Retinal influences on sclera underlie visual deprivation myopia

RNA-seq and GSEA identifies suppression of ligand-gated chloride efflux channels as the major gene pathway contributing to form deprivation myopia

Currently there is no consensus regarding the aetiology of the excessive ocular volume that characterizes high myopia. Thus, we aimed to test whether the gene pathways identified by gene set enrichment analysis of RNA-seq transcriptomics refutes the predictions of the Retinal Ion Driven Efflux (RIDE) hypothesis when applied to the induction of form-deprivation myopia (FDM) and subsequent recovery (post-occluder removal). We found that the induction of profound FDM led to significant suppression in the ligand-gated chloride ion channel transport pathway via suppression of glycine, GABA_A and GABA_C ionotropic receptors. Post-occluder removal for short term recovery from FDM of 6 h and 24 h, induced significant upregulation of the gene families linked to cone receptor phototransduction, mitochondrial energy, and complement pathways. These findings support a model of form deprivation myopia as a Cl⁻ ion driven adaptive fluid response to the modulation of the visual signal cascade by form deprivation that in turn affects the resultant ionic environment of the outer and inner retinal tissues, axial and vitreal elongation as predicted by the RIDE model. Occluder removal and return to normal light conditions led to return to more normal upregulation of phototransduction, slowed growth rate, refractive recovery and apparent return towards physiological homeostasis.

Genome-Wide Association of Genetic Variants With Refraction, Axial Length, and Corneal Curvature: A Longitudinal Study of Chinese Schoolchildren

Background

Myopia is a common eye disorder that is approaching epidemic proportions worldwide. A genome-wide association study identified AREG (rs12511037), GABRR1 (rs13215566), and PDE10A (rs12206610) as being associated with refractive error in Asian populations. The present study investigated the associations between these three genetic variants and the occurrence and development of myopia, spherical equivalent refraction (SER), axial length (AL), and corneal curvature (CC) in a cohort of southeastern Chinese schoolchildren.

Methods

We examined and followed 550 children in grade 1 enrolled in the Wenzhou Epidemiology of Refractive Error (WERE) project. During the 4-year follow-up, non-cycloplegic refraction was evaluated twice each year, and the AL and CC were measured once every year. Age, sex, and the amounts of time spent on near work and outdoors were documented with a questionnaire. Sanger DNA sequencing was used to genotype single nucleotide polymorphisms (SNPs). SNPtest software was used to identify potential genetic variants associated with myopia, SER, AL, and CC. Ten thousand permutations were used to correct for multiple testing.

Results

In total, 469 children, including 249 (53.1%) boys and 220 (46.9%) girls, were included in analyses. The mean age of all the children was 6.33 ± 0.48 years. After adjusting for age, sex, time spent on near work and time spent outdoors, neither the genotypes nor the allele frequencies of the three SNPs were significantly associated with myopic shift, incident myopia or the change in SER. After adjusting for age, sex, near-work time and outdoor time with 10,000 permutations, the genotype AREG (rs12511037) was associated with an increase in AL (P′-values for the dominant, recessive, additive and general models were 0.0032, 0.0275, 0.0045, and 0.0099, respectively); the genotype PDE10A (rs12206610) was associated with a change in CC in the additive (P′ = 0.0096), dominant (P′ = 0.0096), and heterozygous models (P′ = 0.0096).

Conclusion

These findings preliminarily indicate that AREG SNP rs12511037 and PDE10A SNP rs12206610 are etiologically relevant for ocular traits, providing a basis for further exploration of the development of myopia and its molecular mechanism. However, elucidating the role of AREG and PDE10A in the pathogenesis of myopia requires further animal model and human genetic epidemiology studies. This trial is registered as ChiCTR1900020584 at www.Chictr.org.cn.

Postnatal Chick Choroids Exhibit Increased Retinaldehyde Dehydrogenase Activity During Recovery From Form Deprivation Induced Myopia

Purpose

Increases in retinaldehyde dehydrogenase 2 (RALDH2) transcript in the chick choroid suggest that RALDH2 may be responsible for increases observed in all-trans-retinoic acid (atRA) synthesis during recovery from myopic defocus. The purpose of the present study was to examine RALDH2 protein expression, RALDH activity, and distribution of RALDH2 cells in control and recovering chick ocular tissues.

Methods

Myopia was induced in White Leghorn chicks for 10 days, followed by up to 15 days of unrestricted vision (recovery). Expression of RALDH isoforms in chick ocular tissues was evaluated by Western blot. Catalytic activity of RALDH was measured in choroidal cytosol fractions using an in vitro atRA synthesis assay together with HPLC quantification of synthesized atRA. Distribution of RALDH2 cells throughout the choroid was evaluated by immunohistochemistry.

Results

RALDH2 was expressed predominately in the chick choroid (P < 0.001) and increased after 24 hours and 4 days of recovery (76%, 74%, and 165%, respectively; P < 0.05). Activity of RALDH was detected solely in the choroid and was elevated at 3 and 7 days of recovery compared to controls (70% and 48%, respectively; P < 0.05). The number of RALDH2 immunopositive cells in recovering choroids was increased at 24 hours and 4 to 15 days of recovery (P < 0.05) and were concentrated toward the RPE side compared to controls.

Conclusions

The results of this study suggest that RALDH2 is the major RALDH isoform in the chick choroid and is responsible for the increased RALDH activity seen during recovery.

Die Fledermaus: regarding optokinetic contrast sensitivity and light-adaptation, chicks are mice with wings

BACKGROUND

Through adaptation, animals can function visually under an extremely broad range of light intensities. Light adaptation starts in the retina, through shifts in photoreceptor sensitivity and kinetics plus modulation of visual processing in retinal circuits. Although considerable research has been conducted on retinal adaptation in nocturnal species with rod-dominated retinas, such as the mouse, little is known about how cone-dominated avian retinas adapt to changes in mean light intensity.

METHODOLOGY/PRINCIPAL FINDINGS

We used the optokinetic response to characterize contrast sensitivity (CS) in the chick retina as a function of spatial frequency and temporal frequency at different mean light intensities. We found that: 1) daytime, cone-driven CS was tuned to spatial frequency; 2) nighttime, presumably rod-driven CS was tuned to temporal frequency and spatial frequency; 3) daytime, presumably cone-driven CS at threshold intensity was invariant with temporal and spatial frequency; and 4) daytime photopic CS was invariant with clock time.

CONCLUSION/SIGNIFICANCE

Light- and dark-adaptational changes in CS were investigated comprehensively for the first time in the cone-dominated retina of an avian, diurnal species. The chick retina, like the mouse retina, adapts by using a "day/night" or "cone/rod" switch in tuning preference during changes in lighting conditions. The chick optokinetic response is an attractive model for noninvasive, behavioral studies of adaptation in retinal circuitry in health and disease.

Relationship between higher-order aberrations and myopia progression in schoolchildren: a retrospective study

AIM

To investigate the relationship between higher-order aberration (HOA) and myopic progression in school children.

METHODS

Between April 23, 2011 and August 29, 2011 in the children's myopia outpatient clinic of the West China Hospital of Sichuan University, 148 eyes of 74 schoolchildren were reviewed. HOAs for a 6-mm pupil were measured with an aberrometer. Myopic progression rate was defined according to the change in spherical equivalent refraction (SER) divided by the time span (years). Subjects with myopic progression rate of ≥0.50 diopters (D) were classified as the 'fast' group and the subjects with myopic progression rate of <0.50D were classified as the 'slow' group. A retrospective study was conducted to compare HOA between the two groups, using root mean square (RMS) values and Zernike coefficients.

RESULTS

The RMS values of HOA (t=2.316, P=0.02), HOA without Z4 (0) (t=2.224, P=0.03), third-order aberrations (t'=2.62, P=0.01), and coma (t'=2.49, P=0.01) were significantly higher in the fast group than those in the slow group. The individual Zernike coefficients of Z3 (-1) (t=-2.072, P=0.04) and Z5 (1) (Z =-2.627, P=0.01) displayed statistically significant differences between the two groups. Significant correlations were found between the RMS values of HOA (r=0.193, P=0.019), RMS values of HOA without Z4 (0) (r=0.23, P =0.005), RMS values of coma (r=0.235, P=0.004), RMS values of third-order aberrations (r=0.243, P =0.003), and the progression rate.

CONCLUSION

Our results provide evidence of a relationship between HOA and myopic progression. In a future prospective longitudinal study, we aim to verify whether HOA is a risk factor for myopic progression.

Gene profiling in experimental models of eye growth: clues to myopia pathogenesis

To understand the complex regulatory pathways that underlie the development of refractive errors, expression profiling has evaluated gene expression in ocular tissues of well-characterized experimental models that alter postnatal eye growth and induce refractive errors. Derived from a variety of platforms (e.g. differential display, spotted microarrays or Affymetrix GeneChips), gene expression patterns are now being identified in species that include chicken, mouse and primate. Reconciling available results is hindered by varied experimental designs and analytical/statistical features. Continued application of these methods offers promise to provide the much-needed mechanistic framework to develop therapies to normalize refractive development in children.

Axial Length: A Risk Factor for Cataractogenesis

Introduction: To evaluate whether eyes with longer axial lengths are associated more often with clinically significant cataracts than eyes with shorter axial lengths. Materials and Methods: Charts of consecutive patients who underwent cataract surgery by 4 resident surgeons at Los Angeles County Hospital from July 2001 through May 2002 were retrospectively reviewed. Those patients whose axial lengths were significantly different between the 2 eyes (≥0.30 mm) and who had no pathology (other than cataracts) affecting visual acuity were included in the study. The 2 eyes in each patient were compared for preoperative best-corrected visual acuity and severity of cataracts. Results: Thirty-four of 353 patients had interocular axial length differences of at least 0.3 mm and were included in this study. Thirty-one patients had worse, 1 had equal, and 2 had better preoperative vision in the eye with longer versus the shorter axial length. Fourteen patients had more severe, 11 had the same, and 1 had less severe posterior subcapsular cataract (PSC) in the eye with longer axial length. In 8 patients, PSC severity could not be assessed due to obscuring nuclear sclerosis. Twenty-four patients had more severe, 7 patients had equal, and 3 patients had less severe nuclear sclerosis in the longer eye. Overall, longer axial lengths correlated with worse visual acuity, posterior subcapsular cataracts, and nuclear sclerosis. Diabetic status did not affect the correlation. The correlations were stronger with greater axial length asymmetry. Conclusions: Eyes with longer axial lengths have a higher prevalence of cataracts. Key words: Axial myopia, Cataract formation

Role of Motor and Visual Experience During Development of Bipedal Locomotion in Chicks

The purpose of this research was to investigate the role of motor and visual experience during the development of locomotion in chicks. We have previously demonstrated that when locomotor activity is restricted immediately posthatching, chicks walk with shorter stride lengths and attenuated head bobbing movements. Head bobbing is an optokinetic response in birds, driven by the movement of the visual world across the retina (i.e., optic flow). During locomotion, optic flow is generated by forward translation, and we have shown that the magnitude of head bobbing movements and stride lengths are moderately correlated in walking chicks. In the present study, we investigated this relationship more closely by examining whether imposed changes in stride length could affect head excursions during head bobbing. We manipulated stride length by hobbling chicks immediately after hatching and subsequently quantified kinematic parameters, including step timing and head excursions, during walking. Imposition of shorter stride lengths induced chicks to take more frequent steps, spend less time in contact with the ground, and shortened head excursions during head bobbing. Nevertheless, the developmental changes in head excursions were not fully accounted for by altered stride lengths, so in a separate experiment, we investigated whether the development of head bobbing relies on the normal experience of optic flow. We raised chicks under stroboscopic illumination to eliminate chicks' experience of optic flow but found that this did not significantly alter head bobbing. These results are discussed along with related findings in other species and the possible neural and biomechanical constraints underlying development of walking and head bobbing in birds.

Cholinergic amacrine cells are not required for the progression and atropine-mediated suppression of form-deprivation myopia

Muscarinic cholinergic pathways have been implicated in the visual control of ocular growth. However, the source(s) of acetylcholine and the tissue(s) which regulate ocular growth via muscarinic acetylcholine receptors (mAChRs) remain unknown. We sought to determine whether retinal sources of acetylcholine and mAChRs contribute to visually guided ocular growth in the chick. Cholinergic amacrine cells were ablated by intraocular injections of either ethylcholine mustard aziridinium ion (ECMA; a selective cholinotoxin) or quisqualic acid (QA; an excitotoxin that destroys many amacrine cells, including those that release acetylcholine). Disruption of cholinergic pathways was assessed immunocytochemically with antibodies to the acetylcholine-synthesizing enzyme choline acetyltransferase (ChAT) and three different isoforms of mAChR, and by biochemical assay for ChAT activity. ECMA (25 nmol) destroyed two of the four subtypes of cholinergic amacrine cells and attenuated retinal ChAT activity, but left retinal mAChR-immunoreactivity intact. QA (200 nmol) destroyed the majority of all four subtypes of cholinergic amacrine cells, and ablated most mAChR-immunoreactivity and ChAT activity in the retina. ECMA and QA had no apparent effect on mAChRs or cholinergic fibres in the choroid, only marginally reduced choroidal ChAT activity, and had little effect on ChAT activity in the anterior segment. Toxin-treated eyes remained emmetropic and responded to form-deprivation by growing excessively and becoming myopic. Furthermore, daily intravitreal injection of 40 microg atropine for 6 days into form-deprived toxin-treated eyes completely prevented ocular elongation and myopia. We conclude that neither cholinergic amacrine cells nor mAChRs in the retina are required for visual regulation of ocular growth, and that atropine may exert its growth-suppressing influence by acting upon extraretinal mAChRs, possibly in the choroid, retinal pigmented epithelium, or sclera.

The effect of an interrupted daily period of normal visual stimulation on form deprivation myopia in chicks

The aim of this study was to determine whether an integrator of neural activity influences the amount of myopia and axial elongation resulting from deprivation of form vision. The effects on ocular parameters of a continuous period of 30 min per day of normal vision was compared to two exposures of 15 min duration each, or three exposures of 10 min each. For the remaining time, chicks had monocular translucent occlusion in a 12 hr light/12 hr dark diurnal cycle, for either 2 or 3 weeks. Fellow eyes and the eyes of bilaterally unoccluded chicks were used as controls. We found that several short periods of normal visual stimulation per day were more effective in preventing the development of form deprivation myopia and axial elongation than was one single period of the same total duration, after both 2 and 3 weeks of treatment. This study suggests that the level of neural activity in the retina may have a cumulative effect in influencing ocular growth.

Congenital and developmental myopia

Both hereditary and environmental factors are important in the interactive growth of the ocular tissues responsible for determining the refractive state of the eye. Myopia has a low prevalence in otherwise healthy children and is seen with an increased prevalence early in life in many systemic and ocular diseases. Predicting how refractive error will change in any individual child after birth or at any stage of ocular development is not possible at present, although, trends can be seen in longitudinal studies. In the disease states associated with an increased prevalence of myopia, information regarding the time of onset of myopia and the specific values for the refractive components, is lacking, so that underlying mechanisms of myopia development and whether the myopia is congenital or developmental, are not known. In adults, three different types of myopia can be characterised on the basis of clinical characteristics which have prognostic significance for ocular disease. The mechanisms of ocular growth that lead to these forms of myopia are not clear. At present, treatments to prevent or slow myopic progression have been marginally beneficial and of questionable value.