Endothelial Tyrosine Kinase Tie1 Is Required for Normal Schlemm's Canal Development-Brief Report.

BACKGROUND: Schlemm's canal (SC) is a large vessel residing in the iridocorneal angle and is required to regulate aqueous humor outflow. Normal SC structure and function is indispensable for maintaining normal intraocular pressure, and elevated intraocular pressure is a risk factor for development of glaucoma. Recent reports have identified a key role of the angiopoietin-Tie2 pathway for SC development and function; however, the role of the orphan receptor Tie1 has not been clarified. METHODS: We used Tie1 knock out mice to study the function of Tie1 in SC development and function. Real-time quantitative polymerase chain reaction and Western blot analyses were used to verify Tie1 deletion. High-resolution microscopy of mouse SC whole mount and cross sections were used to study SC morphology. Measurement of intraocular pressure in live mice was used to study the impact of Tie1 on SC function. RESULTS: Tie1 is highly expressed in both human and mouse SC. Tie1 knock out mice display hypomorphic SC and elevated intraocular pressure as a result of attenuated SC development. CONCLUSIONS: Tie1 is indispensable for SC development and function, supporting it as a novel target for future SC-targeted glaucoma therapies and a candidate gene for glaucoma in humans.

Reduced expression of Pax6 in lens and cornea of mutant mice leads to failure of chamber angle development and juvenile glaucoma.

Heterozygous mutations in PAX6 are causative for aniridia, a condition that is frequently associated with juvenile glaucoma. Defects in morphogenesis of the iridocorneal angle, such as lack of trabecular meshwork differentiation, absence of Schlemm's canal and blockage of the angle by iris tissue, have been described as likely causes for glaucoma, and comparable defects have been observed in heterozygous Pax6-deficient mice. Here, we employed Cre/loxP-mediated inactivation of a single Pax6 allele in either the lens/cornea or the distal optic cup to dissect in which tissues both alleles of Pax6 need to be expressed to control the development of the tissues in the iridocorneal angle. Somatic inactivation of one allele of Pax6 exclusively from epithelial cells of lens and cornea resulted in the disruption of trabecular meshwork and Schlemm's canal development as well as in an adhesion between iris periphery and cornea in juvenile eyes, which resulted in the complete closure of the iridocorneal angle in the adult eye. Structural changes in the iridocorneal angle presumably caused a continuous increase in intraocular pressure leading to degenerative changes in optic nerve axons and to glaucoma. In contrast, the inactivation of a single Pax6 allele in the distal optic cup did not cause obvious changes in iridocorneal angle formation. We conclude that the defects in iridocorneal angle formation are caused by non-autonomous mechanisms due to Pax6 haploinsufficiency in lens or corneal epithelial cells. Pax6 probably controls the expression of signaling molecules in lens cells that regulate the morphogenetic processes during iridocorneal angle formation.

[Morpho-functional interactions of the iris peripheral nervous fibers with the neurons developing in the rat anterior eye chamber].

The intraocular grafts of the septal or hippocampal embryonic tissues developing in the rat anterior eye chamber for three to four months were investigated by electron microscopy. The aim of this study was both the ultrastructural identification of the peripheral nervous fibers entering the grafts from host iris and the estimation of their capacity to establish true synaptic contacts with the central nervous system neurons of the grafts. The bundles of myelinated and unmyelinated axons, surrounded by the Schwann cell cytoplasm, were observed within the perivascular spaces of the ingrowing blood vessels. In the neuropil areas of the grafts, both types of the peripheral nervous fibers were also identified. It was demonstrated on the ultrastructural level that the unmyelinated axons lost their glial envelope of the Schwann cell and formed the typical asymmetric synapses with the dendrites and dendritic spines of the grafted neurons. The results are indicative of the high morpho-functional plasticity of both parts of the nervous system.

Two models of experimental myopia in the mouse.

PURPOSE: The purpose of this study was to test the response of the mouse eye to two methods for the induction of experimental myopia. METHODS: Growth patterns of eyes were determined by axial length measurements from birth to adult in eyes of both sexes of normal mice examined on post-natal day 1 to 6 months and at 1 year. For the induction of experimental myopia, Balb/cJ mice were prepared with either unilateral lid suture or by a -10D spectacle lens placed over one eye at post-natal day 10. Other mice received a plano lens as a control for lens wear. Refraction was carried out at post-natal days of 28, 42 and 56 in lid suture and spectacle lens wear group by streak retinoscopy. Axial length was measured by a combination of video image photography, digital caliper, or Optical Low Coherence Interferometry (OLCI). Corroborative optical modeling of the mouse eye was carried out using ZEMAX ray tracing software. RESULTS: Axial length (AL) increased linearly between post-natal day 1 to day 56, plateauing at about 140 days. After 18 days of unilateral lid suture initiated 10 days after birth, the AL of experimental eyes was 3.032+/-0.003 mm, while AL in contra-lateral control eyes was 2.981+/-0.005 mm (mean+/-sem, p<0.05, n=40), after 32 days, the AL of experimental eyes was 3.290+/-0.004 mm, and the AL of control eyes was 3.104+/-0.002 mm (p<0.001, n=60). After 46 days of lid closure AL of experimental eyes was 3.592+/-0.003 mm, while AL of control eyes was 3.363+/-0.003 mm (p<0.001, n=80). Spectacle lens wear of 46 days duration increased AL in experimental eyes to 3.721+/-0.002 mm, while AL in control eyes was 3.354+/-0.003 mm (p<0.001, n=100). Refraction and ray tracing analysis substantiated the dimensional changes to be consistent with increased AL. CONCLUSIONS: Two procedures to induce experimental myopia, initiated at eye opening, produced significant myopic shifts corresponding to increases in axial lengths after 32 and 46 days of lid suture and after 46 days wearing a -10D spectacle lens.

Patching fellow eyes during subjective night does not prevent disruption to minus lens compensation in constant light-reared chicks.

PURPOSE: This study re-examined an earlier claim that monocular patching during subjective night (i.e. patched at the usual time that night would occur) in the chicks reared in continuous lighting (CL), offered unpatched eyes some protection from the ocular effects of CL. It also examined whether this monocular patching protected unpatched eyes against the disruptive effect of CL on compensation to minus lenses. METHODS: Hatchling White-Leghorn chicks were reared in either constant or diurnal lighting conditions (n=28) for 2 weeks. Some CL chicks had their right eyes patched every night during the entire study. Lenses of either +10 or -10D power were fitted to the unpatched eyes of some patched chicks at the beginning of the second week. Retinoscopy, IR photo-keratometry and high-frequency A-scan ultrasonography were used to track refractions, corneal radius of curvature and ocular axial dimensions respectively; data were collected on experimental days 0, 7, 9 and 14. RESULTS: The patched eyes were completely protected from the ocular growth effects of CL, i.e. accelerated posterior segment (vitreous chamber) growth and inhibited anterior segment growth. Although the unpatched eyes showed no protection from the anterior chamber effects of CL, they were completely protected from the effects of CL on vitreous chamber growth. Nonetheless, the response to the -10D lenses was disrupted in unpatched eyes, which responded in the wrong direction for compensation (+5.5+/-0.25D more hyperopic than no lens-unpatched eyes). The response to the +10D lenses was preserved (+9.25+/-0.25D more hyperopic than no lens-unpatched eyes). CONCLUSION: These data provide further support for local control of emmetropization, as reflected in compensatory lens responses, but point to additional influences on eye growth as reflected in CL-induced ocular changes.

Effect of peripheral retinal ablation with cryotherapy versus diode laser photocoagulation on axial length in the growing rabbit eye.

AIMS: To evaluate and compare the effects of peripheral retinal cryotherapy and diode laser photocoagulation on axial length, anterior chamber depth, and lens thickness in developing rabbit eyes. METHODS: 26 eyes of 6 week old Abbit rabbits were randomly assigned to undergo laser photocoagulation or cryotherapy of the peripheral retina. Eight eyes of four untreated rabbits served as controls. Biometric and intraocular pressure measurements were performed at 0, 5, and 10 weeks after treatment. RESULTS: Five rabbits died, leaving 10 rabbits (20 eyes) in the study group and two (four eyes) in the control group. Average axial lengths for the control, laser treated, and cryo treated eyes were 15.72 mm, 16.08 mm, and 16.11 mm, respectively, at baseline and 17.48 mm, 18.09 mm, and 19.4 mm, respectively, at 10 weeks after treatment (p = 0.028, paired Wilcoxon test). Anterior chamber depth increased from 2.2 mm to 2.5 mm in both treatment groups, and from 2.14 mm to 2.28 mm in the control group. Lens thickness averaged 5.11 mm in the control group and 5.38 mm in the treatment groups before treatment, and 6.34 mm, 6.31 mm, and 6.38 mm, respectively, 10 weeks after treatment. CONCLUSIONS: Peripheral retinal cryotherapy causes a significantly greater elongation of the eye compared to diode laser photocoagulation in a rabbit model.

Comparison of ocular component growth curves among refractive error groups in children.

PURPOSE: To compare ocular component growth curves among four refractive error groups in children. methods Cycloplegic refractive error was categorized into four groups: persistent emmetropia between -0.25 and +1.00 D (exclusive) in both the vertical and horizontal meridians on all study visits (n = 194); myopia of at least -0.75 D in both meridians on at least one visit (n = 247); persistent hyperopia of at least +1.00 D in both meridians on all visits (n = 43); and emmetropizing hyperopia of at least +1.00 D in both meridians on at least the first but not at all visits (n = 253). Subjects were seen for three visits or more between the ages of 6 and 14 years. Growth curves were modeled for the persistent emmetropes to describe the relation between age and the ocular components and were applied to the other three refractive error groups to determine significant differences. results At baseline, eyes of myopes and persistent emmetropes differed in vitreous chamber depth, anterior chamber depth, axial length, and corneal power and produced growth curves that showed differences in the same ocular components. Persistent hyperopes were significantly different from persistent emmetropes in most components at baseline, whereas growth curve shapes were not significantly different, with the exception of anterior chamber depth (slower growth in persistent hyperopes compared with emmetropes) and axial length (lesser annual growth per year in persistent hyperopes compared with emmetropes). The growth curve shape for corneal power was different between the emmetropizing hyperopes and persistent emmetropes (increasing corneal power compared with decreasing power in emmetropes). conclusions Comparisons of growth curves between persistent emmetropes and three other refractive error groups showed that there are many similarities in the growth patterns for both the emmetropizing and persistent hyperopes, whereas the differences in growth lie mainly between the emmetropes and myopes.

Eye growth changes in myopic children in Singapore.

AIMS: To assess the longitudinal changes in biometric parameters and associated factors in young myopic children aged 7--9 years followed prospectively in Singapore. METHODS: Children aged 7--9 years from three Singapore schools were invited to participate in the SCORM (Singapore Cohort study Of the Risk factors for Myopia) study. Yearly eye examinations involving biometry measures were performed in the schools. Only myopic children (n=543) with 3 year follow up data were included in this analysis. RESULTS: The 3 year increases in axial length, anterior chamber depth, lens thickness, vitreous chamber depth, and corneal curvature were 0.89 mm, -0.02 mm, -0.01 mm, 0.92 mm, and 0.01 mm, respectively. Children who were younger, female, and who had a parental history of myopia were more likely to have greater increases in axial length. After adjustment for school, age, sex, race, parental myopia and reading in books per week, the age (p<0.001), sex (p=0.012), and parental myopia (p=0.027) remained significantly associated with the 3 year change in axial length. Reading in books per week, however, was not associated with axial length change. Children with faster rates of progression of myopia had greater increases in axial length (Pearson correlation coefficient (r)=-0.69) and vitreous chamber depth (r=-0.83). CONCLUSIONS: The 3 year change in axial length of Singapore children aged 7--9 years at baseline was high and greater in younger children, females, and children with a parental history of myopia. Myopia progression was driven largely by vitreous chamber depth increase.

In vivo assessment of postnatal murine ocular development by ultrasound biomicroscopy.

PURPOSE: Ultrasound biomicroscopy (UBM) can noninvasively provide anatomical information about mouse ocular structures. We present the quantitation of postnatal murine eye development using UBM. MATERIALS AND METHODS: The eyes from CD-1 mice were examined at 1, 2, 4, 6, and 8 weeks of postnatal development using 40 MHz UBM. Patterns of ocular tissue growth including the lens, globe, and anterior chamber were calculated. RESULTS: Postnatal CD-1 lens and globe volumes are consistent with an exponential decay of growth during the first 8 postnatal weeks. Anterior chamber depth increases most sharply in the first 2 postnatal weeks but continues to increase up to the 8th postnatal week. Anterior segment angle was observed to increase from 1 to 4 weeks. CONCLUSIONS: UBM can be used to obtain in vivo quantitative measurements of postnatal murine ocular structures. Our ability to obtain ocular anatomical information will facilitate future assessments of mouse models of human disease.

Molecular description of eye defects in the zebrafish Pax6b mutant, sunrise, reveals a Pax6b-dependent genetic network in the developing anterior chamber.

The cornea is a central component of the camera eye of vertebrates and even slight corneal disturbances severely affect vision. The transcription factor PAX6 is required for normal eye development, namely the proper separation of the lens from the developing cornea and the formation of the iris and anterior chamber. Human PAX6 mutations are associated with severe ocular disorders such as aniridia, Peters anomaly and chronic limbal stem cell insufficiency. To develop the zebrafish as a model for corneal disease, we first performed transcriptome and in situ expression analysis to identify marker genes to characterise the cornea in normal and pathological conditions. We show that, at 7 days post fertilisation (dpf), the zebrafish cornea expresses the majority of marker genes (67/84 tested genes) found also expressed in the cornea of juvenile and adult stages. We also characterised homozygous pax6b mutants. Mutant embryos have a thick cornea, iris hypoplasia, a shallow anterior chamber and a small lens. Ultrastructure analysis revealed a disrupted corneal endothelium. pax6b mutants show loss of corneal epithelial gene expression including regulatory genes (sox3, tfap2a, foxc1a and pitx2). In contrast, several genes (pitx2, ctnnb2, dcn and fabp7a) were ectopically expressed in the malformed corneal endothelium. Lack of pax6b function leads to severe disturbance of the corneal gene regulatory programme.

The mouse anterior chamber angle and trabecular meshwork develop without cell death.

BACKGROUND: The iridocorneal angle forms in the mammalian eye from undifferentiated mesenchyme between the root of the iris and cornea. A major component is the trabecular meshwork, consisting of extracellular matrix organized into a network of beams, covered in trabecular endothelial cells. Between the beams, channels lead to Schlemm's canal for the drainage of aqueous humor from the eye into the blood stream. Abnormal development of the iridocorneal angle that interferes with ocular fluid drainage can lead to glaucoma in humans. Little is known about the precise mechanisms underlying angle development. There are two main hypotheses. The first proposes that morphogenesis involves mainly cell differentiation, matrix deposition and assembly of the originally continuous mesenchymal mass into beams, channels and Schlemm's canal. The second, based primarily on rat studies, proposes that cell death and macrophages play an important role in forming channels and beams. Mice provide a potentially useful model to understand the origin and development of angle structures and how defective development leads to glaucoma. Few studies have assessed the normal structure and development of the mouse angle. We used light and electron microscopy and a cell death assay to define the sequence of events underlying formation of the angle structures in mice. RESULTS: The mouse angle structures and developmental sequence are similar to those in humans. Cell death was not detectable during the period of trabecular channel and beam formation. CONCLUSIONS: These results support morphogenic mechanisms involving organization of cellular and extracellular matrix components without cell death or atrophy.

Different visual deprivations produce different ametropias and different eye shapes.

To compare the effects on the postnatal development of the eye of both total and partial form deprivation in diurnally reared chicks and of dark-rearing, chicks were reared with occluders covering one eye from hatching for up to 6 weeks. In diurnally reared birds, both total and partial form deprivation resulted in severe axial myopia and increased eye size. These effects were greatest for the eyes of chicks raised with total form deprivation; they had highly curved corneas and very deep anterior and vitreous chambers. In addition, the amount of myopia produced in eyes with total form deprivation was the same at 2 and 6 weeks, whereas eyes with partial form deprivation showed substantial remission even with the occluders left on. The partially deprived eyes developed a striking shape asymmetry: the posterior globe only became enlarged in the deprived region of the retina. The eyes of dark-reared chicks, regardless of whether or not an occluder was worn, also were enlarged but were hyperopic owing to a severe flattening of the cornea. This hyperopia was slow to develop compared to the myopia produced in the diurnally reared visually restricted eyes. Finally, the shape of the posterior globe of these hyperopic eyes was no different from that of normal eyes.

Refractive compensation to optical defocus depends on the temporal profile of luminance modulation of the environment.

The refractive state of hatchling chicks rapidly compensates to applied optical defocus through alteration in eye growth. The mechanism is capable of sensing whether the plane of focus lies in front of or behind the photoreceptors, however, its nature and site of action within the retina are unknown. We attempted to create an imbalance in the adaptation of the retinal ON and OFF mechanisms previously implicated in refractive control through pharmacological interventions, by rearing chicks from 4 to 9 days of age with a monocular +10 D, 0 D or -10 D lens, in an environment illuminated by a moving or stationary plaid of luminance gradients. When the plaid moved in one direction a local Fast-ON sawtooth luminance modulation was produced, while plaid motion in the other direction resulted in a Fast-OFF sawtooth modulation. Significantly reduced refractive compensation accompanied +10 D lens/Fast-OFF and -10 D lens/Fast-ON rearing, but not for the other conditions. Thus the refractive compensation mechanism depends on the nature of the temporal contrast of the environment, suggesting a relationship between the sign of defocus and the state of adaptation of the retinal ON and OFF subsystems.

A longitudinal study of the biometric and refractive changes in full-term infants during the first year of life.

Changes in ocular axial dimensions and refraction were followed longitudinally, using ultrasonography and retinoscopy, during the first year of life (mean ages 4-53 weeks) of a group of 20 full-term infants (10 male, 10 female). Using a mixed-model regression analysis, axial length changes as a function of time were found to be best described by a quadratic expression (AL=17.190+0.128x-0.0013x(2), where AL is the axial length in mm and x is the age in weeks), while anterior chamber depth changed linearly (ACD=2.619+0.018x, where ACD is the anterior chamber depth in mm): lens thickness was essentially constant. Spherical equivalent refraction through most of the first year showed a steady reduction in hypermetropia (SER=2.982-0.032x, where SER is the spherical equivalent refraction in dioptres): astigmatism also tended to diminish. Mean hyperopic refractive errors through the year were negatively correlated with corresponding axial lengths (SER=12.583-0.541AL), but some individual subjects showed marked departures from this pattern. These results are discussed in relation to concepts of emmetropization.

[Ultrastructure of nervous tissue developing in the anterior chamber of the eye. 1. Perikaryons and dendrites]. / Ul'trastruktura nervnoi tkani, razvivaiushcheisia v perednei kamere glaza. 1. Perikariony i dendrity.

Embryonic tissues of septum and hippocampus were transplanted into the anterior eye chamber (AEC) of adult rats. The morphology of initial embryonic tissues and of transplants within 3 to 4 months of cultivation in AEC was studied. The transplanted tissue consists of neuroblasts and immature neurones: no synaptic contacts are observed. Within 3 to 4 months, highly differentiated neurones establishing synaptic contacts can be seen in the transplants. At the same time the fine structure of perikaryons and dendrites undergoes some changes: increased vacuolization, transformation of ergastoplasm into lamellar bodies. These can be due to an elevated functional activity of some neurones. Another group of morphological abnormalities (increased number of dendrite processes and microphyllopodia, somatic spines, dendrite cones of growth, tight junctions between perikaryons) suggests incomplete tissue maturation. These might be due to the absence of normal afferent and trophic influences in AEC.

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.

The effect of simultaneous negative and positive defocus on eye growth and development of refractive state in marmosets.

PURPOSE: We evaluated the effect of imposing negative and positive defocus simultaneously on the eye growth and refractive state of the common marmoset, a New World primate that compensates for either negative and positive defocus when they are imposed individually. METHODS: Ten marmosets were reared with multizone contact lenses of alternating powers (-5 diopters [D]/+5 D), 50:50 ratio for average pupil of 2.80 mm over the right eye (experimental) and plano over the fellow eye (control) from 10 to 12 weeks. The effects on refraction (mean spherical equivalent [MSE]) and vitreous chamber depth (VC) were measured and compared to untreated, and -5 D and +5 D single vision contact lens-reared marmosets. RESULTS: Over the course of the treatment, pupil diameters ranged from 2.26 to 2.76 mm, leading to 1.5 times greater exposure to negative than positive power zones. Despite this, at different intervals during treatment, treated eyes were on average relatively more hyperopic and smaller than controls (experimental-control [exp-con] mean MSE ± SE +1.44 ± 0.45 D, mean VC ± SE -0.05 ± 0.02 mm) and the effects were similar to those in marmosets raised on +5 D single vision contact lenses (exp-con mean MSE ± SE +1.62 ± 0.44 D. mean VC ± SE -0.06 ± 0.03 mm). Six weeks into treatment, the interocular growth rates in multizone animals were already lower than in -5 D-treated animals (multizone -1.0 ± 0.1 µm/day, -5 D +2.1 ± 0.9 µm/day) and did not change significantly throughout treatment. CONCLUSIONS: Imposing hyperopic and myopic defocus simultaneously using concentric contact lenses resulted in relatively smaller and less myopic eyes, despite treated eyes being exposed to a greater percentage of negative defocus. Exposing the retina to combined dioptric powers with multifocal lenses that include positive defocus might be an effective treatment to control myopia development or progression.

Ocular component growth curves among Singaporean children with different refractive error status.

PURPOSE: To describe and compare ocular component growth curves among different refractive error groups in Singaporean children. METHODS: Data collected yearly in 1775 Asian children aged 6 to 10 years with at least three visits were analyzed. Cycloplegic refractive error and biometry variables were measured by autorefractor and A-scan ultrasound machine. Growth curves were compared between five groups: persistent hyperopia of spherical equivalent (SE) > +1.00 D, emmetropizing hyperopia of SE > +1.00 D on the first visit and between -0.50 D and +1.00 D subsequently, persistent emmetropia of SE between -0.50 D and +1.00 D, incident myopia of SE

Morphofunctional interactions of peripheral nerve fibers of the iris with neurons developing in the anterior chamber of the eye in rats.

Electron microscopic studies were performed on intraocular transplants of embryonic septal and hippocampal tissue developing in the anterior chamber of the eye in rats for 3-4 months. The aim of the study was to seek ultrastructural identification of peripheral nerve fibers entering transplants from the iris, and to assess their ability to establish true synaptic contacts with transplanted CNS neurons. Bundles of myelinated and unmyelinated axons surrounded by Schwann cell cytoplasm were seen within the perivascular spaces of ingrowing blood vessels. Both types of peripheral fiber were also identified in the neuropil areas of transplants. At the ultrastructural level, unmyelinated axons were found to be free of glial Schwann cell sheaths and to form typical asymmetrical synapses with the dendrites and dendritic spines of transplant neurons. These results provide evidence of the high morphofunctional plasticity of both parts (central, peripheral) of the nervous system.