Photodynamic Therapy for Choroidal Neovascularization in Patients with Multifocal Choroiditis and Panuveitis

Purpose

To evaluate the visual benefit of photodynamic therapy (PDT) with verteporfin in patients with choroidal neovascularization (CNV) secondary to multifocal choroiditis and panuveitis over a longer follow-up period.

Methods

A total of 14 eyes of 12 patients (mean age 34 years) with a classic subfoveal CNV (13/14) or juxtafoveal CNV (1/14) were treated with PDT Visual outcome was assessed by best-corrected visual acuity (VA). Morphologic characteristics of CNVs such as localization, size, and activity were monitored by fluorescein angiography.

Results

Patients were followed for 3 to 45 months (mean 23 months). During this period, one to six PDTs (mean 2.4) were performed. At the time of the first PDT no acute inflammation was seen in the affected eyes. Improved or stabilized visual function (VA loss ≤ 2 lines in the Early Treatment Diabetic Retinopathy Study chart) was observed in 71.4% of the eyes. A total of 78% of the eyes showed an inactive scar in the area of CNV after PDT. Treatment failure after PDT occurred due to uninfluenced CNV growth. No further complications were observed.

Conclusions

PDT in subfoveal or juxtafoveal classic CNV secondary to multifocal choroiditis and panuveitis stabilized or improved VA in the majority of patients over a longer follow-up period. No risk factor for failed VA rehabilitation could be defined.

Generation and characterization of electron bunches with ramped current profiles in a dual-frequency superconducting linear accelerator

We report on the successful experimental generation of electron bunches with ramped current profiles. The technique relies on impressing nonlinear correlations in the longitudinal phase space using a superconducing radio frequency linear accelerator operating at two frequencies and a current-enhancing dispersive section. The produced ~700-MeV bunches have peak currents of the order of a kilo-Ampère. Data taken for various accelerator settings demonstrate the versatility of the method and, in particular, its ability to produce current profiles that have a quasilinear dependency on the longitudinal (temporal) coordinate. The measured bunch parameters are shown, via numerical simulations, to produce gigavolt-per-meter peak accelerating electric fields with transformer ratios larger than 2 in dielectric-lined waveguides.

BBS genotype-phenotype assessment of a multiethnic patient cohort calls for a revision of the disease definition

Bardet-Biedl syndrome (BBS) is a ciliopathy characterized by retinal degeneration, obesity, polydactyly, renal abnormalities, and cognitive impairment for which 15 causative genes have been identified. Here we present the results of a mutational analysis of our multiethnic cohort of 83 families (105 cases); 75.9% of them have their mutations identified including 26 novel changes. Comprehensive phenotyping of these patients demonstrate that the spectrum of clinical features is greater than expected and overlapped with the features of other ciliopathies; specifically Alström and McKusick-Kauffman syndromes.

Mutations in chaperonin-like BBS genes are a major contributor to disease development in a multiethnic Bardet-Biedl syndrome patient population

BACKGROUND

Bardet-Biedl syndrome is a pleiotropic disorder with 14 BBS genes identified. BBS1, BBS2, BBS4, BBS5, BBS7, BBS8, and BBS9 form a complex called the BBSome, which is believed to recruit Rab8(GTP) to the primary cilium and promote ciliogenesis. The second group, the chaperonin-like proteins BBS6, BBS10, and BBS12, have been defined as a vertebrate-specific branch of the type II chaperonin superfamily. These may play a role in the regulation of BBSome assembly.

METHODS AND RESULTS

Using sequence analysis, the role of BBS6, 10 and 12 was assessed in the patient population comprising 93 cases from 74 families. Systemic and ocular phenotypes were defined. In the study, chaperonin-like BBS gene mutations accounted for the disease in approximately 36.5% of BBS families. A total of 38 different non-polymorphic exonic sequence variants were identified in 40.5% of BBS families (41.9% cases), of which 26 were novel (68%). Six cases had mutations present in more than one chaperonin-like BBS gene. One case with four mutations in BBS10 had a phenotype of overall greater severity. The phenotypes observed were beyond the classic BBS phenotype as they overlapped with characteristics of MKKS (congenital heart defect, vaginal atresia, hydrometrocolpos, cryptorchidism), as well as Alström syndrome (diabetes, hearing loss, liver abnormalities, endocrine anomalies, cardiomyopathy).

CONCLUSIONS

While overlap between the MKKS and BBS phenotypes has previously been reported for cases with BBS6 mutations, we also observed MKKS phenotypes involving BBS10 and BBS12 and Alström-like phenotypes associated with mutations in BBS1, BBS2, BBS6, BBS7, BBS9, BBS10 and BBS12 for the first time.

Ocular phenotype in patients with methylmalonic aciduria and homocystinuria, cobalamin C type

PURPOSE

To assess and compare longitudinal visual function and retinal morphology in patients with methylmalonic aciduria with homocystinuria, cobalamin C type (cblC), and identified mutations in the MMACHC gene.

METHODS

Vision function, anterior segment, and fundi were evaluated in patients with homozygous or compound heterozygous MMACHC mutations. Best-corrected visual acuity, full-field electroretinogram (ERG), refractive error, and retinopathy were assessed and compared for different genotypes and ages at onset, defined as early (<1 year of age) or late (>5 years).

RESULTS

We identified 7 patients (homozygous mutation: 6 of 7; compound heterozygous mutations: 1 of 7) between the ages of 3 months and 20.6 years. Six patients were reexamined after 3.2 to 11.5 years (mean, 6.5) Ocular phenotype ranged from normal to severely compromised visual function. Visual acuity was reduced from 0.2 logMAR to counting fingers and from 0.0 to 0.3 logMAR in the early- (3 of 7) and in the late-onset group (4 of 7), respectively. No retinopathy was evident in the late-onset group. Only patients with the homozygous c.547_548 delGT mutations (n = 2) demonstrated advanced retinopathy associated with cone-rod or rod-cone dysfunction. Retinopathy occurred despite systemic treatment for cblC.

CONCLUSIONS

Ocular phenotype in patients with cblC is variable. Ocular involvement seems to be correlated with age at onset. Patients with early-onset cblC developed generally progressive retinal disease ranging from subtle retinal nerve fiber layer loss to advanced macular and optic atrophy with "bone spicule" pigmentation. Patients with late-onset disease showed no definite evidence of retinal degeneration.

Detailed analysis of retinal function and morphology in a patient with autosomal recessive bestrophinopathy (ARB)

The objective of the paper is to study the retinal microstructure and function in a patient with autosomal recessive bestrophinopathy (ARB). Retinal function and morphology assessment in a patient diagnosed with a biallelic mutation in the BEST1 gene (heterozygote mutations: Leu88del17 and A195V) included: full-field electroretinogram (ffERG) and multifocal electroretinogram (mfERG), electro-oculogram (EOG) testing, and imaging with a high-resolution Fourier-domain optical coherence tomography (Fd-OCT) system (UC Davis Medical Center; axial resolution: 4.5 microm, acquisition speed: 9 frames/s, 1,000 A-scans/frame) combined with a flexible scanning head (Bioptigen Inc.). The 11-year old asymptomatic boy showed a well-demarcated retinopathy with deposits. Functional assessment revealed normal visual acuity, reduced central mfERG responses, delayed rod and rod-cone b-wave ffERG responses, and reduced light rise in the EOG. Fd-OCT demonstrated RPE deposits, photoreceptor detachment, elongated and thickened photoreceptor outer segments, but preserved inner retinal layers. In conclusion, ARB associated retinal dystrophy shows functional and morphological changes that overlap with classic Best disease. For the first time, high-resolution imaging provided in vivo evidence of RPE and photoreceptor involvement in ARB.

Timing of surgery for infantile esotropia in humans: effects on cortical motion visual evoked responses

PURPOSE

Infantile esotropia is associated with maldevelopment of cortical visual motion processing, manifested as directional asymmetry of motion visual evoked potentials (mVEPs). The purpose of this study was to determine whether early surgery at or before age 11 months could promote the development of cortical visual motion processing in human infants, compared with standard surgery at age 11 to 18 months.

METHODS

Sixteen children with a constant, infantile esotropia >or=30 prism diopters and onset before age 6 months were recruited prospectively. Eight of them underwent early surgery at

RESULTS

The mean asymmetry index and interocular phase difference in the early surgery group were comparable to that in age-matched control subjects, and they were significantly lower than those in the standard surgery group.

CONCLUSIONS

Early surgery for infantile esotropia promotes the development of cortical visual motion processing, whereas standard surgery is associated with abnormal mVEPs. The results provide additional evidence that early strabismus repair is beneficial for cortical development in human infants.

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MESH Headings

• Evoked Potentials, Visual/physiology
• Eye Movements/physiology
• Female
• Humans
• Infant
• Male
• Motion Perception/physiology
• Nystagmus, Congenital/physiopathology
• Nystagmus, Congenital/surgery
• Oculomotor Muscles/surgery
• Prospective Studies
• Tendons/surgery
• Time Factors
• Visual Cortex/physiology

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Grants

• 67104 CIHR

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Retinal morphological changes of patients with X-linked retinoschisis evaluated by Fourier-domain optical coherence tomography

OBJECTIVE

To investigate the retinal microstructure and lamination of patients affected with X-linked retinoschisis (XLRS) using high-resolution imaging modalities.

METHODS

Patients diagnosed as having XLRS underwent assessment. Visual function testing included visual acuity, color vision, and full-field electroretinography. We used a high-resolution Fourier-domain optical coherence tomography (FD-OCT) system (4.5-mum axial resolution; 9 frames/s; 1000 A-scans per frame) combined with a handheld scanner. Macular image evaluation included schisis localization and retinal layer integrity.

RESULTS

Six patients with XLRS and identified mutations in the XLRS1 gene underwent testing. Visual acuity ranged from 0.2 to 1.6 logMAR (logarithm of the minimum angle of resolution). Results of FD-OCT revealed foveal schisis extending from the outer to the inner plexiform layer in 4 of 6 patients. Bullous foveal schisis was associated with younger age. All patients showed extrafoveal schisis within the outer and inner nuclear and ganglion cell layer, alone or in combination. Photoreceptor outer and inner segment layers were disrupted and irregular in all patients.

CONCLUSIONS

Retinal dystrophy in XLRS is reflected by morphological changes within the inner and outer retinal layers. Disturbed foveal photoreceptor integrity was identified in all patients. Retinal layer abnormalities correlated with age but did not appear to correlate with visual acuity or genotypic variation.

The role of the ERG in the diagnosis and treatment of Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is affecting an increasing number of people, with 2.95 million people estimated to be affected in the USA by 2020. Possible preventive agents, such as vitamins and supplements have been studied and new treatment options for AMD have been developed in recent years. What role does electrophysiology play as a sensitive outcome measure? The most commonly used tests are the full-field electroretinogram (ffERG) and the multifocal ERG (mfERG). Test results from patients with AMD and reduced central vision need special attention in respect to fixation pattern, age-matched control data, and retinal luminance. Advantages, disadvantages and limitations of techniques will be considered, together with a review of published studies.

A comparison of signal detection techniques in the multifocal electroretinogram

A common task in the analysis of the multifocal electroretinogram (mfERG) is determining which retinal areas have preserved signal in recordings which are attenuated by the effects of disease. Several automated methods have been proposed for signal detection from multifocal recordings, but no systematic study has been published comparing the performance of each. This article compares the sensitivity and specificity of expert human scoring with three different automated methods of mfERG signal detection. Recordings from control subjects were artificially modified to simulate decrease in signal amplitudes (attenuation) as well as total signal loss. Human scorers were able to identify areas with preserved signal at both low and high attenuation levels with a high specificity (minimum 0.99), sensitivities ranged from 0.2 to 0.94. Automated methods based on template correlation performed better than chance at all attenuation levels, with a slide fit method having the best performance. Signal detection based on signal to noise ratio performed poorly. In conclusion automated methods of signal detection can be used to increase signal detection sensitivity in the mfERG.

Retinal morphology in patients with BBS1 and BBS10 related Bardet-Biedl Syndrome evaluated by Fourier-domain optical coherence tomography

Retinal dystrophy in Bardet-Biedl Syndrome (BBS) is caused by defective genes that are expressed within ciliated cells such as photoreceptors. The purpose of this study was to characterize and compare the retinal structure and lamination of two groups of patients, carrying mutations in BBS1 or BBS10. Eight patients with BBS (ages 11.9-28.5 years) and mutations in BBS1 (4/8) or BBS10 (4/8) were tested. A high-resolution hand-held probe Fourier-domain optical coherence tomography system (Fd-OCT) was used for retinal image acquisition. Macular scans were evaluated with respect to structure, retinal layering and photoreceptor integrity. Micro-structural in-vivo analysis showed abnormalities within retinal layers but preserved retinal lamination. Photoreceptor integrity was disrupted in all patients. Macular scans from patients with BBS10 mutations most often showed 'deposits' adjacent and anterior to Bruch's membrane. Age, genotype and presence of macular changes did not correlate with the structural changes observed. Retinal dystrophy in BBS is reflected by major changes in the outer retinal layers. This is the first report of in-vivo micro-structural analysis of retinal layers in patients with BBS. Mutations in different BBS genes seem to be associated with similar micro-structural changes in retinal layers.

Novel RDH12 mutations associated with Leber congenital amaurosis and cone-rod dystrophy: biochemical and clinical evaluations

The purpose of this study was to determine the role of the retinol dehydrogenase 12 (RDH12) gene in patients affected with Leber congenital amaurosis (LCA), autosomal recessive retinitis pigmentosa (arRP) and autosomal dominant/recessive cone-rod dystrophies (CORD). Changes in the promoter region, coding regions and exon/intron junctions of the RDH12 gene were evaluated using direct DNA sequencing of patients affected with LCA (n=36 cases), RP (n=62) and CORD (n=21). The allele frequency of changes observed was assessed in a multiethnic control population (n=159 individuals). Detailed biochemical and structural modeling analysis of the observed mutations were performed to assess their biological role in the inactivation of Rdh12. A comprehensive clinical assessment of retinal structure and function in LCA patients carrying mutations in the RDH12 gene was completed. Of the six changes identified, three were novel including a homozygous C201R change in a patient affected with LCA, a heterozygous A177V change in patients affected with CORD and a heterozygous G46G change in a patient affected with LCA. A novel compound heterozygote T49M/A269fsX270 mutation was also found in a patient with LCA, and both homozygous and heterozygous R161Q changes were seen in 26 patients affected with LCA, CORD or RP. These R161Q, G46G and the A177V sequence changes were shown to be polymorphic. We found that Rdh12 mutant proteins associated with LCA were inactive or displayed only residual activity when expressed in COS-7 and Sf9 cells, whereas those mutants that were considered polymorphisms were fully active. Thus, impairment of retinal structure and function for patients carrying these mutations correlated with the biochemical properties of the mutants.

Assessment of Central Retinal Function in Patients with Advanced Retinitis Pigmentosa

PURPOSE

To assess central retinal function in patients with advanced retinitis pigmentosa (RP) using the multifocal (mf)ERG and static perimetry.

METHODS

Patients with RP; a nonrecordable, full-field (ff)ERG; and visual acuity (VA) of </= 1.0 logMAR were included. All patients underwent mfERG testing (103 hexagons, and 2.67 and 5.33 cd . s . m(-2) flash intensities) and static perimetry (103 corresponding areas) in the better eye. First-order kernel mfERGs were analyzed for total noise, signal-to-noise ratio, response amplitude, and implicit time. The number of areas with recordable mfERG responses were counted and compared with visual field (VF) sensitivity.

RESULTS

Twenty-nine patients aged 16 to 68 years with a VA of 0.02 to 1.0 logMAR and a kinetic VF of 10 degrees to 60 degrees in diameter were included. mfERGs were successfully performed in 22 of 29 patients. Responses were detected in at least one stimulated area in 22 of 22 patients, with an overall response detection of 9.8% in all stimulated areas and no difference between flash intensities. All responses were diminished severely in response density P1-N1, with normal P1 implicit time in 50% of the recordings. No predictive factors for recordable mfERG responses were identified. VF results were recorded reliably in 27 of 29 patients, with a 40% response detection rate.

CONCLUSIONS

mfERG responses were recordable in at least one area in all successfully tested patients with advanced RP. Response detection and performance was significantly higher for static perimetry. Static perimetry may be a more sensitive primary outcome measure of central vision function than the mfERG in patients with advanced RP and nonrecordable ffERGs.

Clinical application of rapid serial fourier-domain optical coherence tomography for macular imaging

PURPOSE

To introduce and examine the utility of a retinal imaging technique using high-speed optical coherence tomography (OCT) for creating a more complete retinal structural map to aid in the evaluation of patients with macular pathology.

DESIGN

Prospective observational case series.

PARTICIPANTS

Five patients with a variety of macular pathologies.

METHODS

Patients were imaged with a Fourier-domain high-speed high-resolution OCT system built at our institution. A sweeping serial OCT B-scan of the macula was acquired to create a detailed retinal structural map. The data were then used to make individual clinical observations.

RESULTS

Rapid serial OCT B-scans produced detailed macular maps for all 5 patients. Diagnoses of imaged patients included macular hole, lamellar macular hole, regressed macular hole or macular microhole, choroidal neovascular membrane (CNV) from age-related macular degeneration, and CNV from presumed ocular histoplasmosis syndrome. Reconstructed B-scans and C-scans are shown for selected patients to illustrate the additional perspectives gained by obtaining a detailed retinal map.

CONCLUSIONS

Rapid serial Fourier-domain OCT B-scanning can be used to create a detailed retinal structural map. This technique provides additional information that can be missed on single OCT images and provides an accurate way to image large or complex lesions, and allows B-scan and C-scan reconstructions to be made that provide additional perspectives into retinal structures that may be missed using traditional imaging methods.

Cone-mediated multifocal electroretinogram in age-related macular degeneration: progression over a long-term follow-up

OBJECTIVE

To evaluate the progression of change in the cone-driven multifocal electroretinogram (mfERG) responses in patients previously identified as having high-risk, soft drusen 63 mum or greater.

METHODS

Seventeen eyes of 14 patients were reevaluated after 28 to 41 months. Fundus changes were graded depending on drusen size and extent. Each of the 103 mfERG responses was analyzed and compared with age-matched normal controls and with the baseline measurement.

RESULTS

Stable visual acuity was found in 12 of the 17 eyes. Drusen size or extent was increased, decreased, and unchanged in 6, 3, and 8 eyes, respectively. The mfERG responses demonstrated a significant progression in the response density loss and in N1 and P1 implicit time delay compared with the baseline evaluation regardless of drusen change. The extent of response deterioration occurred over the entire retinal area tested. Eyes having decreased drusen at follow-up were typically associated with higher response delays at baseline and follow-up than eyes with stable or increased drusen.

CONCLUSIONS

Early age-related macular degeneration is associated with a progressive loss in the cone-driven mfERG response despite stable visual acuity. The response deterioration extended beyond the visible drusen area. Implicit times seem to be an important predictor of drusen regression.

Impact of intravenous oxygen therapy on the expression of reticulocyte-type 15-lipoxygenase in human volunteers

Intravenous oxygen infusion is used in complementary medicine to fight inflammatory disorders and repeated application of this therapeutic method leads to an increase in eosinophilic granulocytes in the peripheral blood. Since this subset of human peripheral leukocytes are known to express large amounts of the reticulocyte-type 15-lipoxygenase (15-lipoxygenase 1), which was suggested to exhibit anti-inflammatory activities, we profiled expression of this enzyme in the peripheral blood during the time course of typical oxygen infusion therapy. For this purpose seven volunteers were treated with intravenous infusion of oxygen gas for 4 weeks and the time-course of 15-lipoxygenase expression as well as the eosinophil count were monitored during and after the treatment interval. We found that 15-lipoxygenase 1 expression and the eosinophil count were significantly increased during the treatment period but returned to normal after the therapy was stopped. There was a striking correlation between the relative number of 15-lipoxygenase transcripts and the eosinophil counts suggesting eosinophils as major source of 15-lipoxygenase 1 expression. Since 15-lipoxygenase has been implicated in the resolving phase of acute inflammatory diseases the anti-inflammatory effects of intravenous oxygen infusion may be explained at least in part by our experimental findings.

Lutein, zeaxanthin, macular pigment, and visual function in adult cystic fibrosis patients

BACKGROUND

Pancreatic insufficiency in cystic fibrosis (CF), even with replacement pancreatic enzyme therapy, is often associated with decreased carotenoid absorption. Because the macular pigment of the retina is largely derived from 2 carotenoids, lutein and zeaxanthin, the decreased serum concentrations seen in CF may have consequences for ocular and retinal health

OBJECTIVES

Our aims were to determine plasma carotenoid concentrations, determine absorption and distribution of macular pigment, and assess retinal health and visual function in CF patients.

DESIGN

In 10 adult CF patients (ages 21-47 y) and 10 age- and sex-matched healthy control subjects, we measured macular pigment density in vivo, measured serum lutein and zeaxanthin concentrations, and comprehensively assessed visual performance (including contrast sensitivity, color discrimination, and retinal function) under conditions of daylight illumination.

RESULTS

Serum lutein and zeaxanthin were significantly reduced (P < 0.005) in CF patients ( +/- SD: 87 +/- 36.1 and 27 +/- 15.8 nmol/L, respectively) compared with control subjects (190 +/- 72.1 and 75 +/- 23.6 nmol/L, respectively). Although macular pigment optical density was significantly lower (P < 0.0001) in the CF group (0.24 +/- 0.11) than in the control group (0.53 +/- 0.12), no significant differences in visual function were observed.

CONCLUSIONS

Adults with CF have dramatically low serum and macular concentrations of carotenoids (lutein and zeaxanthin), but their ocular status and visual function are surprisingly good. The clinical implications of low plasma concentrations of carotenoids in CF are yet to be clarified.

Senescence of human multifocal electroretinogram components: a localized approach

BACKGROUND

Previous studies have shown significant age-related changes in the first-order kernel of multifocal ERG (mfERG) responses. All of these reports were based upon ring averages across the retinal field. This study was carried out to determine age-related changes in the localized response and localized variability in the mfERG parameters: N1P1 amplitude, scalar product and implicit time of P1.

METHODS

MfERG recordings from 70 normal phakic subjects (ages 9-80 years) were analyzed with VERIS 4.8. Scalar product values (for each hexagon based on ring average templates) were obtained and analyzed for age-related changes. Statistical measures such as coefficient of variation (CV) and parameters of a linear regression model were applied. Point-by-point comparisons were made across hemifields.

RESULTS

Each localized response showed a significant aging effect either in scalar product or in N1P1 amplitude. The average decline of the response was approximately 5% per decade, varying from 3.3% (peripherally) to 7.5% (perifoveally). The decline was significantly higher for the superior than for the inferior retina for amplitude parameters, corresponding to larger increases in P1 implicit time. The relative rate of change with age was similar for the nasal and the temporal retina. The average CV for all subjects at all locations was 29.4% (+/-4.1%).

CONCLUSIONS

The localized approach revealed patterns of age-related change that were not apparent in the ring averages. Information about changes in discrete retinal areas with age should make the mfERG more useful in quantitatively monitoring progression of retinal disease.

Assessment of multifocal electroretinogram abnormalities and their relation to morphologic characteristics in patients with large drusen

OBJECTIVES

To determine the extent of functional changes in the first-order kernel multifocal electroretinogram (mfERG) responses in patients with large drusen by means of a localized analysis and to determine correlations between mfERG responses and morphologic changes.

METHODS

Thirty-one eyes from 20 patients ages 58 to 84 years with large drusen (> or =5 drusen > or =63 microm diameter) were studied. The mfERGs were recorded with a stimulus of 103 hexagons and a flash intensity of 2.67 candela (cd).s-1.m-2. Each of the 103 single first-order kernel mfERG responses was analyzed and compared with those of age-matched healthy control subjects. Imaging studies, including color stereo fundus photography, red-free fundus photography, and fluorescein angiography, were performed in all patients, and morphologic changes (drusen in red-free fundus photography, staining or window defect in fluorescein angiography) were determined with a digital measurement tool. The mfERG responses were correlated to areas with and without morphologic changes.

RESULTS

Reduced responses were found in 10.0% (scalar products) and 4.0% (response densities) and delayed implicit times in 13.8% (N1), 18.9% (P1), and 23.8% (N2) of all mfERGs. Abnormal mfERG responses extended up to 25 degrees in radius. Significant morphologic-functional relations were detected in only a few patients. Abnormal mfERG variables were present in areas without morphologic changes.

CONCLUSIONS

Patients with large drusen exhibit functional changes in the cone-driven pathways evaluated by the mfERG, indexed particularly by implicit times. Morphologically visible changes do not predict retinal function. Large drusen are associated with a more general retinal dysfunction.

mfERG response dynamics of the aging retina

PURPOSE

To determine age-related changes in retinal response dynamics derived from multifocal electroretinograms (mfERGs).

METHODS

MfERG data were obtained from 70 subjects with normal phakic eyes, age 9 to 80 years. Whereas the first- and higher-order kernels resulting from the mfERG contain detailed information regarding the nonlinear response dynamics of the retina, they do not lend themselves directly to an easy and intuitive interpretation. To achieve a better appreciation of fast adaptive mechanisms and their changes with aging, regional averages of the kernel series were translated at different retinal eccentricities (0 degrees -5 degrees, 5 degrees -15 degrees, and 15 degrees -25 degrees ) into responses generated in different contexts. Specifically, the effect of aging on responses to stimuli presented in isolation was compared with the effect on responses adapted by preceding stimuli ("forward" effect). The interference of the immediately following stimuli with the response generation ("backward effect") was also considered.

RESULTS

Age-related changes were found in the isolated flash response as well as in the backward and forward interactions between consecutive flash responses. Larger fractional changes with age were found in response density than in implicit time, and the rate of change with age was larger for responses to isolated flashes than for responses adapted by preceding flashes.

CONCLUSIONS

Senescent changes in the isolated flash response and in consecutive flash interactions derived from the binary kernel series indicate an aging process at an early stage in the visual system. Mechanisms of retinal adaptation may partially compensate for age-related reductions in the isolated flash response.