Visual function and mobility after multifocal versus monofocal intraocular lens implantation.

Clinical relevance: Mobility and fall risk may be important considerations in choosing between intraocular lenses.Background: Fall risk in older adults increases when wearing multifocal spectacles, but little is known about mobility among individuals with different types of intraocular lenses. This study compared visual function, fall risk and balance control following bilateral implantation of monofocal or multifocal intraocular lenses.Methods: This was a non-randomised, cross-sectional study involving adults with bilateral intraocular lenses. Participants completed questionnaires concerning physical functioning, fall history and balance-related confidence. Binocular visual acuity, contrast sensitivity (Pelli-Robson chart and computerized testing), depth perception and glare sensitivity were assessed. Physical performance measures included the Sensory Organization Test, preferred gait speed, Dynamic Gait Index and wayfinding in a virtual environment.Results: Fifteen participants (mean ± standard deviation, 67.1 ± 6.8 years) had monofocal intraocular lenses and 14 participants (68.1 ± 6.1 years) had multifocal intraocular lenses. Contrast sensitivity in the monofocal group was significantly better than that in the multifocal group (p = 0.02) at intermediate and high spatial frequencies. Contrast sensitivity of the monofocal group also was less affected by glare than the contrast sensitivity of the multifocal group, at an intermediate spatial frequency (p = 0.02). However, the multifocal group had significantly better Dynamic Gait Index scores (p = 0.04), even after controlling for perceived physical function.Conclusions: The participants with monofocal intraocular lenses generally had better contrast sensitivity than did those with multifocal intraocular lenses. However, the scores on a mobility test that is associated with fall risk were worse for those with monofocal lenses.

Reliability of Semiautomated Kinetic Perimetry (SKP) and Goldmann Kinetic Perimetry in Children and Adults With Retinal Dystrophies.

PURPOSE: To investigate the precision of visual fields (VFs) from semiautomated kinetic perimetry (SKP) on Octopus 900 perimeters, for children and adults with inherited retinal degenerations (IRDs). Goldmann manual kinetic perimetry has long been used in the diagnosis and follow-up of these patients, but SKP is becoming increasingly common. Octopus VFs (OVFs) and Goldmann VFs (GVFs) were both mapped on two occasions. METHODS: Nineteen females and 10 males with IRDs were tested on OVFs and GVFs, with two targets per test (V4e and one smaller target). Tests were performed in the same (randomized) order at two visits about 1 week apart. The VFs were digitized to derive isopter solid angles. Comparisons, within and between visits, were performed with paired t-tests and Bland-Altman plots. RESULTS: Median age was 20 years (range, 7-70; 10 participants aged ≤17 years old). There were no significant differences in solid angles between OVFs and GVFs (P ≥ 0.06) or between the two visits' solid angles on either perimeter (P ≥ 0.30). Between-visit test-retest variability for GVFs and OVFs was similar (P ≥ 0.73), with median values of approximately 9% to 13%. Overall variability was lower for children than adults (medians of 7.5% and 12.8%, respectively). CONCLUSIONS: Octopus SKP and Goldmann perimetry produced VFs of similar size and variability. TRANSLATIONAL RELEVANCE: Our study indicates that SKP provides a viable alternative to traditional Goldmann perimetry in clinical trials or care involving both children and adults with IRDs.

ISCEV extended protocol for the photopic On-Off ERG.

The International Society for Clinical Electrophysiology of Vision (ISCEV) standard for full-field electroretinography (ERG) describes a minimum procedure, but encourages more extensive testing. This ISCEV extended protocol describes an extension to the ERG standard, namely the photopic On-Off ERG, and outlines common clinical applications. A light stimulus duration of 150-200 ms is used in the presence of a rod-suppressing background to elicit cone-driven On- and Off-system ERG components. The On-response occurs after the stimulus onset and has a negative a-wave and positive b-wave. The Off d-wave is a positive component evoked by stimulus offset. Common diagnoses that may benefit from additional photopic On-Off ERG testing include retinal dystrophies and retinal disorders that cause dysfunction at a level that is post-phototransduction or post-receptoral. On-Off ERGs assess the relative involvement of On- and Off-systems and may be of use in the diagnosis of disorders such as complete and incomplete congenital stationary night blindness (complete and incomplete CSNB), melanoma-associated retinopathy, and some forms of autoimmune retinopathy. The photopic On-Off ERGs may also be useful in X-linked retinoschisis, Batten disease, Duchenne muscular dystrophy, spinocerebellar degeneration, quinine toxicity, and other retinal disorders.

Rodent Hyperglycemia-Induced Inner Retinal Deficits are Mirrored in Human Diabetes.

PURPOSE: To evaluate the utility of low luminance stimuli to functionally probe inner retinal rod pathways in the context of diabetes mellitus in both rat and human subjects. METHODS: Inner retinal dysfunction was assessed using oscillatory potential (OP) delays in diabetic rats. Scotopic electroretinograms (ERGs) in response to a series of increasing flash luminances were recorded from streptozotocin (STZ)-treated and control Sprague-Dawley rats after 7, 14, 20, and 29 weeks of hyperglycemia. We then evaluated OP delays in human diabetic subjects with (DR) and without (DM) diabetic retinopathy using the International Society for Clinical Electrophysiology in Vision (ISCEV) standard scotopic protocol and two additional dim test flashes. RESULTS: Beginning 7 weeks after STZ, OP implicit times in diabetic rats were progressively delayed in response to dim, but not bright stimuli. In many diabetic subjects the standard ISCEV dim flash failed to illicit measureable OPs. However, OPs became measurable using a brighter, nonstandard dim flash (Test Flash 1, -1.43 log cd s/m2), and exhibited prolonged implicit times in the DM group compared with control subjects (CTRL). CONCLUSIONS: Delays in scotopic OP implicit times are an early response to hyperglycemia in diabetic rats. A similar, inner retinal, rod-driven response was detected in diabetic human subjects without diabetic retinopathy, only when a nonstandard ISCEV flash intensity was employed during ERG testing. TRANSLATIONAL RELEVANCE: The addition of a dim stimulus to standard ISCEV flashes with assessment of OP latency during ERG testing may provide a detection method for early retinal dysfunction in diabetic patients.

Evaluation of telemedicine for screening of diabetic retinopathy in the Veterans Health Administration.

OBJECTIVE: To explore the cost-effectiveness of telemedicine for the screening of diabetic retinopathy (DR) and identify changes within the demographics of a patient population after telemedicine implementation. DESIGN: A retrospective medical chart review (cohort study) was conducted. PARTICIPANTS: A total of 900 type 1 and type 2 diabetic patients enrolled in a medical system with a telemedicine screening program for DR. METHODS: The cost-effectiveness of the DR telemedicine program was determined by using a finite-horizon, discrete time, discounted Markov decision process model populated by parameters and testing frequency obtained from patient records. The model estimated the progression of DR and determined average quality-adjusted life years (QALYs) saved and average additional cost incurred by the telemedicine screening program. MAIN OUTCOME MEASURES: Diabetic retinopathy, macular edema, blindness, and associated QALYs. RESULTS: The results indicate that telemedicine screening is cost-effective for DR under most conditions. On average, it is cost-effective for patient populations of >3500, patients aged <80 years, and all racial groups. Observable trends were identified in the screening population since the implementation of telemedicine screening: the number of known DR cases has increased, the overall age of patients receiving screenings has decreased, the percentage of nonwhites receiving screenings has increased, the average number of miles traveled by a patient to receive a screening has decreased, and the teleretinal screening participation is increasing. CONCLUSIONS: The current teleretinal screening program is effective in terms of being cost-effective and increasing population reach. Future screening policies should give consideration to the age of patients receiving screenings and the system's patient pool size because our results indicate it is not cost-effective to screen patients aged older than 80 years or in populations with <3500 patients.

Negative electroretinograms in the pediatric and adult population.

Objective To assess the frequency of negative waveform electroretinograms (ERGs) in a tertiary referral center. Design Retrospective chart review. Participants All patients who had an ERG performed at the electrophysiology clinic at Emory University from January 1999 through March 2008 were included in the study. Methods Patients with b-wave amplitude ≤ a-wave amplitude during the dark-adapted bright flash recording, in at least one eye, were identified as having a "negative ERG". Clinical information, such as age, gender, symptoms, best corrected visual acuity, and diagnoses were recorded for these patients when available. Results A total of 1,837 patients underwent ERG testing during the study period. Of those, 73 patients had a negative ERG, for a frequency of 4.0%. Within the adult (≥ 18 years of age) and pediatric populations, the frequencies of a negative ERG were 2.5 and 7.2%, respectively. Among the 73 cases, negative ERGs were more common among male than female patients, 6.7% versus 1.8% (P < 0.0001). Negative ERGs were most common among male children and least common among female adults, 9.6% versus 1.1%, respectively, (P < 0.0001). Overall in this group of patients, the most common diagnoses associated with a negative ERG were congenital stationary night blindness (CSNB, n = 29) and X-linked retinoschisis (XLRS, n = 7). Conclusions The overall frequency of negative ERGs in this large retrospective review was 4.0%. Negative ERGs were most common among male children and least common among female adults. Despite the growing number of new diagnoses associated with negative ERGs, CSNB, and XLRS appear to be the most likely diagnoses for a pediatric patient who presents with a negative ERG.

A test of face discrimination ability in aging and vision loss.

PURPOSE: The ability to recognize faces is fundamental to social interactions but has not been studied extensively in visual disorders such as age-related macular degeneration (AMD). We report here the development of a face discrimination test, in which both response times (RTs) and accuracies are measured. Results are compared for young and older control subjects and older adults with AMD to determine the factors underlying performance on this test. METHODS: Subjects were 14 older controls, 11 young adult controls, and 34 individuals with binocular AMD. In the face discrimination test, colored reference photographs of eight people were presented continuously (male faces in the first half of the test, female faces in the second). On each trial, subjects reported which reference face matched the test face (shown with different poses and/or expressions). In addition, the older controls then identified the expression on the test face. RESULTS: The older controls showed generally small numbers of errors (0 to 9%) on the face identifications but more errors on expression identifications (up to 22%). They tended to show shorter RTs (but no changes in accuracy) with repeated presentations of the same face. The young controls responded more quickly, and they made almost no mistakes. Although performance varied, as a group, those with AMD were slower and showed more errors in identification than the older controls did. Across all subjects, both visual acuity and contrast sensitivity contributed significantly to the variances in RTs and accuracy. CONCLUSIONS: The group of older controls had poorer and more variable RTs and accuracies than the young controls. Difficulties in face matching, in terms of both accuracy and RT, were observed for subjects with AMD. Performance accuracy and RTs for this new test depended on both visual acuity and contrast sensitivity.

A negative electroretinogram (ERG) in a case of probable multiple system atrophy (MSA).

Recent articles have described negative ERGs in a small number of patients with cerebellar degeneration. Five of the previously reported seven cases were hereditary (2/5 had spinocerebellar ataxia-1 (SCA-1) gene mutations) and the other two were sporadic. We report a negative ERG in a case of cerebellar degeneration that differs significantly from earlier cases. The 65-year-old man had a 5-year history of ataxia, unsteady gait, orthostatic hypotension, and bladder and erectile dysfunction, with no family history of neurological or retinal disease. Visual acuity was 20/30 OD, 20/40 OS, but reportedly was never 20/20. His fundus exam showed optic nerve pallor, but otherwise was normal. Visual fields had enlarged blind spots but no central scotomas. Autofluorescence was normal. Photopic flash and 30-Hz ERG responses were normal. Rod b-waves were reduced and delayed. Standard flash a-waves were normal, but the b-waves were smaller than the a-waves. Blood tests were negative for Leber's hereditary optic neuropathy, dominant optic atrophy, and for expansions in SCA genes including SCA-1. This is only the third reported case of sporadic ataxia with a negative ERG. The patient's prominent autonomic dysfunction differs from the previous cases, and meets the clinical criteria for probable multiple system atrophy (MSA). This introduces another possible diagnosis in cases of negative ERGs with ataxia, and suggests that the visual system may be affected in MSA.

Characteristics of contrast processing deficits in X-linked retinoschisis.

Contrast sensitivity and contrast discrimination were evaluated in six males with X-linked retinoschisis (XLRS), a form of early-onset macular degeneration, using testing paradigms designed to favor either the magnocellular (MC) or parvocellular (PC) pathway. Compared to a group of age-similar control observers, the patients with XLRS showed a pronounced loss of contrast sensitivity at high spatial frequencies, consistent with their reduced visual acuities. At low spatial frequencies, the patients' deficits were greater under conditions favoring the MC pathway, for both contrast sensitivity and contrast discrimination. The pattern of contrast sensitivity loss shown by the patients with XLRS could be simulated in control observers by testing at a parafoveal locus, although by optical coherence tomography, none of the patients with XLRS had eccentric fixation. The pattern of findings indicates that the foveas of patients with XLRS functionally resemble the normal parafoveal retina.

Voluntary alteration of full-field electroretinogram.

PURPOSE: To evaluate whether a normal subject can deliberately produce abnormal electroretinogram (ERG) results that simulate disorders of the retina. DESIGN: Prospective study. METHODS: Five normal subjects were evaluated twice with full-field ERGs. The subjects were randomly assigned to be compliant or noncompliant (i.e., to deliberately attempt to alter the test results) at each visit. Results from compliant eyes were compared with those of noncompliant eyes. RESULTS: While the amplitudes of all parameters were decreased in the noncompliant group, the difference was not statistically significant, and the results were usually within the normal limits of our laboratory. No subject was able to alter the results to mimic a retinal disease or to reproduce a specific pattern of changes. CONCLUSIONS: Although ERG results can be altered by noncompliant subjects, the results are usually only "borderline abnormal" and do not correspond to any pattern of retinal disease. These results confirm that abnormal full-field ERGs indicate true retinal disease.

Contrast sensitivity deficits in inferred magnocellular and parvocellular pathways in retinitis pigmentosa.

PURPOSE: To define the contrast sensitivity deficits of patients with retinitis pigmentosa (RP) under testing conditions designed to emphasize threshold mediation by either the magnocellular (MC) or parvocellular (PC) pathway. METHOD: Contrast sensitivity was measured with spatially localized, narrow-band test patterns at peak spatial frequencies ranging from 0.25 to 8 cycles per degree (cpd), using a steady-pedestal paradigm (brief presentation of the test stimulus against a continuously presented luminance pedestal) and a pulsed-pedestal paradigm (simultaneous brief presentation of the test stimulus and luminance pedestal) to favor the MC and PC pathways, respectively. The contrast sensitivity functions of 12 patients with RP who had visual acuities ranging between 20/12.5 and 20/40 were compared to those of 10 visually normal, age-equivalent control observers. RESULTS: Five of the patients with RP who had Snellen visual acuities better than 20/25 had contrast sensitivity functions that were within the normal limits at all spatial frequencies for both testing paradigms. The other seven patients with RP had reduced contrast sensitivities for both paradigms, with the greatest reduction in sensitivity occurring at the highest spatial frequency. Their contrast sensitivity deficits were equivalent for the steady- and pulsed-pedestal paradigms. CONCLUSIONS: As observed in previous studies, the degree of contrast sensitivity loss shown by the patients with RP was greatest at the highest stimulus spatial frequency. However, in comparison to prior studies of contrast discrimination in patients with RP, there was no evidence of a preferential contrast sensitivity loss within the MC pathway. This apparent discrepancy is attributed to differences in the test targets and psychophysical judgments that were used in the studies, which emphasizes the importance of task characteristics in evaluating relative deficits within the MC and PC processing streams in visual disorders.

Contrast-processing deficits in melanoma-associated retinopathy.

PURPOSE: To evaluate the hypothesis that patients with melanoma-associated retinopathy (MAR) have a selective functional loss within the magnocellular (MC) pathway of the cone system, with sparing of parvocellular (PC) pathway function. METHODS: Two patients with MAR, ages 57 and 61 years, with normal Snellen visual acuity, participated in the study. Contrast sensitivity was measured at spatial frequencies ranging from 0.25 to 8 cycles per degree (cpd), using two paradigms (steady pedestal and pulsed pedestal) designed to assess the functional integrity of the MC and PC pathways, respectively. Results in patients with MAR were compared with those in 10 visually normal observers, aged 23 to 57 years. RESULTS: Both patients with MAR showed a loss of contrast sensitivity compared to normal observers, but the pattern of loss differed for the two testing paradigms. For the steady-pedestal paradigm (presumed MC-pathway mediation), the patients' sensitivity loss was greatest at the lowest spatial frequency (0.25 cpd) and the sensitivity loss decreased systematically with increasing spatial frequency. For the pulsed-pedestal paradigm (presumed PC-pathway mediation), the sensitivity loss was greatest at an intermediate spatial frequency of 1 cpd. For both paradigms, the patients' sensitivities were within the normal range at the highest spatial frequency (8 cpd), consistent with their normal visual acuity. CONCLUSIONS: The contrast sensitivity deficits of patients with MAR under photopic conditions are not specific to the MC pathway, as proposed previously, but instead are related to the spatial frequency of the test target. The overall pattern of contrast sensitivity loss shown by the patients with MAR is consistent with the dysfunction at the level of the retinal bipolar cells that is presumed to underlie the MAR syndrome.

ON-pathway dysfunction and timing properties of the flicker ERG in carriers of X-linked retinitis pigmentosa.

PURPOSE: Carriers of X-linked retinitis pigmentosa (XLRP) frequently show prolonged implicit times of the flicker electroretinogram (ERG). This study tested the hypothesis that a preferential response attenuation within the cone depolarizing (ON) bipolar cell (DBC) pathway is a major contributing factor. METHODS: Light-adapted, full-field ERGs were recorded from 10 XLRP carriers and 12 visually normal control subjects. Fundamental amplitudes and phases of ERG responses to sinusoidally flickering stimuli at temporal frequencies ranging from 8 to 96 Hz were analyzed within the framework of a recent vector summation model of the cone system ERG to test for evidence of a response attenuation within the DBC pathway. In addition, ERG responses to sawtooth flicker were examined for a reduced b- to d-wave amplitude ratio, indicative of ON pathway dysfunction. RESULTS: The carriers' fundamental response phases at 32 Hz correlated significantly with their log ratios of response amplitudes at 32 versus 12 Hz (r = 0.89, P < 0.001) and with their log b- to d-wave amplitude ratios (r = 0.71, P < 0.05), both of which were used as indices of response attenuation within the DBC pathway. A control experiment demonstrated that a reduced sensitivity of cone phototransduction made at most only a minimal contribution to the timing changes in the carriers' flicker ERG responses. CONCLUSIONS: The overall pattern of results indicates that a preferential response attenuation within the DBC pathway is the primary source of timing changes in the flicker ERGs of these carriers of XLRP. These findings illustrate the value of analyzing ERG responses to flickering stimuli at multiple temporal frequencies to evaluate mechanisms of disease action in photoreceptor degenerations.

Deficits in temporal integration for contrast processing in retinitis pigmentosa.

PURPOSE: The purpose of this study was to evaluate the properties of foveal temporal integration in patients with retinitis pigmentosa (RP) within the framework of contrast processing by the magnocellular (MC) and parvocellular (PC) pathways. METHODS: Temporal integration functions were measured in eight patients with RP whose visual acuities ranged from 20/25 to 20/63. Contrast thresholds were obtained at durations ranging from 15 to 480 ms, using steady-pedestal and pulsed-pedestal paradigms to bias performance toward the MC and PC pathways, respectively. The patients' results were compared with those of 10 age-similar control observers with normal vision. For both paradigms, contrast thresholds as a function of duration were fit with a two-limbed function to derive the critical duration for temporal integration (t(c)) and the asymptotic threshold at long durations (Delta L(infinity)). RESULTS: The log t(c)s of the patients with RP were significantly longer than those of the control subjects for the steady-pedestal paradigm (presumed MC-pathway mediation; t = 3.67, P < 0.001), but not for the pulsed-pedestal paradigm (presumed PC-pathway mediation; t = 0.76, P = 0.45). Further, the patients with RP showed a significant correlation between log t(c) and log Delta L(infinity) for the steady-pedestal paradigm (r = 0.72, P < 0.05) but not for the pulsed-pedestal paradigm (r = -0.37, P = 0.36). CONCLUSIONS: The patients with RP in this study showed greater deficits in contrast sensitivity and a more prolonged critical duration under test conditions that favor the MC rather than the PC pathway. A likely explanation is a high-frequency response attenuation at the level of the cone photoreceptors that has a differential effect on contrast-processing tasks that emphasize different postreceptoral mechanisms.

Mutated alleles of the rod and cone Na-Ca+K-exchanger genes in patients with retinal diseases.

PURPOSE: To study the possible involvement of the rod (SLC24A1) and cone (SLC24A2) Na-Ca+K exchanger (NCKX) genes in retinal diseases. METHODS: DNA was collected from unrelated patients with retinal disease, mainly from North America. A human genomic library was screened with the cone NCKX cDNA, and hybridizing clones were sequenced to determine the genomic organization of the SLC24A2 gene. The single-strand conformation polymorphism (SSCP) technique and direct sequencing were used to screen the patients' DNA for mutations in SLC24A1 and SLC24A2. The effect of selected missense changes on protein function was tested by measuring potassium-dependent Na-Ca exchange of the mutant proteins expressed in insect cells. RESULTS: Twenty-seven novel sequence changes were found in the rod NCKX gene, 21 of which are unlikely to be pathogenic, because they did not cosegregate with the disease or did not affect conserved regions of the protein. Of the remaining six, two were frameshift mutations found in one patient each. If translated, these alleles would encode nonfunctional proteins. Three of the six possibly pathogenic mutations were missense changes located in conserved regions, and their protein functions were assayed. Only one (Ile992Thr) had a significantly low level of exchanger function, but it was found in two unrelated patients who were heterozygotes with different retinal diseases, and this mutation could not be unequivocally associated with either disease. The last of the six changes is likely to create a new splice acceptor site. The genomic organization of the cone NCKX gene was determined, and it contained 11 exons with a few splice variants. Fifteen novel sequence changes were identified in the cone exchanger gene in patients with a cone dysfunction or degeneration. Only three of these sequence changes, all missense changes found in heterozygous patients, were considered possibly pathogenic. Functional analysis showed only a slight reduction in the activity of the corresponding mutant proteins. CONCLUSIONS: Although variant alleles of the rod and cone NCKX genes were found, none could be definitively associated with a specific retinal disease. The human phenotype associated with mutant exchanger alleles remains unknown.

A distinctive form of congenital stationary night blindness with cone ON-pathway dysfunction.

PURPOSE: To characterize a distinctive form of congenital stationary night blindness (CSNB). DESIGN: Observational case report. PARTICIPANTS: A 30-year-old male with a history of night blindness, several members of his family, a patient with "complete" congenital stationary night blindness (CSNB1), and groups of age-similar control subjects. METHODS: Rod-system function was evaluated by measuring psychophysical dark-adapted thresholds, by recording dark-adapted electroretinograms (ERGs), and by fundus reflectometry. Cone-system function was evaluated by recording light-adapted ERGs, including those to sawtooth flicker, and by recording light-adapted visually evoked potentials (VEPs) to luminance increments and decrements. MAIN OUTCOME MEASURES: Dark-adapted thresholds, ERGs, rhodopsin double densities, Goldmann visual fields, and VEPs. RESULTS: The patient's visual acuity, visual fields, and color vision were normal. His peripheral dark-adapted thresholds were rod-mediated but elevated by approximately 3 log units above normal. Rhodopsin double density and bleaching recovery were normal. His dark-adapted maximal-flash ERG showed a "negative" waveform, in which the b-wave was more reduced in amplitude than the a-wave, although the a-wave amplitude was also reduced. The rod photoreceptors contributed to the patient's dark-adapted ERGs, as illustrated by the unequal responses to cone-matched stimuli. The patient's cone-mediated thresholds for long-wavelength stimuli were within the normal range. However, his light-adapted brief-flash b-wave was abnormal in amplitude and implicit time. Selective abnormalities of the ON responses of the cone system were apparent in the patient's reduced b-wave amplitude to rapid-on flicker with a normal response to rapid-off flicker, and his prolonged VEP latencies to increments but not to decrements. CONCLUSIONS: The overall pattern of findings distinguishes this patient from previously described forms of CSNB. The results suggest that two factors likely contribute to the patient's night blindness: (1) a rod phototransduction defect and (2) a postreceptoral defect. The results also indicate dysfunction within the cone ON pathway.

Nature of the cone ON-pathway dysfunction in melanoma-associated retinopathy.

PURPOSE: To establish the basis for an ON-pathway abnormality of the cone system in melanoma-associated retinopathy (MAR) through analysis of the electroretinogram (ERG) and visual evoked potential (VEP). METHODS: Two patients with MAR syndrome whose sera produced immunolabeling of retinal bipolar cells participated in the study. Full-field ERGs were recorded in response to brief flashes, to rapid-on and rapid-off sawtooth stimuli at a temporal frequency of 8 Hz, and to sine-wave stimuli at temporal frequencies ranging from 8 to 96 Hz. Fundamental responses to the sine-wave stimuli were evaluated within the context of a vector-summation model of the depolarizing bipolar cell (DBC) and hyperpolarizing bipolar cell (HBC) contributions to the response fundamental. VEPs were recorded to the onset of luminance increments and decrements that had contrasts of 10%, 20%, and 50%. The patients' results were compared with those of age-similar control subjects. RESULTS: The patients with MAR showed abnormal ERG responses to luminance increments, consisting of a marked attenuation of the initial portion of the b-wave, but their ERG responses to luminance decrements were normal in amplitude and timing. The ERG temporal response functions of the patients with MAR had normal amplitudes at frequencies of 32 Hz and higher, with a constant phase lag across these frequencies, but larger-than-normal amplitudes at frequencies below 32 Hz, and a phase lead at 8 Hz. Their VEP responses showed a marked delay to increments but only a minimal delay to decrements. CONCLUSIONS: Within the context of the vector-summation model, the ERG findings in the patients with MAR are more consistent with an attenuation of the DBC contribution to the ERG response than with a DBC response delay. The delayed VEP responses of the patients with MAR to luminance increments may represent a late response of the OFF system to increment onset.

Simultaneous S-cone contrast.

Chromatic induction is the change in appearance of one light caused by a second, nearby light. We measured chromatic induction in a central test viewed within an inducing field that was varied in only short-wavelength-sensitive (S) cone stimulation. The observer matched the appearance of the central test by adjusting the chromaticity of a haploscopically presented comparison field, seen by the other eye on a dark background. When the central test weakly stimulated S cones, the S-cone level in the surround caused little change in the color appearance of the test. When the central test substantially stimulated S cones, on the other hand, the appearance of the center showed S-cone contrast: raising the level of S in the surround reduced the level of S set to match the central test. Further, a surround that weakly stimulated S cones raised the matching S-cone level above that required without a surround (dark-adapted condition). These results cannot be explained by S-cone sensitivity loss or by a two-process model of adaptation. A cortical mechanism is proposed to mediate S-cone antagonism.