Prospective comparison of ultrasound biomicroscopy and anterior segment optical coherence tomography for evaluation of anterior chamber dimensions in European eyes with primary angle closure.

PURPOSE: To compare the accuracy in measurement of the anterior chamber (AC) angle by anterior segment optical coherence tomography (AS-OCT) and ultrasound biomicroscopy (UBM) in European patients with suspected primary angle closure (PACS), primary angle closure (PAC), or primary angle-closure glaucoma (PACG). DESIGN: Cross-sectional study. METHODS: In all, 55 eyes of 33 consecutive patients presenting with PACS, PAC, or PACG were examined with AS-OCT, followed by UBM. The trabecular-iris angle (TIA) was measured in all four quadrants. The angle-opening distance (AOD) was measured at 500 microm from the scleral spur. The Bland-Altman method was used for assessing agreement between the two methods. RESULTS: The mean (+/-SD) superior TIA was 19.3+/-15.8 degrees in AS-OCT and 15.7+/-15.0 degrees in UBM (P=0.50) and inferior TIA was 17.9+/-12.9 degrees (AS-OCT) and 16.7+/-14.1 degrees (UBM) (P=0.71). The superior AOD(500) was 0.17+/-0.16 mm in UBM and 0.21+/-0.16 mm in AS-OCT (P=0.06). Bland-Altman analysis showed a mean SD of+/-9.4 degrees for superior and inferior TIA and a mean SD of +/-0.10 mm for superior and inferior AOD(500). CONCLUSIONS: This comparative study shows that AS-OCT measurements are significantly correlated with UBM measurements but show poor agreement with each other. We do not believe that AS-OCT can replace UBM for the quantitative assessment of the AC angle.

Coupling of HRT II and AS-OCT to evaluate corneal endothelial cell loss and in vivo visualization of the Ahmed glaucoma valve implant.

AIMS: To report corneal endothelial cell loss and in vivo visualization of the Ahmed glaucoma valve implant in eyes with refractory glaucoma. METHODS: Ten eyes underwent Ahmed valve implant surgery and were followed-up for 12 months. Data collected included intraocular pressure (IOP), number of antiglaucoma medications and surgery-related complications. At 6 and 12 months postoperatively, the intracameral length of the drainage tube (ICL) and the distance between the tube and the cornea (T-C distance), and the iris (T-I distance) were assessed using anterior segment optical coherence tomography (AS-OCT). Heidelberg cornea tomograph II (HRT II) was used to measure the corneal endothelial cell density. RESULTS: Mean (+/-SEM) preoperative IOP was 29.5+/-4 mmHg. Mean postoperative IOP was 11.6+/-2 at 12 months (P<0.01). Over a 6-month period, mean corneal endothelial loss was 7.9%+/-2.5 in the central and 7.5%+/-2.4 in the peripheral cornea (P<0.01). There was no correlation between central or peripheral corneal endothelial cell loss and the T-C, T-I distance or the ICL of the tube. CONCLUSIONS: Corneal endothelial cell loss occurs following Ahmed valve implant surgery, this appears to be multifactorial. AS-OCT and HRT II are promising methods for the follow-up of patients with a glaucoma drainage device.

Subretinal electrode implantation in the P23H rat for chronic stimulations.

BACKGROUND: In age related macular degeneration and inherited dystrophies, preservation of retinal ganglion cells has been demonstrated. This finding has led to the development of various models of subretinal or epiretinal implant in order to restore vision. This study addresses the development of a polyimide subretinal electrode platform in the dystrophic P23H rat in vivo. METHODS: A technique was developed for implanting a subretinal electrode into the subretinal space and stabilising the distal extremity of the cabling on the rat cranium in order to allow future electrical stimulations of the retina. RESULTS: In vivo imaging of the retina with the scanning laser ophthalmoscope demonstrated reabsorption of the surgically induced retinal detachment and the absence of major tissue reactions. These in vivo observations were confirmed by retinal histology. The extraocular fixation system on the rat cranium was effective in stabilising the distal connector for in vivo stimulation. CONCLUSION: This study demonstrates that a retinal implant can be introduced into the subretinal space of a dystrophic rat with a stable external connection for repeatable electrical measurements and stimulation. This in vivo model should therefore allow us to evaluate the safety and efficacy of electrical stimulations on dystrophic retina.

Ganglion cells from chick retina display multiple functional nAChR subtypes.

We have examined the properties of nicotinic acetylcholine receptors in embryonic chick retinal ganglion cells. Ganglion cells, identified according to morphological and physiological criteria, displayed spontaneous or induced action potentials. In 94/99 cells acetylcholine pulses evoked responses. In current clamp mode, acetylcholine provoked membrane depolarization and triggered action potentials. Under voltage clamp conditions, acetylcholine evoked inward currents that were readily blocked by d-tubocurarine. Antagonists specific for homomeric (alpha-bungarotoxin) and heteromeric (dihydro-beta-erythroidine) receptors revealed that ganglion cells express multiple functional receptor subtypes. These findings demonstrate that ACh modulates the electrical activity of these cells and is likely to mediate synaptic transmission. The presence of multiple receptor subtypes may contribute to processing and transmission of information in the retina.

[Necessary visual information for restoring reading with a retinal implant in a blind patients with massive retinal degeneration of photoreceptors]. / Information visuelle nécessaire à la restauration d'une lecture au moyen d'un implant rétinien chez un aveugle par dégénérescence massive des photorécepteurs.

DEFINITION OF THE PROBLEM: Our goal is to determine the minimum of information necessary for elementary reading, using a retinal implant. This concerns particularly the fragmentation (pixellisation) of the presented image and its position in the visual field. Fragmentation corresponds to the number of electrodes available, the position of the image in the visual field is equivalent to the site of the implant on the retina. MATERIAL AND METHODS: 10 degrees x 10 degrees windows, containing isolated words or letters, were presented to six healthy subjects on a computer screen. A coupling between the computer and an eye tracker stabilizes these images in an area of the visual field. This coupling constantly corrects the position of the image on the screen according to the direction of gaze. RESULTS: 1) A rapid decrease of the performance is observed at a certain threshold of pixellisation, dependent on the eccentricity of presentation of the images. 2) In central vision, about 400 pixels are sufficient to recognize 80% of the four-letters words. At 10 degrees of eccentricity, about 1225 pixels are needed. 3) An acceptable comprehension of a text (identification of four words out of five), is impossible at eccentricities higher than 10 degrees 4) About 50 pixels are sufficient for a satisfactory recognition of isolated letters, independently of their eccentricity. CONCLUSION: These data validate the method of investigation and provide valuable indications regarding minimal visual requirements in prosthetic vision.

[Prenatal ultrasonic measurements of the eye and the interorbital distance]. / Mesures échographiques anténatales de l'oeil et de la distance interorbitaire.

OBJECTIVES: The two-fold objective of this study was to ascertain whether the antero-posterior diameter of the fetal eye is comparable to the transversal diameter and to establish nomograms based on the measurements obtained for ocular diameter (OD), mean interorbital distance (MIOD) and the MIOD/biparietal diameter (BPD) ratio related to gestational age. TYPE: A prospective monocentric study based on 398 sonographic fetal eye measurements. RESULTS: The antero-posterior and transverse ocular diameters of the fetal eye remain comparable throughout pregnancy (R = 0.997, p < 0.0001). They were related to gestational age and BPD. The MIOD/BDP ratio decreased with gestational age. The OD/BPD ratio remained nearly constant. Nomograms were established for OD, MIOD and the MIOD/BPD ratio related to gestational age. DISCUSSION AND CONCLUSION: The fetal eye can be measured on any diameter provided the sonographic scan for the measurement is flawless. Nomograms and values are given. Hyper- and hypotelorism and microphthalmia can be found in numerous malformative syndromes. Previously published tables are not well-suited to the French population.

Contrast sensitivity in obese dyslipidemic patients with insulin resistance.

OBJECTIVE: To evaluate contrast sensitivity in insulin-resistant obese patients and in aretinopathic diabetic patients. METHODS: Contrast sensitivity was measured at 3 letter sizes (44 x 44, 9 x 9, and 5 x 5 mm) in mesopic (5 candela [cd]/m2) and low photopic (85 cd/m2) vision in 20 dyslipidemic obese patients with insulin resistance, 20 age-matched patients with type 2 diabetes mellitus, and 20 aged-matched healthy control subjects. RESULTS: Significant loss of contrast sensitivity at all 3 letter sizes was observed in low photopic vision (at 44 x 44-mm letter size, control vs obese, P<.002, and control vs diabetic, P<.005; at 9 x 9-mm letter size, control vs obese, P<.02, and control vs diabetic, P<.001; and at 5 x 5-mm letter size, control vs obese, P<.05, and control vs diabetic, P<.005) and mesopic vision (at 44 x 44-mm letter size, control vs diabetic, P<.005; at 9 x 9-mm letter size, control vs obese, P<.005, and control vs diabetic, P<.01; and at 5 x 5-mm letter size, control vs obese, P<.005, and control vs diabetic, P<.001) in insulin-resistant obese and diabetic patients. CONCLUSION: The results suggest that an early neurosensory dysfunction may occur without visible vascular involvement and without overt hyperglycemia.

Colour vision in AIDS patients without HIV retinopathy.

Patients suffering from AIDS develop ocular complications, the most frequent being HIV retinopathy. It is however not clear, if functional visual impairments can be observed as early indicators of ocular complications, before clinical diagnosis of HIV retinopathy is made at fundus examination. To address this issue, we measured colour vision in a group of 49 AIDS subjects with normal clinical fundi using the 'two equation method'. This method, combining red-green Rayleigh and the blue-green Moreland metameric matches, enables more complete and quantitative assessments of colour vision than those based on pigmentary tests. Data were collected on our computer controlled colorimeter and compared to those of normal subjects. While most AIDS subjects without HIV retinopathy demonstrated normal colour vision, a significant portion of them had wider matches than normal subjects (11% for the Rayleigh equation and 16% for the Moreland equation). Furthermore, matching ranges of the Moreland equation were significantly correlated with CD4 lymphocyte counts. Patients with low CD4 values tended to produce larger matching ranges than the patients with high CD4 values. A within subject study on 17 patients confirmed this trend and showed that the patients who increased/decreased their CD4 blood counts generally improved/impaired their colour discrimination in the Moreland match. No such correlation was found between the matching ranges of the Rayleigh equation and the CD4 counts. These results show that colour discrimination is slightly reduced in some AIDS subjects, although there are no detectable ocular complications. They also suggest two different types of colour vision impairments in AIDS patients without retinopathy: one reversible process affecting colour discrimination in the blue-green range; and another irreversible process affecting colour discrimination in the red-green range.

[Stimulation parameters for automatic examination of color vision]. / Paramètres de stimulation pour l'examen automatisé de la vision colorée.

PURPOSE: We have developed a polyvalent computer controlled instrument, which uses the "two equation method" (Rayleigh and Moreland equations) to measure human colour vision. This "colorimeter" (or anomaloscope) was used to determine the influence of some important stimulation parameters. METHODS: The influence of stimulus exposure time, observation field size, absolute stimulus luminance, saturation and luminance mismatches between mixture and reference stimuli were measured on our computer controlled colorimeter. All subjects were normal observers. RESULTS: 1) An exposure time of 2s was found to be optimal for clinical work. 2) The Moreland equation on a 7 degrees observation field yields results in which population variability is comparable to a Rayleigh equation on a 2 degrees field. 3) A retinal illuminance between 40 and 1000 trolands can be used for automated Moreland matches. 4) The saturation of the reference field for the Moreland match can be preset to a fixed value. 5) It is important to vary automatically the radiance of the reference field to provide an approximate luminance match as the ratio of primaries in the mixture field is changed. CONCLUSION: These measurements allows us to determine optimal conditions for automated colour vision examinations and to make recommendations for an international standard.

[The examination of color vision using a 2 metameric equation method]. / L'examen de la vision colorée par la méthode des deux équations métamériques.

Modern anomaloscopes with four independent light channels (i.e. Besançon-Anomalometer which was presented in 1979 at the SFO Congress) allow accurate examinations of color vision. In our routine clinical examination, we use two metameric equations: the red-green Rayleigh equation and the blue-green Moreland equation. This so called Two-Equation-Method enables the diagnosis of congenital and acquired color vision defects in a precise qualitative as well as quantitative way. For both equations the goal of the examination is to measure the absolute matching range. Abnormal color vision is diagnosed if the absolute matching range is shifted and/or enlarged in one or both of the two metameric equations. In congenital colour vision deficiencies, the results are similar to those obtained with the Nagel anomaloscop. The different types of acquired defects are compared with the types of Verriest's classification. A computer controlled clinical examination of color vision, which will make the procedure simplier and shorter for the patient is actually being developed.

[Recent trends and developments in the clinical study of color vision--the 2-comparison method]. / Neuere Uberlegungen und Entwicklungen zur klinischen Untersuchung des Farbensehens--die Zwei-Gleichungsmethode.

Modern anomaloscopes with four independent light channels (i.e., the Besançon Anomalometer which was presented in 1980 at the DOG) allow accurate examinations of color vision. In our routine clinical examination, we use two metameric equations: the red-green Rayleigh equation and the blue-green Moreland equation. This two-equation method permits the diagnosis of congenital and acquired color vision defects in a precise quantitative way. In both equations the goal of the examination is to measure the absolute matching range. The diagnosis is abnormal color vision if the absolute matching range is shifted and/or enlarged in one or both of the two metameric equations. A computer-controlled clinical examination of color vision, which will make the procedure simpler and shorter for the patient, is presently being developed.