Effects of pirenzepine on pupil size and accommodation in rhesus monkeys

A Spontaneous Nonhuman Primate Model of Myopic Foveoschisis

Purpose

Foveoschisis involves the pathologic splitting of retinal layers at the fovea, which may occur congenitally in X-linked retinoschisis (XLRS) or as an acquired complication of myopia. XLRS is attributed to functional loss of the retinal adhesion protein retinoschisin 1 (RS1), but the pathophysiology of myopic foveoschisis is unclear due to the lack of animal models. Here, we characterized a novel nonhuman primate model of myopic foveoschisis through clinical examination and multimodal imaging followed by morphologic, cellular, and transcriptional profiling of retinal tissues and genetic analysis.

Methods

We identified a rhesus macaque with behavioral and anatomic features of myopic foveoschisis, and monitored disease progression over 14 months by fundus photography, fluorescein angiography, and optical coherence tomography (OCT). After necropsy, we evaluated anatomic and cellular changes by immunohistochemistry and transcriptomic changes using single-nuclei RNA-sequencing (snRNA-seq). Finally, we performed Sanger and whole exome sequencing with focus on the RS1 gene.

Results

Affected eyes demonstrated posterior hyaloid traction and progressive splitting of the outer plexiform layer on OCT. Immunohistochemistry showed increased GFAP expression in Müller glia and loss of ramified Iba-1+ microglia, suggesting macro- and microglial activation with minimal photoreceptor alterations. SnRNA-seq revealed gene expression changes predominantly in cones and retinal ganglion cells involving chromatin modification, suggestive of cellular stress at the fovea. No defects in the RS1 gene or its expression were detected.

Conclusions

This nonhuman primate model of foveoschisis reveals insights into how acquired myopic traction leads to phenotypically similar morphologic and cellular changes as congenital XLRS without alterations in RS1.

Epiregulin, epigen and betacellulin antibodies and axial elongation in young guinea pigs with lens-induced myopization

Background

To examine an effect of intravitreally applied antibodies against epidermal growth factor family members, namely epiregulin, epigen and betacellulin, on ocular axial elongation.

Methods

The experimental study included 30 guinea pigs (age:3–4 weeks) which underwent bilateral lens-induced myopization and received three intraocular injections of 20 µg of epiregulin antibody, epigen antibody and betacellulin antibody in weekly intervals into their right eyes, and of phosphate-buffered saline into their left eyes. Seven days after the last injection, the animals were sacrificed. Axial length was measured by sonographic biometry.

Results

At baseline, right eyes and left eyes did not differ (all P > 0.10) in axial length in neither group, nor did the interocular difference in axial length vary between the groups (P = 0.19). During the study period, right and left eyes elongated (P < 0.001) from 8.08 ± 0.07 mm to 8.59 ± 0.06 mm and from 8.08 ± 0.07 mm to 8.66 ± 0.07 mm, respectively. The interocular difference (left eye minus right eye) in axial elongation increased significantly in all three groups (epiregulin-antibody:from 0.03 ± 0.06 mm at one week after baseline to 0.16 ± 0.08 mm at three weeks after baseline;P = 0.001); epigen-antibody group:from -0.01 ± 0.06 mm to 0.06 ± 0.08 mm;P = 0.02; betacellulin antibody group:from -0.05 ± 0.05 mm to 0.02 ± 0.04 mm;P = 0.004). Correspondingly, interocular difference in axial length increased from -0.02 ± 0.04 mm to 0.13 ± 0.06 mm in the epiregulin-antibody group (P < 0.001), and from 0.01 ± 0.05 mm to 0.07 ± 0.05 mm in the epigen-antibody group (P = 0.045). In the betacellulin-antibody group the increase (0.01 ± 0.04 mm to 0.03 ± 0.03 mm) was not significant (P = 0.24).

Conclusions

The EGF family members epiregulin, epigen and betacellulin may be associated with axial elongation in young guinea pigs, with the effect decreasing from epiregulin to epigen and to betacellulin.

Blockade of epidermal growth factor and its receptor and axial elongation in experimental myopia

To examine the influence of epidermal growth factor (EGF) and its receptor (EGFR) on axial ocular elongation, we intraocularly injected an EGF antibody and an EGFR antibody into young guinea pigs with lens-induced axial elongation (myopization). Mean axial elongation was reduced in the eyes injected with the EGF/EGFR-antibody compared with the contralateral control eyes injected with PBS (phosphate-buffered solution) (0.43 ± 0.13 mm vs 0.53 ± 0.13 mm; P < .001). The intereye difference in axial length increased (P = .005) as the doses of the EGF antibody and EGFR antibody increased. As a corollary, the thickness of the retina at the posterior pole was dose-dependently increased in the injected eyes compared to the contralateral control eyes. Immunohistochemical staining for EGF and the relative mRNA expression of EGF and EGFR were the highest in eyes not injected with the EGF antibody or EGFR antibody and decreased (P < .05) as the dose of EGF antibody or EGFR antibody increased. In an in vitro study, EGF had a stimulating effect and the EGF antibody had an inhibitory effect on the proliferation and migration of RPE cells. The findings showed that the intravitreal application of an EGF antibody and EGFR antibody is associated with a dose-dependent reduction in lens-induced axial elongation in young guinea pigs. The EGFR family may play a role in axial elongation of the eye and in the development of myopia.

Amphiregulin and ocular axial length

PURPOSE

To assess the potential role of amphiregulin as messenger molecule in ocular axial elongation.

METHODS

The experimental study included guinea pigs (total n = 78) (age: 3-4 weeks) which underwent bilateral lens-induced myopization and received 15 days later three intraocular injections in weekly intervals of amphiregulin antibody (doses:5 μg, 10 μg, 20 μg) into their right eyes, and three phosphate-buffered saline injections into their left eyes; and guinea pigs without lens-induced myopization and which received three unilateral intraocular injections of amphiregulin antibody (dose: 20 μg) or amphiregulin (doses: 1 ng; 10 ng; 20 ng) into their right eyes, and three phosphate-buffered saline injections into their left eyes. Seven days later, the animals were sacrificed. Intravitally, we performed biometry, and histology and immunohistochemistry post-mortem.

RESULTS

In animals with bilateral lens-induced myopization, the right eyes receiving amphiregulin antibody showed reduced axial elongation in a dose-dependent manner (dose: 5 μg: side difference: 0.14 ± 0.05 mm;10 μg: 0.22 ± 0.06 mm; 20 μg: 0.32 ± 0.06 mm; p < 0.001), thicker sclera (all p < 0.05) and higher cell density in the retinal nuclear layers and retinal pigment epithelium (RPE) (all p < 0.05). In animals without lens-induced myopia, the right eyes with amphiregulin antibody application (20 μg) showed reduced axial elongation (p = 0.04), and the right eyes with amphiregulin injections experienced increased (p = 0.02) axial elongation in a dose-dependent manner (1 ng: 0.04 ± 0.06 mm; 10 ng: 0.10 ± 0.05 mm; 20 ng: 0.11 ± 0.06 mm). Eyes with lens-induced axial elongation as compared to eyes without lens-induced axial elongation revealed an increased visualization of amphiregulin upon immunohistochemistry and higher expression of mRNA of endogenous amphiregulin and epidermal growth factor receptor, in particular in the outer part of the retinal inner nuclear layer and in the RPE.

CONCLUSION

Amphiregulin may be associated with axial elongation in young guinea pigs.

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.

Update in myopia and treatment strategy of atropine use in myopia control

The prevalence of myopia is increasing globally. Complications of myopia are associated with huge economic and social costs. It is believed that high myopia in adulthood can be traced back to school age onset myopia. Therefore, it is crucial and urgent to implement effective measures of myopia control, which may include preventing myopia onset as well as retarding myopia progression in school age children. The mechanism of myopia is still poorly understood. There are some evidences to suggest excessive expansion of Bruch’s membrane, possibly in response to peripheral hyperopic defocus, and it may be one of the mechanisms leading to the uncontrolled axial elongation of the globe. Atropine is currently the most effective therapy for myopia control. Recent clinical trials demonstrated low-dose atropine eye drops such as 0.01% resulted in retardation of myopia progression, with significantly less side effects compared to higher concentration preparation. However, there remain a proportion of patients who are poor responders, in whom the optimal management remains unclear. Proposed strategies include stepwise increase of atropine dosing, and a combination of low-dose atropine with increase outdoor time. This review will focus on the current understanding of epidemiology, pathophysiology in myopia and highlight recent clinical trials using atropine in the school-aged children, as well as the treatment strategy in clinical implementation in hyperopic, pre-myopic and myopic children.

α-adrenergic agonist brimonidine control of experimentally induced myopia in guinea pigs: A pilot study

PURPOSE

To investigate the efficacy of α-adrenergic agonist brimonidine either alone or combined with pirenzepine for inhibiting progressing myopia in guinea pig lens-myopia-induced models.

METHODS

Thirty-six guinea pigs were randomly divided into six groups: Group A received 2% pirenzepine, Group B received 0.2% brimonidine, Group C received 0.1% brimonidine, Group D received 2% pirenzepine + 0.2% brimonidine, Group E received 2% pirenzepine + 0.1% brimonidine, and Group F received the medium. Myopia was induced in the right eyes of all guinea pigs using polymethyl methacrylate (PMMA) lenses for 3 weeks. Eye drops were administered accordingly. Intraocular pressure was measured every day. Refractive error and axial length measurements were performed once a week. The enucleated eyeballs were removed for hematoxylin and eosin (H&E) and Van Gieson (VG) staining at the end of the study.

RESULTS

The lens-induced myopia model was established after 3 weeks. Treatment with 0.1% brimonidine alone and 0.2% brimonidine alone was capable of inhibiting progressing myopia, as shown by the better refractive error (p=0.024; p=0.006) and shorter axial length (p=0.005; p=0.0017). Treatment with 0.1% brimonidine and 0.2% brimonidine combined with 2% pirenzepine was also effective in suppressing progressing refractive error (p=0.016; p=0.0006) and axial length (p=0.017; p=0.0004). The thickness of the sclera was kept stable in all groups except group F; the sclera was much thinner in the lens-induced myopia eyes compared to the control eyes.

CONCLUSIONS

Treatment with 0.1% brimonidine alone and 0.2% brimonidine alone, as well as combined with 2% pirenzepine, was effective in inhibiting progressing myopia. The result indicates that intraocular pressure elevation is possibly a promising mechanism and potential treatment for progressing myopia.

Training regimen involving cyclic induction of pupil constriction during far accommodation improves visual acuity in myopic children

PURPOSE

Myopia in school-age children has become increasingly prevalent in industrialized countries, especially in Asia. A large population of school-age children still suffers from low visual acuity. We have developed a novel, safe and noninvasive training method to activate a pupillary constriction response during far accommodation that results in improved visual acuity.

METHODS

Myopic children (n = 95) were treated for 3-minute sessions up to twice a week for 12-106 weeks. We stimulated quick cycles of near/far accommodation by displaying a visual object on a LCD screen and moving the screen in cycles from a near (25 cm) to a far (70 cm) point and back, while keeping the retinal projection size and brightness of the object constant.

RESULTS

Mechanistically, we noted pupillary constriction upon far accommodation in trained myopic children, which was not seen in normal subjects or in untrained myopic children. Eighty five percent (52/61) of trained myopic right eyes with two sessions weekly experienced improved visual acuity (VA) by more than 0.1 logMAR units with an average improvement of 0.30 +/- 0.03 standard error of mean (SEM) logMAR units. With maintained training, most eyes' improved VA stayed almost constant, for more than 50 weeks in the case of 12 long trained subjects.

CONCLUSIONS

This simple, short and safe accommodation training greatly improves the quality of vision in a large population suffering from refractive abnormalities.

Autonomic drugs and the accommodative system in rhesus monkeys

Accommodation and pupil constriction result from parasympathetic stimulation from the Edinger-Westphal (EW) nucleus of the midbrain resulting in release of acetylcholine at the neuromuscular junctions of the ciliary muscle and iris. Cholinergic and adrenergic drugs can be applied topically to evaluate the effects on the pupil and accommodative system without input from the EW nucleus. This study is directed at characterizing how topical low dose echothiophate, an anti-cholinesterase inhibitor (i.e., an indirect cholinergic agonist), epinephrine, an adrenergic agonist, and timolol maleate, a beta adrenergic antagonist, affect pupil diameter, resting refraction and accommodative amplitude and dynamics in rhesus monkeys. The effects of 0.015% echothiophate, 2% epinephrine, 0.5% timolol maleate and saline on pupil diameter and resting refraction were measured in one eye each of four normal rhesus monkeys for 60-90 min following topical instillation. Pupil diameter was measured with infrared videography and refraction was measured with a Hartinger coincidence refractometer. Effects on static and dynamic EW stimulated accommodation were studied in three iridectomized monkeys (ages 5, 6 and 12 years) with permanent indwelling stimulating electrodes in the EW nucleus. Dynamic accommodative responses were measured with infrared photorefraction for increasing current amplitudes before and during the course of action of the pharmacological agents. Echothiophate caused a significant decrease in pupil diameter of 3.07 +/- 0.65 mm (mean +/- SEM, p < 0.01), and a myopic shift in resting refraction of 1.30 +/- 0.39 D (p < 0.05) 90 min after instillation. Epinephrine caused a 2.76 +/- 0.38 mm (p < 0.01) increase in pupil diameter with no change in resting refraction 60 min after instillation. Timolol maleate resulted in no significant change in either pupil diameter or resting refraction 60 min after instillation. There was no significant change in maximum EW stimulated accommodative amplitude after any agent tested. The amplitude vs. peak velocity relationship for accommodation was significantly different after echothiophate and timolol maleate, and for disaccommodation after echothiophate, epinephrine and timolol maleate. In conclusion, when tested objectively in anesthetized monkeys, epinephrine and timolol maleate did not alter resting refraction or accommodative amplitude, but did have small, significant affects on accommodative dynamics. This suggests that there is an adrenergic component to the accommodative system. Low dose echothiophate had significant effects on pupil diameter and resting refraction, with only small effects on the dynamics of the accommodative response.

Glucagon-related peptides in the mouse retina and the effects of deprivation of form vision

BACKGROUND

In chickens, retinal glucagon amacrine cells play an important role in emmetropization, since they express the transcription factor ZENK (also known as NGFI-A, zif268, tis8, cef5, Krox24) in correlation with the sign of imposed image defocus. Pharmacological studies have shown that glucagon can act as a stop signal for axial eye growth, making it a promising target for pharmacological intervention of myopia. Unfortunately, in mammalian retina, glucagon itself has not yet been detected by immunohistochemical staining. To learn more about its possible role in emmetropization in mammals, we studied the expression of different members of the glucagon hormone family in mouse retina, and whether their abundance is regulated by visual experience.

METHODS

Black wildtype C57BL/6 mice, raised under a 12/12 h light/dark cycle, were studied at postnatal ages between P29 and P40. Frosted hemispherical thin plastic shells (diffusers) were placed in front of the right eyes to impose visual conditions that are known to induce myopia. The left eyes remained uncovered and served as controls. Transversal retinal cryostat sections were single- or double-labeled by indirect immunofluorescence for early growth response protein 1 (Egr-1, the mammalian ortholog of ZENK), glucagon, glucagon-like peptide-2 (GLP-2), glucose-dependent insulinotropic polypeptide (GIP), peptide histidine isoleucine (PHI), growth hormone-releasing hormone (GHRH), pituitary adenylate cyclase-activating polypeptide (PACAP), secretin, and vasoactive intestinal polypeptide (VIP). In total, retinas of 45 mice were studied, 28 treated with diffusers, and 17 serving as controls.

RESULTS

Glucagon itself was not detected in mouse retina. VIP, PHI, PACAP and GIP were localized. VIP was co-localized with PHI and Egr-1, which itself was strongly regulated by retinal illumination. Diffusers, applied for various durations (1, 2, 6, and 24 h) had no effect on the expression of VIP, PHI, PACAP, and GIP, at least at the protein level. Similarly, even if the analysis was confined to cells that also expressed Egr-1, no difference was found between VIP expression in eyes with diffusers and in eyes with normal vision.

CONCLUSIONS

Several members of the glucagon super family are expressed in mouse retina (although not glucagon itself), but their expression pattern does not seem to be regulated by visual experience.

Effects of pharmacologically manipulated amplitude and starting point on edinger-westphal-stimulated accommodative dynamics in rhesus monkeys

PURPOSE

The aim of this study was to determine whether pharmacologically manipulated resting refraction, amplitude, and starting point affect accommodative and disaccommodative dynamics in anesthetized adolescent rhesus monkeys.

METHODS

Pilocarpine and atropine were applied topically to manipulate resting refraction, accommodative amplitude, starting point, and end point in two monkeys with permanent electrodes in the Edinger-Westphal nucleus. Accommodation was centrally stimulated with submaximal and maximal current amplitudes. Dynamic accommodative responses were measured with infrared photorefraction before and during the course of action of the drugs. Accommodative and disaccommodative dynamics were analyzed in terms of peak velocity as a function of amplitude, starting point, and end point.

RESULTS

Pilocarpine caused a myopic shift in resting refraction of 11.62 +/- 1.17 D. Centrally stimulated accommodative amplitude was 10.08 +/- 1.15 D before pilocarpine and 0.68 +/- 0.29 D after pilocarpine. Changes were found in accommodative dynamics as a function of starting point and in disaccommodative dynamics as a function of amplitude and end point. Accommodative amplitude was 11.25 +/- 0.18 D before atropine administration and 0.52 +/- 0.11 D after atropine administration. Accommodative dynamics as a function of amplitude were not substantially altered during the course of pilocarpine-induced accommodation or atropine-induced cycloplegia.

CONCLUSIONS

Accommodative response amplitude is reduced with pilocarpine by shifting the eye to a more myopic state and with atropine by cycloplegia. Pharmacologic manipulations showed that accommodative and disaccommodative dynamics in anesthetized monkeys depend on amplitude, starting point, and end point of the response and on the contributions of neural and receptor activity.

Effects of intravitreally and intraperitoneally injected atropine on two types of experimental myopia in chicken

Atropine, a non-selective muscarinic receptor antagonist, is currently the most potent agent used to prevent myopia in animal models and children. However, the ocular target tissues are not well defined. To learn more about the effect of atropine on experimental myopia, atropine was applied both intravitreally and systemically (intraperitoneally) to chickens wearing either negative lenses or light diffusers. Furthermore, the effect of ipsilateral intravitreal atropine on myopia development in the saline-treated fellow eye was studied. Monocular intravitreal injections of atropine were performed daily for a period of 4 successive days, starting at day 8 post-hatching. Fellow eyes received saline injections. Chicks were fitted with -7D lenses, either over the atropine-injected eyes only (unilateral "lens-induced myopia (LIM)"), or over both eyes (bilateral LIM). Other groups of chicks were fitted with translucent diffusers over the atropine-injected eyes (unilateral "form deprivation myopia (FDM)"). Finally, atropine was intraperitoneally injected for 4 days in chicks that wore monocularly -7D lenses. Refractive errors (RE) were measured with infrared photoretinoscopy and axial length (AL) with A-scan ultrasonography. Atropine prevented development of myopia in both unilateral LIM and FDM in a dose-dependent fashion. Fifty percent inhibition of myopia was observed at a dose of 25 microg (unilateral LIM) or 90 microg atropine (bilateral LIM) and complete inhibition at 750 microg; in unilateral FDM, 50% inhibition occurred at 2.5 microg and almost 100% inhibition at 250 microg. Interestingly, at the highest dose of atropine (2500 microg), the treated eyes became even more hyperopic compared to the saline-injected contralateral eyes with normal visual experience. In the bilateral LIM model, atropine suppressed development of myopia in both the treated and the saline-injected control eye. However, about 8.3 times higher doses were necessary to achieve comparable contralateral suppression. Since this ratio is lower than the vitreous volume to blood volume ratio (about 1:23 in young chicks), it seems unlikely that systemic dilution of the intravitreally injected drug can fully account for the contralateral suppression. Intraperitoneal injection inhibited myopia development only at the highest dose (2500 microg) but, strikingly, this inhibition was still less when the same dose was provided through the vitreous of the fellow eye. Both eyes seem to be coupled by a yet unknown, perhaps neuronal pathway. Estimations of the scleral concentrations of atropine after intravitreal injection are compatible with the assumption that the suppression of myopia by atropine occurs by direct inhibition of scleral chondrocytes.

HPLC determination of pirenzepine dihydrochloride in rabbit aqueous humor

Pirenzepine was considered as a pharmacologic agent of preventing form-deprivation myopia. To assess the ocular bioavailability of pirenzepine, a HPLC method for determination of pirenzepine in rabbit aqueous humor was developed. An HPLC system was used in the reverse phase mode for the determination of pirenzepine. A Luna RP18 5 microm 4.6 mm x 150 mm column was employed at 35 degrees C. The mobile phase was methanol/0.02 M KH2PO4/sodium 1-pentanesulfonate (350/650/1, v/v/m, pH was adjusted to 8.0 by dropping 1M NaOH). The flow rate was 1 ml/min. Pirenzepine was monitored at 280 nm. Sample treatment procedure consists of deproteinisation with methanol. Calibration curves fitted by plotting the peak area versus concentration were linear in the range 20-400 ng/ml. The limit of quantification (LOQ) of present method was 20 ng/ml. Within-day and inter-day coefficient of variation was lower than 10%. Analytical recoveries were determined as 92.4, 95.4 and 101.4% at concentrations of 40, 200 and 400 ng/ml. In conclusion, this HPLC method using a simple sample treatment procedure appears suitable for monitoring ocular concentration of pirenzepine.

Dynamics of accommodative fatigue in rhesus monkeys and humans

Changes in accommodative dynamics with repeated accommodation were studied in three anesthetized rhesus monkeys and two conscious humans. Maximum accommodation was centrally stimulated via the Edinger-Westphal nucleus in monkeys with a 4 s on, 4 s off paradigm (4 x 4) for 17 min, 4 x 1.5 for 27 min and 2 x 1 for 16 min. Humans accommodated repeatedly to visual targets (5 x 5; 5D and 2 x 2; 6D) for 30 min. In all cases, accommodation was sustained throughout. The anesthetized monkeys showed inter-individual variability in the extent of changes in accommodative dynamics over time while no systematic changes were detected in the human accommodative responses. Little accommodative fatigue was found compared to previous studies which have reported a complete loss of accommodation after 5 min of repeated stimulation in monkeys.