Taro Kominami

Focal cone ERGs of rhodopsin Pro347Leu transgenic rabbits.

A rhodopsin P347L transgenic (Tg) rabbit, a model of retinitis pigmentosa, has been generated in our laboratory. The purpose of this study was to determine the properties of focal areas of the retina in this rabbit model during the course of retinal degeneration. To accomplish this, we recorded focal ERGs from wild-type (WT) and Tg rabbits at ages 3, 6, and 12 months. A 15° stimulus spot was used to elicit the focal ERGs from the center of the visual streak and from four surrounding areas. We found that the amplitudes of the focal cone ERG b-waves and oscillatory potentials (OPs) of the Tg rabbits in the five areas decreased progressively with increasing age and became almost non-recordable at 12 months. There were no significant regional differences in the b-waves of Tg rabbits recorded from the 5 areas. The amplitudes of the OPs were better preserved than the b-waves and the OPs/b-wave ratio was higher than that in WT rabbits at every recording area. The summed OPs amplitudes, which most likely originate from the amacrine and/or ganglion cells, recorded from the area superior to the optic disc was significantly larger than that from other areas at 3- and 6-months-old. This indicated that the inner retinal neurons were not altered equally after photoreceptor degeneration in this rabbit model.

Pathologic Changes of Cone Photoreceptors in Eyes With Occult Macular Dystrophy

PURPOSE Occult macular dystrophy (OMD) is an inherited retinal disease characterized by a progressive decrease of vision and appearance of normal fundus. To determine the pathologic features of OMD, we investigated the alternation of the photoreceptors using quantitative image analysis. METHODS We studied 22 eyes of 11 OMD patients. Three of them had a mutation (R45W) in RP1L1. The relative intensities of the ellipsoid zone in the spectral-domain optical coherence tomography (SD-OCT) images and the density of the cone photoreceptors in the adaptive optics (AO) fundus images of the OMD patients were compared to those of normal controls. RESULTS The relative intensities of the ellipsoid zone in the SD-OCT images of patients with OMD were significantly lower (P < 0.001) by an average of 16% compared to that of the normal controls. Normal cone mosaics were not observed in the AO images of the macula in the eyes with OMD. The mean ± SD of cone density of the 9 OMD patients was 1970 ± 884 cells/mm2 at 2°, 1124 ± 483 cells/mm2 at 3°, and 1288 ± 715 cells/mm2 at 4° nasal to the fovea. The cone densities at 2°, 3°, and 4° nasal to the fovea of OMD were significantly lower than those of the normal controls (P < 0.001). CONCLUSIONS A sparse array of cone photoreceptors with significantly reduced density of the macula is one of the morphologic features of OMD.

Restoration of Cone Interdigitation Zone Associated With Improvement of Focal Macular ERG After Fovea-Off Rhegmatogenous Retinal Reattachment

PURPOSE To determine whether a correlation exists between the parameters of the focal macular ERGs (FMERGs) and the microstructural changes of the photoreceptors after successful surgery for fovea-off rhegmatogenous retinal detachment (RRD). METHODS Twenty eyes of 20 patients who had undergone successful surgery to reattach the retina in eyes with fovea-off RRD were studied. Focal macular ERGs and spectral-domain OCT (SD-OCT) were recorded at 1 and 6 months after the surgery. Changes of the components of the FMERGs, as well as changes of the SD-OCT parameters including the length of the external limiting membrane (ELM), ellipsoid zone (EZ), cone interdigitation zone (CIZ), and size of the outer photoreceptor area (between ELM and RPE), were determined. RESULTS During the postoperative period, the mean amplitudes of the a-waves increased by 1.4 times and the b-waves by 1.7 times. Spectral-domain OCT showed that the mean length of the EZ and CIZ and the size of the outer photoreceptor area had increased significantly at 6 months. The degree of the increase in the CIZ and outer photoreceptor area was significantly correlated with the increase in the amplitudes of the b-waves of the FMERGs (r = 0.56, P = 0.042, r = 0.57, P = 0.040, respectively; Spearman rank correlation test). However, the length of the EZ was not significantly correlated with the increase of the b-waves. CONCLUSIONS A restoration of the EZ alone might not be enough to improve the FMERGs, and a restoration of the EZ accompanied by that of the CIZ was essential for the recovery of the FMERGs after fovea-off RRD.

Pikachurin Protein Required for Increase of Cone Electroretinogram B-Wave during Light Adaptation.

In normal eyes, the amplitude of the b-wave of the photopic ERGs increases during light adaptation, but the mechanism causing this increase has not been fully determined. The purpose of this study was to evaluate the contribution of receptoral and post-receptoral components of the retina to this phenomenon. To accomplish this, we examined the ERGs during light adaptation in Pikachurin null-mutant (Pika -/-) mice, which have a misalignment of the bipolar cell dendritic tips to the photoreceptor ribbon synapses. After dark-adaptation, photopic ERGs were recorded from Pika -/- and wild type (WT) mice during the first 9 minutes of light adaptation. In some of the mice, post-receptoral components were blocked pharmacologically. The photopic b-waves of WT mice increased by 50% during the 9 min of light adaptation as previously reported. On the other hand, the b-waves of the Pika -/- mice decreased by 20% during the same time period. After blocking post-receptoral components, the b-waves were abolished from the WT mice, and the ERGs resembled those of the Pika -/- mice. The extracted post-receptoral component increased during light adaptation in the WT mice, but decreased for the first 3 minutes to a plateau in Pika -/- mice. We conclude that the normal synaptic connection between photoreceptor and retinal ON bipolar cells, which is controlled by pikachurin, is required for the ERGs to increase during light-adaptation. The contributions of post-receptoral components are essential for the photopic b-wave increase during the light adaptation.

Longitudinal study of visual field changes determined by Humphrey Field Analyzer 10-2 in patients with Retinitis Pigmentosa

The aim of this study is to determine the progress of the visual field defects obtained by the Humphrey Field Analyzer 10-2 program (HFA 10-2) in patients with retinitis pigmentosa (RP). The medical records of 45 eyes of 45 RP patients who had at least 3 visual field tests were reviewed. Linear mixed models were used to follow the changes of the mean deviation and the average sensitivity of 4, 12, and 20 points in three concentric squares, designated as S4, S12, and S20. The median follow-up time was 3.86 years [range: 1.93 to 9.86, IQR (Interquartile range): 3.01 to 4.93]. The median number of the visual field tests was 3 (range: 3 to 15, IQR: 3 to 4). The mean change of the MD was −0.46 dB/year (−5.80%/year). When the patients were grouped by the average initial MD, the less advanced group had slower progressions than the more advanced group in S4, S12, and S20. These results should be useful in understanding the pathological changes of RP in the central visual field.

Samd7 is a cell type-specific PRC1 component essential for establishing retinal rod photoreceptor identity

Significance Each retinal rod and cone photoreceptor cell subtype expresses a distinct set of genes including the genes encoding phototransduction components such as opsins and transducins. This subtype-specific gene expression is essential for achieving proper function in each photoreceptor cell. While the various cone and rod photoreceptor cell gene expressions are regulated by multiple transcription factors, whether epigenetic regulation plays an important role for photoreceptor cell-specific gene expression has been unclear. In the current study, we found that a photoreceptor-specific protein, Samd7, functions as a component of the epigenetic gene-silencing complex and is essential for establishing rod photoreceptor cell identity and function by silencing nonrod gene expression in developing rod photoreceptor cells. Precise transcriptional regulation controlled by a transcription factor network is known to be crucial for establishing correct neuronal cell identities and functions in the CNS. In the retina, the expression of various cone and rod photoreceptor cell genes is regulated by multiple transcription factors; however, the role of epigenetic regulation in photoreceptor cell gene expression has been poorly understood. Here, we found that Samd7, a rod-enriched sterile alpha domain (SAM) domain protein, is essential for silencing nonrod gene expression through H3K27me3 regulation in rod photoreceptor cells. Samd7-null mutant mice showed ectopic expression of nonrod genes including S-opsin in rod photoreceptor cells and rod photoreceptor cell dysfunction. Samd7 physically interacts with Polyhomeotic homologs (Phc proteins), components of the Polycomb repressive complex 1 (PRC1), and colocalizes with Phc2 and Ring1B in Polycomb bodies. ChIP assays showed a significant decrease of H3K27me3 in the genes up-regulated in the Samd7-deficient retina, showing that Samd7 deficiency causes the derepression of nonrod gene expression in rod photoreceptor cells. The current study suggests that Samd7 is a cell type-specific PRC1 component epigenetically defining rod photoreceptor cell identity.

Quantification of Macular Microvascular Changes in Patients With Retinitis Pigmentosa Using Optical Coherence Tomography Angiography

Purpose To evaluate the microvascular changes in eyes with RP quantitatively using optical coherence tomography angiography (OCTA) and to determine whether the correlations between these indices and the severity of RP are significant. Methods This was a retrospective, observational study. The medical records of 53 RP patients and 46 controls were reviewed. The OCTA images were obtained with the Cirrus 5000 with Angioplex, and an automated program was used to analyze the microvascular patterns. The perfusion density (PD) and vessel length density (VLD) were used as indices of the microvascular density, whereas the vessel diameter index (VDI) was used as a measure of the caliber of the vessels. The width of the ellipsoid zone (EZ) in the OCT images and the mean deviation (MD) of the Humphry Field Analyzer (HFA) were used to determine the severity of the RP. Students t-tests and Spearmans correlation tests were used. Results Both the PD and VLD in the superficial and deep plexuses and the whole retina were significantly reduced, and the VDI was significantly increased in RP patients compared with the corresponding values of the controls (P < 0.001). Spearmans rank tests indicated the RP severity was significantly correlated with the PD and VLD in all three layers (P < 0.001, r ranging from 0.50 to 0.87) and significantly correlated with VDI in the deep and the whole retina (P < 0.001, ranging from -0.64 to -0.73). Conclusions Quantitative changes in the microvascular density might be useful for examining the pathophysiology of RP.

Contributions of Second- and Third-Order Retinal Neurons to Cone Electroretinograms After Loss of Rod Function in Rhodopsin P347L Transgenic Rabbits

Purpose To determine the contribution of second- and third-order retinal neurons to the photopic electroretinograms (ERGs) after the degeneration of the rods in rhodopsin P347L transgenic rabbits (Tg). Methods Four wild-type (WT) rabbits and four Tg rabbits were studied at 18 months of age. The photopic ERGs elicited at stimulus onset and offset were analyzed. To block different retinal pathways, 2-amino-4-phosphonobutyric acid (APB), 6-cyano-7-nitroquinoxaline-2, 3 (1H,4H)-dione (CNQX), tetrodotoxin (TTX), and N-methyl-DL-aspartic acid (NMDA) were injected intravitreally. Digital subtraction of the postdrug ERGs from the predrug ERGs was used to determine the contributions of the ON-components blocked by APB, the OFF-components blocked by CNQX, and the third-order neurons blocked by TTX+NMDA. Results Contribution of the cone photoreceptors to the photopic ERGs in Tg rabbits was approximately 10% of that in WT rabbits. The amplitudes of the positive waves of the ON-components at stimulus onset in Tg rabbits were approximately one-half as large as those in WT. On the other hand, the amplitudes of the positive waves of the OFF-components at stimulus offset in Tg rabbits were approximately 1.4 to 2.3 times larger than those in WT. Transgenic rabbits had a positive wave at stimulus offset, which was reduced after the TTX+NMDA injection. Conclusions A reduced ON-component and an augmented OFF-component with abnormal responses of the third-order neurons contributed to the cone ERGs after the loss of rod function in Tg rabbits. Our results suggest a complex synaptic remodeling of the residual retinal cells in the advanced stage in Tg rabbits.

Associations Between Outer Retinal Structures and Focal Macular Electroretinograms in Patients With Retinitis Pigmentosa

Purpose Our earlier study showed that the width of the intact ellipsoid zone (EZ) of the photoreceptors was significantly but weakly correlated with the amplitudes of the focal macular ERGs (FMERGs). The aim of this study was to determine a microstructure of the photoreceptors in the spectral-domain optical coherence tomographic (SD-OCT) images that was more strongly correlated with the FMERG parameters in eyes with retinitis pigmentosa (RP). Methods This was a retrospective, observational study. The medical records of 65 patients with RP were reviewed. FMERGs were elicited by a 15-degree stimulus spot. The width of the EZ and the outer segment (OS) area surrounded by EZ and retinal pigment epithelium in the SD-OCT images within 15 degrees of the fovea were evaluated. Spearman correlation tests and multiple stepwise regression analyses were performed. Results There was a strong correlation between the amplitudes of FMERGs and the EZ width (r = 0.68 for a-wave amplitude; r = 0.64 for b-wave amplitude), and also between the amplitudes of the FMERGs and the OS area (r = 0.69 for a-wave amplitude; r = 0.67 for b-wave amplitude). However, some patients had long EZ widths but had severely reduced FMERGs. Multiple stepwise regression analyses showed that the OS area was the only significant independent predictor of the amplitudes of FMERGs (P < 0.001). Conclusions The OS area might be a better morphological structure to use to predict the physiological function of the macula.

Differences in ocular findings in two siblings: one with complete and other with incomplete achromatopsia

PurposePatients with complete achromatopsia (ACHM) lack cone function, and patients with incomplete ACHM have relatively good visual acuity with residual color vision. The pathological mechanism(s) underlying incomplete ACHM has not been determined. The purpose of this study was to determine the pathophysiology of ACHM in two siblings: one with complete ACHM and the other with incomplete ACHM.MethodsThe medical charts of the two siblings were reviewed.ResultsThe sibling with incomplete ACHM had decimal visual acuities that ranged from 0.4 to 0.6 and had moderate color blindness in both eyes. Her younger brother was diagnosed with complete ACHM and was not able to hold fixation, had severe pendular nystagmus, visual acuity that ranged from 0.08 to 0.1, and severe color vision abnormalities in both eyes. Optical coherence tomography (OCT) showed that the ellipsoid zone (EZ) was disruptive in the macular region in both patients. However, careful examination of the OCT images in the incomplete ACHM patient showed a high-density EZ in the central fovea. Adaptive optics (AO) fundus imaging of the sibling with incomplete ACHM revealed sparse cone mosaics remaining within 1° of the foveal center with no mosaics visible outside the central fovea. AO fundus imaging could not be performed in Case 2 because of the severe nystagmus.ConclusionOur results showed that cone mosaics were present in the central fovea in the sibling with incomplete ACHM patient. This may explain the better visual acuity and color vision in this sibling.