Electrophysiology in the investigation of acquired retinal disorders

Intrinsic signal optoretinography of dark adaptation abnormality due to rod photoreceptor degeneration

This research aims to investigate the potential of using intrinsic optical signal (IOS) optoretinography (ORG) to objectively detect dark adaptation (DA) abnormalities related to rod photoreceptor degeneration. Functional optical coherence tomography (OCT) was employed in both wild-type (WT) and retinal degeneration 10 (rd10) mice to conduct this assessment. Dynamic OCT measurements captured the changes in retinal thickness and reflectance from light-to-dark transition. Comparative analysis revealed significant IOS alterations within the outer retina. Specifically, a reduction in thickness from external limiting membrane (ELM) peak to retinal pigment epithelium (RPE) peak was observed (WT: 1.13 ± 0.69 µm, 30 min DA; rd10: 2.64 ± 0.86 µm, 30 min DA), as well as a decrease in the intensity of the inner segment ellipsoid zone (EZ) in 30 min DA compared to light adaptation (LA). The reduction of relative EZ intensity was notable in rd10 after 5 min DA and in WT after 15 min DA, with a distinguishable difference between rd10 and WT after 10 min DA. Furthermore, our findings indicated a significant decrease in the relative intensity of the hypo-reflective band between EZ and RPE in rd10 retinas during DA, which primarily corresponds to the outer segment (OS) region. In conclusion, the observed DA-IOS abnormalities, including changes in ELM-RPE thickness, EZ, and OS intensity, hold promise as differentiators between WT and rd10 mice before noticeable morphological abnormalities occur. These findings suggest the potential of this non-invasive imaging technique for the early detection of dysfunction in retinal photoreceptors.

Vitamin A deficiency retinopathy related to medical interventions in a Swiss cohort: a case series

AIMS OF THE STUDY

Vitamin A deficiency retinopathy is a potentially blinding disease. In developed countries, vitamin A deficiency due to malnutrition is rare. However, vitamin A deficiency can be caused by malabsorption resulting from bowel resection or medication. In this retrospective study, we present five cases of vitamin A deficiency retinopathy related to malabsorption secondary to medical interventions.

METHODS

Electronic charts over a ten-year period (2012-2022) were screened for vitamin A deficiency retinopathy. Only patients with vitamin A deficiency confirmed by laboratory tests were included. Symptoms, medical history, visual acuity, optical coherence tomography, fundus autofluorescence, electrophysiological examination, and vitamin A levels were reviewed.

RESULTS

Five eligible cases were identified. Median age was 44.7 years (range 22.2-88.9), median duration of ocular symptoms prior to diagnosis was 14 months, and median visual acuity was 1.0 (range 0.5-1.0, Snellen, decimal). Three patients had a history of bariatric surgery, one patient had a small bowel resection and was on octreotide treatment, and one patient suffered from cystic fibrosis and had a history of small bowel resection and severe hepatopathy. Optical coherence tomography showed various abnormalities, including a reduced interdigitation zone, subretinal drusenoid deposits, and a thinned outer nuclear layer. Electroretinogram findings ranged from abnormal oscillatory potentials to non-recordable rod responses.

CONCLUSIONS

Vitamin A deficiency retinopathy can occur following medical interventions associated with malabsorption. In cases of night blindness, vitamin A levels should be measured.

HIF2α activation and mitochondrial deficit due to iron chelation cause retinal atrophy

Iron accumulation causes cell death and disrupts tissue functions, which necessitates chelation therapy to reduce iron overload. However, clinical utilization of deferoxamine (DFO), an iron chelator, has been documented to give rise to systemic adverse effects, including ocular toxicity. This study provided the pathogenic and molecular basis for DFO-related retinopathy and identified retinal pigment epithelium (RPE) as the target tissue in DFO-related retinopathy. Our modeling demonstrated the susceptibility of RPE to DFO compared with the neuroretina. Intriguingly, we established upregulation of hypoxia inducible factor (HIF) 2α and mitochondrial deficit as the most prominent pathogenesis underlying the RPE atrophy. Moreover, suppressing hyperactivity of HIF2α and preserving mitochondrial dysfunction by α-ketoglutarate (AKG) protects the RPE against lesions both in vitro and in vivo. This supported our observation that AKG supplementation alleviates visual impairment in a patient undergoing DFO-chelation therapy. Overall, our study established a significant role of iron deficiency in initiating DFO-related RPE atrophy. Inhibiting HIF2α and rescuing mitochondrial function by AKG protect RPE cells and can potentially ameliorate patients' visual function.

Presumed retinal lead poisoning: a case report

PURPOSE

To describe a case of presumed retinal lead poisoning.

METHODS

Clinical examination, optical coherence tomography, fundus autofluorescence, fluorescein angiography, and electroretinography were used to study a 42-year-old male with the complaint of bilateral reduced vision following systemic lead poisoning.

RESULTS

The fundus examination showed venous tortuosity, as well as macular atrophy, and pigmentary changes in his both eyes. Optical coherence tomography revealed retinal thinning, outer retinal and retinal pigment epithelium atrophy, as well as foveal schitic changes. Blue autofluorescence showed moderately hypoautofluorescence in peripapillary area of both eyes. Fluorescein angiogram showed a leopard-like pattern of hypo- and hyperfluorescence in the posterior pole. Electroretinogram showed a moderate reduction in photopic and scotopic responses.

CONCLUSIONS

The most probable diagnosis of this case is early onset retinal lead poisoning.

Serial ERG monitoring of response to therapy in vitamin A deficiency related night blindness

Two male patients with known systemic disorders who presented with complaints of nyctalopia underwent a complete ophthalmic examination including electrophysiological evaluation and serum vitamin A (retinol) levels. A significant vitamin A deficiency was detected, supplementation started and repeat electroretinogram (ERG) testing was carried out to monitor the timeline of recovery. Restoration of rod and generalised cone function was rapid within the first week of receiving treatment and near normal recovery was seen after 1 month of supplementation. Serial monitoring of ERG changes in vitamin A deficiency (VAD) associated night blindness plays an important role to demonstrate functional recovery post-treatment. The different effects of VAD on rod and cone function, and their rate of recovery, may reflect differences in the visual cycle between the two photoreceptors. We report the serial ERG changes in VAD related night blindness secondary to intestinal lipofuscinosis and liver cirrhosis in two patients.

All-printed stretchable corneal sensor on soft contact lenses for noninvasive and painless ocular electrodiagnosis

Electroretinogram examinations serve as routine clinical procedures in ophthalmology for the diagnosis and management of many ocular diseases. However, the rigid form factor of current corneal sensors produces a mismatch with the soft, curvilinear, and exceptionally sensitive human cornea, which typically requires the use of topical anesthesia and a speculum for pain management and safety. Here we report a design of an all-printed stretchable corneal sensor built on commercially-available disposable soft contact lenses that can intimately and non-invasively interface with the corneal surface of human eyes. The corneal sensor is integrated with soft contact lenses via an electrochemical anchoring mechanism in a seamless manner that ensures its mechanical and chemical reliability. Thus, the resulting device enables the high-fidelity recording of full-field electroretinogram signals in human eyes without the need of topical anesthesia or a speculum. The device, superior to clinical standards in terms of signal quality and comfortability, is expected to address unmet clinical needs in the field of ocular electrodiagnosis.

Comparative study of wild-type and rd10 mice reveals transient intrinsic optical signal response before phosphodiesterase activation in retinal photoreceptors

Transient intrinsic optical signal (IOS) has been observed in stimulus-evoked retinal photoreceptors. This study is to compare IOS changes in wild-type and retinal degeneration 10 (rd10) mouse retinas, to evaluate the effect of cyclic guanosine monophosphate phosphodiesterase on photoreceptor-IOS. Time-lapse near-infrared light microscopy was employed to monitor the spatiotemporal dynamics of the IOS responses in freshly isolated retinas activated by visible light stimulation. Comparative IOS recordings were conducted at postnatal days 14 (P14) and P16. At P14, intrinsic optical signal magnitudes and spatiotemporal dynamics in wild-type and rd10 retinas were similar, indicating that the phosphodiesterase deficiency in rd10 did not affect the formation of photoreceptor-IOS. At P16, IOS magnitude in rd10 significantly decreased compared to that in wild-type, suggesting the IOS sensitivity to the photoreceptor degeneration in rd10. Our experimental results and theoretical analysis indicate that early disc-based stages of the phototransduction cascade before the activation of phosphodiesterase may contribute to the formation of the photoreceptor-IOS responses; and the IOS can be a sensitive biomarker for objective assessment of retinal function.

Impact statement

Comparative study of wild-type and rd10 mice was implemented to reveal that transient intrinsic optical signal (IOS) was initiated before the phosphodiesterase activation in stimulus-activated photoreceptors and the IOS magnitude was sensitive to photoreceptor degeneration. The photoreceptor-IOS promises a noninvasive biomarker for objective assessment of age-related macular degeneration, retinitis pigmentosa, and other eye diseases that can produce photoreceptor dysfunctions.

Ocular abnormalities in beta thalassemia patients: prevalence, impact, and management strategies

BACKGROUND

Beta thalassemia (β-thalassemia) is a hereditary disease caused by defective globin synthesis and can be classified into three categories of minor (β-TMi), intermedia (β-TI), and major (β-TM) thalassemia. The aim of our study is to investigate the effects of β-thalassemia and its treatment methods on different parts of the eye and how early-diagnostic methods of ocular complications in this disorder would prevent further ocular complications in these patients by immediate treatment and diet change.

METHODS

We developed a search strategy using a combination of the words Beta thalassemia, Ocular abnormalities, Iron overload, chelation therapy to identify all articles from PubMed, Web of Science, Scopus, and Google Scholar up to December 2018. To find more articles and to ensure that databases were thoroughly searched, the reference lists of selected articles were also reviewed.

RESULTS

Complications such as retinopathy, crystalline lens opacification, color vision deficiency, nyctalopia, depressed visual field, reduced visual acuity, reduced contrast sensitivity, amplitude reduction in a-wave and b-wave in Electroretinography (ERG), and decrease in the Arden ratio in Electrooculography (EOG) have all been reported in β-thalassemia patients undergoing chelation therapy.

CONCLUSION

Ocular problems due to β-thalassemia may be a result of anemia, iron overload in the body tissue, side effects of iron chelators, and the complications of orbital bone marrow expansion.

Multifocal electroretinogram in eyes with intravitreal silicone oil and changes following silicone oil removal

PURPOSE

To determine the effect of intravitreal silicone oil (SO) on multifocal electroretinogram (mfERG) and the changes in mfERG following SO removal.

METHODS

Twelve eyes of 12 patients with SO in vitreous cavity with corrected distance visual acuity (CDVA) > 20/200 were prospectively enrolled as cases over a period from July 2016 to June 2018. The fellow normal eyes served as control. The eyes were evaluated with P1 and N1 wave amplitude and implicit time on mfERG at baseline, 1 and 4 weeks after SO removal.

RESULTS

The mean age was 44.9 ± 18.9 (range 18-74) years. The indication for SO injection was retinal detachment (n = 9, three macula-on eyes, six macula-off eyes) and endophthalmitis (n = 3). The median (range) LogMAR CDVA at baseline was 0.54 (0.18-0.78) in cases and did not change post-SO removal (p = 0.29). There was a significant decrease in average P1 and N1 wave amplitude (p = 0.0001 and 0.0001, respectively) and delay in average P1 and N1 wave implicit time (p = 0.0002 and 0.021, respectively) in cases as compared to controls. The macular status and duration of SO tamponade did not have a significant correlation with mfERG parameters. There was a significant increase in average P1 and N1 wave amplitude (p = 0.009 and 0.003, respectively) at 1 week following SO removal but no change in average P1 and N1 wave implicit time (p = 0.41 and 0.37, respectively).

CONCLUSION

mfERG may be reliably performed for the assessment of macular function in SO-filled eyes. Intravitreal SO exerts an insulating effect on the density of the electric potentials.

Detection and monitoring of subclinical ocular siderosis using multifocal electroretinogram

BACKGROUND

Although full-field electroretinogram (ffERG) is the gold standard test to detect physiological dysfunction in siderosis, it measures overall retinal function. This study aims to determine if multifocal electroretinogram (mfERG) can detect subclinical siderosis in eyes with an iron intraocular foreign body (IOFB).

METHODS

Twenty eyes of 20 patients with retained iron IOFB, clear ocular media and good visual acuity (≥20/120) were enroled in this prospective case-control study. The fellow eyes served as control. These were evaluated with ffERG and mfERG at baseline. Serial mfERG was done till six months after pars plana vitrectomy with IOFB removal. Primary outcomes measures were amplitude and peak time of P1 and N1 wave of mfERG.

RESULTS

The median age was 25 years (range 18-55). Most patients (n = 14/20) presented within a month of trauma. Baseline ffERG showed no difference in either 'a' or 'b' wave amplitude or peak time between cases and controls. However, on mfERG, there was a significant decrease in P1 and N1 wave amplitude and delay in P1 wave peak time in <2° retinal ring in cases as compared to controls (p = 0.001, 0.001 and 0.02 respectively) despite variability in results. At 6 months, P1 amplitude showed significant improvement from baseline in cases (p = 0.010). However, P1 peak time did not show significant recovery (p = 0.65).

CONCLUSIONS

mfERG may reveal subclinical electrophysiological retinal dysfunction in eyes with iron IOFB in cases with normal ffERG. P1 peak time may serve as an electrophysiological marker for past retinal damage.

Functional optical coherence tomography of retinal photoreceptors

IMPACT STATEMENT

Retinal photoreceptors are the primary target of age-related macular degeneration (AMD) which is the leading cause of severe vision loss and legal blindness. An objective method for functional assessment of photoreceptor physiology can benefit early detection and better treatment evaluation of AMD and other eye diseases that are known to cause photoreceptor dysfunctions. This article summarizes in vitro study of IOS mechanisms and in vivo demonstration of IOS imaging of intact animals. Further development of the functional IOS imaging may provide a revolutionary solution to achieve objective assessment of human photoreceptors.

Comparative investigation of stimulus-evoked rod outer segment movement and retinal electrophysiological activity

Transient retinal phototropism (TRP) has been observed in rod photoreceptors activated by oblique visible light flashes. Time-lapse confocal microscopy and optical coherence tomography (OCT) revealed rod outer segment (ROS) movements as the physical source of TRP. However, the physiological source of TRP is still not well understood. In this study, concurrent TRP and electroretinogram (ERG) measurements disclosed a remarkably earlier onset time of the ROS movements (≤10 ms) than that (∼38 ms) of the ERG a-wave. Furthermore, low sodium treatment reversibly blocked the photoreceptor ERG a-wave, which is known to reflect hyperpolarization of retinal photoreceptors, but preserved the TRP associated rod OS movements well. Our experimental results and theoretical analysis suggested that the physiological source of TRP might be attributed to early stages of phototransduction, before the hyperpolarization of retinal photoreceptors.

Stimulus-evoked outer segment changes occur before the hyperpolarization of retinal photoreceptors

Transient retinal phototropism (TRP) has been predominantly observed in rod photoreceptors activated by oblique visible light stimulation. Dynamic confocal microscopy and optical coherence tomography (OCT) have revealed rod outer segment (ROS) movement as the physical source of TRP. However, the physiological source of ROS movement is still not well understood. In this study, concurrent near-infrared imaging of TRP and electroretinogram (ERG) measurement of retinal electrophysiology revealed that ROS movement occurs before the onset of the ERG a-wave, which is known to reflect the hyperpolarization of retinal photoreceptors. Moreover, substitution of normal superfusing medium with low-sodium medium reversibly blocked the photoreceptor ERG a-wave, but largely preserved the stimulus-evoked ROS movements. Our experimental results and theoretical analysis indicate that early, disc-based stages of the phototransduction cascade, which occur before the hyperpolarization of retinal photoreceptors, contribute to the TRP associated ROS movement.

Thyroid malignancy presenting with visual loss: an unusual case of paraneoplastic retinopathy

Paraneoplastic retinopathy is a rare cause of painless vision loss, associated with an underlying (and often occult) systemic malignancy. Ocular examination findings are subtle, and the diagnosis is often made on the basis of electrophysiology findings. This report describes the case of a 48-year-old Caucasian man with paraneoplastic retinopathy presenting as visual disturbance, central scotomata and abnormal electrophysiology. He was subsequently diagnosed with papillary thyroid malignancy.

In vivo optical coherence tomography of stimulus-evoked intrinsic optical signals in mouse retinas

Intrinsic optical signal (IOS) imaging promises a noninvasive method for advanced study and diagnosis of eye diseases. Before pursuing clinical applications, it is essential to understand anatomic and physiological sources of retinal IOSs and to establish the relationship between IOS distortions and eye diseases. The purpose of this study was designed to demonstrate the feasibility of <italic<in vivo</italic< IOS imaging of mouse models. A high spatiotemporal resolution spectral domain optical coherence tomography (SD-OCT) was employed for depth-resolved retinal imaging. A custom-designed animal holder equipped with ear bar and bite bar was used to minimize eye movements. Dynamic OCT imaging revealed rapid IOS from the photoreceptor’s outer segment immediately after the stimulation delivery, and slow IOS changes were observed from inner retinal layers. Comparative photoreceptor IOS and electroretinography recordings suggested that the fast photoreceptor IOS may be attributed to the early stage of phototransduction before the hyperpolarization of retinal photoreceptor.

Sensitivity of multifocal electroretinography (mfERG) in detecting siderosis

OBJECTIVE

To evaluate use of multifocal electroretinography (mfERG) in diagnosing retinal toxicity from siderosis with normal ERG.

DESIGN

Prospective case series.

PARTICIPANTS

Six patients with retained intraocular foreign body were recruited.

METHODS

The affected eye of the patients had no clinical evidence of siderosis, had similar full-field photopic 3.0 ERG compared with the fellow eye, and had subnormal visual acuity. Group averages in each MfERG ring for implicit time and amplitude at P1 wave were compared between affected and fellow eye to look for latent siderosis.

RESULTS

On mfERG, no statistical difference in group averaged amplitude was observed; however, a significant difference (p < 0.05) was found in group averaged latency between fellow and affected eye at most tested rings (<2 degree, 2-5 degree, and >15 degree rings). Average latency for overall retinal area mapped also showed significant difference (p = 0.010).

CONCLUSIONS

Increased mfERG latency may serve as an early predictor of retinal damage from siderosis when full-field ERG is normal.

Aged complement factor H knockout mice kept in a clean barriered environment have reduced retinal pathology

Age-related macular degeneration (AMD) is the largest cause of visual loss in those over 60 years in the West and is a condition increasing in prevalence. Many diseases result from genetic/environmental interactions and 50% of AMD cases have an association with polymorphisms of the complement system including complement factor H. Here we explore interactions between genetic predisposition and environmental conditions in triggering retinal pathology in two groups of aged complement factor H knock out (Cfh(-/-)) mice. Mice were maintained over 9 months in either a conventional open environment or a barriered pathogen free environment. Open environment Cfh(-/-) mice had significant increases in subretinal macrophage numbers, inflammatory and stress responses and reduced photoreceptor numbers over mice kept in a pathogen free environment. Hence, environmental factors can drive retinal disease in these mice when linked to complement deficits impairing immune function. Both groups of mice had similar levels of retinal amyloid beta accumulation. Consequently there is no direct link between this and inflammation in Cfh(-/-) mice.

Clinical biomarkers and molecular basis for optimized treatment of diabetic retinopathy: current status and future prospects

Diabetic retinopathy is a highly specific microvascular complication of diabetes and a leading cause of blindness worldwide. It is triggered by hyperglycemia which causes increased oxidative stress leading to an adaptive inflammatory assault to the neuroretinal tissue and microvasculature. Prolonged hyperglycemia causes increased polyol pathway flux, increased formation of advanced glycation end-products, abnormal activation of signaling cascades such as activation of protein kinase C (PKC) pathway, increased hexosamine pathway flux, and peripheral nerve damage. All these changes lead to increased oxidative stress and inflammatory assault to the retina resulting in structural and functional changes. In addition, neuroretinal alterations affect diabetes progression. The most effective way to manage diabetic retinopathy is by primary prevention such as hyperglycemia control. While the current mainstay for the management of severe and proliferative diabetic retinopathy is laser photocoagulation, its role is diminishing with the development of newer drugs including corticosteroids, antioxidants, and antiangiogenic and anti-VEGF agents which work as an adjunct to laser therapy or independently. The current pharmacotherapy of diabetic retinopathy is incomplete as a sole treatment option in view of limited efficacy and short-term effect. There is a definite clinical need to develop new pharmacological therapies for diabetic retinopathy, particularly ones which would be effective through the oral route and help recover lost vision. The increasing understanding of the mechanisms of diabetic retinopathy and its biomarkers is likely to help generate better and more effective medications.

In vivo intrinsic optical signal imaging of mouse retinas

Intrinsic optical signal (IOS) imaging is a promising noninvasive method for advanced study and diagnosis of eye diseases. Before pursuing clinical applications, more IOS studies employing animal models are necessary to establish the relationship between IOS distortions and eye diseases. Ample mouse models are available for investigating the relationship between IOS distortions and eye diseases. However, in vivo IOS imaging of mouse retinas is challenging due to the small ocular lens (compared to frog eyes) and inevitable eye movements. We report here in vivo IOS imaging of mouse retinas using a custom-designed functional OCT. The OCT system provided high resolution (3 μm) and high speed (up to 500 frames/s) imaging of mouse retinas. An animal holder equipped with a custom designed ear bar and bite bar was used to minimize eye movement due to breathing and heartbeats. Residual eye movement in OCT images was further compensated by accurate image registration. Dynamic OCT imaging revealed rapid IOSs from photoreceptor outer segments immediately (<10 ms) after the stimulation delivery, and unambiguous IOS changes were also observed from inner retinal layers with delayed time courses compared to that of photoreceptor IOSs.

Intrinsic optical signal imaging of retinal physiology: a review

Intrinsic optical signal (IOS) imaging promises to be a noninvasive method for high-resolution examination of retinal physiology, which can advance the study and diagnosis of eye diseases. While specialized optical instruments are desirable for functional IOS imaging of retinal physiology, in depth understanding of multiple IOS sources in the complex retinal neural network is essential for optimizing instrument designs. We provide a brief overview of IOS studies and relationships in rod outer segment suspensions, isolated retinas, and intact eyes. Recent developments of line-scan confocal and functional optical coherence tomography (OCT) instruments have allowed in vivo IOS mapping of photoreceptor physiology. Further improvements of the line-scan confocal and functional OCT systems may provide a feasible solution to pursue functional IOS mapping of human photoreceptors. Some interesting IOSs have already been detected in inner retinal layers, but better development of the IOS instruments and software algorithms is required to achieve optimal physiological assessment of inner retinal neurons.

Endophenotypes for Age-Related Macular Degeneration: Extending Our Reach into the Preclinical Stages of Disease

The key to reducing the individual and societal burden of age-related macular degeneration (AMD)-related vision loss, is to be able to initiate therapies that slow or halt the progression at a point that will yield the maximum benefit while minimizing personal risk and cost. There is a critical need to find clinical markers that, when combined with the specificity of genetic testing, will identify individuals at the earliest stages of AMD who would benefit from preventive therapies. These clinical markers are endophenotypes for AMD, present in those who are likely to develop AMD, as well as in those who have clinical evidence of AMD. Clinical characteristics associated with AMD may also be possible endophenotypes if they can be detected before or at the earliest stages of the condition, but we and others have shown that this may not always be valid. Several studies have suggested that dynamic changes in rhodopsin regeneration (dark adaptation kinetics and/or critical flicker fusion frequencies) may be more subtle indicators of AMD-associated early retinal dysfunction. One can test for the relevance of these measures using genetic risk profiles based on known genetic risk variants. These functional measures may improve the sensitivity and specificity of predictive models for AMD and may also serve to delineate clinical subtypes of AMD that may differ with respect to prognosis and treatment.

Photopic full-field electroretinography and optical coherence tomography in type 1 diabetic retinopathy

Purpose

The purpose of this study was to evaluate the role of photopic full-field electroretinography (ERG) and retinal thickness measurements by spectral-domain optical coherence tomography (SD-OCT) in the assessment of disease severity in type 1 diabetic retinopathy.

Methods

A population-based cohort of 151 patients with type 1 diabetes underwent a complete ophthalmic examination, including photopic full-field ERG and SD-OCT for retinal thickness measurements. Stereoscopic fundus photographs were taken according to the Early Treatment Diabetic Retinopathy Study protocol, and the classification of diabetic retinopathy was based on the International Clinical Diabetic Retinopathy Disease Severity Scale. Associations between photographically determined retinopathy level, b-wave amplitude and peak time of the photopic single-flash and 30-Hz flicker ERG, and central retinal thickness parameters were evaluated.

Results

For all ERG measurements, the amplitude decreased and peak time increased with progression of the disease, but these associations lost statistical significance after adjusting for age and excluding laser-treated patients. Mean retinal thickness was significantly associated with the b-wave amplitude of photopic single-flash and 30-Hz flicker responses (r² = 0.08, p = 0.006; and r² = 0.05, p = 0.025, respectively), but revealed no association with retinopathy level.

Conclusions

Photopic full-field ERG and SD-OCT-derived retinal thickness parameters have limited clinical value in the staging of diabetic retinopathy. However, thinning of the central retina leads to significant functional impairment and may reflect an ongoing neurodegenerative process in the retinal tissue.

Retinal and visual system: occupational and environmental toxicology

Occupational chemical exposure often results in sensory systems alterations that occur without other clinical signs or symptoms. Approximately 3000 chemicals are toxic to the retina and central visual system. Their dysfunction can have immediate, long-term, and delayed effects on mental health, physical health, and performance and lead to increased occupational injuries. The aims of this chapter are fourfold. First, provide references on retinal/visual system structure, function, and assessment techniques. Second, discuss the retinal features that make it especially vulnerable to toxic chemicals. Third, review the clinical and corresponding experimental data regarding retinal/visual system deficits produced by occupational toxicants: organic solvents (carbon disulfide, trichloroethylene, tetrachloroethylene, styrene, toluene, and mixtures) and metals (inorganic lead, methyl mercury, and mercury vapor). Fourth, discuss occupational and environmental toxicants as risk factors for late-onset retinal diseases and degeneration. Overall, the toxicants altered color vision, rod- and/or cone-mediated electroretinograms, visual fields, spatial contrast sensitivity, and/or retinal thickness. The findings elucidate the importance of conducting multimodal noninvasive clinical, electrophysiologic, imaging and vision testing to monitor toxicant-exposed workers for possible retinal/visual system alterations. Finally, since the retina is a window into the brain, an increased awareness and understanding of retinal/visual system dysfunction should provide additional insight into acquired neurodegenerative disorders.

Cellular responses following retinal injuries and therapeutic approaches for neurodegenerative diseases

Retinal neurodegenerative diseases like age-related macular degeneration, glaucoma, diabetic retinopathy and retinitis pigmentosa each have a different etiology and pathogenesis. However, at the cellular and molecular level, the response to retinal injury is similar in all of them, and results in morphological and functional impairment of retinal cells. This retinal degeneration may be triggered by gene defects, increased intraocular pressure, high levels of blood glucose, other types of stress or aging, but they all frequently induce a set of cell signals that lead to well-established and similar morphological and functional changes, including controlled cell death and retinal remodeling. Interestingly, an inflammatory response, oxidative stress and activation of apoptotic pathways are common features in all these diseases. Furthermore, it is important to note the relevant role of glial cells, including astrocytes, Müller cells and microglia, because their response to injury is decisive for maintaining the health of the retina or its degeneration. Several therapeutic approaches have been developed to preserve retinal function or restore eyesight in pathological conditions. In this context, neuroprotective compounds, gene therapy, cell transplantation or artificial devices should be applied at the appropriate stage of retinal degeneration to obtain successful results. This review provides an overview of the common and distinctive features of retinal neurodegenerative diseases, including the molecular, anatomical and functional changes caused by the cellular response to damage, in order to establish appropriate treatments for these pathologies.

Electrophysiological examination in uveitis: a review of the literature

Purpose

Uveitis is the inflammation of the uveal tract, which usually also affects the retina and vitreous humor. The electrophysiological examination is an objective ocular examination that includes the electroretinogram, visual evoked potentials, the electrooculogram, the multifocal electroretinogram, and multifocal visual evoked potentials. Our aim is to review the literature of the use of the electrophysiological examination in cases of uveitis.

Methods

We performed a systematic search of the literature of published papers until October 2012 using the PubMed search engine. The key terms that were used were “uveitis”, “electrophysiological examination”, “electroretinogram”, “visual evoked potentials”, “electrooculogram”, “multifocal electroretinogram”, and “multifocal visual evoked potentials” in multiple combinations. To the best of our knowledge, this is the first review concerning the assessment of electrophysiology in uveitis.

Results

Our search of the literature demonstrated that the electrophysiological examination, mainly by means of electroretinogram, multifocal electroretinogram, and visual evoked potentials, is performed in several cases of uveitis for many purposes, including diagnosis and monitoring of disease progression and treatment efficacy. The electrophysiological examination is more useful in patients with multiple evanescent white dot syndrome, acute posterior multifocal placoid pigment epitheliopathy, birdshot chorioretinopathy, Vogt–Koyanagi–Harada disease, Adamantiades–Behçet disease, ocular syphilis, and Fuchs heterochromic cyclitis.

Conclusion

This review summarizes the use of the electrophysiological examination in uveitic patients and underlines its value as a useful tool in the objective assessment and the monitoring of the disease.

En face optical coherence tomography of transient light response at photoreceptor outer segments in living frog eyecup

This study was designed to test the feasibility of en face mapping of the transient intrinsic optical signal (IOS) response at photoreceptor outer segments and to assess the effect of spatial resolution on functional IOS imaging of retinal photoreceptors. A line-scan optical coherence tomography (LS-OCT) was constructed to achieve depth-resolved functional IOS imaging of living frog eyecups. Rapid en face OCT revealed transient IOS almost immediately (<3 ms) after the onset of visible light flashes at photoreceptor outer segments. Quantitative analysis indicated that the IOS kinetics may reflect dynamics of G-protein binding and releasing in early phases of visual transduction, and high resolution is essential to differentiate positive and negative IOS changes in adjacent locations.

In vivo confocal intrinsic optical signal identification of localized retinal dysfunction

PURPOSE

The purposes of this study were to investigate the physiological mechanism of stimulus-evoked fast intrinsic optical signals (IOSs) recorded in dynamic confocal imaging of the retina, and to demonstrate the feasibility of in vivo confocal IOS mapping of localized retinal dysfunctions.

METHODS

A rapid line-scan confocal ophthalmoscope was constructed to achieve in vivo confocal IOS imaging of frog (Rana pipiens) retinas at cellular resolution. In order to investigate the physiological mechanism of confocal IOS, comparative IOS and electroretinography (ERG) measurements were made using normal frog eyes activated by variable-intensity stimuli. A dynamic spatiotemporal filtering algorithm was developed to reject the contamination of hemodynamic changes on fast IOS recording. Laser-injured frog eyes were employed to test the potential of confocal IOS mapping of localized retinal dysfunctions.

RESULTS

Comparative IOS and ERG experiments revealed a close correlation between the confocal IOS and retinal ERG, particularly the ERG a-wave, which has been widely used to evaluate photoreceptor function. IOS imaging of laser-injured frog eyes indicated that the confocal IOS could unambiguously detect localized (30 μm) functional lesions in the retina before a morphological abnormality is detectable.

CONCLUSIONS

The confocal IOS predominantly results from retinal photoreceptors, and can be used to map localized photoreceptor lesion in laser-injured frog eyes. We anticipate that confocal IOS imaging can provide applications in early detection of age-related macular degeneration, retinitis pigmentosa, and other retinal diseases that can cause pathological changes in the photoreceptors.

Male sex, erythema nodosum, and electroretinography as predictors of visual prognosis after cataract surgery in patients with Behçet disease

PURPOSE

To evaluate factors that predict the visual prognosis after cataract surgery in patients with Behçet disease.

SETTING

The First Affiliated Hospital of Chongqing Medical University, Chongqing, China.

DESIGN

Retrospective clinical study.

METHODS

Patients with Behçet disease and complicated cataract had phacoemulsification and intraocular lens implantation between September 2008 and March 2011. Analyzed were the corrected distance visual acuity (CDVA), full-field electroretinogram (ERG) results, intraocular inflammation, extraocular manifestations, and complications before and after surgery.

RESULTS

Twenty-one men (26 eyes) and 6 women (10 eyes) Behçet disease patients with complicated cataract were enrolled. There were no postoperative complications, although a mild to moderate anterior chamber reaction occurred in all patients. At the last visit, the CDVA was improved in 35 eyes. Twenty-seven eyes (75%) achieved a final CDVA of 0.1 or better. No female patient had obvious fundus complications, and all female patients achieved a final CDVA of 0.25 or better. The common causes for poor visual prognosis were optic atrophy, atrophy of the retina, and cystoid macular edema. Eyes with marked ERG a-wave and b-wave abnormalities had a significantly worse postoperative CDVA. Seven (10 eyes) of 8 patients (11 eyes) with a history of erythema nodosum had a postoperative visual acuity below 0.1.

CONCLUSIONS

Phacoemulsification and IOL implantation in patients with Behçet disease can be safely and successfully performed in quiet eyes. A poor visual prognosis was associated with male sex, severe fundus complications, and erythema nodosum and could be predicted by ERG abnormalities.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Electroretinographic findings associated with panretinal photocoagulation (PRP) versus PRP plus intravitreal ranibizumab treatment for high-risk proliferative diabetic retinopathy

To evaluate changes in electroretinographic (ERG) findings after panretinal photocoagulation (PRP) compared to PRP plus intravitreal injection of ranibizumab (IVR) in eyes with high-risk proliferative diabetic retinopathy (PDR). Patients with high-risk PDR and no prior laser treatment were assigned randomly to receive PRP (PRP group; n = 9) or PRP plus IVR (PRPplus group; n = 11). PRP was administered in two sessions (weeks 0 and 2), and IVR was administered at the end of the first laser session (week 0) in the PRPplus group. Standardized ophthalmic evaluations including (ETDRS) best-corrected visual acuity (BCVA), and fluorescein angiography to measure area of fluorescein leakage (FLA), were performed at baseline and at weeks 16 (±2), 32 (±2) and 48 (±2). ERG was measured according to ISCEV standards at baseline and at week 48 (±2). At 48 weeks, 2,400-3,000 laser spots had been placed in eyes in the PRP group, while only 1,400-1,800 spots had been placed in the PRPplus group. Compared to baseline, there was a statistically significant (P < 0.05) FLA reduction observed at all study visits in both groups, with the reduction observed in the PRPplus group significantly larger than that in the PRP group at week 48. ROD b-wave amplitude was significantly reduced to 46 ± 5% (P < 0.05) of baseline in the PRP group and 64 ± 6% (P < 0.05) in the PRPplus group. This reduction was significantly larger in the PRP group than in the PRPplus group (P = 0.024; t Test). Similar results were observed for the dark-adapted Combined Response (CR) b-wave amplitude, with a reduction at 48 weeks compared to baseline of 45 ± 4% in the PRP group and 62 ± 5% in the PRPplus group; the reduction in CR b-wave amplitude was significantly larger in the PRP group than in the PRPplus group (P = 0.0094). CR a-wave, oscillatory potentials, cone single flash, and 30 Hz flicker responses showed statistically significant within-group reductions, but no differences in between-group analyses. These results suggest that treating high-risk PDR with PRP plus IVR is effective for PDR control, and permits the use of less extensive PRP which, in turn, induces less retinal functional loss, in particular for rod-driven post-receptoral responses, than treatment with PRP alone.

Comparative intrinsic optical signal imaging of wild-type and mutant mouse retinas

Functional measurement is important for retinal study and disease diagnosis. Transient intrinsic optical signal (IOS) response, tightly correlated with functional stimulation, has been previously detected in normal retinas. In this paper, comparative IOS imaging of wild-type (WT) and rod-degenerated mutant mouse retinas is reported. Both 2-month and 1-year-old mice were measured. In 2-month-old mutant mice, time course and peak value of the stimulus-evoked IOS were significantly delayed (relative to stimulus onset) and reduced, respectively, compared to age matched WT mice. In 1-year-old mutant mice, stimulus-evoked IOS was totally absent. However, enhanced spontaneous IOS responses, which might reflect inner neural remodeling in diseased retina, were observed in both 2-month and 1-year-old mutant retinas. Our experiments demonstrate the potential of using IOS imaging for noninvasive and high resolution identification of disease-associated retinal dysfunctions. Moreover, high spatiotemporal resolution IOS imaging may also lead to advanced understanding of disease-associated neural remodeling in the retina.

Oxidative stress in preretinopathic diabetes subjects and antioxidants

BACKGROUND

This study assessed the effect of a systemic oral treatment with antioxidants (AOs) in preretinopathic diabetes (PRD) patients, through the evaluation of oxidative stress in plasma and changes in the full-field electroretinogram (ERG).

METHODS

Thirty-two PRD subjects with good metabolic control were recruited. Patients were randomized in two groups, one of which received oral AO treatment with α-lipoic acid at 400 mg/day in association with genistein and vitamins, whereas the other group received a placebo. Free radicals and the AO barrier were evaluated in plasma with the Free Radical Analytical System 4 instrument (H&D srl, Parma, Italy), and the same day the electrophysiological response was measured by ERG. These analyses were performed at enrollment and after 30 days of treatment.

RESULTS

Statistically significant increases of plasma AO levels and ERG oscillatory potential values were observed in the group treated with AO, but not in the control group.

CONCLUSIONS

Results of this preliminary study suggest that an oral treatment with AOs in PRD subjects may have a protective effect on retinal cells, as detected by ERG analysis, through the strengthening of the plasma AO barrier.

Vitamin D rejuvenates aging eyes by reducing inflammation, clearing amyloid beta and improving visual function

Vitamin D(3) plays a key role in immune regulation and may protect against the aging process. A focal point for age-related changes is the outer retina of the eye where there is high metabolic demand resulting in a gradual increase in extracellular deposition, inflammation, and cell loss giving rise to visual decline. Here, we demonstrate that vitamin D(3) administration for only 6 weeks in aged mice significantly impacts on this aging process. Treated mice showed significant reductions in retinal inflammation and levels of amyloid beta (Aβ) accumulation, which is a hallmark of aging. They also had significant reductions in retinal macrophage numbers and marked shifts in their morphology. These changes were reflected in a significant improvement in visual function, revealing that vitamin D(3) is a route to avoiding the pace of age-related visual decline. Excess amyloid beta deposition and inflammation are risk factors leading to age-related macular degeneration (AMD), the largest cause of blindness in those older than 50 years in developed countries. Recently, vitamin D(3) has been linked epidemiologically to protection against age-related macular degeneration. Hence, vitamin D(3) enrichment is likely to represent a beneficial route for those at risk.

In vivo confocal imaging of fast intrinsic optical signals correlated with frog retinal activation

Using freshly isolated animal retinas, we have conducted a series of experiments to test fast intrinsic optical signals (IOSs) that have time courses comparable to electrophysiological kinetics. In this Letter, we demonstrate the feasibility of in vivo imaging of fast IOSs in intact frogs. A rapid line-scan confocal ophthalmoscope was constructed to achieve high-speed IOS recording. By rejecting out-of-focus background light, the line-scan confocal imager provided the resolution to differentiate individual photoreceptors in vivo. Rapid confocal imaging disclosed robust IOSs with time courses comparable to retinal electroretinogram kinetics. High-resolution IOS images revealed both positive (increasing) and negative (decreasing) light responses, with subcellular complexity.

Retinal disorders

The retina represents part of the central nervous system (CNS). After modifying the neural signal, the axon of the last neuron enters the optic nerve and leaves the eye. In most cases of retinal disease leading to visual loss, the diagnosis will be made by an ophthalmologist after examining the ocular fundus. Some retinal disorders, however, might not be detectable at the time of examination. Those patients will be referred to a neurologist for "unexplained visual loss" when suspecting a lesion behind the optic nerve. Moreover, knowledge of potential retinal abnormalities is useful for the neurologist when seeing patients with CNS disease, which can manifest itself also in the retina. This chapter aims to give an overview about retinal disorders causing no or only few retinal abnormalities, those associated with neurological diseases, as well as the most important retinal diseases involving the tissues of the ocular fundus (vitreous body, retina, pigment epithelium, and the choroid). The most frequently used examination techniques and diagnostic tools are described. Tumors, vascular disease, especially diabetic retinopathy, age-related macular degeneration, chorioretinal inflammatory and toxic disorders, paraneoplastic retinopathies, inherited retinal dystrophies, and retinal involvement in CNS disease such as phakomatoses and multiple sclerosis are discussed.

Multifocal electroretinography

Multifocal electroretinography (mfERG) provides functional and objective evidence of retinal dysfunction. We have found mfERG to be especially useful in the management of occult outer retinopathy and Stargardt's disease.

High spatiotemporal resolution imaging of fast intrinsic optical signals activated by retinal flicker stimulation

High resolution monitoring of stimulus-evoked retinal neural activities is important for understanding retinal neural mechanisms, and can be a powerful tool for retinal disease diagnosis and treatment outcome evaluation. Fast intrinsic optical signals (IOSs), which have the time courses comparable to that of electrophysiological activities in the retina, hold the promise for high resolution imaging of retinal neural activities. However, application of fast IOS imaging has been hindered by the contamination of slow, high magnitude optical responses associated with transient hemodynamic and metabolic changes. In this paper we demonstrate the feasibility of separating fast retinal IOSs from slow optical responses by combining flicker stimulation and dynamic (temporal) differential image processing. A near infrared flood-illumination microscope equipped with a high-speed (1000 Hz) digital camera was used to conduct concurrent optical imaging and ERG measurement of isolated frog retinas. High spatiotemporal resolution imaging revealed that fast IOSs could follow flicker frequency up to at least 6 Hz. Comparable time courses of fast IOSs and ERG kinetics provide evidence that fast IOSs are originated from stimulus activated retinal neurons.

Fundus white spots and acquired night blindness due to vitamin A deficiency

To report a successfully treated case of acquired night blindness associated with fundus white spots secondary to vitamin A deficiency. An ocular examination, electrophysiologic testing, as well as visual field and OCT examinations were obtained on a 61-year-old man with vitamin A deficiency who had previously undergone gastric bypass surgery. The patient had a re-evaluation after treatment with high doses of oral vitamin A. The patient was observed to have numerous white spots in the retina of each eye. Best-corrected visual acuity was initially 20/80 in each eye, which improved to 20/40-1 OU after oral vitamin A therapy for 2 months. Full field electroretinogram (ERG) testing, showed non-detectable rod function and a 34 and 41% reduction for 32-Hz flicker and single flash cone responses, respectively, below the lower limits of normal. Both rod and cone functions markedly improved after initiation of vitamin A therapy. Vitamin A deficiency needs to be considered in a patient with white spots of the retina in the presence of poor night vision.

ERGs in children with pancreatic enzyme insufficient and pancreatic enzyme sufficient cystic fibrosis

OBJECTIVES

We recorded scotopic and photopic flash electroretinograms (ERGs) in pediatric subjects with cystic fibrosis, aged 4 to 18 years, who were either pancreatic insufficient (PI) or pancreatic sufficient (PS). The aim of the study was to determine whether vitamin supplementation in the PI group allowed comparable retinal function in these two groups.

METHODS

ERGs were recorded from a mixed-gender group of 41 children and adolescents (4 to 17 years of age) with cystic fibrosis. The subjects were grouped according to pancreatic function into PI (n = 29) and PS (n = 12). Full-field flash ERGs were recorded from one eye using a DTL fiber. The pupil was dilated prior to recording using two drops of 0.5% tropicamide. ISCEV photopic and scotopic stimuli and recording conditions were used. Serum levels of vitamin A, beta carotene and retinol binding protein (RBP) were measured on the day of ERG recording.

RESULTS

There was no significant difference in ERG amplitudes or implicit times between PI and PS groups. Vitamin A, beta carotene, and RBP levels were not significantly different across the two groups and were not correlated with implicit times or amplitudes of any of the ERG types recorded here.

CONCLUSION

Similarity of ERGs across the PI and PS cystic fibrosis patient populations tested here suggests that the supplementation protocol applied to these populations allows similar levels of retinal function (as indicated by flash ERG parameters) in the two groups.

Optical dissection of stimulus-evoked retinal activation

Better understanding of stimulus-evoked intrinsic optical signals (IOSs) in the retina promises new methodology for study and diagnosis of retinal function. Using a flood-illumination near infrared (NIR) light microscope equipped with high-speed CCD (80 Hz) and CMOS (1000 Hz) cameras, we validated depth-resolved enface imaging of fast IOSs in isolated retina of leopard frog. Both positive (increasing) and negative (decreasing) IOSs were observed at the photoreceptor and inner layers of the retina. The distribution of IOSs with opposite polarities showed a center-surround pattern. At the photoreceptor layer, negative IOSs dominated the center area illuminated by the stimulus light spot, while positive signals dominated the surrounding area. In contrast, at inner retinal layers, positive IOSs dominated the center area covered by the stimulus light spot, and negative IOSs were mainly observed in the surrounding area. Fast CMOS imaging disclosed rapid IOSs within 5 ms after the stimulus onset, and both ON and OFF optical responses were observed associated with a step light stimulus.

Cancer-associated retinopathy (CAR) with electronegative ERG: a case report

Cancer-associated retinopathy (CAR) should be suspected in patients who present with visual symptoms such as rapid unexplained visual loss and seeing shimmering lights, with an abnormal ERG. Electronegative ERG responses are not exclusive to melanoma-associated retinopathy (MAR) but may be seen in CAR as well. We describe a patient with CAR who presented with an electronegative ERG. A 67-year old woman, who presented with complaints of seeing shimmering lights, underwent an extensive ophthalmological and electrophysiological examination. Best-corrected visual acuity was 7/10 in the right and 9/10 in the left eye. Goldmann visual fields showed relative central scotomata and concentric narrowing. Slit-lamp and fundus examination were normal as was fluorescein angiography. Rod-specific ERG responses were severely reduced, with electronegative maximal combined rod-cone responses and delayed cone-responses with normal amplitudes. Melanoma-associated retinopathy was suspected. Extensive dermatological and internal evaluation eventually revealed an oat-cell carcinoma in the right lung. The patient died of pneumonia 2 years after presentation.

Safety monitoring in bevacizumab (Avastin) treatment: retinal function assessed by psychophysical (visual fields, colour vision) and electrophysiological (ERG/EOG) tests in two subgroups of patients

BACKGROUND

Bevacizumab (Avastin) has been used as off-label treatment for the specific inhibition of the vascular endothelial growth factor (VEGF). Although only intravenous administration of the drug is approved in combination therapy of colorectal carcinoma, promising short-term results have been reported about its intravitreal administration. However, VEGF is also known to exhibit neurotrophic capabilities. Therefore, blockage of all VEGF isoforms by bevacizumab could induce toxic effects. Missing randomized controlled studies and unclear long-term risks require further evaluation.

METHODS

Intensified monitoring of bevacizumab treatment was performed in consecutive patients. In ten patients, the functional field score was calculated after obtaining Goldmann visual fields at baseline and 1 year after injection. The other subgroup was examined by means of EOG, ERG and colour testing at baseline and 4 months following treatment. Naka-Rushton plots were calculated to enable statements about retinal function. Lanthony desaturated D15 test was used for repeated colour testing.

RESULTS

Baseline parameters already disclosed predominant cone dysfunction. Drug-related effects caused a significant improvement of visual acuity. There was no sign of clinically relevant retinal toxicity following the bevacizumab injection. No progression of visual field defects was seen within the follow-up of 1 year. Performance in EOG testing was affected by restricted fixation stability, but no parameter indicated deterioration within the 4-month-period.

CONCLUSIONS

Short-term results underline that intraocular bevacizumab injection promises to be not only a cost-effective, but safe treatment option. Assessed functional parameters as error scores (e.g., Lanthony) corresponded to the impaired retinal function which was presumed to be disease-related. Further long-term results have to confirm the good tolerability in repeated treatment.

Frequency spectrum and amplitude analysis of dark- and light-adapted oscillatory potentials in albino mouse, rat and rabbit

We studied frequency spectrum, implicit time and amplitude of oscillatory potentials (OPs) in albino mice, rats, and rabbits. Oscillatory potentials were extracted digitally from dark- and light-adapted electroretinograms (ERGs) recorded with a protocol commonly used in our laboratory. The frequency spectra of OPs were analyzed by using Fast Fourier Transform (FFT). Oscillatory potential amplitudes were calculated via numerically integrating the power spectrum. Oscillatory potential frequency spectra vary among species and are light-intensity dependent. In dark-adapted ERG, mouse and rat OPs have one major component with a frequency peak at approximately 100 Hz. Rabbits show multiple frequency peaks with a low frequency peak around 75 Hz. In all the three species, the implicit time of light-adapted OP is longer than that of the dark-adapted OPs. At a given intensity, mice have the highest OP responses. Our data suggest that the commonly used bandpass of 75 Hz (or even 100 Hz) to 300 Hz for OP extraction is insufficient in these animals. In order to acquire the complete OP responses from the ERG signals, it is necessary to determine the OP frequency spectrum. In this study, the lower end cutoff frequency was set at 40 Hz in mice, 65 Hz in rats and rabbits.

Optophysiology: depth-resolved probing of retinal physiology with functional ultrahigh-resolution optical coherence tomography

Noncontact, depth-resolved, optical probing of retinal response to visual stimulation with a <10-microm spatial resolution, achieved by using functional ultrahigh-resolution optical coherence tomography (fUHROCT), is demonstrated in isolated rabbit retinas. The method takes advantage of the fact that physiological changes in dark-adapted retinas caused by light stimulation can result in local variation of the tissue reflectivity. fUHROCT scans were acquired from isolated retinas synchronously with electrical recordings before, during, and after light stimulation. Pronounced stimulus-related changes in the retinal reflectivity profile were observed in the inner/outer segments of the photoreceptor layer and the plexiform layers. Control experiments (e.g., dark adaptation vs. light stimulation), pharmacological inhibition of photoreceptor function, and synaptic transmission to the inner retina confirmed that the origin of the observed optical changes is the altered physiological state of the retina evoked by the light stimulus. We have demonstrated that fUHROCT allows for simultaneous, noninvasive probing of both retinal morphology and function, which could significantly improve the early diagnosis of various ophthalmic pathologies and could lead to better understanding of pathogenesis.