The structure and function of the human choroid.

In this manuscript, the structure of the human choroid is reviewed with emphasis of the macro- and microscopic anatomy including Bruch's membrane, choriocapillaris, Sattler's and Haller's layer, and the suprachoroid. We here discuss the development of the choroid, as well as the question of choroidal lymphatics, and further the neuronal control of this tissue, as well as the pathologic angiogenesis. Wherever possible, functional aspects of the various structures are included and reviewed.

OCT Optic Nerve Head Morphology in Myopia IV: Neural Canal Scleral Flange Remodeling in Highly Myopic Eyes.

PURPOSE: To compare the prevalence, location and magnitude of optic nerve head (ONH) OCT-detected, exposed neural canal (ENC), externally oblique choroidal border tissue (EOCBT) and exposed scleral flange (ESF) regions in 122 highly myopic (Hi-Myo) versus 362 nonhighly myopic healthy (Non-Hi-Myo-Healthy) eyes. DESIGN: Cross-sectional study. METHODS: After OCT radial B-scan, ONH imaging, Bruch's membrane opening (BMO), the anterior scleral canal opening (ASCO), and the scleral flange opening (SFO) were manually segmented in each B-scan and projected to BMO reference plane. The direction and magnitude of BMO/ASCO offset and BMO/SFO offset as well as the location and magnitude of ENC, EOCBT and ESF regions, perineural canal (pNC) retinal nerve fiber layer thickness (RNFLT) and pNC choroidal thickness (CT) were calculated within 30° sectors relative to the Foveal-BMO (FoBMO) axis. Hi-ESF eyes were defined to be those with an ESF region ≥100 µms in at least 1 sector. RESULTS: Hi-Myo eyes more frequently demonstrated Hi-ESF regions (87/122) than Non-Hi-myo-Healthy eyes (73/362) and contained significantly larger ENC, EOCBT, and ESF regions (P < .001) which were greatest in magnitude and prevalence within the inferior-temporal FoBMO sectors where Hi-Myo pNC-RNFLT and pNCCT were thinnest. BMO/ASCO offset and the BMO/SFO offset were both significantly increased (P < .001) in the Hi-Myo eyes, with the latter demonstrating a greater increase. CONCLUSIONS: ENC region tissue remodeling that includes the scleral flange is enhanced in Hi-Myo compared to Non-Hi-Myo-Healthy eyes. Longitudinal studies are necessary to determine whether the presence of an ENC region influences ONH susceptibility to aging and/or glaucoma.

Myopia: Anatomic Changes and Consequences for Its Etiology.

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

Variation of Peripapillary Scleral Shape With Age.

Purpose: To define the shape of the anterior surface of the peripapillary sclera (PPS) and evaluate its relationship with age and ocular determinants in a population-based Chinese cohort. Methods: The optic nerve heads of 619 healthy Chinese subjects were imaged with spectral-domain optical coherence tomography. To assess the shape of the PPS/Bruch's membrane (BM), we measured the angle between a line parallel to the nasal anterior PPS/BM boundary and one parallel to the temporal side. A negative value indicated that the PPS/BM followed an inverted v-shaped configuration (peak pointing toward the vitreous), whereas a positive value indicated that it followed a v-shaped configuration (peak pointing toward the orbital tissues). A linear regression model was used to evaluate the relationship between the PPS angle and other ocular parameters. Results: The mean PPS angle was 3.68° ± 6.73° and the BM angle was 9.69° ± 5.05°. The PPS angle increased on average by 0.233 deg/y. A v-shaped PPS was significantly associated with age (ß = 0.087, P = 0.004), peripapillary choroidal thickness (ß = -0.479, P < 0.001), lamina cribrosa depth (ß = 0.307, P < 0.001), and BM angle (ß = 0.487, P < 0.001) after adjusting for best corrected visual acuity, central corneal thickness, and axial length. Conclusions: The anterior surface of PPS of an elderly adult population had a v-shaped configuration and was more pronounced with increasing age, thin peripapillary choroid, and a deep cup. Such a change in shape with age could have an impact on the biomechanical environment of the optic nerve head.

OCT-Detected Optic Nerve Head Neural Canal Direction, Obliqueness, and Minimum Cross-Sectional Area in Healthy Eyes.

PURPOSE: To assess anterior scleral canal opening (ASCO) offset relative to Bruch's membrane opening (BMO) (ASCO/BMO offset) so as to determine neural canal direction, obliqueness, and minimum cross-sectional area (NCMCA) in 362 healthy eyes. DESIGN: Cross-sectional study. METHODS: After optical coherence tomography optic nerve head and retinal nerve fiber layer thickness (RNFLT) imaging, BMO and ASCO were manually segmented. Planes, centroids, size, and shape were calculated. Neural canal direction was defined by projecting the neural canal axis vector (connecting BMO and ASCO centroids) onto the BMO plane. Neural canal obliqueness was defined by the angle between the neural canal axis and the BMO plane perpendicular vector. NCMCA was defined by projecting BMO and ASCO points onto a neural canal axis perpendicular plane and measuring the area of overlap. The angular distance between superior and inferior peak RNFLT was measured, and correlations between RFNLT, BMO, ASCO, ASCO/BMO offset, and NCMCA were assessed. RESULTS: Mean (SD) NCMCA was significantly smaller than either the BMO or ASCO area (1.33 (0.42), 1.82 (0.38), 2.22 (0.43) mm2, respectively), and most closely correlated to RNFLT (P < .001, R2 = 0.158). Neural canal direction was most commonly superior-nasal (55%). Mean neural canal obliqueness was 39.4° (17.3°). The angular distance between superior and inferior peak RNFLT correlated to neural canal direction (P ≤ .008, R2 = 0.093). CONCLUSIONS: ASCO/BMO offset underlies neural canal direction, obliqueness, and NCMCA. RNFLT is more strongly correlated to NCMCA than to BMO or ASCO, and its peripapillary distribution is influenced by neural canal direction.

Interocular Asymmetry of Minimum Rim Width and Retinal Nerve Fiber Layer Thickness in Healthy Brazilian Individuals.

PURPOSE: To determine interocular differences in Bruch's membrane opening minimum rim width (BMO-MRW) and retinal nerve fiber layer thickness (RNFLT) in healthy Brazilian individuals. MATERIALS AND METHODS: Both eyes of 220 healthy individuals were included in this observational, cross-sectional study. All individuals had normal clinical examination and visual fields. Global and sectorial interocular BMO-MRW and RNFLT differences, acquired and regionalized relative to the fovea to BMO center (FoBMO) axis, were calculated. The effect of age, axial length, and BMO area asymmetry on the parameters' asymmetry was evaluated. RESULTS: The 95th limits for interocular BMO-MRW and RNFLT global differences were 49 and 9 µm, respectively. BMO-MRW asymmetry was negatively correlated (ß=-33.87 µm/mm, R=0.06, P<0.001), whereas RNFLT asymmetry was positively correlated (ß= 6.13 µm/mm, R=0.09, P<0.001) with BMO area asymmetry. Neither BMO-MRW nor RNFLT asymmetries were correlated with axial length asymmetry (ß=-16.90 µm/mm, R=0.00, P=0.15; ß=-1.18 µm/mm, R=0.00, P=0.52, respectively). Similarly, BMO-MRW and RNFLT asymmetries were not correlated with age (ß=0.17 µm/y, R=0.01, P=0.22; ß=0.0 µm/y, R=0.00, P=0.19, respectively). CONCLUSIONS: Our results suggest that global BMO-MRW and RNFLT interocular differences exceeding 49 and 9 µm, respectively, may indicate statistically abnormal asymmetry, which may suggest early structural damage. Asymmetry in BMO area should be accounted for when considering interocular asymmetry in BMO-MRW and RNFLT.

The Fovea-BMO Axis Angle and Macular Thickness Vertical Asymmetry Across The Temporal Raphe.

PURPOSE: To test the hypothesis that the fovea-Bruch's membrane opening (FoBMO) axis angle influences the thickness symmetry of the macular ganglion cell/inner plexiform layer (GCIPL) across the temporal horizontal meridian in normal subjects. DESIGN: Cross-sectional diagnostic study at a tertiary academic center. METHODS: One hundred sixteen eyes of 60 normal subjects aged 40 to 85 years underwent spectral domain optical coherence tomography(SD-OCT) imaging. The FoBMO angle was estimated on en face infrared SD-OCT images. Posterior Pole algorithm images acquired with Spectralis SD-OCT were used to define vertical asymmetry as follows. The average thickness difference between the 3 most temporal superpixels above and below the horizontal meridian, the second row of superpixels from the horizontal meridian, and 3 central superpixels above and below the horizontal meridian were calculated. Factors influencing GCIPL thickness asymmetry were explored and changes in thickness asymmetry as a function of FoBMO angle were investigated. RESULTS: No demographic or clinical factors affected temporal GCIPL asymmetry (P>0.05 for all). A more (negatively) tilted FoBMO angle was associated with relatively thinner inferior compared with superior GCIPL thickness in superpixels immediately adjacent to the temporal raphe (P<0.001). The second row of temporal superpixels from the horizontal meridian (P=0.349) or central superpixels (P=0.292) did not show this tendency. CONCLUSIONS: Vertical GCIPL symmetry across the horizontal meridian is influenced by the FoBMO angle. SD-OCT algorithms using vertical asymmetry as a diagnostic index should be adjusted for the FoBMO angle.

Optimization Strategies for Bruch's Membrane Opening Minimum Rim Area Calculation: Sequential versus Simultaneous Minimization.

To compare a simultaneously optimized continuous minimum rim surface parameter between Bruch's membrane opening (BMO) and the internal limiting membrane to the standard sequential minimization used for calculating the BMO minimum rim area in spectral domain optical coherence tomography (SD-OCT). In this case-control, cross-sectional study, 704 eyes of 445 participants underwent SD-OCT of the optic nerve head (ONH), visual field testing, and clinical examination. Globally and clock-hour sector-wise optimized BMO-based minimum rim area was calculated independently. Outcome parameters included BMO-globally optimized minimum rim area (BMO-gMRA) and sector-wise optimized BMO-minimum rim area (BMO-MRA). BMO area was 1.89 ± 0.05 mm2. Mean global BMO-MRA was 0.97 ± 0.34 mm2, mean global BMO-gMRA was 1.01 ± 0.36 mm2. Both parameters correlated with r = 0.995 (P < 0.001); mean difference was 0.04 mm2 (P < 0.001). In all sectors, parameters differed by 3.0-4.2%. In receiver operating characteristics, the calculated area under the curve (AUC) to differentiate glaucoma was 0.873 for BMO-MRA, compared to 0.866 for BMO-gMRA (P = 0.004). Among ONH sectors, the temporal inferior location showed the highest AUC. Optimization strategies to calculate BMO-based minimum rim area led to significantly different results. Imposing an additional adjacency constraint within calculation of BMO-MRA does not improve diagnostic power. Global and temporal inferior BMO-MRA performed best in differentiating glaucoma patients.

Progressive Deformation of the Optic Nerve Head and Peripapillary Structures by Graded Horizontal Duction.

Purpose: We investigated the effect of graded range of horizontal duction on the shape of the peripapillary Bruch's membrane (ppBM) and optic nerve head (ONH). Methods: In 50 eyes of 25 normal subjects, the ONH and peripapillary retina were imaged by optical coherence tomography (OCT) in central gaze and incremental angles of add- and abduction. Displacements of the Bruch's membrane opening (BMO), optic cup (OC), and change in ONH angle in eccentric gazes were compared to those of central gaze, in add- and abduction. Results: With increasing duction, the nasal edge of the BMO (nBMO) shifted progressively anteriorly in adduction and posteriorly in abduction, while the temporal edge of the BMO (tBMO) shifted posteriorly in adduction and anteriorly in abduction. The summed absolute nBMO and tBMO displacements in 30° and 35° adduction significantly exceeded those in comparable abduction angles (P < 0.005 for both). The ONH progressively tilted temporally in adduction and nasally in abduction; absolute ONH tilt in adduction was significantly greater than that in abduction for 30° and 35° ductions (P < 0.005 for both). BMO displacement and ONH tilt in adduction exhibited bilinear behavior, with greater effects for both at angles exceeding 26°. The OC shifted significantly farther anteriorly in abduction than adduction at every angle from 10° to 35°. Conclusions: Horizontal duction deforms the ONH and ppBM, but more in adduction than in abduction, and increasingly so for angles greater than 26°. This behavior is consistent with optic nerve sheath tethering for adduction exceeding 26°.

Bruch´s membrane thickness in relationship to axial length.

PURPOSE: To assess a potential role of Bruch´s membrane (BM) in the biomechanics of the eye, we measured its thickness and the density of retinal pigment epithelium (RPE) cells in various ocular regions in eyes of varying axial length. METHODS: Human globes, enucleated because of an ocular tumor or end-stage glaucoma were prepared for histological examination. Using light microscopy, the histological slides were histomorphometrically examined applying a digitized image analysis system. RESULTS: The study included 104 eyes with a mean axial length of 27.9±3.2 mm (range:22.6mm-36.5mm). In eyes without congenital glaucoma, BM was significantly thickest (P<0.001) at the ora serrata, followed by the posterior pole, the midpoint between equator and posterior pole (MBEPP), and finally the equator. BM thickness was not significantly correlated with axial length (ora serrata: P = 0.93; equator:P = 0.31; MBEPP:P = 0.15; posterior pole:P = 0.35). RPE cell density in the pre-equatorial region (P = 0.02; regression coefficient r = -0.24) and in the retro-equatorial region (P = 0.03; r = -0.22) decreased with longer axial length, while RPE cell density at the ora serrata (P = 0.35), the MBEPP (P = 0.06; r = -0.19) and the posterior pole (P = 0.38) was not significantly correlated with axial length. Highly myopic eyes with congenital glaucoma showed a tendency towards lower BM thickness and lower RPE cell density at all locations. CONCLUSIONS: BM thickness, in contrast to scleral and choroidal thickness, was independent of axial length in eyes without congenital glaucoma. In association with an axial elongation associated decrease in the RPE cell density in the midperiphery, the findings support the notion of a biomechanical role BM may play in the process of emmetropization/myopization.

The Impact of Lens Opacity on SD-OCT Retinal Nerve Fiber Layer and Bruch's Membrane Opening Measurements Using the Anatomical Positioning System (APS).

Purpose: To evaluate the impact of lens opacity on retinal nerve fiber layer thickness (RNFLT) and Bruch's membrane opening (BMO) measurements. Methods: Fifty-nine randomly selected patients without any other relevant ocular pathology undergoing elective routine cataract surgery in two specialized eye clinics were enrolled. RNFLT, BMO area, and BMO minimum rim width (BMO-MRW) were assessed with the Heidelberg Engineering Spectralis OCT using the anatomical positioning system (APS) prior to and 1 day after cataract surgery using a ring scan at different eccentricities of the disc (3.5, 4.1 and 4.7 mm). Lens opacity was quantified using densitometry based on Scheimpflug images (Oculus Pentacam AXL). Results: RNFLT, BMO area, and BMO-MRW were virtually identical before and following removal of the cataractous lens. This held when assessed overall, within the six sectors for the 3.5-mm scan, or at any other eccentricity. Baseline RNFLT was not associated with lens opacity. Conclusions: Using the APS, RNFLT remained unchanged following cataract surgery, contrary to results reported by previous studies. Our results imply that the APS may have contributed to more precise spectral-domain optical coherence measurements, minimizing the influence of cataract on RNFLT and BMO assessments in our cohort.

Serial Changes in Lamina Cribrosa Depth and Neuroretinal Parameters in Glaucoma: Impact of Choroidal Thickness.

PURPOSE: To determine whether: (1) change in lamina cribrosa depth occurs more frequently than change in neuroretinal parameters in glaucoma, and (2) Bruch's membrane or anterior sclera should be used as a reference plane when measuring laminar depth. DESIGN: Prospective observational study. PARTICIPANTS: One hundred fifty-five glaucoma patients and 35 healthy controls. METHODS: Anterior laminar depth from a Bruch's membrane (LD-BM) or anterior sclera (LD-AS) reference plane were measured with optical coherence tomography. Two neuroretinal parameters, minimum rim width and retinal nerve fiber layer thickness, in addition to peripapillary choroidal thickness were measured. Factors related to laminar depth were determined with mixed-effects modeling. Cutoffs for significant change in each parameter were estimated from variability in healthy controls over 1 year. The occurrences of significant change in laminar depth and neuroretinal parameters were compared with survival models. Because normal aging has a clear effect on neuroretinal parameters, but not on laminar depth, changes in neuroretinal parameters were adjusted for age-related reduction. MAIN OUTCOME MEASURES: Longitudinal changes in laminar depth and neuroretinal parameters. RESULTS: Glaucoma patients were followed up for a mean of 3.90 years (range, 2.03-5.44 years). The LD-BM was influenced significantly more by choroidal thickness (1.14 µm/µm; 95% confidence interval, 1.07-1.21) than was the LD-AS (0.15 µm/µm; 95% confidence interval, 0.08-0.22). Posterior movement of the lamina (LD-BM increase or LD-AS increase) occurred with the same frequencies as thinning in neuroretinal parameters. Anterior movement of the lamina was detected more frequently with the Bruch's membrane (LD-BM decrease) compared with the anterior sclera (LD-AS decrease) reference plane (hazard ratio, 3.23; P < 0.01). Significant choroidal thinning occurred in most patients (25/28 [89%]) in whom anterior movement of the lamina occurred with the Bruch's membrane, but not the anterior sclera, reference plane (LD-BM decrease without LD-AS decrease). Patients had a wide range of individual rates of change of choroidal thickness, from -20.00 to 17.09 µm/year (mean, -1.62 µm/year). CONCLUSIONS: Lamina cribrosa depth should be measured from an anterior sclera reference plane to reduce the influence of choroidal thickness changes. In glaucoma patients, lamina cribrosa depth changes are detected with similar frequency as neuroretinal parameter changes.

Associations with Retinal Pigment Epithelium Thickness Measures in a Large Cohort: Results from the UK Biobank.

PURPOSE: To describe associations of ocular and systemic factors with retinal pigment epithelium (RPE)-Bruch's membrane (BM) complex thickness as measured by spectral-domain (SD) optical coherence tomography (OCT). DESIGN: Multisite community-based study. This research has been conducted using the UK Biobank Resource. PARTICIPANTS: Sixty-seven thousand three hundred eighteen people 40 to 69 years old received questionnaires, physical examination, and eye examination, including macular SD OCT. Systematic selection process identified 34 652 eyes with high-quality SD OCT images from normal individuals for analysis. METHODS: We included people with no self-reported ocular disease, diabetes, or neurologic disorders; visual acuity of ≥20/25; refraction between -6 diopters (D) to 6 D, and IOP of 6 to 21 mmHg. Only high-quality, well-centered SD OCT images with central, stable fixation were included. Descriptive statistics, t tests, and regression analyses were performed. Multivariate regression modeling was used to adjust for covariates and to identify relationships between RPE-BM thickness and ocular and systemic features. MAIN OUTCOME MEASURES: Retinal pigment epithelium-BM thickness, as measured by SD OCT segmentation using Topcon Advanced Boundary Segmentation at 9 Early Treatment of Diabetic Retinopathy Study subfields. RESULTS: Mean RPE-BM thickness was 26.3 µm (standard deviation, 4.8 µm) at central subfield. Multivariate regression with age stratification showed that RPE thinning became apparent after age 45. Among those aged ≤45, RPE-BM was significantly thicker among those of black or mixed/other race (+3.61 and +1.77 µm vs. white, respectively; P < 0.001) and higher hyperopia (+0.4 µm/D; P < 0.001), but not for other variables considered. Among those age >45, RPE-BM was significantly thinner with older age (-0.10 µm/year; P < 0.001), Asian ethnicity (-0.45 µm vs. white; P = 0.02), taller height (-0.02 µm/cm; P < 0.001), higher IOP (-0.03 µm/mmHg; P < 0.001), and regular smoking (-0.27 µm vs. nonsmokers; P = 0.02). In contrast, RPE-BM was significantly thicker among black or mixed/other race (+3.29 µm and +0.81 µm vs. white, respectively; P < 0.001) and higher hyperopia (+0.28 µm/D; P < 0.001). There was no significant association with sex or Chinese ethnicity. CONCLUSIONS: We describe novel findings of RPE-BM thickness in normal individuals, a structure that varies with age, ethnicity, refraction, IOP, and smoking. The significant association with IOP is especially interesting and may have relevance for the etiology of glaucoma, while the association between age and smoking may have relevance for the etiology of age-related macular degeneration.

Comparison of Bruch's Membrane Opening Minimum Rim Width Among Those With Normal Ocular Health by Race.

PURPOSE: To examine if racial differences in Bruch's membrane opening minimum rim width (BMO-MRW) in spectral-domain optical coherence tomography (SDOCT) exist, specifically between people of African descent (AD) and European descent (ED) in normal ocular health. DESIGN: Cross-sectional study. METHODS: Patients presenting for a comprehensive eye examination at retail-based primary eye clinics were enrolled based on ≥1 of the following at-risk criteria for glaucoma: AD aged ≥40 years, ED aged ≥50 years, diabetes, family history of glaucoma, and/or pre-existing diagnosis of glaucoma. Participants with normal optic nerves on examination received SDOCT of the optic nerve head (24 radial scans). Global and regional (temporal, superotemporal, inferotemporal, nasal, superonasal, and inferonasal) BMO-MRW were measured and compared by race using generalized estimating equations. Models were adjusted for age, sex, and BMO area. RESULTS: SDOCT scans from 269 eyes (148 participants) were included in the analysis. Mean global BMO-MRW declined as age increased. After adjusting for age, sex, and BMO area, there was not a statistically significant difference in mean global BMO-MRW by race (P = .60). Regionally, the mean BMO-MRW was lower in the crude model among AD eyes in the temporal, superotemporal, and nasal regions and higher in the inferotemporal, superonasal, and inferonasal regions. However, in the adjusted model, these differences were not statistically significant. CONCLUSIONS: BMO-MRW was not statistically different between those of AD and ED. Race-specific normative data may not be necessary for the deployment of BMO-MRW in AD patients.

Spectral-Domain Optical Coherence Tomography-Derived Characteristics of Bruch Membrane Opening in a Young Adult Australian Population.

PURPOSE: To characterize and quantify Bruch membrane opening (BMO)-based optic nerve head (ONH) parameters in a large, young and healthy, predominantly white population. DESIGN: Cross-sectional study and reliability analysis. METHODS: The ONH of 1344 predominantly white subjects were imaged with spectral-domain optical coherence tomography (SD-OCT). A customized script, coded in Matlab, was used to manually segment and measure multiple BMO-based parameters of the ONH. Measurements were compared to those obtained with confocal scanning laser ophthalmoscopy (Heidelberg Retina Tomograph; HRT). Regression analysis was performed to assess the relationship between BMO parameters and other ocular and demographic variables. RESULTS: Mean BMO disc and neuroretinal rim (NRR) areas ranged from 0.94 to 4.06 mm(2) (mean 1.77 ± 0.38 mm(2)) and 0.94 to 3.99 mm(2) (mean 1.56 ± 0.31 mm(2)), respectively. When compared to the equivalent HRT measurements, SD-OCT-derived measures differed significantly for all comparable ONH parameters (P < .001). The limits of agreement computed from Bland-Altman plots comparing SD-OCT and HRT measurements showed suboptimal agreement between the techniques. Linear regression analysis demonstrated an effect of ethnicity, axial length, and refractive error on BMO-based parameters. CONCLUSIONS: We have quantified BMO-based parameters in a large cohort of young adults using SD-OCT. These data will be informative in constructing normative profiles for clinical and research purposes in glaucoma diagnosis and management.

CHOROIDAL THICKNESS IN RELATION TO ETHNICITY MEASURED USING ENHANCED DEPTH IMAGING OPTICAL COHERENCE TOMOGRAPHY.

PURPOSE: To investigate the posterior choroidal thickness in healthy subjects of three different ethnicities. METHODS: In this prospective cross-sectional study, the choroidal thickness of 88 individuals (176 eyes) was measured using enhanced depth imaging-spectral domain optical coherence tomography. Subfoveal choroidal thickness was measured between the retinal pigment epithelium-Bruch membrane complex and chorioscleral interface. Nasal, temporal, superior, and inferior choroidal thicknesses at 0.5, 1.5, and 3.0 mm locations from the fovea were evaluated as well. RESULTS: Males and females were perfectly matched by number in all groups. The mean age of the entire study population was 27.43 ± 1 years. Mean subfoveal choroidal thicknesses of whites, Africans, Asians, and entire study population were 403.62 ± 37.4 µm, 372.47 ± 31.4 µm, 383.64 ± 40 µm, 386.64 ± 10.5 µm, respectively. Mean spherical error of the entire study population was -1.2685 diopter. Whites had the longest eyes on average 24.17 mm > 24.08 mm (Africans) > 23.86 mm (Asians), with the statistical mean of 24.04 mm for the entire study population. Subfoveal choroidal thickness was not significantly correlated with ethnicity in either ethnic group (P > 0.05). Subfoveal choroid thinned by 2.51 µm per 1 year increase in age (P = 0.282). Subfoveal choroidal thickness and sex were not significantly correlated to (P = 0.402). Subfoveal choroidal thickness was in strong negative correlation only with refractive error (P = 0.01) and axial length (P = 0.008). The intereye difference in subfoveal choroidal thickness was not statistically significant (P = 0.845). CONCLUSION: Enhanced depth imaging-spectral domain optical coherence tomography is a productive imaging method to study the choroidal thickness. Subfoveal choroidal thickness is not significantly correlated with ethnicity. The study reproduced previously found relations between thinner choroids and longer axial lengths, and increasing myopic refraction and showed no significant associations between subfoveal choroidal thickness and age and sex. Either the right or left eye can be used in future studies.

Bruch's Membrane Opening Minimum Rim Width and Retinal Nerve Fiber Layer Thickness in a Normal White Population: A Multicenter Study.

PURPOSE: Conventional optic disc margin-based neuroretinal rim measurements lack a solid anatomic and geometrical basis. An optical coherence tomography (OCT) index, Bruch's membrane opening minimum rim width (BMO-MRW), addresses these deficiencies and has higher diagnostic accuracy for glaucoma. We characterized BMO-MRW and peripapillary retinal nerve fiber layer thickness (RNFLT) in a normal population. DESIGN: Multicenter cross-sectional study. PARTICIPANTS: Normal white subjects. METHODS: An approximately equal number of subjects in each decade group (20-90 years of age) was enrolled in 5 centers. Subjects had normal ocular and visual field examination results. We obtained OCT images of the optic nerve head (24 radial scans) and peripapillary retina (1 circular scan). The angle between the fovea and BMO center (FoBMO angle), relative to the horizontal axis of the image frame, was first determined and all scans were acquired and analyzed relative to this eye-specific FoBMO axis. Variation in BMO-MRW and RNFLT was analyzed with respect to age, sector, and BMO shape. MAIN OUTCOME MEASURES: Age-related decline and between-subject variability in BMO-MRW and RNFLT. RESULTS: There were 246 eyes of 246 subjects with a median age of 52.9 years (range, 19.8-87.3 years). The median FoBMO angle was -6.7° (range, 2.5° to -17.5°). The BMO was predominantly vertically oval with a median area of 1.74 mm(2) (range, 1.05-3.40 mm(2)). Neither FoBMO angle nor BMO area was associated with age or axial length. Both global mean BMO-MRW and RNFLT declined with age at a rate of -1.34 µm/year and -0.21 µm/year, equivalent to 4.0% and 2.1% loss per decade of life, respectively. Sectorially, the most rapid decrease occurred inferiorly and the least temporally; however, the age association was always stronger with BMO-MRW than with RNFLT. There was a modest relationship between mean global BMO-MRW and RNFLT (r = 0.35), whereas sectorially the relationship ranged from moderate (r = 0.45, inferotemporal) to nonexistent (r = 0.01, temporal). CONCLUSIONS: There was significant age-related loss of BMO-MRW in healthy subjects and notable differences between BMO-MRW and RNFLT in their relationship with age and between each other. Adjusting BMO-MRW and RNFLT for age and sector is important in ensuring optimal diagnostics for glaucoma.

A Global Shape Index to Characterize Anterior Lamina Cribrosa Morphology and Its Determinants in Healthy Indian Eyes.

PURPOSE: Lamina cribrosa (LC) morphology could be implicated in the progression of glaucoma. To date, no established, quantifiable parameter to assess LC shape in vivo exists. We aim to introduce a new global shape index for the anterior LC (LC-GSI) and to identify associations with ocular factors in a healthy Indian population. METHODS: Optical coherence tomography (OCT) scans of the optic nerve head (ONH) were performed on 162 healthy subjects. Optic nerve head structures were delineated and a geometric characterization of anterior LC morphology was obtained by measuring curvature along 180 LC cross sections and representing it as LC-GSI ranging from -1 to +1. Lamina cribrosa depth and curvature were also reported. Linear regression was used to identify factors associated with LC morphology. RESULTS: The typical healthy LC had a saddle rut-like appearance, with a central ridge visible in superior-inferior cross sections. A more prominent central ridge (larger LC-GSI) was associated with shorter axial length (P < 0.001), smaller Bruch's membrane opening (BMO) area (P = 0.020), smaller vertical cup-to-disc ratio (VCDR) (P = 0.007), and larger minimum rim width (BMO-MRW) (P = 0.001). A deeper LC was associated with male sex (P < 0.001), shorter axial length (P = 0.003), larger VCDR (P < 0.001), and smaller BMO-MRW (P = 0.002). Age and IOP were not significantly associated with LC morphology in healthy eyes. CONCLUSIONS: The LC-GSI is a single index that quantifies overall LC shape in an intuitive way. Ocular determinants of LC-GSI in healthy eyes included risk factors for glaucoma (axial length, VCDR, and BMO-MRW), highlighting the potential role of LC morphological characterization in the diagnosis and monitoring of glaucoma.

Determinants of optical coherence tomography-derived minimum neuroretinal rim width in a normal Chinese population.

PURPOSE: To characterize an optical coherence tomography (OCT)-derived parameter, Bruch's membrane opening-minimum rim width (BMO-MRW), and its association with demographic and clinical parameters in normal Chinese subjects. METHODS: Right eyes of 466 consecutive healthy subjects from a population-based study of Singaporean Chinese underwent Cirrus OCT imaging. The retinal internal limiting membrane (ILM) and BMO were automatically delineated using the built-in Cirrus algorithm. The standard 36 interpolated radial B-scans (72 BMO points, 5° increments) of each optic nerve head were manually extracted from the central circle (3.46-mm diameter). We used Matlab to measure the shortest distance from the BMO points to the ILM. Associations of BMO-MRW with demographic and clinical parameters were evaluated using marginal general estimating equations analysis. RESULTS: There was a slight preponderance of male subjects (50.9%), with a mean age of 54.8 ± 7.63 years. Mean BMO-MRW was 304.67 ± 58.96 µm (range, 173.32-529.23 µm), which was highly associated with OCT-derived disc area (DA) (ß = -91.78, P < 0.001) and rim area (RA) (ß = 194.31, P < 0.001), followed by spherical refractive error (SRE) (ß = -2.23, P = 0.02) and retinal nerve fiber layer (RNFL) thickness (ß = 0.5, P = 0.04), after adjusting for the associated factors such as age, sex, intraocular pressure (IOP), and vertical cup-disc ratio (VCDR). CONCLUSIONS: Disc area and RA had the strongest association with BMO-MRW, followed by SRE and RNFL thickness. The availability of this normative database will facilitate optic nerve head assessment using the BMO-MRW parameter in Chinese subjects.

Influence of translaminar pressure dynamics on the position of the anterior lamina cribrosa surface.

PURPOSE: To determine how the translaminar pressure difference (TLPD) and gradient (TLPG) influence the position of anterior lamina cribrosa (LC) surface. METHODS: Twenty-six eyes of 26 healthy subjects were subjected to enhanced-depth imaging volume scanning of the optic nerve using spectral-domain optical coherence tomography (SD-OCT). The anterior LC surface depth (LCD) relative to the Bruch's membrane (BM) opening was measured at 11 equidistant planes, and the LC thickness (LCT) was measured at three locations (superior midperipheral, midhorizontal, and inferior midperipheral). Intraocular pressure and lumbar cerebrospinal fluid pressure (CSFP) were measured on the same day as the SD-OCT examination. The TLPD was defined as the difference between IOP and CSFP (i.e., IOP-CSFP), and the TLPG as the TLPD divided by LCT (i.e., TLPD/LCT). RESULTS: Subjects were aged 63.4 ± 8.0 years and comprised 12 males and 14 females. Regression analyses revealed a significant association between a larger mean LCD and male sex (P = 0.002), and between a larger central LCD and male sex (P ≤ 0.012), larger TLPD (P = 0.048), and higher TLPG (P = 0.029). There was no significant association between IOP, CSFP, and LCT, and either the mean LCD (P = 0.438, 0.368, and 0.416, respectively) or central LCD (P = 0.284, 0.085, and 0.144, respectively). CONCLUSIONS: A larger central LCD was associated with larger TLPD and higher TLPG in healthy eyes, which indicates that the translaminar pressure dynamics may play a role in the position of the anterior LC surface relative to BM opening in healthy human eyes.