Ophthalmic and Genetic Features of Bardet Biedl Syndrome in a German Cohort.

The aim of this study was to characterize the ophthalmic and genetic features of Bardet Biedl (BBS) syndrome in a cohort of patients from a German specialized ophthalmic care center. Sixty-one patients, aged 5−56 years, underwent a detailed ophthalmic examination including visual acuity and color vision testing, electroretinography (ERG), visually evoked potential recording (VEP), fundus examination, and spectral domain optical coherence tomography (SD-OCT). Adaptive optics flood illumination ophthalmoscopy was performed in five patients. All patients had received diagnostic genetic testing and were selected upon the presence of apparent biallelic variants in known BBS-associated genes. All patients had retinal dystrophy with morphologic changes of the retina. Visual acuity decreased from ~0.2 (decimal) at age 5 to blindness 0 at 50 years. Visual field examination could be performed in only half of the patients and showed a concentric constriction with remaining islands of function in the periphery. ERG recordings were mostly extinguished whereas VEP recordings were reduced in about half of the patients. The cohort of patients showed 51 different likely biallelic mutations­of which 11 are novel­in 12 different BBS-associated genes. The most common associated genes were BBS10 (32.8%) and BBS1 (24.6%), and by far the most commonly observed variants were BBS10 c.271dup;p.C91Lfs*5 (21 alleles) and BBS1 c.1169T>G;p.M390R (18 alleles). The phenotype associated with the different BBS-associated genes and genotypes in our cohort is heterogeneous, with diverse features without genotype−phenotype correlation. The results confirm and expand our knowledge of this rare disease.

Characteristics of Retinitis Pigmentosa Associated with ADGRV1 and Comparison with USH2A in Patients from a Multicentric Usher Syndrome Study Treatrush.

In contrast to USH2A, variants in ADGRV1 are a minor cause of Usher syndrome type 2, and the associated phenotype is less known. The purpose of the study was to characterize the retinal phenotype of 18 ADGRV1 patients (9 male, 9 female; median age 52 years) and compare it with that of 204 USH2A patients (111 male, 93 female; median age 43 years) in terms of nyctalopia onset, best corrected visual acuity (BCVA), fundus autofluorescence (FAF), and optical coherence tomography (OCT) features. There was no statistical difference in the median age at onset (30 and 18 years; Mann-Whitney U test, p = 0.13); the mean age when 50% of the patients reached legal blindness (≥1.0 log MAR) based on visual acuity (64 years for both groups; log-rank, p = 0.3); the risk of developing advanced retinal degeneration (patch or atrophy) with age (multiple logistic regression, p = 0.8); or the frequency of cystoid macular edema (31% vs. 26%, Fisher's exact test, p = 0.4). ADGRV1 and USH2A retinopathy were indistinguishable in all major functional and structural characteristics, suggesting that the loss of function of the corresponding proteins produces similar effects in the retina. The results are important for counseling ADGRV1 patients, who represent the minor patient subgroup.

The perception threshold of the panda illusion, a particular form of 2D pulse-width-modulated halftone, correlates with visual acuity.

To call attention to the danger of extinction of the panda bear, the Lithuanian artist Ilja Klemencov created the artwork "They can disappear". The illustration is composed of black-and-white zigzagged lines, which form the famous panda logo of the World Wild Fund For Nature (WWF) when seen from a distance. If one is too close to the artwork, it is difficult to spot the bear, however, if one steps back or takes off one's glasses the panda suddenly appears. This led us to ask if the ability to see the panda is related to the visual acuity of the observer and if therefore, the panda illusion can be used to assess the spatial resolution of the eye. Here we present the results of the comparison between visual acuity determined using the Landolt C and that predicted from the panda illusion in 23 healthy volunteers with artificially reduced visual acuity. Furthermore, we demonstrate that the panda illusion is based on a 2D pulse-width modulation, explain its technical history, and provide the equations required to create the illusion. Finally, we explain why the illusion indeed can be used to predict visual acuity and discuss the neural causes of its perception with best-corrected visual acuity.

Correlating Adaptive Optics Images to Clinical Findings in Juvenile Macular Dystrophy with Hypotrichosis in Siblings with Homozygous CDH3 Pathogenic Variation.

OBJECTIVE: We report on two German siblings diagnosed with congenital hypotrichosis and juvenile macular dystrophy, an extremely rare syndrome affecting both hair growth and visual functions. METHODS: A detailed ophthalmological examination was carried out including fundus examination, visual acuity assessment, visual field determination, color vision testing, and electrophysiology (electroretinography [ERG]). Additionally, fundus photography and autofluorescence imaging (FAF) was performed, along with optical coherence tomography (OCT) and adaptive optics (AO) fundus imaging. Targeted Sanger sequencing and next-generation gene panel sequencing were carried out. RESULTS: Macular dystrophy was evident in the fundus of both patients, as was a central scotoma in the static visual field. The kinetic visual field was normal. The ERG recordings were also normal, but the amplitudes of the multifocal ERG were reduced in the central 4-5° of the retina. The FAF images revealed a large central hypofluorescent area surrounded by a hyperfluorescent ring. The OCT images showed atrophy in the outer layers and tubulations. The AO images depicted a loss of central photoreceptors, as well as severe central atrophy in patient 1. A cone mosaic was observable in the peripheral AO fundus images of both patients. The disrupted cone mosaic on the AO images correlated with the hypofluorescent areas on autofluorescence. DNA testing identified the homozygous, likely pathogenic variant c.1508G>A/p.(Arg503His) (chr16:68719191) in the CDH3 gene. CONCLUSIONS: The two siblings revealed hypotrichosis and macular dystrophy in both eyes. The identification of a homozygous CDH3 mutation in each patient confirms the syndromic entity of hypotrichosis with juvenile macular degeneration.

Ophthalmic features of retinitis pigmentosa in Cohen syndrome caused by pathogenic variants in the VPS13B gene.

PURPOSE: The aim of this study is to report on the phenotype and genotype of five patients diagnosed with Cohen syndrome, an extremely rare autosomal recessive disorder manifesting with mental and physiological defects. METHODS: Five patients from three German families and one Syrian family underwent a comprehensive ophthalmological examination. The scheduled visual acuity measurements, fundus ophthalmoscopy, spectral domain optical coherence tomography (OCT), full-field electrophysiological recordings of scotopic and photopic electroretinograms (ERGs) and colour vision testing could not be carried out in all subjects, because of the mental and physical retardation. The genetic diagnosis was achieved by next-generation sequencing. RESULTS: The ophthalmic and systemic phenotype of the patients is typical for Cohen syndrome including myopia, night blindness, photophobia, fundus pigmentary changes and bull's eye maculopathy. Electroretinograms (ERGs) were extinguished in the four patients, whose recording was possible. Genetic testing revealed homozygous or two heterozygous bi-allelic mutations in the VPS13B (COH1) gene in all five patients, with five different allelic variants observed. The homozygous mutation c.6055_6056delGA; p.Asp2019Glnfs*15 in two sibling patients as well as the homozygous nonsense mutation c.8112C>G;p.Tyr2704* have not previously been reported. CONCLUSIONS: The phenotype of the five patients reported here is typical for Cohen syndrome; however, their genotype is heterogeneous. Two new allelic variants were found to be the causative mutation.

Visual Evoked Potentials Used to Evaluate a Commercially Available Superabsorbent Polymer as a Cheap and Efficient Material for Preparation-Free Electrodes for Recording Electrical Potentials of the Human Visual Cortex.

The aim of this study was to investigate the use of inexpensive and easy-to-use hydrogel "marble" electrodes for the recording of electrical potentials of the human visual cortex using visual evoked potentials (VEPs) as example. Top hat-shaped holders for the marble electrodes were developed with an electrode cap to acquire the signals. In 12 healthy volunteers, we compared the VEPs obtained with conventional gold-cup electrodes to those obtained with marble electrodes. Checkerboards of two check sizes-0.8° and 0.25°-were presented. Despite the higher impedance of the marble electrodes, the line noise could be completely removed by averaging 64 single traces, and VEPs could be recorded. Linear mixed-effect models using electrode type, stimulus, and recording duration revealed a statistically significant effect of the electrode type on only VEP N75 peak latency (mean ± SEM: 1.0 ± 1.2 ms) and amplitude (mean ± SEM: 0.8 ± 0.9 µV) The mean amplitudes of the delta, theta, alpha, beta, and gamma frequency bands of marble electrodes were statistically significantly different and, on average, 25% higher than those of gold-cup electrodes. However, the mean amplitudes showed a statistically significant strong correlation (Pearson's r = 0.8). We therefore demonstrate the potential of the inexpensive and efficient hydrogel electrode to replace conventional gold-cup electrodes for the recording of VEPs and possibly other recordings from the human cortex.

Full-field electroretinography, visual acuity and visual fields in Usher syndrome: a multicentre European study.

PURPOSE: Usher syndrome (USH) is a multisensory deficiency involving vision, hearing and the vestibular system. The purpose of this study is to report on the functional data (i.e. electroretinography, visual fields, visual acuity) of patients with retinitis pigmentosa (RP) due to Usher syndrome that were collected in a multicentre European study (TREATRUSH). METHODS: A total of 268 genetically confirmed USH patients underwent electrophysiological examinations in the context of multimodal ophthalmological examination in the study (75 USH1, 189 USH2 and four USH3). Full-field electroretinography (ERG) was performed according to ISCEV standards, visual field determination was carried out with either the Octopus or Goldmann perimeters and visual acuity was examined with either ETDRS or Snellen charts. The data were compared between USH subtypes (USH1/USH2/USH3) and correlated with age. RESULTS: Visual acuity decreases significantly with age for both USH1 and USH2 (p < 0.001), without a difference between the two cohorts. When corrected for age, the preserved kinetic visual field was significantly larger in USH2 than in USH1 (p = 0.04). Furthermore, the preserved kinetic visual field area showed a significant decrease with age (based on an exponential fit) in both USH1 and USH2 (p < 0.001). In USH1 patients, however, the visual field was already vastly reduced at an early age. The ERG results were abnormal in all patients. Detectable data for scotopic ERG were obtained from nine patients, and data of photopic ERG were obtained from 24 patients, without a difference between USH1 and USH2 subtypes. CONCLUSIONS: There are differences in the phenotypes of RP in USH subtypes, most visible in the progression of visual fields between USH1 and USH2. The perimetric reduction occurs earlier in USH1 than in USH2. In both subtypes, visual acuity decreases significantly with age and the ERG is not detectable already at early ages.

Objective assessment of visual acuity: a refined model for analyzing the sweep VEP.

PURPOSE: The aim of this study was to develop a simple and reliable method for the objective assessment of visual acuity by optimizing the stimulus used in commercially available systems and by improving the methods of evaluation using a nonlinear function, the modified Ricker model. METHODS: Subjective visual acuity in the normal subjects was measured with Snellen targets, best-corrected, and in some cases also uncorrected and with plus lenses (+ 1 D, + 2 D, + 3 D). In patients, subjective visual acuity was measured best-corrected using the Freiburg Visual Acuity Test. Sweep VEP recordings to 11 spatial frequencies, with check sizes in logarithmically equidistant steps (0.6, 0.9, 1.4, 2.1, 3.3, 4.9, 7.3, 10.4, 18.2, 24.4, and 36.5 cpd), were obtained from 56 healthy subjects aged between 17 and 69 years (mean 42.5 ± 15.3 SD years) and 20 patients with diseases of the lens (n = 6), retina (n = 8) or optic nerve (n = 6). The results were fit by a multiple linear regression (2nd-order polynomial) or a nonlinear regression (modified Ricker model) and parameters compared (limiting spatial frequency (sflimiting) and the spatial frequency of the vertex (sfvertex) of the parabola for the 2nd-order polynomial fitting, and the maximal spatial frequency (sfmax), and the spatial frequency where the amplitude is 2 dB higher than the level of noise (sfthreshold) for the modified Ricker model. RESULTS: Recording with 11 spatial frequencies allows a more accurate determination of acuities above 1.0 logMAR. Tuning curves fitted to the results show that compared to the normal 2nd-order polynomial analysis, the modified Ricker model is able to describe closely the amplitudes of the sweep VEP in relation to the spatial frequencies of the presented checkerboards. In patients with a visual acuity better than about 0.5 (decimal), the predicted acuities based on the different parameters show a good match of the predicted visual acuities based on the models established in healthy volunteers to the subjective visual acuities. However, for lower visual acuities, both models tend to overestimate the visual acuity (up to ~ 0.4 logMAR), especially in patients suffering from AMD. CONCLUSIONS: Both models, the 2nd-order polynomial and the modified Ricker model performed equally well in the prediction of the visual acuity based on the amplitudes recorded using the sweep VEP. However, the modified Ricker model does not require the exclusion of data points from the fit, as necessary when fitting the 2nd-order polynomial model making it more reliable and robust against outliers, and, in addition, provides a measure for the noise of the recorded results.

Usher Syndrome and Color Vision.

PURPOSE: The aim of this study is to report on the results of color vision testing in a European cohort of patients with Usher syndrome (USH). We describe the results in relation to Usher type (USH1 and USH2), age and visual acuity. METHODS AND METHODS: The color vision of 220 genetically confirmed adult USH patients, aged 18-70 years, was analyzed with one of three methods: the Farnsworth D-15 Dichotomous test (D-15) along with the Lanthony desaturated 15 Hue tests (D-15d), the Roth 28-Hue test, or the Ishihara 14-plate test. Visual acuity was measured with either the ETDRS or the SNELLEN charts. The Confusion index, the Selectivity index and the Confusion angle were calculated for the panel tests and used for analysis. The numbers of plates that could not be read were analyzed for the Ishihara test. RESULTS: For the panel tests, the degree of color loss (Confusion index) is similar in both subtypes of USH, but the polarization of error scores (Selectivity index) is significantly lower in USH1 than USH2, showing more diffuse errors than those found in USH2. There is no significant correlation between logMAR visual acuity and the Confusion or the Selectivity indices. Additionally, we find a significant correlation between patient age and the degree and the polarity of the loss only in USH2. There was no difference between USH1 and USH2 in the results of the Ishihara test. CONCLUSIONS: The examination of color vision in patients with USH shows a significant difference in the pattern of color vision loss in USH1 and USH2 patients, but not in the severity of the loss. In USH2, we find a correlation between patient age and the degree and the polarity of the loss. These results may be due to differences in the pathogenesis of retinal dystrophy in USH1 and USH2.

The Tuebingen Scotopic Threshold Test (TSTT).

Measurement of the dark-adaptation threshold plays a key role in the diagnosis and estimation of disease progression of many retinal disorders. Determining the threshold is, however, difficult to perform in young children. We present here a prototype for a dark adaptometer, the Tuebingen Scotopic Threshold Test aimed to ease measurement of photoreceptor thresholds in young subjects. The device consists of two 7 cm ×10 cm fields with either blue or yellow LEDs, for testing rod or cone sensitivity, respectively. Presentation of homogenous field patterns or a flickering stimulus is also possible. The luminance threshold is measured by the method of ascending limits and the stimulus luminance, data recording and analysis are computer controlled. Preliminary results for six adults and two older children were ascertained and the influence of pupil dilation, binocular presentation, and a flickering stimulus examined. The method provides credible and consistent evaluations of the absolute threshold.

CLINICAL PRESENTATION AND DISEASE COURSE OF USHER SYNDROME BECAUSE OF MUTATIONS IN MYO7A OR USH2A.

PURPOSE: To evaluate differences in the visual phenotype and natural history of Usher syndrome caused by mutations in MYO7A or USH2A, the most commonly affected genes of Usher syndrome Type I (USH1) and Type II (USH2), respectively. METHODS: Eighty-eight patients with a clinical diagnosis of USH1 (26 patients) or USH2 (62 patients) were retrospectively evaluated. Of these, 48 patients had 2 disease-causing mutations in MYO7A (10 USH1 patients), USH2A (33 USH2 patients), and other USH (5 patients) genes. Clinical investigation included best-corrected visual acuity, Goldmann visual field, fundus photography, electroretinography, and audiologic and vestibular assessments. Longitudinal analysis was performed over a median follow-up time of 3.5 years. RESULTS: Patients carrying mutations in MYO7A had a younger age of onset of hearing and visual impairments than those carrying mutations in USH2A, leading to an earlier diagnosis of the disease in the former patients. Longitudinal analysis showed that visual acuity and visual field decreased more rapidly in subjects carrying MYO7A mutations than in those carrying USH2A mutations (mean annual exponential rates of decline of 3.92 vs. 3.44% and of 8.52 vs. 4.97%, respectively), and the former patients reached legal blindness on average 15 years earlier than the latter. CONCLUSION: The current study confirmed a more severe progression of the retinal disease in USH1 patients rather than in USH2 patients. Furthermore, most visual symptoms (i.e., night blindness, visual acuity worsening) occurred at an earlier age in USH1 patients carrying mutations in MYO7A.

The diagnostic accuracy of chromatic pupillary light responses in diseases of the outer and inner retina.

PURPOSE: To compare the chromatic pupillary light responses (PLR) in healthy subjects with those from patients with diseases of the outer or inner retina under various stimulus conditions, and to ascertain the parameters required to optimally distinguish between disease and control groups. METHODS: Fifteen patients with retinitis pigmentosa (RP), 19 patients with optic nerve disease (ON), and 16 healthy subjects were enrolled in this prospective study. ON included optic neuritis (NNO) and non-arteritic anterior ischemic optic neuropathy (NAION). For each subject, the PLR was recorded, to red, yellow, green, and blue stimuli for durations of 4 and 12 s, and for stimulus intensities of 4 lx and 28 lx. RESULTS: Comparison between control and RP or ON patient results showed that responses after stimulus onset were significantly different for most stimulus conditions, but the post-stimulus amplitudes at 3 s and 7 s after light extinction were not. On the other hand, the difference between the ON and RP groups was significant only for post-stimuli time-points and only for blue stimuli. Differences between responses to blue and red were significantly different, predominantly at post stimulus time-points. A ROC analysis revealed that the maximal constriction amplitudes to a 4 lx, 4 s yellow stimulus are significantly different in ON vs RP patients, and the responses to a 4 s, 28 lx blue stimulus at 7 s post-stimulus are significantly different in controls vs ON vs RP patients with a high specificity. CONCLUSIONS: Pupillary light responses to blue light in healthy, RP, and ON subjects are significantly different from one another. The optimal stimuli for future protocols was found to be a 4 s blue stimulus at 28 lx, and a 4 s yellow stimulus at 4 lx.

An innovative strategy for the molecular diagnosis of Usher syndrome identifies causal biallelic mutations in 93% of European patients.

Usher syndrome (USH), the most prevalent cause of hereditary deafness-blindness, is an autosomal recessive and genetically heterogeneous disorder. Three clinical subtypes (USH1-3) are distinguishable based on the severity of the sensorineural hearing impairment, the presence or absence of vestibular dysfunction, and the age of onset of the retinitis pigmentosa. A total of 10 causal genes, 6 for USH1, 3 for USH2, and 1 for USH3, and an USH2 modifier gene, have been identified. A robust molecular diagnosis is required not only to improve genetic counseling, but also to advance gene therapy in USH patients. Here, we present an improved diagnostic strategy that is both cost- and time-effective. It relies on the sequential use of three different techniques to analyze selected genomic regions: targeted exome sequencing, comparative genome hybridization, and quantitative exon amplification. We screened a large cohort of 427 patients (139 USH1, 282 USH2, and six of undefined clinical subtype) from various European medical centers for mutations in all USH genes and the modifier gene. We identified a total of 421 different sequence variants predicted to be pathogenic, about half of which had not been previously reported. Remarkably, we detected large genomic rearrangements, most of which were novel and unique, in 9% of the patients. Thus, our strategy led to the identification of biallelic and monoallelic mutations in 92.7% and 5.8% of the USH patients, respectively. With an overall 98.5% mutation characterization rate, the diagnosis efficiency was substantially improved compared with previously reported methods.

Investigation of summation mechanisms in the pupillomotor system.

BACKGROUND: To ascertain whether the pupillary response amplitude shows spatial summation of responses with increasing size of retinal stimulation, and to examine the pupillary responses for evidence of surround inhibition, analogous to that found in the receptive fields of the retinal ganglion cells. METHODS: By means of infrared-video-pupillography, the pupil reaction to stimuli of increasing size (1-15°) was measured in 30 normal subjects. Four different retinal locations (0°, 20° and 40° eccentricity on the upper temporal retina and 20° eccentricity on the lower nasal retina) were examined at four different stimulus luminances (17, 47, 87 and 140 cd/m(2)). RESULTS: When the average log amplitude of the pupil light reaction from the 30 subjects is plotted as a function of the log area of the stimulus, a bi-linear response is observed, which is most pronounced for the two higher luminances. The intersection points of the two linear responses are 2.01° in the fovea, 2.80° at 20° upper temporal retina, 2.85° at 20° lower nasal retina and 4.86° at 40° upper temporal retina. CONCLUSIONS: This study suggests that pupillomotor summation areas consist of both summation and inhibitory zones. They show larger diameters than receptive fields of retinal ganglion cells and do not appear to reflect pupillary summation areas of the pretectal olivary nucleus luminance neurons.

A comparison of the performance of three visual evoked potential-based methods to estimate visual acuity.

PURPOSE: To compare visual acuities estimated by three methods of visual evoked potential (VEP) recordings to those obtained by two subjective measures [ETDRS and FrACT (Freiburg acuity test)]. METHODS: Ten healthy subjects, aged between 26 and 67 years (mean 43.5), were examined. Best-corrected acuity determined by the ETDRS was between 0.03 and -0.3 logMAR (mean -0.06). Sweep VEPs (sweepVEP), pattern appearance VEPs (pappVEP) and steady-state VEPs (ssVEP) were recorded with two electrode placements (10-20 and Laplace) with best optical correction and with artificially degraded vision using five Bangerter occlusion foils, reducing acuity to about 0.1, 0.22, 0.52, 0.7 and 1.0 logMAR (0.8, 0.6, 0.3, 0.2 and 0.1 decimal scale). Two runs were performed. RESULTS: ETDRS and FrACT acuities showed good agreement, even though ETDRS seemed to underestimate acuity compared with FrACT at higher acuities. Laplace derivation did not improve any of the VEP-estimated acuities over the 10-20. SweepVEP tended to overestimate lower FrACT acuities, but showed good repeatability. PappVEP placed FrACT acuities into correct or neighboring categories in 87 % of cases. Average ssVEP acuity showed little difference to those of FrACT but variance was larger. ROC analysis for typical clinical application showed good performance for all three methods. CONCLUSIONS: The two subjective measurements of acuities are well correlated. Under the conditions of our experiment, sweepVEP results were less variable and had a better repeatability than ssVEP acuities, whose analysis, in contrast to sweepVEP, can be automated. PappVEP estimates, however, offer a viable alternative, that is, quicker but of lower performance regarding the detection of low acuity thresholds. All methods had a good performance regarding minimum acuity detection if an average of two runs is used.

Topographical alterations of inner retinal activity during systemic hyperoxia-hypercapnia in normal subjects and patients with type 1 diabetes.

The purpose of this study was to investigate whether an increase in the circulating oxygen supply can alter inner retinal function, assessed by recordings of multifocal oscillatory potentials. We studied 9 subjects with type 1 diabetes (8 without overt retinopathy, one with 2 microaneurysms) and 10 similar-aged normal subjects. The central 60 degrees of the retina was stimulated by an array of 61 hexagonal elements, and mfOP recordings were obtained while breathing room air or carbogen. First-order kernel analysis of the recordings shows 2 potentials (first-order OP1, OP2), whereas second-order kernel analysis produces 3 potentials (second-order OP1, OP2, OP3). Two methods were used to analyze the results: First, we performed a ring analysis for each subject and measured the amplitudes and latencies of the five potentials. We demonstrate that during carbogen inhalation, the control subjects, but not the patients with diabetes, showed significantly increased second-order OP3 amplitudes, for a retinal ring from around 1.8-13 degrees eccentricity. Secondly, a topographical analysis was performed on the amplitude of the second-order OP3 in all 61 traces (from the average recordings of each subject group), which revealed significant alterations not visible in a ring analysis. A similar topographical analysis of the amplitude of the first-order OP2 revealed a small increase in its amplitude during carbogen inhalation for both subject groups. This study demonstrates that some aspects of inner retinal function are modified by the inhalation of carbogen. The reduced effect of carbogen inhalation on the recordings from the patients with diabetes may be due to compromised vascular perfusion in these subjects.

Age-related changes in retinal functional topography.

PURPOSE: To perform a detailed topographical analysis of functional age-related changes over the retina. METHODS: Fifty-nine normal phakic subjects aged 10 to 69 years were divided into six groups, according to decade of age. mfERG traces were recorded from the central 60 degrees of the retina, with a resolution of 61 and 103 scaled hexagons. Group medians of peak amplitude and latency of the first- and second-order (first slice) responses were used to generate 3-D topographical maps. RESULTS: With age, there was a continuous loss of amplitude and delay of implicit time of the first- and the second-order response components, but the topography of the loss was not uniform across the retina. Trend analyses on ring group data showed a significant decrease in amplitude of first- and second-order responses although the age relationship of second-order responses was more complex. The loss of first-order kernel amplitude was generally accompanied by a rise in implicit time. Second-order kernel latencies showed no uniform alteration with age. CONCLUSIONS: Consistent with previous work, a steady loss of amplitude and increase of implicit time was observed with age. The topographical 3-D data, however, reveal age-related functional alterations in the retina beyond those found in ring averages, suggesting that these are masked by the standard analysis. Thus, the choice of physiologically coherent regions of interest may increase the sensitivity of detecting age-related change in multifocal analysis of retinal function.

The multifocal pattern electroretinogram (mfPERG) and cone-isolating stimuli.

The number of L cones in the retina normally exceeds that of the M cones. Because normal color vision does not depend on the ratio of L- and M-photoreceptors, their signals must undergo an alteration in gain before being analyzed in the cortex. Previous studies have shown that this gain must take place before the cortex, but after the bipolar/amacrine cell layer of the retina. The aim of this study was to obtain topographical information about L- and M-cone activity at the ganglion cell layer using multifocal pattern electroretinography (mfPERG). A standard (black and white) stimulus was used, as well as stimuli modulating only the long wavelength-sensitive (L) or only the middle wavelength-sensitive (M) cones. The L:M ratio was calculated from the amplitude of the L-cone isolating mfPERG to that of the M-cone isolating mfPERG of 10 trichromats. Both the positive and negative components of the waveform were analyzed. Additional recordings of single cone modulated mfERGs were obtained from nine of the 10 subjects. We also recorded from one protanope and one deuteranope. The L:M cone amplitude ratios for both deflections of the mfPERG in the trichromats were around unity (medians 1.18 and 1.16, respectively) for the central 8 degrees of retina. In the peripheral retina between 12.8 degrees and 26 degrees , this ratio increased to 1.42 for the positive component, and 1.37 for the negative component. The median L:M cone amplitude ratios for the mfPERG were higher and ranged between 1.00-2.78 in the central 8 degrees and 1.29-2.78 in the periphery. The results indicate that a major gain adjustment of the retinal signals takes place at the ganglion cell level, and that the ratio is higher at eccentric locations than in the central retinal area.

L:M-cone ratio estimates of the outer and inner retina and its impact on sex differences in ERG amplitudes.

The relative number of L- and M-cones varies greatly between individuals. Differences in the relative number of L- and M-cones may also contribute to the sex difference in the ERG response amplitude reported several times. We therefore investigated the relative number of L- and M-cones and its impact on sex differences in ERG amplitudes. Multifocal ERG (mfERG) and multifocal oscillatory potentials (mfOP) combined with a cone silent substitution technique were used to investigate outer and inner retinal signals recorded from 7 female and 7 male trichromats. L:M ratios were estimated from peak amplitude as well as from area under curve (AUC) analysis. For mfERGs the L:M ratios estimates were independent of the method of analysis, while for mfOPs, differences were found which are possibly due to an artefact in the calculation of ratios for small responses. There was a tendency for lower L:M ratios in female than in male subjects for both analysis of mfERG and mfOP responses. The (L+M)-response amplitudes at both sites were slightly higher and the L:M ratios were lower for female than for male observers. Because the magnitude of the ERG amplitude differences is larger than could be explained by L:M-ratio and axial length differences, we conclude that it may be due to a direct effect of sex hormones on ion channel function.