Bright light induces choroidal thickening in chickens

Myopia Is an Ischemic Eye Condition: A Review from the Perspective of Choroidal Blood Flow

Myopia is a common refractive error that affects a large proportion of the population. Recent studies have revealed that alterations in choroidal thickness (ChT) and choroidal blood flow (ChBF) play important roles in the progression of myopia. Reduced ChBF could affect scleral cellular matrix remodeling, which leads to axial elongation and further myopia progression. As ChT and ChBF could be used as potential biomarkers for the progression of myopia, several recent myopia treatments have targeted alterations in ChT and ChBF. Our review provides a comprehensive overview of the recent literature review on the relationship between ChBF and myopia. We also highlight the importance of ChT and ChBF in the progression of myopia and the potential of ChT as an important biomarker for myopia progression. This summary has significant implications for the development of novel strategies for preventing and treating myopia.

Retinal and choroidal structure and vascularity in Chinese emmetropic and myopic children

PURPOSE

This study evaluated the structural features of the retinal and choroidal regions and their correlations with ocular biometric and vascular parameters in Chinese children using optical coherence tomography angiography (OCTA).

METHODS

A total of 159 children, 6-13 years of age, were included in this prospective study. The sample consisted of 55 emmetropes (spherical equivalent ≤ +0.75 and > -0.50 D), 53 low-moderate myopes (≤ -0.50 to > -6.00 D) and 51 high myopes without pathological changes (≤ -6.00 D). Optical coherence biometry was used to measure axial length (AL) and anterior segment parameters. Swept-source optical coherence tomography/OCTA was used to assess the macular structures and vascular characteristics in a 6 × 6 mm region centred on the macula.

RESULTS

In a comprehensive analysis adjusting for age, sex, AL, macular blood perfusion, intraocular pressure and anterior segment parameters, retinal thickness (RT) showed a significant positive association with deep retinal vascular density and superficial retinal vascular density in the foveal area, but not with AL. Moreover, RT exhibited a significant negative association with AL in the parafoveal and perifoveal regions. Further, a significant positive correlation was observed between choroidal thickness and both choroidal vascular volume and choriocapillaris perfusion area, along with a negative correlation with AL across the entire macular region.

CONCLUSIONS

This study showed that the thickness of retina and choroid in Chinese children was not only associated with AL but also showed dynamic properties such as the blood perfusion of the retina and choroid, particularly in the foveal area.

Quantitative Evaluation of the Topographical Maps of Three-Dimensional Choroidal Vascularity Index in Children With Different Degrees of Myopia

Purpose

To investigate topographical maps of the three-dimensional choroidal vascularity index (3D-CVI) in children with different levels of myopia.

Methods

We enrolled 274 eyes from 143 children with various severity of myopia, including emmetropia (EM), low myopia (LM), and moderate-high myopia (MHM). The choroidal vessel volume (CVV), choroidal stroma volume (CSV), and 3D-CVI in different eccentricities (fovea, parafovea, and perifovea) and quadrants (nasal, temporal, superior, and inferior) were obtained from swept-source optical coherence tomography angiography (SS-OCTA) volume scans. All choroidal parameters were compared among groups, and the associated factors contributing to different 3D-CVIs were analyzed.

Results

Compared to the less myopic group, the more myopic group showed a significant decrease in CVV and CSV (MHM < LM < EM) and a significant increase in the 3D-CVI (MHM > LM > EM) in most areas (all P < 0.05). The nasal quadrant had the greatest 3D-CVI and lowest CSV and CVV, and vice versa in the temporal quadrant. The 3D-CVIs of the EM and LM groups gradually increased from the fovea to the perifovea, whereas the 3D-CVI of the MHM group first decreased and then increased. Regression analysis showed that axial length was an independent risk factor affecting foveal and parafoveal 3D-CVIs. Restricted cubic spline analysis revealed that the 3D-CVI increased with spherical equivalent (SE) when the SE was less than threshold and decreased when the SE was greater than threshold (SE thresholds for foveal, parafoveal, and perifoveal 3D-CVIs were -5.25 D, -5.125 D, and -2.00 D, respectively; all P < 0.05).

Conclusions

Children with myopia exhibited decreased CSV and CVV, increased 3D-CVIs, and altered 3D-CVI eccentricity characteristics (from the fovea to the perifovea). The quadratic relationship between the 3D-CVI and SE should be explored in longitudinal investigations.

Changes in choroidal hemodynamics of form-deprivation myopia in Guinea pigs

PURPOSE

We studied changes in the choroid, particularly variation in blood flow, during the development of myopia. The hemodynamic mechanism in play remains unclear. We evaluated blood flow by quantitating indocyanine green (ICG) fluorescence in a guinea pig model of form-deprivation myopia.

METHODS

Guinea pigs were divided into form-deprivation myopia (FDM) and normal control (NC) groups. Ocular biometric and choroidal hemodynamics parameters were quantitatively derived via ICG imaging, and included the maximal ICG fluorescence intensity (Imax), rising time (Trising), blood flow index (BFI), and mean transit time (MTT).

RESULTS

Form deprivation was associated with significant interocular differences in terms of both refractive error and axial length. ICG fluorescence hemodynamic maps of fundal blood flow and vasculature density were evident. In deprived eyes, the fluorescence signals exhibited significantly longer Trising and MTT but lower Imax and BFI than fellow eyes and NC group. The interocular differences in terms of the ocular biometric and hemodynamic parameters were significantly correlated. Hemodynamic analysis of choriocapillaris lobules revealed weakened fluorescence intensity and prolonged arrival and filling times in deprived eyes. Form deprivation reduced the number of lobulated choriocapillaris structures.

CONCLUSION

Form-deprivation myopia triggered changes in the hemodynamic and vascular network structures of the choroid and choriocapillaris. The ICG fluorescence imaging/analysis method provides a unique tool for further myopia research.

Impact of text contrast polarity on the retinal activity in myopes and emmetropes using modified pattern ERG

Environmental factors favoring myopia development are still being studied and there is accumulating evidence for a significant role of nearwork. Recently, reading standard black-on-white text was found to activate the retinal OFF pathway and induce choroidal thinning, which is associated with myopia onset. Contrarily, reading white-on-black text led to thicker choroids, being protective against myopia. Respective effects on retinal processing are yet unknown. Here, we exploratively assessed the impact of contrast polarity on the retinal activity and possible interactions with eccentricity and refractive error. We recorded pattern electroretinograms in myopic and emmetropic adults while presenting a dead leaves stimulus (DLS), overlaid by masks of different size in ring or circle shape, either filled with uniform gray or text of inverted or standard contrast. In myopes, retinal responses for DLS with standard and inverted contrast were larger when the perifovea was stimulated (6-12 deg), however, including the fovea resulted in smaller amplitudes for inverted contrast than in emmetropes. The retina of emmetropes was more sensitive to inverted contrast than to standard and gray within 12 deg, but most sensitive for gray in the perifovea. This demonstrates that the refractive error influences the sensitivity to text contrast polarity, with a special role of the peripheral retina, which is in line with previous studies about blur sensitivity. Defining whether the differences derive from retinal processing or anatomical features of a myopic eye requires further investigation. Our approach might be a first step to explain how nearwork promotes the eye's elongation.

The outdoor environment affects retinal and choroidal thickness

PURPOSE

Accumulating evidence suggests that time outdoors is protective against myopia development and that the choroid may be involved in this effect. The goal of this study was to examine the effect of 2 h of time outdoors in sunlight on retinal and choroidal thickness in adults.

METHODS

Twenty adults, ages 23-46 years, each participated in three experimental sessions on different days, consisting of 2 h of exposure to (1) indoor illumination (350 lux), (2) darkness (<0.1 lux) or (3) outdoor environment (6000-50,000 lux). Spectral-domain optical coherence tomography (SD-OCT) imaging was conducted at baseline, after 1 and 2 h of exposure, and after 1 and 2 h of follow-up. Choroidal, total retinal, photoreceptor outer segment + retinal pigment epithelium (RPE) and photoreceptor inner segment thicknesses were determined.

RESULTS

At 2 h, the choroid was significantly thinner during the outdoor compared with the indoor and dark conditions (p < 0.01) but was not significantly different at follow-up. Total retinal thickness was significantly thicker during and after the outdoor compared with the indoor and dark conditions. The outer segment + RPE was significantly thinner during the outdoor compared with the indoor condition but was not significantly different at follow-up. The inner segment was significantly thicker during the outdoor compared with the indoor and dark conditions during exposure and follow-up.

CONCLUSIONS

Spending 2 h outdoors under high-intensity sunlight resulted in an unexpected thinning of the choroid, which recovered post-exposure. Retinal thickness showed different responses to the outdoor and indoor environments and was sensitive to the duration of exposure.

Studies on the interactions of retinal dopamine with choroidal thickness in the chicken

PURPOSE

Recently, an increasing number of studies relied on the assumption that visually induced changes in choroidal thickness can serve as a proxy to predict future axial eye growth. The retinal signals controlling choroidal thickness are, however, not well defined. We have studied the potential roles of dopamine, released from the retina, in the choroidal response in the chicken.

METHODS

Changes in retinal dopamine release and choroidal thickness changes were induced by intravitreal injections of either atropine (250 µg or 360 nMol), atropine combined with a dopamine antagonist, spiperone (500 µMol), or spiperone alone and were tracked by optical coherence tomography (OCT). To visually stimulate dopamine release, other chicks were exposed to flicker light of 1, 10, or 400 Hz (duty cycle 0.2) and choroidal thickness was tracked. In all experiments, dopamine and 3,4-Dihydroxyphenylacetic acid (DOPAC) were measured in vitreous, retina, and choroid by high-performance liquid chromatography with electrochemical detection (HLPC-ED). The distribution of the rate-limiting enzyme of dopamine synthesis, tyrosine hydroxylase (TH), neuronal nitric oxide synthase (nNOS), vascular endothelial growth factor (VEGF), and alpha2A adrenoreceptors (alpha2A-ADR) was studied in the choroid by immunofluorescence.

RESULTS

The choroid thickened strongly in atropine-injected eyes, less so in atropine + spiperone-injected eyes and became thinner over the day in spiperone alone-, vehicle-, or non-injected eyes. Flickering light at 20 lx, both 1 and 10 Hz, prevented diurnal choroidal thinning, compared to 400 Hz, and stimulated retinal dopamine release. Correlation analysis showed that the higher retinal dopamine levels or release, the thicker became the choroid. TH-, nNOS-, VEGF-, and alpha2A adrenoreceptor-positive nerve fibers were localized in the choroid around lacunae and in the walls of blood vessels with colocalization of TH and nNOS, and TH and VEGF.

CONCLUSIONS

Retinal DOPAC and dopamine levels were positively correlated with choroidal thickness. TH-positive nerve fibers in the choroid were closely associated with peptides known to play a role in myopia development. Findings are in line with the hypothesis that dopamine is related to retinal signals controlling choroidal thickness.

Seasonal Variation in Diurnal Rhythms of the Human Eye: Implications for Continuing Ocular Growth in Adolescents and Young Adults

Purpose

To investigate the diurnal rhythms in the human eye in winter and summer in southeast Norway (latitude 60°N).

Methods

Eight measures (epochs) of intraocular pressure, ocular biometry, and optical coherence tomography were obtained from healthy participants (17–24 years of age) on a mid-winter's day (n = 35; 6 hours of daylight at solstice) and on a day the following summer (n = 24; 18 hours of daylight at solstice). Participants wore an activity monitor 7 days before measurements. The epochs were scheduled relative to the individual's habitual wake and sleep time: two in the day (morning and midday) and six in the evening (every hour until and 1 hour after sleep time). Saliva was collected for melatonin. A linear mixed-effects model was used to determine significant diurnal variations, and a sinusoid with a 24-hour period was fitted to the data with a nonlinear mixed-effects model to estimate rhythmic statistics.

Results

All parameters underwent significant diurnal variation in winter and summer (P < 0.002). A 1-hour phase advance was observed for melatonin and ocular axial length in the summer (P < 0.001). The degree of change in axial length was associated with axial length phase advance (R² = 0.81, P < 0.001) and choroidal thickening (R² = 0.54, P < 0.001) in summer.

Conclusions

Diurnal rhythms in ocular biometry appear to be synchronized with melatonin secretion in both winter and summer, revealing seasonal variation of diurnal rhythms in young adult eyes. The association between axial length and seasonal changes in the phase relationships between ocular parameters and melatonin suggests a between-individual variation in adaptation to seasonal changes in ocular diurnal rhythms.

Quantitative evaluation of retinal and choroidal vascularity and retrobulbar blood flow in patients with myopic anisometropia by CDI and OCTA

AIMS

To investigate the association between the myopic severity and retinal microvascular density, choroidal vascularity and retrobulbar blood flow in adult anisomyopes.

METHODS

This study comprised 90 eyes of 45 myopic anisomyopes who were recruited for Colour Doppler imaging (CDI) and optical coherence tomography angiography (OCTA). The superficial vessel density (SVD), deep vessel density (DVD), choroidal thickness (ChT) and choroidal vascularity, including total choroidal area (TCA), luminal area (LA), stromal area (SA) and Choroidal Vascularity Index (CVI), were measured using OCTA. Moreover, the Pulsatile Index, peak systolic velocity (PSV) and end diastolic velocity (EDV) of posterior ciliary artery (PCA), central retinal artery (CRA) and ophthalmic artery (OA) were quantified by CDI, and all parameters were compared between two eyes and the correlations among parameters were analysed.

RESULTS

The mean difference of spherical equivalent (SE) and axial lengths (AL) between eyes were -6.00±2.94 D and 2.48±1.31 mm, respectively. The SVD, DVD, ChT, TCA, LA, SA and CVI were significantly lower in more myopic eyes compared with the contralateral eyes. In more myopic eyes, CDI parameters of CRA and PSV and EDV of PCA were also significantly lower. After adjusting for age and sex, the binocular asymmetry in LA and ChT was independent risk factor affecting interocular difference in both AL and SE.

CONCLUSION

Retinal microvascular density, choroidal vascularity and retrobulbar blood flow were simultaneously lower in adult myopic anisomyopes with more myopic eyes and disturbed choroid circulation was related to the severity of myopia. Further longitudinal study was helped to identify the effect of choroidal parameters for myopic progression.

Recovery From Form-Deprivation Myopia in Chicks Is Dependent Upon the Fullness and Correlated Color Temperature of the Light Spectrum

Purpose

The purpose of this study was to evaluate the impact of full-spectrum light-emitting diodes mimicking sunlight (Sunlike LEDs) on ocular growth and refractive error development in a chicken model of myopia.

Methods

One-day old chicks (n = 39) were distributed into 3 groups and raised for 28 days in isoluminant (approximately 285 lux) fluorescent (n = 18, [FL-4000], correlated color temperature [CCT] = 4000 K) or Sunlike LED (n = 12, [SL-4000], CCT = 4000 K; n = 9, [SL-6500], CCT = 6500 K) white lighting environments. Form-deprivation myopia was induced monocularly from day 1 post-hatching (D1) until D14. On D14, form deprivation was halted and the recovery of form-deprived (FD) eyes was monitored until D28. Axial length (AL), refraction, choroidal thickness, and anterior chamber depth were measured in vivo on D1, D7, D14, D22, and D28. Differences in outcome measures between eyes and groups were compared using 2-way repeated-measures ANOVA.

Results

AL and myopic refraction of FD eyes increased similarly among groups during form-deprivation. FD eyes of animals raised under SL-4000 (D22: P < 0.001 and D28: P < 0.001) and SL-6500 (D22: P = 0.006 and D28: P < 0.001) recovered faster from axial elongation compared with animals raised under FL-4000. The refractive status of FD eyes reared under SL-6500, not under FL-4000 or SL-4000, was similar to control eyes on D28 (P > 0.05). However, SL-4000 and SL-6500 exhibited similar refraction on D28 than FL-4000 (P > 0.05). Choroidal thickness was significantly greater in FD eyes of chickens raised under SL-6500 than in animals raised under FL-4000 (P = 0.03).

Conclusions

Compared to fluorescent light, moderate intensities of full-spectrum Sunlike LEDs can accelerate recovery from form-deprivation myopia in chickens, potentially through a change in the choroid-mediated pathway.

The influence of the choroid on the onset and development of myopia: from perspectives of choroidal thickness and blood flow

Myopia is the most common type of refractive errors characterized by excessive elongation of the ocular globe. With the increasing prevalence of myopia, improved knowledge of factors involved in myopia development is of particular importance. There are growing evidence suggesting that the choroid plays an important role in the regulation of eye growth and the development of myopia. Studies have demonstrated that thinning choroid is a structural feature of myopia, with a negative correlation between choroidal thickness and axial length, suggesting that the change in choroidal thickness may be a predictive biomarker for long-term changes in ocular elongation. Given the fact that the choroid is primarily a vascular structure capable of rapidly changing blood flow, variations of choroidal thickness might be primarily caused by changes in choroidal blood flow. Considering that hypoxia is associated with myopia and choroidal blood flow is the main source of oxygen and nourishment supply, apart from the effect on myopia possibly by changing choroidal thickness, decreasing choroidal blood flow may contribute to scleral ischaemia and hypoxia, resulting in alterations in the scleral structure and thus leading to myopia. This review aims to provide an overview of recent work exploring the influence of the choroid on myopia from perspectives of choroidal thickness and blood flow, which may present new predictive indicators for the onset of myopia and new targets for the development of novel therapeutic approaches for myopia.

Increased Choroidal Blood Perfusion Can Inhibit Form Deprivation Myopia in Guinea Pigs

Purpose

In guinea pigs, choroidal thickness (ChT) and choroidal blood perfusion (ChBP) simultaneously decrease in experimental myopia, and both increase during recovery. However, the causal relationship between ChBP and myopia requires further investigation. In this study, we examined the changes of ChBP with three different antimyopia treatments. We also actively increased ChBP to examine the direct effect on myopia development in guinea pigs.

Methods

Experiment 1: Guinea pigs wore occluders on the right eye for two weeks to induce form-deprivation myopia (FDM). Simultaneously they received daily antimyopia treatments: peribulbar injections of atropine or apomorphine or exposure to intense light. Experiment 2: The vasodilator prazosin was injected daily into the form-deprivation eyes to increase ChBP during the two-week induction of FDM. Other FDM animals received appropriate control treatments. Changes in refraction, axial length, ChBP, ChT, and hypoxia-labeled pimonidazole adducts in the sclera were measured.

Results

The antimyopia treatments atropine, apomorphine, and intense light all significantly inhibited myopia development and the decrease in ChBP. The treatments also reduced scleral hypoxia, as indicated by the decrease in hypoxic signals. Furthermore, actively increasing ChBP with prazosin inhibited the progression of myopia, as well as the increase in axial length and scleral hypoxia.

Conclusions

Our data strongly indicate that increased ChBP attenuates scleral hypoxia, and thereby inhibits the development of myopia. Thus ChBP may be a promising target for myopia retardation. As such, it can serve as an immediate predictor of myopia development as well as a long-term marker of it.

Investigation of Macular Choroidal Thickness and Blood Flow Change by Optical Coherence Tomography Angiography After Posterior Scleral Reinforcement

Purpose: This work aimed to study the effect of posterior scleral reinforcement (PSR) on choroidal thickness (CT) and blood flow.

Methods: This study included 25 eyes of 24 patients with high myopia ( ≤ -6.0 dioptres or axial length ≥ 26.0 mm) who underwent PSR surgery. All patients completed the 1-month follow-up visit. Myopic macular degeneration (MMD) was graded according to the International Meta-Analysis for Pathologic Myopia (META-PM) classification based on color fundus photographs. Swept-source optical coherence tomography angiography (SSOCTA) was performed to investigate CT, choroidal perfusion area (CPA), and choriocapillaris perfusion area (CCPA) change following PSR surgery.

Results: The distribution of MMD categories was 9 (36.0%) in category 1, 10 (40.0%) in category 2, and 6 (24.0%) in category 3 or 4. MMD severity was strongly correlated with CT (all P < 0.01) and CPA (all P < 0.04). Postoperative CT at each sector increased significantly at 1 week's follow-up, compared to preoperative measures (all P < 0.05). Postoperative CPA at subfoveal, superior, inferior, and nasal sectors also increased significantly 1 week after PSR surgery (all P < 0.05). Moreover, the increased CT, CPA, and CCPA remain after PSR surgery at 1 month's follow-up, but the difference was not statistically significant.

Conclusions: We demonstrated that the CT and choroidal blood flow increased significantly in patients with high myopia who underwent PSR surgery in a short period of time. In addition, the CT and CPA were independently associated with MMD. However, whether the transient improvement of the choroidal circulation could prevent long-term progression of high myopia warrants further study in the future.

Ocular growth and metabolomics are dependent upon the spectral content of ambient white light

Myopia results from an excessive axial growth of the eye, causing abnormal projection of remote images in front of the retina. Without adequate interventions, myopia is forecasted to affect 50% of the world population by 2050. Exposure to outdoor light plays a critical role in preventing myopia in children, possibly through the brightness and blue-shifted spectral composition of sunlight, which lacks in artificial indoor lighting. Here, we evaluated the impact of moderate levels of ambient standard white (SW: 233.1 lux, 3900 K) and blue-enriched white (BEW: 223.8 lux, 9700 K) lights on ocular growth and metabolomics in a chicken-model of form-deprivation myopia. Compared to SW light, BEW light decreased aberrant ocular axial elongation and accelerated recovery from form-deprivation. Furthermore, the metabolomic profiles in the vitreous and retinas of recovering form-deprived eyes were distinct from control eyes and were dependent on the spectral content of ambient light. For instance, exposure to BEW light was associated with deep lipid remodeling and metabolic changes related to energy production, cell proliferation, collagen turnover and nitric oxide metabolism. This study provides new insight on light-dependent modulations in ocular growth and metabolomics. If replicable in humans, our findings open new potential avenues for spectrally-tailored light-therapy strategies for myopia.

Effects of Single and Repeated Intravitreal Applications of Atropine on Choroidal Thickness in Alert Chickens

INTRODUCTION

Atropine, a muscarinic antagonist, is known since the 19th century to inhibit myopia development in children. One of its effects is that it stimulates choroidal thickening. Thicker choroids, in turn, have been linked to myopia inhibition. We used the atropine-stimulated choroidal response in the chicken to learn more about the time courses and amplitudes of the effects of atropine, as well as whether repeated applications lead to accumulation or desensitization.

METHODS

Intravitreal injections containing 250 µg atropine sulfate were performed in 1 eye around 10:00 in the morning, the fellow eye received vehicle. Chickens with bilateral vehicle injections served as controls. Choroidal thickness was measured over the day for every 2-3 h in alert animals, using spectral domain optical coherence tomography, with 3-5 independent measurements in each eye. Three experiments were done - (1) single injection and time course measured over 1 day, (2) single injection and time course measured over 4 days, and (3) daily injections and time course measured over 4 days for measuring the effects of atropine on vitreal, retinal, and choroidal dopamine, and 3,4-dihydroxyphenylacetic acid levels by using high-performance liquid chromatography with electrochemical detection.

RESULTS

Atropine induced an increase in choroidal thickness by about 60 percent, with a peak amplitude after about 2 h. The effect persisted only for a few hours and had nearly disappeared by evening. Initially, similar amounts of choroidal thickening were observed in vehicle-injected fellow eyes but recovery to baseline was faster. When atropine was injected daily for 4 days, choroids thickened every day with similar amplitudes and time courses, with no signs of either accumulation or desensitization effects. Interestingly, while dopamine release from the retina was stimulated by atropine and followed approximately, the time course of choroidal thickening, its tissue concentration dropped in the choroid.

CONCLUSIONS

Even at relatively high intravitreal doses, effects of atropine on choroidal thickness remained transient, similar to its effects on retinal dopamine. With repeated application every day, the diurnal patterns of choroidal thickening could be reproduced for 4 days with similar amplitudes and time courses. The transient nature of the effects of atropine on the choroid may be relevant for application protocols of atropine against myopia.

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.

Axial length shortening in a myopic child with anisometropic amblyopia after wearing violet light-transmitting eyeglasses for 2 years

PURPOSE

To report a case in which the axial length (AL) shortened and the choroid thickened due to the use of violet light-transmitting eyeglasses.

OBSERVATIONS

A 4-year-old boy with high myopia was referred to Keio University Hospital. He was prescribed standard eyeglasses. Six months after the first visit, his best-corrected visual acuities were 1.2 and 0.4 in the right and left eyes, respectively, with the standard eyeglasses, and he was diagnosed with anisometropic amblyopia. The right eye then was patched for 6 hours daily during the daytime. Because of the availability of violet light-transmitting eyeglasses, we changed the eyeglasses and instructed his parents to have him engage in outdoor activities for over 2 hours daily to be exposed to sufficient violet light. As a result, the violet light entered his left eye and minimal violet light entered his right eye. The changes in the ALs, choroidal thicknesses, and cycloplegic objective refractions in the right and left eyes during 2 years of wearing violet light-transmitting eyeglasses were +0.85 and -0.20 mm, +4.9 and + 115.7 μm, and -1.02 and + 1.88 D, respectively.

CONCLUSIONS AND IMPORTANCE

We successfully described a case in which the myopia improved, the AL shortened, and the choroid thickened after using violet light-transmitting eyeglasses.

Effects of low intensity ambient lighting on refractive development in infant rhesus monkeys (Macaca mulatta)

Studies in chickens suggest low intensity ambient lighting causes myopia. The purpose of this experiment was to examine the effects of low intensity ambient lighting (dim light) on normal refractive development in macaque monkeys. Seven infant rhesus monkeys were reared under dim light (room illumination level: ~55 lx) from 24 to ~310 days of age with otherwise unrestricted vision. Refractive error, corneal power, ocular axial dimensions, and choroidal thickness were measured in anesthetized animals at the onset of the experiment and periodically throughout the dim-light-rearing period, and were compared with those of normal-light-reared monkeys. We found that dim light did not produce myopia; instead, dim-light monkeys were hyperopic relative to normal-light monkeys (median refractive errors at ~155 days, OD: +3.13 D vs. +2.31 D; OS: +3.31D vs. +2.44 D; at ~310 days, OD: +2.75D vs. +1.78D, OS: +3.00D vs. +1.75D). In addition, dim-light rearing caused sustained thickening in the choroid, but it did not alter corneal power development, nor did it change the axial nature of the refractive errors. These results showed that, for rhesus monkeys and possibly other primates, low ambient lighting by itself is not necessarily myopiagenic, but might compromise the efficiency of emmetropization.

Features of the Choroidal Structures in Myopic Children Based on Image Binarization of Optical Coherence Tomography

Purpose

To evaluate the features of the choroidal structures in the eyes of myopic children obtained by enhanced depth imaging optical coherence tomography (EDI-OCT).

Methods

Ninety-six myopic children with low to moderate myopia (spherical equivalent refractive error [SER], –5.75 to –1.00 diopter) were included in this cross-sectional study. Ocular biometrics were measured using an optical low-coherence reflectometry device. Data of the choroidal structures extracted from a 7500-µm cross-sectional arc of the choroid extending from the temporal optic disc margin, including the total choroidal area, luminal area, stromal area, and choroidal vascularity index, were determined by image binarization of the EDI-OCT. Associations between demographic factors, ocular parameters, and choroidal structures were evaluated using univariate and multiple linear regression analyses.

Results

The study participants (mean age, 11.02 ± 1.70 years) had a mean axial length (AL) of 24.94 ± 0.70 mm. The mean total choroidal area was 2.64 ± 0.49 mm² (luminal area, 1.68 ± 0.32 mm²; stromal area, 0.95 ± 0.19 mm²), and the choroidal vascularity index was 0.64 ± 0.03. Multiple regression analysis showed that the luminal area was significantly associated with the AL (standard β = –0.24, P = 0.022) after adjusting for sex and corneal radius (CR), whereas the stromal area (standard β = –0.30, P = 0.003) and choroidal vascularity index (standard β = 0.36, P = 0.001) were significantly associated with age after adjusting for sex, CR, and lens thickness (LT). Sex, CR, LT, and SER showed no significant association with choroidal structures after adjusting for age and AL (all P > 0.05).

Conclusions

The luminal area of the choroid tends to decrease with a longer AL, whereas the stromal area tends to decrease with increasing age in myopic children. These findings require further exploration in a longitudinal study.

Comparison of choroidal thickness in high myopic eyes after FS-LASIK versus implantable collamer lens implantation with swept-source optical coherence tomography

AIM

To investigate the changes in choroidal thickness (CT) in high myopic eyes after femtosecond laser-assisted in situ keratomileusis (FS-LASIK) surgery or central hole implantable collamer lens (ICL V4c) implantation using swept-source optical coherence tomography (SS-OCT).

METHODS

We examined the right eyes of 116 patients with high myopia who were candidates for FS-LASIK surgery and ICL implantation. Sixty eyes underwent ICL V4c implantation and 56 eyes were subjected to FS-LASIK surgery. The CT was measured with SS-OCT. All data were recorded preoperatively and 2h, 1wk, 1 and 3mo postoperatively. Other demographic information was collected, including age, sex, uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), spherical equivalent (SE), intraocular pressure (IOP) and axial length (AL).

RESULTS

The UCVA improved in both groups and showed no significant differences between groups. There also were no significant differences between the two groups in postoperative BCVA and SE (P=0.581 and 0.203, respectively). The foveal CTs, inner nasal and outer nasal CTs were significantly thicker at 2h postoperatively in both groups (P<0.05) but returned to baseline levels in 1wk; after 1mo, no significant differences were found relative to the preoperative values. At 3mo in each group, nine regions showed variations in the CT as compared with preoperative thickening, but only the foveal and nasal area CTs preoperative differences were statistically significant (P<0.05). In addition, there was no significant difference in 9 regions of CT between the two groups at all follow-up times (P>0.05).

CONCLUSION

The CTs after ICL implantation and FS-LASIK surgery are significantly thicker than those before operation, especially in the foveal and nasal areas, but there is no significant difference between the two methods.

Visual Image Quality Impacts Circadian Rhythm-Related Gene Expression in Retina and in Choroid: A Potential Mechanism for Ametropias

Purpose

Stimulated by evidence implicating diurnal/circadian rhythms and light in refractive development, we studied the expression over 24 hours of selected clock and circadian rhythm-related genes in retina/retinal pigment epithelium (RPE) and choroid of experimental ametropias in chicks.

Methods

Newly hatched chicks, entrained to a 12-hour light/dark cycle for 12 to 14 days, either experienced nonrestricted vision OU (i.e., in both eyes) or received an image-blurring diffuser or a minus 10-diopter (D) or a plus 10-D defocusing lens over one eye. Starting 1 day later and at 4-hour intervals for 24 hours, the retina/RPE and choroid were separately dissected. Without pooling, total RNA was extracted, converted to cDNA, and assayed by quantitative PCR for the expression of the following genes: Opn4m, Clock, Npas2, Per3, Cry1, Arntl, and Mtnr1a.

Results

The expression of each gene in retina/RPE and in choroid of eyes with nonrestricted vision OU varied over 24 hours, with equal levels OU for most genes and times. Altered visual input influenced gene expression in complex patterns that varied by gene, visual input, time, and eye, affecting experimental eyes with altered vision and also contralateral eyes with nonrestricted vision.

Discussion

Altering visual input in ways known to induce ametropias alters the retinal/RPE and choroidal expression of circadian rhythm-related genes, further linking circadian biology with eye growth regulation. While further investigations are needed, studying circadian processes may help understand refractive mechanisms and the increasing myopia prevalence in contemporary societies where lighting patterns can desynchronize endogenous rhythms from the natural environmental light/dark cycle.

Studies on retinal mechanisms possibly related to myopia inhibition by atropine in the chicken

PURPOSE

While low-dose atropine eye drops are currently widely used to inhibit myopia development in children, the underlying mechanisms are poorly understood. Therefore, we studied possible retinal mechanisms and receptors that are potentially involved in myopia inhibition by atropine.

METHODS

A total of 250 μg atropine were intravitreally injected into one eye of 19 chickens, while the fellow eyes received saline and served as controls. After 1 h, 1.5 h, 2 h, 3 h, and 4 h, eyes were prepared for vitreal dopamine (DA) measurements, using high-pressure liquid chromatography with electrochemical detection. Twenty-four animals were kept either in bright light (8500 lx) or standard light (500 lx) after atropine injection for 1.5 h before DA was measured. In 10 chickens, the α_2A-adrenoreceptor (α_2A-ADR) agonists brimonidine and clonidine were intravitreally injected into one eye, the fellow eye served as control, and vitreal DA content was measured after 1.5 h. In 6 chickens, immunohistochemical analyses were performed 1.5 h after atropine injection.

RESULTS

Vitreal DA levels increased after a single intravitreal atropine injection, with a peak difference between both eyes after 1.97 h. DA was also enhanced in fellow eyes, suggesting a systemic action of intravitreally administered atropine. Bright light and atropine (which both inhibit myopia) had additive effects on DA release. Quantitative immunolabelling showed that atropine heavily stimulated retinal activity markers ZENK and c-Fos in cells of the inner nuclear layer. Since atropine was recently found to also bind to α_2A-ADRs at doses where it can inhibit myopia, their retinal localization was studied. In amacrine cells, α_2A-ADRs were colocalized with tyrosine hydroxylase (TH), glucagon, and nitric oxide synthase, peptides known to play a role in myopia development in chickens. Intravitreal atropine injection reduced the number of neurons that were double-labelled for TH and α_2A-ADR. α_2A-ADR agonists clonidine and brimonidine (which were also found by other authors to inhibit myopia) severely reduced vitreal DA content in both injected and fellow eyes, compared to eyes of untreated chicks.

CONCLUSIONS

Merging our results with published data, it can be concluded that both muscarinic and α_2A-adrenergic receptors are expressed on dopaminergic neurons and both atropine and α_2A-ADR antagonists stimulate DA release whereas α_2A-ADR agonists strongly suppress its release. Stimulation of DA by atropine was enhanced by bright light. Results are in line with the hypothesis that inhibition of deprivation myopia is correlated with DA stimulation, as long as no toxicity is involved.

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.

The Interactions Between Bright Light and Competing Defocus During Emmetropization in Chicks

Purpose

The environment comprises multiple optical signals that affect eye growth. We aimed to determine if the inhibitory effects of myopic defocus and bright light (BL) against myopia are additive in the presence of the myopia-genic hyperopic defocus.

Methods

In experiment 1, three groups of 24 chicks each were fitted with the following multizone dual-power lenses (pl): pl/-10 D (50:50 area), +10/-10 D (50:50 area), and +10/-10 D (33:67 area) monocularly for 6 days. Half of each group were raised under normal illumination of 500 lux, 12/12-hour light/dark cycle, whereas the remainder were exposed to 6-hour BL of 40 klx and 6-hour 500 lux during the light cycle. In experiment 2, 38 chicks wore +10/-10 D (33:67 area) lenses monocularly for 8 days and were exposed to one of four light intensities for 6 hours per day-500 lux, 10 klx, 20 klx, or 40 klx-and received 500 lux for the remainder of the light cycle.

Results

In experiment 1, interocular difference in refractions after 6 days for the three groups were -3.6 D, +2.0 D, and -4.2 D, respectively, under normal light and were -0.9 D, +4.2 D, and +0.67 D under BL, manifesting as a shorter anterior segment and vitreous chamber. In experiment 2, the effect of BL increased with light intensity in the +10/-10 D (33:67) group, with a significant difference in refraction between the 10 klx and 20 klx groups (interocular difference -2.75 ± 2.76 D vs. 1.70 ± 2.40 D, P < 0.01), but plateaued between 20 klx and 40 klx (1.70 ± 2.40 D vs. 1.70 ± 0.35 D, P > 0.05).

Conclusions

The protective effects of myopic defocus and BL against experimental myopia were additive. The inhibitory effect of BL against myopia was dose dependent at 10 klx and above but plateaued at 20 klx.

Influence of seasons upon personal light exposure and longitudinal axial length changes in young adults

PURPOSE

To investigate the association between objectively measured ambient light exposure and longitudinal axial length changes (and their seasonal variations) over a period of 12 months in young adults.

METHODS

This prospective longitudinal observational study included 43 healthy young adult university students (21 emmetropes and 22 myopes) aged between 18 and 30 years. Three axial length measurements were collected at 6-month intervals (i.e. at baseline, 6 and 12 months), in summer and winter to determine the axial eye growth. Personal ambient light exposure data were measured in winter and summer months with wearable sensors, from which the mean daily time exposed to bright (outdoor) light levels (>1000 lux) was derived.

RESULTS

Greater daily bright light exposure was associated with less axial eye growth (β = -0.002, p = 0.006) over 12 months. In summer, myopes exhibited significantly greater changes in axial length (mean change 0.04 ± 0.05 mm) compared to emmetropes (-0.01 ± 0.05 mm) (p = 0.001), but there was no significant difference between refractive groups in winter. Emmetropes also spent significantly greater time in outdoor light levels in summer compared to winter (p < 0.0001), while myopes spent similar time outdoors during both seasons (p = 0.12). Differences in light exposure between summer and winter were also associated with seasonal differences in axial eye growth (p = 0.026).

CONCLUSION

In young adults, greater time spent in bright light was associated with slower longitudinal axial eye growth. Seasonal light exposure and axial length changes were dependent on refractive error in this population and also exhibited an inverse relationship.

Choroidal changes in human myopia: insights from optical coherence tomography imaging

The choroid is a vascular tissue which plays a range of critical roles in the normal physiology of the eye, such as supplying the outer retina with oxygen and nutrients and the regulation of intraocular pressure. There is also substantial evidence, particularly from animal studies, that the choroid plays an important role in the regulation of eye growth and the development of common refractive errors like myopia. In recent years, advances in optical coherence tomography technology have improved our ability to image and measure the choroid in the human eye. Research using this technology over the past decade has dramatically improved our knowledge of the normal choroid, and its potential role in the regulation of eye growth and refractive error development. This review aims to provide an overview of recent work examining the normal human choroid, its changes with myopia and the possible role of the choroid in the mechanism regulating eye growth. Studies have demonstrated that choroidal thinning accompanies the development and progression of myopia, and have established a close link between eye growth and choroidal thickness changes. Dramatic thinning of the choroid is seen with high myopia, and associations are also observed between choroidal thinning and reduced vision, and the development of retinal pathology associated with high myopia. In the short-term, environmental factors known to be associated with myopia development and more rapid eye growth typically lead to a thinning of the choroid, whereas factors linked to a slowing of eye growth are typically associated with short-term choroidal thickening. Collectively, these findings suggest that the choroid is an important biomarker of eye growth in the human eye, and additional research to better understand the human choroid is likely to further our knowledge of the signals and pathways regulating eye growth, myopia development and progression.

Daily morning light therapy is associated with an increase in choroidal thickness in healthy young adults

Ambient light exposure is one environmental factor thought to play a role in the regulation of eye growth and refractive error development, and choroidal thickness changes have also been linked to longer term changes in eye growth. Therefore in this study we aimed to examine the influence of a 1-week period of morning light therapy upon choroidal thickness. Twenty two healthy young adult subjects had a series of macular choroidal thickness measurements collected with spectral domain optical coherence tomography before, and then following a 7-day period of increased daily light exposure. Increased light exposure was delivered through the use of commercially available light therapy glasses, worn for 30 minutes in the morning each day. A significant increase in subfoveal choroidal thickness (mean increase of +5.4 ± 10.3 µm) was found following 7-days of increased daily light exposure (p = 0.02). An increase in choroidal thickness was also observed associated with light therapy across the central 5 mm macular region. This study provides the first evidence in the human eye that daily morning light therapy results in small magnitude but statistically significant increases in choroidal thickness. These changes may have implications for our understanding of the impact of environmental factors upon eye growth.

Novel method using 3-dimensional segmentation in spectral domain-optical coherence tomography imaging in the chick reveals defocus-induced regional and time-sensitive asymmetries in the choroidal thickness

Studies into the mechanisms underlying the active emmetropization process by which neonatal refractive errors are corrected, have described rapid, compensatory changes in the thickness of the choroidal layer in response to imposed optical defocus. While high frequency A-scan ultrasonography, as traditionally used to characterize such changes, offers good resolution of central (on-axis) changes, evidence of local retinal control mechanisms make it imperative that more peripheral, off-axis changes also be tracked. In this study, we used in vivo high resolution spectral domain-optical coherence tomography (SD-OCT) imaging in combination with the Iowa Reference Algorithms for 3-dimensional segmentation, to more fully characterize these changes, both spatially and temporally, in young, 7-day old chicks (n = 15), which were fitted with monocular +15 D defocusing lenses to induce choroidal thickening. With these tools, we were also able to localize the retinal area centralis, which was used as a landmark along with the ocular pectin in standardizing the location of scans and aligning them for subsequent analyses of choroidal thickness (CT) changes across time and between eyes. Values were derived for each of four quadrants, centered on the area centralis, and global CT values were also derived for all eyes. Data were compared with on-axis changes measured using ultrasonography. There were significant on-axis choroidal thickening that was detected after just one day of lens wear (∼190 µm), and regional (quadrant-related) differences in choroidal responses were also found, as well as global thickness changes 1 day after treatment. The ratio of global to on-axis choroidal thicknesses, used as an index of regional variability in responses, was also found to change significantly, reflecting the significant central changes. In summary, we demonstrated in vivo high resolution SD-OCT imaging, used in combination with segmentation algorithms, to be a viable and informative approach for characterizing regional (spatial), time-sensitive changes in CT in small animals such as the chick.

The epidemics of myopia: Aetiology and prevention

There is an epidemic of myopia in East and Southeast Asia, with the prevalence of myopia in young adults around 80-90%, and an accompanying high prevalence of high myopia in young adults (10-20%). This may foreshadow an increase in low vision and blindness due to pathological myopia. These two epidemics are linked, since the increasingly early onset of myopia, combined with high progression rates, naturally generates an epidemic of high myopia, with high prevalences of "acquired" high myopia appearing around the age of 11-13. The major risk factors identified are intensive education, and limited time outdoors. The localization of the epidemic appears to be due to the high educational pressures and limited time outdoors in the region, rather than to genetically elevated sensitivity to these factors. Causality has been demonstrated in the case of time outdoors through randomized clinical trials in which increased time outdoors in schools has prevented the onset of myopia. In the case of educational pressures, evidence of causality comes from the high prevalence of myopia and high myopia in Jewish boys attending Orthodox schools in Israel compared to their sisters attending religious schools, and boys and girls attending secular schools. Combining increased time outdoors in schools, to slow the onset of myopia, with clinical methods for slowing myopic progression, should lead to the control of this epidemic, which would otherwise pose a major health challenge. Reforms to the organization of school systems to reduce intense early competition for accelerated learning pathways may also be important.

Effects of a high level of illumination before sleep at night on chorioretinal thickness and ocular biometry

The choroid is affected by many factors. One of the factors, change in illumination has been suggested to influence choroidal thickness. However, the effects of bright light before sleep at night on the human eye are not well established. The purpose of this study was to investigate the effects of a high level of illumination in the evening on ocular measurements. Twenty-seven men with myopia spent seven consecutive nights in the sleep laboratory. During the first two nights, subjects were exposed to light at 150 lux between 20:00 and midnight. Then, for five consecutive nights, they were exposed to ambient light at 1000 lux between 20:00 and midnight. Ocular parameters and their diurnal variations were compared between the two periods and the effects of a high level of illumination were analyzed. After subjects were exposed to 1000 lux of illumination, axial length increased with borderline significance (p = 0.064). Macular volume and retinal thickness did not change. However, subfoveal choroidal thickness after exposure to 1000 lux of illumination (245.37 ± 52.84 μm) was significantly lower than that after 150 lux of illumination (268.00 ± 57.10 μm), (p < 0.001). Significant diurnal variations were found in mean keratometry (p = 0.039), intraocular pressure (IOP, p = 0.003), ocular perfusion pressure (OPP, p < 0.0001), macular volume (p = 0.019), and subfoveal choroidal thickness (p < 0.0001). A high level of illumination had significant effects on only IOP and OPP (p = 0.027 and 0.017, respectively). Bright light exposure before sleep at an intensity as high as 1000 lux reduced subfoveal choroidal thickness in healthy young men. In conclusion, diurnal variation in choroidal thickness can be affected by bright light exposure before sleep.

Effect of prolonged photoperiod on ocular tissues of domestic turkeys

OBJECTIVE

The objective of this study is to investigate the structural and functional ocular changes that develop in turkeys exposed to a photoperiod of 23 h of light (23L) compared with a photoperiod of 14 h of light (14L).

PROCEDURES

Ten-day-old Nicholas heavy strain poults were exposed to either a 14L or 23L photoperiod. Between 16 and 18 weeks of age, equal numbers of turkeys per treatment group underwent ophthalmic examination (biomicroscopy, indirect ophthalmoscopy) (n = 14), refractometry (n = 20), keratometry (n = 20), tonometry (n = 20), and full-field electroretinography (ERG) (n = 14). Postmortem analyses included orbital magnetic resonance imaging (MRI) (n = 10) and light microscopy (n = 24) at 18 weeks of age.

RESULTS

Autorefraction revealed a median of -0.13 for sphere in both groups (P = 0.69), which is approximately emmetropia. The radius of curvature of the cornea was significantly higher (P = 0.0001) and the refractive power of the cornea was significantly lower (P = 0.0001) in the 23L group. The astigmatic power was significantly greater in the 23L group (P = 0.0001). Mean intraocular pressure did not differ between groups (P = 0.085). Turkeys from the 23L group had significantly larger globes in nasotemporal (P = 0.0007), dorsoventral (P = 0.015), and anterioposterior (P = 0.021) directions, and anterior chambers were more shallow (P = 0.0002). ERGs revealed the 23L group to have lower a- and b-wave amplitudes and significantly lower cone flicker amplitudes (P = 0.0008). Light microscopic examination revealed 23L turkeys to have significantly decreased numbers of nuclei in the outer nuclear layer (P = 0.0001) and inner nuclear layer (P = 0.0186), and decreased choroidal thickness (P = 0.0008). The prevalence of cataract in the 23L group was significantly higher (P = 0.001).

CONCLUSIONS

Exposing turkeys to a prolonged photoperiod induces significant ocular disease.

Effects of a human VEGF antibody (Bevacizumab) on deprivation myopia and choroidal thickness in the chicken

Vascular endothelial growth factor (VEGF) is a dimeric glycoprotein which is responsible for neovascularization and fenestrations of the choriocapillaris. In neovascular maculopathies secondary to age-related degeneration (nAMD) or pathologic myopia (PM-CNV), its inhibition by humanized antibodies is currently the most successful therapy. The choroid has an important role in maintaining retinal health and its thickness declines with age and with myopia. Since choroidal thickness depends on its perfusion rate, one would expect that anti-VEGF agents can also change choroidal thickness. We have tested the hypothesis in the chicken model, using a humanized antibody, Bevacizumab, and also studied the distribution of VEGF-A in the chicken fundal layers by immunohistochemical techniques. Even though it was raised against human VEGF, Bevacizumab had several long lasting effects in the chicken eye (1) after a single unilateral intravitreal injection of 0.5 mg, it partially suppressed the development of deprivation myopia, similarly in both eyes, (2) it completely suppressed choroidal thickening that normally occurs when eyes recover from induced myopia over a time period of about 10 days, (3) it had little effect on the choroidal thickness in eyes that had normal visual experience, (4) VEGF-A was absent in sclera, but highly expressed in the walls of choroidal blood vessels and presumed nerve fiber bundles, as well as in retinal photoreceptors and cells of the inner and outer nuclear layer. One day after the injection of Bevacizumab, the immunoreactivity against VEGF-A had largely disappeared. In conclusion, Bevacizumab is similary effective in human and chicken tissue, has similar time constants (few days), has almost symmetrical effects on myopia in both eyes even after monocular application, and fully suppresses choroidal thickening that normally occurs during recovery from deprivation myopia. The mechanisms by which Bevacizumab acts on the choroidal thickness are perhaps most interesting, both to better understand the role of the choroid in myopia development but also to clarify its potential side effects during nAMD and PM-CNV treatment in the clinics.