Scleral thickness in human eyes

Retinal pigment epithelium cell density in relationship to axial length in human eyes

PURPOSE

To assess associations between axial length and density of retinal pigment epithelium (RPE) cells in various ocular regions.

METHODS

The histomorphometric investigation included histological sections of enucleated eyes of Caucasian patients. Using a light microscope, we counted the number of RPE cells on Bruch's membrane at the ora serrata, in the pre-equatorial region, the equatorial and retro-equatorial region, at the midpoint equator/posterior pole, and at the posterior pole.

RESULTS

The study included 65 globes with a mean axial length 25.9 ± 3.5 mm (range: 21.0-34.0 mm). Retinal pigment epithelium (RPE) cell count in the equatorial to retro-equatorial region (p < 0.001; correlation coefficient r² : 0.44), in the pre-equatorial region (p < 0.001; r² : 0.39) and at the midpoint equator/posterior pole (p = 0.03; r² : 0.12) decreased with increasing axial length. Retinal pigment epithelium (RPE) cell count at the ora serrata (p = 0.49) and posterior pole (p = 0.44) was not significantly correlated with axial length. As a corollary, mean RPE cell density was higher (p < 0.001) at the posterior pole than at the midpoint equator/posterior pole or at the ora serrata region, where it was higher than in pre-equatorial region (p < 0.001) and in the equatorial to retro-equatorial region (p < 0.001).

CONCLUSIONS

The decrease in the RPE cell density mainly in the equatorial to retro-equatorial region in association with longer axial length suggests a region of enlargement of Bruch's membrane in the equatorial to retro-equatorial area in association with axial elongation. The finding may be of interest to elucidate the process of emmetropization/myopization.

Lamina cribrosa thickness correlated with posterior scleral thickness and axial length in monkeys

PURPOSE

To explore associations of lamina cribrosa thickness with axial length and thickness of the posterior sclera in monkeys.

METHODS

Examining histological sections by light microscopy, we measured the thickness of the lamina cribrosa and posterior sclera and axial length.

RESULTS

The study included 28 animals (28 eyes) with a mean age of 13.3 ± 4.9 years (range: 3-24 years) and mean axial length of 18.9 ± 1.4 mm (range: 17-21 mm) (22 eyes after experimental temporary central retinal artery occlusion; four eyes after a permanent occlusion of the posterior ciliary artery; and two eyes without any intervention). Mean thickness of the lamina cribrosa was 167 ± 30 μm (range: 115-273 μm). Thinner lamina cribrosa thickness was significantly associated with longer axial length (standardized correlation coefficient beta: -0.42; p = 0.026), with thinner sclera at the posterior pole (beta: 0.56; p = 0.002) and with thinner sclera at the disc border (beta: 0.55; p = 0.002). Lamina cribrosa thickness was not significantly related to temporary central retinal artery occlusion (p = 0.14) or to permanent posterior ciliary artery occlusion (p = 0.49) or age (p = 0.46).

CONCLUSIONS

As in humans, lamina cribrosa thickness in non-glaucomatous monkeys got thinner with longer axial length and with thinner posterior sclera. These data may be of interest for studies on the process of emmetropization/myopization in monkeys, and they may be of interest for the studies on the biomechanics of the optic nerve head.

Anterior eye tissue morphology: Scleral and conjunctival thickness in children and young adults

The sclera and conjunctiva form part of the eye's tough, protective outer coat, and play important roles in the eye's mechanical protection and immune defence, as well as in determining the size and shape of the eye globe. Advances in ocular imaging technology now allow these tissues in the anterior eye to be imaged non-invasively and with high resolution, however there is a paucity of data examining the dimensions of these tissues in paediatric populations. In this study, we have used optical coherence tomography (OCT) imaging to examine the normal in vivo thickness profile of the anterior sclera and overlying conjunctiva in 111 healthy young participants, including a large proportion of paediatric subjects. We demonstrate that the thickness of the anterior sclera varies significantly with measurement location and meridian. Tissue thickness also varied significantly with age, with younger subjects exhibiting significantly thinner scleras and significantly greater conjunctival thickness. Males were also found to exhibit significantly greater scleral thickness. Refractive error however was not significantly associated with either scleral or conjunctival thickness in this population. These findings provide new data describing the normative dimensions of anterior eye tissues in children and the factors that can influence these dimensions in young populations.

The contribution of glycosaminoglycans to the mechanical behaviour of the posterior human sclera

We characterized the structural and mechanical changes after experimental digestion of sulfated glycosaminoglycans (s-GAGs) in the human posterior sclera, using ultrasound thickness measurements and an inflation test with three-dimensional digital image correlation (3D-DIC). Each scleral specimen was first incubated in a buffer solution to return to full hydration, inflation tested, treated in a buffer solution with chondroitinase ABC (ChABC), then inflation tested again. After each test series, the thickness of eight locations was measured. After enzymatic treatment, the average scleral thickness decreased by 13.3% (p < 0.001) and there was a stiffer overall stress-strain response (p < 0.05). The stress-strain response showed a statistically significant increase in the low-pressure stiffness, high-pressure stiffness and hysteresis. Thus, s-GAGs play a measurable role in the mechanical behaviour of the posterior human sclera.

Use and Misuse of Laplace's Law in Ophthalmology

PURPOSE

Laplace's Law, with its compactness and simplicity, has long been employed in ophthalmology for describing the mechanics of the corneoscleral shell. We questioned the appropriateness of Laplace's Law for computing wall stress in the eye considering the advances in knowledge of ocular biomechanics.

METHODS

In this manuscript we recapitulate the formulation of Laplace's Law, as well as common interpretations and uses in ophthalmology. Using numerical modeling, we study how Laplace's Law cannot account for important characteristics of the eye, such as variations in globe shape and size or tissue thickness, anisotropy, viscoelasticity, or that the eye is a living, dynamic organ.

RESULTS

We show that accounting for various geometrical and material factors, excluded from Laplace's Law, can alter estimates of corneoscleral wall stress as much as 456% and, therefore, that Laplace's Law is unreliable.

CONCLUSIONS

We conclude by illustrating how computational techniques, such as finite element modeling, can account for the factors mentioned above, and are thus more suitable tools to provide quantitative characterization of corneoscleral biomechanics.

Scleral and choroidal volume in relation to axial length in infants with retinoblastoma versus adults with malignant melanomas or end-stage glaucoma

PURPOSE

To measure scleral and choroidal volume in eyes of Chinese, and to assess associations with age and axial length.

METHODS

We histomorphometrically examined globes from infants and adults which had been enucleated due to retinoblastoma, uveal melanoma, or absolute painful glaucoma. Thickness of sclera and choroid were measured, and volumes were calculated.

RESULTS

The study included 225 globes (mean axial length: 24.6 ± 4.2 mm; range:17.0-35.7 mm; mean age: 30.4 ± 22.6 years; range: 1-83 years). Mean computed scleral volume was 648 ± 136 mm(3). Scleral volume in children aged <5 years significantly increased with longer axial length (P = 0.001; correlation coefficient r: 0.42) and older age (P = 0.003; r: 0.39) in univariate analysis. In multivariate analysis within the group of children aged ≤2 years, larger scleral volume increased with longer axial length (P = 0.04; standardized correlation coefficient beta: 0.32; correlation coefficient B: 21.6; 95 % confidence interval (CI): 0.52, 42.7) and showed a statistically non-significant tendency to increase with older age (P = 0.06;b eta: 0.30; B: 56.9; 95% CI: -1.5,115). In individuals aged ≥ 5 years, scleral volume was not significantly associated with axial length (P = 0.75) or age (P = 0.13). Mean choroidal volume as measured and calculated in 95 individuals (age: 16-81 years) was 44.1 ± 14.1 mm(3), and was not significantly associated with age (P = 0.47; r: -0.08) or axial length (P = 0.83; r: -0.02).

CONCLUSIONS

This study on children eyes with retinoblastoma and adult eyes with malignant melanomas or end-stage glaucoma suggests that primary eye growth up to an age of 2 years is associated with an increase in scleral volume. After the age of 2 years, scleral volume and choroidal volume remain unchanged, leading to scleral and choroidal thinning with longer axial length, in particular at the posterior pole.

Diurnal variation of anterior scleral and conjunctival thickness

PURPOSE

To examine whether anterior scleral and conjunctival thickness undergoes significant diurnal variation over a 24-h period.

METHODS

Nineteen healthy young adults (mean age 22 ± 2 years) with minimal refractive error (mean spherical equivalent refraction -0.08 ± 0.39 D), had measures of anterior scleral and conjunctival thickness collected using anterior segment optical coherence tomography (AS-OCT) at seven measurement sessions over a 24-h period. The thickness of the temporal anterior sclera and conjunctiva were determined at six locations (each separated by 0.5 mm) at varying distances from the scleral spur (SS) for each subject at each measurement session.

RESULTS

Both the anterior sclera and conjunctiva were found to undergo significant diurnal variations in thickness over a 24-h period (both p < 0.01). The sclera and conjunctiva exhibited a similar pattern of diurnal change, with a small magnitude thinning observed close to midday, and a larger magnitude thickening observed in the early morning immediately after waking. The amplitude of diurnal thickness change was larger in the conjunctiva (mean amplitude 69 ± 29 μm) compared to the sclera (21 ± 8 μm). The conjunctiva exhibited its smallest magnitude of change at the SS location (mean amplitude 56 ± 17 μm) whereas the sclera exhibited its largest magnitude of change at this location (52 ± 21 μm).

CONCLUSIONS

This study provides the first evidence of diurnal variations occurring in the thickness of the anterior sclera and conjunctiva. Studies requiring precise measures of these anatomical layers should therefore take time of day into consideration. The majority of the observed changes occurred in the early morning immediately after waking and were of larger magnitude in the conjunctiva compared to the sclera. Thickness changes at other times of the day were of smaller magnitude and generally not statistically significant.

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.

An examination of the relation between intraocular pressure, fundal stretching and myopic pathology

Pathological myopia is one of the leading causes of visual impairment worldwide. Myopic development and progression is biomechanical and dominated by axial elongation. This clinical perspective examines some of the stretch-related fundal changes, which are associated with axial elongation and myopic pathology. The biomechanics of stretching of the fundus appears to depend on genetically and/or visual experience-based scleral changes, which reduce its thickness and elastic modulus so that it becomes more susceptible to the distending forces of intraocular pressure. These changes include reduced collagen synthesis, altered collagen fibres, tissue loss, altered proteoglycans and increased matrix metalloproteinase activity. Such changes are associated with reduced scleral rigidity and related increased potential to stretch in response to intraocular pressure. As axial elongation progresses, the sclera appears likely to continue to reduce in thickness and in its capacity to resist intraocular pressure, especially when pressure becomes elevated. Tessellation, lacquer cracks, myopic crescents, staphylomata, chorioretinal atrophy and retinal detachment are examined within a model for stretching of the fundus. Age, refractive error and axial length, for example, are associated with increased pathological progression. Myopic pathological progression can become dominated by vascular changes and include a greater risk of loss of acuity and blindness. Measures to control myopic pathology, which successfully slow or prevent stretching of the fundus, appear to be key factors in reducing or even avoiding permanent visual loss associated with this condition. For example, limiting axial elongation and related myopic fundus pathology by inhibiting changes which reduce the elastic modulus of scleral tissue is a desirable outcome from interventions to control myopia. Similarly, reducing exposure to the distending stress of elevated intraocular pressure appears to be a desirable form of intervention to control myopia, especially if myopic pathology can be reduced or prevented.

Mapping 3D Strains with Ultrasound Speckle Tracking: Method Validation and Initial Results in Porcine Scleral Inflation

This study aimed to develop and validate a high frequency ultrasound method for measuring distributive, 3D strains in the sclera during elevations of intraocular pressure. A 3D cross-correlation based speckle-tracking algorithm was implemented to compute the 3D displacement vector and strain tensor at each tracking point. Simulated ultrasound radiofrequency data from a sclera-like structure at undeformed and deformed states with known strains were used to evaluate the accuracy and signal-to-noise ratio (SNR) of strain estimation. An experimental high frequency ultrasound (55 MHz) system was built to acquire 3D scans of porcine eyes inflated from 15 to 17 and then 19 mmHg. Simulations confirmed good strain estimation accuracy and SNR (e.g., the axial strains had less than 4.5% error with SNRs greater than 16.5 for strains from 0.005 to 0.05). Experimental data in porcine eyes showed increasing tensile, compressive, and shear strains in the posterior sclera during inflation, with a volume ratio close to one suggesting near-incompressibility. This study established the feasibility of using high frequency ultrasound speckle tracking for measuring 3D tissue strains and its potential to characterize physiological deformations in the posterior eye.

Optic Disc - Fovea Angle: The Beijing Eye Study 2011

Purpose

To determine the optic disc-fovea angle (defined as angle between the horizontal and the line between the optic disc center and the fovea) and to assess its relationships with ocular and systemic parameters.

Methods

The population-based cross-sectional Beijing Eye Study 2011 included 3468 individuals. A detailed ophthalmic examination was carried out. Using fundus photographs, we measured the disc-fovea angle.

Results

Readable fundus photographs were available for 6043 eyes of 3052 (88.0%) individuals with a mean age of 63.6±9.3 years (range: 50–91 years) and a mean axial length of 23.2±1.0 mm (range: 18.96–28.87 mm). Mean disc-fovea angle was 7.76 ± 3.63° (median: 7.65°; range: -6.3° to 28.9°). The mean inter-eye difference was 4.01 ± 2.94° (median: 3.49°; range: 0.00–22.3°). In multivariate analysis, larger disc-fovea angle was associated (regression coefficient r²: 0.08) with older age (P = 0.009; standardized regression coefficient beta: 0.05), thinner RNFL in the nasal superior sector (P<0.001; beta: -0.17), superior sector (P<0.001; beta: -0.10) and temporal superior sector (P<0.001; beta: -0.11) and thicker RNFL in the inferior sector (P<001; beta: 0.13), nasal inferior sector (P<001; beta: 0.13) and nasal sector (P = 0.007; beta: 0.06), higher prevalence of retinal vein occlusion (P = 0.02; beta: 0.04), and with larger cylindrical refractive error (P = 0.04; beta: 0.04).

Conclusions

The optic disc-fovea angle markedly influences the regional distribution of the RNFL thickness pattern. The disc-fovea angle may routinely be taken into account in the morphological glaucoma diagnosis and in the assessment of structure-function relationship in optic nerve diseases. Future studies may address potential associations between a larger disc-fovea angle and retinal vein occlusions and between the disc-fovea angle and the neuroretinal rim shape.

Optic Disc-Fovea Distance, Axial Length and Parapapillary Zones. The Beijing Eye Study 2011

Purpose

To measure the distance between the optic disc center and the fovea (DFD) and to assess its associations.

Methods

The population-based cross-sectional Beijing Eye Study 2011 included 3468 individuals aged 50+ years. The DFD was measured on fundus photographs.

Results

Readable fundus photographs were available for 2836 (81.8%) individuals. Mean DFD was 4.76 ± 0.34mm (median: 4.74 mm; range: 3.76–6.53mm). In multivariate analysis, longer DFD was associated with longer axial length (P<0.001; standardized correlation coefficient beta: 0.62), higher prevalence of axially high myopia (P<0.001; beta:0.06), shallower anterior chamber depth (P<0.001; beta:-0.18), thinner lens thickness (P = 0.004; beta: -0.06), smaller optic disc-fovea angle (P = 0.02; beta: -0.04), larger parapapillary alpha zone (P = 0.008; beta: 0.05), larger parapapillary beta/gamma zone (P<0.001; beta: 0.11), larger optic disc area (P<0.001; beta: 0.08), lower degree of cortical cataract (P = 0.002; beta: -0.08), and lower prevalence of age-related macular degeneration (P = 0.001; beta: -0.06). Bruch´s membrane opening-fovea distance (DFD minus disc radius minus parapapillary beta/gamma zone width) in non-glaucomatous eyes was not significantly (P = 0.60) related with axial length in emmetropic or axially myopic eyes (axial length ≥23.5 mm), while it increased significantly (P<0.001; r: 0.32) with longer axial length in eyes with an axial length of <23.5mm. Ratio of mean DFD to disc diameter was 2.65 ± 0.30. If the ratio of disc-fovea distance to disc diameter was considered constant and if the individual disc diameter was calculated as the individual disc-fovea distance divided by the constant factor of 2.65, the resulting calculated disc diameter differed from the directly measured disc diameter by 0.16 ±0.13 mm (median: 0.13 mm, range: 0.00–0.89 mm) or 8.9 ± 7.3% (median: 7.4%; range: 0.00–70%) of the measured disc diameter.

Conclusions

DFD (mean: 4.76mm) increases with longer axial length, larger parapapillary alpha zone and parapapillary beta/gamma zone, and larger disc area. The axial elongation associated increase in DFD was due to an enlargement of parapapillary beta/gamma zone while the Bruch’s membrane opening-fovea distance did not enlarge with longer axial length. This finding may be of interest for the process of emmetropization and myopization. Due to its variability, the disc-fovea distance has only limited clinical value as a relative size unit for structures at the posterior pole.

Macular Bruch's Membrane Length and Axial Length. The Beijing Eye Study

PURPOSE

To assess whether macular Bruch´s membrane gets lengthened in axial myopia.

METHODS

Using the enhanced depth imaging mode of spectral-domain optical coherence tomography and examining a subgroup of participants of the population-based cross-sectional Beijing Eye Study, we measured the length of Bruch´s membrane ("MacBMLength") from the fovea to the temporal edge of parapapillary gamma zone, and the distance between the fovea and the temporal optic disc border. Parapapillary gamma zone was defined as the parapapillary region without Bruch's membrane. We additionally measured ocular biometric parameters and assessed non-ophthalmologic variables.

RESULTS

Measurements of MacBMLength were performed on 322 individuals. MacBMLength (mean: 3.99 ± 0.33 mm; range: 3.17-4.93 mm) was not significantly associated with any systemic parameter or ocular biometric parameter. Gamma zone width (mean: 0.18 ± 0.30 mm; range: 0.00-2.61 mm) was associated (multivariate analysis; correlation coefficient r:0.80) with longer axial length (P<0.001; standardized correlation coefficient beta: 0.60; non-standardized correlation coefficient B:0.11; 95%CI: 0.09,0.14) and with longer fovea-optic disc border distance (P<0.001; beta:0.28; B:0.19; 95%CI:0.14,0.25), but not with MacBMLength (P = 0.42). Fovea-temporal disc border distance (mean: 4.16 ± 0.44 mm; range: 3.17-5.86 mm) was associated (overall correlation coefficient: 0.68) with longer axial length (P<0.001; beta: 0.36; B: 0.10; 95%CI: 0.06, 0.13), after adjusting for flatter anterior chamber depth (P = 0.003; beta:-0.14; B:-0.14; 95%CI: -0.23,-0.05) and wider parapapillary gamma zone (P<0.001; beta:0.42; B:0.62; 95%CI:0.44,0.81).

CONCLUSIONS

In contrast to parapapillary gamma zone width and fovea-disc border distance, MacBMLength was not significantly associated with axial length. Axial elongation associated increase in fovea-disc distance may predominantly occur through development or elongation of parapapillary gamma zone, while macular Bruch´s membrane may mostly be independent of axial elongation.

Measurement of Scleral Thickness in Humans Using Anterior Segment Optical Coherent Tomography

Anterior segment optical coherent tomography (AS-OCT, Visante; Zeiss) is used to examine meridional variation in anterior scleral thickness (AST) and its association with refractive error, ethnicity and gender. Scleral cross-sections of 74 individuals (28 males; 46 females; aged between 18-40 years (27.7±5.3)) were sampled twice in random order in 8 meridians: [superior (S), inferior (I), nasal (N), temporal (T), superior-temporal (ST), superior-nasal (SN), inferior-temporal (IT) and inferior-nasal (IN)]. AST was measured in 1mm anterior-to-posterior increments (designated the A-P distance) from the scleral spur (SS) over a 6mm distance. Axial length and refractive error were measured with a Zeiss IOLMaster biometer and an open-view binocular Shin-Nippon autorefractor. Intra- and inter-observer variability of AST was assessed for each of the 8 meridians. Mixed repeated measures ANOVAs tested meridional and A-P distance differences in AST with refractive error, gender and ethnicity. Only right eye data were analysed. AST (mean±SD) across all meridians and A-P distances was 725±46 μm. Meridian SN was the thinnest (662±57 μm) and I the thickest (806±60 μm). Significant differences were found between all meridians (p<0.001), except S:ST, IT:IN, IT:N and IN:N. Significant differences between A-P distances were found except between SS and 6 mm and between 2 and 4 mm. AST measurements at 1mm (682±48 μm) were the thinnest and at 6mm (818±49 μm) the thickest (p<0.001); a significant interaction occurred between meridians and A-P distances (p<0.001). AST was significantly greater (p<0.001) in male subjects but no significant differences were found between refractive error or ethnicity. Significant variations in AST occur with regard to meridian and distance from the SS and may have utility in selecting optimum sites for pharmaceutical or surgical intervention.

Glaucoma-related Changes in the Mechanical Properties and Collagen Micro-architecture of the Human Sclera

Objective

The biomechanical behavior of the sclera determines the level of mechanical insult from intraocular pressure to the axons and tissues of the optic nerve head, as is of interest in glaucoma. In this study, we measure the collagen fiber structure and the strain response, and estimate the material properties of glaucomatous and normal human donor scleras.

Methods

Twenty-two posterior scleras from normal and diagnosed glaucoma donors were obtained from an eyebank. Optic nerve cross-sections were graded to determine the presence of axon loss. The specimens were subjected to pressure-controlled inflation testing. Full-field displacement maps were measured by digital image correlation (DIC) and spatially differentiated to compute surface strains. Maps of the collagen fiber structure across the posterior sclera of each inflated specimen were obtained using synchrotron wide-angle X-ray scattering (WAXS). Finite element (FE) models of the posterior scleras, incorporating a specimen-specific representation of the collagen structure, were constructed from the DIC-measured geometry. An inverse finite element analysis was developed to estimate the stiffness of the collagen fiber and inter-fiber matrix.

Results

The differences between glaucoma and non-glaucoma eyes were small in magnitude. Sectorial variations of degree of fiber alignment and peripapillary scleral strain significantly differed between normal and diagnosed glaucoma specimens. Meridional strains were on average larger in diagnosed glaucoma eyes compared with normal specimens. Non-glaucoma specimens had on average the lowest matrix and fiber stiffness, followed by undamaged glaucoma eyes, and damaged glaucoma eyes but the differences in stiffness were not significant.

Conclusion

The observed biomechanical and microstructural changes could be the result of tissue remodeling occuring in glaucoma and are likely to alter the mechanical environment of the optic nerve head and contribute to axonal damage.

Metrics of the normal anterior sclera: imaging with optical coherence tomography

BACKGROUND

To investigate anterior scleral thickness in a cohort of healthy subjects using enhanced depth imaging anterior segment optical coherence tomography.

METHODS

Observational case series. The mean scleral thickness in the inferonasal, inferotemporal, superotemporal, and superonasal quadrant was measured 2 mm from the scleral spur on optical coherence tomography in healthy volunteers.

RESULTS

Fifty-three eyes of 53 Caucasian patients (25 male and 28 female) with an average age of 48.6 years (range: 18 to 92 years) were analysed. The mean scleral thickness was 571 μm (SD 84 μm) in the inferonasal quadrant, 511 μm (SD 80 μm) in the inferotemporal quadrant, 475 (SD 81 μm) in the superotemporal, and 463 (SD 64 μm) in the superonasal quadrant. The mean scleral thickness was significantly different between quadrants (p < 0.0001, repeated measures one-way ANOVA). The association between average scleral thickness and age was statistically significant (p < 0.0001, Pearson r = 0.704).

CONCLUSIONS

Enhanced depth imaging optical coherence tomography revealed the detailed anatomy of the anterior sclera and enabled non-invasive measurements of scleral thickness in a non-contact approach. The anterior scleral thickness varies significantly between quadrants, resembling the spiral of Tillaux. An association of increasing scleral thickness with age was found.

Topical Ocular Drug Delivery to the Back of the Eye by Mucus-Penetrating Particles

PURPOSE

Enhanced drug exposure to the ocular surface typically relies on inclusion of viscosity-enabling agents, whereas delivery to the back of the eye generally focuses on invasive means, such as intraocular injections. Using our novel mucus-penetrating particle (MPP) technology, which rapidly and uniformly coats and penetrates mucosal barriers, we evaluated if such drug formulations could increase ocular drug exposure and improve topical drug delivery.

METHODS

Pharmacokinetic (PK) profiling of topically administered loterprednol etabonate formulated as MPP (LE-MPP) was performed in rabbits and a larger species, the mini-pig. Pharmacodynamic evaluation was done in a rabbit model of VEGF-induced retinal vascular leakage. Cellular potency and PK profile were determined for a second compound, KAL821, a novel receptor tyrosine kinase inhibitor (RTKi).

RESULTS

We demonstrated in animals that administration of LE-MPP increased exposure at the ocular surface and posterior compartments. Furthermore using a rabbit vascular leakage model, we demonstrated that biologically effective drug concentrations of LE were delivered to the back of the eye using the MPP technology. We also demonstrated that a novel RTKi formulated as MPPs provided drug levels to the back of the eye above its cellular inhibitory concentration.

CONCLUSIONS

Topical dosing of MPPs of LE or KAL821 enhanced drug exposure at the front of the eye, and delivered therapeutically relevant drug concentrations to the back of the eye, in animals.

TRANSLATIONAL RELEVANCE

These preclinical data support using MPP technology to engineer topical formulations to deliver therapeutic drug levels to the back of the eye and could provide major advancements in managing sight-threatening diseases.

Effects of age and diabetes on scleral stiffness

The effects of diabetes on the collagen structure and material properties of the sclera are unknown but may be important to elucidate whether diabetes is a risk factor for major ocular diseases such as glaucoma. This study provides a quantitative assessment of the changes in scleral stiffness and collagen fiber alignment associated with diabetes. Posterior scleral shells from five diabetic donors and seven non-diabetic donors were pressurized to 30 mm Hg. Three-dimensional surface displacements were calculated during inflation testing using digital image correlation (DIC). After testing, each specimen was subjected to wide-angle X-ray scattering (WAXS) measurements of its collagen organization. Specimen-specific finite element models of the posterior scleras were generated from the experimentally measured geometry. An inverse finite element analysis was developed to determine the material properties of the specimens, i.e., matrix and fiber stiffness, by matching DIC-measured and finite element predicted displacement fields. Effects of age and diabetes on the degree of fiber alignment, matrix and collagen fiber stiffness, and mechanical anisotropy were estimated using mixed effects models accounting for spatial autocorrelation. Older age was associated with a lower degree of fiber alignment and larger matrix stiffness for both diabetic and non-diabetic scleras. However, the age-related increase in matrix stiffness was 87% larger in diabetic specimens compared to non-diabetic controls and diabetic scleras had a significantly larger matrix stiffness (p = 0.01). Older age was associated with a nearly significant increase in collagen fiber stiffness for diabetic specimens only (p = 0.06), as well as a decrease in mechanical anisotropy for non-diabetic scleras only (p = 0.04). The interaction between age and diabetes was not significant for all outcomes. This study suggests that the age-related increase in scleral stiffness is accelerated in eyes with diabetes, which may have important implications in glaucoma.

In vivo volumetric depth-resolved vasculature imaging of human limbus and sclera with 1μm swept source phase-variance optical coherence angiography

We present nnnnnin vivo volumetric depth-resolved vasculature images of the anterior segment of the human eye acquired with phase-variance based motion contrast using a high-speed (100 kHz, 10⁵ A-scans/s) swept source optical coherence tomography system (SSOCT). High phase stability SSOCT imaging was achieved by using a computationally efficient phase stabilization approach. The human corneo-scleral junction and sclera were imaged with swept source phase-variance optical coherence angiography and compared with slit lamp images from the same eyes of normal subjects. Different features of the rich vascular system in the conjunctiva and episclera were visualized and described. This system can be used as a potential tool for ophthalmological research to determine changes in the outflow system, which may be helpful for identification of abnormalities that lead to glaucoma.

Collagen structure and mechanical properties of the human sclera: analysis for the effects of age

The objective of this study was to measure the collagen fiber structure and estimate the material properties of 7 human donor scleras, from age 53 to 91. The specimens were subjected to inflation testing, and the full-field displacement maps were measured by digital image correlation. After testing, the collagen fiber structure was mapped using wide-angle X-ray scattering. A specimen-specific inverse finite element method was applied to calculate the material properties of the collagen fibers and interfiber matrix by minimizing the difference between the experimental displacements and model predictions. Age effects on the fiber structure and material properties were estimated using multivariate models accounting for spatial autocorrelation. Older age was associated with a larger matrix stiffness (p = 0.001), a lower degree of fiber alignment in the peripapillary sclera (p = 0.01), and a lower mechanical anisotropy in the peripapillary sclera (p = 0.03).

Corneal curvature radius and associated factors in Chinese children: the Shandong Children Eye Study

PURPOSE

To investigate the distribution of the (CCR) and its associated factors in children.

METHODS

Using a random cluster sampling method, the school-based, cross-sectional Shandong Children Eye Study included children aged 4 to 18 years from the rural county of Guanxian and the city of Weihai in the province of Shandong in East China. CCR was measured by ocular biometry.

RESULTS

CCR measurements were available for 5913 (92.9%) out of 6364 eligible children. Mean age was 10.0±3.3 years, and mean CCR was 7.84±0.27 mm (range: 6.98 to 9.35 mm). In multivariate linear regression analysis, longer CCR (i.e. flatter cornea) was significantly associated with the systemic parameters of male sex (P<0001; standardized regression coefficient beta: -0.08; regression coefficient B: -0.04; 95% Confidence Interval (CI): -0.05, -0.03), younger age (P<0.001; beta: -0.37; B: -0.03; 95%CI: -0.04, -0.03), taller body height (P = 0.002; beta: 0.06; B: 0.001; 95%CI: 0.000, 0.001), lower level of education of the father (P = 0.001; beta: -0.04; B: -0.01; 95%CI: -0.02, -0.01) and maternal myopia (P<0.001; beta: -0.07; B: -0.04; 95%CI: -0.06, -0.03), and with the ocular parameters of longer ocular axial length (P<0.001; beta: 0.59; B: 0.13; 95%CI: 0.12, 0.14), larger horizontal corneal diameter (P<0.001; beta: 0.19; B: 0.13; 95%CI: 0.11, 0.14), and smaller amount of cylindrical refractive error (P = 0.001; beta: -0.09; B: -0.05; 95%CI: -0.06, -0.04).

CONCLUSIONS

Longer CCR (i.e., flatter corneas) (mean:7.84±0.27 mm) was correlated with male sex, younger age, taller body height, lower paternal educational level, maternal myopia, longer axial length, larger corneas (i.e., longer horizontal corneal diameter), and smaller amount of cylindrical refractive error. These findings may be of interest for elucidation of the process of emmetropization and myopization and for corneal refractive surgery.

Dome-shaped macular configuration: longitudinal changes in the sclera and choroid by swept-source optical coherence tomography over two years

PURPOSE

To study longitudinal changes in the posterior pole in eyes with dome-shaped macular configuration within the staphyloma.

DESIGN

Prospective, longitudinal study.

METHODS

We prospectively examined the macular area in 35 eyes (26 patients) with dome-shaped macular configuration and high myopia (mean spherical equivalent, -14.83 ± 4.50 diopters) using swept-source optical coherence tomography. Scleral and choroidal thicknesses were measured at the fovea and at 4 parafoveal locations 2000 μm from the foveal center. Height of the macular bulge was measured as well.

RESULTS

During the mean follow-up of 24.8 ± 2.5 months, the scleral thickness significantly decreased at the fovea from 496.1 ± 95.7 μm to 484.7 ± 96.2 μm (P < .001) and at all 4 parafoveal locations (P < .001, respectively). The scleral thinning was asymmetric, with an estimated decrease per year of 5.6 μm at the foveal center, 11.1 μm superiorly, 12.1 μm inferiorly, 10.4 μm temporally, and 5.8 μm nasally. The ocular concavities deepened over time, and mean macular bulge height increased from 136.5 ± 60.9 μm to 157.6 ± 67.0 μm (P < .001). The choroid within the staphyloma showed generalized thinning during follow-up. Mean choroidal thickness decreased significantly at the fovea from 28.3 ± 17.2 μm at baseline to 22.9 ± 17.2 μm (P < .001).

CONCLUSIONS

Progressive asymmetric scleral thinning occurred in the macular region of eyes with dome-shaped macular configuration. The scleral thinning was more pronounced in the parafoveal area than at the foveal center, resulting in an increase of the macular bulge height.

Clinical prediction of the need for interventions for the control of myopia

The prevalence of myopia is increasing in Western populations but in East Asian countries, it is increasing to epidemic levels, where there are also markedly increased rates of progression to pathological myopia. Measures to more effectively control the development and progression of myopia are urgently needed. Notwithstanding a large volume of research, especially regarding the different mechanisms for the development of myopia and the efficacy of particular methods of intervention, there is still a great need and scope for improvements in clinical efforts to prevent and/or control myopic progression. Too often clinical efforts may involve only one method of intervention; however, the heterogenous nature of myopia suggests that clinical intervention may be more successful when interventions are employed in combination. The decision to prescribe interventions for the control of myopia in children, especially prior to onset, may be better framed by a comprehensive estimation of the degree of risk for the development and/or progression of myopia. For example, rather than ascribing equal weight to any degree of parental myopia, more accurate estimates may be obtained, if risk is judged to increase with the degree of parental myopia and the extent of any associated degenerative pathology. Risk estimates may be limited to broad mild, moderate and severe classifications due to lack of accurate weighting of risk factors. Nevertheless, comprehensive assessment of risk factors appears likely to better inform a prognosis and discussions with parents. Consideration of numerous environmental influences, for example, such as continuity and intensity of near work and time spent outdoors, may contribute to better risk estimation. Family-based practice appears to be ideally suited for risk estimation and the clinical application of approaches to control myopia. A proactive approach to estimating risk of developing myopia prior to its onset may be beneficial. Earlier implementation of interventions to control myopia could significantly reduce the chance of progression to pathological myopia.

Medical therapy for uveal effusion syndrome

PURPOSE

To report a case series of three patients with bilateral uveal effusion syndrome (UES), treated conservatively with oral carbonic anhydrase inhibitors and topical prostaglandin analogues (PAs).

METHODS

Three patients with bilateral UES were treated with the same initial therapy. Topical PA latanoprost 0.005% and acetazolamide 250 mg were administered in order to reduce intraocular pressure, improve uveoscleral outflow, and facilitate resolution of uveal effusion.

RESULTS

The chorioretinal detachment resolved within 3 months in two reported patients while the third one underwent surgery on his left eye. After clinical improvement, further oral therapy with acetazolamide was stopped, while topical prostaglandins were continued for at least the next 3 months. All patients were free from recurrence during the follow-up period.

CONCLUSION

Although the usually recommended UES therapy is partial or full-thickness sclerectomy, our case series showed apparent resolution of chorioretinal detachment in two patients on medical therapy alone. Conservative therapy may be the first step before the standard recommended surgical approach, but further studies are needed to verify the effectiveness of reported therapy.

Measurement of scleral thickness using swept-source optical coherence tomography in patients with open-angle glaucoma and myopia

PURPOSE

To use swept-source optical coherence tomography (OCT) to image the posterior sclera at the posterior pole and around the optic nerve head (ONH) and measure the subfoveal scleral thickness and laminar thickness to evaluate the relationship between the measured thicknesses and ocular parameters.

DESIGN

Prospective, cross-sectional design.

METHODS

The study included 103 patients with glaucoma and 43 controls with axial lengths more than 26 mm. Swept-source OCT images were obtained to capture the subfoveal and ONH regions. Subfoveal scleral thickness and laminar thickness were measured from obtained B-scan images. To verify the reproducibility of the measurement, intraclass correlation coefficients were calculated from selected B-scans. Scleral and laminar thicknesses in patients with normal-tension glaucoma (NTG) was compared with that in patients with primary open-angle glaucoma (POAG). A Pearson correlation was calculated to assess the relationships of scleral and laminar thicknesses with ocular parameters.

RESULTS

Posterior scleral thickness could be measured in 68.4% of patients, and laminar thickness could be measured in 88.6% by using swept-source OCT. Interobserver and intraobserver measurement reproducibility was moderate to excellent. The subfoveal scleral thickness was 670.84 ± 160.60 μm in the POAG group and 496.55 ± 115.20 μm in the NTG group; a significant difference between the groups was observed. Subfoveal scleral thickness (r = -0.677, P < 0.001) was negatively correlated with axial length only in patients with NTG, not in patients with POAG.

CONCLUSIONS

Swept-source OCT detected differences in the thicknesses of the posterior sclera between eyes with NTG and eyes with POAG. Subfoveal scleral thickness was negatively correlated with axial length only in eyes with NTG.

Imaging the posterior segment of the eye using swept-source optical coherence tomography in myopic glaucoma eyes: comparison with enhanced-depth imaging

PURPOSE

To compare the detection rates of identifying the posterior border of the sclera and lamina cribrosa and measurement reproducibility of scleral and laminar thicknesses using the enhanced depth imaging (EDI) of Heidelberg Spectralis optical coherence tomography (OCT) and swept-source OCT.

DESIGN

Cross-sectional design.

METHODS

Both EDI-OCT and swept-source OCT images were obtained in 32 myopic glaucoma patients. Subfoveal choroidal, subfoveal scleral, and central laminar thicknesses were measured from obtained B-scan images. Each measurement was performed at 3 locations by 2 masked observers. The detection rates and measurement reproducibility were evaluated from selected B-scans.

RESULTS

The posterior border of the sclera was visible in 10 eyes (31%) using EDI-OCT. This was improved to be visible in 17 eyes (53%) using swept-source OCT. According to the McNemar χ(2) test, the detection rate of the posterior border of the sclera was significantly different between EDI-OCT and swept-source OCT (P = 0.008). The detection rate of the posterior border of the lamina cribrosa was similar for the 2 devices. In highly myopic eyes, the detection rate of the posterior border of the sclera and lamina cribrosa was not statistically different between EDI-OCT and swept-source OCT. Intersystem ICCs was 0.769 (95% CI, 0.714-0.893) for subfoveal scleral thickness and 0.900 (95% CI, 0.887-0.917) for laminar thickness. The mean subfoveal scleral thickness was 464.32 ± 213.24 μm using EDI-OCT and 650.26 ± 222.30 μm using swept-source OCT. There was statistical difference in the measured subfoveal scleral thickness by the 2 devices (P = 0.018).

CONCLUSIONS

Compared with EDI-OCT, swept-source OCT had an advantage in imaging the posterior sclera. Imaging the lamina cribrosa was similar when using both devices.

Biomechanics of the Posterior Eye: A Critical Role in Health and Disease

The posterior eye is a complex biomechanical structure. Delicate neural and vascular tissues of the retina, choroid, and optic nerve head that are critical for visual function are subjected to mechanical loading from intraocular pressure, intraocular and extraorbital muscles, and external forces on the eye. The surrounding sclera serves to counteract excessive deformation from these forces and thus to create a stable biomechanical environment for the ocular tissues. Additionally, the eye is a dynamic structure with connective tissue remodeling occurring as a result of aging and pathologies such as glaucoma and myopia. The material properties of these tissues and the distribution of stresses and strains in the posterior eye is an area of active research, relying on a combination of computational modeling, imaging, and biomechanical measurement approaches. Investigators are recognizing the increasing importance of the role of the collagen microstructure in these material properties and are undertaking microstructural measurements to drive microstructurally-informed models of ocular biomechanics. Here, we review notable findings and the consensus understanding on the biomechanics and microstructure of the posterior eye. Results from computational and numerical modeling studies and mechanical testing of ocular tissue are discussed. We conclude with some speculation as to future trends in this field.

Peripapillary arterial circle of Zinn-Haller: location and spatial relationships with myopia

Purpose

To measure histomorphometrically the location of the peripapillary arterial circle of Zinn-Haller (ZHAC) and assess its associations with axial length.

Methods

Using a light microscope, we measured the distance from the ZHAC to the peripapillary ring (optic disc border), the merging point of the dura mater with the posterior sclera (“dura-sclera point”), and the inner scleral surface. In the parapapillary region, we differentiated between beta zone (presence of Bruch's membrane, absence of retinal pigment epithelium) and gamma zone (absence of Bruch's membrane). The peripapillary scleral flange as roof of the orbital cerebrospinal fluid space was the connection between the end of the lamina cribrosa and the posterior full-thickness sclera starting at the dura-sclera point.

Results

The study included 101 human globes (101 patients) with a mean axial length of 26.7±3.7 mm (range: 20.0–39.0 mm). The distance between the ZHAC and the peripapillary ring increased significantly with longer axial length (P<0.001; correlation coefficient r = 0.49), longer parapapillary gamma zone (P<0.001;r = 0.85), longer (P<0.001;r = 0.73) and thinner (P<0.001;r = −0.45) peripapillary scleral flange, and thinner sclera posterior to the equator (P<0.001). ZHAC distance to the peripapillary ring was not significantly associated with length of parapapillary beta zone (P = 0.33). Including only non-highly myopic eyes (axial length <26.5 mm), the ZHAC distance to the disc border was not related with axial length (P = 0.84). In non-highly myopic eyes, the ZHAC was located close to the dura-sclera point. With increasing axial length and decreasing thickness of the peripapillary scleral flange, the ZHAC was located closer to the inner scleral surface.

Conclusions

The distance between the ZHAC and the optic disc border is markedly enlarged in highly myopic eyes. Since the ZHAC is the main arterial source for the lamina cribrosa blood supply, the finding may be of interest for the pathogenesis of the increased glaucoma susceptibility in highly myopic eyes.

Histological changes of high axial myopia

To describe pathological changes in the anatomy of highly myopic (axially elongated) eyes, enucleated globes were examined by light microscopy and ocular structures were measured histomorphometrically. These studies revealed that highly axially myopic eyes show continuous thinning of the sclera starting at or behind the equator with a maximal thinning at the posterior pole; a profound thinning of the choroid decreasing from ∼ 250 to <10 μm in extreme axial myopia, secondary macular defects in the Bruch's membrane associated with a complete loss of retinal pigment epithelium and choriocapillaris, and retinal photoreceptors; a Bruch's membrane of normal thickness in contrast to the profound thinning of the choroid and the sclera; an up to 10-fold elongation and thinning of the peripapillary scleral flange as anterior roof of the orbital cerebrospinal fluid space, and subsequently a retrobulbar extension of the cerebrospinal fluid space; an increased distance of the peripapillary arterial circle of Zinn-Haller to the optic disc border; an elongation and thinning of the lamina cribrosa with a subsequently decreased distance between the intraocular pressure compartment and the retrobulbar orbital cerebrospinal fluid pressure compartment; an increasing exposure of the peripheral posterior lamina cribrosa surface to the cerebrospinal fluid space, no longer buffered by the solid optic nerve tissue; and the development and enlargement of parapapillary gamma zone, in contrast to a myopia-independent parapapillary beta zone. These anatomical changes may be associated with high axial myopia-related complications such as an increased susceptibility of glaucomatous optic neuropathy and myopic retinopathy.

Scleral anisotropy and its effects on the mechanical response of the optic nerve head

This paper presents a computational modeling study of the effects of the collagen fiber structure on the mechanical response of the sclera and the adjacent optic nerve head (ONH). A specimen-specific inverse finite element method was developed to determine the material properties of two human sclera subjected to full-field inflation experiments. A distributed fiber model was applied to describe the anisotropic elastic behavior of the sclera. The model directly incorporated wide-angle X-ray scattering measurements of the anisotropic collagen structure. The converged solution of the inverse method was used in micromechanical studies of the mechanical anisotropy of the sclera at different scales. The effects of the scleral collagen fiber structure on the ONH deformation were evaluated by progressively filtering out local anisotropic features. It was found that the majority of the midposterior sclera could be described as isotropic without significantly affecting the mechanical response of the tissues of the ONH. In contrast, removing local anisotropic features in the peripapillary sclera produced significant changes in scleral canal expansion and lamina cribrosa deformation. Local variations in the collagen structure of the peripapillary sclera significantly influenced the mechanical response of the ONH.

Peripapillary scleral deformation and retinal nerve fiber damage in high myopia assessed with swept-source optical coherence tomography

PURPOSE

To study peripapillary morphologic changes in highly myopic eyes using swept-source optical coherence tomography at a longer wavelength.

DESIGN

Prospective cross-sectional study.

METHODS

Peripapillary regions of 196 eyes of 107 patients with high myopia (refractive error, <-8.0 diopters or axial length, >26.0 mm) were analyzed quantitatively and qualitatively with an swept-source optical coherence tomography prototype system that uses a tunable laser light source operated at a 100,000-Hz A-scan repetition rate in the 1-μm wavelength region. The visual field was evaluated by standard automated perimetry. Area of peripapillary atrophy β and presence of scleral protrusion temporal to the optic disc were assessed.

RESULTS

Peripapillary atrophy β area, but not disc area, was significantly larger in eyes with visual field defect (3.16 ± 2.70 mm(2); range, 0.00 to 12.85 mm(2)) than those without visual field defect (2.31 ± 2.83 mm(2); range, 0.00 to 17.70 mm(2)). Temporal scleral protrusion was detected by color stereo disc photography in 22 (19.5%) of 113 eyes with visual field defect and in 4 (4.8%) of 83 eyes without visual field defect. Scleral bending demonstrated a wide range of angles (mean, 31.0 ± 21.1 degrees; range, 2 to 80 degrees). The angle of scleral bending, but not the distances from scleral bend to disc margin or foveal center, correlated significantly with retinal nerve fiber layer thickness above the bend (r = -0.557, P = .007) and visual field defect severity (r = -0.445, P = .038).

CONCLUSIONS

Swept-source optical coherence tomography visualizes peripapillary deep structures in high myopia. Some cases of high myopia may be affected by direct scleral compression or stretching at the peripapillary region.

Three-dimensional tomographic features of dome-shaped macula by swept-source optical coherence tomography

PURPOSE

To study the tomographic and pathomorphologic features of dome-shaped maculas with swept-source optical coherence tomography (OCT).

DESIGN

Prospective, cross-sectional study.

METHODS

The macular area of 51 highly myopic eyes (35 patients) with dome-shaped maculas was studied with swept-source OCT at 1050 nm. Three-dimensional (3-D) data sets were obtained with raster scanning covering a 12 × 8-mm(2) area; 3-D images of the posterior pole were constructed by autosegmentation of the retinal pigment epithelium (RPE).

RESULTS

In all reconstructed 3-D images of the RPE, 2 outward concavities were seen within the posterior staphyloma and a horizontal ridge was formed between these 2 concavities. In 42 of these eyes, this horizontal ridge was band shaped. The vertical OCT section through the fovea showed a convex configuration of RPE, but the horizontal section showed an almost flat RPE line. In 9 eyes, 3-D images showed a typical dome-shaped convexity within the staphyloma. OCT scans showed no outward protrusions in the external scleral surface, but marked scleral thinning was seen consistent with the 2 outward concavities of the RPE. The sclera of the fovea (518.6 ± 97.6 μm) was significantly thicker than that in all 4 quadrants of the parafoveal area (range, 277.2 to 360.3 μm; P < .001).

CONCLUSIONS

In highly myopic eyes with a dome-shaped macula, a horizontal ridge is formed within the posterior staphyloma by uneven thinning of the sclera.

Subfoveal choroidal thickness: the Beijing Eye Study

PURPOSE

To study subfoveal choroidal thickness (SFCT) in adult Chinese subjects and its correlation with ocular biometric parameters, refractive error, and age.

DESIGN

Population-based longitudinal study.

PARTICIPANTS

The population-based Beijing Eye Study 2011 included 3468 individuals with a mean age of 64.6±9.8 years (range, 50-93 years).

METHODS

A detailed ophthalmic examination was performed, including spectral-domain optical coherence tomography (SD-OCT) with enhanced depth imaging for measurement of SFCT.

MAIN OUTCOME MEASURES

Subfoveal choroidal thickness.

RESULTS

The SFCT measurements were available for 3233 subjects (93.2%). Mean SFCT was 253.8±107.4 μm (range, 8-854 μm). In multivariate analysis, SFCT increased with younger age (P<0.001; correlation coefficient r=4.12; beta coefficient=0.37), shorter axial length (P<0.001; r=44.7; beta coefficient=0.46), male gender (P<0.001; r=28.5; beta coefficient=-0.13), deeper anterior chamber depth (P<0.001; r=39.3; beta coefficient=0.13), thicker lens (P<0.001; r=26.8; beta coefficient=0.08), flatter cornea (P<0.001; r=46.0; beta coefficient=0.11), and better best-corrected visual acuity (BCVA) (logarithm of minimal angle of resolution; P=0.001; r=48.4; beta coefficient=0.06). In multivariate analysis, SFCT was not significantly associated with blood pressure, ocular perfusion pressure, intraocular pressure, cigarette smoking, alcohol consumption, serum concentrations of lipids and glucose, diabetes mellitus, and arterial hypertension. In the myopic refractive error range of more than -1 diopter (D), SFCT decreased by 15 μm (95% confidence interval [CI], 11.9-18.5) for every increase in myopic refractive error of 1 D, or by 32 μm (95% CI, 37.1-26.0) for every increase in axial length of 1 mm. For each year increase in age, the SFCT decreased by 4.1 μm (95% CI, 4.6-3.7) (multivariate analysis).

CONCLUSIONS

Subfoveal choroidal thickness with a mean of 254±107 μm in elderly subjects with a mean age of 65 years decreased with age (4 μm per year of age) and myopia (15 μm per diopter [D] of myopia). It was also associated with male gender and the ocular biometric parameters of a deeper anterior chamber and thicker lens. The association between SFCT and BCVA indicates a functional aspect of SFCT.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Ocular axial length and its associations in Chinese: the Beijing Eye Study

PURPOSE

To investigate the normative data of ocular axial length and its associations in Chinese.

METHOD

The population-based Beijing Eye Study 2011 is a cross-sectional study performed in Greater Beijing. The study included 3468 individuals (1963 (56.6%) women) with a mean age of 64.6±9.8 years (range: 50-93 years). A detailed ophthalmic and medical examination was performed. Axial length was measured by optical low-coherence reflectometry.

RESULTS

Axial length measurements were available for 3159 (91.1%) study participants. Mean axial length was 23.25±1.14 mm (range: 18.96-30.88 mm). In multivariate analysis, axial length was significantly associated with the systemic parameters of higher age (P<0.001), higher body height (P = 0.003), higher level of education (P<0.001) and urban region of habitation (P<0.001), and with the ocular parameters of thicker central cornea (P = 0.001), higher corneal curvature radius (P<0.001), deeper anterior chamber (P<0.001), thicker lens (P<0.001), more myopic refractive error (P<0.001), larger pupil diameter (P = 0.018), and higher best corrected visual acuity (P<0.001). It was additionally and negatively associated with the lens vault (P<0.001). In highly myopic eyes, axial length was significantly associated with lower level of education (P = 0.008), more myopic refractive error (P<0.001), and lower best corrected visual acuity (P = 0.034).

CONCLUSIONS

Mean ocular axial length in the older adult population of Greater Beijing (23.25±1.14 mm) was similar to the value measured in other urban populations and was higher than in a rural Central Indian population. The association between axial length and older age may potentially be associated with a survival artifact. The association between axial length and body height agrees with the general association between anthropomorphic measures and eye globe size. The association with the level of education and urban region of habitation confirms with previous studies. In contrast in highly myopic eyes, axial length was negatively associated with educational level and best corrected visual acuity.