Gen Hanazono

Distribution of Retinal Responses Evoked by Transscleral Electrical Stimulation Detected by Intrinsic Signal Imaging in Macaque Monkeys

PURPOSE The distribution of the electrical current over the retina when electrical pulses are delivered transsclerally has not been clearly determined objectively and quantitatively in humans. The purpose of this study was to determine the pattern of electrically evoked neural activity in the monkey retina by using intrinsic signal imaging. METHODS The intrinsic signals of monkey retinas were recorded as changes in the reflectance of infrared light from the retina after transscleral electrical stimulation by DTL electrodes. The effects of changing the stimulus parameters (e.g., intensity, duration, and frequency) of the electrical current, were investigated. RESULTS Electrical stimulation evoked a uniform change in the reflectivity across the posterior pole of the retina; that is, the intrinsic signals changed uniformly. A peak of the intrinsic signal was not observed at the fovea. The threshold of the intrinsic signal was not significantly different for the macula, perimacula, and optic disc, and the threshold did not differ under dark- and light-adapted conditions. The strength of the signals increased with longer stimulus durations, and the maximum signals were obtained when the stimulus frequency was between 15 and 20 Hz. CONCLUSIONS Intrinsic signals of the monkey retina evoked by transscleral electrical stimulation are elicited uniformly across the posterior pole of the fundus and most likely arise from activation of the inner or middle layers of the retina. These functional measurements could serve as a diagnostic tool for mapping the inner retinal activity, by which the site of a lesion can be noninvasively imaged.

Evaluating Neural Activity of Retinal Ganglion Cells by Flash-Evoked Intrinsic Signal Imaging in Macaque Retina

PURPOSE Intrinsic signal imaging (ISI) detects light-induced microstructural or metabolic changes in retinal tissues. Thus, activities of the rod and cone systems could be mapped topographically. However, no direct evidence indicates the cellular origin of the signals. The purpose of this study was to determine whether and how retinal ganglion cells (RGCs) contribute to ISI. METHODS In anesthetized macaque monkeys, the properties of intrinsic signals were investigated by simultaneous measurement of the retina and the primary visual cortex (V1) with different wavelengths of observation light, measurement of the flash-induced blood flow changes by laser Doppler flowmetry, and intravitreal injection of tetrodotoxin (TTX). RESULTS Slow components of ISI correspond well to the flash-induced blood flow increase. Intrinsic signals of the posterior retina are partially decreased, and the signal of the optic disc is completely abolished by intravitreal injection of TTX at a concentration that should reduce the neural activities of RGCs. The intrinsic signal at the fovea did not change significantly after TTX injection. CONCLUSIONS Photoreceptors in the outer retina and RGCs in the inner retina are major contributors to the intrinsic signals, and the activity of the RGCs can be mapped by using fast and slow components of the signal in the posterior retina. The functional organization of the RGC layer has not been objectively mapped; results presented here indicate that the ISI has the potential to do this.

Fundus autofluorescence in autosomal dominant occult macular dystrophy.

OBJECTIVE To characterize fundus autofluorescence (FAF) images of eyes with autosomal dominant occult macular dystrophy (OMD). METHODS All patients received a comprehensive ophthalmologic examination for diagnosis of OMD. We evaluated the FAF images in 13 eyes of 7 patients with autosomal dominant OMD by confocal scanning laser ophthalmoscopy with excitation at 488 nm and emission more than 500 nm. RESULTS The FAF images showed unspecific weak foveal hyperfluorescence in 4 eyes of 2 patients; one showed a thin hyperfluorescence in the temporal fovea bilaterally and the other showed weak hyperfluorescence in the fovea bilaterally. The optical coherence tomographic images showed abnormalities of the photoreceptor inner segment-outer segment line and cone outer segment tip line in all patients. However, 5 patients had normal FAF images regardless of morphological abnormalities of the photoreceptor. CONCLUSIONS Fundus autofluorescence is a useful method to acquire additional information of photoreceptor/retinal pigment epithelium function in eyes with OMD. Fundus autofluorescence will be also helpful for the differential diagnosis of eyes with OMD vs eyes with other dystrophies that have a distinctive FAF pattern.

Clinical characteristics of occult macular dystrophy in family with mutation of RP1l1 gene.

Purpose: To report the clinical characteristics of occult macular dystrophy (OMD) in members of one family with a mutation of the RP1L1 gene. Methods: Fourteen members with a p.Arg45Trp mutation in the RP1L1 gene were examined. The visual acuity, visual fields, fundus photographs, fluorescein angiograms, full-field electroretinograms, multifocal electroretinograms, and optical coherence tomographic images were examined. The clinical symptoms and signs and course of the disease were documented. Results: All the members with the RP1L1 mutation except one woman had ocular symptoms and signs of OMD. The fundus was normal in all the patients during the entire follow-up period except in one patient with diabetic retinopathy. Optical coherence tomography detected the early morphologic abnormalities both in the photoreceptor inner/outer segment line and cone outer segment tip line. However, the multifocal electroretinograms were more reliable in detecting minimal macular dysfunction at an early stage of OMD. Conclusion: The abnormalities in the multifocal electroretinograms and optical coherence tomography observed in the OMD patients of different durations strongly support the contribution of RP1L1 mutation to the presence of this disease.

Origins of retinal intrinsic signals: A series of experiments on retinas of macaque monkeys

Diffuse flash stimuli applied to the ocular fundus evoke light reflectance decreases of the fundus illuminated with infrared observation light. This phenomenon, which is independent of the photopigment bleaching observed as an increase in the reflectance of visible light, is called intrinsic signals. Intrinsic signals, in general, are stimulus-evoked light reflectance changes of neural tissues due to metabolic changes, and they have been extensively investigated in the cerebral cortex. This noninvasive objective technique of functional imaging has good potential as a tool for the early detection of retinal dysfunction. Once the signal properties were studied in detail, however, it became apparent that the intrinsic signals observed in the retina have uniquely interesting properties of their own due to the characteristic layered structure of the retina. Experiments on anesthetized macaque monkeys are reviewed, and the possible origins of the intrinsic signals of the retina are discussed.

Outer Retinal Microstructure in a Case of Acute Idiopathic Blind Spot Enlargement Syndrome

Purpose: To present a patient with acute idiopathic blind spot enlargement syndrome who had abnormal changes in the outer retinal microstructure limited to areas with reduced responses on multifocal electroretinograms as well as to the area involving a scotoma. Methods and Results: We report the case of a 44-year-old man who developed an arcuate scotoma which was associated with a physiological blind spot in the left eye. The ophthalmoscopic, fluorescein angiographic, and full-field electroretinogram findings were normal. The amplitudes of the multifocal electroretinograms were reduced in the area of the scotoma. Optical coherence tomography showed that both the external limiting membrane and the inner and outer segment (IS/OS) line were intact, but that the middle cone outer segment tip line between the IS/OS line and the retinal pigment epithelium was absent in the nasal macular area of the left eye. Conclusions: These findings indicate that the integrity of not only the external limiting membrane and IS/OS line but also the cone outer segment tip line is important for the function of the retina.

Stimulus-Induced Changes of Reflectivity Detected by Optical Coherence Tomography in Macaque Retina

PURPOSE To investigate the properties and origin of retinal intrinsic signals by functional optical coherence tomography (fOCT) in macaque retinas. METHODS We modified a spectral domain OCT system to be able to give short-duration flashes or continuous light stimulation to the retina of three adult macaque monkeys (Macaca mulatta) under general anesthesia. Changes in the intensities of the OCT signals following the stimulus were determined. RESULTS Stimulus-evoked decreases or increases in the OCT signals were observed in the photoreceptor inner segment ellipsoids and outer segments, respectively. Experiments with focal and colored stimuli confirmed that these fOCT signals originated from the photoreceptors. No diffuse changes in the OCT signals were detected in the inner retinal layers; however, there were slow changes in small discrete areas where the retinal vessels were located. The polarity of the fOCT signals in the inner retinal layer was dependent on each activated region, and one of the possible sources of the reflectance changes was the light-scattering changes of the retinal vessels. CONCLUSIONS The fOCT signals in the macaque retina consist of at least three components: light-scattering changes from the photoreceptor inner segment ellipsoids, light-scattering changes from the outer segments, and slow light-scattering changes from the blood vessels in the inner retina. This technique has the potential of mapping local neuronal activity three-dimensionally and may help in the diagnosis of retinal disorders of different retinal origins.

Functional Topography of Rod and Cone Photoreceptors in Macaque Retina Determined by Retinal Densitometry

PURPOSE The purpose of this study is to determine the topography of bleaching in rods, middle/long-wavelength (M/L) and short-wavelength (S) cones in the macaque retina by using a modified retinal densitometry technique. METHODS A modified commercial digital fundus camera system was used to measure continuously the intensity of the light reflectance during bleaching with band pass lights in the ocular fundus of three adult Rhesus monkeys (Macaca mulatta) under general anesthesia. The topography of bleaching in rods, M/L-, and S-cones was obtained separately by considering the characteristic time course of the reflectance changes, depending on the wavelengths of light and retinal locations. RESULTS The distribution of M/L-cones response had a steep peak at the foveal center and was elongated horizontally. The distribution of rod responses was minimum at the foveal center and maximum along a circular region at the eccentricity of the optic disc. The distribution of S-cone responses was highest at the fovea and was excavated centrally. There was a circular region with the maximal responses at 0.38 to 1.0 degrees from the foveal center. CONCLUSIONS With the current imaging technique, not only the steep peak of the M/L-cone responses at the fovea, but the ring-shaped distribution of rod responses in the periphery and the central reduction of S-cone response could be determined with good resolution.

Novel Snapshot Imaging of Photoreceptor Bleaching in Macaque and Human Retinas

PurposeVarious methods have been used to obtain a topographic map of bleached photopigments in human retinas in the past. The purpose of this study was to determine whether the bleaching topography of the photoreceptors could be obtained by snapshot imaging reflectometry.MethodsFour to five fundus photographs of one rhesus monkey and three healthy human subjects were taken by white flashes at intervals of 4 s, with a commercial fundus camera with minimal modifications. The flash-induced reflectance increases (bleaching) were calculated by dividing the reflectance of the first image into the subsequent images, pixel by pixel.ResultsThe topography of the bleached macula corresponded well with the anatomical distribution of the cones. The ratio of reflectance changes in the center to that in the surrounding tissue was high for red and low for green and blue images. These results indicate that the reflectivity changes were not artifacts but were derived from changes in the photopigment density in the cones and rods.ConclusionsThe topography of bleached photoreceptors obtained with a commercial fundus camera from one monkey and three healthy human subjects showed that this technique has potential as a new clinical method for examining photoreceptor function in both normal and diseased retinas.

Valsalva retinopathy developing during Japanese cheerleading training ("ouendan").

PURPOSE Valsalva hemorrhagic retinopathy is characterized by retinal hemorrhages that develop after a Valsalva maneuver that consists of a forcible exhalation against a closed glottis, thereby creating a sudden increase in the intrathoracic or intraabdominal pressure. We present a patient who developed retinal and vitreous hemorrhages with multiple retinal nonperfused areas after extreme physical training with shouting on a mountainous area. This exercise was part of his training as a member of a Japanese traditional cheerleading team. METHOD Case presentation. RESULTS A 19-year-old man developed an acute decrease in the vision to 0.3 in his left eye after running on hilly roads at approximately 800 m while shouting fight songs for several hours. Ophthalmoscopy showed a fresh vitreous hemorrhage that covered the entire macula and was connected to the optic disk in the left eye. The vitreous hemorrhage spontaneously resolved and an intraretinal hemorrhage and nonperfused area emerged. His visual acuity returned to 1.2. CONCLUSION Prolonged, strenuous physical exertion with shouting during training exercises can lead to Valsalva hemorrhagic retinopathy. Several other factors, such as hot weather, altitude, and dehydration, may have played an additive role in increasing the venous pressure and hypoxia in the retinal vessels, which then caused the retinopathy.