Age-related increase of let-7 family microRNA in rat retina and vitreous.

Vitreous alterations occur from early stages and continue through the normal aging, with gradual lamellae formation and the appearance of liquefied spaces, which eventually leads to complications, such as retinal tear, retinal detachment, and intravitreal hemorrhage. The aim of the present study was to investigate the expression of let-7 miRNA family in the vitreous and retina in newborn (1-3- day-old), young adult (2-month-old), and aging (12-month-old) rats, as well as their role as regulators of vitreous components. MicroRNAs are small, non-coding RNAs that post-transcriptionally regulate gene expression. Our results showed detection of all investigated let-7 isoforms (let-7a, let-7b, let-7c, let-7d, let-7e, let-7f and let-7i) in the retina and vitreous. Although most let-7 members were significantly upregulated in the vitreous during development, only let-7b, let-7c, and let-7e followed this same expression pattern in the retina. Let-7b and -7c increased in aging vitreous as well, and were expressed in vitro by Müller glial cells and their extracellular vesicles. Moreover, let-7 targeted hyaluronan synthase 2 (Has2) mRNA, a synthesizing enzyme of hyaluronan. These observations indicate that let-7 function is important during retina and vitreous development, and that isoforms of let-7 increased with aging, potentially modulating hyaluronan content.

7.1 T MRI and T2 mapping of the human and porcine vitreous body post mortem.

Numerous literature reports describe the liquefaction of the vitreous body with increasing age. It must be expected that this process also influences drug distribution and elimination following intravitreal application of active pharmaceutical ingredients (APIs). To better understand the impact and extent of the liquefaction a magnetic resonance imaging (MRI) study was performed examining human donor eyes post mortem. For comparison, eyes of juvenile pigs were also examined representing a fully gelled vitreous. 7.1Tesla ultra-high field MRI and T2 mapping of the vitreous body were used in this study since it must be expected that age-induced degradation processes and structural changes of the vitreous gel to a liquid state will result in changes of the T2 relaxation time of water proton spins. The vitreous bodies were imaged in 12 axial slices and within each image the T2 relaxation times of water proton spins were determined. It was found that T2 relaxation time increased with increasing age of the donor. Whilst the mean T2 relaxation time (±standard deviation) of water proton spins within the central vitreous body of a juvenile porcine eye was 210.1 ±â€¯31.1 ms, the mean T2 relaxation time within the central vitreous body of the 88-year-old and therefore oldest human donor was 528.0 ±â€¯79.3 ms. Within the vitreous body of a single donor, the T2 relaxation time increased from the anterior to the posterior segment, for example in the vitreous body of the oldest human donor from 388.0 ±â€¯31.1 ms on average in the anterior to 631.7 ±â€¯42.8 ms in the posterior segment, indicating an increase in intravitreal liquefaction respectively inhomogeneity from anterior to posterior regions. Additionally, physicochemical parameters were determined yielding averages of 7.54 ±â€¯0.34 for pH, 1.33629 ±â€¯0.00044 for refractive index, 368.99 ±â€¯26.87 mosmol/kg for osmolality, 97.56 ±â€¯0.43% for drying mass loss and 0.73 ±â€¯0.18 mg/mL for total protein content. The aging process and the liquefaction of the vitreous body are expected to affect the pharmacokinetic profile of intravitreally injected APIs, which is of high relevance to drug release from intravitreal drug delivery systems and the therapeutic concept in the treatment of posterior segment diseases. Our data indicate that such processes are not reflected in animal models. Since there is still a need for valid pharmacokinetic data, invitro test systems for the characterization of intraocular drug delivery systems have to be improved according to the current state of knowledge about the vitreous structure and intravitreal transport phenomena.

Lag of accommodation does not predict changes in eye growth in chickens.

Emmetropization is controlled by the defocus in the retinal image. It is a classical problem how changes in focus, introduced by accommodation, are taken into account. We have quantified accommodation errors in chickens wearing negative lenses to find out whether they can predict subsequent eye growth. Two groups of chicks, aged 10 to 13 days, wore lenses (-7D) monocularly for 4-7 days. Fellow eyes remained untreated. Vitreous chamber depth (VCD) was measured in alert hand-held chickens with high resolution, using the Lenstar LS 900 (Haag-Streit, Koeniz, Switzerland). Non-cycloplegic refractive state was measured by automated infrared photoretinoscopy with and without the lenses in place. In group 1 (n = 6), measurements were done 5 times a day to obtain detailed VCD growth curves. In group 2 (n = 10), measurements were only taken twice, at 9 am and 4 pm, to reduce the risk of recovery from induced myopia due to the frequent removal of the lenses. As expected from the negative power of the lenses, refractions measured through the lenses were more hyperopic although not as much as predicted by the lens powers, indicating that chickens partially refocused their eyes by accommodation. Among different animals, accommodation errors varied from 1.1 ±â€¯0.9 to 3.6 ±â€¯1.1D (group 1, mean ±â€¯1 standard deviation) and 0.22 ±â€¯1.25 to 1.72 ±â€¯1.23D (group 2). No correlations were found between the magnitude of the accommodation errors in individual animals and subsequent changes in VCD. With negative lenses, VCD grew both during day and night while fellow eyes grew only during the day but shrank during the night. In conclusion, accommodation errors did not predict future eye growth. This raises the question as to why brief periods of clear vision, when lenses are taken off, have a strong inhibitory effect on myopia development while periods of clear vision due to accommodation have apparently no effect. A possible explanation is that, in addition to retina-driven control of eye growth, there is a second neural pathway for the control of eye growth that carries the signal of accommodation - although it is striking that no neuronal and structural correlate has been identified to date.

Differential Expression of Vitreous Proteins in Young and Mature New Zealand White Rabbits.

Different anatomical regions have been defined in the vitreous humor including central vitreous, basal vitreous, vitreous cortex, vitreoretinal interface and zonule. In this study we sought to characterize changes in the proteome of vitreous humor (VH) related to compartments or age in New Zealand white rabbits (NZW). Vitreous humor was cryo-collected from young and mature New Zealand white rabbit eyes, and dissected into anterior and posterior compartments. All samples were divided into 4 groups: Young Anterior (YA), Young Posterior (YP), Mature Anterior (MA) and Mature Posterior (MP) vitreous. Tryptic digests of total proteins were analyzed by liquid chromatography followed by tandem mass spectrometry. Spectral count was used to determine the relative protein abundances and identify proteins with statistical differences between compartment and age groups. Western blotting was performed to validate some of the differentially expressed proteins. Our results showed that 231, 375, 273 and 353 proteins were identified in the YA, YP, MA and MP respectively. Fifteen proteins were significantly differentially expressed between YA and YP, and 11 between MA and MP. Carbonic anhydrase III, lambda crystallin, alpha crystallin A and B, beta crystallin B1 and B2 were more abundant in the anterior region, whereas vimentin was less abundant in the anterior region. For comparisons between age groups, 4 proteins were differentially expressed in both YA relative to MA and YP relative to MP. Western blotting confirmed the differential expression of carbonic anhydrase III, alpha crystallin B and beta crystallin B2. The protein profiles of the vitreous humor showed age- and compartment-related differences. This differential protein profile provides a baseline for understanding the vitreous compartmentalization in the rabbit and suggests that further studies profiling proteins in different compartments of the vitreous in other species may be warranted.

Creep compliance rheology with a probe-like cylindrical geometry.

BACKGROUND: Rheology experiments have been performed on the vitreous humor, a soft gel that rests inside of the eye, to study its viscoelastic behavior and underlying macromolecular structure. A significant challenge for experimentalists is preserving the macromolecular structure when removing vitreous from in vivo conditions. OBJECTIVE: We have developed a novel probe-like rheometer geometry that allows us to perform shear rheology experiments on the vitreous humor in situ. The aim of this study is to assess the feasibility of the probe geometry. METHODS: Creep compliance responses of silicone oils, Xanthan gum solutions, and bovine and porcine vitreous humor were measured using the probe geometry and compared to measurements performed with standard geometries. RESULTS: Viscosities calculated from the creep responses of silicone oils closely match between the probe and standard geometry. Viscosities and creep compliance values of Xanthan gum measurements achieve order of magnitude agreement between the probe and standard geometry. Significant differences are detected with the probe between bovine and porcine vitreous (p<0.001). CONCLUSIONS: These results suggest the probe may feasibly measure viscosities of Newtonian fluids, and correctly detect differences in the creep response of complex fluids with varying viscoelastic behaviors.

Isolation and characterization of mammalian cells expressing the Arf promoter during eye development.

Although many researchers have successfully uncovered novel functions of the tumor suppressor p19(Arf) utilizing various types of cultured cancer cells and immortalized fibroblasts, these systems do not accurately reflect the endogenous environment in which Arf is developmentally expressed. We addressed this by isolating perivascular cells (PVCs) from the primary vitreous of the mouse eye. This rare cell type normally expresses the p19(Arf) tumor suppressor in a non-pathological, developmental context. We utilized fluorescence activated cell sorting (FACS) to purify the cells by virtue of a GFP reporter driven by the native Arf promoter and then characterized their morphology and gene expression pattern. We further examined the effects of reintroduction of Arf expression in the Arf(GFP/GFP) PVCs to verify expected downstream effectors of p19(Arf) as well as uncover novel functions of Arf as a regulator of vasculogenesis. This methodology and cell culture model should serve as a useful tool to examine p19(Arf) biology.

Involvement of periostin in regression of hyaloidvascular system during ocular development.

PURPOSE: A timely regression of the hyaloid vascular system (HVS) is required for the normal ocular development. Although macrophages have a critical role in this process, the exact mechanism remains undetermined. Periostin is a matricellular protein involved in tissue and vascular remodeling. The purpose of our study was to determine whether periostin is involved in the HVS regression. METHODS: We used wild type (WT) and periostin knockout (KO) mice. Indocyanine green angiography and immunohistochemistry with isolectin B4 were used to evaluate the HVS regression. TUNEL-labeling was used to quantify the number of apoptotic hyaloid vascular endothelial cells. F4/80 and Iba-1 staining was performed to determine the number and location of macrophages in the vitreous. The location of periostin also was investigated by immunohistochemistry. To determine the functional role of periostin, the degree of adhesion of human monocytes to fibronectin was measured by an adhesion assay. RESULTS: The HVS regression and peak in the number of TUNEL-positive apoptotic endothelial cells were delayed in periostin KO mice. The number of F4/80 positive cells in the vitreous was higher in periostin KO mice. Only a small number of Iba-1-positive cells near the hyaloid vessels was co-stained with periostin, and peripheral blood monocytes were not stained with periostin. Adhesion assay showed that periostin increased the degree of attachment of monocytes to fibronectin. CONCLUSIONS: These results suggest that periostin, which is secreted by the intraocular macrophages, enhances the HVS regression by intensifying the adhesion of macrophages to hyaloid vessels.

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.

Lama1 mutations lead to vitreoretinal blood vessel formation, persistence of fetal vasculature, and epiretinal membrane formation in mice.

BACKGROUND: Valuable insights into the complex process of retinal vascular development can be gained using models with abnormal retinal vasculature. Two such models are the recently described mouse lines with mutations in Lama1, an important component of the retinal internal limiting membrane (ILM). These mutants have a persistence of the fetal vasculature of vitreous (FVV) but lack a primary retinal vascular plexus. The present study provides a detailed analysis of astrocyte and vascular development in these Lama1 mutants. RESULTS: Although astrocytes and blood vessels initially migrate into Lama1 mutant retinas, both traverse the peripapillary ILM into the vitreous by P3. Once in the vitreous, blood vessels anastomose with vessels of the vasa hyaloidea propria, part of the FVV, and eventually re-enter the retina where they dive to form the inner and outer retinal capillary networks. Astrocytes continue proliferating within the vitreous to form a dense mesh that resembles epiretinal membranes associated with persistent fetal vasculature and proliferative vitreoretinopathy. CONCLUSIONS: Lama1 and a fully intact ILM are required for normal retinal vascular development. Mutations in Lama1 allow developing retinal vessels to enter the vitreous where they anastomose with vessels of the hyaloid system which persist and expand. Together, these vessels branch into the retina to form fairly normal inner retinal vascular capillary plexi. The Lama1 mutants described in this report are potential models for studying the human conditions persistent fetal vasculature and proliferative vitreoretinopathy.

Remodelling of the human vitreous and vitreoretinal interface--a dynamic process.

The highly hydrated, almost acellular vitreous body of the human eye consists of only 0.1% macromolecules, of which collagens are the most important for its matrix structure. During embryological development, the human vitreous body is a highly dynamic matrix, in which the primary (vascular) vitreous is gradually replaced by the secondary (avascular) vitreous. With aging, the human vitreous undergoes a slowly progressive remodelling, characterized by the gradual formation of collagenous condensations and liquefied spaces in the gel structure. The former is probably the result of collagen synthesis and the deposition of newly formed collagen into the matrix, while the latter is probably due to collagen breakdown. Therefore, remodelling of the vitreous matrix starts at a very early age and continues into old age, albeit at a slower pace. Older theories and concepts of a strict spatial separation between the primary and secondary vitreous during embryonic development, and morphological changes in the aging vitreous being due to a simple aggregation of collagen fibrils are questioned. This review describes the embryological and postnatal remodelling of the human vitreous matrix and vitreoretinal interface, in addition to the mechanisms and cells that are potentially involved in this process.

A detailed paraxial schematic eye for the White Leghorn chick.

We studied the normal ocular development of the chick (Gallus gallus domesticus, White Leghorn) up to 15 days of age using both longitudinal and cross-sectional methods. The change in refractive error, corneal curvature and axial ocular distances were used to construct schematic eyes. Equations are presented which allow prediction of refractive error changes associated with changes in vitreous chamber depth. The mean refractive error was +3.2 D at hatching, which reduced by 66% over the first 3 days and stabilized by 11 days of age. The lens thickened and the anterior chamber deepened from hatching, but vitreal elongation and corneal flattening were delayed until after the first 3 days, suggesting that normal eye growth may be initially inhibited or inactive during an initial emmetropization period, and subsequently activated in response to myopic defocus arising from the continually expanding lens. Finally, when compared with published data on other chick strains, we find differences in the degree of hyperopia at hatching due to differences in lens thickness. However, the rate of ocular and vitreal expansion and the developmental changes in corneal power are similar, making the schematic eyes presented here generally applicable to different strains of chickens.

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

Imposed anisometropia, accommodation, and regulation of refractive state.

PURPOSE: To determine the effects of imposed anisometropic retinal defocus on accommodation, ocular growth, and refractive state changes in marmosets. METHODS: Marmosets were raised with extended-wear soft contact lenses for an average duration of 10 weeks beginning at an average age of 76 d. Experimental animals wore either a positive or negative power contact lens over one eye and a plano lens or no lens over the other. Another group wore binocular lenses of equal magnitude but opposite sign. Untreated marmosets served as controls and three wore plano lenses monocularly. Cycloplegic refractive state, corneal curvature, and vitreous chamber depth were measured before, during, and after the period of lens wear. To investigate the accommodative response, the effective refractive state was measured through each anisometropic condition at varying accommodative stimuli positions using an infrared refractometer. RESULTS: Eye growth and refractive state are significantly correlated with the sign and power of the contact lens worn. The eyes of marmosets reared with monocular negative power lenses had longer vitreous chambers and were myopic relative to contralateral control eyes (p < 0.01). Monocular positive power lenses produced a significant reduction in vitreous chamber depth and hyperopia relative to the contralateral control eyes (p < 0.05). In marmosets reared binocularly with lenses of opposite sign, we found larger interocular differences in vitreous chamber depths and refractive state (p < 0.001). Accommodation influences the defocus experienced through the lenses, however, the mean effective refractive state was still hyperopia in the negative-lens-treated eyes and myopia in the positive-lens-treated eyes. CONCLUSIONS: Imposed anisometropia effectively alters marmoset eye growth and refractive state to compensate for the imposed defocus. The response to imposed hyperopia is larger and faster than the response to imposed myopia. The pattern of accommodation under imposed anisometropia produces effective refractive states that are consistent with the changes in eye growth and refractive state observed.

Light intensity modulates corneal power and refraction in the chick eye exposed to continuous light.

Continuous exposure of chicks to light was shown to result in severe hyperopia, accompanied by anterior segment changes, such as severe corneal flattening. Since rearing chicks in complete darkness results only in mild hyperopia and minor changes in corneal curvature, we hypothesized that light intensity may play a role in the development of refractive changes under continuous light illumination. To test this hypothesis, we examined the effects of rearing chicks under various continuous light intensities. More specifically, we investigated the refractive parameters of the chicks' eyes, and avoided light cycling effects on ocular development. To this end, thirty-eight chicks were reared under 24-h incandescent illumination, at three different light intensities: 10,000 lux (n=13), 500 lux (n=12), and 50 lux (n=13). Their eyes underwent repeated retinoscopy, keratometry, and ultrasound biometry, as well as caliper measurements of enucleated eyes. Both refraction and corneal refractive power were found to be correlated with light intensity. On day 90 after hatching, exposure to light intensities of 10,000, 500, and 50 lux resulted in hyperopia of +11.97+/-3.7 (mean+/-SD) +7.9+/-4.08 and +0.63+/-3.61 diopters (D), respectively. Under those intensities, corneal refractive power was 46.10+/-3.62, 49.72+/-4.16, and 56.88+/-4.92D, respectively. Axial length did not differ significantly among the groups. The vitreous chamber was significantly deeper in the high than in the low-intensity groups. Thus, during the early life of chicks exposed to continuous lighting, light intensity affects the vitreous chamber depth as well as the anterior segment parameters, most notably the cornea. The higher the intensity, the more severe was the corneal flattening observed and the hyperopia that developed, whereas continuous illumination at low intensities resulted in emmetropia. Thus, light intensity is an important factor that should be taken into account when studying refractive development.

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.

A comparison of refractive development between two subspecies of infant rhesus monkeys (Macaca mulatta).

PURPOSE: Different subspecies of rhesus monkeys (Macaca mulatta) that are derived from different geographical locations, primarily Indian and China, are commonly employed in vision research. Substantial morphological and behavioral differences have been reported between Chinese- and Indian-derived subspecies. The purpose of this study was to compare refractive development in Chinese- and Indian-derived rhesus monkeys. METHODS: The subjects were 216 Indian-derived and 78 Chinese-derived normal infant rhesus monkeys. Cross-sectional data were obtained at 3 weeks of age for all subjects. In addition, longitudinal data were obtained from 10 Indian-derived (male=5, female=5) and 5 Chinese-derived monkeys (male=3, female=2) that were reared with unrestricted vision. Ocular and refractive development was assessed by retinoscopy, keratometry, video-based ophthalmophakometry, and A-scan ultrasonography. RESULTS: Although the course of emmetropization was very similar in these two groups of rhesus monkeys, there were consistent and significant inter-group differences in ocular dimensions and refractive error. Throughout the observation period, the Chinese-derived monkeys were on average about 0.4D less hyperopic than the Indian-derived monkeys and the Chinese-derived monkeys had longer overall axial lengths, deeper anterior and vitreous chamber depths, thicker crystalline lenses, flatter corneas and lower powered crystalline lenses. CONCLUSIONS: The ocular differences observed in this study presumably reflect genetic differences between subspecies but could reflect the differences in the genetic pool between isolated colonies rather than true subspecies differences. Nonetheless, the substantial ocular differences that we observed emphasize that caution must be exercised when comparing and/or pooling data from rhesus monkeys obtained from different colonies. These inter-subspecies differences might be analogous to the ethnic differences in ocular parameters that have been observed in humans.

Histogenesis of the intravitreal membrane and secondary vitreous in the mouse.

PURPOSE: The intravitreal membrane (IVM) is a membranous structure between the primary and secondary vitreous bodies in developing mammalian eyes. In this study, for the first time the histogenesis of the IVM and the relationship between the hyaloid vasculature and the IVM was characterized in newborn mice. METHODS: Eyes of mice less than 12 days old were fixed and embedded. From these, serial paraffin-embedded sections were made for lectin histochemistry, immunohistochemistry, and picrosirius red (PSR) staining, and ultrathin sections were made for transmission electron microscopy (TEM). Eight biotinylated lectins and antibodies for laminin and type IV collagen were used. RESULTS: Among the eight lectins tested, concanavalin A (Con A) agglutinin, Ricinus communis agglutinin I, and wheat germ agglutinin demonstrated strong positive staining in the IVM and vitreous fibrils of the primary and secondary vitreous bodies. They also bound to the internal limiting membrane (ILM) of the retina. At postgestational day 4, the secondary vitreous first appeared between the ILM and the vasa hyaloidea propria (VHP). Immunohistochemical staining revealed that the IVM consists of extracellular matrix components including laminin and type IV collagen, whereas PSR staining and TEM showed that collagen fibrils in the IVM are bundled and continuous with the basement membrane of hyaloid capillaries or the VHP. CONCLUSIONS: Lectin histochemistry and immunohistochemistry provided good methods for visualizing the structures of the IVM and vitreous fibrils. These results suggest that the IVM is separated from the basement membrane of the retinal ILM along with the vascular network of the VHP when the secondary vitreous begins to form.

An age-based method for planning sclerotomy placement during pediatric vitrectomy: a 12-year experience.

PURPOSE: Pars plana vitrectomy (PPV) in children requires that sclerotomy placement be adjusted for changing dimensions of the ciliary body during ocular development. Experience with an aged-based method for sclerotomy placement is described. METHODS: Using data from previously reported morphometric studies on ciliary body length by age, an age-based method was used for planning sclerotomy location in children between 1 month and 18 years of age. Sclerotomies were placed 1.5 mm posterior to the limbus in those aged 1 to 6 months, 2.0 mm in those 6 months to 1 year, 2.5 mm in those 1 to 2 years, 3.0 mm in those 2 to 6 years, and 3.5 mm in those 6 to 18 years. RESULTS: Between 1993 and mid-2005, 82 pediatric PPV procedures were performed using this scheme. None of the 82 procedures were complicated by inadvertent lens trauma or retinal perforation during sclerotomy placement. CONCLUSION: The age-based method for sclerotomy placement may provide a useful guideline for vitrectomy in children with normal ocular growth and development.

Acute effects of dietary retinoic acid on ocular components in the growing chick.

When the eyes of chicks are induced to grow toward myopia or hyperopia by having them wear spectacle lenses or diffusers, opposite changes take place in the retina and choroid in the synthesis and levels of all-trans Retinoic Acid (RA). To explore whether RA plays a causal role in the regulation of eye growth, we fed young chicks RA (doses 0.5 to 24 mg/kg) either twice a day or on alternate days or only once. Refractive error was measured with a Hartinger refractometer; ocular length, lens-thickness and choroidal thickness were measured by A-scan ultrasound. The amount of RA present in ocular tissues was determined using HPLC. Oral delivery of RA effectively increased RA in ocular tissues within 8h. During the first day after feeding RA at levels above 8 mg/kg, the rate of ocular elongation tripled, the choroid thickened and lens thickening was inhibited. The day following a dose of RA, the rate of ocular elongation was inhibited and the lens thickened more than normal. Nonetheless, the cumulative effect of repeated doses was that the eye became longer and the lens became thinner than normal, with no net change in refractive error. The rate of elongation was also increased by feeding 13-cis RA, and was reduced by citral, an inhibitor of RA synthesis. Surprisingly, birds fed RA while being kept in darkness also had normal refractive errors despite increased ocular elongation, and birds wearing either +6D or -6D spectacle lenses compensated normally for the lenses despite the enhanced ocular elongation caused by the RA. These results suggest that RA may act at the level of a coordinated non-visual regulatory system which controls the growth of the various ocular components, arguing that emmetropization does not depend entirely on vision.

Normal development of refractive state and ocular dimensions in guinea pigs.

PURPOSE: This study investigated changes in refraction, corneal curvature, axial components and weight of posterior sclera in guinea pig eyes during the normal development from birth. METHODS: Sixty-four guinea pigs were assigned to eight groups (n=8 each). Each group underwent a series of ocular measurements at one of the eight time-points (0, 1, 2, 3, 5, 7, 9 and 11 weeks), including refraction (streak retinoscopy), corneal radius of curvature (CRC; keratometry), anterior segment length (AS: corneal thickness and depth of the anterior chamber), thickness of the crystalline lens (CL), vitreous chamber length (VC; all A-scan ultrasonography) and dry weight of a circular 6mm diameter punch in the posterior sclera (electronic balance). Results of all the measurements were statistically compared between right eye and left eye, male and female and among different age groups. Artifacts of retinoscopy due to small eye artifact were also estimated at different ages. RESULTS: The refraction in guinea pig eyes was +5.22+/-0.23 D (Mean, SE) at birth. This value decreased rapidly during the first 3 weeks followed by a slow decline. The overall decrease in refraction was highly significant from birth to 11 weeks (p<0.001 one way ANOVA). The small eye artifact was approximately 4.00 D at birth, which reduced to 2.76 D at 11 weeks. The guinea pig eyes were emmetropic by 3 weeks of age when the small eye artifact was taken into account. The CRC (3.24+/-0.01 mm at birth), AS (1.20+/-0.01 mm at birth), CL (2.72+/-0.03 mm at birth) and VC (3.28+/-0.01 mm at birth) increased within the first 3 weeks despite a transient decrease in the CRC within the first week. The increase in CRC, CL and VC continued after 3 weeks, however, the AS remained constant after this age. The increase in VC was better correlated to the decline of hyperopia (R(2)=0.70) than the other components (R(2)=0.33-0.39). Dry weight of the posterior sclera increased linearly from birth (p<0.001 between any two close time-points from 3 to 9 weeks) and had a moderately linear correlation with the VC (R(2)=0.60). There were no significant differences between the right eye and left eye or between male and female in all the measurements. CONCLUSIONS: In guinea pigs, the hyperopia present at birth rapidly reduces to emmetropia within the first 3 weeks of age. The emmetropization process in guinea pigs is mainly related to the increase in the vitreous chamber length. This relationship in guinea pigs is similar to that in chickens, tree shrews, primates and humans. The axial development of the vitreous chamber in guinea pigs appears to be associated with tissue growth of the posterior sclera.