The potential role of Arhgef33 RhoGEF in foveal development in the zebra finch retina.

The fovea is a pit formed in the center of the retina that enables high-acuity vision in certain vertebrate species. While formation of the fovea fascinates many researchers, the molecular mechanisms underlying foveal development are poorly understood. In the current study, we histologically investigated foveal development in zebra finch (Taeniopygia guttata) and found that foveal pit formation begins just before post-hatch day 14 (P14). We next performed RNA-seq analysis to compare gene expression profiles between the central (foveal and parafoveal) and peripheral retina in zebra finch at P14. We found that the Arhgef33 expression is enriched in the middle layer of the inner nuclear layer at the parafovea, suggesting that Arhgef33 is dominantly expressed in Müller glial cells in the developing parafovea. We then performed a pull-down assay using Rhotekin-RBD and observed GEF activity of Arhgef33 against RhoA. We found that overexpression of Arhgef33 in HEK293 cells induces cell contraction and that Arhgef33 expression inhibits neurite extension in Neuro 2A cells, which is partially recovered by a Rho-kinase (ROCK) inhibitor. Taken together, we used zebra finch as a model animal to investigate foveal development and identified Arhgef33 as a candidate protein possibly involved in foveal development through modulating RhoA activity.

Circuit Reorganization Shapes the Developing Human Foveal Midget Connectome toward Single-Cone Resolution.

The human visual pathway is specialized for the perception of fine spatial detail. The neural circuitry that determines visual acuity begins in the retinal fovea, where the resolution afforded by a dense array of cone photoreceptors is preserved in the retinal output by a remarkable non-divergent circuit: cone → midget bipolar interneuron → midget ganglion cell (the "private line"). How the private line develops is unknown; it could involve early specification of extremely precise synaptic connections or, by contrast, emerge slowly in concordance with the gradual maturation of foveal architecture and visual sensitivity. To distinguish between these hypotheses, we reconstructed the midget circuitry in the fetal human fovea by serial electron microscopy. We discovered that the midget private line is sculpted by synaptic remodeling beginning early in fetal life, with midget bipolar cells contacting a single cone by mid-gestation and bipolar cell-ganglion cell connectivity undergoing a more protracted period of refinement.

Clinical characteristics and long-term evolution of lamellar macular hole in high myopia.

PURPOSE: To evaluate the clinical characteristics and evolution of lamellar macular hole (LMH) in high myopia and the parameters associated with structural worsening, defined as the development of foveal detachment or full-thickness macular hole. METHODS: Patients with high myopia and LMH were retrospectively recruited. The clinical characteristics and various parameters of optical coherence tomography were identified at baseline and during follow-up visits. Cox regression analysis was used to evaluate the hazard ratios for foveal detachment and full-thickness macular hole. RESULTS: Among 112 eyes (98 patients), 64.3% were female; the mean axial length of all eyes was 29.6 ± 1.9 mm. The 'LMH without retinoschisis' group accounted for 39.3% of the eyes. Forty-two percent developed structural worsening within a median follow-up of 67 months. Multivariable regression on all cases showed elevated tissue inside the LMH (P = 0.003) protected against structural worsening while V-shaped LMH (P = 0.006) predicted it. In the "LMH with retinoschisis group", ellipsoid zone disruption (P = 0.035), and V-shaped LMH (P = 0.014) predicted structural worsening, while elevated tissue inside the LMH (P = 0.028) protected against it. In the "LMH without retinoschisis group", no associated factor was identified. CONCLUSIONS: LMHs in high myopia are unstable, especially those with V-shaped LMH. Elevated tissue inside LMHs have a protective effect against further structural worsening.

Foveal Microvascular Structures in Eyes with Silicone Oil Tamponade for Rhegmatogenous Retinal Detachment: A Swept-source Optical Coherence Tomography Angiography Study.

Silicone oil (SO) is widely used as a long-term intravitreal tamponading agent for rhegmatogenous retinal detachment (RRD) repair. This study investigated the structural changes of the foveal microvasculature using optical coherence tomography angiography (OCTA) in patients with RRD treated with vitrectomy and SO tamponade. Thirty-eight patients with unilateral RRD who were treated with vitrectomy and SO tamponade and were followed up for ≥3 months after SO removal were included. En face OCTA images were obtained and foveal avascular zone (FAZ) area and vascular density (VD) were compared between study eyes and unaffected contralateral eyes. The FAZ area in deep capillary plexus (DCP) was larger (P < 0.001) and the VD in DCP was lower (P = 0.022) in the study eyes than in the fellow eyes. The duration of SO tamponade was significantly correlated with the enlargement of FAZ area (P = 0.034) and reduction of VD in DCP (P = 0.015). These changes could reflect vascular insufficiency in eyes with SO tamponade and may represent a potential explanation for the pathogenesis of retinal thinning and unexplained visual loss.

Müller glial cells of the primate foveola: An electron microscopical study.

Previous studies on the ultrastructure of the primate foveola suggested the presence of an inverted cone-like structure which is formed by 25-35 specialized Müller cells overlying the area of high photoreceptor density. We investigated the ultrastructure of the Müller cells in the foveola of a human and macaque retina. Sections through the posterior poles of an eye of a 40 years-old human donor and an eye of an adult cynomolgus monkey (Macaca fascicularis) were investigated with transmission electron microscopy. The foveola consisted of an inner layer (thickness, 5.5-12 µm) which mainly contained somata (including nuclei) and inner processes of Müller cells; this layer overlaid the central Henle fibers and outer nuclear layer. The inner layer contained numerous watery cysts and thin lamelliform and tubular Müller cell processes which spread along the inner limiting membrane (ILM). The cytoplasm of the outer Müller cell processes became increasingly dispersed and electron-lucent in the course towards the outer limiting membrane. The ILM of the foveola was formed by a very thin basal lamina (thickness, <40 nm) while the basal lamina of the parafovea was thick (0.9-1 µm). The data show that there are various conspicuous features of foveolar Müller cells. The numerous thin Müller cell processes below the ILM may smooth the inner surface of the foveola (to minimize image distortion resulting from varying light refraction angles at an uneven retinal surface), create additional barriers to the vitreous cavity (compensating the thinness of the ILM), and provide mechanical stability to the tissue. The decreasing density of the outer process cytoplasm may support the optical function of the foveola.

Specialized photoreceptor composition in the raptor fovea.

The retinae of many bird species contain a depression with high photoreceptor density known as the fovea. Many species of raptors have two foveae, a deep central fovea and a shallower temporal fovea. Birds have six types of photoreceptors: rods, active in dim light, double cones that are thought to mediate achromatic discrimination, and four types of single cones mediating color vision. To maximize visual acuity, the fovea should only contain photoreceptors contributing to high-resolution vision. Interestingly, it has been suggested that raptors might lack double cones in the fovea. We used transmission electron microscopy and immunohistochemistry to evaluate this claim in five raptor species: the common buzzard (Buteo buteo), the honey buzzard (Pernis apivorus), the Eurasian sparrowhawk (Accipiter nisus), the red kite (Milvus milvus), and the peregrine falcon (Falco peregrinus). We found that all species, except the Eurasian sparrowhawk, lack double cones in the center of the central fovea. The size of the double cone-free zone differed between species. Only the common buzzard had a double cone-free zone in the temporal fovea. In three species, we examined opsin expression in the central fovea and found evidence that rod opsin positive cells were absent and violet-sensitive cone and green-sensitive cone opsin positive cells were present. We conclude that not only double cones, but also single cones may contribute to high-resolution vision in birds, and that raptors may in fact possess high-resolution tetrachromatic vision in the central fovea.

Contrast sensitivity and foveal microstructure following vitrectomy for epiretinal membrane.

PURPOSE: To evaluate contrast sensitivity (CS) in patients with epiretinal membrane (ERM) following vitrectomy and to investigate the relationship between CS and foveal microstructures with spectral-domain optical coherence tomography (SD-OCT). METHODS: Thirty-one eyes of 31 patients with ERM were included. We examined CS with a CSV-1000E chart, a logMAR best-corrected visual acuity (BCVA), and foveal microstructure by using SD-OCT before and at 6 months after surgery. From the CS data, the area under the log contrast sensitivity function (AULCSF) was calculated. Based on the OCT images, we quantified the mean thickness of the ganglion cell layer (GCL), the inner nuclear layer (INL), and the outer retinal layer (outer nuclear layer and outer plexiform layer [ONL+OPL]). The status of the photoreceptor inner and outer segment junction (IS/OS) and external limiting membrane (ELM) was also evaluated. RESULTS: Vitrectomy significantly improved logMAR BCVA and AULCSF. Even in patients with poor improvement of visual acuity (changes in logMAR BCVA by surgery was ≤0.2), postoperative AULCSF significantly increased by treatment (P < 0.05). Postoperative AULCSF showed a significant correlation with preoperative (P < 0.05) and postoperative (P < 0.05) ONL+OPL thickness, whereas other parameters were not relevant. Postoperative logMAR BCVA significantly correlated with postoperative status of IS/OS (P < 0.05) and preoperative ONL+OPL thickness (P < 0.05). CONCLUSIONS: In patients with ERM, CS improved even though their visual acuity did not recover significantly by vitrectomy. CS was associated with the thickness of outer retinal layer.

Correlation of preoperative retinal pigment epithelium status with foveal microstructure in repaired macular holes.

PURPOSE: To investigate, with spectral-domain optical coherence tomography, if the preoperative status of the retinal pigment epithelium (RPE) affects the postoperative foveal morphology and visual outcomes in eyes with surgically closed macular holes (MHs). METHODS: In 52 eyes with surgically closed MHs, preoperative RPE morphology was evaluated and graded based on the measurement of the largest hyperreflective protrusions above the RPE line. Foveal microstructural features and best-corrected visual acuity (BCVA) were evaluated 12 months after surgery. RESULTS: At 12 months, a significant correlation was found between postoperative degree of integrity of the photoreceptors with preoperative RPE morphology, and base diameter of the hole (p = 0.003 and p = 0.028, respectively); mean BCVA at 12 months in eyes with diffuse RPE alteration was significantly lower than in eyes with small or no RPE alteration (p < 0.05). CONCLUSIONS: Preoperative RPE integrity may be indicative of good photoreceptor restoration and visual recovery in patients with surgically closed MHs.

Vitreomacular interface and outer foveal microstructure in fellow eyes of patients with unilateral macular holes.

PURPOSE: To investigate the relationship between the vitreomacular interface and the integrity of the photoreceptor microstructures in the normal fellow eyes of patients with unilateral macular holes. METHODS: Retrospective observational case series. Fifty-five normal fellow eyes of 55 patients with unilateral macular holes were enrolled in the study. All patients underwent complete ophthalmologic examination including best-corrected visual acuity, slit-lamp biomicroscopy, fundus photography, and spectral domain optical coherence tomography at initial and follow-up visits. The features of the vitreomacular interface were graded based on spectral domain optical coherence tomography findings. RESULTS: At the initial visit, 28 of 55 eyes (51%) had vitreomacular attachments with or without perifoveal posterior vitreous detachment. On their initial visit, a triangular elevation of the cone outer segment tips line was identified in 11 of 18 eyes (61%) with perifoveal posterior vitreous detachment across all quadrants with persistent attachment to the fovea. Conversely, none of the remaining 37 eyes with the other stages of posterior vitreous detachment showed any abnormalities. Over a mean follow-up period of 18 months (range, 12-24 months), the elevation of the cone outer segment tips line resolved after spontaneous vitreomacular separation without macular holes in 3 eyes, remained unchanged in 6 eyes, and showed progression to a full-thickness macular hole in 2 eyes. CONCLUSION: These findings suggest that an elevation of the cone outer segment tips line in the normal fellow eyes of patients with macular holes is caused by the focal traction of the vitreous at the foveal center. This is considered to be an important primary change observed in the macular tissue in full-thickness macular hole formation.

Correlation of fundus autofluorescence with foveal microstructures and vision in branch retinal vein occlusion.

PURPOSE: To investigate the correlation of fundus autofluorescence (FAF) with the findings of spectral domain optical coherence tomography and visual acuity in patients with branch retinal vein occlusion and to determine the visual prognostic factors. METHODS: Retrospectively, an evaluation of FAF, spectral domain optical coherence tomography images, and visual acuity before and after intravitreal injection of bevacizumab (pre- and post-IVB) was obtained in 42 patients with branch retinal vein occlusion who underwent IVB as their first treatment. The FAF of fovea was graded on a scale of 1 to 4. RESULTS: The visual acuity post-IVB was associated with the visual acuity pre-IVB. Preservation of external limiting membrane and photoreceptor inner and outer segment junction pre- and post-IVB were associated with better visual acuity post-IVB. Eyes with less FAF pre-IVB were closely associated with better visual acuity post-IVB. CONCLUSION: The shorter length of photoreceptor inner and outer segment junction and external limiting membrane defect and less FAF pre-IVB showed a significant association with better visual acuity post-IVB. These associations could help to predict potential restoration of photoreceptor integrity and visual recovery in patients with branch retinal vein occlusion, in whom photoreceptor integrity before treatment could not be adequately evaluated, even with spectral domain optical coherence tomography.

[Normal macular thickness and volume using spectral domain optical coherence tomography in a reference population]. / Espesor y volumen macular normal, mediante tomografía de coherencia óptica de dominio espectral, en nuestra población de referencia.

OBJECTIVE: To establish normal values of macular thickness and volume obtained by the Cirrus SD-OCT (Carl ZeissMeditec, Dublin, CA, U.S.A.). Secondly, to assess the association between macular thickness and volume, sex and age. MATERIAL AND METHODS: A prospective study was conducted on patients who were seen in a hospital Retina Unit, and who only had retinal disease in one eye. All the Macular Cube 512 × 128 scan protocols were performed by the same operator. Only the healthy eye was scanned in each patient. RESULTS: A total of 100 eyes of 100 patients were analysed. The mean central foveal thickness was 261.31 ± 17.67 microns, and was significantly (P<.05) higher in males (267.74 ± 16.98 microns) than in females (255.60 ± 16.40 microns). The mean obtained for the volume of the cube was 10.09 ± 0.37mm 3, and the mean thickness of 280.33 ± 10.34 cube um, with no statistically significant differences between gender being found (P<.05). The mean macular thickness is less at central level, increases in the inner perifoveal ring, and then decreases in the outer perifoveal ring. Furthermore, of all quadrants the greatest thickness was the nasal (328.27 ± 12.96 microns), followed by the upper (326.27 ± 11.89 microns), lower (322.53 ± 12.37mm) sectors, with the temporal sector being the thinnest (313.35 ± 14.20 microns). The mean age of the patients was 60.86 ± 14 years. CONCLUSION: The mean central foveal thickness and the thickness of the inner perifoveal ring are significantly higher in men than in women. Both the mean volume and thickness of the cube, as well as nasal and inner superior sectors decrease with age, being significantly only in women.

Associations between metamorphopsia and foveal microstructure in patients with epiretinal membrane.

PURPOSE: To investigate the relationship between the severity of metamorphopsia and the foveal microstructure measured with spectral-domain optical coherence tomography (SD-OCT) in patients with epiretinal membrane (ERM). METHODS: This study included 48 eyes of 48 patients with idiopathic ERM and 18 age-matched normal controls. We examined the logarithm of the minimum angle of resolution best-corrected visual acuity (logMAR BCVA) and the severity of metamorphopsia using M-CHARTS. Central foveal thickness (CFT), central retinal thickness at the fovea (CRT-1mm) and parafovea (CRT-3mm), and macular volume (MV) were measured with SD-OCT software. Based on the obtained OCT image, we divided the 1.0 × 1.0-mm area centered on the fovea into nine sections and quantified the following parameters using an image-processing program: mean thickness of the ganglion cell layer (GCL), inner nuclear layer (INL), and outer retinal layer (ONL+OPL: outer nuclear layer and outer plexiform layer), the degree of the photoreceptor inner and outer segment junction (IS/OS), and external limiting membrane (ELM) disruption. RESULTS: CFT, CRT-1mm, CRT-3mm, MV, mean GCL, INL, and ONL+OPL thickness were significantly larger in patients with ERM than in normal controls. Multiple regression analysis revealed that the severity of metamorphopsia was significantly related to the mean INL thickness (P < 0.0001). LogMAR BCVA had a significant correlation with the degree of IS/OS disruption (P < 0.05), whereas other parameters were not relevant. CONCLUSIONS: In patients with idiopathic ERM, the degree of metamorphopsia is associated with INL thickness, and IS/OS status influences visual acuity.

Disparity between foveal thickness and macular volume in diabetic macular edema.

BACKGROUND: Optical coherence tomography (OCT) quantifies changes of foveal thickness and macular volume after photocoagulation in diabetic macular edema. Macular volume evaluates the whole macula, but it may underestimate changes in foveal thickness induced by photocoagulation. We undertook this study to evaluate the concordance between macular volume and foveal thickness for identifying clinically significant changes of retinal thickness after photocoagulation for diabetic macular edema. METHODS: We carried out an observational, retrospective, longitudinal, analytical study. Center point thickness (CPT), central subfield mean thickness (CSMT) and macular volume were measured with OCT before photocoagulation and 3 weeks after in diabetic patients with focal macular edema (January 2006--January 2010). Concordance among variables to detect clinically significant changes (CPT >17%, CSMT >11%, macular volume >3%) was identified using the kappa test. RESULTS: Sixty eight eyes were included; 47 eyes had nonproliferative retinopathy (69.1%). CPT increased significantly in 14.7% of the sample; CSMT in 8.8%, and macular volume in 11.8%. CPT decreased significantly in 4.4%, CSMT in 8.8%, and macular volume in 42.6%. Concordance was regular for CPT and CSMT increased (57%). Concordance was good for CPT and CSMT decreased (64%). Concordance was regular for CSMT and macular volume decreased in eyes with center involvement (43%). The remaining concordances were poor. DISCUSSION: Two independent events happen after focal photocoagulation: involution of the original thickening and increase in CPT. In order to detect both events, evaluation of either foveal thickness alone or macular volume alone is insufficient. CONCLUSION: Identifying the efficacy and safety of treatments for diabetic macular edema requires simultaneous measurement of CPT and macular volume.

[Low-fluence photodynamic therapy in chronic central serous chorioretinopathy]. / Tratamiento de coriorretinopatía serosa central crónica mediante terapia fotodinámica de baja fluencia.

OBJECTIVE: To evaluate safety and efficacy of low-fluence photodynamic therapy (LFPDT) with verteporfin in patients affected with chronic central serous chorioretinopathy (CCSC), in terms of visual acuity (VA) and macular morphology measured with optical coherence tomography (OCT). METHODS: A retrospective, non-randomized and interventionist analysis was performed on 16 eyes in 15 patients with CCSC treated with LFPDT. Best corrected visual acuity (BCVA) with ETDRS optotypes and central foveal thickness (CFT) in OCT were evaluated as outcome measures. RESULTS: The mean follow-up was 10.8 months. The mean BCVA improved from 58.12 to 68.68 ETDRS letters, and CFT decreased from 280.5 to 172.18 microns, with subretinal fluid resolution in 14 eyes (87.5%), two of them after a second LFTPD. No complications related to treatment were recorded. CONCLUSIONS: LFPDT with verteporfin can be useful in CCSC to stabilise or improve BCVA, reabsorb subretinal fluid and reduce CFT. Randomised studies with a longer follow-up are required to assure the role of this treatment and to optimise parameters for higher efficacy and safety in CCSC patients.

Functional foveal splitting: evidence from neuropsychological and multimodal MRI investigations in a Chinese patient with a splenium lesion.

It remains controversial and hotly debated whether foveal information is double-projected to both hemispheres or split at the midline between the two hemispheres. We investigated this issue in a unique patient with lesions in the splenium of the corpus callosum and the left medial occipitotemporal region, through a series of neuropsychological tests and multimodal MRI scans. Behavioral experiments showed that (1) the patient had difficulties in reading simple and compound Chinese characters when they were presented in the foveal but left to the fixation, (2) he failed to recognize the left component of compound characters when the compound characters were presented in the central foveal field, (3) his judgments of the gender of centrally presented chimeric faces were exclusively based on the left half-face and he was unaware that the faces were chimeric. Functional MRI data showed that Chinese characters, only when presented in the right foveal field but not in the left foveal field, activated a region in the left occipitotemporal sulcus in the mid-fusiform, which is recognized as visual word form area. Together with existing evidence in the literature, results of the current study suggest that the representation of foveal stimuli is functionally split at object processing levels.

Cone synapses in macaque fovea: II. Dendrites of OFF midget bipolar cells exhibit Inner Densities similar to their Outer synaptic Densities in basal contacts with cone terminals.

As described in the companion paper, the synaptic terminal of a cone photoreceptor in macaque monkey makes an average of 35 or 46 basal contacts with the tips of the dendrites of its OFF midget bipolar cell. Each basal contact has one or more symmetrically thickened dense regions. These "Outer Densities," averaging 48 or 67 in number, harbor clusters of ionotropic glutamate receptors and are ~0.8 µm (and ~1-ms diffusion time) from active zones associated with synaptic ribbons. Here, we show similarly appearing "Inner Densities," averaging 53 or 74 in number, located more proximally on the dendrites of these OFF midget bipolar cells, ~0.4 µm inward from the tips of the dendrites and out of contact with the basal surface of the cone terminal. Compared to desmosome-like junctions, Inner Densities are closer to the terminal and are less dense and less thick. Each Inner Density is shared with another cell, the partners including diffuse bipolar cells, ON midget bipolar cells, and horizontal cells. Given the diversity of the partners, the OFF midget bipolar cells are unlikely to be in a synaptic relationship with the partners. Instead, Inner Densities are near enough to the active zones associated with synaptic ribbons to receive pulses of glutamate at concentrations effective for glutamate receptors. The role of Inner Densities is not known, but they might represent additional clusters of glutamate receptors.

Measurement of foveal thickness by optical coherence tomography in adult haemodialysis patients with diabetic nephropathy.

BACKGROUND: Several studies have demonstrated the efficacy of hemodialysis (HD) on macular edema in diabetic patients. OBJECTIVE: To study the effects of a HD session on foveal thickness by optical coherence tomography (OCT) in adult patients with type 2 diabetes mellitus with chronic renal failure (CRF) secondary to stage 5 diabetic nephropathy in HD. PATIENTS AND METHODS: We studied 25 eyes of 14 patients who underwent analytical studies and pre-HD and post-HD OCT. RESULTS: As a group, the foveal thickness did not change after one session of HD in the 25 eyes studied (245.28 ± 52.21 µ versus 240.40 ± 40.25 µ) (p = 0.428) (2% reduction) or correlated with any clinical or laboratory parameters analyzed.When comparing the subgroup of 13 eyes in which the foveal thickness did not change or decreased compared to the subgroup of 12 eyes in which the foveal thickness increased we found that in the first subgroup the bath temperature was significantly higher (37.00 ± 0.00 versus 36.29 ° C, p = 0.008) and the conductivity was significantly lower (14.00 ± 0.00 versus 14.29 ± 0.10 mS / cm, p = 0.030). CONCLUSION: HD may modify the foveal retinal thickness as a function of changing parameters such as bath temperature and conductivity.

[Comparative study of coaxial microincision cataract surgery and standard phacoemulsification]. / Estudio comparativo entre cirugía de catarata por microincisión coaxial y facoemulsificación estándar.

PURPOSE: To analyse and quantitatively compare the outcomes of microincisional cataract surgery (CCMIC) with those of conventional phacoemulsification, evaluating the induced astigmatism, endothelial cell count, corneal thickness and foveal thickness in the pre- and postoperative period. METHODS: Prospective and randomised study, including 74 eyes of 37 patients with a mean age of 72.97±7.55 years. All of them underwent conventional phacoemulsification in one eye and CCMIC in the other eye. The evaluated parameters were refractive and topographic astigmatism, endothelial cell count, corneal thickness and foveal thickness, which were measured preoperatively and at 1 day, 1 week, 1 month and 3 months after surgery. RESULTS: The variations between pre- and postoperative parameters showed no statistically significant differences between the two surgical procedures (p>0.05). CONCLUSIONS: CCMIC is an effective and safe technique that offers an excellent alternative for cataract surgery, with a smaller incision and postoperative outcomes comparable to the standard technique. Prospective studies with more patients and longer follow-ups are needed to establish if there really are statistically significant and clinically relevant differences between both techniques.

Microcircuitry for two types of achromatic ganglion cell in primate fovea.

Synaptic circuits in primate fovea have been quantified for midget/parvocellular ganglion cells. Here, based on partial reconstructions from serial electron micrographs, we quantify synaptic circuits for two other types of ganglion cell: the familiar parasol/magnocellular cell and a smaller type, termed "garland." The excitatory circuits both derive from two types of OFF diffuse cone bipolar cell, DB3 and DB2, which collected unselectively from at least 6 +/- 1 cones, including the S type. Cone contacts to DB3 dendrites were usually located between neighboring triads, whereas half of the cone contacts to DB2 were triad associated. Ribbon outputs were as follows: DB3, 69 +/- 5; DB2, 48 +/- 4. A complete parasol cell (30 microm dendritic field diameter) would collect from approximately 50 cones via approximately 120 bipolar and approximately 85 amacrine contacts; a complete garland cell (25 microm dendritic field) would collect from approximately 40 cones via approximately 75 bipolar and approximately 145 amacrine contacts. The bipolar types contributed differently: the parasol cell received most contacts (60%) from DB3, whereas the garland cell received most contacts (67%) from DB2. We hypothesize that DB3 is a transient bipolar cell and that DB2 is sustained. This would be consistent with their relative inputs to the brisk-transient (parasol) ganglion cell. The garland cell, with its high proportion of DB2 inputs plus its high proportion of amacrine synapses (70%) and dense mosaic, might correspond to the local-edge cell in nonprimate retinas, which serves finer acuity at low temporal frequencies. The convergence of S cones onto both types could contribute S-cone input for cortical areas primary visual cortex and the middle temporal area.