Florence Rigaudière

Is there a systematic location for the pseudo-fovea in patients with central scotoma?

The retinal location of preferential fixations of twenty-four patients with central scotoma were studied when reading digits projected onto their retina with a scanning laser ophthalmoscope. In the majority of cases the fixation was located on the left part, or the inferior part of the visual field relative to the central scotoma. The fact that the inferior visual field is used is coherent with the notion that the lower visual field is important for locomotion. However the preferential use of the left field appears contradictory with data showing superiority of visual faculties in the right visual field. This result may possibly be explained in relation to the need for left-to-right readers to monitor where their eyes have landed relative to the word previously fixated on the left.

Functional assessment of macular hole surgery by scanning laser ophthalmoscopy.

OBJECTIVE This study aimed to evaluate more precisely the benefit of macular hole surgery. DESIGN The design was a prospective study of 40 eyes in 40 patients examined before and after surgery of full-thickness macular holes with a scanning laser ophthalmoscope (SLO). PARTICIPANTS Forty patients with full-thickness macular holes participated. Three of the holes were stage 2, 23 were stage 3, and 14 were stage 4. INTERVENTION The SLO examination consisted of macular imaging and assessment of macular function using tests produced by an acousto-optical modulator. MAIN OUTCOME MEASURES Preferred retinal locus (PRL) was determined, visual acuity was measured, and scotoma was detected by microscotometry and by the line test (modified Watzke-Allen test). RESULTS Anatomic success was achieved in 32 of 40 cases as assessed biomicroscopically. On SLO examination before surgery, macular holes were seen as a central bright round disc outlined by a thin dark edge surrounded by a dark ring and a less dark area with ill-defined limits. In all cases, the PRL was located on the upper edge of the hole, a scotoma was always detected inside the hole, and the line was seen as broken in 26 of 32 cases. After surgery, the hole closed completely in 25 of 32 eyes; it disappeared from 14 of these 25 eyes and was replaced by a dark or clear disc in 11. In the other seven successful cases, its size shrank and its edge flattened but remained faintly visible. The hole remained unchanged in eight cases. Eccentric PRL became central in 28 of 32 cases. The scotoma disappeared in 23 of 32 cases. The line was seen as continuous in 24 of 32 cases. Complete anatomic and functional successes were achieved in 19 of the 32 cases of macular hole closure. CONCLUSION The SLO examination allows accurate assessment of the anatomic and functional results of macular hole surgery. Various degrees of functional success were recorded, depending on the test used.

A practical method to obtain reproducible binocular electroretinograms in dogs

We present a simple method to record highly reproducible binocular electroretinograms in dogs. Rod and cone electroretinograms were elicited in 60 Beagle dogs, with the use of two adjustable photostimulators, one directed at each eye, and maintained in position with the use of a special device. Data analysis revealed no significant differences in amplitudes between the right and the left eye for each animal and each recording session, thus attesting to the high reliability of our approach. In a few instances, however, small interocular timing differences were noted. The proposed approach could therefore be used not only in a clinical setup where the functional status of the two eyes is often needed to reach a diagnosis but also in research projects, such as toxicological assays, where the experimentation is performed on one eye while the other is kept as control.

Recording the photopic electroretinogram from conscious adult Yucatan micropigs.

The micropig is viewed by many as one of the best animal models of human system physiology. The purpose of this study was to develop a simple, rapid and reliable method to record clinical electroretinograms from conscious adult Yucatan micropigs. Photopic ERGs were recorded from 18 conscious animals following a 3-h period of preadaptation to a moderate photopic environment. Rectal temperature and blood pressure were monitored throughout the experiment. In order to test the reproducibility of our procedure, the same protocol was repeated (n=6 micropigs) on three different recording sessions each separated by a 48-h period. Our results indicate that the recording of reproducible ERGs, in the conscious Yucatan micropig, is feasible provided that an adequate experimental approach is used. We believe that our method will enable investigators to perform retinal physiology experiments using an approach which is compatible with that used in a human clinical setup thus facilitating the transposition of experimental data from animal to human.

Contribution of scanning laser ophthalmoscopy to the functional investigation of subjects with macular holes

A study was designed to validate a functional investigation performed with the scanning laser ophthalmoscope before surgery for macular holes in 12 eyes: The assessment included fundus examination, a functional examination resulting in evaluation of the preferred retinal lows, visual acuity and recording of visual evoked potentials. The preferred retinal locus was evaluated by presenting a small square area, and visual acuity was determined by means of calibrated figures. The visual evoked potentials were evoked by three alternating checkerboards (check size, 30′, 2 Hz) centered over the hole and seen at an angle of 6.5 × 6.5°, 2.5 × 2.5° and 6.5 × 6.5° with central exclusion of 2.5 × 2.5°. The appearance of the fundus visualized by scanning laser ophthalmoscopy consisted of a clear central disk corresponding to the hole, surrounded by a very dark ring, associated with a second, less dark ring with unclear margins. Fixation was unstable in one case with a visual acuity of 20/70. In 11 cases, fixation was localized to the superior retina with a visual acuity superior to 20/70. The visual evoked potentials evoked by 6.5 × 6.5° were discernible in all 12 eyes; visual evoked potential by annular stimuli were discernible in 11 cases. The 2.5 × 2.5° stimulus evoked no response in eight cases, proving the area of the hole was nonfunctional. A response was recorded in the four other cases, where the dimension of the holes was less than 2°. The results of this scanning laser ophthalmoscopic assessment demonstrated a precise evaluation of the residual macular function in the cases of full-thickness macular holes.

ERGs in female carriers of incomplete congenital stationary night blindness (I-CSNB). A family report.

ERG findings in five sisters are reported. By pedigree analysis, four of the five must be obligate carriers for I-CSNB since their sons were affected (impaired night vision, reduced visual acuity, variable ametropia, congenital nystagmus and ERG with both scotopic and photopic b-wave reduced amplitude). The fifth was childless at the time of examination and her ERG analysis was normal. Three of the four obligate carriers showed significant reduction in the sum of the OPs amplitude as previously reported as being an electrophysiological signs in female carriers: two without alteration in other ERG components and the third with association with a flicker ERG amplitude significantly increased. The fourth female carrier showed a normal sum of the OPs amplitude whereas the other b-wave ERG or flicker amplitudes were significantly decreased. These last two ERG results suggest a possible modifications of synaptic transmission at a post-receptoral site (outer plexiform layer or involvement of the bipolar pathways) in these two carriers.

Comprendre et tester les déficiences de la vision des couleurs de l'enfant, en pratique

Vision screening of school children at 5-6 years of age must include color vision screening. X-linked dyschromatopsia is the most frequent disorder affecting 8% of boys and 0.4% of girls. This paper presents the physiology of these deficiencies caused by an alteration of the spectral absorption properties of one of the cone pigments (protanomalous or deuteranomalous trichromats) or the absence of one of the pigments (protanopia or deuteranopia), the most frequent. Absence of two of the pigments (blue cone monochromacy) is very rare and differs from achromatopsia. The physiological basis of the main tests for easy clinical screening are presented. Testing methods designed for children are reviewed. The Ishihara test is the most widely used screening test specific for congenital color defects. If the plates are correctly read, the child has normal color vision. If not, arrangement tests such as Panel D 15 and desaturated Panel D 15 tests can be used to diagnose the type of the defect (protan or deutan) and grade the degree of color deficiency according to a strategy adapted to children. Examples of results are presented for each axis along which caps are confused, providing a quick and easy preliminary diagnosis. Early detection of color vision malfunction in children allows parents and teachers to make necessary adjustments to the teaching methods for appropriate learning.Le depistage de la qualite de la vision des enfants en âge d′etre scolarises (a partir de 5-6 ans) doit comprendre un examen de la vision des couleurs, les deficiences liees au chromosome X etant les plus frequentes (8 % des garconnets et 0,4 % des fillettes). Cet article presente les bases neurophysiologiques de ces deficiences, en relation avec les photopigments portes par les cones et leurs classifications. Les principes des tests utilises pour qualifier et quantifier ces deficiences sont rappeles et relies aux bases de la physiologie visuelle, ce qui en facilite la comprehension. Une strategie de depistage est proposee a l′aide de trois tests cliniques faciles a utiliser par le medecin scolaire, generaliste ou pediatre. Le test d′Ishihara est specifique des dyschromatopsies liees a l′X. Si la lecture de ses planches est normale, la vision des couleurs est normale. En cas de doute ou si plusieurs planches sont anormalement percues, les rangements des pions des Panel D 15 standard et desature doivent etre realises successivement. Une strategie est proposee qui aboutit a la qualification de ces deficiences en type protan ou deutan, qui sont les plus frequentes, et a leur quantification : protanopie ou deuteranopie, protanomalie ou deuteranomalie extreme, moderee ou legere. Des exemples sont donnes montrant que, dans la majorite des cas, le depistage est aise et rapide. La reconnaissance precoce d′une deficience de la vision des couleurs est essentielle pour alerter parents ou educateurs sur les limites de la perception coloree de l′enfant et adapter son apprentissage.

Electrophysiological exploration of visual function in mitochondrial diseases

In a group of 10 children (ranging from 5 months to 15 years old) affected by diseases with mitochondrial dysfunction, 4 suffered from mitochondrial myopathy, 4 from mitochondrial encephalopathy and 2 from Friedreichs ataxia. The clinically detectable visual impairment consisted of 3 grey ocular fundi (the other 7 were normal) associated, in 2 subjects, with a mild nystagmus. Electrophysiological assessment, consisting of ERGs and flash VEPs, was systematically performed. The normal ERGs in all subjects confirmed the normal functioning of retinal electrogenesis. In contrast, the VEPs of 6 out of 10 subjects were modified: in 2 of the 4 subjects with mitochondrial myopathy, the VEPs had a hyperamplitude; in the 2 subjects with Friedreichs ataxia, the implicit time of the principal VEP peaks was increased, together with a hyperamplitude in 1 case; lastly, in 2 of the 4 subjects with mitochondrial encephalopathy, the VEPs were altered. These modifications reflected visual pathway conduction disorders with no clinical expression. Various underlying pathophysiological mechanisms possibly responsible for these modifications are discussed.

Colored focal visual evoked potentials by cathode ray tube versus scanning laser ophthalmosope

We compared the focal visual evoked potentials obtained in 52 young subjects with normal vision, evoked by means of three alternating black/color checkerboards generated by a trichromic cathode ray tube (dominant wavelength, 514 nm; colorimetric purity, 0.45) and by means of a scanning laser ophthalmoscope (argon laser beam, 514 nm; colorimetric purity, ≈ 1). These three checkerboards, with an area of 3.5° × 3.5° (stimulating the fovea), then with an area of 3.5° × 3.5° with a central exclusion of 1.5° × 1.5° (stimulating the perifoveola) and finally with an area of 1.5° × 1.5° (stimulating the foveola) were presented within a field (8° × 8°) of homogeneous luminance of 170 cd/m2 and 1500 cd/m2, respectively. Their check sizes were 30′, with a reversal temporal frequency of 0.75 Hz. The transient focal visual evoked potentials recorded with these three stimuli generated by the two types of stimulators were clearly detected for at least 85% of subjects. Their characteristics (waveform, amplitude and culmination times of the different waves) were comparable, regardless of the stimulator used (cathode ray tube or scanning laser ophthalmoscope). These results suggest that, under these various conditions of luminance and colorimetric purity, the neurophysiologic circuits tested function in identical ways. The focal visual evoked potential signs, now clearly defined by means of stimuli generated by cathode ray tubes, therefore apparently can be applied to the focal visual evoked potential evoked by stimuli generated by the scanning laser ophthalmoscope.

Visual Evoked Potentials and Colour Pattern Stimulations

After a historical account and a brief description of the techniques of signal analysis used in the Service Central de Biophysique et Medecine Nucleaire (Hospital Lariboisiere), the authors present the experiments they have undertaken, concerning coloured stimulations. These experiments were carried out in three steps: (a) coloured stimulations on cathode-ray screen, with constant luminance, concerning 8 healthy volunteers; (b) coloured stimulations on patterned screen (pattern reversal), concerning 31 healthy volunteers; (c) development and first stimulations with increased reliability, and offering new possibilities of coloured stimulation. The results evidence two different groups of electrophysiological responses, distinctly related to the presence or absence of a morphoscopic structure in the stimulation. Besides, a significant increase in latencies is observed with blue stimulation.