Refractive Development in the "ROP Rat"

In vivo MRI evaluation of early postnatal development in normal and impaired rat eyes

This study employed in vivo 7-T magnetic resonance imaging (MRI) to evaluate the postnatal ocular growth patterns under normal development or neonatal impairments in Sprague-Dawley rats. Using T2-weighted imaging on healthy rats from postnatal day (P) 1 (newborn) to P60 (adult), the volumes of the anterior chamber and posterior chamber (ACPC), lens, and vitreous humor increased logistically with ACPC expanding by 33-fold and the others by fivefold. Intravitreal potassium dichromate injection at P1, P7, and P14 led to T1-weighted signal enhancement in the developing retina by 188-289%. Upon unilateral hypoxic-ischemic encephalopathy at P7, monocular deprivation at P15, and monocular enucleation at P1, T2-weighted imaging of the adult rats showed decreased ocular volumes to different extents. In summary, in vivo high-field MRI allows for non-invasive evaluation of early postnatal development in the normal and impaired rat eyes. Chromium-enhanced MRI appeared effective in examining the developing retina before natural eyelid opening at P14 with relevance to lipid metabolism. The reduced ocular volumes upon neonatal visual impairments provided evidence to the emerging problems of why some impaired visual outcomes cannot be solely predicted by neurological assessments and suggested the need to look into both the eye and the brain under such conditions.

The Nrf2 inhibitor brusatol has a protective role in a rat model of oxygen-induced retinopathy of prematurity

Nuclear factor-erythroid 2-related factor 2 (Nrf2) has been testified to be involved in the development of retinopathy of prematurity (ROP), which can cause childhood visual impairment. Whether brusatol, an Nrf2 inhibitor, could be utilized to treat ROP was unknown. The oxygen-induced retinopathy rat model was established to mimic ROP, which was further intravitreal administrated with brusatol. Vessel morphology and microglial activation in the retina were assessed with histology analysis. The relative expression levels of angiogenesis and inflammation-related molecules were detected with Western blot and real-time polymerase chain reaction methods. Intravitreal brusatol administration could alleviate both angiogenesis and microgliosis induced by hyperoxia, along with down-regulation of vascular endothelial growth factor, vascular endothelial growth factor receptor (VEGFR)-1, VEGFR-2, cluster of differentiation molecule 11B, tumor necrosis factor alpha, inducible nitric oxide synthase, glial fibrillary acidic protein, and IBA-1 expression. It was further revealed that Nrf2 and heme oxygenease-1 were diminished by brusatol administration. The results demonstrate the potential of intravitreal brusatol deliver to treat ROP with down-regulation of angiogenesis and microgliosis.

Refractive status and optical components of premature babies with or without retinopathy of prematurity at 7 years old

BACKGROUND

This study aimed to investigate the refractive status and optical components of premature babies with or without retinopathy of prematurity (ROP) at 7 years old and to explore the influence of prematurity and ROP on the refractive status and optical components.

METHODS

From January 2009 to February 2011, premature babies receiving fundus photographic screening (FPS) were recruited and divided into non-ROP group and ROP group. Full-term babies matched in age were recruited as controls. Auto-refractometer was employed to detect the corneal refractive power, corneal radius (CR) of curvature and corneal astigmatism, A-scan ultrasonography was performed to detect the anterior chamber depth (ACD), lens thickness (LT), vitreous thickness (VITR) and ocular axial length (AL), and retinoscopy was done following cycloplegia with 1% cyclopentolate in these babies at 7 years old. These parameters were compared among groups, and the correlations of gestational age and birth weight with the refractive status and optical components were further evaluated.

RESULTS

Of 126 subjects, a total of 252 eyes were evaluated in this study, including 50 eyes of 25 subjects in ROP group (pre-threshold stage 1-3), 110 eyes of 55 subjects in non-ROP group and 92 eyes of 46 subjects in control group. The incidence of myopia was the highest in ROP group (9/50, 18%), followed by non-ROP group (11/110; 10%) and control group (6/92; 6.52%). The incidence of hyperopia was the highest in control group (21/92; 22.83%), followed by ROP group (8/50; 16%) and non-ROP group (10/110; 9.09%). The incidence of astigmatism was the highest in ROP group (18/50; 36%), followed by non-ROP group (25/110; 22.73%) and control group (12/92; 13.04%). The corneal astigmatism (-1.58, -1.11, -0.86 DC, P<0.01) and the mean degree of astigmatism (1.38, 1.17, 0.64 DC, P<0.05) in ROP group and non-ROP group were significantly higher than those in control group. The corneal refractive power in ROP group was more potent as compared to non-ROP group and control group (43.98, 43.16, 42.99 D, P<0.05); the corneal curvature in ROP group was significantly higher than that in non-ROP group and control group (7.87, 7.71, 7.67 mm, P<0.05); the ocular AL in ROP group and non-ROP group was significantly shorter than that in control group (2.41, 22.47, 22.78 mm, P<0.05). The LT in ROP group and non-ROP group was markedly thicker than that in control group (4.48, 4.45, 4.37 mm, P>0.05); the ACD in ROP group and non-ROP group was markedly deeper than in control group (3.16, 3.12, 3.21 mm, P>0.05). The gestational age was negatively related to corneal astigmatism (r=-0.208, P=0.013) and astigmatism (r=-0.226, P=0.004), but positively associated with ocular AL (r=0.252, P=0.005). The birth weight was negatively associated with corneal astigmatism (r=-0.30, P<0.001), astigmatism (r=-0.267, P=0.001), corneal refractive power (r=-0.255, P=0.001) and corneal curvature (r=0.242, P=0.001), but positively to ocular AL (r=0.243, P=0.001) and spherical equivalent refraction (SER) (r=0.151, P=0.028).

CONCLUSIONS

(I) Premature babies with or without ROP are susceptible to myopia and astigmatism; (II) low birth weight, prematurity and ROP synergistically influence the development of refractive status and optical components, resulting in myopia and astigmatism; (III) premature babies with or without ROP have increased corneal curvature and LT, which are related to the higher incidence of myopia and astigmatism.

Effects of Hyperoxia on the Refraction in Murine Neonatal and Adult Models

Whether hyperoxia affects the refraction in neonatal and adult mice is unknown. The mice exposed to 85% oxygen at postnatal 8 days (P8d) for 3 days and the mice exposed to normal air were assigned to the neonatal hyperoxia and normoxia groups, respectively. The refraction, the corneal curvature radius (CR) and the axial length (AL) were measured at P30d and P47d. Postnatal 6 weeks (P6w) adult mice were divided into the adult hyperoxia and normoxia groups. These parameters were measured before oxygen exposure, after 1 and 6 weeks, and every 7 weeks. The lens elasticity was measured at P7w and P26w by enucleation. The neonatal hyperoxia group showed a significantly larger myopic change than the neonatal normoxia group (P47d −6.56 ± 5.89 D, +4.11 ± 2.02 D, p < 0.001), whereas the changes in AL were not significantly different (P47d, 3.31 ± 0.04 mm, 3.31 ± 0.05 mm, p = 0.852). The adult hyperoxia group also showed a significantly larger myopic change (P12w, −7.20 ± 4.09 D, +7.52 ± 2.54 D, p < 0.001). The AL did not show significant difference (P12w, 3.44 ± 0.03 mm, 3.43 ± 0.01 mm, p = 0.545); however, the CR in the adult hyperoxia group was significantly smaller than the adult normoxia group (P12w, 1.44 ± 0.03 mm, 1.50 ± 0.03 mm, p = 0.003). In conclusion, hyperoxia was demonstrated to induce myopic shift both in neonatal and adult mice, which was attributed to the change in the CR rather than the AL. Elucidation of the mechanisms of hyperoxia and the application of this result to humans should be carried out in future studies.

Vulnerability of Dopaminergic Amacrine Cells to Chronic Ischemia in a Mouse Model of Oxygen-Induced Retinopathy

Purpose

Retinal dopamine deficiency is a potential cause of myopia and visual deficits in retinopathy of prematurity (ROP). We investigated the cellular mechanisms responsible for lowered levels of retinal dopamine in an oxygen-induced retinopathy (OIR) mouse model of ROP.

Methods

Retinopathy was induced by exposing mice to 75% oxygen from postnatal day 7 (P7) to P12. Oxygen-induced retinopathy and age-matched control mice were euthanized at P12, P17, P25, or P42 to P50. Immunohistochemistry, electrophysiology, and biochemical approaches were used to determine the effect of OIR on the structure and function of dopaminergic amacrine cells (DACs).

Results

The total number of DACs was unchanged in OIR retinas at P12 despite significant capillary dropout in the central retina. However, a significant loss of DACs was observed in P17 OIR retinas (in which neovascularization was maximal), with the cell loss being more profound in the central (avascular) than in the peripheral (neovascular) regions. Cell loss was persistent in both regions at P25, at which time retinal neovascularization had regressed. At P42, the percentage of DACs lost (54%) was comparable to the percent decrease in total dopamine content (53%). Additionally, it was found that DACs recorded in OIR retinas at P42 to P50 had a complete dendritic field and exhibited relatively normal spontaneous and light-induced electrical activity.

Conclusions

The results suggest that remaining DACs are structurally and functionally intact and that loss of DACs is primarily responsible for the decreased levels of retinal dopamine observed after OIR.

Altered Refractive Development in Mice With Reduced Levels of Retinal Dopamine

Purpose

The neuromodulator dopamine (DA) has been implicated in the prevention of excessive ocular elongation and myopia in various animal models. This study used retina-specific DA knockout mice to investigate the role of retinal DA in refractive development and susceptibility to experimental myopia.

Methods

Measurements of refractive error, corneal curvature, and ocular biometrics were obtained as a function of age for both untreated and form-deprived (FD) groups of retina-specific tyrosine hydroxylase knockout (rTHKO) and control (Ctrl) mice. Retinas from each group were analyzed by HPLC for levels of DA and its primary metabolite (DOPAC).

Results

Under normal visual conditions, rTHKO mice showed significantly myopic refractions (F(1,188) = 7.602, P < 0.001) and steeper corneas (main effect of genotype F(1,180) = 5.1, P < 0.01) at 4 and 6 weeks of age compared with Ctrl mice. Retina-specific THKO mice also had thinner corneas (main effect of genotype F(1,181) = 37.17, P < 0.001), thinner retinas (F(6,181) = 6.07, P < 0.001), and shorter axial lengths (F(6,181) = 3.78, P < 0.01) than Ctrl mice. Retina-specific THKO retinas contained less than 15% of DA and DOPAC compared with Ctrl retinas, and the remaining DA had a significantly higher turnover, as indicated by DOPAC/DA ratios (Student's t-test, P < 0.05). Retina-specific THKO mice showed similar, yet more variable, responses to 6 weeks of FD compared with Ctrl mice.

Conclusions

Diminished retinal DA induced spontaneous myopia in mice raised under laboratory conditions without form deprivation. The relative myopic shift in rTHKO mice may be explained by steeper corneas, an unexpected finding. The chronic loss of DA did not significantly alter the FD myopia response in rTHKO mice.

The neural retina in retinopathy of prematurity

Retinopathy of prematurity (ROP) is a neurovascular disease that affects prematurely born infants and is known to have significant long term effects on vision. We conducted the studies described herein not only to learn more about vision but also about the pathogenesis of ROP. The coincidence of ROP onset and rapid developmental elongation of the rod photoreceptor outer segments motivated us to consider the role of the rods in this disease. We used noninvasive electroretinographic (ERG), psychophysical, and retinal imaging procedures to study the function and structure of the neurosensory retina. Rod photoreceptor and post-receptor responses are significantly altered years after the preterm days during which ROP is an active disease. The alterations include persistent rod dysfunction, and evidence of compensatory remodeling of the post-receptor retina is found in ERG responses to full-field stimuli and in psychophysical thresholds that probe small retinal regions. In the central retina, both Mild and Severe ROP delay maturation of parafoveal scotopic thresholds and are associated with attenuation of cone mediated multifocal ERG responses, significant thickening of post-receptor retinal laminae, and dysmorphic cone photoreceptors. These results have implications for vision and control of eye growth and refractive development and suggest future research directions. These results also lead to a proposal for noninvasive management using light that may add to the currently invasive therapeutic armamentarium against ROP.

Retinal, visual, and refractive development in retinopathy of prematurity

The pivotal role of the neurosensory retina in retinopathy of prematurity (ROP) disease processes has been amply demonstrated in rat models. We have hypothesized that analogous cellular processes are operative in human ROP and have evaluated these presumptions in a series on non-invasive investigations of the photoreceptor and post-receptor peripheral and central retina in infants and children. Key results are slowed kinetics of phototransduction and deficits in photoreceptor sensitivity that persist years after ROP has completely resolved based on clinical criteria. On the other hand, deficits in post-receptor sensitivity are present in infancy regardless of the severity of the ROP but are not present in older children if the ROP was so mild that it never required treatment and resolved without a clinical trace. Accompanying the persistent deficits in photoreceptor sensitivity, there is increased receptive field size and thickening of the post-receptor retinal laminae in the peripheral retina of ROP subjects. In the late maturing central retina, which mediates visual acuity, attenuation of multifocal electroretinogram activity in the post-receptor retina led us to the discovery of a shallow foveal pit and significant thickening of the post-receptor retinal laminae in the macular region; this is most likely due to failure of the normal centrifugal movement of the post-receptor cells during foveal development. As for refractive development, myopia, at times high, is more common in ROP subjects than in control subjects, in accord with refractive findings in other populations of former preterms. This information about the neurosensory retina enhances understanding of vision in patients with a history of ROP, and taken as a whole, raises the possibility that the neurosensory retina is a target for therapeutic intervention.

Eye growth in term- and preterm-born eyes modeled from magnetic resonance images

PURPOSE

We generated a model of eye growth and tested it against an eye known to develop abnormally, one with a history of retinopathy of prematurity (ROP).

METHODS

We reviewed extant magnetic resonance images (MRIs) from term and preterm-born patients for suitable images (n = 129). We binned subjects for analysis based upon postmenstrual age at birth (in weeks) and ROP history ("Term" ≥ 37, "Premature" ≤ 32 with no ROP, "ROP" ≤ 32 with ROP). We measured the axial positions and curvatures of the cornea, anterior and posterior lens, and inner retinal surface. We fit anterior chamber depth (ACD), posterior segment depth (PSD), axial length (AL), and corneal and lenticular curvatures with logistic growth curves that we then evaluated for significant differences. We also measured the length of rays from the centroid to the surface of the eye at 5° intervals, and described the length versus age relationship of each ray, L(ray)(x), using the same logistic growth curve. We determined the rate of ray elongation, E(ray)(x), from L(ray)dy/dx. Then, we estimated the scleral growth that accounted for E(ray)(x), G(x), at every age and position.

RESULTS

Relative to Term, development of ACD, PSD, AL, and corneal and lenticular curvatures was delayed in ROP eyes, but not Premature eyes. In Term infants, G(x) was fast and predominantly equatorial; in age-matched ROP eyes, maximal G(x) was offset by approximately 90°.

CONCLUSIONS

We produced a model of normal eye growth in term-born subjects. Relative to normal, the ROP eye is characterized by delayed, abnormal growth.

Visually-driven ocular growth in mice requires functional rod photoreceptors

PURPOSE

Proper refractive eye growth depends on several features of the visual image and requisite retinal pathways. In this study, we determined the contribution of rod pathways to normal refractive development and form deprivation (FD) myopia by testing Gnat1(-/-) mice, which lack functional rods due to a mutation in rod transducin-α.

METHODS

Refractive development was measured in Gnat1(-/-) (n = 30-36) and wild-type (WT) mice (n = 5-9) from 4 to 12 weeks of age. FD was induced monocularly from 4 weeks of age using head-mounted diffuser goggles (Gnat1(-/-), n = 9-10; WT, n = 7-8). Refractive state and ocular biometry were obtained weekly using a photorefractor, 1310 nm optical coherence tomography, and partial coherence interferometry. We measured retinal dopamine and its metabolite, DOPAC, using HPLC.

RESULTS

During normal development, the refractions of WT mice started at 5.36 ± 0.68 diopters (D) and became more hyperopic before plateauing at 7.78 ± 0.64 D. In contrast, refractions in Gnat1(-/-) mice were stable at 7.39 ± 1.22 D across all ages. Three weeks of FD induced a 2.54 ± 0.77 D myopic shift in WT mice, while Gnat1(-/-) mice did not respond to FD at any age. Axial lengths of Gnat1(-/-) and WT mice increased with age, but differences between genotypes or with goggling did not reach statistical significance and fell within the precision of the instruments. The DOPAC levels were significantly lower in Gnat1(-/-) mice from 2 to 12 weeks of age with DOPAC/dopamine ratio peaking earlier in Gnat1(-/-) compared to WT mice. No differences in dopamine were seen in response to FD or between genotypes.

CONCLUSIONS

Functional rod photoreceptors are critical to normal refractive development and the response to FD in mice. Dopamine levels may not directly modulate the refractive state of the mouse eye, but tonic levels of dopamine during development may determine susceptibility to myopia.

The rat with oxygen-induced retinopathy is myopic with low retinal dopamine

PURPOSE

Dopamine (DA) is a neurotransmitter implicated both in modulating neural retinal signals and in eye growth. Therefore, it may participate in the pathogenesis of the most common clinical sequelae of retinopathy of prematurity (ROP), visual dysfunction and myopia. Paradoxically, in ROP myopia the eye is usually small. The eye of the rat with oxygen-induced retinopathy (OIR) is characterized by retinal dysfunction and short axial length. There have been several investigations of the early maturation of DA in rat retina, but little at older ages, and not in the OIR rat. Therefore, DA, retinal function, and refractive state were investigated in the OIR rat.

METHODS

In one set of rats, the development of dopaminergic (DAergic) networks was evaluated in retinal cross-sections from rats aged 14 to 120 days using antibodies against tyrosine hydroxylase (TH, the rate-limiting enzyme in the biosynthesis of DA). In another set of rats, retinoscopy was used to evaluate spherical equivalent (SE), electoretinography (ERG) was used to evaluate retinal function, and high-pressure liquid chromatography (HPLC) was used to evaluate retinal contents of DA, its precursor levodopamine (DOPA), and its primary metabolite 3,4-dihydroxyphenylacetic acid (DOPAC).

RESULTS

The normally rapid postnatal ramification of DAergic neurons was disrupted in OIR rats. Retinoscopy revealed that OIR rats were relatively myopic. In the same eyes, ERG confirmed retinal dysfunction in OIR. HPLC of those eyes' retinae confirmed low DA. Regression analysis indicated that DA metabolism (evaluated by the ratio of DOPAC to DA) was an important additional predictor of myopia beyond OIR.

CONCLUSIONS

The OIR rat is the first known animal model of myopia in which the eye is smaller than normal. Dopamine may modulate, or fail to modulate, neural activity in the OIR eye, and thus contribute to this peculiar myopia.

Retinal degeneration increases susceptibility to myopia in mice

PURPOSE

Retinal diseases are often associated with refractive errors, suggesting the importance of normal retinal signaling during emmetropization. For instance, retinitis pigmentosa, a disease characterized by severe photoreceptor degeneration, is associated with myopia; however, the underlying link between these conditions is not known. This study examines the influence of photoreceptor degeneration on refractive development by testing two mouse models of retinitis pigmentosa under normal and form deprivation visual conditions. Dopamine, a potential stop signal for refractive eye growth, was assessed as a potential underlying mechanism.

METHODS

Refractive eye growth in mice that were homozygous for a mutation in Pde6b, Pde6b(rd1/rd1) (rd1), or Pde6b(rd10/rd10) (rd10) was measured weekly from 4 to 12 weeks of age and compared to age-matched wild-type (WT) mice. Refractive error was measured using an eccentric infrared photorefractor, and axial length was measured with partial coherence interferometry or spectral domain ocular coherence tomography. A cohort of mice received head-mounted diffuser goggles to induce form deprivation from 4 to 6 weeks of age. Dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) levels were measured with high-performance liquid chromatography in each strain after exposure to normal or form deprivation conditions.

RESULTS

The rd1 and rd10 mice had significantly greater hyperopia relative to the WT controls throughout normal development; however, axial length became significantly longer only in WT mice starting at 7 weeks of age. After 2 weeks of form deprivation, the rd1 and rd10 mice demonstrated a faster and larger myopic shift (-6.14±0.62 and -7.38±1.46 diopter, respectively) compared to the WT mice (-2.41±0.47 diopter). Under normal visual conditions, the DOPAC levels and DOPAC/dopamine ratios, a measure of dopamine turnover, were significantly lower in the rd1 and rd10 mice compared to the WT mice, while the dopamine levels were similar or higher than WT in the rd10 mice. Lower basal levels of DOPAC were highly correlated with increasing myopic shifts.

CONCLUSIONS

Refractive development under normal visual conditions was disrupted toward greater hyperopia from 4 to 12 weeks of age in these photoreceptor degeneration models, despite significantly lower DOPAC levels. However, the retinal degeneration models with low basal levels of DOPAC had increased susceptibility to form deprivation myopia. These results indicate that photoreceptor degeneration may alter dopamine metabolism, leading to increased susceptibility to myopia with an environmental visual challenge.

Development of a rat schematic eye from in vivo biometry and the correction of lateral magnification in SD-OCT imaging

PURPOSE

Optical magnification in optical coherence tomography (OCT) depends on ocular biometric parameters (e.g., axial length). Biometric differences between eyes will influence scan location. A schematic model eye was developed to compensate for lateral magnification in OCT images of the healthy rat.

METHODS

Spectral-domain optical coherence tomography images were acquired in 19 eyes of 19 brown Norway rats. Images were scaled using the OCT instrument's built-in scaling function and by calculating the micron per degree from schematic model eyes developed from in vivo biometry (immersion A-scan and videokeratometry). Mean total retinal thickness was measured 500 μm away from the optic nerve head and optic nerve head diameter was measured. Corneal curvature, lens thickness, and axial length were modified to calculate their effects on OCT scan location and total retinal thickness.

RESULTS

Mean total retinal thickness increased by 21 μm and the SD doubles when images were scaled with the Built-in scaling (222 ± 13 μm) compared with scaling with individual biometric parameters (201 ± 6 μm). Optic nerve head diameter was three times larger when images were scaled with the Built-in scaling (925 ± 97 μm) than the individual biometric parameters (300 ± 27 μm). Assuming no other change in biometric parameters, total retinal thickness would decrease by 37 μm for every millimeter increase in anterior chamber depth due to changes in ocular lateral magnification and associated change in scan location.

CONCLUSIONS

Scaling SD-OCT images with schematic model eyes derived from individual biometric data is important. This approach produces estimates of retinal thickness and optic nerve head size that are in good agreement with previously reported measurements.

Next-generation sequencing analysis of gene regulation in the rat model of retinopathy of prematurity

PURPOSE

The purpose of this study was to identify the genes, biochemical signaling pathways, and biological themes involved in the pathogenesis of retinopathy of prematurity (ROP).

METHODS

Next-generation sequencing (NGS) was performed on the RNA transcriptome of rats with the Penn et al. (Pediatr Res 36:724-731, 1994) oxygen-induced retinopathy model of ROP at the height of vascular abnormality, postnatal day (P) 19, and normalized to age-matched, room-air-reared littermate controls. Eight custom-developed pathways with potential relevance to known ROP sequelae were evaluated for significant regulation in ROP: The three major Wnt signaling pathways, canonical, planar cell polarity (PCP), and Wnt/Ca(2+); two signaling pathways mediated by the Rho GTPases RhoA and Cdc42, which are, respectively, thought to intersect with canonical and non-canonical Wnt signaling; nitric oxide signaling pathways mediated by two nitric oxide synthase (NOS) enzymes, neuronal (nNOS) and endothelial (eNOS); and the retinoic acid (RA) signaling pathway. Regulation of other biological pathways and themes was detected by gene ontology using the Kyoto Encyclopedia of Genes and Genomes and the NIH's Database for Annotation, Visualization, and Integrated Discovery's GO terms databases.

RESULTS

Canonical Wnt signaling was found to be regulated, but the non-canonical PCP and Wnt/Ca(2+) pathways were not. Nitric oxide signaling, as measured by the activation of nNOS and eNOS, was also regulated, as was RA signaling. Biological themes related to protein translation (ribosomes), neural signaling, inflammation and immunity, cell cycle, and cell death were (among others) highly regulated in ROP rats.

CONCLUSIONS

These several genes and pathways identified by NGS might provide novel targets for intervention in ROP.

Alterations of the tunica vasculosa lentis in the rat model of retinopathy of prematurity

PURPOSE

To study the relationship between retinal and tunica vasculosa lentis (TVL) disease in retinopathy of prematurity (ROP). Although the clinical hallmark of ROP is abnormal retinal blood vessels, the vessels of the anterior segment, including the TVL, are also altered.

METHODS

ROP was induced in Long-Evans pigmented and Sprague Dawley albino rats; room-air-reared (RAR) rats served as controls. Then, fluorescein angiographic images of the TVL and retinal vessels were serially obtained with a scanning laser ophthalmoscope near the height of retinal vascular disease, ~20 days of age, and again at 30 and 64 days of age. Additionally, electroretinograms (ERGs) were obtained prior to the first imaging session. The TVL images were analyzed for percent coverage of the posterior lens. The tortuosity of the retinal arterioles was determined using Retinal Image multiScale Analysis (Gelman et al. in Invest Ophthalmol Vis Sci 46:4734-4738, 2005).

RESULTS

In the youngest ROP rats, the TVL was dense, while in RAR rats, it was relatively sparse. By 30 days, the TVL in RAR rats had almost fully regressed, while in ROP rats, it was still pronounced. By the final test age, the TVL had completely regressed in both ROP and RAR rats. In parallel, the tortuous retinal arterioles in ROP rats resolved with increasing age. ERG components indicating postreceptoral dysfunction, the b-wave, and oscillatory potentials were attenuated in ROP rats.

CONCLUSIONS

These findings underscore the retinal vascular abnormalities and, for the first time, show abnormal anterior segment vasculature in the rat model of ROP. There is delayed regression of the TVL in the rat model of ROP. This demonstrates that ROP is a disease of the whole eye.

Diminished vision in healthy aging is associated with increased retinal L-type voltage gated calcium channel ion influx

Extensive evidence implicates an increase in hippocampal L-type voltage-gated calcium channel (L-VGCC) expression, and ion influx through these channels, in age-related cognitive declines. Here, we ask if this “calcium hypothesis" applies to the neuroretina: Is increased influx via L-VGCCs related to the well-documented but poorly-understood vision declines in healthy aging? In Long-Evans rats we find a significant age-related increase in ion flux through retinal L-VGCCs in vivo (manganese-enhanced MRI (MEMRI)) that are longitudinally linked with progressive vision declines (optokinetic tracking). Importantly, the degree of retinal Mn²⁺ uptake early in adulthood significantly predicted later visual contrast sensitivity declines. Furthermore, as in the aging hippocampus, retinal expression of a drug-insensitive L-VGCC isoform (α_1D) increased – a pattern confirmed in vivo by an age-related decline in sensitivity to L-VGCC blockade. These data highlight mechanistic similarities between retinal and hippocampal aging, and raise the possibility of new treatment targets for minimizing vision loss during healthy aging.