IMI - Defining and Classifying Myopia: A Proposed Set of Standards for Clinical and Epidemiologic Studies

Purpose

We provide a standardized set of terminology, definitions, and thresholds of myopia and its main ocular complications.

Methods

Critical review of current terminology and choice of myopia thresholds was done to ensure that the proposed standards are appropriate for clinical research purposes, relevant to the underlying biology of myopia, acceptable to researchers in the field, and useful for developing health policy.

Results

We recommend that the many descriptive terms of myopia be consolidated into the following descriptive categories: myopia, secondary myopia, axial myopia, and refractive myopia. To provide a framework for research into myopia prevention, the condition of "pre-myopia" is defined. As a quantitative trait, we recommend that myopia be divided into myopia (i.e., all myopia), low myopia, and high myopia. The current consensus threshold value for myopia is a spherical equivalent refractive error ≤ -0.50 diopters (D), but this carries significant risks of classification bias. The current consensus threshold value for high myopia is a spherical equivalent refractive error ≤ -6.00 D. "Pathologic myopia" is proposed as the categorical term for the adverse, structural complications of myopia. A clinical classification is proposed to encompass the scope of such structural complications.

Conclusions

Standardized definitions and consistent choice of thresholds are essential elements of evidence-based medicine. It is hoped that these proposals, or derivations from them, will facilitate rigorous, evidence-based approaches to the study and management of myopia.

IMI Impact of Myopia

The global burden of myopia is growing. Myopia affected nearly 30% of the world population in 2020 and this number is expected to rise to 50% by 2050. This review aims to analyze the impact of myopia on individuals and society; summarizing the evidence for recent research on the prevalence of myopia and high myopia, lifetime pathological manifestations of myopia, direct health expenditure, and indirect costs such as lost productivity and reduced quality of life (QOL). The principal trends are a rising prevalence of myopia and high myopia, with a disproportionately greater increase in the prevalence of high myopia. This forecasts a future increase in vision loss due to uncorrected myopia as well as high myopia-related complications such as myopic macular degeneration. QOL is affected for those with uncorrected myopia, high myopia, or complications of high myopia. Overall the current global cost estimates related to direct health expenditure and lost productivity are in the billions. Health expenditure is greater in adults, reflecting the added costs due to myopia-related complications. Unless the current trajectory for the rising prevalence of myopia and high myopia change, the costs will continue to grow. The past few decades have seen the emergence of several novel approaches to prevent and slow myopia. Further work is needed to understand the life-long impact of myopia on an individual and the cost-effectiveness of the various novel approaches in reducing the burden.

Age of onset of myopia predicts risk of high myopia in later childhood in myopic Singapore children

PURPOSE

To investigate the effect of age of myopia onset on the severity of myopia later in life among myopic children.

METHODS

In this prospective study, school children aged 7-9 years from the Singapore Cohort Of the Risk factors for Myopia (SCORM) were followed up till 11 years (n = 928). Age of myopia onset was defined either through questionnaire at baseline (age 7-9 years) or subsequent annual follow-up visits. Age of onset of myopia was a surrogate indicator of duration of myopia progression till age 11 years. Cycloplegic refraction and axial length were measured at every annual eye examination. High myopia was defined as spherical equivalent of ≤-5.0 D. A questionnaire determined the other risk factors.

RESULTS

In multivariable regression models, younger age of myopia onset (per year decrease) or longer duration of myopia progression was associated with high myopia (odds ratio (OR) = 2.86; 95% CI: 2.39 to 3.43), more myopic spherical equivalent (regression coefficient (β) = -0.86 D; 95% CI: -0.93 to -0.80) and longer axial length (β = 0.28 mm; 95% CI: 0.24 to 0.32) at aged 11 years, after adjusting for gender, race, school, books per week and parental myopia. In Receiver Operating Curve (ROC) analyses, age of myopia onset alone predicted high myopia by 85% (area under the curve = 0.85), while the addition of other factors including gender, race, school, books per week and parental myopia only marginally improved this prediction (area under the curve = 0.87).

CONCLUSIONS

Age of myopia onset or duration of myopia progression was the most important predictor of high myopia in later childhood in myopic children. Future trials to retard the progression of myopia to high myopia could focus on children with younger age of myopia onset or with longer duration of myopia progression.

Inverse relationship between sleep duration and myopia

PURPOSES

To investigate the association between sleep duration and myopia.

METHODS

This population-based, cross-sectional study using a nationwide, systemic, stratified, multistage, clustered sampling method included a total of 3625 subjects aged 12-19 years who participated in the Korean National Health and Nutrition Examination Survey 2008-2012. All participants underwent ophthalmic examination and a standardized interview including average sleep duration (hr/day), education, physical activity and economic status (annual household income). Refractive error was measured by autorefraction without cycloplegia. Myopia and high myopia were defined as ≤-0.50 dioptres (D) and ≤-6.0 D, respectively. Sleep durations were classified into 5 categories: <5, 6, 7, 8 and >9 hr.

RESULTS

The overall prevalence of myopia and high myopia were 77.8% and 9.4%, respectively, and the overall sleep duration was 7.1 hr/day. The refractive error increased by 0.10 D per 1 hr increase in sleep after adjusting for potential confounders including sex, age, height, education level, economic status and physical activity. The adjusted odds ratio (OR) for refractive error was 0.90 (95% confidence interval [CI], 0.83-0.97) per 1 hr increase in sleep. The adjusted OR for myopia was decreased in those with >9 hr of sleep (OR, 0.59; 95% CI, 0.38-0.93; p for trend = 0.006) than in those with <5 hr of sleep. However, high myopia was not associated with sleep duration.

CONCLUSIONS

This study provides the population-based, epidemiologic evidence for an inverse relationship between sleep duration and myopia in a representative population of Korean adolescents.

"Heavy Eye" syndrome in the absence of high myopia: A connective tissue degeneration in elderly strabismic patients

PURPOSE

In axial high myopes with "heavy eye" syndrome, orbital MRI can be use to demonstrate degeneration of the lateral rectus-superior rectus (LR-SR) band, with the result that the lateral rectus muscle slips inferiorly and causes esotropia and hypotropia. We investigated whether this degeneration might also cause strabismus in nonmyopic elderly patients.

METHODS

Three elderly patients with strabismus, 3 strabismic high myopes, and 12 orthotropic elderly subjects underwent ophthalmic examinations and orbital MRI. The lateral rectus muscle position was determined relative to globe center from quasicoronal images and correlated with LR-SR band structure. MRI scans were compared with histology of 4 cadaveric orbits ranging in age from 17 months to 93 years.

RESULTS

Two strabismic patients exhibited hypotropia; one exhibited esotropia. Mean axial length was 24.1 +/- 0.8 mm (mean +/- SD), compared with 31.6 +/- 1.4 mm for myopes. The lateral rectus muscle position of elderly strabismic subjects averaged 4.6 +/- 1.7 mm inferior to globe center, which was significantly lower than that of orthotropic elderly subjects (2.1 +/- 1.9 mm; p = 0.01) and similar to that of high myopes (5.1 +/- 3.2 mm). On MRI scanning, 100% of strabismic elderly orbits, 67% of strabismic myopic orbits, and 12.5% of control elderly orbits showed LR-SR band thinning, discontinuity, or displacement. LR-SR band degeneration was present histologically only in older cadavers.

CONCLUSIONS

Age-related LR-SR band degeneration permits the lateral rectus muscle to slip inferiorly in elderly nonmyopes, a mechanism of strabismus similar to myopic "heavy eye" syndrome. Imaging may assist in diagnosing this mechanical cause of age-related strabismus.

Genetic and environmental effects on myopia development and progression

This review aims at elucidating the interaction between genetic and environmental factors in the aetiology of primarily low myopia. Genetics greatly influence the growth of the eye, but the fine correlation between the components of refraction for the eye to become emmetrope is affected by environmental factors such as education, metabolism, physical activity, and outdoor activity.

High prevalence of myopia in children and their parents in Hong Kong Chinese Population: the Hong Kong Children Eye Study

PURPOSE

To determine the myopia prevalence in Hong Kong Chinese children and their parents.

METHODS

It was a population-based cross-sectional study. A total of 4257 children aged 6-8 years, and 5880 parents were recruited in the Hong Kong Children Eye Study. Cycloplegic autorefraction was measured for children; and non-cycloplegic autorefraction for parents. Parental educational level, children's outdoor time, and near work were collected by validated questionnaires.

RESULTS

In children aged 6-8 years, 25.0% were myopic, and among them, 12.7% for the 6-year-olds, 24.4% for the 7-year-olds and 36.1% for the 8-year-old. About 0.7% of children aged 8 years were high myopia. In all age groups, boys (their myopia rate: 13.9% at 6 years, 26.7% at 7 years, and 38.3% at 8 years) were more myopic than girls (11.3% at 6 years, 22.0% at 7 years, 33.4% at 8 years). Among parents, 72.2% were myopic (mother, 73.2%; father, 70.7%) and 13.5% high myopia (mother, 12.8%; father, 14.5%). It was observed that prevalence decreased with ages and increased with education level.

CONCLUSION

There is a strikingly high prevalence of myopia in Hong Kong children aged 6-8, much higher than that of other regions of China. Of note, the prevalence of children was similar to that in 15 years ago. Furthermore, the myopia prevalence of parents is high, and it had already increased in this cohort. Prevention of childhood myopia is important, likewise for visual complications from high myopia in adults.

Choroidal thickness and high myopia: a case-control study of young Chinese men in Singapore

PURPOSE

To determine the distribution of choroidal thickness (CT) and ocular factors associated with CT in high myopic eyes in comparison with emmetropic eyes of young healthy adults.

METHODS

A case-control study of 648 young, male subjects, including 520 high myopes and 128 emmetropes. Choroidal imaging was performed using enhanced depth imaging spectral domain optical coherence tomography. Images were postprocessed using adaptive compensation for quality enhancement. CT was measured at nine locations, including subfovea and 1.5 and 3 mm nasal, temporal, superior and inferior to fovea.

RESULTS

The CT at the subfovea was significantly thinner (mean ± standard error: 225.87 ± 5.51 μm) for high myopes compared to emmetropes (375.15 ± 6.58 μm, p < 0.001). Likewise, CT in high myopic group was significantly thinner than emmetropic control group at all locations (p for trend <0.001 for all locations). Distribution of CT showed a markedly different pattern in high myopic eyes (thickest superiorly at 3 mm, 265.97 ± 5.97 μm) and emmetropic eyes (thickest subfoveally, 375.15 ± 6.58 μm). Choroid was thinnest at nasal 3 mm location in both the myopic (108.85 ± 3.97 μm) and emmetropic (238.25 ± 6.72 μm) groups. Among the ocular factors studied, axial length, posterior staphyloma and chorio-retinal atrophy were the significant predictors of CT.

CONCLUSIONS

Highly myopic eyes have significantly thinner choroid and showed different distribution pattern, compared to emmetropes. Axial length, posterior staphyloma and chorio-retinal atrophy are the strongest determinants of CT.

Myopia: Anatomic Changes and Consequences for Its Etiology

The process of emmetropization is the adjustment of the length of the optical axis to the given optical properties of the cornea and lens after the end of the second year of life. Up to the end of the second year of life, the eye grows spherically. Axial elongation in the process of emmetropization after the second year of life is associated with a thinning of the retina and a reduced density of retinal pigment epithelium (RPE) cells in the equatorial and retroequatorial region, and a thinning of the choroid and sclera, starting at the equator and being most marked at the posterior pole. In contrast, retinal thickness and RPE density in the macular region and thickness of Bruch membrane (BM) in any region are independent of axial length. It led to the hypothesis that axial elongation occurs by the production of additional BM in the equatorial and retroequatorial region leading to a decreased RPE density and retinal thinning in that region and a more tube-like than spherical enlargement of the globe, without compromise in the density of the macular RPE cells and in macular retinal thickness. The increased disc-fovea distance in axially myopic eyes is caused by the development and enlargement of parapapillary, BM-free, gamma zone, whereas the length of macular BM, and indirectly macular RPE cell density, and macular retinal thickness, remain constant.

Bruch's membrane thickness in high myopia

PURPOSE

To measure the thickness of Bruch's membrane (BM) and assess its associations with axial length.

METHODS

Using a light microscope, we measured the thickness of Bruch's membrane, choroid and sclera on horizontal anterior-posterior histological sections of enucleated human globes.

RESULTS

The study included 54 eyes (42 with glaucomatous optic nerve damage; 23 globes with axial length ≥26.5 mm) with a mean axial length of 26.6 ± 3.3 mm (range: 21.0-34.0 mm). In the non-highly myopic eyes, BM was significantly thicker at the pars plana region (6.6 ± 1.1 μm) than at the equator (4.1 ± 1.5 μm; p < 0.001), the midpoint between equator and posterior pole (4.1 ± 1.5 μm; p < 0.001), the parapapillary region (4.5 ± 1.0 μm; p = 0.006) or the posterior pole (4.4 ± 1.7 μm; p = 0.001). At any measurement location at or behind the ora serrata, BM thickness did not differ significantly (all p ≥ 0.40) between the non-glaucomatous non-highly myopic group and the glaucomatous non-highly myopic group, or between the non-highly myopic group and the highly myopic group. BM thickness at any location was not significantly (all p > 0.45) related to axial length. The ratio of scleral thickness to BM thickness and the ratio of choroidal thickness to BM thickness significantly decreased with longer axial length for measurements taken behind the equator.

CONCLUSIONS

BM is physiologically thickest in the pars plana, with no major thickness differences between locations at or behind the ora serrata. In contrast to choroidal and scleral thickness, BM thickness is not significantly related to axial length. Axially elongated eyes have a normal BM thickness, despite a thinned choroid and sclera.

Risk factors for high myopia: a 22-year follow-up study from childhood to adulthood

PURPOSE

To determine the effect of the definition of high myopia on its prevalence and risk factors for high myopia.

METHODS

A total of 240 myopic schoolchildren (119 boys and 121 girls) at the mean age of 10.9 years (range 8.8-12.8 years) were recruited to a randomized clinical trial of myopia treatment among children from 3rd- and 5th grades of school referred for an eye examination due to poor distant vision and having no previous spectacles. Clinical follow-ups, including refraction with cycloplegia, were conducted annually at 3 years [third follow-up here = clinical follow-up 1, (n = 237)], and thereafter twice at approximately 10-year intervals [clinical follow-ups 2 (n = 179) and 3, (n = 134)]. Additional refraction values between follow-ups 2 and 3 were received from ophthalmologists and opticians' prescriptions and records. The most recent adulthood refraction measure available was taken as the final refraction value for 204 (85%) of the original cohort [mean follow-up time (±standard deviation) 22.1 (±3.9) years]. Parental myopia, time spent on reading and close work, watching TV and outdoor activities were assessed with a questionnaire at the clinical follow-ups. The influence of different definitions of high myopia on its prevalence was analysed. The associations of different factors with high myopia were investigated.

RESULTS

Mean spherical equivalent (SE) at baseline was -1.43 (±0.60) D, ranging from -0.38 D to -3.00 D. At follow-up end, mean SE of the more myopic eye was -5.29 (±1.95) D, ranging from -1.00 D to -11.25 D. High myopia prevalence with the definitions SE < -6.00 D in the right eye and SE ≤ -6.00 D or ≤-5.00 D in either eye was 24%, 32% and 52%, respectively. In this study, high myopia was defined as spherical equivalent (SE) ≤ -6.00 D in either eye. If both parents were myopic, the odds ratio (OR) of having high myopia was 3.9 (95% CI: 1.5-10.4). Younger age at baseline predicted higher prevalence of high myopia; baseline ages between 8.8 and 9.7 and between 11.9 and 12.8 years gave prevalences 65% and 7%. Higher myopia at baseline, higher myopic progression between the first follow-ups and more time spent on reading and close work as compared with time spent outdoors were associated with high myopia.

CONCLUSION

About 32% of the children receiving first spectacles for myopia between ages of 8.8-12.8 years had high myopia (SE ≤ -6.00 D in either eye) in adulthood. Different definitions of high myopia ranging between -5 D and -6 D lead to large differences in prevalence. A generally accepted definition of high myopia is thus needed. Parental myopia, age at baseline, myopic progression during the first post onset year, and more time spent on reading and close work and less on outdoor activities in childhood were associated with adulthood high myopia.

Evaluation of 12 myopia-associated genes in Chinese patients with high myopia

PURPOSE

Two recent large-scale genome-wide association studies identified significant associations between myopia and single nucleotide polymorphisms (SNPs) near the PRSS56, BMP3, KCNQ5, LAMA2, TOX, TJP2, RDH5, ZIC2, RASGRF1, GJD2, RBFOX1, and SHISA6 genes. Our study is to examine whether rare variants in these genes contribute to high myopia.

METHODS

Whole-exome sequencing was performed on samples of 298 probands with early-onset high myopia (eoHM; spherical refraction in each meridian ≤ -6.00 [diopters] D in both eyes; age of onset < 7 years) and 195 controls (different forms of retinal degeneration including Leber congenital amaurosis, cone-rod dystrophy, and familial exudative vitroretinopathy). Potential variations in these genes were selected for further validation and comparison to the controls. Moreover, Sanger sequencing was used to evaluate the coding regions and the upstream 800 bps of GJD2 in 395 additional subjects with late-onset moderate to high myopia (loMHM; spherical refraction in each meridian ≤ -4.00 D; age of onset ≥ 7 years) and 403 healthy controls (-0.50 D ± 1.00 D).

RESULTS

Exome sequencing of the 298 probands with eoHM identified 25 rare variants that were predicted to affect coding residues. The segregation analysis and the distribution of rare variants between patients and controls did not provide evidence to support their involvement in myopia. Sanger sequencing of GJD2 in an additional 395 subjects with loMHM and 403 healthy controls did not identify myopia-associated variants.

CONCLUSIONS

We did not find evidence to support the association of myopia with rare variants in these genes, probably due to our limited sample size. Additional studies are expected to validate these results.

Longitudinal changes in axial length in high myopia: a 4-year prospective study

AIM

To determine the longitudinal changes in the axial length (AL) in patients with high myopia without any other ophthalmic disease METHODS: Participants were divided into two groups: a high myopia group (60 eyes) without myopic degeneration, such as chorioretinal atrophy or posterior staphyloma, and a control group (60 eyes). Both groups were further divided into subgroups according to the AL: subgroup 1 (≥27.5 mm), subgroup 2 (26.0-27.5 mm), subgroup 3 (24.5-26.0 mm) and subgroup 4 (<24.5 mm). The ALs were measured five times at 1-year interval using an IOL master, and the AL was fitted with linear mixed models.

RESULTS

In the high myopia group, the AL showed a relatively constant increase at each visit, and they were significantly different with previous measurements at most visits, whereas the control group showed no significant change of AL. Subgroups 1,2 and 3 showed significant changes in AL over time (0.064, 0.032 and 0.012 mm/y, respectively). In univariate analyses, age, best-corrected visual acuity, baseline AL and anterior chamber depth were significantly correlated with changes in the AL in the high myopia group. In multivariate analysis, only baseline AL remained significant (p<0.001).

CONCLUSIONS

Myopic eyes, including moderately myopic eyes, showed a consistent increase in AL over 4 years, and eyes with a longer baseline AL showed a greater increase in AL than eyes with a shorter AL.

Comparison of prophylactic higher fluence corneal cross-linking to control, in myopic LASIK, one year results

Purpose

To compare 1-year results: safety, efficacy, refractive and keratometric stability, of femtosecond myopic laser-assisted in situ keratomileusis (LASIK) with and without concurrent prophylactic high-fluence cross-linking (CXL) (LASIK-CXL).

Methods

We studied a total of 155 consecutive eyes planned for LASIK myopic correction. Group A represented 73 eyes that were treated additionally with concurrent prophylactic high-fluence CXL; group B included 82 eyes subjected to the stand-alone LASIK procedure. The following parameters were evaluated preoperatively and up to 1-year postoperatively: manifest refractive spherical equivalent (MRSE), refractive astigmatism, visual acuity, corneal keratometry, and endothelial cell counts. We plotted keratometry measurements pre-operatively and its change in the early, interim and later post-operative time for the two groups, as a means of keratometric stability comparison.

Results

Group A (LASIK-CXL) had an average postoperative MRSE of −0.23, −0.19, and −0.19 D for the 3-, 6-, and 12-month period, respectively, compared to −6.58±1.98 D preoperatively. Flat keratometry was 37.69, 37.66, and 37.67 D, compared to 43.94 D preoperatively, and steep keratometry was 38.35, 38.36, and 38.37 D, compared to 45.17 D preoperatively. The predictability of Manifest Refraction Spherical Equivalent (MRSE) correction showed a correlation coefficient of 0.979. Group B (stand-alone LASIK) had an average postoperative MRSE of −0.23, −0.20, and −0.27 D for the 3-, 6-, and 12-month period, respectively, compared with −5.14±2.34 D preoperatively. Flat keratometry was 37.65, 37.89, and 38.02 D, compared with 43.15 D preoperatively, and steep keratometry was 38.32, 38.57, and 38.66 D, compared with 44.07 D preoperatively. The predictability of MRSE correction showed a correlation coefficient of 0.970. The keratometric stability plots were stable for the LASIK CXL group and slightly regressing in the standard LASIK group, a novel stability evaluation metric that may escape routine acuity and refraction measurements.

Conclusion

Application of prophylactic CXL concurrently with myopic LASIK surgery appears to contribute to improved refractive and keratometric stability compared to standard LASIK. The procedure appears safe and provides a new potential for LASIK correction.

Homozygous loss-of-function mutation of the LEPREL1 gene causes severe non-syndromic high myopia with early-onset cataract

High myopia is a severe visual impairment which can increase the risk of retinal degeneration, subretinal hemorrhage, choroidal neovascularization, cataract and retinal detachment. We recruited an autosomal-recessive high myopia family, with affected subjects who also present early-onset cataract, retinal degeneration and other complications. Using targeted capturing and whole exome sequencing, we identified a homozygous non-sense mutation in the LEPREL1 gene which causes premature termination of the translation at the fifth amino acid (c.13C>T; p.Q5X), co-segregating with the phenotypes. LEPREL1 encodes a proline hydroxylase called prolyl 3-hydroxylase 2 (P3H2), a 2-oxoglutarate-dependent dioxygenase that hydroxylates collagens. The results show that LEPREL1 plays an important role in eye development and homozygous loss-of-function mutation of this gene can cause severely high myopia and early-onset cataract. Our study also strongly suggests that the disruption of collagen modification is one of the pathogenic mechanisms of high myopia and cataract.

Histologic differences between primary high myopia and secondary high myopia due to congenital glaucoma

PURPOSE

To search for histomorphometric differences between eyes with primary high myopia (PHM) or secondary high axial myopia (SHM) caused by congenital glaucoma, and non-highly myopic eyes (NHM).

METHODS

Histologic anterior-posterior sections were histomorphometrically examined.

RESULTS

The investigation included 58 human globes (mean age: 61.5 ± 18.5 years; axial length: 27.3 ± 4.0 mm; range: 21.0-39.0 mm). Bruch's membrane thickness was thinner in SHM than in PHM (posterior pole: p = 0.007; parapapillary region: p = 0.007); midpoint posterior pole/equator = 0.05) and thinner in SHM than in NHM (all p < 0.04), while PHM and NHM did not differ (all p > 0.50). Choroidal thickness did not differ (all p ≥ 0.40) at any measurement location between SHM and PHM, and was thinner (p < 0.05) in both myopic groups than in NHM. Posterior sclera was thinner (p < 0.001) in both myopic groups than in NHM, with no significant difference between both myopic groups. Pars plana scleral thickness was thinner (p = 0.02) in SHM than in PHM after adjusting for axial length. Scleral volume (p = 0.41) and choroidal volume (p = 0.74) did not differ between any of the groups.

CONCLUSIONS

Thinning of Bruch's membrane overall is typical for SHM while eyes with PHM have a normal Bruch's membrane thickness. It may point to Bruch's membrane as an active part in the process of emmetropization/myopization. SHM in contrast to PHM showed scleral thinning in the pars plana region suggesting that the process of emmetropization/myopization takes place posterior to the pars plana. Both SHM and PHM unspecifically showed an axial length associated with thinning of choroid and posterior sclera, while both myopic groups did not differ with NHM in choroidal and scleral volume.

Relationship between vessel density and visual field sensitivity in glaucomatous eyes with high myopia

AIMS

To investigate the global and regional relationships between peripapillary vessel density (pVD) and visual field mean sensitivity (VFMS) in glaucomatous eyes with and without high myopia in comparison with those between peripapillary retinal nerve fibre layer thickness (pRNFLT) and VFMS.

METHODS

A total of 130 eyes from 130 patients with glaucoma consisting of those with and without high myopia were included in a consecutive manner. High myopia was defined as a spherical equivalent <-6.0 dioptres or axial length >26.5 mm. The pVD and pRNFLT were evaluated using optical coherence tomography angiography (OCT-A) and spectral-domain optical coherence tomography. VFMS was assessed using a linear unlogged 1/L scale. The vasculature-function or structure-function relationships were analysed by comparing the pVD or pRNFLT to the corresponding VFMS, according to Garway-Heath map regionalisation.

RESULTS

The global pVD-VFMS association was significantly stronger than the pRNFLT-VFMS association in glaucomatous eyes with high myopia (p=0.009). However, there were no significant differences between global pVD-VFMS and pRNFLT-VFMS associations in glaucomatous eyes without high myopia (p=0.343). Regionally, the pVD-VFMS association was significantly greater than the pRNFLT-VFMS association at the superonasal, nasal and temporal sectors (all p<0.05) in glaucomatous eyes with high myopia.

CONCLUSIONS

The pVD assessment by OCT-A shows a better global and regional correlation with VFMS than a pRNFLT assessment in glaucoma patients with high myopia. The pVD may be a useful parameter in monitoring disease progression of highly myopic glaucomatous eyes.

Unilateral high myopia: optical components, associated factors, and visual outcomes

AIM

To elucidate the optical basis for unilateral high myopia and to identify the factors associated with its development.

METHODS

Medical records of 48 children (aged 4 months to 17 years; mean age 6.8 years) with unilateral high myopia (5 dioptres or more) seen consecutively by the author during a 15 year period were reviewed. 45 (94%) of the 48 patients had unilateral axial myopia.

RESULTS

The mean refractive difference between paired eyes was 9.4 (SD 3.6) dioptres and the more myopic eye was on average 3.3 (1.8) mm longer than the less myopic eye. All but three of the patients had an ocular disorder associated with reduced acuity, central nervous system abnormality, or family history of high myopia.

CONCLUSION

Clinical conditions associated with unilateral high myopia can be identified in the majority of patients and often account for the associated visual impairment.

Association of vitamin D receptor gene start codon (Fok1) polymorphism with high myopia

Background:

High myopia caused primarily due to abnormal emmetropization and excessive axial ocular elongation is associated with sight-threatening ocular pathology. Muscular dysfunction of ocular ciliary muscles due to altered intracellular calcium levels can result in defective mechanotransduction of the eye and retinal defocus. The vitamin D3 receptor (VDR; a intracellular hormone receptor) is known to mediate calcium homeostasis, influencing the development of myopia.

Materials and Methods:

In the present study, a total of 206 high myopia, 98 low myopia and 250 control samples were analyzed for VDR gene Fok1 (exon 2 start codon) polymorphism using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique.

Results:

High myopia patients revealed decrease in the frequency of ff homozygotes (8.3%) as compared to control group (14.0%), with a corresponding increase in frequency of FF homozygotes (68.9% in high myopia vs. 62.8% in controls). The frequency of f allele carriers (Ff and ff) was increased in females of high myopia (35.6%) and low myopia cases (45.4%). Elevated frequency of f allele was found only in early age at onset cases of high myopia (0.227) and later age at onset (10–20 years) cases of low myopia (0.273) as well as in low myopia cases with parental consanguinity (0.458) (P 0.035; χ² = 6.692*).

Conclusion:

The results suggest that VDR gene might not be playing a direct role in the development of myopia, but might contribute indirectly to the risk conferred by mechanical stress factors or growth/development related factors through its role in calcium homeostasis and regulation of ciliary muscle function.

Observational study of clinical characteristics of dome-shaped macula in Chinese Han with high myopia at Zhongshan Ophthalmic Centre

PURPOSE

To evaluate the prevalence of dome-shaped macula (DSM) in highly myopic eyes among Chinese Han and to detect the correlation with myopic maculopathy and macular complications.

METHODS

A total of 736 Chinese Han patients (1384 eyes) with high myopia (refractive error≤6.0 diopters or axial length ≥26.5 mm) are reviewed based on information entered into a high-myopia database at Zhongshan Ophthalmic Centre. Subfoveal choroidal thickness (SFCT) and parafoveal choroidal thickness (PFCT) are measured. The prevalence of DSM in patients with myopic maculopathy is categorised from C0 to C4. Clinical features, including macular complications, SFCT and PFCT, are compared between myopic eyes with and without DSM.

RESULTS

Among the 1384 eyes, 149 (10.77%) show DSM. In highly myopic eyes without macular complications, the best corrected visual acuity is significantly worse in patients with DSM (p=0.002), and the ratio between subfoveal and parafoveal choroidal thickness (S/PCT) is significantly elevated in patients with DSM (p=0.021). The proportion of foveal schisis (17.24% vs 62.86%) is much lower in eyes with DSM compared with those without DSM. However, the proportions of extrafoveal schisis (39.66% vs 5.37%), foveal serous retinal detachment (SRD) (5.17% vs 0) and epiretinal membrane (ERM) (24.14% vs 10.74%) are much higher in eyes with DSM. The proportion of DSM was lower in C0 and C1, but higher proportion of DSM was found in C3 and C4.

CONCLUSIONS

DSM is found in 10.77% of highly myopic eyes among Chinese Han. DSM might be a protective mechanism for foveal schisis and a risk factor for extrafoveal schisis, SRD and ERM.

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.

Choroidal thinning in high myopia measured by optical coherence tomography

Purpose

To investigate the rate of choroidal thinning in highly myopic eyes.

Patients and methods

A retrospective observational study of 37 eyes of 26 subjects (nine males and 17 females, mean age 39.6 ± 7.7 years) with high myopia but no pathologies who had undergone spectral domain optical coherence tomography and repeated the test 1 year later (1 ± 0.25 year) at Osaka University Hospital, Osaka, Japan. Patients older than 50 years with visual acuity worse than 20/40 or with whitish chorioretinal atrophy involving the macula were excluded. Two masked raters measured the choroidal thicknesses (CTs) at the fovea, 3 mm superiorly, inferiorly, temporally, and nasally on the images and averaged the values. The second examination was about 365 days after the baseline examination. The CT reduction per year (CTRPY) was defined as (CT 1 year after – baseline CT)/days between the two examinations × 365. The retinal thicknesses were also investigated.

Results

The CTRPY at the fovea was −1.0 ± 22.0 μm (range −50.2 to 98.5) at the fovea, −6.5 ± 24.3 μm (range −65.8 to 90.2) temporally, −0.5 ± 22.3 μm (range −27.1 to 82.5) nasally, −9.7 ± 21.7 μm (range −40.1 to 60.1) superiorly, and −1.4 ± 25.5 μm (range −85.6 to 75.2) inferiorly. There were no significant differences in the CTRPY at each location (P = 0.34). The CT decreased significantly (P < 0.05) only superiorly. The superior CTRPY was negatively correlated with the axial length (P < 0.05). The retinal thickness at the fovea did not change. Stepwise analysis for CTRPY selected axial length (P = 0.04, R² = 0.13) and age (P = 0.08, R² = 0.21) as relevant factors.

Conclusions

The highly myopic choroid might gradually thin and be affected by many factors. Location and axial length are key factors to regulate the rate of choroidal thinning in highly myopic eyes. Overall choroidal thickness was not found to change significantly. Longer follow-ups are needed.

Integrins: An Important Link between Angiogenesis, Inflammation and Eye Diseases

Integrins belong to a group of cell adhesion molecules (CAMs) which is a large group of membrane-bound proteins. They are responsible for cell attachment to the extracellular matrix (ECM) and signal transduction from the ECM to the cells. Integrins take part in many other biological activities, such as extravasation, cell-to-cell adhesion, migration, cytokine activation and release, and act as receptors for some viruses, including severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2). They play a pivotal role in cell proliferation, migration, apoptosis, tissue repair and are involved in the processes that are crucial to infection, inflammation and angiogenesis. Integrins have an important part in normal development and tissue homeostasis, and also in the development of pathological processes in the eye. This review presents the available evidence from human and animal research into integrin structure, classification, function and their role in inflammation, infection and angiogenesis in ocular diseases. Integrin receptors and ligands are clinically interesting and may be promising as new therapeutic targets in the treatment of some eye disorders.

One-year visual outcomes and optical quality of femtosecond laser small incision lenticule extraction and Visian Implantable Collamer Lens (ICL V4c) implantation for high myopia

PURPOSE

To compare one-year visual outcomes and optical quality after femtosecond laser small incision lenticule extraction (SMILE) and Visian Implantable Collamer Lens with a central hole (ICL V4c) implantation for high myopia.

METHODS

This prospective non-randomized study included 37 eyes of 20 patients who underwent SMILE (G-S) and 39 eyes of 20 patients who underwent ICL V4c implantation (G-V). Spherical equivalent (SE), uncorrected distance visual acuity, corrected distance visual acuity, retinal image quality and intraocular scattering were evaluated at one year after surgery. Each model was adjusted for age, gender, eye and preoperative SE during treatment.

RESULTS

At the one-year follow-up, G-S and G-V showed similar safety index (1.13 ± 0.13 and 1.11 ± 0.15, respectively) and efficacy index (1.05 ± 0.14 and 1.06 ± 0.15, respectively). All 21 eyes with Toric ICL (TICL) had a postoperative astigmatism of ≤0.5 dioptres (D), while the astigmatism was ≤0.5 D in all G-S eyes. Thirty-six G-S eyes (97%) and 35 G-V eyes (90%) were within ± 0.5 D of the target SE. The changes in the modulation transfer function cut-off frequency (MTF_cut-off ) and the objective scatter index from before operation to one year following the operation were not significantly different between the groups (p = 0.523 and 0.826, respectively).

CONCLUSION

Both SMILE and ICL V4c implantation provide good safety, efficacy, predictability, and stability in correcting high myopia. Optical quality including intraocular scattering was great and relatively stable in both groups during the one-year observation period.

Correlation of macular choroidal thickness with concentrations of aqueous vascular endothelial growth factor in high myopia

PURPOSE

To investigate the association of both aqueous and serum vascular endothelial growth factor (VEGF) levels and macular choroidal thickness in high myopia.

MATERIALS AND METHODS

VEGF concentrations were measured in aqueous and serum samples via enzyme-linked immunosorbent assay (ELISA) and compared between high myopia (n = 36 eyes, 36 patients) and normal control (n = 42 eyes, 42 patients) eyes. Macular choroidal thickness, the distance from the retinal pigment epithelium (RPE) to the scleral interface, was determined via enhanced depth-imaging optical coherence tomography (EDI-OCT). Axial length was measured using the intraocular (IOL) lens Master.

RESULTS

Aqueous levels of VEGF from high myopia patients were significantly lower compared with those from control persons (61.4 ± 27.6 versus 122.6 ± 52.4 pg/ml; p < 0.001), respectively. Macular choroidal thickness of high myopia patients was significantly lower compared with that of control persons (111.1 ± 45.0 versus 230.6 ± 81.8 μm; p < 0.001), respectively. Aqueous levels of VEGF were significantly associated with both macular choroidal thickness (R(2)= 0.641; p < 0.001) and axial length (R(2)= 0.679; p < 0.001) in high myopia patients. In addition, there was a significantly negative correlation between macular choroidal thickness and axial length (R(2)= 0.69; p < 0.001). However, no correlation between serum VEGF and either macular choroidal thickness or axial length was detected in high myopia patients (R(2)= 0.009; p = 0.59; R(2)= 0.00002; p = 0.981).

CONCLUSIONS

Macular choroidal thickness was significantly correlated with aqueous, but not serum, levels of VEGF in highly myopic eyes. Macular choroidal thickness may be of predictive value for identifying aqueous VEGF levels in high myopia patients and may, thus, be a useful prognostic modality.