Altered chromatin topologies caused by balanced chromosomal translocation lead to central iris hypoplasia.

Despite the advent of genomic sequencing, molecular diagnosis remains unsolved in approximately half of patients with Mendelian disorders, largely due to unclarified functions of noncoding regions and the difficulty in identifying complex structural variations. In this study, we map a unique form of central iris hypoplasia in a large family to 6q15-q23.3 and 18p11.31-q12.1 using a genome-wide linkage scan. Long-read sequencing reveals a balanced translocation t(6;18)(q22.31;p11.22) with intergenic breakpoints. By performing Hi-C on induced pluripotent stem cells from a patient, we identify two chromatin topologically associating domains spanning across the breakpoints. These alterations lead the ectopic chromatin interactions between APCDD1 on chromosome 18 and enhancers on chromosome 6, resulting in upregulation of APCDD1. Notably, APCDD1 is specifically localized in the iris of human eyes. Our findings demonstrate that noncoding structural variations can lead to Mendelian diseases by disrupting the 3D genome structure and resulting in altered gene expression.

Region-related and layer-specific permeability of the iris vasculature with morphological mechanism: A novel understanding of blood-aqueous barrier.

The permeability of iris blood vessels has an important role in maintaining aqueous humor (AH) homeostasis, contributing to variation in iris volume and probably the pathogenesis of angle closure glaucoma. This study investigates the permeability of the iris microvasculature to plasma-derived protein and correspond it with the morphologic characteristics of vascular mural cells (MCs). Twenty-two enucleated porcine eyes were used in this study. 12 eyes were micro-perfused with vehicle alone as control or with FITC-albumin as a marker of protein leakage and histological sections subsequently made to examine for FITC-albumin presence. The other 10 eyes were immunolabeled via micro-perfusion for αSMA and VE-cadherin to investigate their topographic distribution in the porcine iris vasculature, and to cross correspond with the locations of FITC-albumin deposits. Distribution of FITC-signals exhibited a site-dependent pattern and time-dependent change in the iris. Fluorescence was initially detected around capillaries in the superficial and deep layer of the iris microvascular network. The pupillary region and the iris root retained more fluorescent signal than the iridal ciliary region. At low magnification, αSMA labelling displayed a regional variation which was inversely correlated with vascular permeability. At the cellular level, αSMA labeling corresponded with vascular MCs distribution in the iris vascular network. The correspondence between iris microvascular permeability to FITC-albumin and the pattern of αSMA distribution and MCs coverage adds to the understanding of the elements comprising the blood-aqueous barrier with implications for the bio-mechanics of iris volume change.

Trpm1: Novel function at the intersection of light and pain response in the iris.

In mammals, the retina is the photosensitive tissue that is responsible for the capture of light and the transduction of the light-initiated signals to the brain. These visual signals help to drive image and non-image forming behaviors. The pupillary light reflex (PLR) is an involuntary non-image forming behavior which involves the constriction of the iris muscle tissue in response to ambient light intensity. A subset of photosensitive retinal ganglion cells provides the principal pathway for all light input to the olivary pretectal nucleus which directs the neuronal input to drive iris constriction. Transient receptor potential melastatin 1 (Trpm1) knockout mice have a severe defect in PLR, but it remains unclear how the Trpm1 channel contributes to this behavior. We have demonstrated that the reduced PLR in Trpm1-/- mice at scotopic and photopic intensities is due to a functional loss of Trpm1 in the retina as well as the iris sphincter muscle. We have also tested constriction in isolated eyes and have shown that light-driven constriction independent of signaling from the brain also requires Trpm1 expression. In both the in vivo PLR and the iris photomechanical response, melanopsin is required for the light-dependent activation. Finally, pharmacological experiments using capsaicin to activate pain afferents in the eye demonstrate that Trpm1 expression is required for all sensory driven iris constriction. Our results demonstrate for the first time that Trpm1 has a novel and necessary role in iridial cells and is required for all sensory-driven constriction in the iris.

A transcriptome atlas of the mouse iris at single-cell resolution defines cell types and the genomic response to pupil dilation.

The iris controls the level of retinal illumination by controlling pupil diameter. It is a site of diverse ophthalmologic diseases and it is a potential source of cells for ocular auto-transplantation. The present study provides foundational data on the mouse iris based on single nucleus RNA sequencing. More specifically, this work has (1) defined all of the major cell types in the mouse iris and ciliary body, (2) led to the discovery of two types of iris stromal cells and two types of iris sphincter cells, (3) revealed the differences in cell type-specific transcriptomes in the resting vs. dilated states, and (4) identified and validated antibody and in situ hybridization probes that can be used to visualize the major iris cell types. By immunostaining for specific iris cell types, we have observed and quantified distortions in nuclear morphology associated with iris dilation and clarified the neural crest contribution to the iris by showing that Wnt1-Cre-expressing progenitors contribute to nearly all iris cell types, whereas Sox10-Cre-expressing progenitors contribute only to stromal cells. This work should be useful as a point of reference for investigations of iris development, disease, and pharmacology, for the isolation and propagation of defined iris cell types, and for iris cell engineering and transplantation.

The genetics and evolution of eye color in domestic pigeons (Columba livia).

The eye color of birds, generally referring to the color of the iris, results from both pigmentation and structural coloration. Avian iris colors exhibit striking interspecific and intraspecific variations that correspond to unique evolutionary and ecological histories. Here, we identified the genetic basis of pearl (white) iris color in domestic pigeons (Columba livia) to explore the largely unknown genetic mechanism underlying the evolution of avian iris coloration. Using a genome-wide association study (GWAS) approach in 92 pigeons, we mapped the pearl iris trait to a 9 kb region containing the facilitative glucose transporter gene SLC2A11B. A nonsense mutation (W49X) leading to a premature stop codon in SLC2A11B was identified as the causal variant. Transcriptome analysis suggested that SLC2A11B loss of function may downregulate the xanthophore-differentiation gene CSF1R and the key pteridine biosynthesis gene GCH1, thus resulting in the pearl iris phenotype. Coalescence and phylogenetic analyses indicated that the mutation originated approximately 5,400 years ago, coinciding with the onset of pigeon domestication, while positive selection was likely associated with artificial breeding. Within Aves, potentially impaired SLC2A11B was found in six species from six distinct lineages, four of which associated with their signature brown or blue eyes and lack of pteridine. Analysis of vertebrate SLC2A11B orthologs revealed relaxed selection in the avian clade, consistent with the scenario that during and after avian divergence from the reptilian ancestor, the SLC2A11B-involved development of dermal chromatophores likely degenerated in the presence of feather coverage. Our findings provide new insight into the mechanism of avian iris color variations and the evolution of pigmentation in vertebrates.

Primary angle closure glaucoma is characterized by altered extracellular matrix homeostasis in the iris.

PURPOSE: To characterize the proteome of the iris in primary angle closure glaucoma (PACG). EXPERIMENTAL DESIGN: In this cross-sectional study, iris samples were obtained from surgical iridectomy of 48 adults with PACG and five normal controls. Peptides from iris were analysed using liquid chromatography-tandem mass spectrometry on an Orbitrap Q Exactive Plus mass spectrometer. Verification of proteins of interest was conducted using selected reaction monitoring on a triple quadrupole mass spectrometer. The main outcome was proteins with a log2 two-fold difference in expression in iris between PACG and controls. RESULTS: There were 3,446 non-redundant proteins identified in human iris, of which 416 proteins were upregulated and 251 proteins were downregulated in PACG compared with controls. Thirty-two upregulated proteins were either components of the extracellular matrix (ECM) (fibrillar collagens, EMILIN-2, fibrinogen, fibronectin, matrilin-2), matricellular proteins (thrombospondin-1), proteins involved in cell-matrix interactions (integrins, laminin, histidine-rich glycoprotein, paxillin), or protease inhibitors known to modulate ECM turnover (α-2 macroglobulin, tissue factor pathway inhibitor 2, papilin). Two giant proteins, titin and obscurin, were up- and down-regulated, respectively, in the iris in PACG compared with controls. CONCLUSIONS AND CLINICAL RELEVANCE: This proteomic study shows that ECM composition and homeostasis are altered in the iris in PACG.

Piezo2 downregulation via the Cre-lox system affects aqueous humor dynamics in mice.

Purpose: Proper aqueous humor (AH) dynamics is crucial for maintaining the intraocular pressure (IOP) in the eye. This study aims to investigate the function of Piezo2, a newly discovered mechanosensitive ion channel, in regulating AH dynamics. Methods: Immunohistochemistry (IHC) analysis and western blotting were performed to detect Piezo2 expression. The Cre-lox system was applied to create a conditional knockout model of Piezo2. IOP and aqueous humor outflow facility in live animals were recorded with a Tonometer and a syringe-pump system for up to 2 weeks. Results: We first detected Piezo2 with robust expression in the human trabecular meshwork (TM), Schlemm's canal (SC), the ciliary body's epithelium, and ciliary muscle. In addition, we found Piezo2 in human retinal ganglion cells (RGCs) and astrocytes in the optic nerve head (ONH). Through the Cre-lox system, Piezo2 can be successfully downregulated in mouse iridocorneal angle tissues. However, Piezo2 downregulation cannot significantly influence the IOP and outflow facility through the conventional pathway. Instead, we observed an effect of downregulated Piezo2 on decreasing the intercept in the flow rate versus pressure plot. According to the Goldmann equation, Piezo2 may function in regulating unconventional outflow, AH production, and episcleral venous pressure. Conclusions: These findings, for the first time, demonstrate that Piezo2 acts as an essential mechanosensor in maintaining the proper aqueous humor dynamics in the eye.

Exome sequencing and functional studies in zebrafish identify WDR8 as the causative gene for isolated Microspherophakia in Indian families.

Isolated Microspherophakia (MSP) is an autosomal recessive disorder characterized by a smaller than normal spherical lens. Till date, LTBP2 is the only gene shown to cause MSP. We used homozygosity mapping and whole-exome sequencing and identified a homozygous mutation, c.1148C > T (p.Pro383Leu), in the WDR8 (or WRAP73) gene in two Indian MSP families. In vitro experiments showed that the missense mutation renders the protein unstable. WDR8 is a centriolar protein that has important roles in centrosomal assembly, spindle pole formation and ciliogenesis. Co-immunoprecipitation experiments from HeLa cells indicated that the mutation interferes with the interaction of WDR8 with its binding partners. In zebrafish, both morpholino-mediated knockdown and CRISPR/Cas knockout of wdr8 resulted in decreased eye and lens size. The lack of wdr8 affected cell cycle progression in the retinal cells, causing a reduction in cell numbers in the retina and lens. The reduction in eye size and the cell cycle defects were rescued by exogenous expression of the human wild-type WDR8. However, the human mutant WDR8 (p.Pro383Leu) was unable to rescue the eye defects, indicating that the missense mutation abrogates WDR8 protein function. Thus, our zebrafish results suggested that WDR8 is the causative gene for MSP in these Indian families.

Molecular parallelisms between pigmentation in the avian iris and the integument of ectothermic vertebrates.

Birds exhibit striking variation in eye color that arises from interactions between specialized pigment cells named chromatophores. The types of chromatophores present in the avian iris are lacking from the integument of birds or mammals, but are remarkably similar to those found in the skin of ectothermic vertebrates. To investigate molecular mechanisms associated with eye coloration in birds, we took advantage of a Mendelian mutation found in domestic pigeons that alters the deposition of yellow pterin pigments in the iris. Using a combination of genome-wide association analysis and linkage information in pedigrees, we mapped variation in eye coloration in pigeons to a small genomic region of ~8.5kb. This interval contained a single gene, SLC2A11B, which has been previously implicated in skin pigmentation and chromatophore differentiation in fish. Loss of yellow pigmentation is likely caused by a point mutation that introduces a premature STOP codon and leads to lower expression of SLC2A11B through nonsense-mediated mRNA decay. There were no substantial changes in overall gene expression profiles between both iris types as well as in genes directly associated with pterin metabolism and/or chromatophore differentiation. Our findings demonstrate that SLC2A11B is required for the expression of pterin-based pigmentation in the avian iris. They further highlight common molecular mechanisms underlying the production of coloration in the iris of birds and skin of ectothermic vertebrates.

UVR-B-induced NKR-1 Expression in Ocular Tissues is blocked by Substance P Receptor Antagonist Fosaprepitant in the Exposed as well as Unexposed Partner Eye.

Purpose: To investigate the effect of NKR-1 antagonists in an established UVR-B-induced cataract mouse model. Furthermore, to examine the expression of pro-inflammatory cytokines/chemokines in mouse eyes following unilateral UVR-B exposure.Methods: Mice received intraperitoneally injections of Fosaprepitant and Spantide I, before and after unilateral exposure to UVR-B. After day 3 and 7 post-exposure, ocular tissues were extracted for the detection of NKR-1 protein level by ELISA.Results: Pretreatment with Fosaprepitant decreases NKR-1 expression in exposed ocular tissues as well as in the unexposed lens epithelium compared to the saline group. Spantide I treatment showed a tendency of NKR-1 overexpression in ocular tissues.Conclusion: The clinically approved NKR-1 receptor antagonist Fosaprepitant decreases NKR-1 protein expression effectively not only in the exposed but also in the unexposed partner eye in a UVR-B irradiation mouse model. No effect was seen on the protein concentration of pro-inflammatory cytokines/chemokines in either eye.

Expression of Cytokines in Porcine Iris, Retina and Choroidal Tissues Stimulated by Microbe-associated Molecular Patterns.

PURPOSE: The innate immune system is strongly implicated in the pathogenesis of uveitis. This study was designed to clarify the responses of the innate immune system in uveal tissues. MATERIALS AND METHODS: We utilized quantitative, real-time RT-PCR to measure mRNA of innate immune system receptors from porcine iris, choroid, and retina tissues. We used RT-PCR for cytokines to evaluate the responses of these tissues to specific ligands or extracts of whole bacteria that activate the innate immune system. We used ELISA for IL-6 on selected choroidal supernatants to confirm that the mRNA measurement correlated with protein levels. RESULTS: In each of the studied tissues, we detected the expression of important receptors belonging to the innate immune system including dectin-1, TLR4, TLR8, and NOD2. Relative mRNA expression was generally lower in the retina compared to iris or choroid. All three tissues demonstrated upregulation of cytokine mRNA in response to a range of ligands that activate the innate immune system. The measurement of IL-6 protein was consistent with results based on mRNA. Notably, the expression of mRNA for IL-23 was more pronounced than IL-12 in all three tissues after stimulation with various innate immune system ligands. CONCLUSIONS: These data provide evidence of a potent innate immune response intrinsic to uveal tissues. Specific innate immune system ligands as well as bacterial extracts enhanced the production of several inflammatory cytokines. Furthermore, the observation of higher upregulation of IL-23 mRNA, compared to IL-12 in response to innate immune stimuli, suggested that a local TH17 response might be more robust than a local TH1 response in uveal tissues. Our results expand the understanding as to how the innate immune system may contribute to uveitis.

Iris Colour and the Risk of Developing Uveal Melanoma.

Uveal melanoma (UM) is a global disease which especially occurs in elderly people. Its incidence varies widely between populations, with the highest incidence among Caucasians, and a South-to-North increase in Europe. As northern Europeans often have blond hair and light eyes, we wondered whether iris colour may be a predisposing factor for UM and if so, why. We compared the distribution of iris colour between Dutch UM patients and healthy Dutch controls, using data from the Rotterdam Study (RS), and reviewed the literature regarding iris colour. We describe molecular mechanisms that might explain the observed associations. When comparing a group of Dutch UM patients with controls, we observed that individuals from Caucasian ancestry with a green/hazel iris colour (Odds Ratio (OR) = 3.64, 95% Confidence Interval (CI) 2.57-5.14) and individuals with a blue/grey iris colour (OR = 1.38, 95% CI 1.04-1.82) had a significantly higher crude risk of UM than those with brown eyes. According to the literature, this may be due to a difference in the function of pheomelanin (associated with a light iris colour) and eumelanin (associated with a brown iris colour). The combination of light-induced stress and aging may affect pheomelanin-carrying melanocytes in a different way than eumelanin-carrying melanocytes, increasing the risk of developing a malignancy.

Molecular and biochemical mechanisms of human iris color: A comprehensive review.

Eye color is determined as a polymorphism and polygenic trait. Brown is the most common eye color in the world, accounting for about 79%, blue eye color for about 8-10%, hazel for 5%, and green for 2%. Rare-colored eyes include gray and red/violet. Different factors are involved in determining eye color. The two most important factors are the iris pigment and the way light is scattered from the iris. Gene expression determines the iris pigmentation and how much melanin is present in the eye, which is the number of melanin subunits that identify eye color. The genes involved in the pigmentation of single-nucleotide polymorphism (SNP) have a significant role; and even some genes are included only in the eye color through SNP. MicroRNAs also affect melanocyte synthesis, which is usually affected by the downregulation of essential genes involved in pigmentation. In this study, we assess the biochemical pathways of melanin synthesis, and the role of each gene in this pathway also has been examined in the signaling pathway that stimulates melanin synthesis.

Features of p53 protein distribution in the corneal epithelium and corneal tear film.

Tumor suppressor protein p53 is the key factor in the regulation of cell proliferation. Its concentration is low in the cytoplasm of most cell types. However, in corneal epithelium cells, abnormally high p53 content is detected. The aim of the present study was to characterize p53 distribution in the corneal epithelium. For this purpose, immunohistochemistry, western blot analysis and electronic microscope examinations were performed. A low level of p53 was identified in the lens, iris and retina; by contrast, a significantly high concentration of this protein was observed in the corneal epithelium. In opposite, MDM2 was identified in the lens, iris and retina while it is completely absent in the corneal epithelium. In addition, we found a significant amount of exosomes and other microvesicles containing p53 in the corneal mucin layer. We thus hypothesize that a significantly high level of p53 was caused by a combination of absents of MDM2 in parallel with p53 microvesicles storage.

Near-infrared transillumination imaging combined with aperture photometry for the quantification of melanin in the iris pigment epithelium.

Near-infrared transillumination is used in the diagnosis and the management of different eye diseases. In particular, it enables the visualization of melanin in the pigment epithelium of the iris. This technique is valuable in such conditions as pigment dispersion syndrome and Adie's tonic pupil. Thus, objective quantification of the amount of melanin shedded from the iris pigment epithelium may help in the management of these conditions. By combining aperture photometry with near-infrared iris transillumination this can be achieved. A total of 4 patients (7 eyes) were examined. Three patients were diagnosed with pigment dispersion syndrome in both eyes. One patient had Adie's tonic pupil in one eye. Near-infrared iris transillumination was performed by using a prototype apparatus. Aperture photometry measurements were carried out through specially developed software. The signal-to-noise ratio of the prototype apparatus was 52 dB (399:1). Each pixel within the near-infrared transillumination image corresponded with an area size of the iris of 85 µm x 83 µm. Measurements were taken from several points of the iris in all patients. The average aperture photometry value of transillumination defects was 1321.53 (ADU) ± 501.08 SD, while the average aperture photometry value of the papillary ruff was 90.83 (ADU) ± 53.4. On average transillumination defects transmit 14.55 times more near-infrared light than the papillary ruff. A prototype apparatus for the capture of near-infrared iris transillumination images and custom software enabling aperture photometry measurements of the obtained images has been developed for the purpose of this study. This study demonstrates a potential application of this technique in the diagnosis and management of patients with such conditions as pigment dispersion syndrome and Adie's tonic pupil.

Mutation spectrum of PAX6 and clinical findings in 95 Chinese patients with aniridia.

Purpose: Aniridia is a rare congenital panocular disease caused by mutations in PAX6. The purposes of this study were to clarify the mutation features of PAX6 in a cohort of Chinese patients with aniridia and to describe their clinical characteristics. Methods: We recruited 95 patients from 65 unrelated families clinically diagnosed with aniridia. All patients underwent ophthalmic examinations. Sanger sequencing and multiplex ligation probe amplification of PAX6 were performed to detect intragenic variants and copy number variations (CNVs). Results: We identified 58 disease-causing mutations in PAX6 in 63 families; the detection rate was 96.9%. The 58 mutations included frameshift indels (27.6%), splice site changes (25.9%), nonsense mutations (20.7%), CNVs (19.0%), missense mutations (3.4%), run-on mutations (1.7%), and a synonymous mutation (1.7%). Clinical examinations revealed that 71 patients had complete or almost complete iris loss, 16 patients showed partial iris loss, and six patients had a full iris but with an abnormal structure. Conclusions: The results confirmed that mutations in PAX6 are the predominant cause of aniridia, and the majority are loss-of-function mutations that usually result in classical aniridia. In contrast, missense mutations, run-on mutations, and small numbers of splicing mutations mostly lead to atypical aniridia and an intrafamilial phenotypic variability of iris hypoplasia.

Circadian Regulation of IOP Rhythm by Dual Pathways of Glucocorticoids and the Sympathetic Nervous System.

Purpose: Elevated IOP can cause the development of glaucoma. The circadian rhythm of IOP depends on the dynamics of the aqueous humor and is synchronized with the circadian rhythm pacemaker, that is, the suprachiasmatic nucleus. The suprachiasmatic nucleus resets peripheral clocks via sympathetic nerves or adrenal glucocorticoids. However, the detailed mechanisms underlying IOP rhythmicity remain unclear. The purpose of this study was to verify this regulatory pathway. Methods: Adrenalectomy and/or superior cervical ganglionectomy were performed in C57BL/6J mice. Their IOP rhythms were measured under light/dark cycle and constant dark conditions. Ocular administration of corticosterone or norepinephrine was also performed. Localization of adrenergic receptors, glucocorticoid receptors, and clock proteins Bmal1 and Per1 were analyzed using immunohistochemistry. Period2::luciferase rhythms in the cultured iris/ciliary bodies of adrenalectomized and/or superior cervical ganglionectomized mice were monitored to evaluate the effect of the procedures on the local clock. The IOP rhythm of retina and ciliary epithelium-specific Bmal1 knockout mice were measured to determine the significance of the local clock. Results: Adrenalectomy and superior cervical ganglionectomy disrupted IOP rhythms and the circadian clock in the iris/ciliary body cultures. Instillation of corticosterone and norepinephrine restored the IOP rhythm. ß2-Adrenergic receptors, glucocorticoid receptors, and clock proteins were strongly expressed within the nonpigmented epithelia of the ciliary body. However, tissue-specific Bmal1 knock-out mice maintained their IOP rhythm. Conclusions: These findings suggest direct driving of the IOP rhythm by the suprachiasmatic nucleus, via the dual corticosterone and norepinephrine pathway, but not the ciliary clock, which may be useful for chronotherapy of glaucoma.

Local synthesis of hepcidin in the anterior segment of the eye: A novel observation with physiological and pathological implications.

PURPOSE: The avascular cornea, trabecular meshwork (TM), and lens obtain iron, an essential biometal, from the aqueous humor (AH). The mechanism by which this exchange is regulated, however, is unclear. Recently we reported that non-pigmented ciliary epithelial cells express ferroportin (Fpn) (Ashok, 2018b), an iron export protein modulated by hepcidin, the master regulator of iron homeostasis secreted mainly by the liver. Here, we explored whether ciliary epithelial and other cells in the anterior segment synthesize hepcidin, suggesting local regulation of iron exchange at this site. METHODS: Human and bovine eyes were dissected to isolate the ciliary body (CB), corneal endothelial (CE), TM, lens epithelial (LE), and outer epithelial cell layer of the iris. Total mRNA and protein lysates were processed to evaluate the synthesis and expression of hepcidin, the iron regulatory peptide hormone, Fpn, the only known iron export protein, ceruloplasmin (Cp), a ferroxidase necessary for iron export, transferrin receptor (TfR), a major iron uptake protein, and ferritin, a major iron storage protein. A combination of techniques including reverse transcription polymerase chain reaction (RT-PCR) of total mRNA, Western blotting of protein lysates, and immunofluorescence of fixed tissue sections were used to accomplish these goals. RESULTS: RT-PCR of isolated tissue samples revealed hepcidin-specific mRNA in the CB, TM, CE, and LE of the bovine eye. Western blotting of protein lysates from these tissues showed reactivity for hepcidin, Fpn, ferritin, and TfR. Western blotting and immunohistochemistry of similar tissues isolated from cadaveric human eyes showed expression of hepcidin, Fpn, and Cp in these samples. Notably, Fpn and Cp were expressed on the basolateral membrane of non-pigmented ciliary epithelial cells, facing the AH. CONCLUSIONS: Synthesis and expression of hepcidin and Fpn in the ciliary epithelium suggests local regulation of iron transport from choroidal plexus in the ciliary body to the AH across the blood-aqueous barrier. Expression of hepcidin and Fpn in CE, TM, and LE cells indicates additional regulation of iron exchange between the AH and cornea, TM, and lens, suggesting autonomous regulation of iron homeostasis in the anterior segment. Physiological and pathological implications of these observations are discussed.

Correlation of iris collagen and in-vivo anterior segment structures in patients in different stages of chronic primary angle-closure in both eyes.

Purpose: To compare the density of iris collagen and anterior segment parameters in eyes with chronic primary angle closure glaucoma (CPACG) and their fellow eyes with confirmed or suspected primary angle closure (PAC/PACS). Methods: Nineteen patients with CPACG in one eye and PAC/PACS in the fellow eye requiring trabeculectomy in the CPACG eye and iridectomy in the fellow eye were recruited. Anterior segment optical coherence tomography (AS-OCT) measurements were conducted under light and dark conditions. Iris specimens, obtained by iridectomy/trabeculectomy, were analyzed by sirius red polarization for quantifying type I/III collagen density. AS-OCT parameters and type I/III collagen densities were compared between the two eyes. Results: The iris curvatures were flatter in CPACG eyes in light and dark conditions (P < 0.05). The iris areas in light condition and iris thicknesses in dark condition were smaller in CPACG eyes (P < 0.05). The density of collagen type I in CPACG eyes was lower (P = 0.048). The light-to-dark changes in CPACG eyes and PAC/PACS eyes, respectively, were -0.679 ± 0.701 and -1.627 ± 0.802 mm for pupil diameters, and 0.069 ± 0.113 and 0.258 ± 0.157 mm2 for iris areas, which differed significantly (P < 0.001). With the decrease of type I collagen, anterior chamber width increased and iris areas decreased in dark condition. Conclusion: Dynamic changes in pupil diameter and iris areas differed significantly between CPACG eyes and their fellow PAC/PACS eyes. Decreased type I collagen density in iris tissue was associated with decreased iris area and increased anterior chamber width, which may contribute to disease progression.