Influence of Aberration-Free, Narrowband Light on the Choroidal Thickness and Eye Length.

Purpose: To determine whether light chromaticity without defocus induced by longitudinal chromatic aberration (LCA) is sufficient to regulate eye growth. Methods: An interferometric setup based on a spatial light modulator was used to illuminate the dominant eyes of 23 participants for 30 minutes with three aberration-free stimulation conditions: (1) short wavelength (450 nm), (2) long wavelength (638 nm), and (3) broadband light (450-700 nm), covering a retinal area of 12°. The non-dominant eye was occluded and remained as the control eye. Axial length and choroidal thickness were measured before and after the illumination period. Results: Axial length increased significantly from baseline for short-wavelength (P < 0.01, 7.4 ± 2.2 µm) and long-wavelength (P = 0.01, 4.8 ± 1.7 µm) light. The broadband condition also showed an increase in axial length with no significance (P = 0.08, 5.1 ± 3.5 µm). The choroidal thickness significantly decreased in the case of long-wavelength light (P < 0.01, -5.7 ± 2.2 µm), but there was no significant change after short-wavelength and broadband illumination. The axial length and choroidal thickness did not differ significantly between the test and control eyes or between the illumination conditions (all P > 0.05). Also, the illuminated versus non-illuminated choroidal zone did not show a significant difference (all P > 0.05). Conclusions: All stimulation conditions with short- and long-wavelength light and broadband light led to axial elongation and choroidal thinning. Therefore, light chromaticity without defocus induced by LCA is suggested to be insufficient to regulate eye growth. Translational Relevance: This study helps in understanding if light chromaticity alone is a sufficient regulator of eye growth.

The P300/XBP1s/Herpud1 axis promotes macrophage M2 polarization and the development of choroidal neovascularization.

Neovascular age-related macular degeneration (AMD), which is characterized by choroidal neovascularization (CNV), leads to vision loss. M2 macrophages produce vascular endothelial growth factor (VEGF), which aggravates CNV formation. The histone acetyltransferase p300 enhances the stability of spliced X-box binding protein 1 (XBP1s) and promotes the transcriptional activity of the XBP1s target gene homocysteine inducible endoplasmic reticulum protein with ubiquitin-like domain 1 (Herpud1). Herpud1 promotes the M2 polarization of macrophages. This study aimed to explore the roles of the p300/XBP1s/Herpud1 axis in the polarization of macrophages and the pathogenesis of CNV. Hypoxia-induced p300 interacted with XBP1s to acetylate XBP1s in RAW264.7 cells. Additionally, hypoxia-induced p300 enhanced the XBP-1s-mediated unfolded protein response (UPR), alleviated the proteasome-dependent degradation of XBP1s and enhanced the transcriptional activity of XBP1s for Herpud1. The hypoxia-induced p300/XBP1s/Herpud1 axis facilitated RAW264.7 cell M2 polarization. Knockdown of the p300/XBP1s/Herpud1 axis in RAW264.7 cells inhibited the proliferation, migration and tube formation of mouse choroidal endothelial cells (MCECs). The p300/XBP1s/Herpud1 axis increased in infiltrating M2-type macrophages in mouse laser-induced CNV lesions. Blockade of the p300/XBP1s/Herpud1 axis inhibited macrophage M2 polarization and alleviated CNV lesions. Our study demonstrated that the p300/XBP1s/Herpud1 axis in infiltrating macrophages increased the M2 polarization of macrophages and the development of CNV.

Exosomal MiRNA Transfer between Retinal Microglia and RPE.

The retinal pigment epithelium (RPE), the outermost layer of the retina, provides essential support to both the neural retina and choroid. Additionally, the RPE is highly active in modulating functions of immune cells such as microglia, which migrate to the subretinal compartment during aging and age-related degeneration. Recently, studies have highlighted the important roles of microRNA (miRNA) in the coordination of general tissue maintenance as well as in chronic inflammatory conditions. In this study, we analyzed the miRNA profiles in extracellular vesicles (EVs) released by the RPE, and identified and validated miRNA species whose expression levels showed age-dependent changes in the EVs. Using co-culture of RPE and retinal microglia, we further demonstrated that miR-21 was transferred between the two types of cells, and the increased miR-21 in microglia influenced the expression of genes downstream of the p53 pathway. These findings suggest that exosome-mediated miRNA transfer is a signaling mechanism that contributes to the regulation of microglia function in the aging retina.

Optical Coherence Tomography Findings After Childhood Lensectomy.

Purpose: To explore the impact of childhood lensectomy on posterior segment development. Methods: Cross-sectional observational study at children's eye clinics at a tertiary referral center in London, UK. We included 45 children age 4 to 16 years with healthy eyes and 38 who had undergone lensectomy. We acquired posterior segment optical coherence tomography scans of both eyes. We used parametric and nonparametric tests in SPSS24 for the comparison of parameters between groups and within individuals; a P value less than 0.05 was considered significant. The main outcome measures were foveal pit depth and subfoveal choroidal thickness (CT). Secondary outcomes were inner and outer ring CT and photoreceptor layer parameters, macular and peripapillary retinal nerve fiber layer thickness. Results: Foveal pit depth and subfoveal CT are significantly reduced in eyes that have undergone lensectomy compared with nonoperated eyes. Inner ring CT and outer ring CT are reduced. Foveal inner retinal layer thickness is increased. Mean inner retinal and outer nuclear layer thickness are not affected. Conclusions: Childhood lensectomy is associated with a reduction in developmental foveal pit deepening and lack of developmental thickening of the posterior choroid. Mechanical and optical disruption of foveal and subfoveal choroidal development may affect structural foveal development after childhood lensectomy.

Cross-Inhibition of Norrin and TGF-ß Signaling Modulates Development of Retinal and Choroidal Vasculature.

Purpose: Norrin is essential for the formation of the retinal vasculature during development and promotes its repair after damage via activation of Wnt/ß-catenin signaling. Since retinal TGF-ß signaling has essentially opposite effects on the retinal vasculature we investigated if and how Norrin inhibits TGF-ß signaling, and vice versa. Methods: Eyes from transgenic mice with an overexpression of Norrin (ßB1-Norrin) and/or active TGF-ß (ßB1-TGF-ß1) in the lens were generated and analyzed by light microscopy, immunohistochemistry, and TUNEL. Further on, protein as well as mRNA levels were investigated by Western blot analyses and real-time RT-PCR, respectively. Results: In ßB1-TGF-ß1 mice, the lack of retinal vascular development and choriocapillaris maintenance was rescued when transgenic Norrin was additionally overexpressed in the eye. In addition, retinal Wnt/ß-catenin signaling and the levels of SMAD7, an inhibitor of the canonical TGF-ß pathway, were substantially suppressed in retinae of ßB1-TGF-ß1 mice. In contrast, Norrin normalized Wnt/ß-catenin signaling and SMAD7 levels in double transgenic mice. Moreover, in retinae of ßB1-TGF-ß1 mice, the amounts of phosphorylated SMAD3, a downstream mediator of TGF-ß signaling, were increased compared to those of ßB1-Norrin/ßB1-TGF-ß1 mice. In vitro, Norrin substantially reduced the TGF-ß-mediated induction of target genes, an effect that was blocked by Dickkopf-1, a specific inhibitor of Wnt/ß-catenin signaling. Conclusions: High amounts of TGF-ß in the eye cause a substantial reduction in the activity of Wnt/ß-catenin signaling. This effect is inhibited in the presence of high amounts of Norrin, which further induce the expression of SMAD7 to inhibit TGF-ß signaling.

Melanocytes contribute to the vasculature of the choroid.

Melanocytes develop from the vertebrate embryo-specific neural crest, migrate, and localize in various organs, including not only the skin but also several extracutaneous locations such as the heart, inner ear and choroid. Little is known about the functions of extracutaneous melanocytes except for cochlear melanocytes, which are essential for hearing ability. In this study, we focused on the structure of the choroid, in which melanocytes are abundant around the well-developed blood vascular system. By comparing structural differences in the choroid of wild-type and melanocyte-deficient Mitfmi-bw/Mitfmi-bw mutant mice, our observations suggest that choroidal melanocytes contribute to the morphogenesis and/or maintenance of the normal vasculature structure of that tissue.

Iron accumulates in the primate choroid of the eye with aging as revealed with synchrotron X-ray fluorescence microscopy.

Aging leads to an increase in iron-loaded cellular structures in the choroid of the eye. This study was carried out to determine the distribution and content of iron, zinc and copper in the macular retina, choroid and retrobulbar optic nerve of young (4-5 years, n = 3) and aged (15-16 years, n = 5) male non-human primates, Macaca fascicularis, whose ocular anatomy is similar to humans. Thirty µm-thick tissue sections were analysed with synchrotron X-ray fluorescence and stained histologically for iron deposition. Quantitative measurements showed high levels of iron, zinc and copper in the choroid and retinal pigment epithelium in the macular area and arachnoid layer in the retrobulbar optic nerve. In aged animals compared to young ones, there was an increase in iron in the choroid with larger deposits and iron-loaded cellular structures. Iron-accumulation within these cellular structures may contribute to choroidal function impairment in aging and age-related macular degeneration.

RPE and Choroid Mechanisms Underlying Ocular Growth and Myopia.

Myopia is the most common type of refractive errors and one of the world's leading causes of blindness. Visual manipulations in animal models have provided convincing evidence for the role of environmental factors in myopia development. These models along with in vitro studies have provided important insights into underlying mechanisms. The key locations of the retinal pigment epithelium (RPE) and choroid make them plausible conduits for relaying growth regulatory signals originating in the retina to the sclera, which ultimately determines eye size and shape. Identifying the key signal molecules and their targets may lead to the development of new myopia control treatments. This section summarizes findings implicating the RPE and choroid in myopia development. For RPE and/or choroid, changes in morphology, activity of ion channels/transporters, as well as in gene and protein expression, have been linked to altered eye growth. Both tissues thus represent potential targets for novel therapies for myopia.

Evidence for lymphatics in the developing and adult human choroid.

PURPOSE: Lymphatics subserve many important functions in the human body including maintenance of fluid homeostasis, immune surveillance, and tumor metastasis. Our aim was to provide structural and phenotypic evidence of lymphatic-like structures in the human choroid, including details of its development. METHODS: Using multiple-marker immunohistochemistry (IHC), choroids from human fetal eyes (8-26 weeks gestation) and adults (17-74 years) were examined with lymphatic- and vascular-specific markers: prospero homeobox-1 (PROX-1), lymphatic vascular endothelium receptor-1 (LYVE-1), podoplanin, D2-40, endomucin, VEGF-C, vascular endothelial growth factor receptor-3 (VEGFR-3 or Flt4), UEA lectin, platelet endothelial cell adhesion molecule-1 (PECAM-1), CD34, and CD39. Transmission electron microscopy (TEM) was used to establish evidence for choroidal lymphatics, and to provide details of stratification and relative frequency of lymphatics compared to choroidal blood vessels. RESULTS: Immunohistochemistry and TEM indicated a central-to-peripheral topography of lymphatic formation, with numerous blind-ended lymph sacs just external to the choriocapillaris, as well as the presence of infrequent precollector and collector lymphatic channels. Characteristic ultrastructural features of lymphatics in adult human choroid included anchoring filaments, luminal flocculent protein but absence of erythrocytes, fragmented and/or absent basal lamina, absence of intracellular Weibel-Palade bodies, infrequent pericyte ensheathment, and lack of fenestrae. CONCLUSIONS: The system of blind-ended initial lymphatic segments seen just external to the fenestrated vessels of the choriocapillaris is ideally placed for recirculating extracellular fluid and strategically placed for immune surveillance. The presence of a system of lymphatic-like channels in the human choroid provides an anatomical basis for antigen presentation in the posterior eye, with a possible route from the eye to the sentinel lymph nodes, similar to that already described for anterior eye lymphatics.

Age-dependent increase in miRNA-34a expression in the posterior pole of the mouse eye.

PURPOSE: MicroRNA-34a (miR-34a) has been implicated in neurodegeneration. MiR-34a belongs to a signaling network involving p53 and Sirt-1. This network responds to DNA damage with further downstream signals that induce senescence or apoptosis. Our goal was to measure the expression level of miR-34a in the mouse retina and RPE as a function of age. METHODS: The age-dependent change in miR-34a expression was quantified using a real-time PCR (RT-PCR) assay on microRNA isolates from eye tissue: the retina and RPE/choroid (4, 18, 24, and 32 months of age). Tissue localization of miR-34a was determined by in situ hybridization (ISH) for a series of time points. Expression of the miR-34a target gene Sirt1 was analyzed using RT-PCR and immunohistochemistry. RESULTS: MiR-34a examined with real-time PCR showed a linear increase in expression with age when compared to that of 4-month-old mice. However, the level of expression between the 24 and 32-month-old animals showed mild downregulation. An age-related increase in miR-34a expression was confirmed in the mouse eye using in situ hybridization. An inverse relationship between the levels of expression of miR-34a and its target Sirt1 mRNA was found at 18 and 24 months of age. CONCLUSIONS: Our data showed that miR-34a expression increased in the retina and RPE with age. The level of DNA damage in mitochondria in the retina and RPE followed a similar time course. This suggests that miR-34a may play a role in the senescence and apoptosis of the retina and RPE cells in the aging eye.

Neural crest origin of retinal and choroidal pericytes.

PURPOSE: The origin of pericytes (PCs) has been controversially discussed and at least three different sources of PCs are proposed: a neural crest, mesodermal, or bone marrow origin. In the present study we investigated a potential neural crest origin of ocular PCs in a transgenic Rosa26-YFP-Sox10-Cre neural crest-specific reporter mouse model at different developmental stages. METHODS: The Rosa26-YFP-Sox10-Cre mouse model expresses the yellow fluorescent protein (YFP) reporter in cells with an active Sox10 promoter and was here used for cell fate studies of Sox10-positive neural crest derived progeny cells. Detection of the YFP signal in combination with double and triple immunohistochemistry of chondroitin sulfate proteoglycan (NG2), platelet derived growth factor receptor ß (PDGFRß), α smooth muscle actin (αSMA), oligodendrocyte transcription factor 2 (Olig2), and lectin was performed and analyzed by confocal microscopy. RESULTS: Sox10-YFP-positive cells and profiles were detected in the inner nuclear layer, the ganglionic cell layer, and the axons of the nerve fiber layer in postnatal retinas. An additional population has been identified in the retina, optic nerve, and choroid that displays strong perivascular localization. These cells were colocalized with the PC-specific markers NG2 and PDGFRß in embryonic (E14.5) as well as postnatal (P4, P12, 6-week-old) vasculature. Beside PCs, vascular smooth muscle cells (vSMCs) were also labeled by the Sox10-YFP reporter protein in all ocular tissues investigated. CONCLUSIONS: Since YFP-positive PCs and vSMCs are colocalized with NG2 and PDGFRß, we propose that capillary PCs and vSMCs in the retina and the optic nerve, both parts of the central nervous system, as well as in the choroid, a tissue of mesodermal origin, derive from the neural crest.

In vitro effects of insulin and RPE on choroidal and scleral components of eye growth in chicks.

In chick eyes, exogenous insulin prevents the choroidal thickening caused by wearing positive lenses and increases ocular elongation and scleral glycosaminoglycan (GAG) synthesis, an indicator of eye growth. Using in vitro eye-cups, a novel experimental system, we examined the role of the retinal pigment epithelium (RPE) and insulin on choroidal thickness and scleral GAG synthesis. Specifically, we asked whether insulin causes the release of diffusible factors from the RPE that affect the choroid. We studied the effect of insulin on choroidal thickness and scleral GAG synthesis by making eye-cups consisting of RPE, choroid, and sclera (RCS), choroid and sclera (CS), or just sclera from pairs of eyes. One eye-cup was cultured in 0.037, 0.37, 3.7 or 37 µM insulin dissolved in L-15 medium, and its pair was cultured in L-15 medium without insulin. Choroidal thickness in eye-cups was measured by A-scan ultrasonography before and after 20 h of incubation. Sulfate incorporation into GAGs (scleral GAG synthesis) was measured after 44 h of incubation. To further study the effect of RPE and insulin on the choroids, we prepared pairs of CS eye-cups cultured with vs. without RPE transplanted from donor eyes, in the presence or absence of 37 µM insulin. To study if insulin caused the RPE to produce diffusible factors that affected the choroid, we prepared medium conditioned by the RPE in the presence (experimental conditioned medium) or absence (control conditioned medium) of 37 µM insulin for 20 h. Experimental and control conditioned media were pooled separately, and an equal volume of medium containing 37 µM insulin was added to both experimental and control media. Pairs of CS eye-cups were cultured in conditioned medium (experimental vs. control). Choroidal thickness was measured before and after 20 h of incubation. Choroids in all eye-cups thickened after 20 h of incubation. Insulin reduced this natural choroidal thickening seen in culture significantly, but only if the RPE was present. This effect was dose-dependent and strongest at 37 µM. Insulin increased scleral GAG synthesis in both RCS and CS eye-cups, having a greater effect in the CS eye-cups. Insulin had no effect on scleral GAG synthesis in scleral eye-cups. Choroids of CS eye-cups cultured with transplanted RPE plus insulin thickened significantly less than choroids of eye-cups cultured with insulin but without the RPE. The reduction in choroidal thickening was similar to that seen in eye-cups with intact RPE (RCS). Choroidal thickening of CS eye-cups cultured with experimental conditioned medium was significantly reduced compared with their pairs cultured with control conditioned medium. In vitro, as in vivo, insulin prevents choroidal thickening and increases scleral GAG synthesis. Insulin causes the RPE to synthesize diffusible molecules that inhibit choroidal thickening. Insulin might also cause the choroid to produce secondary signals that affect scleral GAG synthesis.

Choroidal volume variations during childhood.

PURPOSE: We analyzed choroidal volume (CV) variations during childhood using enhanced depth imaging optical coherence tomography, and evaluated its association with age, axial length (AXL), sex, weight, and height. METHODS: Imaging studies of the right eyes of 52 healthy children were reviewed and included in this study. Subjects underwent a complete ocular examination and AXL measurement, as well as a raster macular scan using the Heidelberg Spectralis device. The choroid was segmented manually. RESULTS: Subjects included 21 males and 31 females, with mean age of 9 years (range, 2-17 years) and mean AXL of 22.8 ± 0.98 mm. Mean CV was 0.263 ± 0.068 mm(3) for the foveal circle and 8.545 ± 1.822 mm(3) for the total Early Treatment of Diabetic Retinopathy Study (ETDRS) grid. The CV of the nasal quadrant was significantly lower than all others (P < 0.001). Total and foveal CV showed significant negative correlation with AXL after adjustment for age (P < 0.001), and significant positive correlation with age after adjustment for AXL (P < 0.001). Total CV was correlated significantly with sex after adjusting for AXL (P = 0.01), while no correlations were found between total CV and height or weight. The CV increased by 0.214 mm(3) (2.5%) for every year, and decreased by 1.0 mm(3) (11.7%) for every millimeter of axial length. Regression analysis confirmed a trend of higher CV in females than in males (P = 0.056). CONCLUSIONS: The CV increases with age during childhood, but decreases with AXL. This finding supports the hypothesis that the choroid grows progressively during childhood. Intersexual differences of CV also may be present.

Effects of muscarinic agents on chick choroids in intact eyes and eyecups: evidence for a muscarinic mechanism in choroidal thinning.

PURPOSE: In chicks, ocular growth inhibition is associated with choroidal thickening and growth stimulation with choroidal thinning, suggesting a mechanistic link between the two responses. Because muscarinic antagonists inhibit the development of myopia in animal models by a non-accommodative mechanism, we tested the hypothesis that agonists would stimulate eye growth and thin the choroid. We also hypothesized that the effective growth-inhibiting antagonists would thicken the choroid. METHODS: Chicks, age 12-16 days, were used. In vivo: Agonists: Single intravitreal injections (20 µL) of oxotremorine (oxo), pilocarpine (pilo), carbachol (carb), or arecaidine (arec) were given to otherwise untreated eyes. A-scan ultrasonography was done prior to injections, and at 3, 24, 48 and 72 h. Antagonists: -10D lenses were worn on one eye for 4 days. Atropine (atro), pirenzepine (pirz), oxyphenonium (oxy) or dicyclomine (dicy) were injected (20 µL) daily into lens-wearing eyes; saline injections were done as controls. Ultrasonography was done on d1 and on d4; on d4 measurements were done before and 3 h after injections. In vitro: Paired eyecups of retinal pigment epithelium (RPE), choroid and sclera were made from 1-week old chicks. All drugs except atropine were tested on one eyecup, its pair in plain medium. Choroidal thickness was measured at various times over 48 h. RESULTS: Agonists: In vivo, oxotremorine caused an increase in the rate of axial elongation (drug vs saline: 24-72 h: 338 µm vs 250 µm; p < 0.001). All except pilocarpine caused choroidal thinning by 24 h (oxo, carb and arec vs saline: -25, -35 and -46 µm vs 3 µm). In vitro, all agonists thinned choroids by 24 h (oxo: -6 vs 111 µm; pilo: 45 vs 212 µm; carb: -58 vs 65 µm; arec: 47 vs 139 µm; p < 0.05). Antagonists: Atropine, pirenzepine and oxyphenonium inhibited the development of myopia in negative lens-wearing eyes, and also caused choroidal thickening (drug vs saline: 42, 80, 88 vs 10 µm per 3 h). In vitro, pirenzepine thickened choroids by 3 h (77 vs 2 µm, p < 0.01). CONCLUSIONS: Muscarinic agonists caused choroidal thinning in intact eyes and eyecups, supporting a role for acetylcholine in the choroidal response to hyperopic defocus or form deprivation. Only oxotremorine stimulated eye growth, which is inconsistent with a muscarinic receptor mechanism for antagonist-induced eye growth inhibition. The dissociation between choroidal thinning and ocular growth stimulation for the other agonists in vivo suggest separate pathways for the two.

Choroidal thickness in childhood.

PURPOSE: We examined choroidal thickness (ChT) and its spatial distribution across the posterior pole in pediatric subjects with normal ocular health and minimal refractive error. METHODS: ChT was assessed using spectral domain optical coherence tomography (OCT) in 194 children aged 4 to 12 years, with spherical equivalent refractive errors between +1.25 and -0.50 diopters sphere (DS). A series of OCT scans were collected, imaging the choroid along 4 radial scan lines centered on the fovea (each separated by 45°). Frame averaging was used to reduce noise and enhance chorioscleral junction visibility. The transverse scale of each scan was corrected to account for magnification effects associated with axial length. Two independent masked observers segmented the OCT images manually to determine ChT at foveal center, and averaged across a series of perifoveal zones over the central 5 mm. RESULTS: The average subfoveal ChT was 330 ± 65 µm (range, 189-538 µm), and was influenced significantly by age (P = 0.04). The ChT of the 4- to 6-year-old age group (312 ± 62 µm) was significantly thinner compared to the 7- to 9-year-olds (337 ± 65 µm, P < 0.05) and bordered on significance compared to the 10- to 12-year-olds (341 ± 61 µm, P = 0.08). ChT also exhibited significant variation across the posterior pole, being thicker in more central regions. The choroid was thinner nasally and inferiorly compared to temporally and superiorly. Multiple regression analysis revealed age, axial length, and anterior chamber depth were associated significantly with subfoveal ChT (P < 0.001). CONCLUSIONS: ChT increases significantly from early childhood to adolescence. This appears to be a normal feature of childhood eye growth.

Choroid development and feasibility of choroidal imaging in the preterm and term infants utilizing SD-OCT.

PURPOSE: To determine whether choroidal imaging is feasible in preterm and term infants using an 840-nm portable spectral domain optical coherence tomography (SD-OCT) system without the use of enhanced-depth imaging techniques and to assess choroidal development by comparing choroidal thickness of preterm infants, term infants, and adults. METHODS: SD-OCT images were obtained from 86 preterm infants, 59 term infants, and nine adults using a portable SD-OCT system plus nine adults using a tabletop system. An unprocessed image across the macula from one randomly selected eye of each participant was selected for determination of whether the choroidal-scleral junction (CSJ) could be visualized and for measurement of choroidal thickness. RESULTS: Subfoveal CSJ was visualized in 96% of young-preterm infants (imaged from 30-36 weeks postmenstrual age [PMA]); 78% of term-aged preterm infants (imaged from 37-42 weeks PMA); 49% of term infants; and 39% of adult subjects. Racial pigmentation did not affect CSJ visibility in young-preterm infants (P = 0.57). Subfoveal choroidal thickness (SFCT) in young-preterm infants, term-aged preterm infants, term infants, and adults was 176 ± 53 µm, 289 ± 92 µm, 329 ± 66 µm, and 258 ± 66 µm, respectively, and these were all statistically significantly different from one another except term-aged preterms to adults. CONCLUSIONS: Infant choroid can be imaged with a portable SD-OCT system without enhanced depth imaging. Melanin in the RPE and choroid does not hinder outer choroidal imaging in young-preterm infants without advanced retinopathy of prematurity (ROP). In preterm infants, choroidal thickness increased with age but was thinner when compared to term infants suggesting delayed development due to ROP.