups included: (1) untreated retinal sheet transplants, (2) GDNF-treated transplants, (3) BDNF-treated transplants, (4) none surgical, age-matched RD rats, (5) sham surgery RD controls, (6) progenitor cortex transplant RD controls, and (7) normal pigmented rat controls. At 2-8 months after transplantation, multi-unit visual responses were recorded from the SC using a 40 ms full-field stimulus (−5.9 to +1 log cd/m²) after overnight dark-adaptation. Responses were analyzed for light thresholds, spike counts, response latencies, and location within the SC. Transplants were grouped into laminated or rosetted (more disorganized) transplants based on histological analysis. Visual stimulation of control RD rats evoked no responses. In RD rats with retinal transplants, a small area of the SC corresponding to the position of the transplant in the host retina, responded to light stimulation between −4.5 and −0.08 log cd/m², whereas the light threshold of normal rats was at or below −5 log cd/m² all over the SC. Overall, responses in the SC in rats with laminated transplants had lower response thresholds and were distributed over a wider area than rats with rosetted transplants. BDNF treatment improved responses (spike counts, light thresholds and responsive areas) of rats with laminated transplants whereas GDNF treatment improved responses from rats with both laminated and rosetted (more disorganized) transplants. In conclusion, treatment of retinal transplants with GDNF and BDNF improved the restoration of visual responses in RD rats; and GDNF appears to exert greater overall restoration than BDNF.     

Retinal OFF-Pathway Overstimulation Leads to Greater Accommodation-Induced Choroidal Thinning

PurposeTo examine the interactions between accommodation and overstimulation of the retinal ON- and OFF-pathways, and their association with changes in choroidal thickness (ChT) and vascularity.MethodsOptical coherence tomography imaging of the choroid of twenty young adults (ages 25 ± 5 years) was performed before and after a series of 30-minute-long viewing tasks, including reading a bright text on dark background (ON-pathway overstimulation) and dark text on bright background (OFF-pathway overstimulation), and a control task of viewing a movie with unbiased ON-/OFF-pathway activation. The viewing tasks were performed with relaxed, and 5 diopter (D) accommodation (induced by soft contact lenses) demands. Both reading texts were matched for the mean luminance (35 cd/m²), luminance contrast (87%), and letter size (approximately 11.8 arc minutes). The change in ChT from baseline associated with contrast polarity and accommodation was examined using linear mixed model analysis.ResultsThe subfoveal ChT decreased significantly by −7 ± 1 µm with 5 D accommodation compared with relaxed accommodation (−3 ± 1 µm; P < 0.001), and by −9 ± 1 µm with OFF-pathway compared with ON-pathway overstimulation (−4 ± 1 µm; P = 0.002) and the control condition (−2 ± 1 µm; P < 0.001). Overstimulation of the OFF-pathway, but not the ON-pathway, resulted in a significantly greater choroidal thinning compared with the control condition, both at relaxed (−7 ± 1 µm; P = 0.003) and 5 D (−11 ± 1 µm; P = 0.005) accommodation levels. Similar changes were also observed for macular total, stromal, and luminal ChT.ConclusionsRetinal OFF-pathway stimulation enhanced the choroidal thinning associated with accommodation, thereby providing a potential mechanism that involves accommodation and the retinal OFF-signaling pathway, linking near work and myopia.