Intravitreal brimonidine inhibits form-deprivation myopia in guinea pigs

Key role for inflammation-related signaling in the pathogenesis of myopia based on evidence from proteomics analysis

The mechanisms underlying myopia pathogenesis are not well understood. Using publicly-available human and animal datasets, we expound on the roles of known, implicated proteins, and new myopia-related signaling pathways were hypothesized. Proteins identified from human serum or ocular fluids, and from ocular tissues in myopic animal models, were uploaded and analyzed with the QIAGEN Ingenuity Pathway Analysis (IPA) software (March 2023). With each IPA database update, more potentially-relevant proteins and signaling pathways previously unavailable during data acquisition are added, allowing extraction of novel conclusions from existing data. Canonical pathway analysis was used to analyze these data and calculate an IPA activation z-score-which indicates not only whether an association is significant, but also whether the pathway is likely activated or inhibited. Cellular immune response and cytokine signaling were frequently found to be affected in both human and animal myopia studies. Analysis of two publicly-available proteomic datasets highlighted a potential role of the innate immune system and inflammation in myopia development, detailing specific signaling pathways involved such as Granzyme A (GzmA) and S100 family signaling in the retina, and activation of myofibroblast trans-differentiation in the sclera. This perspective in myopia research may facilitate development of more effective and targeted therapeutic agents.

The potential of brimonidine for myopia treatment: Targeting MMP-2 to regulate choroidal thickness and control eye growth

Drug treatment studies are a focal point for identifying novel approaches to reduce myopia progression through basic science research. Here, we investigated the effects of various brimonidine administration routes and concentrations on form-deprivation myopia (FDM) progression, matrix metalloproteinase-2 (MMP-2), and collagen alpha1 chain of type I (COL1A1) expression in the retinal pigment epithelial (RPE)-choroid complex and sclera of guinea pigs. They demonstrate that brimonidine has the capacity to impede choroidal thinning induced by FDM, potentially through the induction of choroidal vasodilation. Additionally, we observed that brimonidine effectively counteracts FDM-induced downregulation of choroidal and scleral MMP-2 expression. Suppression of MMP-2 expression may reduce disruption of scleral and choroidal structural integrity which reduces declines in choroidal blood circulation and mitigates increases in ocular elongation. This research elucidates the effects of brimonidine on myopia progression, offering potential insights into therapeutic interventions for myopia.

Retinoscopes: Past and present

BACKGROUND

Retinoscopy is arguably the most important method in the eye clinic for diagnosing and managing refractive errors. Advantages of retinoscopy include its non-invasive nature, ability to assess patients of all ages, and usefulness in patients with limited cooperation or communication skills.

AIM

To discuss the history of retinoscopes and examine current literature on the subject.

METHODS

A search was conducted on the PubMed and with the reference citation analysis (https://www.referencecitationanalysis.com) database using the term "Retinoscopy," with a range restricted to the last 10 years (2013-2023). The search string algorithm was: "Retinoscopy" (MeSH Terms) OR "Retinoscopy" (All Fields) OR "Retinoscopes" (All Fields) AND [(All Fields) AND 2013: 2023 (pdat)].

RESULTS

This systematic review included a total of 286 records. Publications reviewed iterations of the retinoscope into autorefractors, infrared photo retinoscope, television retinoscopy, and the Wifi enabled digital retinoscope.

CONCLUSION

The retinoscope has evolved significantly since its discovery, with a significant improvement in its diagnostic capabilities. While it has advantages such as non-invasiveness and broad applicability, limitations exist, and the need for skilled interpretation remains. With ongoing research, including the integration of artificial intelligence, retinoscopy is expected to continue advancing and playing a vital role in eye care.

Construction of glaucoma model and comparing eyeball enlargement with myopia in Guinea pig

This study aimed to develop and evaluate a guinea pig model for glaucoma, comparing resultant eyeball enlargement with an existing myopia model. Thirty guinea pigs underwent intracameral injection of magnetic microspheres to induce chronic ocular hypertension (COH). Intraocular pressure (IOP) was systematically monitored, revealing a successful induction of COH in 73.33% of the guinea pigs. The mean IOP increased from a baseline of 18.04 ± 1.33 mmHg, reaching a peak at week 3 (36.31 ± 6.13 mmHg) and remaining elevated for at least 7 weeks. All data are presented as mean ± standard deviation of the mean. Subsequently, detailed assessments were conducted to validate the established glaucoma model. Immunofluorescent staining demonstrated a significant decrease in the density of retinal ganglion cells (RGC) in the glaucoma group. Optic disc excavation and notable thinning of the lamina cribrosa (LC) were observed. The quantity of optic nerve ax·ons in glaucoma group gradually decreased from baseline (44553 ± 3608/mm2) to week 4 (28687 ± 2071/mm2) and week 8 (17977 ± 3697/mm2). Moreover, regarding the global enlargement of eyeballs, both the transverse and longitudinal axis in glaucomatous eyes were found to be significantly larger than that in myopic eyes, particularly in the anterior chamber depth (1.758 ± 0.113 mm vs. 1.151 ± 0.046 mm). These findings indicate distinct patterns of structural changes associated with glaucoma and myopia in the guinea pig model. This guinea pig model holds promise for future research aimed at exploring biomechanical mechanisms, therapeutic interventions, and advancing our understanding of the relationship between glaucoma and myopia.

Brimonidine as a possible treatment for myopia

BACKGROUND

Myopia is becoming a huge burden on the world's public health systems. The purpose of this study was to explore the effect of brimonidine in the treatment of form-deprivation myopia (FDM) and the relationship between intraocular pressure (IOP) and myopia development.

METHODS

Monocular form deprivation myopia (FDM) was induced in three-week-old pigmented male guinea pigs. They were treated with 3 different methods of brimonidine administration (eye drops, and subconjunctival or intravitreal injections). Four different concentrations of brimonidine were tested for each method (2µg/µL, 4µg/µL, 20µg/µL, and 40µg/µL). All treatments continued for a period of 21 days. Tonometry, retinoscopy, and A-scan ultrasonography were used to monitor intraocular pressure, refractive error and axial length (AL), respectively.

RESULTS

Treatment with subconjunctival brimonidine at 40µg/µL, and intravitreal brimonidine at 2µg/µL and 4µg/µL, inhibited the development of FDM. The myopic refraction, excessive axial length, and elevation of IOP were significantly decreased. Brimonidine in eye drops was ineffective.

CONCLUSION

Brimonidine at appropriate doses significantly reduced the development of FD myopia in guinea pigs. The IOP may change with FD myopia.

Ocular Posterior Segment Distribution and Pharmacokinetics of Brimonidine After Intravitreal Administration in Guinea Pigs

Purpose: Brimonidine is a highly alpha-2 adrenergic agonist, which provides a potential myopia control effect. This study aimed to examine the pharmacokinetics and concentration of brimonidine in the posterior segment tissue of eyes in guinea pigs. Methods: A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was successfully used for brimonidine pharmacokinetics and tissue distribution research in guinea pigs following intravitreal administration (20 μg/eye). Results: Brimonidine concentrations in the retina and sclera were maintained at a high level (>60 ng/g) at 96 h postdosing. Brimonidine concentration peaked in the retina (377.86 ng/g) at 2.41 h and sclera (306.18 ng/g) at 6.98 h. The area under curve (AUC0-∞) was 27,179.99 ng h/g in the retina and 39,529.03 ng h/g in the sclera. The elimination half-life (T1/2e) was 62.43 h in the retina and 67.94 h in the sclera. Conclusions: The results indicated that brimonidine was rapidly absorbed and diffused to the retina and sclera. Meanwhile, it maintained higher posterior tissue concentrations, which can effectively activate the alpha-2 adrenergic receptor. This may provide pharmacokinetic evidence for the inhibition of myopia progression by brimonidine in animal experiments.

Epitranscriptomic investigation of myopia-associated RNA editing in the retina

Myopia is one of the most common causes of vision loss globally and is significantly affected by epigenetics. Adenosine-to-inosine (A-to-I RNA) editing is an epigenetic process involved in neurological disorders, yet its role in myopia remains undetermined. We performed a transcriptome-wide analysis of A-to-I RNA editing in the retina of form-deprivation myopia mice. Our study identified 91 A-to-I RNA editing sites in 84 genes associated with myopia. Notably, at least 27 (32.1%) of these genes with myopia-associated RNA editing showed existing evidence to be associated with myopia or related ocular phenotypes in humans or animal models, such as very low-density lipoprotein receptor (Vldlr) in retinal neovascularization and hypoxia-induced factor 1 alpha (Hif1a). Moreover, functional enrichment showed that RNA editing enriched in FDM was primarily involved in response to fungicides, a potentially druggable process for myopia prevention, and epigenetic regulation. In contrast, RNA editing enriched in controls was mostly involved in post-embryonic eye morphogenesis. Our results demonstrate altered A-to-I RNA editing associated with myopia in an experimental mouse model and warrant further study on its role in myopia development.

Effects of exogenous retinoic acid on ocular parameters in Guinea pigs with form deprivation myopia

Aim: Myopia is a common chronic eye disease, this study is to investigate the effects of exogenous retinoic acid (RA) on intraocular parameters, especially choroidal thickness (CT) and retinal thickness (RT), in guinea pigs with form deprivation myopia (FDM).

Methods: A total of 80 male guinea pigs were divided randomly into 4 groups: Control, FDM, FDM + RA, and FDM + Citral groups. The FDM + RA group was given 24 mg/kg RA dissolved in 0.4 mL peanut oil; the FDM + Citral group was given citral 445 mg/kg dissolved in 0.4 mL peanut oil; The other two groups were given 0.4 mL peanut oil. After 4 weeks, the refractive error (RE), axial length (AL), and intraocular pressure (IOP) of all guinea pigs were measured, and the parameters of RT and CT were obtained using enhanced depth imaging optical coherence tomography (EDI-OCT).

Results: After 4 weeks, both the RE and AL in the FDM and FDM + RA groups were increased, and the RT and CT in both groups were smaller than those in the Control group (p < 0.05). Only the IOP of the right eye in the FDM + RA group increased significantly (p < 0.05). The RT of the right eye of the 4 groups was compared: Control group > FDM + Citral group > FDM group > FDM + RA group. Compared with the RT of the left eye and the right eye among the 4 groups, the RT of the right eye in the FDM and FDM + RA groups was significantly less than that in the left eye (p < 0.05). Moreover, the CT of the right eye in the Control group was greater than that in the other three groups (p < 0.0001). There was no significant difference in the CT among the FDM, FDM + RA, and FDM + Citral groups (p > 0.05). In contrast to the RT results, the CT results of the left and right eyes in the FDM + Citral group showed statistically significant differences (p < 0.05).

Conclusion: RA participates in the progression of FDM as a regulatory factor. Exogenous RA can increase the RE, AL, and IOP of FDM guinea pigs, and might aggravate the retinal thinning of FDM guinea pigs. Citral can inhibit these changes, but RA might not affect the thickness of the choroid.

Comparison of the accuracy of axial length measurement by different imaging methods in Sprague Dawley rats

Background

Obtaining accurate axial length (AL) is very important for the establishment of animal models of myopia. The purpose of this study is to compare the accuracy of Quantel A-B scan, OD-1 A scan, and vernier caliper in measuring AL in Sprague Dawley (SD) rats.

Methods

In total, 60 5-week-old SD rats were divided into female rat group (n = 30) and male rat group (n = 30). Quantel A-B scan and OD-1 A scan were, respectively, used to measure the AL of both eyes of each living rat, and vernier caliper was used to measure the anterior-posterior diameter of each rat's eyeball. Besides, the correlation between refractive error (RE) and AL measured by different instruments was evaluated, and the accuracy of the three measurement methods was compared according to gender and left/right eyes.

Results

There were significant differences in AL and diopter of SD rats at the same age (p < 0.05). the AL of male rats was greater than that of female rats, while diopter (D) was the opposite; There was no significant difference in AL and D between left and right eyes in the same SD rats (p > 0.05); There were statistical differences among the three measurement methods (p < 0.05), AL measured by vernier caliper was the largest, followed by Quantel A-B scan, OD-1 A scan; Difference in AL between male and female was not statistically significant between the results obtained by Quantel A-B scan and vernier caliper (p > 0.05), but there were statistically significant differences between the other two measurement methods (p < 0.05).

Conclusion

Sex is the influencing factor of AL and RE. Imaging measurement can accurately measure the AL in living small rodents. Compared with OD-1 A scan, Quantel A-B scan may be more accurate.

Lowering Intraocular Pressure: A Potential Approach for Controlling High Myopia Progression

High myopia is among the most common causes of vision impairment, and it is mainly characterized by abnormal elongation of the axial length, leading to pathologic changes in the ocular structures. Owing to the close relationship between high myopia and glaucoma, the association between intraocular pressure (IOP) and high myopia progression has garnered attention. However, whether lowering IOP can retard the progression of high myopia is unclear. On reviewing previous studies, we suggest that lowering IOP plays a role in progressive axial length elongation in high myopia, particularly in pathologic myopia, wherein the sclera is more remodeled. Based on the responses of the ocular layers, we further proposed the potential mechanisms. For the sclera, lowering the IOP could inhibit the activation of scleral fibroblasts and then reduce scleral remodeling, and a decrease in the scleral distending force would retard the ocular expansion like a balloon. For the choroid, lowering IOP results in an increase in choroidal blood perfusion, thereby reducing scleral hypoxia and slowing down scleral remodeling. The final effect of these pathways is slowing axial elongation and the development of scleral staphyloma. Further animal and clinical studies regarding high myopia with varied degree of IOP and the changes of choroid and sclera during IOP fluctuation in high myopia are needed to verify the role of IOP in the pathogenesis and progression of high myopia. It is hoped that this may lead to the development of a prospective treatment option to prevent and control high myopia progression.