Marko Hawlina

Standard for pattern electroretinography. International Society for Clinical Electrophysiology of Vision.

The pattern electroretinogram (PERG) is a retinal response evoked by viewing an alternating checkerboard or grating. It receives clinical and research attention because it can provide information about inner retinal cells and the macula. However, clinicians may have trouble choosing between different techniques for recording the PERG that have been described in the literature. The International Society for Clinical Electrophysiology of Vision has prepared a standard for a basic PERG recording procedure to aid new users in obtaining reliable responses and to encourage more uniformity among existing users.

New noncorneal HK-loop electrode for clinical electroretinography

A new noncorneal electrode for clinical electroretinography was developed. It consists of a thin wire forming a loop modeled to fit into the lower conjunctival sac. Electrical contact is made with the scleral conjunctiva through an exposed portion of otherwise insulated wire. The recorded pattern electroretinograms are in the same amplitude range as if recorded by the gold foil electrode, while the flash electroretinograms with the new electrode are of about two-thirds the amplitude of corneal electrodes. The new electrode is more durable and hence less expensive than gold foil electrodes and can likewise be used without topical anesthetic. Cleaning is easy and effective. The electrode rarely causes discomfort and produces stable responses for at least 2 hours. The electrode aims to match stability of skin electrodes with sensitivity of fragile foil and fiber electrodes.

Phenotypic Variation in Enhanced S-cone Syndrome

PURPOSEnTo characterize the clinical, psychophysical, and electrophysiological phenotype of 19 patients with enhanced S-cone syndrome (ESCS) and relate the phenotype to the underlying genetic mutation.nnnMETHODSnPatients underwent ophthalmic examination and functional testing including pattern ERG, full-field ERG, and long-duration and short-wavelength stimulation. Further tests were performed in some patients, including color contrast sensitivity (CCS), multifocal ERG, fundus autofluorescence imaging (FAI), optical coherence tomography (OCT), and fundus fluorescein angiography (FFA). Mutational screening of NR2E3 was undertaken in 13 patients.nnnRESULTSnThe fundus appearance was variable, from normal to typical nummular pigment clumping at the level of the retinal pigment epithelium in older patients. Nine patients had foveal schisis, and one had peripheral schisis. Pattern ERG was abnormal in all patients. In all patients, ISCEV Standard photopic and scotopic responses had a similar waveform, the rod-specific-ERG was undetectable and the 30-Hz flicker ERG was markedly delayed with an amplitude lower than the photopic a-wave. Most ERG responses arose from short-wavelength-sensitive mechanisms, and a majority of patients showed possible OFF-related activity. Multifocal ERG showed relative preservation of central function, but reduced responses with increased eccentricity. Mutations were identified in NR2E3 in 12 of 13 patients including four novel variants.nnnCONCLUSIONSnThe phenotype in ESCS is variable, both in fundus appearance and in the severity of the electrophysiological abnormalities. The ERGs are dominated by short-wavelength-sensitive mechanisms. The presence, in most of the patients, of possible OFF-related ERG activity is a finding not usually associated with S-cones.

Diurnal variations in the electroretinographic c-wave and retinal melatonin content in rats with inherited retinal dystrophy

The inability of retinal pigment epithelium to phagocytose shed photoreceptor disks is a cause of retinal degeneration in the Royal College of Surgeons rat; retinal pigment epithelial phagocytosis and disk shedding are regulated by the diurnal rhythm of retinal melatonin level. The diurnal rhythms of the electroretinogram (particularly that of the retinal pigment epithelial potential, the electroretinographic c-wave) and retinal melatonin content were thus investigated in Royal College of Surgeons rats from postnatal day 17 to 24, the period preceding retinal degeneration. The amplitudes of both the b- and c-waves of the electroretinogram fell significantly during the peak time of rod disk shedding and rose after the time of expected light off in the control and dystrophic rats. While the b-wave rhythms did not differ between the two strains, diurnal changes in the c-wave were significantly less distinct in the dystrophic rats than in controls. This difference may reflect lack of phagocytosis in dystrophic rats. Furthermore, the ERG c-wave was significantly larger and prolonged, and the retinal melatonin content higher, in dystrophic rats of this age group than in controls. It appears that retinal melatonin metabolism may play an important role in the maintenance of retinal pigment epithelial and photoreceptor function.

Central fiber contribution to W-shaped visual evoked potentials in patients with optic neuritis.

We studied W-shaped waveforms that occurred in full-field responses to pattern large-field stimulation in patients who had optic neuritis. Affected eyes showed no absolute scotomata; visual acuity was normal at the time of recording. To evaluate the contribution of macular- and paramacular-derived components to the development of the W-shaped waveforms in the patients, half-field and central full-field stimulation was used. The responses were compared with those obtained with the use of experimental scotomata in healthy subjects.The W-shaped waveforms recorded in the patients closely resembled the responses observed in healthy subjects after the introduction of experimental scotomata. In all affected eyes, half-field stimulation showed absence of the ipsilateral P100 component or its interaction with the P135 component. Enhanced paramacular N105 and P135 components were seen over the contralateral hemisphere. Responses to central full-field stimulation were an attenuated and prolonged P100 in the majority of affected eyes.Results of our study showed that W-shaped waveforms in response to large full-field stimulation may reflect impaired function of macular fibers. These electrophysiologic findings, however, were not always associated with evidence of a central field defect demonstrated by Friedmann perimetry.

Electroretinography and optical coherence tomography reveal abnormal post-photoreceptoral activity and altered retinal lamination in patients with enhanced S-cone syndrome

PurposeTo compare functional abnormalities of enhanced S-cone syndrome (ESCS), as examined using standard and extended electroretinography (ERG), with structural findings and retinal architecture obtained by spectral domain optical coherence tomography (SD-OCT).MethodsFour patients with ESCS underwent standard full-field and multifocal ERGs, with extended S-cone and ON/OFF ERG protocols also performed. SD-OCT was also carried out, and longitudinal reflectivity profiles (LRPs) were calculated for the perifoveolar retina.ResultsAll four patients exhibited pathognomonic full-field ERG findings for ESCS, with delayed responses of similar waveforms to the same intensity flash under both scotopic and photopic conditions. The amplitudes of the full-field ERGs showed considerable variation between patients, which were not related to the extent of the visual field defects. Multifocal ERGs reflected preserved central function in eyes with good visual acuity (Snellen visual acuity >0.7). The ERGs to S-cone-specific stimulation confirmed the expected predominant activity of the S-cone system in all four patients. The ON/OFF ERG recordings revealed abnormal presence of both ON-response and OFF-response activities in three patients; the remaining patient showed only OFF-response activity. SD-OCT showed a significantly thickened outer nuclear layer in all four patients, as obtained by LRP analysis. Furthermore, in the patient with selective preservation of the OFF-response activity, LRP showed reduced numbers of hyper-reflectivity sub-peaks in the inner plexiform layer.ConclusionPatients with ESCS show characteristic full-field ERG waveform abnormality, predominance of S-cone ERG activity, and thickening of the outer nuclear layer on SD-OCT. Moreover, they can also show abnormal post-photoreceptor connectivity through S-cone-related OFF-bipolar cell activity.

Enhanced S-cone syndrome with preserved macular structure and severely depressed retinal function

We present ophthalmic features and genetic analysis findings of a 44-year-old croatian patient with enhanced S-cone syndrome (ESCS). Complete ophthalmic examination, Ishihara colour vision test, dark adaptometry, spectral-domain optical coherence tomography (SD-OCT), fundus autofluorescence imaging, Goldmann visual field and automated perimetry, full-field electroretinography (ERG), multifocal ERG, S-cone ERG and ON–OFF ERG were performed. Mutation screening of the NR2E3 gene, which encodes a photoreceptor-specific orphan nuclear receptor, was performed with polymerase chain reaction amplification and direct sequencing. The patient has good visual acuity and normal colour vision. Fundus examination showed normal posterior pole and nummular pigment depositions at the level of the retinal pigment epithelium in the mid-periphery of the retina. The SD-OCT images showed normal macular structure and thickness. The ERG showed characteristic findings: photopic and scotopic responses to the same stimulus had a similar waveform and were dominated by short-wavelength-sensitive mechanisms. Mutation analysis revealed the known NR2E3 mutation c.481delA (p.Thr161HisFsX18) and the novel NR2E3 variant c.1120Cxa0>xa0T (p.Leu374Phe). To the best of our knowledge, this is the only ESCS patient older than 40xa0years who phenotypically has preserved macular structure, good central visual acuity and severely depressed full-field ERG as well as the first reported patient with NR2E3 mutation from Croatia.

Light-emitting diodes and half-cell electrodes in experimental recording of electroretinogram c-wave

A method of electroretinogram c-wave recording in the rat was developed that uses a contact lens electrode connected through a saline bridge with a silver-silver chloride half-cell. A cluster of light-emitting diodes, regulated by an electronic light-emitting diode stimulator, was used as a light source. The method enables recordings of c-waves of 0.4–1.6 mV amplitude as well as other electroretinogram components in narrow limits of variation. The two main sources of response variability are voltage shunting and eyeball protrusion.

Laser Clearance of Drusen Deposit in Patients With Autosomal Dominant Drusen (p.Arg345Trp in EFEMP1)

PURPOSEnTo assess whether laser treatment to the retinal pigment epithelium anterior to drusen in eyes of patients with EFEMP1-related maculopathy affects visual acuity, deposit volume, and retinal sensitivity.nnnDESIGNnProspective, interventional case series.nnnMETHODSnIn 11 patients with autosomal dominant drusen and confirmed disease-causing EFEMP1 mutation, the worse-seeing eye was treated with Argon green laser (10 to 15 laser spots; 200-μm spot size, 0.1-second duration, 80 to 120 mW). Patients were examined before treatment as well as 1, 3, 6, and 12xa0months after the procedure. Clinical assessment included visual acuity, fundus-controlled perimetry, spectral-domain optical coherence tomography, and autofluorescence imaging. Custom-made software allowed for coregistration of fundus-controlled perimetry and spectral-domain optical coherence tomography data sets. The main outcome measures were change in visual acuity, retinal sensitivity, and drusen volume.nnnRESULTSnThe untreated eyes lost an average of 0.8 letters, whereas the treated eyes gained an average of 4.9 letters. For fundus-controlled perimetry, locus-by-locus differences in sensitivity were calculated between pretreatment and posttreatment assessments; subsequently, the overall difference in the treated and untreated eye was compared. Five patients showed significant improvement in retinal sensitivity, 5 patients showed no change, and 1 patient showed significant deterioration. An increase in mean drusen thickness was observed in the untreated eyes, but not in the treated eyes (Pxa0= .0322). The thickness of the drusen correlated with retinal sensitivity (ρxa0=xa0-0.49; P < .0001). Safety was demonstrated and no adverse events were observed.nnnCONCLUSIONSnLow-energy laser treatment is safe andxa0may be effective in the treatment of autosomal dominant drusen. Further evaluation with long-term assessment is required to confirm the benefits.

Visual evoked potential abnormalities in compressive chiasmal lesions: the relevance of central visual field defects

In healthy subjects, the pattern visual evoked potential (VEP) arises predominantly from the stimulation of the central 5 degrees of the visual field. This central-field paradigm is well confirmed in VEP studies of retrochiasmal lesions, but it appears to be more ambiguous in patients with compressive lesions of the chiasm. To further clarify how central and peripheral visual field defects affect VEP, we compared the Goldmann perimetric charts with the frequency and type of VEP abnormalities in 25 patients in whom a compressive chiasmal lesion had been confirmed by CT. Perimetric findings were compared with the full-field and half-field VEP records with regard to the presence or absence of defects within the 0-5 degrees of the visual field. Full-field VEP abnormalities were present in all eyes with absolute, in 81% of the eyes with relative central visual field defects, and in 59% of the eyes with no impairment of the central visual field. Half-field VEP abnormalities were found in all half-fields with ab...