Machelle T. Pardue

Purpose: Animal models of myopia typically induce monocular refractive shifts via form deprivation (FD) or lens-induced myopia (LIM), modeling susceptibility to myopia, but with potentially limited applicability to childhood myopia. Here we describe a novel, genetically diverse mouse model of naturally occurring refractive error (NORE) with three distinct refractive phenotypes: hyperopic, myopic, and intermediate. Methods: C57BL/6J mice were mated to 129S2/SvPasCrl mice to create F1 or F2 offspring. Refractive errors in male and female F1 (N=21) and F2 (N=101) mice were assessed on postnatal days (P) 28 and 42 using photorefractometry. In a subset of mice (N=30–40), corneal radius of curvature, axial ocular dimensions, retinal and visual function were assessed. Results: F2 mice were classified as NORE with either hyperopic (RE≥0 diopters (D) at P28 and P42), myopic (RE<0D at P28 and P42) or intermediate (RE<0D at P28 and RE≥0D at P42) refractions based on individual trajectories. All ocular parameters changed with age, with significantly slower growth in axial length and vitreous chamber depth in the intermediate versus myopic mice (p<0.05). Lens thickness was smaller in the myopic group at P28. Differences in refraction were not attributed to variances in retinal function or dopamine signaling. Conclusions: NORE mice represent a novel, genetically diverse wild-type mouse model that, unlike traditional models, does not require interventions such as FD or LIM to induce myopia. NORE mice provide a valuable tool for future investigations of genetic and environmental mechanisms and targeted therapeutic strategies for refractive errors.

While previous work has shown a sustained protective effect of levodopa (L-DOPA) on retinal function in early-stage diabetic retinopathy (DR) in humans, its underlying biology is unknown. Using noninvasive measures in diabetic mice, we found L-DOPA protects retinal neurovascular function as measured by oscillatory potential timing and flicker-evoked retinal vasodilation, as well as visual behavior, for at least two weeks past treatment end. Assessing changes in retinal gene expression, differentially expressed genes were broadly comparable between diabetic mice experiencing washout of L-DOPA versus continued L-DOPA treatment, with gene co-expression network analysis identifying distinct modules across L-DOPA–treated diabetic mice associated with synaptic function and cytoskeletal organization that correlated with functional protection. Together, these findings demonstrate that L-DOPA restores and sustains retinal neurovascular function in early DR and links this protection to transcriptional programs supporting synapse activity and structural integrity. Teaser: L-DOPA restores neuronal and vascular performance in the diabetic retina, with benefits that lasted after treatment stopped.

Myopia, or near-sightedness, is rapidly growing in prevalence, with significant long-term implications for ocular health. There is thus great impetus to better understand molecular signalling pathways leading to myopia. We and others have reported that all- trans retinoic acid (atRA) is involved in myopigenic signalling, yet the understanding of how atRA is transported and exerts a myopigenic influence is poor. Here we measured the concentrations of atRA in the serum in wild-type C57BL/6 mice under control conditions and after atRA feeding, previously shown to induce myopia. We also developed a mathematical model that describes fluid fluxes and the advective-diffusive transport of atRA in choroid and sclera, including atRA synthesis in the choriocapillaris, atRA degradation by scleral cells, and binding of atRA to the carrier protein serum albumin. This model, developed for both mice and humans, showed that atRA produced in the choriocapillaris was able to permeate well into the sclera in both mice and humans at biologically relevant concentrations, and that atRA feeding greatly increased tissue levels of atRA across both the choroid and sclera. We were also able to identify which parameters most influence atRA concentration in ocular tissues, guiding future experimental work. Our findings support atRA’s role in myopigenic signalling.

This study investigated the long-term progression of oscillatory potential (OP) implicit times (ITs) in individuals with preclinical diabetic retinopathy (DR) with and without levodopa (L-DOPA) treatment by quantifying functional and structural retinal changes. Participants from the Motz et al. (2020) study were re-evaluated after 5 years, including individuals with diabetes mellitus (DM) who received L-DOPA treatment for 2 weeks (the DM + L-DOPA group; n = 14), those who did not (the DM group; n = 6), and non-diabetic healthy controls (the control group; n = 37). Retinal function and structure were assessed using dim-flash electroretinography (ERG) and optical coherence tomography (OCT). After 5 years, OP 1 and OP 2 ITs showed no significant differences among the groups (P > 0.05). The DM + L-DOPA OP IT values remained improved compared to baseline. The outer region thickness of the outer plexus layer (OPL) and ganglion cell layer (GCL) were significantly thinner in the DM + L-DOPA group compared to the DM group (P < 0.05). The DM group showed strong correlations between OP IT and OCT thickness across all retinal regions, whereas the DM + L-DOPA group correlations were similar to the control group. Short-term L-DOPA treatment led to significant functional improvements after 2 weeks, with trends suggesting sustained benefit over 5 years. Inner retinal structural differences suggest potential long-term benefit of L-DOPA on retinal health. These findings support OP IT delays as early biomarkers for preclinical DR and suggest L-DOPA may provide lasting neuroprotective benefits. Retinal dysfunction and inner retinal structural changes could be potential biomarkers for preclinical DR, and L-DOPA treatment may provide sustained benefits for the diabetic retina.

Ambient light exposure is linked to myopia development in children and affects myopia susceptibility in animal models. Currently, it is unclear which signals mediate the effects of light on myopia. All-trans retinoic acid (atRA) and dopamine (DA) oppositely influence experimental myopia and may be involved in the retinoscleral signaling cascade underlying myopic eye growth. However, how ocular atRA responds to different lighting and whether atRA and DA interact remains unknown. Dark-adapted C57BL/6J mice (29-31 days old) were exposed to dim (1 lux), mid (59 lux), or bright (12,000 lux) ambient lighting for 5 to 60 minutes. Some mice were also systemically administered the DA precursor, LDOPA, or atRA before light exposure. After exposure, the retina and the back of the eye (BOE) were collected and analyzed for levels of atRA, DA, and the DA metabolite, DOPAC. DA turnover (DOPAC/DA ratio) in the retina increased in magnitude after only 5 minutes of exposure to higher ambient luminance, but was minimal in the BOE. In contrast, atRA levels in the retina and BOE significantly decreased with higher ambient luminance and longer duration exposure. Intriguingly, LDOPA-treated mice had a transient reduction in retinal atRA compared with saline-treated mice, whereas atRA treatment had no effect on ocular DA. Ocular atRA was affected by the duration of exposure to different ambient lighting, and retinal atRA levels decreased with increased DA. Overall, these data suggest specific interactions between ambient lighting, atRA, and DA that could have implications for the retinoscleral signaling cascade underlying myopic eye growth.

Purpose: Ambient light exposure is linked to myopia development in children and affects myopia susceptibility in animal models. Currently, it is unclear which signals mediate the effects of light on myopia. All- trans retinoic acid (atRA) and dopamine (DA) oppositely influence experimental myopia and may be involved in the retino-scleral signaling cascade underlying myopic eye growth. However, how ocular atRA responds to different lighting and whether atRA and DA interact remains unknown. Methods: Dark-adapted C57BL/6J mice (29-31 days old) were exposed to Dim (1 lux), Mid (59 lux), or Bright (12,000 lux) ambient lighting for 5-60 minutes. Some mice were also systemically administered the DA precursor, LDOPA, or atRA prior to light exposure. After exposure, the retina and the back-of-the-eye (BOE) were collected and analyzed for levels of atRA, DA, and the DA metabolite, DOPAC. Results: DA turnover (DOPAC/DA ratio) in the retina increased in magnitude after only five minutes of exposure to higher ambient luminance but was minimal in the BOE. In contrast, atRA levels in the retina and BOE significantly decreased with higher ambient luminance and longer duration exposure. Intriguingly, LDOPA-treated mice had a transient reduction in retinal atRA compared to saline-treated mice, whereas atRA treatment had no effect on ocular DA. Conclusions: Ocular atRA was affected by the duration of exposure to different ambient lighting and retinal atRA levels decreased with increased DA. Overall, these data suggest specific interactions between ambient lighting, atRA, and DA that could have implications for the retino-scleral signaling cascade underlying myopic eye growth.

Animal models are critical for understanding the initiation and progression of myopia, a refractive condition that causes blurred distance vision. The prevalence of myopia is rapidly increasing worldwide, and myopia increases the risk of developing potentially blinding diseases. Current pharmacological, optical, and environmental interventions attenuate myopia progression in children, but it is still unclear how this occurs or how these interventions can be improved to increase their protective effects. To optimize myopia interventions, directed mechanistic studies are needed. The mouse model is well-suited to these studies because of its well-characterized visual system and the genetic experimental tools available, which can be combined with pharmacological and environmental manipulations for powerful investigations of causation. This review describes aspects of the mouse visual system that support its use as a myopia model and presents genetic, pharmacological, and environmental studies that significantly contribute to our understanding of the mechanisms that underlie myopigenesis.

Whole-body physical exercise has been shown to promote retinal structure and function preservation in animal models of retinal degeneration. It is currently unknown how exercise modulates retinal inflammatory responses. In this study, we investigated cytokine alterations associated with retinal neuroprotection induced by voluntary running wheel exercise in a retinal degeneration mouse model of class B1 autosomal dominant retinitis pigmentosa, I307N Rho. I307N Rho mice undergo rod photoreceptor degeneration when exposed to bright light (induced). Our data show, active induced mice exhibited significant preservation of retinal and visual function compared to inactive induced mice after 4 weeks of exercise. Retinal cytokine expression revealed significant reductions of proinflammatory chemokines, keratinocyte-derived chemokine (KC) and interferon gamma inducible protein-10 (IP-10) expression in active groups compared to inactive groups. Through immunofluorescence, we found KC and IP-10 labeling localized to retinal vasculature marker, collagen IV. These data show that whole-body exercise lowers specific retinal cytokine expression associated with retinal vasculature. Future studies should determine whether suppression of inflammatory responses is requisite for exercise-induced retinal protection.