The effect of daily transient +4 D positive lens wear on the inhibition of myopia in the tree shrew

Association between inflammatory cytokines and oxidative stress levels in aqueous humor with axial length in human myopia

This study investigated the content of inflammatory cytokines and oxidative stress levels in the aqueous humor (AH) of patients with high myopia (HM) and explored the relationship between these factors and the axial length (AL) of the eye, to explore the roles of mild intraocular inflammation and oxidative stress imbalance in the occurrence and development of myopia. AH samples from 40 patients (70 eyes) were collected during implantable collamer lens (ICL-V4c) surgery. The subjects were divided into three groups according to AL: group A (AL ≤ 26 mm), group B (26 < AL ≤ 28 mm), and group C (AL ≥ 28 mm). The concentrations of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), matrix metalloproteinase-2 (MMP-2), and interleukin-1β (IL-1β) in the AH of the three groups were measured using the Luminex system. Oxidative stress levels were measured using reagent kits targeting total antioxidant capacity (T-AOC), catalase (CAT), and nitric oxide (NO) and malonaldehyde (MDA) content. The results showed compared with group A, IL-1β, MMP-2, and IL-6 concentrations were significantly higher and T-AOC levels were significantly lower in group C. There were no significant differences in CAT, NO, MDA, or TNF-α levels among the groups. The concentrations of IL-6 (r = 0.379, p = 0.016), MMP-2 (r = 0.469, p = 0.002), and MDA (r = 0.354, p = 0.025) in AH were positively correlated with the AL, whereas T-AOC (r = -0.678, p = 0.000) was negatively correlated with AL. These results suggest that mild intraocular inflammation and oxidative stress imbalance may be associated with myopia. Further experiments are needed to confirm the role of mild intraocular inflammation and oxidative stress imbalance in the occurrence and development of myopia.

Pharmacotherapeutic candidates for myopia: A review

This review provides insights into the mechanism underlying the pathogenesis of myopia and potential targets for clinical intervention. Although the etiology of myopia involves both environmental and genetic factors, recent evidence has suggested that the prevalence and severity of myopia appears to be affected more by environmental factors. Current pharmacotherapeutics are aimed at inhibiting environmentally induced changes in visual input and subsequent changes in signaling pathways during myopia pathogenesis and progression. Recent studies on animal models of myopia have revealed specific molecules potentially involved in the regulation of eye development. Among them, the dopamine receptor plays a critical role in controlling myopia. Subsequent studies have reported pharmacotherapeutic treatments to control myopia progression. In particular, atropine treatment yielded favorable outcomes and has been extensively used; however, current studies are aimed at optimizing its efficacy and confirming its safety. Furthermore, future studies are required to assess the efficacy of combinatorial use of low-dose atropine and contact lenses or orthokeratology.

The human axial length and choroidal thickness responses to continuous and alternating episodes of myopic and hyperopic blur

PURPOSE

To investigate the change in axial length (AxL) and choroidal thickness (ChT) in response to continuous and alternating episodes of monocular myopic and hyperopic defocus.

METHODS

The right eye of sixteen young adults was exposed to 60 minute episodes of either continuous or alternating myopic and hyperopic defocus (+3 DS & -3 DS) over six separate days, with the left eye optimally corrected for distance. During alternating defocus conditions, the eye was exposed to either 30 or 15 minute cycles of myopic and hyperopic defocus, with the order of defocus reversed in separate sessions. The AxL and ChT of the right eye were measured before, during and after each defocus condition.

RESULTS

Significant changes in AxL were observed over time, dependent upon the defocus condition (p < 0.0001). In general, AxL exhibited a greater magnitude of change during continuous than alternating defocus conditions. The maximum AxL elongation was +7 ± 7 μm (p = 0.010) in response to continuous hyperopic defocus and the maximum AxL reduction was -8 ± 10 μm of (p = 0.046) in response to continuous myopic defocus. During both 30 and 15 minute cycles of alternating myopic and hyperopic defocus of equal duration, the effect of opposing blur sessions cancelled each other and the AxL was near baseline levels following the final defocus session (mean change from baseline across all alternating defocus conditions was +2 ± 10 μm, p > 0.05). Similar, but smaller magnitude, changes were observed for ChT.

CONCLUSIONS

The human eye appears capable of temporal averaging of visual cues from alternating myopic and hyperopic defocus. In the short term, this integration appears to be a cancellation of the effects of the preceding defocus condition of opposite sign.

The Adaptation and Acceptance of Defocus Incorporated Multiple Segment Lens for Chinese Children

PURPOSE

We investigated the adaptability and acceptance of a novel spectacle lens design that was recently reported to achieve a significant antimyopia effect.

DESIGN

A prospective, cross-over study.

METHODS

Twenty children were recruited to wear both Defocus Incorporated Multiple Segments (DIMS) and single vision (SV) lens, with a random assignment of which type of lens was experienced first. For each type of lens, high and low contrast central distant visual acuity (VA) and high contrast mid-peripheral near VA were measured at both 500 lux and 50 lux ambient illuminance after 30 minutes' and a week's wearing of the lens. A self-developed questionnaire was applied to evaluate the visual discomfort at the 1-week visit. All quantitative data were analyzed by paired t test, while qualitative data were analyzed with the χ² or Wilcoxon signed-rank tests.

RESULTS

Central VA was not affected by DIMS lens compared with SV lens in all circumstances (all P > .05). However, the mid-peripheral near VA was found to reduce by approximately 0.06 logarithm of minimal angle of resolution unit in 2 of 4 quadrants (500 lux; P < .05) and in 3 quadrants (50 lux; P < .05) for DIMS lenses. No improvement was detected in the 1-week visit. Mid-peripheral blurred vision was the main visual complaint, which was noticed only once or twice a day. Being aware of the average antimyopic efficacy, 90% of children subjects preferred DIMS lenses.

CONCLUSION

Mid-peripheral vision through DIMS lenses was slightly affected compared with SV lenses. Otherwise, DIMS lenses received good tolerance and acceptance by Chinese children.

Short Interruptions of Imposed Hyperopic Defocus Earlier in Treatment are More Effective at Preventing Myopia Development

The purpose of this study was to evaluate the effect of interrupting negative lens wear for short periods early or late during the development of lens-induced myopia in marmosets. Sixteen marmosets were reared with a −5D contact lens on their right eye (plano on contralateral eye) for 8 weeks. Eight marmosets had lenses removed for 30 mins twice/day during the first four weeks (early interruption) and eight during the last four weeks (late interruption). Data were compared to treated controls that wore lenses continuously (N = 12) and untreated controls (N = 10). Interocular differences (IOD) in vitreous chamber (VC) depth and central and peripheral mean spherical refractive error (MSE) were measured at baseline and after four (T₄) and eight (T₈) weeks of treatment. Visual experience during the interruptions was monitored by measuring refraction while marmosets were seated at the center of a 1 m radius viewing cylinder. At T₄ the eyes that were interrupted early were not different from untreated controls (p = 0.10) and at T₈ had grown less and were less myopic than those interrupted later (IOD change from baseline, VC: +0.07 ± 0.04 mm vs +0.20 ± 0.03 mm, p < 0.05; MSE: −1.59 ± 0.26D vs −2.63 ± 0.60D, p = 0.13). Eyes interrupted later were not different from treated controls (MSE, p = 0.99; VC, p = 0.60) and grew at the same rate as during the first four weeks of uninterrupted lens wear (T₄ − T₀: 3.67 ± 1.1 µm/day, T₈ − T₄: 3.56 ± 1.3 µm/day p = 0.96). Peripheral refraction was a predictive factor for the amount of myopia developed only when the interruption was not effective. In summary, interrupting hyperopic defocus with short periods of myopic defocus before compensation occurs prevents axial myopia from developing. After myopia develops, interruption is less effective.

The effect of part-time wear of 2-zone concentric bifocal spectacle lenses on refractive error development & eye growth in young chicks

The purpose of this study is to characterize in young chicks the myopia control effects of part-time wear of two-zone concentric bifocal lenses. Nine-day-old chicks (n = 115) were first made myopic with monocular -10 Diopter (D) single vision (SV) lenses worn for 3 days. Over the 6 days following myopia induction, either 1) two-zone bifocal lenses (-10 D center/-5 D periphery, BFDC) were worn for 12 (full-time), 10, 8, or 6 h, with -10 D SV lenses worn for the remainder of the day, or 2) BFDC or BFNC (-5 D center/-10 D periphery) lenses were worn every other day (EOD). Control birds wore -10 D SV lenses every day. Refractive error (RE) and axial ocular dimensions were monitored every three days with retinoscopy and high frequency A-scan ultrasonography respectively. Mean interocular RE and axial length differences after 3 days of myopia induction (±SEM) were -9.6 ± 0.19 D and 0.26 ± 0.01 mm across the groups. At the end of the following 6-day treatment period, equivalent values were: -10.66 ± 0.28 D, 0.42 ± 0.02 mm (SV-control); 1) -4.61 ± 0.29 D, 0.26 ± 0.02 mm (BFDC, 12 h); -4.82 ± 0.23 D, 0.28 ± 0.02 mm (BFDC, 10 h); -5.21 ± 0.27 D, 0.24 ± 0.02 mm (BFDC, 8 h); -6.34 ± 0.34 D, 0.25 ± 0.03 mm (BFDC, 6 h); 2) -8.29 ± 0.29 D, 0.32 ± 0.03 mm (BFDC, EOD), and -8.83 ± 0.36 D, 0.33 ± 0.03 mm (BFNC, EOD). Overall, full-time BFDC and part-time BFDC and BFNC lens groups exhibited similar changes and were less myopic than the SV group. The results suggest that bifocal lenses may have myopia control effects even when worn part-time, interleaved with standard (SV) myopic corrections, especially if worn for at least 6 h per day.

Tree shrew (Tupaia belangeri) as a novel laboratory disease animal model

The tree shrew (Tupaia belangeri) is a promising laboratory animal that possesses a closer genetic relationship to primates than to rodents. In addition, advantages such as small size, easy breeding, and rapid reproduction make the tree shrew an ideal subject for the study of human disease. Numerous tree shrew disease models have been generated in biological and medical studies in recent years. Here we summarize current tree shrew disease models, including models of infectious diseases, cancers, depressive disorders, drug addiction, myopia, metabolic diseases, and immune-related diseases. With the success of tree shrew transgenic technology, this species will be increasingly used in biological and medical studies in the future.

A study of Epstein-Barr virus infection in the Chinese tree shrew(Tupaia belangeri chinensis)

Background

Epstein–Barr virus (EBV) is closely associated with many human diseases, including a variety of deadly human malignant tumours. However, due to the lack of ideal animal models,the biological characteristics of EBV, particularly its function in tumourigenesis, have not been determined. Chinese tree shrews (Tupaia belangeri chinensis), which are similar to primates, have been used to establish a variety of animal models and have recently received much attention. Here, we established tree shrews as a model for EBV infection by intravenous injection.

Methods

Ten tree shrews were inoculated with EBV by intravenous injection,and blood was collected at regular intervals thereafter from the femoral artery or vein to detect EBV markers.

Results

Eight of 10 tree shrews showed evidence of EBV infection. In the 8 EBV-infected tree shrews, EBV copy number increased intermittently or transiently, EBV-related gene expression was detected, and anti-EBV antibodies increased to varying degrees. Macroscopic hepatomegaly was observed in 1 tree shrew, splenomegaly was observed in 4 tree shrews, and enlarged mesenteric lymph nodes were observed in 3 tree shrews. Haematoxylin and eosin (HE) staining showed splenic corpuscle hyperplasia in the spleens of 4 tree shrews and inflammatory cell infiltration of the liver of 1 tree shrew and of the mesenteric lymph nodes of 3 tree shrews. EBER in situ hybridization(ISH) and immunohistochemical (IHC) staining showed that EBER-, LMP1- and EBNA2- positive cells were present in the spleens and mesenteric lymph nodes of some tree shrews. Western blotting (WB) revealed EBNA1-positive cells in the spleens of 4 tree shrews. EBV markers were not detected by HE, EBER-ISH or IHC in the lung or nasopharynx.

Conclusions

These findings suggest that EBV can infect tree shrews via intravenous injection. The presented model offers some advantages for exploring the pathophysiology of EBV infection in humans.

The Effects of the Relative Strength of Simultaneous Competing Defocus Signals on Emmetropization in Infant Rhesus Monkeys

Purpose

We investigated how the relative surface area devoted to the more positive-powered component in dual-focus lenses influences emmetropization in rhesus monkeys.

Methods

From 3 to 21 weeks of age, macaques were reared with binocular dual-focus spectacles. The treatment lenses had central 2-mm zones of zero-power and concentric annular zones that had alternating powers of either +3.0 diopters (D) and 0 D (+3 D/pL) or −3.0 D and 0 D (−3 D/pL). The relative widths of the powered and plano zones varied from 50:50 to 18:82 between treatment groups. Refractive status, corneal curvature, and axial dimensions were assessed biweekly throughout the lens-rearing period. Comparison data were obtained from monkeys reared with binocular full-field single-vision lenses (FF+3D, n = 6; FF−3D, n = 10) and from 35 normal controls.

Results

The median refractive errors for all of the +3 D/pL lens groups were similar to that for the FF+3D group (+4.63 D versus +4.31 D to +5.25 D; P = 0.18–0.96), but significantly more hyperopic than that for controls (+2.44 D; P = 0.0002–0.003). In the −3 D/pL monkeys, refractive development was dominated by the zero-powered portions of the treatment lenses; the −3 D/pL animals (+2.94 D to +3.13 D) were more hyperopic than the FF−3D monkeys (−0.78 D; P = 0.004–0.006), but similar to controls (+2.44 D; P = 0.14–0.22).

Conclusions

The results demonstrate that even when the more positive-powered zones make up only one-fifth of a dual-focus lens' surface area, refractive development is still dominated by relative myopic defocus. Overall, the results emphasize that myopic defocus distributed across the visual field evokes strong signals to slow eye growth in primates.

Refractive plasticity of the developing chick eye: a summary and update

PURPOSE

To summarize the OPO 1992 Classic Paper: Refractive plasticity of the developing chick eye (12: 448-452) and discuss recent findings in refractive development.

SUMMARY AND RECENT FINDINGS

The classic paper shows that when lightweight plastic goggles with rigid contact lens inserts are applied to the eyes of newly hatched chicks, the eye responds accurately to defocus between -10 and +20 D, although hyperopia develops more rapidly. While the changes largely are due to change in axial length, high levels of hyperopia are associated with corneal flattening. Also, newly hatched chicks are better able to compensate for the induced defocus than chicks that are 9 days old. In addition, astigmatism of 2-6 D can be produced by applying 9 D toric inducing lenses on the day of hatching, and the most myopic meridian coincides with the power meridian of the inducing lens. This astigmatism appears to be primarily due to corneal toricity. Furthermore, the greatest magnitude was produced when the plano meridian of the inducing lens was placed 45° from the line of the palpebral fissure. Since our publication in 1992, it has been shown that similar results can be produced in a variety of species, including; tree shrews, marmosets, monkeys and fish. Considerable effort has been spent in trying to determine what the eye uses, if not the brain, as the signal to the sign of the defocus. Accommodation, chromatic aberration, diurnal variation, astigmatism and higher order monochromatic aberrations have all been considered. Choroidal thinning and thickening play a role in myopia and hyperopia development, respectively, in chicks. High light levels (15,000 lux) increase the rate at which chicks compensate for positive lenses and decrease the compensation rate for negative lenses. However these light levels do not prevent the eye from fully compensating for either type of lens. It has also been shown that brief periods of normal vision prevent the development of form deprivation myopia. Finally, the importance of the peripheral retina in refractive development has been explored and lenses designed to reduce relative peripheral hyperopia have resulted in variable effects as far as myopia control is concerned.

CONCLUSIONS

A growing body of evidence, from both animal models and human clinical trials indicates that the development of myopia is related both to genetics and environment / lifestyle. Nevertheless, we are far from understanding how this interaction takes place.

The effects of simultaneous dual focus lenses on refractive development in infant monkeys

PURPOSE

We investigated the effects of two simultaneously imposed, competing focal planes on refractive development in monkeys.

METHODS

Starting at 3 weeks of age and continuing until 150 ± 4 days of age, rhesus monkeys were reared with binocular dual-focus spectacle lenses. The treatment lenses had central 2-mm zones of zero power and concentric annular zones with alternating powers of +3.0 diopter [D] and plano (pL or 0 D) (n = 7; +3D/pL) or -3.0 D and plano (n = 7; -3D/pL). Retinoscopy, keratometry, and A-scan ultrasonography were performed every 2 weeks throughout the treatment period. For comparison purposes data were obtained from monkeys reared with full field (FF) +3.0 (n = 4) or -3.0 D (n = 5) lenses over both eyes and 33 control animals reared with unrestricted vision.

RESULTS

The +3 D/pL lenses slowed eye growth resulting in hyperopic refractive errors that were similar to those produced by FF+3 D lenses (+3 D/pL = +5.25 D, FF +3 D = +4.63 D; P = 0.32), but significantly more hyperopic than those observed in control monkeys (+2.50 D, P = 0.0001). One -3 D/pL monkey developed compensating axial myopia; however, in the other -3 D/pL monkeys refractive development was dominated by the zero-powered portions of the treatment lenses. The refractive errors for the -3 D/pL monkeys were more hyperopic than those in the FF -3 D monkeys (-3 D/pL = +3.13 D, FF -3D = -1.69 D; P = 0.01), but similar to those in control animals (P = 0.15).

CONCLUSIONS

In the monkeys treated with dual-focus lenses, refractive development was dominated by the more anterior (i.e., relatively myopic) image plane. The results indicate that imposing relative myopic defocus over a large proportion of the retina is an effective means for slowing ocular growth.

Integration of defocus by dual power Fresnel lenses inhibits myopia in the mammalian eye

PURPOSE

Eye growth compensates in opposite directions to single vision (SV) negative and positive lenses. We evaluated the response of the guinea pig eye to Fresnel-type lenses incorporating two different powers.

METHODS

A total of 114 guinea pigs (10 groups with 9-14 in each) wore a lens over one eye and interocular differences in refractive error and ocular dimensions were measured in each of three experiments. First, the effects of three Fresnel designs with various diopter (D) combinations (-5D/0D; +5D/0D or -5D/+5D dual power) were compared to three SV lenses (-5D, +5D, or 0D). Second, the ratio of -5D and +5D power in a Fresnel lens was varied (50:50 compared with 60:40). Third, myopia was induced by 4 days of exposure to a SV -5D lens, which was then exchanged for a Fresnel lens (-5D/+5D) or one of two SV lenses (+5D or -5D) and ocular parameters tracked for a further 3 weeks.

RESULTS

Dual power lenses induced an intermediate response between that to the two constituent powers (lenses +5D, +5D/0D, 0D, -5D/+5D, -5D/0D and -5D induced +2.1 D, +0.7 D, +0.1 D, -0.3 D, -1.6 D and -5.1 D in mean intraocular differences in refractive error, respectively), and changing the ratio of powers induced responses equal to their weighted average. In already myopic animals, continued treatment with SV negative lenses increased their myopia (from -3.3 D to -4.2 D), while switching to SV positive lenses or -5D/+5D Fresnel lenses reduced their myopia (by 2.9 D and 2.3 D, respectively).

CONCLUSIONS

The mammalian eye integrates competing defocus to guide its refractive development and eye growth. Fresnel lenses, incorporating positive or plano power with negative power, can slow ocular growth, suggesting that such designs may control myopia progression in humans.

Temporal properties of the myopic response to defocus in the guinea pig

PURPOSE

Hyperopic defocus induces myopia in all species tested and is believed to underlie the progression of human myopia. We determined the temporal properties of the effects of hyperopic defocus in a mammalian eye.

METHODS

In Experiment 1, the rise and decay time of the responses elicited by hyperopic defocus were calculated in 111 guinea pigs by giving repeated episodes of monocular -4 D lens wear (from 5 to 6 days of age for 12 days) interspersed with various dark intervals. In Experiment 2, the decay time constant was calculated in 152 guinea pigs when repeated periods of monocular -5 D lens-wear (from 4 days of age for 7 days) were interrupted with free viewing periods of different lengths. At the end of the lens-wear period, ocular parameters were measured and time constants were calculated relative to the maximum response induced by continuous lens wear.

RESULTS

When hyperopic defocus was experienced with dark intervals between episodes, the time required to induce 50% of the maximum achievable myopia and ocular elongation was at most 30 min. Saturated 1 h episodes took at least 22 h for refractive error and 31 h for ocular length, to decay to 50% of the maximum response. However, the decay was an order of magnitude faster when hyperopic defocus episodes were interrupted with a daily free viewing period, with only 36 min required to reduce relative myopia and ocular elongation by 50%.

CONCLUSIONS

Hyperopic defocus causes myopia with brief exposures and is very long lasting in the absence of competing signals. However, this myopic response rapidly decays if interrupted by periods of 'normal viewing' at least 30 min in length, wherein ocular growth appears to be guided preferentially by the least amount of hyperopic defocus experienced.

Temporal integration of visual signals in lens compensation (a review)

Postnatal eye growth is controlled by visual signals. When wearing a positive lens that causes images to be focused in front of the retina (myopic defocus), the eye reduces its rate of ocular elongation and increases choroidal thickness to move the retina forward to meet the focal plane of the eye. When wearing a negative lens that causes images to be focused behind the retina (hyperopic defocus), the opposite happens. This review summarizes how the retina integrates the constantly changing visual signals in a non-linear fashion to guide eye growth in chicks: (1a) When myopic or hyperopic defocus is interrupted by a daily episode of normal vision, normal vision is more effective in reducing myopia caused by hyperopic defocus than in reducing hyperopia caused by myopic defocus; (1b) when the eye experiences alternating myopic and hyperopic defocus, the eye is more sensitive to myopic defocus than to hyperopic defocus and tends to develop hyperopia, even if the duration of hyperopic defocus is much longer than the duration of myopic defocus; (2) when the eye experiences brief, repeated episodes of defocus by wearing either positive or negative lenses, lens compensation depends on the frequency and duration of individual episodes of lens wear, not just the total daily duration of lens wear; and (3) further analysis of the time constants for the hypothesized internal emmetropization signals show that, while it takes approximately the same amount of time for the signals to rise and saturate during lens-wearing episodes, the decline of the signals between episodes depends strongly on the sign of defocus and the ocular component. Although most extensively studied in chicks, the nonlinear temporal integration of visual signals has been found in other animal models. These findings may help explain the complex etiology of myopia in school-aged children and suggest ways to slow down myopia progression.

[Clinical risk factors for progressive myopia]

The average worldwide frequency of myopia is approximately 30 % and is traditionally subdivided into school myopia and pathological myopia. A further distinction is made between progressive myopia and stationary myopia. There is a high correlation between the frequency of myopia and urbanization and training. Risk factors for development of myopia are close-up work, lack of outdoor activity, biometrical variables of the eye and genetic risk factors. Development of myopia can be positively influenced by peripheral focusing, increased exposure to light and in the future possibly pharmacologically.

The cause(s) of myopia and the efforts that have been made to prevent it

In spite of a long history of study, as well as a significant, recent increase in research attention, the cause(s) and the means of preventing or mitigating the progression of myopia in children are still elusive. The high and growing prevalence of myopia, especially in Asian populations, as well as its progressive nature in children and its effect on visual acuity, have contributed to the recent surge in interest. Animal research carried out in the 1970s also helped spark this interest by legitimising the study of environmental influences on the refractive development of the eye. Efforts that include the use of visual training or biofeedback, bifocal and progressive lenses, contact lenses and pharmaceuticals are reviewed. Current research trends that focus on the relationship between genetics and environment, as well as studies, both animal and human, that explore the effect of peripheral refractive error on the refractive development of the central retina are also reviewed.