Ocular Biometry Percentile Curves and Their Relation to Myopia Development in Indian Children.

Background: The aim of the present study was to provide ocular biometry percentile values for Indian children between the ages of 6 and 12 and to validate the usefulness of centiles in predicting myopia development. Methods: The study was part of a longitudinal study-the Sankara Nethralaya Tamil Nadu Essilor Myopia Study (STEM), where objective refraction and ocular biometry were measured for children studying in grades 1, 4, and 6 at baseline (2019-2020). These data were used to generate ocular biometry percentile curves (both for axial length (AL) and AL/corneal curvature (AL/CR) ratios). The usefulness of percentile values in predicting myopia development was estimated from follow-up data (2022). Results: The total number of children in the three grades at baseline was 4514 (age range 6 to 12). Boys represented 54% (n = 2442) of the overall sample. The prevalence of myopia at baseline was 11.7% (95% CI from 10.8 to 12.7%) in these three grades. Both the AL and AL/CR ratio centiles showed a linear trend with an increase in AL and AL/CR with increasing grades (p < 0.001) for all percentiles (2, 5, 10, 25, 50, 75, 90, 95, 98, and 99) when stratified by sex. In the follow-up data (n = 377), the 75th and 50th percentiles of the AL/CR ratio had an area under the curve (AUC) of 0.79 and 0.72 to predict myopia onset for grade 4 and 6 children at baseline. Combining baseline AL with the centile shift in follow-up as a predictor increased the AUC to 0.83. Conclusions: The present study has provided centile values specific for Indian children between the ages of 6 and 12 to monitor and intervene where children are at a higher risk of myopia development.

Clinical indicators for diabetic eyecare delivered by optometrists in Australia: a Delphi study.

CLINICAL RELEVANCE: Valid and updated clinical indicators can serve as important tools in assessing and improving eyecare delivery. BACKGROUND: Indicators for diabetic eyecare in Australia were previously developed from guidelines published before 2013 and then used to assess the appropriateness of care delivery through a nationwide patient record card audit (the iCareTrack study). To reflect emerging evidence and contemporary practice, this study aimed to update clinical indicators for optometric care for people with type 2 diabetes in Australia. METHODS: Forty-five candidate indicators, including existing iCareTrack and new indicators derived from nine high-quality evidence-based guidelines, were generated. A two-round modified Delphi process where expert panel members rated the impact, acceptability, and feasibility of the indicators on a 9-point scale and voted for inclusion or exclusion of the candidate indicators was used. Consensus on inclusion was reached when the median scores for impact, acceptability, and feasibility were ≥7 and >75% of experts voted for inclusion. RESULTS: Thirty-two clinical indicators with high acceptability, impact and feasibility ratings (all median scores: 9) were developed. The final indicators were related to history taking (n = 12), physical examination (n = 8), recall period (n = 5), referral (n = 5), and patient education/communication (n = 2). Most (14 of 15) iCareTrack indicators were retained either in the original format or with modifications. New indicators included documenting the type of diabetes, serum lipid level, pregnancy, systemic medications, nephropathy, Indigenous status, general practitioner details, pupil examination, intraocular pressure, optical coherence tomography, diabetic retinopathy grading, recall period for high-risk diabetic patients without retinopathy, referral of high-risk proliferative retinopathy, communication with the general practitioner, and patient education. CONCLUSION: A set of 32 updated diabetic eyecare clinical indicators was developed based on contemporary evidence and expert consensus. These updated indicators inform the development of programs to assess and enhance the eyecare delivery for people with diabetes in Australia.

Myopia and Its Association with Near Work, Outdoor Time, and Housing Type among Schoolchildren in South India.

SIGNIFICANCE: In this comprehensive assessment of environmental associations with refractive status among schoolchildren in India, outdoor time was the key modifiable risk factor associated with myopia rather than time spent on near work. PURPOSE: This study aimed to investigate the environmental risk factors associated with myopia among adolescent schoolchildren in South India. METHODS: Children in grades 8 to 10 from 11 schools in Tamil Nadu, South India, underwent eye examination and risk factor assessments through a modified version of the Sydney myopia questionnaire. Time spent on near work and outdoors was analyzed after division into three groups based on tertiles. Mixed-effects logistic regression was performed to assess the factors associated with myopia. RESULTS: A total of 3429 children (response rate, 78.4%) provided both questionnaire and refraction data. The mean (standard deviation) age was 14 (0.93) years with an equal distribution of sexes. Myopia was present among 867 children (noncycloplegic spherical equivalent refraction, ≤-0.75 D). Refraction was not associated with near work tertiles ( P = .22), whereas less time outdoors was associated with higher myopic refractions ( P = .01). Refraction shifted toward increased myopia with an increase in the near-work/outdoor time ratio ( P = .005). Children living in apartment housing had a higher prevalence of myopia compared with other types of housing ( P < .001). In multivariate analysis, increased time outdoors was a protective factor against myopia (odds ratio, 0.79; 95% confidence interval, 0.63 to 0.99; P = .04), whereas living in apartment housing (odds ratio, 1.27; 95% confidence interval, 1.04 to 1.55; P = .02) was a significant risk factor. CONCLUSIONS: In this cohort of Indian children, outdoor time, increased near-work/outdoor time ratio, and type of housing were the factors associated with myopia. Policies should target implementing a balance between near-work and outdoor time among children.

Prevalence of myopia among urban and suburban school children in Tamil Nadu, South India: findings from the Sankara Nethralaya Tamil Nadu Essilor Myopia (STEM) Study.

PURPOSE: To report the baseline prevalence of myopia among school children in Tamil Nadu, South India from a prospective cohort study. METHODS: Children between the ages of 5 and 16 years from 11 schools in two districts of Tamil Nadu underwent vision screening. All children underwent visual acuity assessment using a Pocket Vision Screener followed by non-cycloplegic open-field autorefraction (Grand Seiko WAM-5500). Myopia was defined as a spherical equivalent (SE) refraction of ≤-0.75 D and high myopia was defined as SE ≤ -6.00 D. Distribution of refraction, biometry and factors associated with prevalence of myopia were the outcome measures. RESULTS: A total of 14,699 children completed vision screening, with 2% (357) of them having ocular abnormalities other than refractive errors or poor vision despite spectacle correction. The remaining 14,342 children (7557 boys; 52.69%) had a mean age of 10.2 (Standard Deviation [SD] 2.8) years. A total of 2502 had myopia in at least one eye, a prevalence of 17.5% (95% CI: 14.7-20.5%), and 74 (0.5%; 95% CI: 0.3-0.9%) had high myopia. Myopia prevalence increased with age (p < 0.001), but sex was not associated with myopia prevalence (p = 0.24). Mean axial length (AL; 23.08 (SD = 0.91) mm) and mean anterior chamber depth (ACD; 3.45 (SD = 0.27) mm) positively correlated with age (p < 0.001). The mean flat (K1; 43.37 (SD = 1.49) D) and steep (K2; 44.50 (SD = 1.58) D) corneal curvatures showed negative correlation with age (p = 0.02 and p < 0.001, respectively). In the multivariable logistic regression, older age and urban school location had higher odds for prevalence of myopia. CONCLUSION: The baseline prevalence of myopia among 5- to 16-year-old children in South India is larger than that found in previous studies, indicating that myopia is becoming a major public health problem in this country.

Developing consensus-based referral criteria for low vision services in Australia.

PURPOSE: To develop expert consensus on referral criteria for low vision services in Australia. METHODS: In a modified online Delphi process, a panel of 38 Australian experts in low vision (including ophthalmologists, optometrists, orthoptists, occupational therapists, orientation and mobility professionals, researchers and managers) participated in three rounds of consensus building over a period of 5 months commencing in 2019. Initially, 90 statements were developed, addressing what should be included in best-practice low vision referral criteria, currently used criteria, timing of referral and responsibility for referral. By the third round, these had been reduced and refined to a total of four statements. RESULTS: In three Delphi rounds, the expert panel produced three key recommendations for low vision referral: (1) that low vision referral should be based mainly on the impact of uncorrectable vision impairment on function and well-being; (2) clinical measures of visual acuity and visual field might be a secondary consideration and (3) it is important to fully inform a person about low vision services at an early stage of vision loss and to involve them in decision making about referral. There was consensus on the need for clear referral pathways and that both ophthalmologists and optometrists have primary responsibility to refer for low vision services. CONCLUSIONS: Although recommendations and guidelines should not replace sound individual clinical judgement, promotion and adoption of these consensus recommendations could assist health care professionals in providing appropriate and timely referral for low vision services to the benefit of people with vision impairment.

The Sankara Nethralaya Tamil Nadu Essilor Myopia (STEM) Study-Defining a Threshold for Non-Cycloplegic Myopia Prevalence in Children.

The aim of this study was to investigate the agreement between cycloplegic and non-cycloplegic autorefraction with an open-field auto refractor in a school vision screening set up, and to define a threshold for myopia that agrees with the standard cycloplegic refraction threshold. The study was conducted as part of the Sankara Nethralaya Tamil Nadu Essilor Myopia (STEM) study, which investigated the prevalence, incidence, and risk factors for myopia among children in South India. Children from two schools aged 5 to 15 years, with no ocular abnormalities and whose parents gave informed consent for cycloplegic refraction were included in the study. All the children underwent visual acuity assessment (Pocket Vision Screener, Elite school of Optometry, India), followed by non-cycloplegic and cycloplegic (1% tropicamide) open-field autorefraction (Grand Seiko, WAM-5500). A total of 387 children were included in the study, of whom 201 were boys. The mean (SD) age of the children was 12.2 (±2.1) years. Overall, the mean difference between cycloplegic and non-cycloplegic spherical equivalent (SE) open-field autorefraction measures was 0.34 D (limits of agreement (LOA), 1.06 D to -0.38 D). For myopes, the mean difference between cycloplegic and non-cycloplegic SE was 0.13 D (LOA, 0.63D to -0.36D). The prevalence of myopia was 12% (95% CI, 8% to 15%) using the threshold of cycloplegic SE ≤ -0.50 D, and was 14% (95% CI, 11% to 17%) with SE ≤ -0.50 D using non-cycloplegic refraction. When myopia was defined as SE of ≤-0.75 D under non-cycloplegic conditions, there was no difference between cycloplegic and non-cycloplegic open-field autorefraction prevalence estimates (12%; 95% CI, 8% to 15%; p = 1.00). Overall, non-cycloplegic refraction underestimates hyperopia and overestimates myopia; but for subjects with myopia, this difference is minimal and not clinically significant. A threshold of SE ≤ -0.75 D agrees well for the estimation of myopia prevalence among children when using non-cycloplegic refraction and is comparable with the standard definition of cycloplegic myopic refraction of SE ≤ -0.50 D.

Stakeholder acceptance of digital team-based learning.

Team-Based Learning (TBL) can be associated with administrative processes that are labour intensive. A commercially-available online system offered an opportunity to reduce this burden. The aims of this study were to test the feasibility of integrating digital TBL into health curricula, and to explore the experiences and perspectives of students and educators participating in digital TBL. A prospective mixed methods design was used to survey postgraduate nursing and optometry students (n = 162), and educators (n = 8) at an Australian university. Student and educator perceptions of digital TBL collected were: usability (System Usability Scale); level of student engagement (Student Self-Report of Engagement); and user satisfaction post-participation in digital TBL (Post-Study System Usability Questionnaire). Mean Student Self-Report of Engagement Scores reflected high student engagement with significantly higher levels of engagement reported for digital (x‾=4.16, SD = 0.199) over paper-based (x‾=3.97, SD = 0.267) TBL (p = 0.001). System Usability Scores revealed students (during: x‾ = 72.35, SD = 15.70; post: x‾ = 74.02, SD = 14.00) and educators (x‾=75.0, SD = 15.12) perceived usability of digital TBL to be above average for systems on this scale. Students (x‾=2.40, SD = 0.19) and educators (x‾=2.36, SD = 0.80) were highly satisfied with digital TBL (Post-Study System Usability Questionnaire). High satisfaction and engagement outcomes suggest digital TBL is feasible, efficient, engaging and well accepted by stakeholders.

Impact of Axial Eye Size on Retinal Microvasculature Density in the Macular Region.

Mechanical tissue stresses are important contributors to the increased risk of sight-threatening pathology in larger, more myopic eyes. The contribution of altered ocular vasculature to the development of this pathology is less well defined. The current study investigated the impact of eye size on the superficial vasculature of the macula. Subjects (n = 104) aged 18-50, with no history of ocular or vascular disease, or myopia control, were recruited from university staff and student populations in Australia and Hong Kong. Refractive error, ocular size, retinal morphology and vascular morphology were quantified through open field autorefraction, ocular biometry and ocular coherence tomography angiography. Morphology of the superficial retinal capillary plexus was assessed over a 3 × 3 mm fovea-centred area. Perfusion area and vessel length densities were analysed relative to axial eye length and retinal thickness. A significant inverse association was found between axial length and vascular density measures (perfusion area density r2 = 0.186, p < 0.001; and vessel length density r2 = 0.102, p = 0.001). Perfusion area and vessel length densities were reduced by 5.8% (p = 0.001) in the longest, relative to the shortest, eyes. The aggregated ganglion cell layer inner plexiform layer thickness was also inversely associated with eye size (r2 = 0.083, p = 0.003), and reduced, by 8.1% (p < 0.001), in the longest eyes. An inverse association of eye size and superficial retinal vasculature density, that is not simply explained by retinal expansion or image magnification factors, was confirmed. These data support the hypothesis that ongoing metabolic challenges may underlie the development of myopia-related and -associated pathology in larger eyes.

Multiple scan averaging to yield accurate quantitative analysis of optical coherence tomography angiograms.

Optical coherence tomography angiography (OCTA) is widely used in ophthalmic practice. Most OCTA studies based their findings on a single OCTA measurement. We conducted an observational study of 82 eyes from 82 healthy subjects to compare variations of OCTA parameters among five successive measurements. A 3 × 3 mm Early Treatment of Diabetic Retinopathy Study grid centred at fovea was used. An average from five successive OCTA measurements (both perfusion density and vessel density) was calculated to be used as the reference standard. There was no significant difference in perfusion and vessel densities among five successive OCTA measurements, and from different levels of averaging. Perfusion density was close to the reference standard when average from three measurements was used (discrepancy within 1.5%) as compared with using just one measurement (discrepancy from 3.2% to 4.5%). Vessel density was also close to reference standard when average from three measurements was used (within 0.8 mm-1) as compared with using just one measurement (2 mm-1). Software feature that allows OCTA devices to average quantitative parameters for analysis will be useful.

Reduced Scleral TIMP-2 Expression Is Associated With Myopia Development: TIMP-2 Supplementation Stabilizes Scleral Biomarkers of Myopia and Limits Myopia Development.

Purpose: The purpose of this study was to determine the endogenous regulation pattern of tissue inhibitor of metalloproteinase-2 (TIMP-2) in the tree shrew sclera during myopia development and investigate the capacity of exogenous TIMP-2 to inhibit matrix metalloproteinase-2 (MMP-2) in vitro and both scleral collagen degradation and myopia development in vivo. Methods: TIMP-2 expression in the sclera during myopia development was assessed using polymerase chain reaction. In vitro TIMP-2 inhibition of MMP-2 was investigated using a gelatinase activity plate assay and zymography. Tree shrews were injected with a collagen precursor before undergoing monocular form deprivation and concurrent daily subconjunctival injections of either TIMP-2 or vehicle to the form-deprived eye. In vivo ocular biometry changes were monitored, and scleral tissue was collected after 12 days and assayed for collagen degradation. Results: The development of myopia was associated with a mean reduction in TIMP-2 mRNA expression after 5 days of form deprivation (P < 0.01). Both activation and activity of MMP-2 were inhibited by TIMP-2 with an IC50 of 10 to 20 and 2 nM, respectively. In vivo exogenous addition of TIMP-2 significantly reduced myopia development (P < 0.01), due to reduced vitreous chamber elongation (P < 0.01). In vivo TIMP-2 treatment also significantly inhibited posterior scleral collagen degradation relative to vehicle-treated eyes (P < 0.01), with levels similar to those in control eyes. Conclusions: Myopia development in mammals is associated with reduced expression of TIMP-2, which contributes to increased degradative activity in the sclera. It follows that replenishment of this TIMP-2 significantly reduced the rate of both scleral collagen degradation and myopia development.

The M4 muscarinic antagonist MT-3 inhibits myopia in chick: evidence for site of action.

PURPOSE: It is well established that the broad-band muscarinic antagonist, atropine is effective at inhibiting the progression of myopia and does so by preventing the elongation of the vitreous chamber of the eye. However, uncertainty remains as to whether this effect occurs through a receptoral mechanism and, if so, which muscarinic receptor subtype mediates this effect. Previous work, in avian and mammalian models of myopia, implicates the M1 and M4 receptors as potential targets. The current study used physiologically relevant concentrations of highly selective muscarinic antagonists (MT-3 and MT-7) to further characterise the role of the M4 receptor in the control of myopia in the chick model of refractive development. METHODS: Nine groups of week-old chicks underwent 5 days of monocular deprivation, with a translucent occluder, to induce myopia. These animals had either no injection, scleral puncture with a needle, or daily intravitreal injections of MT-3 (M4-selective), MT-7 (M1-selective) or vehicle. Three concentrations of each antagonist were delivered (250 nm, 2.5 µm and 10 µm). After the treatment period, keratometry, retinoscopy and A-Scan ultrasound were used to assess ocular biometry. RESULTS: MT-3 treatment produced a significant dose-dependent reduction in relative myopia (treated-control eye) compared to vehicle treatment (vehicle -10.1 ± 1.1 D vs 10 µm MT-3 -4.0 ± 1.5 D, p < 0.01). The majority of this effect was due to reduced relative vitreous chamber elongation in drug treated eyes (vehicle +0.26 ± 0.04 mm, 10 µm MT-3 +0.08 ± 0.07 mm, p < 0.05). In contrast, MT-7 had no significant effect on the development of myopia (MT-7 10 µm: myopia, -12.1 ± 0.8 D and vitreous chamber depth, +0.23 ± 0.07 mm). Calculations indicate that the experimentally achieved concentrations of MT-3 at intraocular receptors necessary to inhibit 50% of myopia development (between 5 and 50 nm) were consistent with published in vitro affinity constants for the M4 receptor and below those for the M1 receptor. Histology demonstrated that MT-3 at the doses used had no gross effects on the retina, indicating a non-toxic mode of action. CONCLUSIONS: In the chick, which lacks a homologue of the mammalian M1 receptor, the above findings represent compelling evidence that muscarinic antagonists prevent myopia progression through an M4-receptor mediated mechanism, most likely located in the retina.

Inhibition of matrix metalloproteinase activity in the chick sclera and its effect on myopia development.

PURPOSE: To investigate the contribution of matrix degradation in the two-layer avian sclera to the development of myopia. METHODS: Tissue inhibitor of metalloproteinase-2 (TIMP-2) was used to inhibit chick scleral collagen degradation with (3)H-proline, a marker for this effect. Ex vivo scleral culture experiments confirmed TIMP-2 doses for in vivo experimentation. Ocular growth and refractive response to exogenous TIMP-2 (11.25, 2.25, and 0.45 picomoles, plus vehicle only) were monitored in 7-day-old chicks during the induction of myopia over 4 days with a translucent occluder. Collagen degradation was assessed, in whole sclera and in separated scleral layers by using the same paradigm (11.25 picomoles TIMP-2; vehicle only). RESULTS: Approximately 60% of collagen degradation was inhibited with low (2 nM) doses of TIMP-2 in the ex vivo sclera. Degradative activity in the in vivo chick sclera increased significantly (46%) during myopia development, with all the altered activity confined to the fibrous layer. Addition of TIMP-2 significantly reduced (by 46%) this accelerated scleral collagen degradation, also by acting in the fibrous layer. TIMP-2 had no significant effect on (3)H-proline incorporated in the cartilaginous scleral layer and cornea. Despite inhibiting collagen degradation TIMP-2 had no significant effect on myopia development. CONCLUSIONS: Increased collagen degradation is a feature of scleral remodeling in chick myopia development, but is confined to the fibrous scleral layer. Significant inhibition of this collagenolytic activity with TIMP-2 has little effect on refractive error development, suggesting that collagen degradation in the sclera contributes little to the development of myopia in the chick.

Regulation of scleral cell contraction by transforming growth factor-beta and stress: competing roles in myopic eye growth.

Reduced extracellular matrix accumulation in the sclera of myopic eyes leads to increased ocular extensibility and is related to reduced levels of scleral transforming growth factor-beta (TGF-beta). The current study investigated the impact of this extracellular environment on scleral cell phenotype and cellular biomechanical characteristics. Scleral cell phenotype was investigated in vivo in a mammalian model of myopia using the myofibroblast marker, alpha-smooth muscle actin (alpha-SMA). In eyes developing myopia alpha-SMA levels were increased, suggesting increased numbers of contractile myofibroblasts, and decreased in eyes recovering from myopia. To understand the factors regulating this change in scleral phenotype, the competing roles of TGF-beta and mechanical stress were investigated in scleral cells cultured in three-dimensional collagen gels. All three mammalian isoforms of TGF-beta altered scleral cell phenotype to produce highly contractile, alpha-SMA-expressing myofibroblasts (TGF-beta3>TGF-beta2>TGF-beta1). Exposure of cells to the reduced levels of TGF-beta found in the sclera in myopia produced decreased cell-mediated contraction and reduced alpha-SMA expression. These findings are contrary to the in vivo gene expression data. However, when cells were exposed to both the increased stress and the reduced levels of TGF-beta found in myopia, increased alpha-SMA expression was observed, replicating in vivo findings. These results show that although reduced scleral TGF-beta is a major contributor to the extracellular matrix remodeling in the myopic eye, it is the resulting increase in scleral stress that dominates the competing TGF-beta effect, inducing increased alpha-SMA expression and, hence, producing a larger population of contractile cells in the myopic eye.

Retinal and choroidal TGF-beta in the tree shrew model of myopia: isoform expression, activation and effects on function.

A visually evoked signalling cascade, which begins in the retina, transverses the choroid, and mediates scleral remodelling, is considered to control eye growth. The ubiquitous cytokine TGF-beta has been associated with alterations in ocular growth, where alterations in scleral TGF-beta isoforms mediate the scleral remodelling that results in myopia. However, while the TGF-beta isoforms have been implicated in the scleral change during myopia development, it is unclear whether alterations in retinal and choroidal isoforms constitute part of the retinoscleral cascade. This study characterised the retinal and choroidal TGF-beta isoform profiles and TGF-beta2 activation during different stages of myopia development, as induced by form deprivation, in a mammalian model of eye growth. Using quantitative real-time PCR, the mRNA for all three mammalian isoforms of TGF-beta was detected in tree shrew retina and choroid. Distinct tissue-specific isoform profiles were observed for the retina (TGF-beta1:TGF-beta2:TGF-beta3=20:2085:1) and choroid (TGF-beta1:TGF-beta2:TGF-beta3=16:23:1), which remained constant over the development period under investigation. The active and latent pools of retinal TGF-beta2 were quantified using ELISA with the majority (>94%) of total TGF-beta2 found in the latent form. Unlike previous scleral data showing early and continuous decreases in TGF-beta isoform expression during myopia development, the levels of the three isoforms remained within normal ranges for retinal (TGF-beta1, -14 to +14%; TGF-beta2, -2 to +20%; TGF-beta3, -10 to +26%) and choroidal (TGF-beta1, -19 to +21%; TGF-beta2, -26 to +8%; TGF-beta3, -11 to +28%) tissues during myopia development (induction times of 3h, 7h, 11h, 24h, and 5 days). A 40% decrease in retinal TGF-beta2 activation was observed after 5 days of myopia development, however, there was no functional correlate of altered TGF-beta2 activity, as assessed by the retinal ERG response. Overall, these data highlight the specific nature of TGF-beta isoform expression, which reflects the differences in tissue structure and function. While TGF-beta isoforms are involved in scleral regulation during myopia development in mammals, they do not have a primary role in the retinal and choroidal signals. Thus, the regulation of eye growth via the retinoscleral cascade involves more than one factor, which is likely to be tissue-specific in nature.

Biomechanics of the sclera in myopia: extracellular and cellular factors.

PURPOSE: Excessive axial elongation of the eye is the principal structural cause of myopia. The increase in eye size results from active remodelling of the sclera, producing a weakened scleral matrix. The present study will detail the biomechanics of the sclera and highlight the matrix and cellular factors important in the control of eye size. METHODS: Scleral elasticity (load vs. tissue extension) and creep rate (tissue extension vs. time) have been measured postmortem in human eyes. Animal models of myopia have allowed the direct relevance of scleral biomechanics to be investigated during myopia development. Recently, data on tissue matrices incorporating scleral fibroblasts have highlighted the role of cellular contraction in scleral biomechanics. RESULTS: Scleral elasticity is increased in eyes developing myopia, with a reduction in the failure load of the tissue. Scleral creep rate is increased in the sclera from eyes developing myopia, and reduced in eyes recovering from myopia. These changes in biomechanical properties of the sclera occur early in the development of myopia (within 24 h). Alterations in scleral biomechanics during myopia development have been attributed to changes in matrix constituents, principally reduced collagen content. Although the biochemical structure of the sclera plays a critical role in defining the mechanical properties, recent studies investigating the cellular mechanics of the sclera, implicate myofibroblasts in scleral biomechanics. Scleral myofibroblasts have the capacity to contract the matrix and are regulated by tissue stress and growth factors such as transforming growth factor-beta. Changes in these regulatory factors have been observed during myopia development, implicating cellular factors in the resultant weakened sclera. CONCLUSIONS: Changes in the biomechanical properties of the sclera are important in facilitating the increase in axial length that results in myopia. Understanding the matrix and cellular factors contributing to the weakened sclera may aid in the development of a clinically appropriate treatment for myopia.

Expression of collagen-binding integrin receptors in the mammalian sclera and their regulation during the development of myopia.

PURPOSE: The sclera has a collagen-rich extracellular matrix that undergoes significant biochemical and biomechanical remodeling during myopic eye growth. The integrin family of cell surface receptors play critical roles in extracellular matrix and biomechanical remodeling in connective tissues. This study identified the major collagen-binding integrin receptors in the mammalian sclera and investigated their mRNA expression during the development of and recovery from experimental myopia. METHODS: The presence of the alpha1, alpha2, and beta1 integrin subunits was examined by using tree-shrew-specific primers and RT-PCR. Scleral expression of alpha1beta1 and alpha2beta1 receptor proteins was further investigated by using Western blot analysis and immunocytochemistry. Myopia was induced monocularly by occluding pattern vision and scleral tissue collected after 24 hours and 5 days. In a subset of the 5-day treatment group, vision was restored for 24 hours before tissue was isolated. Total RNA was extracted, and integrin subunit expression levels were assessed with quantitative real-time PCR. RESULTS: The presence of the major collagen-binding integrin subunits alpha1, alpha2, and beta1 was confirmed by RT-PCR in both scleral tissue and cultured scleral fibroblasts. Both the alpha1 and alpha2 integrin subunit proteins were identified in tree shrew scleral tissues, and integrin receptor expression was localized to scleral fibroblast focal adhesions. After only 24 hours of myopia induction, a time when no structural elongation has occurred, significant decreases were observed in the expression of the alpha1 (-36%) and beta1 (-44%) integrin subunits. After 5 days of myopia induction, alpha1 integrin expression had returned to baseline levels, whereas the alpha2 subunit showed a significant decrease in expression (-52%). The 5-day integrin profiles were maintained during recovery from the induced myopia, with only alpha2 integrin showing a statistically significant relative decrease in expression (-41%). CONCLUSIONS: The mammalian sclera expresses the major collagen-binding integrin subunits. The alpha1 and beta1 subunit expression was decreased early during the development of myopia, whereas the regulation of alpha2 integrin occurred at a later time point. The differential regulation of alpha1beta1 and alpha2beta1 during the development of myopia may reflect specific roles for these receptors in the scleral extracellular matrix and biomechanical remodeling that accompanies myopic eye growth.

Altered visual sensitivity in axial high myopia: a local postreceptoral phenomenon?

PURPOSE: The present study investigated retinal integrity in high myopia using spatial psychophysical tasks. METHODS: Ten axial high myopes (-8.5 to -11.5 D) and 10 age-matched control subjects (+/-1.0 D) were recruited. All participants underwent clinical examination and ocular biometry and demonstrated no visible macular disease with visual acuities better than 6/12. Foveal summation thresholds were determined for white and S-cone-isolating spots of various diameters up to 5.4 degrees and spatial contrast sensitivity to luminance sine wave gratings (0.5-9.7 cyc/deg). Data were analyzed after correction for the magnification induced by eye size and correcting lens power. RESULTS: Spatial summation for both white and S-cone-isolating spots showed a generalized loss of sensitivity at all spot sizes in myopes relative to control subjects (P = 0.01). Critical areas at maximum summation were significantly larger in myopes, for S-cone isolating spots only, after image size correction (P = 0.048). Sensitivity at maximum summation correlated negatively with vitreous chamber depth for both targets (P = 0.005). Sensitivities for S-cone and luminance spots also correlated (P < 0.001), indicating widespread dysfunction. Myopes displayed contrast sensitivity losses at high spatial frequencies (P

Characterization of the integrin receptor subunit profile in the mammalian sclera.

PURPOSE: During the increased eye growth that results in myopia, the sclera undergoes biochemical and biomechanical remodeling. The cell surface integrin receptor family has important roles during tissue remodeling, regulating the extracellular matrix environment and cellular biomechanical properties. As integrin receptors may have a role in remodeling during myopia, this study detailed subunit gene expression in the mammalian sclera. METHODS: Several tissues, including sclera, were isolated from the tree shrew, a mammalian model used in eye growth studies. Total RNA was purified, reverse transcribed and primers for the alpha- and beta-integrin subunits were designed to the published human sequence in areas of high inter-species homology. PCR was used to amplify products of predetermined size and all tree shrew integrin subunits were sequenced to confirm their identity. Multiple PCR conditions were used to identify the scleral integrin subunits, and positive control tissues were included to reduce the possibility of false negative results. RESULTS: Integrin PCR products corresponding to the beta1-, beta4-, beta5-, and beta8-integrin subunits and the alpha-integrin subunits, alpha1-6-, alpha9-11- and alphav-integrin were identified in the sclera and in scleral fibroblast cultures. The respective sequences showed a high identity (>81%) to their human counterparts. The beta2-, beta3-, beta6-, beta7-, alpha7-, and alpha8-integrin subunits were not detected in tree shrew scleral samples, despite being present in the respective positive controls. Association of the 4 beta-integrin subunits with the 10 alpha-integrin subunits suggests that the mammalian sclera is capable of expressing 13 of the 24 identified integrin receptors. CONCLUSIONS: This is the first systematic description of the integrin subunit expression profile in the sclera. Due to the multiple roles of integrin receptors during tissue remodeling, the identification of these scleral integrins is an important preliminary step in determining the role of these receptors during normal eye growth and myopia development.

Expression and cDNA sequence of matrix metalloproteinase-2 (MMP-2) in a mammalian model of human disease processes: Tupaia belangeri.

Matrix metalloproteinase-2 (MMP-2) is one of a family of proteolytic enzymes that are involved in the remodelling of tissue during normal growth processes and is capable of degrading structural components of the extracellular matrix. Increases in MMP-2 expression and activity have been reported in diseases that involve degradation of the extracellular matrix. Reported here for the first time are the relative levels of expression of MMP-2 in tissues of the tree shrew along with 2587 bases of the mRNA sequence. Translation of this sequence predicts a protein 660 amino acids in length, containing all of the features expected of mammalian MMP-2. The tree shrew is a species close to the primate line and is an emerging animal model for a variety of human diseases, including hepatitis and myopia that feature MMP-2 mediated remodelling of the extracellular matrix.