Mechanism of Cone Degeneration in Retinitis Pigmentosa.

Retinitis pigmentosa (RP) is a group of genetic disorders resulting in inherited blindness due to the degeneration of rod and cone photoreceptors. The various mechanisms underlying rod degeneration primarily rely on genetic mutations, leading to night blindness initially. Cones gradually degenerate after rods are almost eliminated, resulting in varying degrees of visual disability and blindness. The mechanism of cone degeneration remains unclear. An understanding of the mechanisms underlying cone degeneration in RP, a highly heterogeneous disease, is essential to develop novel treatments of RP. Herein, we review recent advancements in the five hypotheses of cone degeneration, including oxidative stress, trophic factors, metabolic stress, light damage, and inflammation activation. We also discuss the connection among these theories to provide a better understanding of secondary cone degeneration in RP. Five current mechanisms of cone degenerations in RP Interactions among different pathways are involved in RP.

Inhibitory effect of blue light intervention on lens-induced myopia development in guinea pigs and the mechanism of cone density change / 中华实验眼科杂志

Objective:To observe the effects of blue light intervention on the development of optical defocus-induced myopia in guinea pigs and investigate its underlying mechanisms.Methods:Forty-eight normal-grade two-week-old tricolor guinea pigs were randomly divided into a blue light group and a white light group, with 24 animals in each group.The right eye of guinea pigs was fitted with a -5.00 D lens to establish an optical defocus model as the experimental eye, while the left eye served as the control without any covering.Before the experiment and after 8-week intervention, the refractive power of guinea pigs was measured by streak retinoscopy.The anterior chamber depth, lens thickness, and axial length were measured by A-scan ultrasonography.Corneal curvature radius was determined using a keratometer.After 8-week intervention, the guinea pigs were euthanized through overanesthesia, and the right eyeballs were enucleated and the retinas were isolated.The density of S and M cone cells of the guinea pig retinal sections were observed via immunofluorescence staining.The expression of retinal retinoic acid was assessed by high-performance liquid chromatography.The expressions of retinoic acid receptor (RAR-β) in the retina and matrix metalloproteinase-2 (MMP-2), tissue inhibitor of metalloproteinase-2 (TIMP-2), and type Ⅰ collagen in the sclera were detected by real-time fluorescence quantitative PCR.Changes in scleral thickness were observed through hematoxylin-eosin staining.The use and care of the animals complied with Regulations for the Administration of Affair Concerning Experimental Animals by State Science and Technology Commission.The study protocol was approved by the Ethics Committee of Eye and ENT Hospital of Fudan University (No.2022ETKLD10032).Results:After 8 weeks of intervention, guinea pigs in the blue light group showed (0.63±0.12)D of relative hyperopia and a deceleration of axial elongation by (0.08±0.00)mm compared with the white light group in the right eye.In the left eye, guinea pigs in the blue light group showed (0.42±0.09)D of relative hyperopia and a deceleration of axial elongation by (0.08±0.00)mm compared with the white light group.The guinea pigs in blue light group showed (1.52±0.09)D of myopia in the right eye compared with the left eye, with an increase in axial elongation of (0.06±0.00)mm.The guinea pigs in white light group showed (1.66±0.07)D of myopia in the right eye compared with the left eye, with an increase in axial elongation of (0.13±0.00)mm, and the differences were statistically significant (all at P<0.05). The density of M cone cells was lower and density of S cone cells was higher in the blue light group in the dorsal and ventral sides of the retinal sections compared with the white light group, showing statistically significant differences ( t=32.33, 52.23, 42.09, 25.02; all at P<0.05). The deceleration of myopia progression in the blue light group was strongly positively correlated with the increase in S cone cell density on the ventral side ( r=0.95, P<0.01). The expression levels of retinoic acid, RAR-β, and MMP-2 were decreased, and expression levels of TIMP-2 and type Ⅰ collagen were increased in blue light group compared with the white light group, showing statistically significant differences ( t=18.73, 7.45, 3.72, 6.19, 9.03; all at P<0.05). The scleral thickness in the blue light group was (125.0±7.8)μm, which was significantly thicker than (102.0±6.3)μm in the white light group ( t=26.93, P<0.05). Conclusions:Blue light intervention can inhibit the progression of defocus-induced myopia in guinea pigs.Refractive power changes in guinea pigs may be influenced by alterations in retinal cone cell density, retinoic acid expression, and scleral collagen expression.

Conception and features of bacillary layer detachment / 中华实验眼科杂志

The separation of outer retinal photoreceptors in patients with toxoplasmosis chorioretinitis was first named bacillary layer detachment (BALAD), which was manifested as a split at the level of the photoreceptor inner segment myoid creating a distinctive intraretinal cavity in optical coherence tomography.Subsequently BALAD has been reported by many researchers in different diseases.In the outer retina, the myoid is a relatively weak structure in photoreceptor inner segment.When the outward force that promotes the attachment of the photoreceptor outer segment to the retinal pigment epithelium exceeds the tensile strength of the photoreceptor inner segment myoid, the myoid zone splits and BALAD occurs.BALAD has its unique multimodal imaging characteristics, and the identification of it can provide a new idea for the diagnosis, detection and treatment of ocular diseases.This paper reviewed the development of BALAD nomenclature, its anatomical structure, pathophysiological mechanism and multimodal image features.

Electrical responses from human retinal cone pathways associate with a common genetic polymorphism implicated in myopia.

Myopia is the commonest visual impairment. Several genetic loci confer risk, but mechanisms by which they do this are unknown. Retinal signals drive eye growth, and myopia usually results from an excessively long eye. The common variant most strongly associated with myopia is near the GJD2 gene, encoding connexin-36, which forms retinal gap junctions. Light-evoked responses of retinal neurons can be recorded noninvasively as the electroretinogram (ERG). We analyzed these responses from 186 adult twin volunteers who had been genotyped at this locus. Participants underwent detailed ERG recordings incorporating international standard stimuli as well as experimental protocols aiming to separate dark-adapted rod- and cone-driven responses. A mixed linear model was used to explore association between allelic dosage at the locus and international standard ERG parameters after adjustment for age, sex, and family structure. Significant associations were found for parameters of light-adapted, but not dark-adapted, responses. Further investigation of isolated rod- and cone-driven ERGs confirmed associations with cone-driven, but not rod-driven, a-wave amplitudes. Comparison with responses to similar experimental stimuli from a patient with a prior central retinal artery occlusion, and from two patients with selective loss of ON-bipolar cell signals, was consistent with the associated parameters being derived from signals from cone-driven OFF-bipolar cells. Analysis of single-cell transcriptome data revealed strongest GJD2 expression in cone photoreceptors; bipolar cell expression appeared strongest in OFF-bipolar cells and weakest in rod-driven ON-bipolar cells. Our findings support a potential role for altered signaling in cone-driven OFF pathways in myopia development.

An Investigation of the Role of Macular Pigment in Attenuating Photostress through Comparison between Blue and Green Photostress Recovery Times.

PURPOSE: Photostress recovery time (PSRT) is the time required for the macula to return to its normal functioning after the bleaching of cone photopigments due to light exposure, usually white. This work investigates the role of macular pigment (MP) as an optical filter that attenuates photostress by analyses of PSRT at different wavelengths. METHODS: Thirty-nine subjects (19-28 years) were exposed to blue/green photostress varying in irradiance. During photostress, pupil constriction (Cp) was measured. Twenty-seven subjects (20-27 years) were exposed to white photostress. After 25 s of photostress, the time (PSRT) required to read correctly a 0.2 logMAR letter was measured. Correlation was studied between PSRT, CP, and irradiance. Statistical significance of differences between PSRTs was evaluated at Log(irradiance(quanta s-1 cm-2)) = 14 by Student's t statistics. RESULTS: Cp and PSRT were found linearly correlated to Log(irradiance) for blue, green, and white. At Log(irradiance(quanta s-1 cm-2)) = 14, blue and green mean PSRTs resulted different (p < 0.001) with 3.8 ± 0.8 s and 6.7 ± 1.7 s, respectively. After correcting irradiance for the optical absorption of MP, mean blue PSRT became 6.6 ± 0.8 s, at the logarithm of MP-corrected irradiance in quanta s-1 cm-2 equal to 14 (p = 0.571 compared to green PSRT). For white light, at the logarithm of MP-corrected irradiance in quanta s-1 cm-2 equal to 14, mean PSRT was 7.5 ± 2.2 s, not significantly different from blue and green PSRT (p > 0.05). CONCLUSIONS: MP plays the role of an optical filter attenuating photostress. PSRT was substantially proportional to the number of incident photons corrected for the MP optical absorption, regardless of their wavelength.

Autoimmune retinopathy: A Review.

Autoimmune retinopathy (AIR) is a rare and still poorly understood immune-mediated disease that may cause inflammation from circulating autoantibodies against the retina. It may be related to history of autoimmune disease in the patient or in a family member or the presence of neoplastic disease in the individual. The disease may be subdivided into paraneoplastic and non-paraneoplastic AIR. When related to melanoma, it is referred to as MAR, and when related to other cancers, it is called CAR. The exact prevalence of AIR is unknown. It mainly affects older adults. Patients present with bilateral and asymmetric scotomas, photopsias, visual field defects, with rapidly progressive visual loss in late onset. In the initial stage, fundus examination is unremarkable, and in late stages, there is limited retinal epitheliopathy and vascular attenuation, with or without optic disc pallor, associated or not with intraocular inflammation and with no evidence of degenerative retinal disease. A clinical investigation with detailed anamnesis and laboratory tests should be performed to search for an associated neoplasm. Ophthalmologic and complementary examinations such as full-field electroretinogram, optical coherence tomography, visual field and fundus autofluorescence, help the diagnosis. Blood tests to search for autoantibodies should be requested. Management consists of prolonged immunosuppression, which may be combined with antioxidant vitamins. In general, the prognosis is uncertain, so the disease still needs to be better understood. More studies should be performed to improve diagnostic measures and define specific management that could preserve or even restore vision.

Leber congenital amaurosis/early-onset severe retinal dystrophy: clinical features, molecular genetics and therapeutic interventions.

Leber congenital amaurosis (LCA) and early-onset severe retinal dystrophy (EOSRD) are both genetically and phenotypically heterogeneous, and characterised clinically by severe congenital/early infancy visual loss, nystagmus, amaurotic pupils and markedly reduced/absent full-field electroretinograms. The vast genetic heterogeneity of inherited retinal disease has been established over the last 10 - 20 years, with disease-causing variants identified in 25 genes to date associated with LCA/EOSRD, accounting for 70-80% of cases, with thereby more genes yet to be identified. There is now far greater understanding of the structural and functional associations seen in the various LCA/EOSRD genotypes. Subsequent development/characterisation of LCA/EOSRD animal models has shed light on the underlying pathogenesis and allowed the demonstration of successful rescue with gene replacement therapy and pharmacological intervention in multiple models. These advancements have culminated in more than 12 completed, ongoing and anticipated phase I/II and phase III gene therapy and pharmacological human clinical trials. This review describes the clinical and genetic characteristics of LCA/EOSRD and the differential diagnoses to be considered. We discuss in further detail the diagnostic clinical features, pathophysiology, animal models and human treatment studies and trials, in the more common genetic subtypes and/or those closest to intervention.

Differentiation and Transplantation of Embryonic Stem Cell-Derived Cone Photoreceptors into a Mouse Model of End-Stage Retinal Degeneration.

The loss of cone photoreceptors that mediate daylight vision represents a leading cause of blindness, for which cell replacement by transplantation offers a promising treatment strategy. Here, we characterize cone differentiation in retinas derived from mouse embryonic stem cells (mESCs). Similar to in vivo development, a temporal pattern of progenitor marker expression is followed by the differentiation of early thyroid hormone receptor ß2-positive precursors and, subsequently, photoreceptors exhibiting cone-specific phototransduction-related proteins. We establish that stage-specific inhibition of the Notch pathway increases cone cell differentiation, while retinoic acid signaling regulates cone maturation, comparable with their actions in vivo. MESC-derived cones can be isolated in large numbers and transplanted into adult mouse eyes, showing capacity to survive and mature in the subretinal space of Aipl1-/- mice, a model of end-stage retinal degeneration. Together, this work identifies a robust, renewable cell source for cone replacement by purified cell suspension transplantation.

Cyclic nucleotide-gated channels and retinal cone photoreceptor cells function / 中华实验眼科杂志

Cyclic nucleotide-gated (CNG) channels are ion channels which are activated by the binding of cyclic guanosine monophosphate (cGMP) or cyclic adenosine monophosphate (cAMP),they play a central role in the signal transduction pathways of vision and olfaction.Six different genes encode CNG protein,containing four A subunits (A1-A4) and two B subunits (B1 and B3).CNGA3 and CNGB3 have been found to be implicated in achromatopsia-associated mutations.Recently,a huge amount of researches showed the good responses to gene therapy in achromatopsia animal models.This article briefly reviewed the physiological roles of CNG channel in retinal cone photoreceptor cells and the recent research achievements of gene therapy in CNG channel-deficient mouse models with achromatopsia.

Reliability of cone counts using an adaptive optics retinal camera.

BACKGROUND: To assess the reproducibility and repeatability of cone imaging in healthy human eyes, using the RTx-1 Adaptive Optics Retinal Camera and its proprietary cone-counting software. DESIGN: Single-centre, prospective study. PARTICIPANTS: Ten healthy adults. METHODS: Macular cones were imaged. Intrasession repeatability was assessed by comparing 10 consecutive acquisitions obtained by the same operator from each subject. For the intersession study, each subject was imaged five consecutive days. Interoperator reproducibility was also evaluated by comparing the images obtained from 10 different subjects by two independent operators. Finally, intergrader agreement was evaluated by comparing the cone counts measured by two masked graders. MAIN OUTCOME MEASURES: Mean cone density (cells/mm(2) ), spacing between cells (µm) and percentage of cones with six neighbours calculated on Voronoi diagrams were measured. Correlation coefficients, intraclass correlation coefficients, and coefficients of variation were calculated. RESULTS: Correlation coefficient and intraclass correlation coefficient were respectively 0.81 and 0.96 between operators, and 0.97 and 0.98 between the two graders. The intrasession and intersession coefficients of variation were under 7%. The percentage of cells with six neighbours and the spacing between cones varied in the same proportion (coefficients of variation ranged from 1.66 to 10.05%). CONCLUSIONS: Overall, the test-retest variability of RTx-1 and its software was good in normal human eyes. Further studies in the normal clinical setting are mandatory.