Loss-of-function variants in UBAP1L cause autosomal recessive retinal degeneration

PURPOSE

Inherited retinal diseases (IRDs) are a group of monogenic conditions that can lead to progressive blindness. Their missing heritability is still considerable, due in part to the presence of disease genes that await molecular identification. The purpose of this work was to identify novel genetic associations with IRDs.

METHODS

Patients underwent a comprehensive ophthalmological evaluation using standard-of-care tests, such as detailed retinal imaging (macular optical coherence tomography and short-wavelength fundus autofluorescence) and electrophysiological testing. Exome and genome sequencing, as well as computer-assisted data analysis were used for genotyping and detection of DNA variants. A minigene-driven splicing assay was performed to validate the deleterious effects of 1 of such variants.

RESULTS

We identified 8 unrelated families from Hungary, the United States, Israel, and The Netherlands with members presenting with a form of autosomal recessive and nonsyndromic retinal degeneration, predominantly described as rod-cone dystrophy but also including cases of cone/cone-rod dystrophy. Age of disease onset was very variable, with some patients experiencing first symptoms during their fourth decade of life or later. Myopia greater than 5 diopters was present in 5 of 7 cases with available refractive data, and retinal detachment was reported in 2 cases. All ascertained patients carried biallelic loss-of-function variants in UBAP1L (HGNC: 40028), a gene with unknown function and with homologies to UBAP1, encoding a protein involved in ubiquitin metabolism. One of these pathogenic variants, the intronic NM_001163692.2:c.910-7G>A substitution, was identified in 5 unrelated families. Minigene-driven splicing assays in HEK293T cells confirmed that this DNA change is responsible for the creation of a new acceptor splice site, resulting in aberrant splicing.

CONCLUSION

We identified UBAP1L as a novel IRD gene. Although its function is currently unknown, UBAP1L is almost exclusively expressed in photoreceptors and the retinal pigment epithelium, hence possibly explaining the link between pathogenic variants in this gene and an ocular phenotype.

The Association Between Acquired Color Deficiency and PET Imaging of Neurodegeneration in Mild Cognitive Impairment and Alzheimer Disease

Purpose

To evaluate color vision changes and retinal processing of chromatic and luminance pathways in subjects with Alzheimer disease (AD) and mild cognitive impairment (MCI) compared with a matched control group and whether such changes are associated with impaired brain glucose metabolism and β-amyloid deposition in the brain.

Methods

We evaluated 13 patients with AD (72.4 ± 7.7 years), 23 patients with MCI (72.5 ± 5.5 years), and 18 controls of comparable age (P = 0.44) using Cambridge color test and the heterochromatic flicker ERG (HF-ERG). The Cambridge color test was performed using the trivector protocol to estimate the protan, deutan and tritan color confusion axes. HF-ERG responses were measured at a frequency of 12 Hz, which ERGs reflect chromatic activity, and at 36 Hz, reflecting luminance pathway. A study subsample was performed using neuropsychological assessments and positron emission tomography.

Results

Patients with AD presented higher mean values indicating poorer color discrimination for protan (P = 0.04) and deutan (P = 0.001) axes compared with the controls. Along the tritan axis, both patients with AD and patients with MCI showed decreased color vision (P = 0.001 and P = 0.001) compared with controls. The analyses from the HF-ERG protocol revealed no differences between the groups (P = 0.31 and P = 0.41). Diffuse color vision loss was found in individuals with signs of neurodegeneration (protan P = 0.002, deutan P = 0.003 and tritan P = 0.01), but not in individuals with signs of β-amyloid deposition only (protan P = 0.39, deutan P = 0.48, tritan P = 0.63), regardless of their clinical classification.

Conclusions

Here, patients with AD and patients with MCI present acquired color vision deficiency that may be linked with impaired brain metabolism.

Effects of fixed cutoff filtering on dark- and light-adapted ERG components and the application of variable cutoff filter

Purpose

Human oscillatory potentials (OPs) are derived from dark-adapted (DA) electroretinograms (ERGs) with fixed frequency cutoff filters while light-adapted (LA) OPs are generally not isolated from ERGs. Our purpose was to analyze the effect of cutoff frequencies on DA and LA ERG components using a series of fixed and variable filters.

Methods

DA and LA ERGs were recorded from 10 healthy eyes of 10 subjects (mean age = 20.5 ± 6.7 years) following ISCEV standards. Each signal was filtered in the Fourier domain to acquire slow (a- and b-waves; below cutoff frequency) and fast (OPs; above cutoff frequency) components. Fixed cutoff frequencies ranged from 60 to 105 Hz and a variable cutoff frequency was calculated. Results were analyzed with statistical tests and specific models.

Results

DA ERG components were slightly influenced by the filter cutoff frequency. In contrast, fixed and variable filters significantly changed LA components: the lower the cutoff frequency the smaller the b-wave and OP3 and the higher the OP2/OP4 amplitudes. Analyzing the filter frequency limits a transition range between 68.9 Hz and 83.9 Hz was observed where amplitudes vary.

Conclusions

The present report shows that DA OPs may be isolated from ERGs using filtering procedures with high-pass cutoff frequency at about 75 Hz as recommended by ISCEV. On the other hand, the spectral distribution of low-frequency and high-frequency LA ERG components may overlap. Accordingly, filtering the signal using different cutoff frequencies is not necessarily separating b-wave and OPs.

Fixation stability after surgical treatment of strabismus and biofeedback fixation training in amblyopic eyes

Background

Visual fixation may be affected in amblyopic patients and, moreover, its stability may be associated with the effects of amblyopic treatments on visual performance in patients with strabismus. Therefore, fixation stability is a relevant biomarker that might predict the recurrence of amblyopia after a therapeutic intervention. Microperimetric biofeedback fixation training (BFT) can stabilize visual fixation in adult patients with central vision loss. It was the purpose of the present study to evaluate the effects of BFT on fixation stability in adult amblyopic patients after surgical intervention to treat strabismus.

Methods

Participants were 12 patients with strabismus (mean age = 29.6 ± 8.5 years; 6 females) and 12 healthy volunteers (mean age = 23.8 ± 1.5 years; 9 females). The protocol included ophthalmological and microperimetric follow-ups to measure fixation stability and macular sensitivity. BFT was applied monocularly to four amblyopic eyes either on the spontaneous preferential retinal locus or to a fixation area closer to the anatomical fovea after surgical treatment of strabismus.

Results

Baseline measurements showed significantly altered microperimetric average threshold in amblyopic eyes compared to fellow eyes (p = 0.024) and compared to control eyes (p < 0.001). Fixation was unstable in amblyopic eyes compared to control eyes (p < 0.001). Fixation stability did not significantly change after surgical alignment of strabismus (p = 0.805). BFT applied to operated eyes resulted in a more stable fixation with improvements of about 50% after three months of training.

Conclusions

Fixation stability improvements following BFT highlight its potential use in adult amblyopic eyes after the surgical alignment of the strabismus. Future investigations may also consider applying this method in combination with standard treatments to improve vision in amblyopic patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12886-021-02020-3.

Correlations Between Dark-Adapted Rod Threshold Elevations and ERG Response Deficits in Duchenne Muscular Dystrophy

Purpose

The purpose of this study was to characterize changes in the full-field flash electroretinogram (ERG) in association with psychophysical dark-adapted visual thresholds in patients with genetically characterized Duchenne muscular dystrophy (DMD) either lacking Dp427 (Up 30) or at least Dp260 in addition to Dp427 (Down 30).

Methods

Twenty-one patients with DMD and 27 age-similar controls participated in this study. Dark-adapted (0.01, 3.0, and 10 cd.s/m² flashes) and light-adapted (3.0 cd.s/m² flash) ERGs were recorded following International Society for Clinical Electrophysiology of Vision (ISCEV) standard protocols. Visual detection thresholds to 625-nm (cone function) and 527-nm (rod function) light-emitting diode (LED) flashes (2 degree diameter) were measured during a dark adaptation period after a 1-minute exposure to a bleaching light (3000 cd/m²). Initially, 8 minutes of interleaved 625-nm and 527-nm thresholds were measured. After an additional 5 minutes of dark-adaptation, a second set of threshold measurements to 527-nm stimuli was performed during the subsequent 6 minutes.

Results

Dark-adapted b-wave amplitude was significantly reduced to all strengths of flash and a-wave in response to the strong flash stimulus was delayed (15.6 vs. 14.7 ms, P < 0.05) in patients with Down 30 compared with controls. Dark-adapted cone thresholds did not differ among the groups (−2.0, −1.8, and −1.7 log cd/m² for Down 30, Up 30, and controls, respectively, P = 0.21). In contrast, dark-adapted rod thresholds were elevated (F_(2,36) = 8.537, P = 0.001) in patients with Down 30 (mean = −3.2 ± 1.1 log cd/m²) relative to controls (mean = −4.2 ± 0.3 log cd/m²). Dark-adapted b-wave amplitudes were correlated with dark-adapted rod sensitivity in patients with DMD (Spearman Rho = 0.943, P = 0.005). The changes were much smaller or absent in patients with intact Dp260.

Conclusions

Dp260 is particularly required for normal rod-system function in dark adaptation.

Dichoptic Spatial Contrast Sensitivity Reflects Binocular Balance in Normal and Stereoanomalous Subjects

Purpose

To study binocular balance by comparing dichoptic and standard monocular contrast sensitivity function (CSF) in stereonormal and stereoanomalous/stereoblind amblyopic subjects.

Methods

Sixteen amblyopes and 17 controls participated. Using the capability of the passive three-dimensional display, we measured their CSF both monocularly and dichoptically at spatial frequencies 0.5, 1, 2, 4, and 8 cpds using achromatic Gabor patches on a luminance noise background. During monocular stimulation, the untested eye was covered, while for the dichoptic stimulation the untested eye viewed background noise. Dichoptic CSF of both eyes was acquired within one block.

Results

In patients with central fixation, dichoptic viewing had a large negative impact on the CSF of the amblyopic eye, although it hardly affected that of the dominant eye. In contrast, dichoptic viewing had a small but significant effect on both eyes for controls. In addition, all participants lay along a continuum in terms of how much their two eyes were affected by dichoptic stimulation: by using two predefined contrast sensitivity ratios, namely, amblyopic sensitivity decrement and dichoptic sensitivity decrement, not only did we find a significant correlation between these variables among all participants, but also the two groups were identified with minimum error using a cluster analysis.

Conclusions

Dichoptic CSF may be considered to measure visual performance in patients with altered binocular vision, because it better reflects the visual capacity of the amblyopic eye than the standard monocular examinations. It may also be a more reliable parameter to assess the efficacy of modern approaches to treat amblyopia.

Rescue of Defective Electroretinographic Responses in Dp71-Null Mice With AAV-Mediated Reexpression of Dp71

Purpose

To study the potential effect of a gene therapy, designed to rescue the expression of dystrophin Dp71 in the retinas of Dp71-null mice, on retinal physiology.

Methods

We recorded electroretinograms (ERGs) in Dp71-null and wild-type littermate mice. In dark-adapted eyes, responses to flashes of several strengths were measured. In addition, flash responses on a 25-candela/square meters background were measured. On- and Off-mediated responses to sawtooth stimuli and responses to photopic sine-wave modulation (3–30 Hz) were also recorded. After establishing the ERG phenotype, the ShH10-GFP adeno-associated virus (AAV), which has been previously shown to target specifically Müller glial cells (MGCs), was delivered intravitreously with or without (sham therapy) the Dp71 coding sequence under control of a CBA promoter. ERG recordings were repeated three months after treatment. Real-time quantitative PCR and Western blotting analyses were performed in order to quantify Dp71 expression in the retinas.

Results

Dp71-null mice displayed reduced b-waves in dark- and light-adapted flash ERGs and smaller response amplitudes to photopic rapid-on sawtooth modulation and to sine-wave stimuli. Three months after intravitreal injections of the ShH10-GFP-2A-Dp71 AAV vector, ERG responses were completely recovered in treated eyes of Dp71-null mice. The functional rescue was associated with an overexpression of Dp71 in treated retinas.

Conclusions

The present results show successful functional recovery accompanying the reexpression of Dp71. In addition, this experimental model sheds light on MGCs influencing ERG components, since previous reports showed that aquaporin 4 and Kir4.1 channels were mislocated in MGCs of Dp71-null mice, while their distribution could be normalized following intravitreal delivery of the same ShH10-GFP-2A-Dp71 vector.

Longitudinal visual acuity development in ZIKV-exposed children

PURPOSE

To follow the visual acuity development of children exposed to or infected with the Zika virus (ZIKV) during gestation and to relate potential visual acuity deficits to their clinical condition.

METHODS

In this prospective study, visual acuity was measured via Teller Acuity Cards in three groups of children: (1) those with confirmed ZIKV exposure (ZE) through the mother only, (2) those with confirmed infection (ZI), and (3) unaffected controls. Visual acuity was measured 2-4 times in each child during the first 30 months of age.

RESULTS

The study included 22 children in the ZE group, 11 in the ZI group, and 27 controls. Visual acuity developed normally in both patient groups, including infected patients (ZI) that did not manifest clinical symptoms. In a small subgroup of patients with characteristics consistent with congenital Zika syndrome (CZS), visual acuity was within normative values, with the exception of single child with chorioretinal atrophy.

CONCLUSIONS

In this southeastern Brazil study cohort, visual acuity development seemed to progress normally in infected children without CZS symptoms.

Alterations in visual acuity and visual development in infants 1-24 months old either exposed to or infected by Zika virus during gestation, with and without microcephaly

PURPOSE

To evaluate visual acuity and visual acuity development in children from the state of São Paulo, Brazil, who were exposed to the Zika virus (ZIKV) gestationally.

METHODS

Children who had been exposed to ZIKV during gestation and age-matched control subjects received visual acuity and funduscopic examination. ZIKV exposure was confirmed by maternal quantitative polymerase chain reaction testing or serology assay. The ZIKV group was divided into two subgroups: exposed (ZE), with only the mother having confirmed ZIKV infection, and infected (ZI), with confirmed infection. Visual acuity development was compared with prior norms and quantified by measuring visual acuity correlation with age.

RESULTS

A total of 110 children were included: 47 who had been exposed to ZIKV (ZE, 23; ZI, 24) and 63 controls. Abnormal visual acuity was found in 5 of 24 ZI children. Of the 4 children with microcephaly, only 2 had visual acuity loss (only 1 also had abnormal funduscopic findings). There was significant correlation between age and visual acuity in both the control group (R² = 0.8; P < 0.0000) and the ZE subgroup (R² = 0.6; P < 0.0000). However, visual acuity did not correlate with age in the ZI subgroup (R² = 0.04; P = 0.38). Furthermore, the increment in octaves/month was much lower in the ZI subgroup.

CONCLUSIONS

Our data indicate that visual acuity losses only occur in infants who suffered gestational-infection, not simply exposure. Lack of correlation between age and visual acuity in the ZI subgroup suggests a slowing of visual development even in the absence of microcephaly. This result may have broad implications for the deleterious effects of ZIKV on the central nervous system.

Electrodiagnosis of dichromacy

Retinal and cortical signals initiated by a single cone type can be recorded using the spectral compensation (or silent substitution) paradigm. Moreover, responses to instantaneous excitation increments combined with gradual excitation decreases are dominated by the response to the excitation increment. Similarly, the response to a sudden excitation decrement dominates the overall response when combined with a gradual excitation increase. Here ERGs and VEPs were recorded from 34 volunteers [25.9 ± 10.4 years old (mean ± 1 SD); 25 males, 9 females] to sawtooth flicker (4 Hz) stimuli that elicited L- or M-cone responses using triple silent substitution. The mean luminance (284 cd/m²) and the mean chromaticity (x = 0.5686, y = 0.3716; CIE 1931 color space) remained constant and thus the state of adaptation was the same in all conditions. Color discrimination thresholds along protan, deutan, and tritan axes were obtained from all participants. Dichromatic subjects were genetically characterized by molecular analysis of their opsin genes. ERG responses to L-cone stimuli were absent in protanopes whereas ERG responses to M-cone stimuli were strongly reduced in deuteranopes. Dichromats showed generally reduced VEP amplitudes. Responses to cone-specific stimuli obtained with standard electrophysiological methods may give the same classification as that obtained with the Cambridge Colour Test and in some cases with the genetic analysis of the L- and M-opsin genes. Therefore, cone-specific ERGs and VEPs may be reliable methods to detect cone dysfunction. The present data confirm and emphasize the potential use of cone-specific stimulation, combined with standard visual electrodiagnostic protocols.

Individual Test Point Fluctuations of Macular Sensitivity in Healthy Eyes and Eyes With Age-Related Macular Degeneration Measured With Microperimetry

Purpose

To establish fluctuation limits, it was considered that not only overall macular sensitivity but also fluctuations of individual test points in the macula might have clinical value.

Methods

Three repeated measurements of microperimetry were performed using the Standard Expert test of Macular Integrity Assessment (MAIA) in healthy subjects (N = 12, age = 23.8 ± 1.5 years old) and in patients with age-related macular degeneration (AMD) (N = 11, age = 68.5 ± 7.4 years old). A total of 37 macular points arranged in four concentric rings and in four quadrants were analyzed individually and in groups.

Results

The data show low fluctuation of macular sensitivity of individual test points in healthy subjects (average = 1.38 ± 0.28 dB) and AMD patients (average = 2.12 ± 0.60 dB). Lower sensitivity points are more related to higher fluctuation than to the distance from the central point. Fixation stability showed no effect on the sensitivity fluctuation. The 95th percentile of the standard deviations of healthy subjects was, on average, 2.7 dB, ranging from 1.2 to 4 dB, depending on the point tested.

Conclusion

Point analysis and regional analysis might be considered prior to evaluating macular sensitivity fluctuation in order to distinguish between normal variation and a clinical change.

Translational Relevance

Statistical methods were used to compare repeated microperimetry measurements and to establish fluctuation limits of the macular sensitivity. This analysis could add information regarding the integrity of different macular areas and provide new insights into fixation points prior to the biofeedback fixation training.

L-/M-cone opponency in visual evoked potentials of human cortex

L and M cones send their signals to the cortex using two chromatic (parvocellular and blue-yellow koniocellular) and one luminance (magnocellular) pathways. These pathways contain ON and OFF subpathways that respond to excitation increments and decrements respectively. Here, we report on visually evoked potentials (VEP) recordings that reflect L- and M-cone driven increment (LI and MI) and decrement (LD and MD) activity. VEP recordings were performed on 12 trichromats and four dichromats (two protanopes and two deuteranopes). We found that the responses to LI strongly resembled those to MD, and that LD and MI responses were very similar. Moreover, the lack of a photoreceptor type (L or M) in the dichromats led to a dominance of the ON pathway of the remaining photoreceptor type. These results provide electrophysiological evidence that antagonistic L/M signal processing, already present in the retina and the lateral geniculate nucleus (LGN), is also observed at the visual cortex. These data are in agreement with results from human psychophysics where MI stimuli lead to a perceived brightness decrease whereas LI stimuli resulted in perceived brightness increases. VEP recording is a noninvasive tool that can be easily and painlessly applied. We propose that the technique may provide information in the diagnosis of color vision deficiencies.

The influence of stimulus size on heterochromatic modulation electroretinograms

When combined with the electroretinogram (ERG), the heterochromatic flicker photometry procedure allows an objective in vivo assessment of postreceptoral activity. Responses evoked at intermediate (approximately 12 Hz) and high (>30 Hz) temporal frequencies reflect the red-green cone opponent (possibly parvocellular) and the luminance (possibly magnocellular) responses, respectively. Previously, we found that cone-isolating stimuli at intermediate temporal frequencies elicited ERG responses with similar amplitudes and phases for different spatial arrangements of the stimuli, whereas response amplitudes at high temporal frequencies were positively correlated with stimulus size. The purpose of this study was to investigate whether the influence of stimulus size was confined to cone-isolating stimuli or whether it was a general feature of heterochromatic stimulation. Furthermore, we aimed to determine the smallest spatial extent for a significant response in the two postreceptoral mechanisms. Monocular ERGs were recorded to red-green counterphase modulated sinusoidal stimuli (mean luminance of 200 cd/m2) presented at 12 and 36 Hz at different stimulus sizes. At each stimulus condition, a series of ERGs were recorded with the red-contrast fraction (FR) [FR = CR/(CR + CR)] of the stimulus varying between 0.0 and 1.0. Response amplitudes at 36 Hz changed with FR for all subjects, exhibiting a V-shaped amplitude profile with a minimum close to the psychophysics-based isoluminance, where the ERG phase changed by 180°. As stimulus size decreased, the amplitudes to 36 Hz also decreased. In contrast, amplitudes and phases at 12 Hz generally were constant for all values of FR. These amplitudes were invariant to stimulus sizes larger than 10° but decreased with decreasing stimulus size below 10°. Phase also changed in this range. Thus, luminance pathway ERG responses (36 Hz) show direct dependency on stimulus size, whereas chromatic pathway responses (12 Hz) are independent of the stimulus size above 10°.

Dystrophin Is Required for Proper Functioning of Luminance and Red-Green Cone Opponent Mechanisms in the Human Retina

PURPOSE

Visual information is processed in parallel pathways in the visual system. Parallel processing begins at the synapse between the photoreceptors and their postreceptoral neurons in the human retina. The integrity of this first neural connection is vital for normal visual processing downstream. Of the numerous elements necessary for proper functioning of this synaptic contact, dystrophin proteins in the eye play an important role. Deficiency of muscle dystrophin causes Duchenne muscular dystrophy (DMD), an X-linked disease that affects muscle function and leads to decreased life expectancy. In DMD patients, postreceptoral retinal mechanisms underlying scotopic and photopic vision and ON- and OFF-pathway responses are also altered.

METHODS

In this study, we recorded the electroretinogram (ERG) while preferentially activating the (red-green) opponent or the luminance pathway, and compared data from healthy participants (n = 16) with those of DMD patients (n = 10). The stimuli were heterochromatic sinusoidal modulations at a mean luminance of 200 cd/m2. The recordings allowed us also to analyze ON and OFF cone-driven retinal responses.

RESULTS

We found significant differences in 12-Hz response amplitudes and phases between controls and DMD patients, with conditions with large luminance content resulting in larger response amplitudes in DMD patients compared to controls, whereas responses of DMD patients were smaller when pure chromatic modulation was given.

CONCLUSIONS

The results suggest that dystrophin is required for the proper function of luminance and red-green cone opponent mechanisms in the human retina.

Asymmetrical Functional Deficits of ON and OFF Retinal Processing in the mdx3Cv Mouse Model of Duchenne Muscular Dystrophy

Purpose

The dystrophin mouse mutant mdx3Cv exhibits scotopic electroretinograpic (ERG) abnormalities, which resemble clinical changes observed in Duchenne muscular dystrophy (DMD) patients. In the present study, ERGs obtained from mdx3Cv and their wild-type littermates under scotopic, mesopic, and photopic conditions were analyzed to provide further insight on the affected retinal pathways, and to compare them with human data.

Methods

Electroretinograms of mdx3Cv (n = 9) and age-matched C57BL/6J mice (n = 10) included the scotopic full-field flash (for outer retinal deficits in rod pathway), scotopic threshold response (for inner retinal integrity), photopic flash, sinusoidal flicker (for outer retinal deficits in cone pathway), mesopic rapid-on/-off sawtooth flicker, and photopic long-duration flash measurements (for separate ON-/OFF-responses under different conditions).

Results

The mdx3Cv mice exhibited diminished and delayed scotopic and photopic ERGs, particularly in their b-wave and oscillatory potentials. Interestingly, homologues to the a- and b-wave of the mesopic ON-response were affected in their peak/trough times but not in their amplitude, whereas changes to both features were uncovered for photopic ON-response and sinusoidal flicker. Mesopic and photopic OFF-components were within the norm.

Conclusions

Abnormal scotopic and photopic flash ERGs were observed in mdx3Cv, which corroborate with deficits that are likely restricted to the level of photoreceptor-to-bipolar cell transmission. Further overlaps between mdx3Cv mice and DMD patients exist, including asymmetrical ON versus OFF ERG alterations under mesopic versus photopic vision. In mice, ON-pathway function is compromised, whereas the OFF-pathway is spared.

Longitudinal measurements of luminance and chromatic contrast sensitivity: comparison between wavefront-guided LASIK and contralateral PRK for myopia

PURPOSE

The present study aimed to compare the postoperative contrast sensitivity functions between wavefront-guided LASIK eyes and their contralateral wavefront-guided PRK eyes.

METHODS

The participants were 11 healthy subjects (mean age=32.4 ± 6.2 years) who had myopic astigmatism. The spatial contrast sensitivity functions were measured before and three times after the surgery. Psycho and a Cambridge graphic board (VSG 2/4) were used to measure luminance, red-green, and blue-yellow spatial contrast sensitivity functions (from 0.85 to 13.1 cycles/degree). Longitudinal analysis and comparison between surgeries were performed.

RESULTS

There was no significant contrast sensitivity change during the one-year follow-up measurements neither for LASIK nor for PRK eyes. The comparison between procedures showed no differences at 12 months postoperative.

CONCLUSIONS

The present data showed similar contrast sensitivities during one-year follow-up of wave-front guided refractive surgeries. Moreover, one year postoperative data showed no differences in the effects of either wavefront-guided LASIK or wavefront-guided PRK on the luminance and chromatic spatial contrast sensitivity functions.

ON and OFF electroretinography and contrast sensitivity in Duchenne muscular dystrophy

PURPOSE

The study investigated possible asymmetric dysfunction of the ON and OFF visual mechanisms in DMD (Duchenne muscular dystrophy) patients associated with specific genetic alterations.

METHODS

nineteen DMD patients and 7 heterozygous dmd carriers were tested, as well as 19 age-matched controls.Full-field ergs were recorded using mesopic (1 cd/m(2)) and photopic (250 cd/m(2)) sawtooth luminance modulations as stimuli: rapid increase and ramping decrease (to isolate ON responses) or rapid decrease and ramping increase (for OFF responses). In addition, a psychophysical study comprised contrast sensitivity tests using two checkerboard stimuli at either higher (ON) or lower (OFF) luminance relative to the background: 0.3 cycles per degree (cpd) presented for 33 ms (low spatial frequency, short duration) and 2 cpd presented for 1500 ms (high spatial frequency, long duration).

RESULTS

A significant ERG amplitude reduction, relative to controls, was detected in the DMD patients in the mesopic positive peaks for both ON and OFF stimuli, as well as for the photopic ON stimulus (P < 0.05). Contrast sensitivity was significantly lower in the DMD patients (P < 0.05) relative to controls for the ON stimuli. Neither the ERG nor the contrast sensitivities were altered in the carriers.

CONCLUSIONS

This study suggests that there are ON and OFF ERG alterations when both rods and cones contribute to the ERG responses in DMD patients. When only cones are activated there is an asymmetrical ERG alteration, also revealed by the contrast sensitivity measurements.

Chromatic spatial contrast sensitivity estimated by visual evoked cortical potential and psychophysics

The purpose of the present study was to measure contrast sensitivity to equiluminant gratings using steady-state visual evoked cortical potential (ssVECP) and psychophysics. Six healthy volunteers were evaluated with ssVECPs and psychophysics. The visual stimuli were red-green or blue-yellow horizontal sinusoidal gratings, 5° × 5°, 34.3 cd/m² mean luminance, presented at 6 Hz. Eight spatial frequencies from 0.2 to 8 cpd were used, each presented at 8 contrast levels. Contrast threshold was obtained by extrapolating second harmonic amplitude values to zero. Psychophysical contrast thresholds were measured using stimuli at 6 Hz and static presentation. Contrast sensitivity was calculated as the inverse function of the pooled cone contrast threshold. ssVECP and both psychophysical contrast sensitivity functions (CSFs) were low-pass functions for red-green gratings. For electrophysiology, the highest contrast sensitivity values were found at 0.4 cpd (1.95 ± 0.15). ssVECP CSF was similar to dynamic psychophysical CSF, while static CSF had higher values ranging from 0.4 to 6 cpd (P < 0.05, ANOVA). Blue-yellow chromatic functions showed no specific tuning shape; however, at high spatial frequencies the evoked potentials showed higher contrast sensitivity than the psychophysical methods (P < 0.05, ANOVA). Evoked potentials can be used reliably to evaluate chromatic red-green CSFs in agreement with psychophysical thresholds, mainly if the same temporal properties are applied to the stimulus. For blue-yellow CSF, correlation between electrophysiology and psychophysics was poor at high spatial frequency, possibly due to a greater effect of chromatic aberration on this kind of stimulus.

Long-term occupational exposure to organic solvents affects color vision, contrast sensitivity and visual fields

The purpose of this study was to evaluate the visual outcome of chronic occupational exposure to a mixture of organic solvents by measuring color discrimination, achromatic contrast sensitivity and visual fields in a group of gas station workers. We tested 25 workers (20 males) and 25 controls with no history of chronic exposure to solvents (10 males). All participants had normal ophthalmologic exams. Subjects had worked in gas stations on an average of 9.6±6.2 years. Color vision was evaluated with the Lanthony D15d and Cambridge Colour Test (CCT). Visual field assessment consisted of white-on-white 24–2 automatic perimetry (Humphrey II-750i). Contrast sensitivity was measured for sinusoidal gratings of 0.2, 0.5, 1.0, 2.0, 5.0, 10.0 and 20.0 cycles per degree (cpd). Results from both groups were compared using the Mann–Whitney U test. The number of errors in the D15d was higher for workers relative to controls (p<0.01). Their CCT color discrimination thresholds were elevated compared to the control group along the protan, deutan and tritan confusion axes (p<0.01), and their ellipse area and ellipticity were higher (p<0.01). Genetic analysis of subjects with very elevated color discrimination thresholds excluded congenital causes for the visual losses. Automated perimetry thresholds showed elevation in the 9°, 15° and 21° of eccentricity (p<0.01) and in MD and PSD indexes (p<0.01). Contrast sensitivity losses were found for all spatial frequencies measured (p<0.01) except for 0.5 cpd. Significant correlation was found between previous working years and deutan axis thresholds (rho = 0.59; p<0.05), indexes of the Lanthony D15d (rho = 0.52; p<0.05), perimetry results in the fovea (rho = −0.51; p<0.05) and at 3, 9 and 15 degrees of eccentricity (rho = −0.46; p<0.05). Extensive and diffuse visual changes were found, suggesting that specific occupational limits should be created.

Heterochromatic flicker electroretinograms reflecting luminance and cone opponent activity in glaucoma patients

PURPOSE

To measure heterochromatic flicker electroretinograms (ERGs) at high (36 Hz) and intermediate (12 Hz) temporal frequencies to evaluate luminance and cone opponent responses, respectively, in glaucoma eyes with (perimetric) and without (preperimetric) visual field defects.

METHODS

Flicker ERGs were recorded from one randomly chosen dilated eye of 32 patients (mean age, 61 ± 11 years; 15 men, 17 women) from the Erlangen Glaucoma Registry and from 24 healthy volunteers (mean age, 43 ± 11 years; 14 men, 10 women). Red and green light-emitting diodes in a Ganzfeld stimulator were sine wave-modulated in counterphase. The responses were measured at 36 Hz, the frequency at which ERGs reflect activity of the luminance pathway, and at 12 Hz, the frequency at which ERGs reflect chromatic activity.

RESULTS

Response amplitudes were similar in glaucoma patients and controls. Phase differences were observed in patients with visual field defects (perimetric) compared with the control group at 36 and 12 Hz in the first harmonic and second harmonic responses. Patients without visual field defects (preperimetric) showed phase differences for the second harmonic component at 36 Hz. No age effect on response amplitudes and phases was found in any of the subject groups (controls and patients).

CONCLUSIONS

The responses displayed phase differences but not amplitude differences in perimetric glaucoma patients at both 36 and 12 Hz, suggesting that both magnocellular and parvocellular pathways are affected. Preperimetric glaucoma patients also showed phase differences. The response phase may be sensitive to early dysfunction of the inner retina. (ClinicalTrials.gov number, NCT00494923).

Absence of ocular interaction in flicker ERG responses reflecting cone opponent and luminance signals

The aim of the study was to investigate whether there is an ocular interaction in the flicker ERG responses reflecting luminance and cone opponency in normal human subjects. Flicker ERGs were recorded from one dilated eye of 10 healthy volunteers. Each subject was tested twice: once with and once without occluding the opposite eye. Red and green LEDs were modulated in counterphase in a Ganzfeld stimulator. ERG responses were recorded for different ratios of the modulation in the red and green LEDs and at 12 and 36 Hz. The amplitudes and phases of the fundamental components were compared between the conditions with and without occlusion. The 12-Hz flicker ERGs reflected activity of the cone opponent channel, whereas the 36-Hz data reflected luminance activity. There were no significant differences between the conditions with and without occluding the opposite eye for any of the stimulus protocols. Ocular interaction is absent in flicker ERGs reflecting cone opponent and luminance activity.

Visual field losses in workers exposed to mercury vapor

Visual field losses associated with mercury (Hg) exposure have only been assessed in patients exposed to methylmercury. Here we evaluate the automated visual field in 35 ex-workers (30 males; 44.20+/-5.92 years) occupationaly exposed to mercury vapor and 34 controls (21 males; 43.29+/-8.33 years). Visual fields were analyzed with the Humphrey Field Analyzer II (model 750i) using two tests: the standard automated perimetry (SAP, white-on-white) and the short wavelength automated perimetry (SWAP, blue-on-yellow) at 76 locations within a 27 degrees central visual field. Results were analyzed as the mean of the sensitivities measured at the fovea, and at five successive concentric rings, of increasing eccentricity, within the central field. Compared to controls, visual field sensitivities of the experimental group measured using SAP were lower for the fovea as well as for all five eccentricity rings (p<0.05). Sensitivities were significantly lower in the SWAP test (p<0.05) for four of the five extra-foveal eccentricity rings; they were not significant for the fovea (p=0.584) or for the 15 degrees eccentricity ring (p=0.965). These results suggest a widespread reduction of sensitivity in both visual field tests. Previous reports in the literature describe moderate to severe concentric constriction of the visual field in subjects with methylmercury intoxication measured manually with the Goldman perimeter. The present results amplify concerns regarding potential medical risks of exposure to environmental mercury sources by demonstrating significant and widespread reductions of visual sensitivity using the more reliable automated perimetry.