Jean-Eric Guez

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.

Eye fixations near corners : evidence for a centre of gravity calculation based on contrast, rather than luminance or curvature

Subjects scanned line drawings of polygons in order to count the number of corners. The positions their eyes fixated were studied as a function of the size of the angle and whether the apex of the angle was present or absent. The results showed that the eyes tended to land at a position near the centre of gravity of the corner configurations. The observed landing positions were coherent with the hypothesis that the centre of gravity was calculated within an attentional spotlight centered on the apex of the corners, and that the calculation was based not on the total luminance distribution, nor on the distribution of energy in a neurophysiologically motivated curvature detector, but simply on the basis of a contrast detector.

Scanning laser ophthalmoscope imaging of fluorescein-labelled blood cells

Abstract• Purpose: To demonstrate the feasibility of a technique for the visualization by scanning laser ophthalmoscope (SLO) of fluores cein-labelled autologous leukocytes and platelets in retinal vessels. • Method: Individual blood samples from rats and rabbits were centrifuged to isolate platelets and leukocytes, then passively labelled with fluorescein and reinjected into the same animal. An SLO was used to visualize and record cell displacement in the retinal circulation. Labelled platelets were analysed by flow cytometry. • Results: By SLO, platelets appeared as a heterogeneous particle flow, and individual leukocytes appearing as brighter spots could easily be traced. Flow cytometry showed that after labelling platelets were well individualized and their size was slightly increased. • Conclusion: Circulating blood cells can be visualized in retinal vessels by a simple method consisting of passive labelling of autologous platelets and leukocytes by fluorescein. No platelet toxicity was detected. This method could be applied to the study of blood cell movement in human retinal vascular diseases.

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.

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.

3321 Quantification of metamorphopsia using a scanning laser ophthalmoscope (SLO)

PURPOSE; To assess metamorphopsia in patients with epimacular membrane, using a SLO. METHOD& A SLO wa.s used to project I7 spots on the retina. A first spot considered as a reference appears at a constant place above a central flickering spot. The task consists in moving 15 other spots, appearing one after the other, in order to draw two regular squares as shown in the figure below. ~QQE: C-m of Bkcd-W Barrier (BRB) inward and outward fluxes of flu”#sceia inmlmalindivid”alsatlddiahdicpatialtswithml zically visible rciim&y using high-resdution vitmus

3324 SLO angiography using autologous fluorescent labeled platelets and leukocytes in rabbits

PURPOSE; To assess metamorphopsia in patients with epimacular membrane, using a SLO. METHOD& A SLO wa.s used to project I7 spots on the retina. A first spot considered as a reference appears at a constant place above a central flickering spot. The task consists in moving 15 other spots, appearing one after the other, in order to draw two regular squares as shown in the figure below. ~QQE: C-m of Bkcd-W Barrier (BRB) inward and outward fluxes of flu”#sceia inmlmalindivid”alsatlddiahdicpatialtswithml zically visible rciim&y using high-resdution vitmus