Amino acid signatures in the developing mouse retina

This study characterizes the developmental patterns of seven key amino acids: glutamate, γ-amino-butyric acid (GABA), glycine, glutamine, aspartate, alanine and taurine in the mouse retina. We analyze amino acids in specific bipolar, amacrine and ganglion cell sub-populations (i.e. GABAergic vs. glycinergic amacrine cells) and anatomically distinct regions of photoreceptors and Müller cells (i.e. cell bodies vs. endfeet) by extracting data from previously described pattern recognition analysis. Pattern recognition statistically classifies all cells in the retina based on their neurochemical profile and surpasses the previous limitations of anatomical and morphological identification of cells in the immature retina. We found that the GABA and glycine cellular content reached adult-like levels in most neurons before glutamate. The metabolic amino acids glutamine, aspartate and alanine also reached maturity in most retinal cells before eye opening. When the overall amino acid profiles were considered for each cell group, ganglion cells and GABAergic amacrine cells matured first, followed by glycinergic amacrine cells and finally bipolar cells. Photoreceptor cell bodies reached adult-like amino acid profiles at P7 whilst Müller cells acquired typical amino acid profiles in their cell bodies at P7 and in their endfeet by P14. We further compared the amino acid profiles of the C57Bl/6J mouse with the transgenic X-inactivation mouse carrying the lacZ gene on the X chromosome and validated this animal model for the study of normal retinal development. This study provides valuable insight into normal retinal neurochemical maturation and metabolism and benchmark amino acid values for comparison with retinal disease, particularly those which occur during development

Metabolic profiling of the mouse retina using amino acid signatures: Insight into developmental cell dispersion patterns

Pattern recognition has been used for the complete and statistically rigid classification of retinal neurons in vertebrates such as the adult cat, primate, rat and goldfish. Here, we label the mouse retina with antibodies against seven amino acids and use pattern recognition to characterize distinct retinal neurochemical cell classes based on their unique amino acid signatures. We followed the development of the cell classes in the X-inactivation transgenic mouse expressing the lacZ reporter gene on one X-chromosome. This mouse allows clonally related cells to be identified through differential β-galactosidase activity due to random X-chromosome inactivation. Pattern recognition analysis partitioned the retina into nine neuronal classes at birth, increasing to 19 classes at eye opening and 26 classes by adulthood. Emergence of new cell classes was partly attributed to new neuron types and partly to the splitting of classes from early ages from refinement of their amino acid profiles. All six GABAergic amacrine cell classes and most ganglion cell classes appeared by P7 whilst all the glycinergic amacrine cell classes did not appear till adulthood. Separable bipolar cell classes were not detected till eye opening. Photoreceptor cell classes were detected at P3 but inner and outer segments did not form separable classes until adulthood. More importantly, we show that cells which share common amino acid profiles also shared cell dispersion patterns. GABAergic amacrine cell classes with conventional and displaced counterparts transgressed clonal boundaries whereas GABAergic amacrine cell classes found exclusively in the inner nuclear layer and all glycinergic amacrine cell classes did not transgress. Ganglion cells displayed both dispersion patterns. This study provides a comprehensive neurochemical atlas of the developing mouse retina, tracking the amino acid levels within distinct neuronal populations and highlighting unique migratory patterns within subpopulations of inner retinal neurons

High-Density Optical Coherence Tomography Analysis Provides Insights into Early/Intermediate Age-Related Macular Degeneration Retinal Layer Changes

PURPOSE. To topographically map all of the thickness differences in individual retinal layers between early/intermediate age-related macular degeneration (AMDearly/AMDint) and normal eyes and to determine interlayer relationships. METHODS. Ninety-six AMDtotal (48 AMDearly and 48 AMDint) and 96 normal eyes from 192 participants were propensity-score matched by age, sex, and refraction. Retrospective optical coherence tomography (OCT) macular cube scans were acquired, and high-density (60 × 60 0.01-mm2) grid thicknesses were custom extracted for comparison between AMDtotal and normal eyes corrected for confounding. Resultant “normal differences” underwent cluster, interlayer correlation, and dose–response analyses for the retinal nerve fiber layer (RNFL), ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer (INL), outer plexiform layer (OPL), outer nuclear layer + Henle’s fiber layer (ONL+HFL), inner and outer segment (IS/OS) thickness, and retinal pigment epithelium (RPE) to Bruch’s membrane (BM) thickness. RESULTS. AMDtotal inner retinal clusters demonstrated extensively thinned RNFL, GCL, IPL, and paracentral INL and thickened INL elsewhere, with normal difference means ranging from −8.13 μm (95% confidence interval [CI], −11.12 to −5.13) to 1.58 μm (95% CI, 1.07–2.09) (P +HFL, central IS/OS, and peripheral RPE–BM and thickened central RPE–BM, with means ranging from −1.31 μm (95% CI, −2.06 to −0.55) to 2.99 μm (95% CI, 0.97–5.01] (P < 0.0001 to P <0.05). Effect sizes (−2.56 to 9.93 SD), cluster sizes, and eccentricity effects varied. All interlayer correlations were negligible to moderate regardless of AMD severity. Only the RPE–BM was partly thicker with greater AMD severity (up to 5.44 μm; 95% CI, 4.88–6.00; P < 0.01). CONCLUSIONS. From the early stage, AMD eyes demonstrate thickness differences compared to normal with unique topographies across all retinal layers. Poor interlayer correlations highlight that the outer retina inadequately reflects complete retinal health. The clinical importance of OCT assessment across all individual retinal layers in early/intermediate AMD requires further investigation.</p

Reticular Pseudodrusen Are Associated With More Advanced Para-Central Photoreceptor Degeneration in Intermediate Age-Related Macular Degeneration

PURPOSE. The purpose of this study was to examine retinal topographical differences between intermediate age-related macular degeneration (iAMD) with reticular pseudodrusen (RPD) versus iAMD without RPD, using high-density optical coherence tomography (OCT) cluster analysis. METHODS. Single eyes from 153 individuals (51 with iAMD+RPD, 51 with iAMD, and 51 healthy) were propensity-score matched by age, sex, and refraction. High-density OCT grid-wise (60 × 60 grids, each approximately 0.01 mm2 area) thicknesses were custom-extracted from macular cube scans, then compared between iAMD+RPD and iAMD eyes with correction for confounding factors. These “differences (μm)” were clustered and results de-convoluted to reveal mean difference (95% confidence interval [CI]) and topography of the inner retina (retinal nerve fiber, ganglion cell, inner plexiform, and inner nuclear layers) and outer retina (outer plexiform/Henle’s fiber/outer nuclear layers, inner and outer segments, and retinal pigment epithelium-to-Bruch’s membrane [RPE-BM]). Differences were also converted to Z-scores using normal data. RESULTS. In iAMD+RPD compared to iAMD eyes, the inner retina was thicker (up to +5.89 [95% CI = +2.44 to +9.35] μm, P < 0.0001 to 0.05), the outer para-central retina was thinner (up to −3.21 [95% CI = −5.39 to −1.03] μm, P < 0.01 to 0.001), and the RPE-BM was thicker (+3.38 [95% CI = +1.05 to +5.71] μm, P < 0.05). The majority of effect sizes (Z-scores) were large (−3.13 to +1.91). CONCLUSIONS. OCT retinal topography differed across all retinal layers between iAMD eyes with versus without RPD. Greater para-central photoreceptor thinning in RPD eyes was suggestive of more advanced degeneration, whereas the significance of inner retinal thickening was unclear. In the future, quantitative evaluation of photoreceptor thicknesses may help clinicians monitor the potential deleterious effects of RPD on retinal integrity.</p

Determining Spatial Summation and Its Effect on Contrast Sensitivity across the Central 20 Degrees of Visual Field.

Recent studies propose that the use of target stimuli within or close to complete spatial summation reveal larger threshold elevation in ocular disease. The Humphrey Visual Field Analyzer (HFA) is used to assess visual function yet the spatial summation characteristics are unexplored for the central macular region. We therefore wanted to establish the relationship between contrast sensitivity and stimulus size (spatial summation) within the central 20° visual field using the high sampling density of the 10-2 test grid.Thresholds were measured for one eye from 37 normal subjects using the HFA 10-2 test grid with all five Goldmann (G) targets (GI to GV). Subject data were converted to 50-year-old equivalent using published and calculated location-specific decade correction factors. Spatial summation curves were fitted for all data at all locations. The size of Ricco's critical area (Ac) within which complete spatial summation operates (k = 1), and the slope of partial summation (k < 1: to characterize partial summation), was established.The 50-year-old age normative data were determined for all Goldmann stimulus sizes for the 10-2 HFA test grid and showed a marked change in contrast sensitivity for small test stimuli (e.g. GI) and little change in larger test stimuli (e.g. GV). Both the Ac and k values did not vary with age allowing for the application of the age correction factors. Ac and k values increased with eccentricity with GI remaining within complete spatial summation and GII was close or within complete spatial summation. GIII or larger test sizes were always outside complete spatial summation operating within various levels of partial summation.The developed normative data now allows comparisons of data sets with high sampling density using the 10-2 grid irrespective of subject age. Test size is important when assessing ocular disease yet only GI or GII stimuli operate close to or within complete spatial summation in the macula. Current visual field testing protocols employ GIII which is always outside complete spatial summation and operates under various values of partial summation: GIII may not be the most suitable test size to assess ocular disease affecting the macula

Retinal vessel diameters in intermediate age-related macular degeneration using <i>en face</i> optical coherence tomography

Clinical assessment of age-related macular degeneration (AMD) relies on biomarkers that do not necessarily reflect the contributions of vascular dysfunction. Validation of clinically accessible methods of measuring retinal vascular integrity could provide a more holistic understanding of AMD-related changes to facilitate appropriate care. There is conflicting evidence if retinal vessel calibre is significantly altered in the early stages of AMD. This study examined the outer and inner diameters of first order retinal vessels in intermediate AMD eyes using en face optical coherence tomography (OCT). Retinal en face (6 × 6 mm) OCT images were examined in a single eye of participants with intermediate AMD (n = 46) versus normal macula (n = 43) for arterioles (all identifiable) and venules (40/46 and 39/43 identifiable). All participants were aged ≥50 years without diabetes mellitus, hypertension, or other systemic vascular disease. Intra- and inter-grader agreement was good-to-excellent for all en face OCT measurements of arteriole and venule diameters (intraclass correlation coefficient = 0.87 to 0.99). Arteriolar outer diameters (82.3 ± 19.8 µm vs 73.8 ± 16.1 µm; p p p p = 0.17) in AMD eyes compared to normal eyes. Arteriolar dilation and altered venular inner diameter were observed in intermediate AMD eyes. These results support further investigation of vascular contributions to AMD in the early stages of disease, possibly using the en face OCT imaging modality.</p