Altered Refractive Development in Mice With Reduced Levels of Retinal Dopamine

Loss of ON-Pathway Function in Mice Lacking Lrit3 Decreases Recovery From Lens-Induced Myopia

Purpose

To determine whether the Lrit3-/- mouse model of complete congenital stationary night blindness with an ON-pathway defect harbors myopic features and whether the genetic defect influences the recovery from lens-induced myopia.

Methods

Retinal levels of dopamine (DA) and 3,4 dihydroxyphenylacetic acid (DOPAC) from adult isolated Lrit3-/- retinas were quantified using ultra performance liquid chromatography after light adaptation. Natural refractive development of Lrit3-/- mice was measured from three weeks to nine weeks of age using an infrared photorefractometer. Susceptibility to myopia induction was assessed using a lens-induced myopia protocol with -25 D lenses placed in front of the right eye of the animals for three weeks; the mean interocular shift was measured with an infrared photorefractometer after two and three weeks of goggling and after one and two weeks after removal of goggles.

Results

Compared to wild-type littermates (Lrit3+/+), both DA and DOPAC were drastically reduced in Lrit3-/- retinas. Natural refractive development was normal but Lrit3-/- mice showed a higher myopic shift and a lower ability to recover from induced myopia.

Conclusions

Our data consolidate the link between ON pathway defect altered dopaminergic signaling and myopia. We document for the first time the role of ON pathway on the recovery from myopia induction.

Pupillary Light Reflex Reveals Melanopsin System Alteration in the Background of Myopia-26, the Female Limited Form of Early-Onset High Myopia

Purpose

The purpose of this study was to evaluate pupillary light reflex (PLR) to chromatic flashes in patients with early-onset high-myopia (eoHM) without (myopic controls = M-CTRL) and with (female-limited myopia-26 = MYP-26) genetic mutations in the ARR3 gene encoding the cone arrestin.

Methods

Participants were 26 female subjects divided into 3 groups: emmetropic controls (E-CTRL, N = 12, mean age = 28.6 ± 7.8 years) and 2 myopic (M-CTRL, N = 7, mean age = 25.7 ± 11.5 years and MYP-26, N = 7, mean age = 28.3 ± 15.4 years) groups. In addition, one hemizygous carrier and one control male subject were examined. Direct PLRs were recorded after 10-minute dark adaptation. Stimuli were 1-second red (peak wavelength = 621 nm) and blue (peak wavelength = 470 nm) flashes at photopic luminance of 250 cd/m². A 2-minute interval between the flashes was introduced. Baseline pupil diameter (BPD), peak pupil constriction (PPC), and postillumination pupillary response (PIPR) were extracted from the PLR. Group comparisons were performed with ANOVAs.

Results

Dark-adapted BPD was comparable among the groups, whereas PPC to the red light was slightly reduced in patients with myopia (P = 0.02). PIPR at 6 seconds elicited by the blue flash was significantly weaker (P < 0.01) in female patients with MYP-26, whereas it was normal in the M-CTRL group and the asymptomatic male carrier.

Conclusions

L/M-cone abnormalities due to ARR3 gene mutation is currently claimed to underlie the pathological eye growth in MYP-26. Our results suggest that malfunction of the melanopsin system of intrinsically photosensitive retinal ganglion cells (ipRGCs) is specific to patients with symptomatic MYP-26, and may therefore play an additional role in the pathological eye growth of MYP-26.

Circadian rhythm, ipRGCs, and dopamine signalling in myopia

Myopia, a common ophthalmic disorder, places a high economic burden on individuals and society. Genetic and environmental factors influence myopia progression; however, the underlying mechanisms remain unelucidated. This paper reviews recent advances in circadian rhythm, intrinsically photosensitive retinal ganglion cells (ipRGCs), and dopamine (DA) signalling in myopia and proposes the hypothesis of a circadian rhythm brain retinal circuit in myopia progression. The search of relevant English articles was conducted in the PubMed databases until June 2023. Based on the search, emerging evidence indicated that circadian rhythm was associated with myopia, including circadian genes Bmal1, Cycle, and Per. In both humans and animals, the ocular morphology and physiology show rhythmic oscillations. Theoretically, such ocular rhythms are regulated locally and indirectly via the suprachiasmatic nucleus, which receives signal from the ipRGCs. Compared with the conventional retinal ganglion cells, ipRGCs can sense the presence of light because of specific expression of melanopsin. Light, together with ipRGCs and DA signalling, plays a crucial role in both circadian rhythm and myopia. In summary, regarding myopia progression, a circadian rhythm brain retinal circuit involving ipRGCs and DA signalling has not been well established. However, based on the relationship between circadian rhythm, ipRGCs, and DA signalling in myopia, we hypothesised a circadian rhythm brain retinal circuit.

Acupuncture modulates development of myopia by reducing NLRP3 inflammasome activation via the dopamine-D1R signaling pathway

BACKGROUND

Dopamine has been suggested to be a stop signal for eye growth and affects the development of myopia. Acupuncture is known to increase dopamine secretion and is widely used to treat myopia clinically.

OBJECTIVE

The aim of this study was to determine if acupuncture inhibits myopia progression in form deprived Syrian hamsters by inducing rises in dopamine content that in turn suppress inflammasome activation.

METHODS

Acupuncture was applied at LI4 and Taiyang every other day for 21 days. The levels of molecules associated with the dopamine signaling pathway, inflammatory signaling pathway and inflammasome activation were determined. A dopamine agonist (apomorphine) was used to evaluate if activation of the dopaminergic signaling pathway suppresses myopia progression by inhibiting inflammasome activation in primary retinal pigment epithelial (RPE) cells. A dopamine receptor 1 (D1R) inhibitor (SCH39166) was also administered to the hamsters.

RESULTS

Acupuncture inhibited myopia development by increasing dopamine levels and activating the D1R signaling pathway. Furthermore, we also demonstrated that nucleotide-binding oligomerization domain (NOD)-, leucine-rich repeat (LRR)- and pyrin domain-containing protein 3 (NLR) family pyrin domain-containing 3 (NLRP3) inflammasome activation was inhibited by activation of the D1R signaling pathway.

CONCLUSION

Our findings suggest that acupuncture inhibits myopia development by suppressing inflammation, which is initiated by activation of the dopamine-D1R signaling pathway.

Twenty-four hour diurnal variation in retinal oxygen saturation

Retinal oxygen saturation is influenced by systemic and local vasculature, intraocular pressure (IOP), and individual cellular function. In numerous retinal pathologies, early changes take place at the level of the microvasculature, thereby affecting retinal oxygenation. The purpose of this study was to investigate diurnal variations in retinal oximetry measures and evaluate the relationship with other ocular and systemic physiological processes. Healthy adults (n = 18, mean age 27 ± 5.5 years) participated. Ocular and systemic measures were collected every four hours over 24 h and included retinal oximetry, IOP, optical coherence tomography (OCT), OCT-angiography (OCTA), biometry, blood pressure, and partial pressure of oxygen. Amplitude and acrophase for retinal oxygen saturation, axial length, retinal and choroidal thickness, OCTA parameters, and mean arterial and ocular perfusion pressure (MAP, MOPP) were determined were determined using cosine fits, and multiple regression analysis was performed to compare metrics. Retinal oxygenation saturation demonstrated a significant diurnal variation with an amplitude of 5.84 ± 3.86% and acrophase of 2.35 h. Other parameters that demonstrated significant diurnal variation included IOP, MOPP, axial length, choroidal thickness, superficial vessel density, heart rate, systolic blood pressure, and MAP. Diurnal variations in retinal oxygen saturation were in-phase with choroidal thickness, IOP, and density of the superficial vascular plexus and out-of-phase with axial length and MOPP. In conclusion, retinal oxygenation saturation undergoes diurnal variations over 24 h. These findings contribute to a better understanding of intrinsic and extrinsic factors influencing oxygenation of the area surrounding the fovea.

Congenital aniridia beyond black eyes: From phenotype and novel genetic mechanisms to innovative therapeutic approaches

Congenital PAX6-aniridia, initially characterized by the absence of the iris, has progressively been shown to be associated with other developmental ocular abnormalities and systemic features making congenital aniridia a complex syndromic disorder rather than a simple isolated disease of the iris. Moreover, foveal hypoplasia is now recognized as a more frequent feature than complete iris hypoplasia and a major visual prognosis determinant, reversing the classical clinical picture of this disease. Conversely, iris malformation is also a feature of various anterior segment dysgenesis disorders caused by PAX6-related developmental genes, adding a level of genetic complexity for accurate molecular diagnosis of aniridia. Therefore, the clinical recognition and differential genetic diagnosis of PAX6-related aniridia has been revealed to be much more challenging than initially thought, and still remains under-investigated. Here, we update specific clinical features of aniridia, with emphasis on their genotype correlations, as well as provide new knowledge regarding the PAX6 gene and its mutational spectrum, and highlight the beneficial utility of clinically implementing targeted Next-Generation Sequencing combined with Whole-Genome Sequencing to increase the genetic diagnostic yield of aniridia. We also present new molecular mechanisms underlying aniridia and aniridia-like phenotypes. Finally, we discuss the appropriate medical and surgical management of aniridic eyes, as well as innovative therapeutic options. Altogether, these combined clinical-genetic approaches will help to accelerate time to diagnosis, provide better determination of the disease prognosis and management, and confirm eligibility for future clinical trials or genetic-specific therapies.

Exogenous All-Trans Retinoic Acid Induces Myopia and Alters Scleral Biomechanics in Mice

Purpose

Ocular all-trans retinoic acid (atRA) levels are influenced by visual cues, and exogenous atRA has been shown to increase eye size in chickens and guinea pigs. However, it is not clear whether atRA induces myopic axial elongation via scleral changes. Here, we test the hypothesis that exogenous atRA will induce myopia and alter scleral biomechanics in the mouse.

Methods

Male C57BL/6J mice were trained to voluntarily ingest atRA + vehicle (1% atRA in sugar, 25 mg/kg) (RA: n = 16 animals) or vehicle only (Ctrl: n = 14 animals). Refractive error (RE) and ocular biometry were measured at baseline and after 1 and 2 weeks of daily atRA treatment. Eyes were used in ex vivo assays to measure scleral biomechanics (unconfined compression: n = 18), total scleral sulfated glycosaminoglycan (sGAG) content (dimethylmethylene blue: n = 23), and specific sGAGs (immunohistochemistry: n = 18).

Results

Exogenous atRA caused myopic RE and larger vitreous chamber depth (VCD) to develop by 1 week (RE: -3.7 ± 2.2 diopters [D], P < 0.001; VCD: +20.7 ± 15.1 µm, P < 0.001), becoming more severe by 2 weeks (RE: -5.7 ± 2.2 D, P < 0.001; VCD: +32.3 ± 25.8 µm, P < 0.001). The anterior eye biometry was unaffected. While scleral sGAG content was not measurably affected, scleral biomechanics were significantly altered (tensile stiffness: -30% ± 19.5%, P < 0.001; permeability: +60% ± 95.3%, P < 0.001).

Conclusions

In mice, atRA treatment results in an axial myopia phenotype. Eyes developed myopic RE and larger VCD without the anterior eye being affected. The decrease in stiffness and increase in permeability of the sclera are consistent with the form-deprivation myopia phenotype.

Emmetropization and nonmyopic eye growth

Most eyes start with a hypermetropic refractive error at birth, but the growth rates of the ocular components, guided by visual cues, will slow in such a way that this refractive error decreases during the first 2 years of life. Once reaching its target, the eye enters a period of stable refractive error as it continues to grow by balancing the loss in corneal and lens power with the axial elongation. Although these basic ideas were first proposed over a century ago by Straub, the exact details on the controlling mechanism and the growth process remained elusive. Thanks to the observations collected in the last 40 years in both animals and humans, we are now beginning to get an understanding how environmental and behavioral factors stabilize or disrupt ocular growth. We survey these efforts to present what is currently known regarding the regulation of ocular growth rates.

Altered Structure and Function of Murine Sclera in Form-Deprivation Myopia

Purpose

The sclera is believed to biomechanically influence eye size, facilitating the excessive axial elongation that occurs during myopigenesis. Here, we test the hypothesis that the sclera will be remodeled and exhibit altered biomechanics in the mouse model of form-deprivation (FD) myopia, accompanied by altered retinoid concentrations, a potential signaling molecule involved in the process.

Methods

Male C57 Bl/6J mice were subjected to unilateral FD (n = 44 eyes), leaving the contralateral eye untreated (contra; n = 44). Refractive error and ocular biometry were measured in vivo prior to and after 1 or 3 weeks of FD. Ex vivo measurements were made of scleral biomechanical properties (unconfined compression: n = 24), scleral sulfated glycosaminoglycan (sGAG) content (dimethylmethylene blue: n = 18, and immunohistochemistry: n = 22), and ocular all-trans retinoic acid (atRA) concentrations (retina and RPE + choroid + sclera, n = 24). Age-matched naïve controls were included for some outcomes (n = 32 eyes).

Results

Significant myopia developed after 1 (-2.4 ± 1.1 diopters [D], P < 0.001) and 3 weeks of FD (-4.1 ± 0.7 D, P = 0.025; mean ± standard deviation). Scleral tensile stiffness and permeability were significantly altered during myopigenesis (stiffness = -31.4 ± 12.7%, P < 0.001, and permeability = 224.4 ± 205.5%, P < 0.001). Total scleral sGAG content was not measurably altered; however, immunohistochemistry indicated a sustained decrease in chondroitin-4-sulfate and a slower decline in dermatan sulfate. The atRA increased in the retinas of eyes form-deprived for 1 week.

Conclusions

We report that biomechanics and GAG content of the mouse sclera are altered during myopigenesis. All scleral outcomes generally follow the trends found in other species and support a retina-to-sclera signaling cascade underlying mouse myopigenesis.

Altered Retinal Dopamine Levels in a Melatonin-proficient Mouse Model of Form-deprivation Myopia

Reduced levels of retinal dopamine, a key regulator of eye development, are associated with experimental myopia in various species, but are not seen in the myopic eyes of C57BL/6 mice, which are deficient in melatonin, a neurohormone having extensive interactions with dopamine. Here, we examined the relationship between form-deprivation myopia (FDM) and retinal dopamine levels in melatonin-proficient CBA/CaJ mice. We found that these mice exhibited a myopic refractive shift in form-deprived eyes, which was accompanied by altered retinal dopamine levels. When melatonin receptors were pharmacologically blocked, FDM could still be induced, but its magnitude was reduced, and retinal dopamine levels were no longer altered in FDM animals, indicating that melatonin-related changes in retinal dopamine levels contribute to FDM. Thus, FDM is mediated by both dopamine level-independent and melatonin-related dopamine level-dependent mechanisms in CBA/CaJ mice. The previously reported unaltered retinal dopamine levels in myopic C57BL/6 mice may be attributed to melatonin deficiency.

Hypoxia-Induced Scleral HIF-2α Upregulation Contributes to Rises in MMP-2 Expression and Myopia Development in Mice

Purpose

Scleral hypoxia is a key factor that induces hypoxia-inducible factor-1α (HIF-1α) upregulation, and this response contributes to myopia progression. Currently, we aim to determine if the different HIF subtypes, including HIF-1α and HIF-2α, mediate hypoxia-induced myopia development through promoting scleral MMP-2 expression and collagen degradation.

Methods

Our study included: (1) time-course of scleral HIF-2α, MMP-2, and COL1α1 expression during form-deprivation myopia (FDM) development was determined in C57BL/6J mice. (2) The effect of silencing either HIF-1Α or HIF-2A on hypoxia-induced alterations in MMP-2 expression was analyzed in cultured human scleral fibroblasts (HSFs) under a hypoxic condition (i.e. 1% oxygen). (3) To knock-down either HIF-1α or HIF-2α expression in the sclera, we performed Sub-Tenon's capsule injection of an adeno-associated virus (AAV)8-packaged Cre overexpression vector (AAV8-Cre) in HIF-1α^fl/fl or HIF-2α^fl/fl mice. HIF-1α, HIF-2α, MMP-2, and COL1α1 expression were analyzed by Western blot or quantitative real-time PCR (qRT-PCR). In addition, the effects of scleral HIF-2α knock-down on normal refractive development and FDM development were evaluated.

Results

The time-dependent increases in scleral HIF-2α mimicked the HIF-1α expression profiles as we previously described. Hypoxia significantly promoted MMP-2 expression in HSFs, and this upregulation was solely alleviated by HIF-2A rather than HIF-1A silencing. Scleral HIF-2α knockdown significantly inhibited form-deprivation (FD)-induced MMP-2 upregulation and declines in COL1α1 accumulation and myopia development. Although scleral HIF-1α knockdown also significantly suppressed FD-induced declines in COL1α1 accumulation, it did not abrogate scleral MMP-2 upregulation.

Conclusions

HIF-2α rather than HIF-1α induces myopia development through upregulating MMP-2 and promoting collagen degradation in the sclera.

The role of ipRGCs in ocular growth and myopia development

The increasing global prevalence of myopia calls for elaboration of the pathogenesis of this disease. Here, we show that selective ablation and activation of intrinsically photosensitive retinal ganglion cells (ipRGCs) in developing mice induced myopic and hyperopic refractive shifts by modulating the corneal radius of curvature (CRC) and axial length (AL) in an opposite way. Melanopsin- and rod/cone-driven signals of ipRGCs were found to influence refractive development by affecting the AL and CRC, respectively. The role of ipRGCs in myopia progression is evidenced by attenuated form-deprivation myopia magnitudes in ipRGC-ablated and melanopsin-deficient animals and by enhanced melanopsin expression/photoresponses in form-deprived eyes. Cell subtype-specific ablation showed that M1 subtype cells, and probably M2/M3 subtype cells, are involved in ocular development. Thus, ipRGCs contribute substantially to mouse eye growth and myopia development, which may inspire novel strategies for myopia intervention.

Candidate pathways for retina to scleral signaling in refractive eye growth

The global prevalence of myopia, or nearsightedness, has increased at an alarming rate over the last few decades. An eye is myopic if incoming light focuses prior to reaching the retinal photoreceptors, which indicates a mismatch in its shape and optical power. This mismatch commonly results from excessive axial elongation. Important drivers of the myopia epidemic include environmental factors, genetic factors, and their interactions, e.g., genetic factors influencing the effects of environmental factors. One factor often hypothesized to be a driver of the myopia epidemic is environmental light, which has changed drastically and rapidly on a global scale. In support of this, it is well established that eye size is regulated by a homeostatic process that incorporates visual cues (emmetropization). This process allows the eye to detect and minimize refractive errors quite accurately and locally over time by modulating the rate of elongation of the eye via remodeling its outermost coat, the sclera. Critically, emmetropization is not dependent on post-retinal processing. Thus, visual cues appear to influence axial elongation through a retina-to-sclera, or retinoscleral, signaling cascade, capable of transmitting information from the innermost layer of the eye to the outermost layer. Despite significant global research interest, the specifics of retinoscleral signaling pathways remain elusive. While a few pharmacological treatments have proven to be effective in slowing axial elongation (most notably topical atropine), the mechanisms behind these treatments are still not fully understood. Additionally, several retinal neuromodulators, neurotransmitters, and other small molecules have been found to influence axial length and/or refractive error or be influenced by myopigenic cues, yet little progress has been made explaining how the signal that originates in the retina crosses the highly vascular choroid to affect the sclera. Here, we compile and synthesize the evidence surrounding three of the major candidate pathways receiving significant research attention - dopamine, retinoic acid, and adenosine. All three candidates have both correlational and causal evidence backing their involvement in axial elongation and have been implicated by multiple independent research groups across diverse species. Two hypothesized mechanisms are presented for how a retina-originating signal crosses the choroid - via 1) all-trans retinoic acid or 2) choroidal blood flow influencing scleral oxygenation. Evidence of crosstalk between the pathways is discussed in the context of these two mechanisms.

Form-deprivation myopia downregulates calcium levels in retinal horizontal cells in mice

The process of eye axis lengthening in myopic eyes is regulated by multiple mechanisms in the retina, and horizontal cells (HCs) are an essential interneuron in the visual regulatory system. Wherein intracellular Ca²⁺ plays an important role in the events involved in the regulatory role of HCs in the retinal neural network. It is unknown if intracellular Ca²⁺ regulation in HCs mediates changes in the retinal neural network during myopia progression. We describe here a novel calcium fluorescence indicator system that monitors HCs' intracellular Ca²⁺ levels during form-deprivation myopia (FDM) in mice. AAV injection of GCaMP6s, as a protein calcium sensor, into a Gja10-Cre mouse monitored the changes in Ca²⁺signaling in HC that accompany FDM progression in mice. An alternative Gja10-Cre/Ai96-GCaMP6s mouse model was created by cross mating Gja10-Cre with Ai96 mice. Immunofluorescence imaging and live imaging of the retinal cells verified the identity of these animal models. Changes in retinal horizontal cellular Ca²⁺ levels were resolved during FDM development. The numbers of GCaMP6s and the proportion of HCs were tracked based on profiling changes in GCaMP6s⁺calbindin⁺/calbindin⁺ coimmunostaining patterns. They significantly decreased more after either two days (P < 0.01) or two weeks (P < 0.001) in form deprived eyes than in the untreated fellow eyes. These decreases in their proportion reached significance only in the retinal central region rather than also in the retinal periphery. A novel approach employing a GCaMP6s mouse model was developed that may ultimately clarify if HCs mediate Ca²⁺ signals that contribute to controlling FDM progression in mice. The results indicate so far that FDM progression is associated with declines in HC Ca²⁺ signaling activity.

Melanopsin modulates refractive development and myopia

Myopia, or nearsightedness, is the most common form of refractive abnormality and is characterized by excessive ocular elongation in relation to ocular power. Retinal neurotransmitter signaling, including dopamine, is implicated in myopic ocular growth, but the visual pathways that initiate and sustain myopia remain unclear. Melanopsin-expressing retinal ganglion cells (mRGCs), which detect light, are important for visual function, and have connections with retinal dopamine cells. Here, we investigated how mRGCs influence normal and myopic refractive development using two mutant mouse models: Opn4-/- mice that lack functional melanopsin photopigments and intrinsic mRGC responses but still receive other photoreceptor-mediated input to these cells; and Opn4DTA/DTA mice that lack intrinsic and photoreceptor-mediated mRGC responses due to mRGC cell death. In mice with intact vision or form-deprivation, we measured refractive error, ocular properties including axial length and corneal curvature, and the levels of retinal dopamine and its primary metabolite, L-3,4-dihydroxyphenylalanine (DOPAC). Myopia was measured as a myopic shift, or the difference in refractive error between the form-deprived and contralateral eyes. We found that Opn4-/- mice had altered normal refractive development compared to Opn4+/+ wildtype mice, starting ∼4D more myopic but developing ∼2D greater hyperopia by 16 weeks of age. Consistent with hyperopia at older ages, 16 week-old Opn4-/- mice also had shorter eyes compared to Opn4+/+ mice (3.34 vs 3.42 mm). Opn4DTA/DTA mice, however, were more hyperopic than both Opn4+/+ and Opn4-/- mice across development ending with even shorter axial lengths. Despite these differences, both Opn4-/- and Opn4DTA/DTA mice had ∼2D greater myopic shifts in response to form-deprivation compared to Opn4+/+ mice. Furthermore, when vision was intact, dopamine and DOPAC levels were similar between Opn4-/- and Opn4+/+ mice, but higher in Opn4DTA/DTA mice, which differed with age. However, form-deprivation reduced retinal dopamine and DOAPC by ∼20% in Opn4-/- compared to Opn4+/+ mice but did not affect retinal dopamine and DOPAC in Opn4DTA/DTA mice. Lastly, systemically treating Opn4-/- mice with the dopamine precursor L-DOPA reduced their form-deprivation myopia by half compared to non-treated mice. Collectively our findings show that disruption of retinal melanopsin signaling alters the rate and magnitude of normal refractive development, yields greater susceptibility to form-deprivation myopia, and changes dopamine signaling. Our results suggest that mRGCs participate in the eye's response to myopigenic stimuli, acting partly through dopaminergic mechanisms, and provide a potential therapeutic target underling myopia progression. We conclude that proper mRGC function is necessary for correct refractive development and protection from myopia progression.

Efficacy of low-concentration atropine (0.01%) eye drops for prevention of axial myopic progression in premyopes

Purpose

Low-concentration atropine (LCA; 0.01%) is known to reduce the progression of myopia in axial myopes. The purpose of this study was to understand the role of LCA in premyopic children in preventing progression.

Methods

A randomized case-control study of known premyopes was done between the use of LCA and no intervention. A total of 30 children were included in both groups.

Results

The mean age in the LCA group was 7.7 ± 2.1 years (5-12 years), and in the control group, it was 7.2 ± 1.9 years (4-12 years). The mean baseline progression per year in the LCA group (before starting the eye drops) was - 0.72 ± 0.3 D, and in the control group, it was - 0.69 ± 0.4 D. At the end of the first year, the mean progression in the LCA group was - 0.31 ± 0.3 D versus - 0.76 ± 0.4 D, and the axial length increase was 0.12 ± 0.1 mm in the LCA group and 0.21 ± 0.2 mm in the control group. At the end of the second year, the mean progression compared with the baseline in the LCA group was - 0.6 ± 0.3 D versus - 1.75 ± 0.4 D, and the axial length showed an increase from baseline in the LCA group by 0.21 ± 0.2 mm, and in the control group, the increase was 0.48 ± 0.2 mm in 2 years.

Conclusion

Low-concentration eye drops (0.01%) work in preventing the progression of axial myopia in premyopic children.

Young adults with myopia have lower concentrations of neuromodulators-dopamine and melatonin in serum and tear

The purpose of this experimental case-control study was to explore the association between myopia and concentration of dopamine and melatonin in serum and tear fluid among young myopic adults, compared to age matched non-myopic controls. Healthy myopic adults with Spherical equivalent refraction (SER) of ≤ -0.50 D to -6.00 D and emmetropic adults were included in the study. All participants underwent comprehensive eye examination and ocular biometric measures that included-axial length and corneal radii. Insomnia symptom questionnaire (ISQ) was used to screen the symptoms associated with the diagnostic criteria for primary insomnia. Morning serum and tear concentration of dopamine and melatonin were collected and was quantified using High performance liquid chromatography. A total number of 40 participants, 21 myopes and 19 controls, with a median (IQR) age of myopes 24 [21-34] years and controls 24 [20-29] years were studied. The Median [IQR] of SER was -2.00[-6.25-(-0.50)] D and 0 [(-0.50)-0.25] D for myopes and controls respectively. Myopes were found to have significantly lower concentration of serum dopamine (Median [IQR]) 190 [50-342] ng/mL compared to controls (Median [IQR]) 411 [84-717] ng/mL (U = 88, p < 0.002). Likewise, myopes showed significantly lower serum melatonin concentration of 40 [20-169] ng/mL compared to controls 203 [22-539] ng/mL (U = 88.50, p < 0.001). Myopes exhibited lower concentration of tear dopamine 101 [8-188] ng/mL compared to controls 136 [25-451] ng/mL (U = 103, p < 0.05). Likewise, myopes showed significantly lower tear melatonin concentration 6 [2-18] ng/mL compared to controls 9 [2-23] ng/mL (U = 104, p < 0.05). Both serum dopamine (r = 0.419, p < 0.05) and melatonin (r = 0.323, p < 0.05) showed significant positive association with increase in spherical equivalent refraction (SER). The observed changes in the decreased concentration of Dopamine and Melatonin among young adult myopes and its association with refraction indicates the role of altered circadian rhythm in the human myopia mechanism.

Form-Deprivation and Lens-Induced Myopia Are Similarly Affected by Pharmacological Manipulation of the Dopaminergic System in Chicks

Purpose

Animal models have demonstrated a link between decreases in retinal dopamine levels and the development of form-deprivation myopia (FDM). However, the consistency of dopamine's role in the other major form of experimental myopia, that of lens-induced myopia (LIM), is less clear, raising the question as to what extent dopamine plays a role in human myopia. Therefore, to better define the role of dopamine in both forms of experimental myopia, we examined how consistent the protection afforded by dopamine and the dopamine agonist 6-amino-5,6,7,8-tetrahydronaphthalene-2,3-diol hydrobromide (ADTN) is between FDM and LIM.

Methods

Intravitreal injections of dopamine (0.002, 0.015, 0.150, 1.500 µmol) or ADTN (0.001, 0.010, 0.100, 1.000 µmol) were administered daily to chicks developing FDM or LIM. Axial length and refraction were measured following 4 days of treatment. To determine the receptor subtype by which dopamine and ADTN inhibit FDM and LIM, both compounds were coadministered with either the dopamine D2-like antagonist spiperone (0.005 µmol) or the D1-like antagonist SCH-23390 (0.005 µmol).

Results

Intravitreal administration of dopamine or ADTN inhibited the development of FDM (ED₅₀ = 0.003 µmol and ED₅₀ = 0.011 µmol, respectively) and LIM (ED₅₀ = 0.002 µmol and ED₅₀ = 0.010 µmol, respectively) in a dose-dependent manner, with a similar degree of protection observed in both paradigms (P = 0.471 and P = 0.969, respectively). Coadministration with spiperone, but not SCH-23390, inhibited the protective effects of dopamine and ADTN against the development of both FDM (P = 0.214 and P = 0.138, respectively) and LIM (P = 0.116 and P = 0.100, respectively).

Conclusions

pharmacological targeting of the retinal dopamine system inhibits FDM and LIM in a similar dose-dependent manner through a D2-like mechanism.

Ambient Light Regulates Retinal Dopamine Signaling and Myopia Susceptibility

Purpose

Exposure to high-intensity or outdoor lighting has been shown to decrease the severity of myopia in both human epidemiological studies and animal models. Currently, it is not fully understood how light interacts with visual signaling to impact myopia. Previous work performed in the mouse retina has demonstrated that functional rod photoreceptors are needed to develop experimentally-induced myopia, alluding to an essential role for rod signaling in refractive development.

Methods

To determine whether dim rod-dominated illuminance levels influence myopia susceptibility, we housed male C57BL/6J mice under 12:12 light/dark cycles with scotopic (1.6 × 10⁻³ candela/m²), mesopic (1.6 × 10¹ cd/m²), or photopic (4.7 × 10³ cd/m²) lighting from post-natal day 23 (P23) to P38. Half the mice received monocular exposure to −10 diopter (D) lens defocus from P28–38. Molecular assays to measure expression and content of DA-related genes and protein were conducted to determine how illuminance and lens defocus alter dopamine (DA) synthesis, storage, uptake, and degradation and affect myopia susceptibility in mice.

Results

We found that mice exposed to either scotopic or photopic lighting developed significantly less severe myopic refractive shifts (lens treated eye minus contralateral eye; –1.62 ± 0.37D and −1.74 ± 0.44D, respectively) than mice exposed to mesopic lighting (–3.61 ± 0.50D; P < 0.005). The 3,4-dihydroxyphenylacetic acid /DA ratio, indicating DA activity, was highest under photopic light regardless of lens defocus treatment (controls: 0.09 ± 0.011 pg/mg, lens defocus: 0.08 ± 0.008 pg/mg).

Conclusions

Lens defocus interacted with ambient conditions to differentially alter myopia susceptibility and DA-related genes and proteins. Collectively, these results show that scotopic and photopic lighting protect against lens-induced myopia, potentially indicating that a broad range of light levels are important in refractive development.

Dysfunction of VIPR2 leads to myopia in humans and mice

Background

Myopia is the leading cause of refractive errors. As its pathogenesis is poorly understood, we determined if the retinal VIP-VIPR2 signalling pathway axis has a role in controlling signalling output that affects myopia development in mice.

Methods

Association analysis meta-study, single-cell transcriptome, bulk RNA sequencing, pharmacological manipulation and VIPR2 gene knockout studies were used to clarify if changes in the VIP-VIPR2 signalling pathway affect refractive development in mice.

Results

The SNP rs6979985 of the VIPR2 gene was associated with high myopia in a Chinese Han cohort (randomceffect model: p=0.013). After either 1 or 2 days’ form deprivation (FD) retinal VIP mRNA expression was downregulated. Retinal single-cell transcriptome sequencing showed that VIPR2 was expressed mainly by bipolar cells. Furthermore, the cAMP signalling pathway axis was inhibited in some VIPR2+ clusters after 2 days of FD. The selective VIPR2 antagonist PG99-465 induced relative myopia, whereas the selective VIPR2 agonist Ro25-1553 inhibited this response. In Vipr2 knockout (Vipr2-KO) mice, refraction was significantly shifted towards myopia (p<0.05). The amplitudes of the bipolar cell derived b-waves in 7-week-old Vipr2-KO mice were significantly larger than those in their WT littermates (p<0.05).

Conclusions

Loss of VIPR2 function likely compromises bipolar cell function based on presumed changes in signal transduction due to altered signature electrical wave activity output in these mice. As these effects correspond with increases in form deprivation myopia (FDM), the VIP-VIPR2 signalling pathway axis is a viable novel target to control the development of this condition.

Levodopa inhibits the development of lens-induced myopia in chicks

Animal models have demonstrated a link between dysregulation of the retinal dopamine system and the development of myopia (short-sightedness). We have previously demonstrated that topical application of levodopa in chicks can inhibit the development of form-deprivation myopia (FDM) in a dose-dependent manner. Here, we examine whether this same protection is observed in lens-induced myopia (LIM), and whether levodopa’s protection against FDM and LIM occurs through a dopamine D1- or D2-like receptor mechanism. To do this, levodopa was first administered daily as an intravitreal injection or topical eye drop, at one of four ascending doses, to chicks developing LIM. Levodopa’s mechanism of action was then examined by co-administration of levodopa injections with D1-like (SCH-23390) or D2-like (spiperone) dopamine antagonists in chicks developing FDM or LIM. For both experiments, levodopa’s effectiveness was examined by measuring axial length and refraction after 4 days of treatment. Levodopa inhibited the development of LIM in a dose-dependent manner similar to its inhibition of FDM when administered via intravitreal injections or topical eye drops. In both FDM and LIM, levodopa injections remained protective against myopia when co-administered with SCH-23390, but not spiperone, indicating that levodopa elicits its protection through a dopamine D2-like receptor mechanism in both paradigms.

Short-Wavelength (Violet) Light Protects Mice From Myopia Through Cone Signaling

Purpose

Exposure to short-wavelength light influences refractive development and inhibits myopic development in many animal models. Retinal mechanisms underlying this response remain unknown. This study used a mouse model of lens-induced myopia to evaluate the effect of different wavelength light on refractive development and dopamine levels in the retina. A possible retinal pathway is tested using a mutant mouse with dysfunctional cones.

Methods

Wild-type C57BL/6J (WT) and ALS/LtJ/Gnat2^cpfl3 (Gnat2^−/−) mice were exposed to one of three different light conditions beginning at postnatal day 28: broad-spectrum “white” (420-680 nm), medium wavelength “green” (525 ± 40 nm), and short wavelength “violet” (400 ± 20 nm). One-half of the mice received hyperopic lens defocus. All mice were exposed to the light for 4 weeks; animals were measured weekly for refractive error and axial parameters. Retinal dopamine and the dopamine metabolite 3,4-dihydroxyphenylacetic acid were measured by HPLC.

Results

In WT mice, short-wavelength violet light induced hyperopia and violet light inhibited lens-induced myopia when compared with mice exposed to white light. Hyperopia could be attributed to shallower vitreous chambers in WT animals. There were no changes in the levels of dopamine or its metabolite. In Gnat2^−/− mice, violet light did not induce hyperopia or inhibit lens-induced myopia.

Conclusions

These findings show that short-wavelength light slows refractive eye growth, producing hyperopic responses in mice and inhibiting lens-induced myopia. The lack of inhibition in mice with dysfunctional cones suggests that cone signaling plays a role in the hyperopic response to short-wavelength (violet) light.

Increased endogenous dopamine prevents myopia in mice

Experimental evidence suggests that dopamine (DA) modulates refractive eye growth. We evaluated whether increasing endogenous DA activity using pharmacological or genetic approaches decreased myopia susceptibility in mice. First, we assessed the effects of systemic L-3,4-dihydroxyphenylalanine (L-DOPA) injections on form deprivation myopia (FDM) in C57BL/6 J (WT^C57) mice. WT^C57 mice received daily systemic injections of L-DOPA (n = 11), L-DOPA + ascorbic acid (AA, n = 22), AA (n = 20), or Saline (n = 16). Second, we tested transgenic mice with increased or decreased expression of vesicular monoamine transporter 2 (VMAT2^HI, n = 22; WT^HI, n = 18; VMAT2^LO, n = 18; or WT^LO, n = 9) under normal and form deprivation conditions. VMAT2 packages DA into vesicles, affecting DA release. At post-natal day 28 (P28), monocular FD was induced in each genotype. Weekly measurements of refractive error, corneal curvature, and ocular biometry were performed until P42 or P49. WT^C57 mice exposed to FD developed a significant myopic shift (treated-contralateral eye) in AA (-3.27 ± 0.73D) or saline (-3.71 ± 0.80D) treated groups that was significantly attenuated by L-DOPA (-0.73 ± 0.90D, p = 0.0002) or L-DOPA + AA (-0.11 ± 0.46D, p = 0.0103). The VMAT2^LO mice, with under-expression of VMAT2, were most susceptible to FDM. VMAT2^LO mice developed significant myopic shifts to FD after one week compared to VMAT2^HI and WT mice (VMAT2^LO: -5.48 ± 0.54D; VMAT2^HI: -0.52 ± 0.92D, p < 0.05; WT: -2.13 ± 0.78D, p < 0.05; ungoggled control: -0.22 ± 0.24D, p < 0.001). These results indicate that endogenously increasing DA synthesis and release by genetic and pharmacological methods prevents FDM in mice.

Effectiveness and safety of topical levodopa in a chick model of myopia

Animal models have demonstrated a link between dysregulation of the retinal dopamine system and the excessive ocular growth associated with the development of myopia. Here we show that intravitreal or topical application of levodopa, which is widely used in the treatment of neurological disorders involving dysregulation of the dopaminergic system, inhibits the development of experimental myopia in chickens. Levodopa slows ocular growth in a dose dependent manner in chicks with a similar potency to atropine, a common inhibitor of ocular growth in humans. Topical levodopa remains effective over chronic treatment periods, with its effectiveness enhanced by coadministration with carbidopa to prevent its premature metabolism. No changes in normal ocular development (biometry and refraction), retinal health (histology), or intraocular pressure were observed in response to chronic treatment (4 weeks). With a focus on possible clinical use in humans, translation of these avian safety findings to a mammalian model (mouse) illustrate that chronic levodopa treatment (9 months) does not induce any observable changes in visual function (electroretinogram recordings), ocular development, and retinal health, suggesting that levodopa may have potential as a therapeutic intervention for human myopia.

Optic nerve crush modulates refractive development of the C57BL/6 mouse by changing multiple ocular dimensions

Higher visual centers could modulate visually-guided ocular growth, in addition to local mechanisms intrinsic to the eye. There is evidence that such central modulations could be species (even subspecies)-dependent. While the mouse has recently become an important experimental animal in myopia studies, it remains unclear whether and how visual centers modulate refractive development in mice, an issue that was examined in the present study. We found that optic nerve crush (ONC), performed at P18, could modify normal refractive development in the C57BL/6 mouse raised in normal visual environment. Unexpectedly, sham surgery caused a steeper cornea, leading to a modest myopic refractive shift, but did not induce significant changes in ocular axis length. ONC caused corneal flattening and re-calibrated the refractive set-point in a bidirectional manner, causing significant myopic (<-3 D, 54.5%) or hyperopic (>+3 D, 18.2%) shifts in refractive error in most (totally 72.7%) animals, both due to changes in ocular axial length. ONC did not change the density of dopaminergic amacrine cells, but increased retinal levels of dopamine and DOPAC. We conclude that higher visual centers are likely to play a role in fine-tuning of ocular growth, thus modifying refractive development in the C57BL/6 mouse. The changes in refractive error induced by ONC are accounted for by alternations in multiple ocular dimensions, including corneal curvature and axial length.

The ipRGC-Driven Pupil Response with Light Exposure, Refractive Error, and Sleep

SIGNIFICANCE

We investigated links between the intrinsically photosensitive retinal ganglion cells, light exposure, refractive error, and sleep. Results showed that morning melatonin was associated with light exposure, with modest differences in sleep quality between myopes and emmetropes. Findings suggest a complex relationship between light exposure and these physiological processes.

PURPOSE

Intrinsically photosensitive retinal ganglion cells (ipRGCs) signal environmental light, with pathways to the midbrain to control pupil size and circadian rhythm. Evidence suggests that light exposure plays a role in refractive error development. Our goal was to investigate links between light exposure, ipRGCs, refractive error, and sleep.

METHODS

Fifty subjects, aged 17-40, participated (19 emmetropes and 31 myopes). A subset of subjects (n = 24) wore an Actiwatch Spectrum for 1 week. The Pittsburgh Sleep Quality Index (PSQI) was administered, and saliva samples were collected for melatonin analysis. The post-illumination pupil response (PIPR) to 1 s and 5 s long- and short-wavelength stimuli was measured. Pupil metrics included the 6 s and 30 s PIPR and early and late area under the curve.

RESULTS

Subjects spent 104.8 ± 46.6 min outdoors per day over the previous week. Morning melatonin concentration (6.9 ± 3.5 pg/ml) was significantly associated with time outdoors and objectively measured light exposure (P = .01 and .002, respectively). Pupil metrics were not significantly associated with light exposure or refractive error. PSQI scores indicated good sleep quality for emmetropes (score 4.2 ± 2.3) and poor sleep quality for myopes (5.6 ± 2.2, P = .04).

CONCLUSIONS

We found that light exposure and time outdoors influenced morning melatonin concentration. No differences in melatonin or the ipRGC-driven pupil response were observed between refractive error groups, although myopes exhibited poor sleep quality compared to emmetropes. Findings suggest that a complex relationship between light exposure, ipRGCs, refractive error, and sleep exists.

Altered ocular parameters from circadian clock gene disruptions

The pathophysiology of refractive errors is poorly understood. Myopia (nearsightedness) in particular both blurs vision and predisposes the eye to many blinding diseases during adulthood. Based on past findings of diurnal variations in the dimensions of the eyes of humans and other vertebrates, altered diurnal rhythms of these ocular dimensions with experimentally induced myopia, and evolving evidence that ambient light exposures influence refractive development, we assessed whether disturbances in circadian signals might alter the refractive development of the eye. In mice, retinal-specific knockout of the clock gene Bmal1 induces myopia and elongates the vitreous chamber, the optical compartment separating the lens and the retina. These alterations simulate common ocular findings in clinical myopia. In Drosophila melanogaster, knockouts of the clock genes cycle or period lengthen the pseudocone, the optical component of the ommatidium that separates the facet lens from the photoreceptors. Disrupting circadian signaling thus alters optical development of the eye in widely separated species. We propose that mechanisms of myopia include circadian dysregulation, a frequent occurrence in modern societies where myopia also is both highly prevalent and increasing at alarming rates. Addressing circadian dysregulation may improve understanding of the pathogenesis of refractive errors and introduce novel therapeutic approaches to ameliorate myopia development in children.

IMI - Report on Experimental Models of Emmetropization and Myopia

The results of many studies in a variety of species have significantly advanced our understanding of the role of visual experience and the mechanisms of postnatal eye growth, and the development of myopia. This paper surveys and reviews the major contributions that experimental studies using animal models have made to our thinking about emmetropization and development of myopia. These studies established important concepts informing our knowledge of the visual regulation of eye growth and refractive development and have transformed treatment strategies for myopia. Several major findings have come from studies of experimental animal models. These include the eye's ability to detect the sign of retinal defocus and undergo compensatory growth, the local retinal control of eye growth, regulatory changes in choroidal thickness, and the identification of components in the biochemistry of eye growth leading to the characterization of signal cascades regulating eye growth and refractive state. Several of these findings provided the proofs of concepts that form the scientific basis of new and effective clinical treatments for controlling myopia progression in humans. Experimental animal models continue to provide new insights into the cellular and molecular mechanisms of eye growth control, including the identification of potential new targets for drug development and future treatments needed to stem the increasing prevalence of myopia and the vision-threatening conditions associated with this disease.

Effects of the Tyrosinase-Dependent Dopaminergic System on Refractive Error Development in Guinea Pigs

Purpose

To determine if myopia in albino guinea pigs is linked to altered ocular dopamine (DA) levels in both the retinal and uveal dopaminergic systems.

Methods

Retina and retinal pigment epithelium (RPE)/choroid were dissected from eyes of 2-week-old albino myopic (AM) and pigmented hyperopic (PH) guinea pigs. The levels of DA, dihydroxy-phenyl acetic acid (DOPAC), and homovanillic acid (HVA) were determined. Tyrosine hydroxylase (TH) and tyrosinase activities were also measured. PH animals received daily unilateral peribulbar injections of either kojic acid (tyrosinase inhibitor) or vehicle for 2 to 4 weeks. Refractive errors and ocular axial dimensions were measured by eccentric infrared photoretinoscopy and A-scan ultrasonography.

Results

Retinal DA levels were similar between the two strains, but AM eyes had higher levels of DOPAC. RPE/choroid DA and tyrosinase activity in AM eyes were lower than in PH eyes (P < 0.01); however, the DA turnover was higher (P < 0.05). After 2 weeks of kojic acid treatment, PH eyes developed significant myopia, accompanied by elongated vitreous chambers and axial lengths. Inhibition of tyrosinase activity was linearly correlated with a myopic refraction shift (R = 0.79, P < 0.01). PH animals that received 62.5 ng/mL kojic acid treatment daily for 2 weeks followed by 625 ng/mL for 2 more weeks became more myopic and had deeper anterior chambers compared to those that received the 62.5 ng/mL dose over this period (P = 0.04).

Conclusions

The uveal tyrosinase-dependent dopaminergic system is involved in the development of guinea pig refraction. Enhancing uveal tyrosinase activity might slow down the development of myopia.

Dopamine Deficiency Mediates Early Rod-Driven Inner Retinal Dysfunction in Diabetic Mice

Purpose

Electroretinograms (ERGs) are abnormal in diabetic retinas before the appearance of vascular lesions, providing a possible biomarker for diabetic vision loss. Previously, we reported that decreased retinal dopamine (DA) levels in diabetic rodents contributed to early visual and retinal dysfunction. In the current study, we examined whether oscillatory potentials (OPs) could serve as a potential marker for detecting early inner retinal dysfunction due to retinal DA deficiency.

Methods

Retinal function was tested with dark-adapted ERGs, taken at 3, 4, and 5 weeks after diabetes induction with streptozotocin. Electrical responses were analyzed and correlations were made with previously reported retinal DA levels. The effect of restoring systemic DA levels or removing DA from the retina in diabetic mice on OPs was assessed using L-3,4-dihydroxyphenylalanine (L-DOPA) treatments and retina-specific tyrosine hydroxylase (Th) knockout mice (rTHKO), respectively.

Results

Diabetic animals had significantly delayed OPs compared to control animals in response to dim, but not bright, flash stimuli. L-DOPA treatment preserved OP implicit time in diabetic mice. Diabetic rTHKO mice had further delayed OPs compared to diabetic mice with normal retinal Th, with L-DOPA treatment also providing benefit. Decreasing retinal DA levels significantly correlated with increasing OP delays mediated by rod pathways.

Conclusions

Our data suggest that inner retinal dysfunction in early-stage diabetes is mediated by rod-pathway deficits and DA deficiencies. OP delays may be used to determine the earliest functional deficits in diabetic retinopathy and to establish an early treatment window for DA therapies that may prevent progressive vision loss.

Circadian rhythms, refractive development, and myopia

PURPOSE

Despite extensive research, mechanisms regulating postnatal eye growth and those responsible for ametropias are poorly understood. With the marked recent increases in myopia prevalence, robust and biologically-based clinical therapies to normalize refractive development in childhood are needed. Here, we review classic and contemporary literature about how circadian biology might provide clues to develop a framework to improve the understanding of myopia etiology, and possibly lead to rational approaches to ameliorate refractive errors developing in children.

RECENT FINDINGS

Increasing evidence implicates diurnal and circadian rhythms in eye growth and refractive error development. In both humans and animals, ocular length and other anatomical and physiological features of the eye undergo diurnal oscillations. Systemically, such rhythms are primarily generated by the 'master clock' in the surpachiasmatic nucleus, which receives input from the intrinsically photosensitive retinal ganglion cells (ipRGCs) through the activation of the photopigment melanopsin. The retina also has an endogenous circadian clock. In laboratory animals developing experimental myopia, oscillations of ocular parameters are perturbed. Retinal signaling is now believed to influence refractive development; dopamine, an important neurotransmitter found in the retina, not only entrains intrinsic retinal rhythms to the light:dark cycle, but it also modulates refractive development. Circadian clocks comprise a transcription/translation feedback control mechanism utilizing so-called clock genes that have now been associated with experimental ametropias. Contemporary clinical research is also reviving ideas first proposed in the nineteenth century that light exposures might impact refraction in children. As a result, properties of ambient lighting are being investigated in refractive development. In other areas of medical science, circadian dysregulation is now thought to impact many non-ocular disorders, likely because the patterns of modern artificial lighting exert adverse physiological effects on circadian pacemakers. How, or if, such modern light exposures and circadian dysregulation contribute to refractive development is not known.

SUMMARY

The premise of this review is that circadian biology could be a productive area worthy of increased investigation, which might lead to the improved understanding of refractive development and improved therapeutic interventions.

In Vivo Imaging of the Retina, Choroid, and Optic Nerve Head in Guinea Pigs

PURPOSE

Guinea pigs are increasingly being used as a model of myopia, and may also represent a novel model of glaucoma. Here, optical coherence tomography (OCT) imaging was performed in guinea pigs. In vivo measurements of retinal, choroidal, and optic nerve head parameters were compared with histology, and repeatability and interocular variations were assessed.

METHODS

OCT imaging and histology were performed on adult guinea pigs (n = 9). Using a custom program in MATLAB, total retina, ganglion cell/nerve fiber layer (GC/NFL), outer retina, and choroid thicknesses were determined. Additionally, Bruch's membrane opening (BMO) area and diameter, and minimum rim width were calculated. Intraobserver, interocular, and intersession coefficients of variation (CV) and intraclass correlation coefficients (ICC) were assessed.

RESULTS

Retina, GC/NFL, outer retina and choroid thicknesses from in vivo OCT imaging were 147.7 ± 5.8 μm, 59.2 ± 4.5 μm, 72.4 ± 2.4 μm, and 64.8 ± 11.6 μm, respectively. Interocular CV ranged from 1.8% to 11% (paired t-test, p = 0.16 to 0.81), and intersession CV ranged from 1.1% to 5.6% (p = 0.12 to 0.82), with the choroid showing the greatest variability. BMO area was 0.192 ± 0.023 mm², and diameter was 493.79 ± 31.89 μm, with intersession CV of 3.3% and 1.7%, respectively. Hyper reflective retinal layers in OCT correlated with plexiform and RPE layers in histology.

CONCLUSION

In vivo OCT imaging and quantification of guinea pig retina and optic nerve head parameters were repeatable and similar between eyes of the same animal. In vivo visibility of retinal cell layers correlated well with histological images.

ABBREVIATIONS

optic nerve head (ONH), retinal ganglion cell (RGC), spectral domain optical coherence tomography (SD-OCT), enhanced depth imaging (EDI), minimum rim width (MRW), hematoxylin and eosin (H & E).

Allergic Conjunctivitis-induced Retinal Inflammation Promotes Myopia Progression

Myopia is a highly prevalent eye disease. There is limited information suggesting a relationship between myopia and inflammation. We found children with allergic conjunctivitis (AC) had the highest adjusted odds ratio (1.75, 95% confidence interval [CI], 1.72-1.77) for myopia among the four allergic diseases. A cohort study was conducted and confirmed that children with AC had a higher incidence and subsequent risk of myopia (hazard ratio 2.35, 95%CI 2.29-2.40) compared to those without AC. Lower refractive error and longer axial length were observed in an AC animal model. Myopia progression was enhanced by tumor necrosis factor (TNF)-α or interleukin (IL)-6 administration, two cytokines secreted by mast cell degranulation. The TNF-α or IL-6 weakened the tight junction formed by corneal epithelial (CEP) cells and inflammatory cytokines across the layer of CEP cells, which increased the levels of TNF-α, IL-6, and IL-8 secreted by retinal pigment epithelial cells. The expression levels of TNF-α, IL-6, IL-8, monocyte chemoattractant protein-1, and nuclear factor kappa B were up-regulated in eyes with AC, whereas IL-10 and the inhibitor of kappa B were down-regulated. In conclusion, the experimental findings in mice corroborate the epidemiological data showing that allergic inflammation influences the development of myopia.

Dopamine signaling and myopia development: What are the key challenges

In the face of an "epidemic" increase in myopia over the last decades and myopia prevalence predicted to reach 2.5 billion people by the end of this decade, there is an urgent need to develop effective and safe therapeutic interventions to slow down this "myopia booming" and prevent myopia-related complications and vision loss. Dopamine (DA) is an important neurotransmitter in the retina and mediates diverse functions including retina development, visual signaling, and refractive development. Inspired by the convergence of epidemiological and animal studies in support of the inverse relationship between outdoor activity and risk of developing myopia and by the close biological relationship between light exposure and dopamine release/signaling, we felt it is timely and important to critically review the role of DA in myopia development. This review will revisit several key points of evidence for and against DA mediating light control of myopia: 1) the causal role of extracellular retinal DA levels, 2) the mechanism and action of dopamine D1 and D2 receptors and 3) the roles of cellular/circuit retinal pathways. We examine the experiments that show causation by altering DA, DA receptors and visual pathways using pharmacological, transgenic, or visual environment approaches. Furthermore, we critically evaluate the safety issues of a DA-based treatment strategy and some approaches to address these issues. The review identifies the key questions and challenges in translating basic knowledge on DA signaling and myopia from animal studies into effective pharmacological treatments for myopia in children.

Association of Body Length with Ocular Parameters in Mice

PURPOSE

To determine the association between changes in body length with ocular refraction, corneal radii, axial length, and lens thickness in two different mouse strains.

METHODS

Body length, ocular refraction, corneal radii, axial length, and lens thickness were measured for two inbred mouse strains: 129S1/SvJ (n = 7) and C57BL/6 J (n = 10) from 4 to 12 weeks of age. Body length, from tip of nose to base of tail, was obtained using a digital camera. Biometric parameters, corneal radii, and refractions were measured using spectral-domain optical coherence tomography, automated keratometry, and infrared photorefraction, respectively. A mixed-model ANOVA was performed to examine the changes in ocular parameters as a function of body length and strain in mice controlling for age, gender, and weight over time.

RESULTS

C57BL/6J mice had significantly longer body length (average body length at 10 weeks, 8.60 ± 0.06 cm) compared to 129S1/SvJ mice (8.31 ± 0.05 cm) during development (P < .001). C57BL/6J mice had significantly hyperopic refractions compared to 129S1/SvJ mice across age (mean refraction at 10 weeks, 129S1/SvJ: +0.99 ± 0.44D vs. C57BL/6J: +6.24 ± 0.38D, P < .001). Corneal radius of curvature, axial length, and lens thickness (except 10 weeks lens thickness) were similar between the two strains throughout the measurement. In the mixed-model ANOVA, changes in body length showed an independent and significant association with the changes in refraction (P = .002) and corneal radii (P = .016) for each mouse strain. No significant association was found between the changes in axial length (P = .925) or lens thickness (P = .973) as a function of body length and strain.

CONCLUSIONS

Changes in body length are significantly associated with the changes in ocular refraction and corneal radii in different mouse strains. Future studies are needed to determine if the association between body length and ocular refraction are related to changes in corneal curvature in mice.