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

In vivo assessment of human corneal epithelial cells in orthokeratology lens wearers: A pilot study

SIGNIFICANCE

Central corneal epithelial thinning associated with midperipheral epithelial thickening has been reported as the main factor contributing to the effectiveness of orthokeratology (ortho-k) in myopia control. Yet, the cellular mechanism governing the regional change in refractive power remains elusive.

PURPOSE

This study aimed to evaluate the correlation between the regional change in corneal epithelial thickness and cell density in ortho-k wearers.

METHODS

A new human prototype of a polarization-dependent optical coherence microscope was developed to enable noncontact and noninvasive in vivo imaging of corneal epithelial cells in ortho-k wearers with and without their ortho-k lens. The epithelial thickness and cell density were evaluated at the central and midperipheral corneal locations in four ortho-k wearers and four spectacle wearers serving as controls.

RESULTS

Polarization-dependent optical coherence microscope achieved in vivo volumetric imaging of all epithelial cell types in ortho-k wearers with and without their lens over a field of view of 0.5 × 0.5 mm 2 with an isotropic resolution of ~2.2 mm. The central epithelial thinning and midperipheral epithelial thickening were consistent across all ortho-k wearers. However, the inconsistency in their regional epithelial cell density highlighted a great variability in individual response to ortho-k treatment. There was no strong correlation between epithelial thickness and cell density, especially at the midperipheral cornea, in ortho-k participants.

CONCLUSIONS

This study constitutes our first step toward uncovering the cellular mechanism underlying the effectiveness of ortho-k in myopia control. Future studies will focus on the longitudinal evaluation of epithelial cells before and during ortho-k treatment to identify factors governing individual response to ortho-k treatment and ultimately inform the dynamics of epithelial cells taking place during the ortho-k treatment.

Sustained Retinal Defocus Increases the Effect of Induced Myopia on the Retinal Astrocyte Template

The aim of this article is to describe sustained myopic eye growth's effect on astrocyte cellular distribution and its association with inner retinal layer thicknesses. Astrocyte density and distribution, retinal nerve fiber layer (RNFL), ganglion cell layer, and inner plexiform layer (IPL) thicknesses were assessed using immunochemistry and spectral-domain optical coherence tomography on seventeen common marmoset retinas (Callithrix jacchus): six induced with myopia from 2 to 6 months of age (6-month-old myopes), three induced with myopia from 2 to 12 months of age (12-month-old myopes), five age-matched 6-month-old controls, and three age-matched 12-month-old controls. Untreated marmoset eyes grew normally, and both RNFL and IPL thicknesses did not change with age, with astrocyte numbers correlating to RNFL and IPL thicknesses in both control age groups. Myopic marmosets did not follow this trend and, instead, exhibited decreased astrocyte density, increased GFAP+ spatial coverage, and thinner RNFL and IPL, all of which worsened over time. Myopic changes in astrocyte density, GFAP+ spatial coverage and inner retinal layer thicknesses suggest astrocyte template reorganization during myopia development and progression which increased over time. Whether or not these changes are constructive or destructive to the retina still remains to be assessed.

Development of a novel protocol to evaluate contact-lens related ocular surface health on marmosets (Callithrix jacchus)

Contact lens wear affects the ocular surface and can cause contact lens-induced dry eye (CLIDE). The purpose of this study was bifold: (1) to develop a novel protocol to assess the ocular surface in a non-human primate (NHP) model, the common marmoset (Callithrix jacchus), and (2) to characterize central corneal thickness (CCT), tear osmolarity, blink rate and tear meniscus height (TMH) longitudinally, in untreated marmosets (controls) compared to animals treated with contact lenses (CL). Longitudinal changes in CCT (N = 10 control; N = 10 treated with contact lenses, CL-treated), osmolarity (N = 4 control; N = 6 CL-treated), blink rate (N = 8 control; N = 10 CL-treated) and TMH (N = 8 control; N = 6 CL-treated) were assessed using high frequency A-scan ultrasound, the I-PEN Vet Tear Osmolarity System, a video recording system (745 frames/minute) and Image J respectively, from 70 days to 224 days (5 months) at approx. 9am, and again after 9hrs of CL wear (methafilcon A, 55% water content; Capricornia, Australia) after every 4 weeks of contact lens wear for a total of 22 weeks of treatment. Repeated measures ANOVA was used to compare eyes over time and student t-test was used to compare treated to control eyes at each time point. At baseline, untreated marmosets had a CCT (mean ± SD) of 0.31 ± 0.01 mm, tear osmolarity (mean ± SD) 311.67 ± 11.48 mOsms/L, blink rate (mean ± SD) 1.83 ± 1.79 blinks per minute (bpm) and TMH (mean ± SD) 0.07 ± 0.02 arbitrary units (au), all of which remained stable over 5 months, except blink rate that increased to 5.32 ± 1.58 bpm (p < 0.01) after 5 months. In CL-treated marmosets, however, CCT progressively increased with CL wear (baseline: 0.30 ± 0.01 mm; 5 months: 0.31 ± 0.02 mm, p < 0.05), while osmolarity decreased after 2 and 3 months of CL wear (baseline: 316.11 ± 13.63; 2 months: 302.63 ± 11.27, p < 0.05; 3 months: 302.92 ± 14.58, p < 0.05). The decrease in osmolarity occurred in parallel to an increase in blink rate (baseline: 0.98 ± 1.18 bpm; 2 months: 3.46 ± 3.04 bpm, p < 0.05; 3 months: 3.73 ± 1.50 bpm, p < 0.001). TMH decreased during the third month of CL wear (baseline: 0.06 ± 0.00 au; 3 months: 0.05 ± 0.01 au, p < 0.05), and increased after 4 months (0.08 ± 0.01 au, p < 0.05). As TMH decreased, tear osmolarity increased in both control (R = -0.66, p < 0.05) and CL-treated marmosets (R = -0.64, p < 0.05). The results suggest that marmosets treated with CL for 5 months experienced an increase in blink rate, CCT and TMH, along with a decrease in osmolarity within the first few months of CL treatment that differed from the unaffected stable ocular surface findings observed untreated animals. We hypothesize that CL wear in marmosets might induce mild corneal edema, an increased blink rate and TMH, in turn delaying the development of hyperosmolarity. These findings confirm that the marmoset is a good novel animal model for ocular surface research for the assessment of novel contact lens materials aimed to alleviate CLIDE.

Evaluation and Follow-up of Myopia Prevalence Among School-Aged Children Subsequent to the COVID-19 Home Confinement in Feicheng, China

Importance

Progression of myopia in a school-aged population due to home confinement (January to May 2021) during the COVID-19 pandemic has been previously reported. A key remaining question was whether the myopia spike in children aged 6 to 8 years persisted.

Objective

To investigate the changes in refractive status and prevalence of myopia in school-aged children 1 year after home confinement ended in China.

Design, Setting, and Participants

This cross-sectional study with a cohort substudy prospectively evaluated data from school-based photoscreening in Feicheng, China. Children aged 6 to 13 years participated in 8 screenings from 2015 to 2021.

Exposures

Noncycloplegic photorefraction was conducted using the Spot Vision photoscreener.

Main Outcomes and Measures

The main outcomes were the differences in spherical equivalent refraction (SER) and prevalence of myopia between 2020 (during home confinement) and 2021 (after home confinement). The SER was recorded for each child, and the prevalence of myopia was calculated annually for each age group.

Results

A total of 325 443 children participated in the study (51.4% boys, 48.6% girls; age range, 6 to 13 years). Compared with 2020, the mean SER of children in 2021 increased significantly for those aged 6 (0.42 diopters [D]), 7 (0.41 D), and 8 (0.33 D) years. The prevalence of myopia in 2021 was similar to in 2019 for each age group (aged 6 years: 7.9% vs 5.7%; aged 7 years: 13.9% vs 13.6%; aged 8 years: 29.5% vs 26.2%). Both the prevalence of myopia and mean SER for these children returned to their prepandemic levels.

Conclusions and Relevance

Compared with 2020, the prevalence of myopia among children aged 6 to 8 years in the 2021 screenings decreased, and the mean SER returned to prepandemic level. The refractive development in children aged 6 to 8 years may be most susceptible to environmental changes. These findings support the premise that age 6 to 8 years is a critical period for myopia development and suggest a need to focus preventive interventions for myopia control on children in this age range.

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.

[Changes in accommodation in children with hyperopic anisometropia and unilateral amblyopia after laser refractive surgery and pleoptic treatment]

PURPOSE

This study comparatively analyzes the state of accommodation in children with hyperopic anisometropia and amblyopia after femtosecond laser-assisted in situ keratomileusis (Femto-LASIK) combined with pleoptic treatment, and after conventional pleoptic treatment.

MATERIAL AND METHODS

The first group consisted of 30 children with medium and high hyperopia, high and medium amblyopia, and anisometropia greater than 3.0 diopters, who underwent Femto-LASIK in the amblyopic eye. The second group consisted of 28 children with similar local status, who were prescribed traditional correction and received conservative treatment. The follow-up period was 1.5 years.

RESULTS

After 1.5 years, higher visual acuity (p<0.05) was achieved in the first group. A significant increase in the coefficient of accommodative response (CAR) was observed in the operated amblyopic eyes in group 1 - by 0.1±0.02 c.u. compared to the control group (p<0.05). In both groups there was an upwards trend for the coefficient of microfluctuations (CMF) in the amblyopic eye, but in the first group CMF increased more significantly (p<0.05). The objective accommodative response (OAR) and positive relative accommodation (PRA) of the amblyopic eye showed a double increase - by 1.0±0.23 and 0.9±0.38 diopters, respectively, at the end of treatment in the first group. The increase in similar indicators in the second group was insignificant (p<0.05). In children of the first group the difference in ciliary muscle thickness (CMT) of the amblyopic eye with disabled and enabled accommodation increased by 0.04±0.01 mm (p<0.05) in the anterior part of the ciliary muscle at the levels of CMTmax and CMT1.

CONCLUSION

The data obtained in this study indicate the strong effect of refractive laser surgery in combination with pleoptic treatment on improving the visual acuity and the state of accommodation of the amblyopic and paired dominant eyes in children with hyperopic anisometropia, in contrast to conventional methods of treatment.

The age-related pattern of inner retinal thickening is affected by myopia development and progression

The longitudinal effect of myopic eye growth on each individual retinal layer has not been described to date on an established non-human primate (NHP) model of myopia. We evaluated the changes experienced by the overall and individual central and mid-peripheral retinal thickness profiles in marmosets (Callithrix jacchus) induced with myopia continuously for 5.5 months compared to controls using spectral-domain optical coherence tomography. Cycloplegic refractive state (Rx), vitreous chamber depth (VCD) and retinal thickness were measured at baseline and after 3 and 5.5 months on thirteen marmosets: eight animals with lens-induced myopia and five untreated controls. The overall and individual retinal layer thickness in the central and mid-peripheral retina were obtained and compared between groups. Regression models were used to explore the extent to which VCD or Rx changes could predict the thickness changes observed. While the retinas of control marmosets thickened significantly over 5.5 months, marmosets with lens-induced myopia experienced less retinal thickening and thinning at times, mostly in the inner neuroretinal layers and the ganglion cell-inner plexiform layer. The regression models suggest that 90% of the growth and refractive changes observed could be predicted by the thickness changes in the near to mid peripheral retina. This study confirms the longitudinal effect that myopia has on the inner retina of a NHP model during the early stages of myopia development. The observed myopia-driven differences in inner retina thickness templates might represent early biomarkers of myopia progression and associated complications.

Myopia Alters the Structural Organization of the Retinal Vasculature, GFAP-Positive Glia, and Ganglion Cell Layer Thickness

To describe the effect of myopic eye growth on the structure and distribution of astrocytes, vasculature, and retinal nerve fiber layer thickness, which are critical for inner retinal tissue homeostasis and survival. Astrocyte and capillary distribution, retinal nerve fiber (RNFL), and ganglion cell layer (GCL) thicknesses were assessed using immunochemistry and spectral domain optical coherence tomography on eleven retinas of juvenile common marmosets (Callithrix Jacchus), six of which were induced with lens-induced myopia (refraction, Rx: -7.01 ± 1.8D). Five untreated age-matched juvenile marmoset retinas were used as controls (Rx: -0.74 ± 0.4D). Untreated marmoset eyes grew normally, their RNFL thickened and their astrocyte numbers were associated with RNFL thickness. Marmosets with induced myopia did not show this trend and, on the contrary, had reduced astrocyte numbers, increased GFAP-immunopositive staining, thinner RNFL, lower peripheral capillary branching, and increased numbers of string vessels. The myopic changes in retinal astrocytes, vasculature, and retinal nerve fiber layer thickness suggest a reorganization of the astrocyte and vascular templates during myopia development and progression. Whether these adaptations are beneficial or harmful to the retina remains to be investigated.

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.

Temporal properties of positive and negative defocus on emmetropization

Studying the temporal integration of visual signals is crucial to understand how time spent on different visual tasks can affect emmetropization and refractive error development. In this study we assessed the effect of interrupting positive and negative lens-imposed defocus with brief periods of unrestricted vision or darkness. A total of forty-six marmosets were treated monocularly with soft contact lenses for 4 weeks from 10 weeks of age (OD: + 5D or − 5D; OS: plano). Two control groups wore + 5D (n = 5) or − 5D (n = 13) lenses continuously for 9 h/day. Two experimental groups had lens-wear interrupted for 30 min twice/day at noon and mid-afternoon by removing lenses and monitoring vision while marmosets sat at the center of a viewing cylinder (normal vision interruption, + 5D: n = 7; − 5D: n = 8) or while they were in the dark (dark interruption, + 5D: n = 7; − 5D: n = 6). The interruption period (30 min/day) represented approx. 10% of the total stimulation time (9 h/day). On-axis refractive error (RE) and vitreous chamber depth (VCD) were measured using an autorefractor and high frequency A-scan ultrasound at baseline and after treatment. Wearing + 5D lenses continuously 9 h/day for 4 weeks induced slowed eye growth and hyperopic shifts in RE in treated relative to contralateral control eyes (relative change, VCD: − 25 ± 11 μm, p > 0.05; RE: + 1.24 ± 0.58 D, p > 0.05), whereas − 5D lens wear resulted in larger and myopic eyes (relative change, VCD: + 109 ± 24 μm, p < 0.001; RE: − 2.03 ± 0.56 D, p < 0.05), significantly different from those in the + 5D lens-treated animals (p < 0.01 for both). Interrupting lens induced defocus with periods of normal vision or darkness for approx. 10% of the treatment time affected the resulting compensation differently for myopic and hyperopic defocus. Interrupting defocus with unrestricted vision reduced − 5D defocus compensation but enhanced + 5D defocus compensation (− 5D, VCD: + 18 ± 33 μm; RE: − 0.93 ± 0.50 D, both p > 0.05; + 5D, VCD: − 86 ± 30 μm; RE: + 1.93 ± 0.50 D, both p < 0.05). Interrupting defocus with darkness also decreased − 5D defocus compensation, but had little effect on + 5D defocus compensation (− 5D, VCD: + 73 ± 34 μm, RE: − 1.13 ± 0.77 D, p > 0.05 for both; + 5D, VCD: − 10 ± 28 μm, RE: + 1.22 ± 0.50 D, p > 0.05 for both). These findings in a non-human primate model of emmetropization are similar to those described in other species and confirm a non-linear model of visual signal integration over time. This suggests a mechanism that is conserved across species and may have clinical implications for myopia management in school-aged children.

IMI 2021 Yearly Digest

Purpose

The International Myopia Institute (IMI) Yearly Digest highlights new research considered to be of importance since the publication of the first series of IMI white papers.

Methods

A literature search was conducted for articles on myopia between 2019 and mid-2020 to inform definitions and classifications, experimental models, genetics, interventions, clinical trials, and clinical management. Conference abstracts from key meetings in the same period were also considered.

Results

One thousand articles on myopia have been published between 2019 and mid-2020. Key advances include the use of the definition of premyopia in studies currently under way to test interventions in myopia, new definitions in the field of pathologic myopia, the role of new pharmacologic treatments in experimental models such as intraocular pressure-lowering latanoprost, a large meta-analysis of refractive error identifying 336 new genetic loci, new clinical interventions such as the defocus incorporated multisegment spectacles and combination therapy with low-dose atropine and orthokeratology (OK), normative standards in refractive error, the ethical dilemma of a placebo control group when myopia control treatments are established, reporting the physical metric of myopia reduction versus a percentage reduction, comparison of the risk of pediatric OK wear with risk of vision impairment in myopia, the justification of preventing myopic and axial length increase versus quality of life, and future vision loss.

Conclusions

Large amounts of research in myopia have been published since the IMI 2019 white papers were released. The yearly digest serves to highlight the latest research and advances in myopia.

One-year myopia control efficacy of spectacle lenses with aspherical lenslets

Aims

To evaluate the 1-year efficacy of two new myopia control spectacle lenses with lenslets of different asphericity.

Methods

One hundred seventy schoolchildren aged 8–13 years with myopia of −0.75 D to −4.75 D were randomised to receive spectacle lenses with highly aspherical lenslets (HAL), spectacle lenses with slightly aspherical lenslets (SAL), or single-vision spectacle lenses (SVL). Cycloplegic autorefraction (spherical equivalent refraction (SER)), axial length (AL) and best-corrected visual acuity (BCVA) were measured at baseline and 6-month intervals. Adaptation and compliance questionnaires were administered during all visits.

Results

After 1 year, the mean changes in the SER (±SE) and AL (±SE) in the SVL group were −0.81±0.06 D and 0.36±0.02 mm. Compared with SVL, the myopia control efficacy measured using SER was 67% (difference of 0.53 D) for HAL and 41% (difference of 0.33 D) for SAL, and the efficacy measured using AL was 64% (difference of 0.23 mm) for HAL and 31% (difference of 0.11 mm) for SAL (all p<0.01). HAL resulted in significantly greater myopia control than SAL for SER (difference of 0.21 D, p<0.001) and AL (difference of 0.12 mm, p<0.001). The mean BCVA (−0.01±0.1 logMAR, p=0.22) and mean daily wearing time (13.2±2.6 hours, p=0.26) were similar among the three groups. All groups adapted to their lenses with no reported adverse events, complaints or discomfort.

Conclusions

Spectacle lenses with aspherical lenslets effectively slow myopia progression and axial elongation compared with SVL. Myopia control efficacy increased with lenslet asphericity.

Trial registration number

ChiCTR1800017683.

Choroidal thickness and ocular growth in childhood

The involvement of the choroid in ocular growth regulation has been postulated in studies showing that refractive errors correlate with alterations in choroidal thickness (ChT). The advent of optical coherence tomography imaging has enabled qualitative and quantitative assessment of the choroid. In children, ChT changes correlate with a number of ocular pathologies, including myopia, retinopathy of prematurity, and amblyopia. We synthesize mechanisms and evidence regarding choroidal thickness variation during childhood. Subfoveal ChT is influenced by a number of factors including age, ethnicity, gender, axial length, and intraocular pressure. Myopic eyes have thinner choroids compared to emmetropic and hyperopic eyes. ChT may in fact serve as a marker of myopic progression, as ChT thinning occurs early during myopic development, but this association has not been established quantitatively. In addition, subfoveal ChT appears thicker in amblyopic eyes, while prematurity and retinopathy of prematurity may be associated with thinner ChT. Overall, both animal models and clinical research indicate that ChT induces or reflects physiological changes in the eye pertaining to ocular growth or maturation.

The diversified defocus profile of the near-work environment and myopia development

Purpose

To quantify the defocus characteristics in the near‐work environment at home and investigate the relationship with subsequent myopia progression.

Methods

Fifty subjects (aged 7–12 years) were recruited and followed for 1 year. The home near‐work environment (writing desk) was measured at a baseline home‐visit using the Kinect‐for‐Windows to capture a 3‐dimensional image. The depth values of the image were then converted into scene defocus with respect to the subject’s viewpoint. The defocus characteristics were quantified as the dioptric volume (the total amount of net defocus, or DV) and standard deviation of the defocus values (SD_D). Information on home size, time spent outdoors, and in front of a desk were also obtained. Univariate correlation, and multivariate regression were used to assess the association between myopia progression, defocus characteristics, and other co‐variates.

Results

The baseline spherical equivalent refraction (M) and refraction change over 1 year (∆M) were − 1.51 ± 2.02 D and − 0.56 ± 0.45 D respectively. DV was not significantly correlated with ∆M (Spearman’s ρ = −0.25, p = 0.08), while SD_D was negatively correlated to ∆M (Spearman’s ρ = −0.42, p = 0.003). Although SD_D was not a significant predictor in multivariate analysis, the regional DV at 15°–20° eccentricity was significant (p = 0.001). Home size (F_2,50 = 7.01, p = 0.002) and time spent outdoors (Independent t = −2.13, p = 0.04) were also associated with ∆M, but not time spent in front of desk (Independent t = 0.78, p = 0.44).

Conclusion

The defocus profile in the home environment within the para‐central field of view is associated with childhood refractive error development.