Cone Cells Research Articles

Foxn4 is a temporal identity factor conferring mid/late-early retinal competence and involved in retinal synaptogenesis

During development, neural progenitors change their competence states over time to sequentially generate different types of neurons and glia. Several cascades of temporal transcription factors (tTFs) have been discovered in Drosophila to control the temporal identity of neuroblasts, but the temporal regulation mechanism is poorly understood in vertebrates. Mammalian retinal progenitor cells (RPCs) give rise to several types of neuronal and glial cells following a sequential yet overlapping temporal order. Here, by temporal cluster analysis, RNA-sequencing analysis, and loss-of-function and gain-of-function studies, we show that the Fox domain TF Foxn4 functions as a tTF during retinogenesis to confer RPCs with the competence to generate the mid/late-early cell types: amacrine, horizontal, cone, and rod cells, while suppressing the competence of generating the immediate-early cell type: retinal ganglion cells (RGCs). In early embryonic retinas, Foxn4 inactivation causes down-regulation of photoreceptor marker genes and decreased photoreceptor generation but increased RGC production, whereas its overexpression has the opposite effect. Just as in Drosophila, Foxn4 appears to positively regulate its downstream tTF Casz1 while negatively regulating its upstream tTF Ikzf1. Moreover, retina-specific ablation of Foxn4 reveals that it may be indirectly involved in the synaptogenesis, establishment of laminar structure, visual signal transmission, and long-term maintenance of the retina. Together, our data provide evidence that Foxn4 acts as a tTF to bias RPCs toward the mid/late-early cell fates and identify a missing member of the tTF cascade that controls RPC temporal identities to ensure the generation of proper neuronal diversity in the retina.

Targeting long non-coding RNA MALAT1 alleviates retinal neurodegeneration in diabetic mice.

To observe the effect of inhibiting long non-coding RNA (lncRNA) metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) on diabetic neurodegeneration. Thirty-six 8-week-old C57BL/6 mice were randomly divided into normal control, diabetic control, diabetic scrambled small interfering RNAs (siRNAs) and diabetic MALAT1-siRNA groups. After diabetic induction with streptozocin intraperitoneally-injection, the diabetic MALAT1-siRNA group was intravitreally injected with 1 µL 20 µmol/L MALAT1 siRNA, and the diabetic scrambled siRNA group was injected with the same amount of scrambled siRNA. Electroretinography was performed to examine photoreceptor functions 16wk after diabetes induction. MALAT1 expression was detected via real time polymerase chain reaction. Cone morphological changes were examined using immunofluorescence. Rod morphological changes were examined by determining outer nuclear layer (ONL) thickness. The upregulation of retinal MALAT1 expression was detected in the diabetic control mice, while MALAT1 expression in the diabetic MALAT1-siRNA mice was decreased by 91.48% compared to diabetic control mice. The diabetic MALAT1-siRNA and diabetic control mice showed lower a-wave and b-wave amplitudes than did the normal control mice in scotopic and photopic electroretinogram, while the diabetic MALAT1-siRNA mice showed higher amplitudes than diabetic control mice. Morphological examination revealed that ONL thickness in the diabetic MALAT1-siRNA and diabetic control mice was lower than normal control mice. However, ONL thickness was greater in the diabetic MALAT1-siRNA mice than diabetic control mice. Moreover, the diabetic control mice performed a sparser cone cell arrangement and shorter outer segment morphology than diabetic MALAT1-siRNA mice. Inhibiting retinal MALAT1 results in mitigative effects on the retinal photoreceptors, thus alleviating diabetic neurodegeneration.

Presence of ES1 homolog in the mitochondrial intermembrane space of porcine retinal cells

ES1 homologs are conserved among prokaryotes and eukaryotes, and the gene expression of ES1 homologs has been confirmed in diverse mammalian tissues. However, the localization and function of mammalian ES1 proteins remain poorly understood. ES1 protein was found specifically expressed in the cone cells of zebrafish and was proposed to contribute to the formation of mega mitochondria. We also observed mega mitochondria in the cone cells of porcine retinas, which raised the question regarding the localization of the porcine ES1. Therefore, in the present study, we aimed to determine the localization of ES1 in porcine retinas. We prepared a rabbit polyclonal antibody against the ES1 C-terminal and performed western blotting analysis and immunoelectron microscopy. The ES1 was found to be localized mainly in the mitochondrial intermembrane space of the porcine retinal cells. Immunopositive signals for ES1 were observed in the mitochondria of almost all retinal cells, and not specifically in cone cells. Our results and the ES1 sequences indicated that the glyoxalase III activity of ES1 might contribute to the stable functionality of the active mitochondria in a protective manner.

Repositioning of strongly integrated drugs against achromatopsia (CNGB3)

Achromatopsia (ACHM) is a genetically heterogeneous visual disorder, also known as rod monochromatism, in which human get affected due to cone cells. Mutation in five genes viz. CNGA3, CNGB3, GNAT2, PDE6C, and PDE6H have been reported in ACHM. These genes encode essential constitutes of the cone-specific photo transduction cascade. Present study was focused on CNGB3 gene that accounts 40%-50% mutations of all ACHM cases. A new approach for analyzing drug-drug interactions based on modularity was adopted. This approach depends on the behavioral relationship of drugs against CNGB3 for ACHM, particularly the ADME and toxicity between drugs. Data of 2475 compounds were retrieved, out of which 185 were selected on the basis of Lipinski rule of five. In total, eight clusters were made for which the strongly interacted DDI networks were build based on their modularity values. Strong DDI and minimum toxic values indicates that 5 drugs are effective, but on the basis of docking only 2 drugs indicated no bumps, which shows that they are most appropriate for treating ACHM. Our findings revealed that drug-drug interactions disclose the intervention of drug nature and can also successfully diagnose new indications and more convincing drugs for other diseases as well.

Saliency Consistency-Based Image Re-Colorization for Color Blindness

For patients with color vision defects, owing to the destruction of cone cells and loss of function, some color information is lost, hence changing the originally transmitted information by the image. The purpose of the traditional method of correction is to help patients distinguish between colors, but it does not take into account the problem of the saliency of the image. In this paper, we propose a saliency consistency-based image re-colorization for color blindness. We use image retrieval methods to select a large number of images and use co-saliency methods to detect salient areas of standard color images and color-blind simulated images. According to the detection results, an image with the same detection result was selected as the reference image. We grayscale the significantly changed image, recolor the grayscale image using the reference image, and the color scheme of the recolored image is similar to the reference image. The color matching scheme of the reference image makes the significance of the image basically unchanged in standard vision and color vision defects, thereby making the color blindness patient’s perception of the image close to standard vision. We invite green blind patients to evaluate CVD simulation images with different recoloring methods subjectively. In addition, we use different evaluation criteria to evaluate the experimental results objectively. In the subjective evaluation and objective evaluation, the method proposed in this paper has achieved good results, which validates the effectiveness of our method.

Extending Human Vision to Infrared and Ultraviolet Light: A Study Using Micro-Particles and Fluorescent Molecules

In this study, rare earth doped infrared (IR) to visible, up-converting particles along-with efficient ultraviolet (UV) to visible fluorescent molecules were imbedded in proteins and were used as a mean for increasing the human vision range to infrared and ultraviolet wavelengths. Stilbene-420 fluorescent molecules which convert near UV light to blue light, were chosen for the strong overlap of their fluorescence emission with the sensitivity region of blue cone cells and for the ability of blue light to increase the regeneration of bleached visual pigments. Our data show that the up-conversion efficiency of the IR up-converting particles and blue fluorescing molecules efficiencies remained unchanged when these material are imbedded in proteins compared to their efficiencies in water solutions. Addition of up-converting particles to rod visual cells resulted in the bleaching of the visual pigments, rods, when irradiated with infrared light (980 nm) whereas no bleaching was observed, under the same conditions, without the presence of up-converting particles. This suggests that the up-converted green light induced visual process in the rod visual pigments. In addition, we describe the design and present data of a novel optical device, which can be used as eye glasses, utilizing up-converting particles that allows the wearer to see rather intense infrared light.

UV Visualization: Visualization of UV by Nanopatterned Down‐Shifting Materials Mimicking Human Retinal Cone Cells (Adv. Funct. Mater. 1/2020)

UV Visualization: Visualization of UV by Nanopatterned Down‐Shifting Materials Mimicking Human Retinal Cone Cells (Adv. Funct. Mater. 1/2020)

AAV-Mediated Gene Delivery to Foveal Cones.

Adeno-associated virus (AAV) has emerged as the vector of choice for delivering genes to the mammalian retina. From the first gene therapy to receive FDA approval for the inherited retinal disease (Luxturna™) to more recent clinical trials using microbial opsins to regain light sensitivity, therapeutic transgenes rely on AAV vectors for safe and efficient gene delivery to retinal cells. Such vectors are administered to the retina via subretinal (SR) injection or intravitreal (IVT) injection routes depending on the targeted retinal cell type. An attractive target for gene therapy is the fovea, bearing the highest concentration of cone cells responsible for our high acuity daylight vision. However, previous clinical trials and large animal studies reported that SR administration of vector under the cone-exclusive fovea disrupts its fine structure and might impair visual acuity. Due to its technical difficulty and potential risks, alternatives to vector injection under this delicate region have been investigated by using novel AAV capsid variants identified via rational design or directed evolution. We recently established new vector-promoter combinations to overcome the limitations associated with AAV-mediated cone transduction in the fovea. Our methods provide efficient foveal cone transduction without detaching this delicate region and rely on the use of engineered AAVs and optimal promoters compatible with optogenetic vision restoration. Here we describe in detail our AAV vectors, methods for intravitreal and subretinal injections as well as pre- and postoperative procedures as performed in cynomolgus macaques.

Mechanism of cone cells death in retinitis pigmentosa

AbstractRetinitis pigmentosa (RP) is a group of diseases in which one of a large number of mutations causes death of rod photoreceptors. After rods die, cone photoreceptors slowly degenerate in a characteristic pattern. Rod cell death causes night blindness, but visual disability and blindness result from cone degeneration and therefore it is critical to determine the mechanisms by which it occurs. The death of rods reduces oxygen consumption resulting high tissue levels of oxygen in the outer retina. The excess oxygen stimulates superoxide radical production by mismatches in the electron transport chain in mitochondria and by stimulation of NADPH oxidase activity in cytoplasm. The high levels of superoxide radicals overwhelm the antioxidant defense system and generate more reactive species including peroxynitrite which is extremely damaging and difficult to detoxify. This results in progressive oxidative damage in cones which contributes to cone cell death and loss of function because drugs or gene transfer that reduce oxidative stress promote cone survival and maintenance of function. Oral administration of N‐acetylcysteine (NAC) has shown good efficacy in mouse models of RP prompting the FIGHT RP1 open label clinical trial, the results of which will be presented.

Homozygous Variant in ARL3 Causes Autosomal Recessive Cone Rod Dystrophy.

PurposeCone rod dystrophy (CRD) is a group of inherited retinopathies characterized by the loss of cone and rod photoreceptor cells, which results in poor vision. This study aims to clinically and genetically characterize the segregating CRD phenotype in two large, consanguineous Pakistani families.MethodsFunduscopy, optical coherence tomography (OCT), electroretinography (ERG), color vision, and visual acuity assessments were performed to evaluate the retinal structure and function of the affected individuals. Exome sequencing was performed to identify the genetic cause of CRD. Furthermore, the mutation's effect was evaluated using purified, bacterially expressed ADP-ribosylation factor-like protein 3 (ARL3) and mammalian cells.ResultsFundus photography and OCT imaging demonstrated features that were consistent with CRD, including bull's eye macular lesions, macular atrophy, and central photoreceptor thinning. ERG analysis demonstrated moderate to severe reduction primarily of photopic responses in all affected individuals, and scotopic responses show reduction in two affected individuals. The exome sequencing revealed a novel homozygous variant (c.296G>T) in ARL3, which is predicted to substitute an evolutionarily conserved arginine with isoleucine within the encoded protein GTP-binding domain (R99I). The functional studies on the bacterial and heterologous mammalian cells revealed that the arginine at position 99 is essential for the stability of ARL3.ConclusionsOur study uncovers an additional CRD gene and assigns the CRD phenotype to a variant of ARL3. The results imply that cargo transportation in photoreceptors as mediated by the ARL3 pathway is essential for cone and rod cell survival and vision in humans.

Investigations Into Bioenergetic Neuroprotection of Cone Photoreceptors: Relevance to Retinitis Pigmentosa.

Recent studies suggest cone degeneration in retinitis pigmentosa (RP) may result from intracellular energy depletion. We tested the hypothesis that cones die when depleted of energy by examining the effect of two bioenergetic, nutraceutical agents on cone survival. The study had three specific aims: firstly, we, studied the neuroprotective efficacies of glucose and creatine in an in vitro model of RP. Next, we utilized a well-characterized mouse model of RP to examine whether surviving cones, devoid of their inner segments, continue to express genes vital for glucose, and creatine utilization. Finally, we analyzed the neuroprotective properties of glucose and creatine on cone photoreceptors in a mouse model of RP. Two different bioenergy-based therapies were tested in rd1 mice: repeated local delivery of glucose and systemic creatine. Optomotor responses were tested and cone density was quantified on retinal wholemounts. The results showed that glucose supplementation increased survival of cones in culture subjected to mitochondrial stress or oxidative insult. Despite losing their inner segments, surviving cones in the rd1 retina continued to express the various glycolytic enzymes. Following a single subconjunctival injection, the mean vitreous glucose concentration was significantly elevated at 1 and 8 h, but not at 16 h after injection; however, daily subconjunctival injection of glucose neither enhanced spatial visual performance nor slowed cone cell degeneration in rd1 mice relative to isotonic saline. Creatine dose-dependently increased survival of cones in culture subjected to mitochondrial dysfunction, but not to oxidative stress. Despite the loss of their mitochondrial-rich inner segments, cone somas and axonal terminals in the rd1 retina were strongly positive for both the mitochondrial and cytosolic forms of creatine kinase at each time point examined. Creatine-fed rd1 mice displayed enhanced optomotor responses compared to mice fed normal chow. Moreover, cone density was significantly greater in creatine-treated mice compared to controls. The overall results of this study provide tentative support for the hypothesis that creatine supplementation may delay secondary degeneration of cones in individuals with RP.

Improved Color Opponent Contour Detection Model Based on Dark and Light Adaptation

Brightness and color are two basic visual features of the human visual system. In the retina, color-sensitive cells are sensitive to brightness and color information and exhibit salient direction selectivity. However, evidence from neurobiology indicates that apart from color features, the rod and cone cells of the retina are also sensitive to high or low luminance, respectively termed the light and dark adaptation mechanisms. Classical single-opponent and color-opponent contour detection model frameworks include the computational processes of single red (R), green (G), blue (B) and yellow (Y) channels and opponent R–GB–Y channels, respectively. Thus, to combine luminance cues and traditional color cues to improve boundary detection in natural scenes, we propose the use of a dark and a light channel to simulate light and dark adaptation mechanisms. The results of the proposed model considering three datasets (BSDS300, BSDS500, NYUD) demonstrate an improvement compared with current bio-inspired contour detection models.

Numerical and Experimental Analysis of Copper Electroforming on an Aluminum Substrate as a Rotating Cone Electrode Cell

AbstractIn this paper, the advantages of numerical simulation to improve the process of copper electroforming are demonstrated. In this regard, the finite element model of copper electroforming for a rotating cone electrode was first prepared and then, the effect of the key parameters, such as applied current density, solution conductivity, electrode spacing, and anode height, on the uniformity of the thickness was investigated. The model combines tertiary current distribution with Bulter–Volmer electrode kinetics and computational fluid dynamics at the turbulent condition. In order to validate the model, a cone‐shaped shell was produced by electroforming method in the laboratory. The obtained results illustrate that the tertiary current distribution model on the rotating cone cell cathode is accurate and efficient for the electroforming process simulation and it can be used for parametric studies. Moreover, the effect of the current density on the morphology and properties of the electroformed layer was investigated.

Morphological and optical features of the apposition compound eye of Monochamus alternatus Hope (Coleoptera: Cerambycidae)

The Japanese pine sawyer beetle, Monochamus alternatus Hope (Coleoptera: Cerambycidae) is currently the most destructive forest pest as it transmits the pine wilt nematode Bursaphelenchus xylophilus. Morphological, optical features and dark/light adaptational changes of the compound eyes of M. alternatus adults were examined by light, scanning and transmission electron microscopy. The eye of M. alternatus is apposition type and contains 489–712 ommatidia, depending on the beetle’s body size. Each ommatidium features a large corneal lens, composed of a thick inner lens (ILU) and a thin outer lens unit (OLU); an acone-type of cone of four cone cells, a semi-fused type of rhabdom formed by eight retinular cells (two central cells: R7-R8 surrounded by six peripheral cells: R1-R6). Dark/light adaptational changes affect size and shape of the cones as well as the rhabdom’s cross-sectional area and outline, to optimize the amount of light that reaches the photopigment. The compound eyes of M. alternatus have an F-number of 0.94, an interommatidial angle of 5.34°, an eye parameter P of 4.98 μm rad and a ratio of acceptance to interommatidial angle of 0.45. The eye is characterized by relatively poor spatial resolution, but can be expected to exhibit high absolute sensitivity and contrast in dim light.

Visualization of UV by Nanopatterned Down‐Shifting Materials Mimicking Human Retinal Cone Cells

AbstractThe conversion of invisible ultraviolet (UV) light to visible light by down‐shifting (DS) materials has a variety of important applications in the fields of optoelectronics and photonics. The ability to control emission colors as a function of the wavelength of incident UV light would significantly advance scientific research and technological applications. A novel strategy for UV visualization is demonstrated that employs nanoimprint lithography combined with a sol–gel process. The principles of trichromacy of human vision are applied; three DS materials sensitive to three different ranges of UV light are nanopatterned to mimic the three types of cone cells in the human retina. Each DS material then emits a distinctive color that can be recognized by each type of cone cells for visualization. The nanopatterned structure significantly intensifies the light emission by Mie scattering and spatially separates the three DS materials, thereby minimizing unwanted optical interference among them. The deliberately designed triple‐nanopatterned DS materials exhibit various emission colors ranging from green, to orange, to pink depending on the wavelength of the incident UV light. The current work would contribute to the development of novel strategies for multicolor tunable emission that may lead to innovative applications.

Diurnal rodents as pertinent animal models of human retinal physiology and pathology.

This presentation will survey the retinal architecture, advantages, and limitations of several lesser-known rodent species that provide a useful diurnal complement to rats and mice. These diurnal rodents also possess unusually cone-rich photoreceptor mosaics that facilitate the study of cone cells and pathways. Species to be presented include principally the Sudanian Unstriped Grass Rat and Nile Rat (Arvicanthis spp.), the Fat Sand Rat (Psammomys obesus), the degu (Octodon degus) and the 13-lined ground squirrel (Ictidomys tridecemlineatus). The retina and optic nerve in several of these species demonstrate unusual resilience in the face of neuronal injury, itself an interesting phenomenon with potential translational value.

Spatio-temporal characterization of S- and M/L-cone degeneration in the Rd1 mouse model of retinitis pigmentosa

BackgroundThe Pde6brd1 (Rd1) mouse is widely used as a murine model for human retinitis pigmentosa. Understanding the spatio-temporal patterns of cone degeneration is important for evaluating potential treatments. In the present study we performed a systematic characterization of the spatio-temporal patterns of S- and M/L-opsin+ cone outer segment and cell body degeneration in Rd1 mice, described the distribution and proportion of dual cones in Rd1 retinas, and examined the kinetics of microglial activation during the period of cone degeneration.ResultsOuter segments of S- and M/L-cones degenerated far more rapidly than their somas. Loss of both S- and M/L-opsin+ outer segments was fundamentally complete by P21 in the central retina, and 90% complete by P45 in the peripheral retina. In comparison, degeneration of S- and M/L-opsin+ cell bodies proceeded at a slower rate. There was a marked hemispheric asymmetry in the rate of S-opsin+ and M/L-opsin+ cell body degeneration. M/L-opsin+ cones were more resilient to degeneration in the superior retina, whilst S-opsin+ cones were relatively preserved in the inferior retina. In addition, cone outer segment and cell body degeneration occurred far more rapidly in the central than the peripheral retina. At P14, the superior retina comprised a minority of genuine S-cones with a much greater complement of genuine M/L-opsin cones and dual cones, whilst the other three retinal quadrants had broadly similar numbers of genuine S-cones, genuine M/L-cones and dual cones. At P60, approximately 50% of surviving cones in the superior, nasal and temporal quadrants were dual cones. In contrast, the inferior peripheral retina at P60 contained almost exclusively genuine S-cones with a tiny minority of dual cones. Microglial number and activity were stimulated during rod breakdown, remained relatively high during cone outer segment degeneration and loss of cone somas in the central retina, and decreased thereafter in the period coincident with slow degeneration of cone cell bodies in the peripheral retina.ConclusionThe results of the present study provide valuable insights into cone degeneration in the Rd1 mouse, substantiating and extending conclusions drawn from earlier studies.

Taurine Protects Retinal Cells and Improves Synaptic Connections in Early Diabetic Rats

ABSTRACT Purpose Taurine has long been thought to be involved in retinal protection from retinal degenerative diseases, but the underlying molecular mechanisms remain unclear. Retinal neurodegeneration is an early event in the pathogenesis of diabetic retinopathy (DR) that precedes and participates in the microcirculatory abnormalities that occur in DR. Our objective was to investigate the role and mechanisms of taurine in early diabetic retinas. Methods Eight-week-old STZ-induced diabetic rats and control animals were randomly assigned to receive taurine or vehicle by intraperitoneal injection or by intragastric administration. The retinal function and retinal cell counts were evaluated using an electroretinography (ERG) and immunofluorescence microscopy. Plasma amino acids were measured by ion-exchange chromatography (IEC). The expression levels of retinal taurine transporter (Tau-T), mitochondria-dependent apoptosis-associated genes and reactive gliosis markers were studied by western blotting and immunofluorescence. Pre- and post-synaptic markers (PSD95 and mGluR6) in outer plexiform layer (OPL), and the bipolar cell marker protein kinase C alpha (PKCα) were localized by immunofluorescence. Levels of PSD95 and mGluR6 were determined by quantitative western blot. Results Taurine significantly prevented the reduction of photopic b-wave amplitude and retinal cone cells and ganglion cells loss and maintained the Bcl-2/Bax ratio balance in diabetic rats. Taurine also prevented the upregulation of glial fibrillary acidic protein (GFAP) and reduced retinal reactive gliosis. Taurine reduced plasma glutamate and tyrosine levels, which were elevated in diabetic rats. Moreover, mGluR6 levels reduction detected by western blot and immunofluorescence in diabetic retinas was inhibited and the displacement of mGluR6 in OPL into the inner nuclear layer (INL) detected by immunofluorescence was reduced by Taurine treatment. Conclusion Taurine may protect retinal cells from diabetic attacks by activating Tau-T, reducing retinal reactive gliosis, improving retinal synaptic connections and decreasing retinal cell apoptosis. Thus, taurine treatment may be a novel approach for early DR.

Ephrin-A5 potentiates netrin-1 axon guidance by enhancing Neogenin availability

Axonal growth cones are guided by molecular cues in the extracellular environment. The mechanisms of combinatorial integration of guidance signals at the growth cone cell membrane are still being unravelled. Limb-innervating axons of vertebrate spinal lateral motor column (LMC) neurons are attracted to netrin-1 via its receptor, Neogenin, and are repelled from ephrin-A5 through its receptor EphA4. The presence of both cues elicits synergistic guidance of LMC axons, but the mechanism of this effect remains unknown. Using fluorescence immunohistochemistry, we show that ephrin-A5 increases LMC growth cone Neogenin protein levels and netrin-1 binding. This effect is enhanced by overexpressing EphA4 and is inhibited by blocking ephrin-A5-EphA4 binding. These effects have a functional consequence on LMC growth cone responses since bath addition of ephrin-A5 increases the responsiveness of LMC axons to netrin-1. Surprisingly, the overexpression of EphA4 lacking its cytoplasmic tail, also enhances Neogenin levels at the growth cone and potentiates LMC axon preference for growth on netrin-1. Since netrins and ephrins participate in a wide variety of biological processes, the enhancement of netrin-1 signalling by ephrins may have broad implications.

Retinal development in mandarinfish Siniperca chuatsi and morphological analysis of the photoreceptor layer

We describe the process of retinal development in mandarinfish Siniperca chuatsi from larvae to young fish. The developmental characteristics of the retinal structure and related cells were identified. Siniperca chuatsi were found to exhibit an altricial mode of retinal development that required considerable time to be completed after hatching. The retina was classed as a pure cone type during the early developmental stage. In the subsequent developmental stages, however, double cones gradually occupied the majority of the cone cells, while rod cells represented the majority of the photoreceptor cells. The outer segment (OS) of the rod cells were significantly longer compared with other morphological features, the OS of the two kinds of cone cells were significantly elongated and the diameters of the inner segment (IS) and OS of the double cone cells were significantly narrower in the later developmental stages. Combined with the scattered arrangement of cone cells at the different stages, the retina was found to have sacrificed a considerable part of visual acuity in the developmental process. The distribution of cone cells was observed to have gradually become regionalised during development. The findings of the present study also indicated that S. chuatsi have a high photosensitivity under dim light conditions as a result of specialised structures of the OS of photoreceptor cells and an increased number of rod cells. The loose arrangement of the cone mosaic presumably resulted in a poor imaging quality and, to some extent, the regionalisation of the cone-cell distribution compensated for the above shortcomings, which would enhance the ability of S. chuatsi to perceive targets in important directions for effective predation behaviour.