Change of β-Zone Parapapillary Atrophy During Axial Elongation: Boramae Myopia Cohort Study Report 3

How is eyeball growth associated with optic nerve head shape and glaucoma? The Lamina cribrosa/Bruch's membrane opening offset theory

The optic nerve head (ONH) is a complex structure wherein the axons of the retinal ganglion cells extrude from the eyeball through three openings: 1) the Bruch's membrane opening (BMO) in the retinal layer, 2) the anterior scleral canal opening in the anterior scleral layer, and 3) the lamina cribrosa (LC). Eyeball expansion during growth induces an offset among openings, since the expansion affects the inner retinal and outer scleral layers differently: the posterior polar retinal structure is preserved by the preferential growth in the equatorial region, whereas no such regional difference is observed in the scleral layer. The various modes and extents of eyeball expansion result in diverse directionality and amount of offset among openings, which causes diverse ONH morphology in adults, especially in myopia. In this review, we summarize the ONH changes that occur during myopic axial elongation. These changes were observed prospectively in our previous studies, wherein LC shift and subsequent offset from the BMO center could be predicted by tracing the central retinal vascular trunk position. This offset induces the formation of γ-zone parapapillary atrophy or externally oblique border tissue. As a presumptive site of glaucomatous damage, the LC/BMO offset may render the LC pores in the opposite direction more vulnerable. To support such speculation, we also summarize the relationship between LC/BMO offset and glaucomatous damage. Indeed, LC/BMO offset is not only the cause of diverse ONH morphology in adults, but is also, potentially, an important clinical marker for assessment of glaucoma.

Association between eyeball asymmetry and offset of openings in optic nerve head canal assessed by posterior polar eyeball topography

We investigated three-dimensional (3D) eyeball protrusion and its association with the offset between the lamina cribrosa (LC) and Bruch's membrane opening (BMO). 3D-MRI scans were taken from 93 subjects (186 eyes). An ellipsoid was fitted along the posterior 2/3 contour of each eyeball. Eyeball asymmetry with focal bulging was determined by the existence of an adjacent outward protrusion/reciprocal inward depression pair, and the angular deviation of the outermost protruded point (OPP) was measured from the nasal side of the fovea-BMO axis. The LC/BMO offset was evaluated by measuring the central retinal vascular trunk (CRVT) location from the BMO center: (1) the angular deviation and (2) the offset index as the ratio between the CRVT-BMO center distance and the BMO radius in the same direction. Seventy-nine eyes (42%) were classified as having eyeball asymmetry, which had a more superior LC/BMO offset (P < 0.001) and a larger offset index (P = 0.002). In those eyes, the angular deviation of the OPP showed a significant correlation with that of the LC/BMO offset (r = -0.724, P < 0.001), as did protrusion depth with the offset index (r = 0.291, P = 0.009). The presence of eyeball asymmetry was associated with superior LC/BMO offset (P = 0.004) and larger offset index (P = 0.009). Superior LC/BMO offset was associated with older age (P < 0.001), shorter axial length (P < 0.001) and inferior location of OPP (P < 0.001). The location and extent of focal bulging were closely associated with those of LC/BMO offset. This indicates that focal bulging during expansion might be associated with diverse directionality of LC/BMO offset.

Parapapillary βBM and γ Zones Played Different Roles in Axial Elongation Among Young Adolescents Using Optical Coherence Tomography

Purpose

To evaluate the influencing factors of parapapillary βBM and γ zones incidence in young adolescents and to explore their associations with axial length progression.

Methods

In this prospective cohort study, 976 seventh-grade students from nine secondary schools in Beijing, China, were enrolled and followed up 1 year later. Parapapillary βBM zone was defined as retinal pigment epithelium loss while Bruch's membrane was present. Parapapillary γ zone was defined as the absence of retinal pigment epithelium and Bruch's membrane. Logistic regression model was used to analyze the influencing factors of βBM and γ zone incidence. A linear mixed model was used to analyze the associations between parapapillary zones and axial elongation.

Results

Of the 976 participants, 139 (14.2%) had only βBM zone, 398 (40.8%) had only γ zone, and 171 (17.5%) had both. At follow-up, the incidence of βBM zone was 11.5% (76/659), and the incidence of γ zone was 9.7% (39/404). Optic disc tilt, thinner subfoveal choroid, and longer axial length at baseline showed a higher risk of γ zone incidence. The absence of γ zone at baseline showed a faster axial length progression. When the baseline axial length was 25 mm or longer, the βBM zone was also related to the axial elongation.

Conclusions

The γ zone was associated with axial length progression, and the βBM zone was also associated with the axial length progression when the axial length exceeded 25 mm, which was consistent with the notion that excessive axial length growth not only is the extension of the eyeball but also has its own pathologic changes.

Characteristics of the Peripapillary Structure and Vasculature in Patients With Myopic Anisometropia

Purpose

To evaluate the interocular differences of the peripapillary structural and vascular parameters and that of association with axial length (AL) in participants with myopic anisometropia using swept-source optical coherence tomography.

Methods

This prospective cross-sectional study included 90 eyes of 45 participants. Each participant's eyes were divided into the more and less myopic eye respectively according to spherical equivalent. The β- and γ-parapapillary atrophy (PPA) areas, Bruch's membrane opening distance, border length, and border tissue angle were measured manually. Peripapillary choroidal vascularity index and choroidal thickness (CT) values in superior, nasal, inferior, and temporal were calculated using a custom-built algorithm based on MATLAB.

Results

The interocular difference in AL and spherical equivalent was 0.62 ± 0.26 mm and -1.50 (-2.13, -1.25) diopters (D), respectively. The interocular difference in spherical equivalent was highly correlated with that of the AL. The β- and γ-PPA areas were significantly greater in more myopic eyes. The mean and inferior peripapillary choroidal vascularity index and all regions of peripapillary CT were significantly lower in the more myopic eyes. The interocular difference in AL was significantly positively correlated with the interocular differences in γ-PPA area and border length and negatively correlated with the interocular differences in temporal choroidal vascularity index and mean, inferior, and temporal peripapillary CT. There was an independent correlation between the interocular differences in AL and the interocular differences in γ-PPA area, inferior, and temporal peripapillary CT.

Conclusions

Significant differences between both groups were detected in most peripapillary parameters, especially in peripapillary CT. The γ-PPA area, border length, and peripapillary CT were significantly correlated with the elongation of AL.

Translational Relevance

The current study characterized and analyzed the peripapillary parameters in myopic anisometropia, which helped to monitor myopic progression.

Myopic Vascular Changes Revealed by Optical Tomography Angiography and Their Association with Myopic Fundus Manifestations

INTRODUCTION

We aimed to quantify and evaluate fundal vascular changes at different severities of myopia using optical tomography angiography (OCTA) and explore their association with fundus changes captured by ultra-widefield (UWF) fundus cameras.

METHODS

Seventy-four participants with myopia were enrolled in the study and underwent basic ophthalmic examination, OCTA, and UWF fundus photography. Multiple parameters were obtained using OCTA (flow area, structure thickness, and vessel density) and UWF fundus cameras (tessellation and parapapillary atrophy [PPA]).

RESULTS

The right eye of 30 participants with low and moderate myopia and 44 participants with high myopia (HM) were included. Patients with HM had a larger flow area of the outer retina (FA-OR) and a smaller thickness of choroid (TC). Axial length was significantly correlated with retinal and choroidal flow area and thickness in the different zones. The PPA area was positively correlated with FA-OR and negatively correlated with TC. Tessellation exhibited different levels of correlation with OCTA parameters regarding the flow area, thickness, and vessel density of the fundal layers, mainly in the inner retina.

CONCLUSION

FA-OR and TC exhibited sensitive changes in patients with HM and axial elongation; therefore, they could serve as predictive OCTA biomarkers. The PPA and tessellation were connected to the vascular and structural changes revealed by OCTA.

Myopia: Histology, clinical features, and potential implications for the etiology of axial elongation

Myopic axial elongation is associated with various non-pathological changes. These include a decrease in photoreceptor cell and retinal pigment epithelium (RPE) cell density and retinal layer thickness, mainly in the retro-equatorial to equatorial regions; choroidal and scleral thinning pronounced at the posterior pole and least marked at the ora serrata; and a shift in Bruch's membrane opening (BMO) occurring in moderately myopic eyes and typically in the temporal/inferior direction. The BMO shift leads to an overhang of Bruch's membrane (BM) into the nasal intrapapillary compartment and BM absence in the temporal region (i.e., parapapillary gamma zone), optic disc ovalization due to shortening of the ophthalmoscopically visible horizontal disc diameter, fovea-optic disc distance elongation, reduction in angle kappa, and straightening/stretching of the papillomacular retinal blood vessels and retinal nerve fibers. Highly myopic eyes additionally show an enlargement of all layers of the optic nerve canal, elongation and thinning of the lamina cribrosa, peripapillary scleral flange (i.e., parapapillary delta zone) and peripapillary choroidal border tissue, and development of circular parapapillary beta, gamma, and delta zone. Pathological features of high myopia include development of macular linear RPE defects (lacquer cracks), which widen to round RPE defects (patchy atrophies) with central BM defects, macular neovascularization, myopic macular retinoschisis, and glaucomatous/glaucoma-like and non-glaucomatous optic neuropathy. BM thickness is unrelated to axial length. Including the change in eye shape from a sphere in emmetropia to a prolate (rotational) ellipsoid in myopia, the features may be explained by a primary BM enlargement in the retro-equatorial/equatorial region leading to axial elongation.

Deep Optic Nerve Head Structures Associated With Increasing Axial Length in Healthy Myopic Eyes of Moderate Axial Length

PURPOSE

To elucidate which swept-source optical coherence tomography (OCT)-derived optic nerve head (ONH) parameters are associated with longer axial length (AXL) in healthy myopic eyes.

DESIGN

Prospective cross-sectional observational study.

METHODS

Two hundred eleven healthy eyes of 140 participants (96 emmetropic-mild myopic [AXL: 22.2-24.5 mm], 83 moderately myopic [24.5-26.0 mm], and 32 highly myopic [26.0-27.4 mm] eyes) were enrolled. Bruch membrane opening (BMO), anterior scleral canal opening (ASCO) area and ovality, minimum rim width, parameters defining misalignment between the BMO and ASCO planes, OCT-defined region of perineural canal retinal epithelium atrophy and externally oblique choroidal border tissue, circumpapillary retinal nerve fiber layer thickness (cpRNFLT), circumpapillary choroidal thickness (cpChT), lamina cribrosa parameters, and peripapillary scleral (PPS) angle were calculated from BMO-centered radial scans reconstructed from 3D raster scans. Multivariate linear mixed models were used to elucidate ONH parameters that are independently associated with AXL.

RESULTS

Longer AXL was associated with a greater misalignment between ASCO and BMO planes, larger region of externally oblique choroidal border tissue, thinner cpChT, larger PPS angle, larger ASCO area, and thicker cpRNFLT (all P < .040 after Bonferroni's correction for number of included explanatory variables).

CONCLUSIONS

A greater misalignment between BMO and ASCO planes, thinner choroid, a more posteriorly bowed PPS, an enlargement of ASCO, and thicker cpRNFLT were each associated with longer AXL. An enhanced understanding of these AXL-associated configurations should provide essential information to improve our ability to detect glaucoma-induced ONH morphology in myopic eyes.

Longitudinal Changes of Bruch's Membrane Opening, Anterior Scleral Canal Opening, and Border Tissue in Experimental Juvenile High Myopia

Purpose

To investigate the relative positional changes between the Bruch's membrane opening (BMO) and the anterior scleral canal opening (ASCO), and border tissue configuration changes during experimental high myopia development in juvenile tree shrews.

Methods

Juvenile tree shrews were assigned randomly to two groups: binocular normal vision (n = 9) and monocular -10 D lens treatment starting at 24 days of visual experience to induce high myopia in one eye while the other eye served as control (n = 12). Refractive and biometric measurements were obtained daily, and 48 radial optical coherence tomography B-scans through the center of the optic nerve head were obtained weekly for 6 weeks. ASCO and BMO were segmented manually after nonlinear distortion correction.

Results

Lens-treated eyes developed high degree of axial myopia (-9.76 ± 1.19 D), significantly different (P < 0.001) from normal (0.34 ± 0.97 D) and control eyes (0.39 ± 0.88 D). ASCO-BMO centroid offset gradually increased and became significantly larger in the experimental high myopia group compared with normal and control eyes (P < 0.0001) with an inferonasal directional preference. The border tissue showed a significantly higher tendency of change from internally to externally oblique configuration in the experimental high myopic eyes in four sectors: nasal, inferonasal, inferior, and inferotemporal (P < 0.005).

Conclusions

During experimental high myopia development, progressive relative deformations of ASCO and BMO occur simultaneously with changes in border tissue configuration from internally to externally oblique in sectors that are close to the posterior pole (nasal in tree shrews). These asymmetric changes may contribute to pathologic optic nerve head remodeling and an increased risk of glaucoma later in life.

Prevalence and Characteristics of Myopia in Adult Rhesus Macaques in Southwest China

Purpose

To investigate the prevalence of myopia in a large cohort of adult rhesus macaques at Yunnan Province in southwest China and describe the characteristics of myopic rhesus macaque eyes.

Methods

A total of 219 rhesus macaques 14.07 ± 2.72 years old (range, 8-21) were randomly recruited for this study. We performed fundus photography and measurements of cycloplegic refractive error (RE) and axial length (AL) on macaques.

Results

A total of 429 eyes of 219 macaques were examined. The median RE was -1.25 diopters (D), and the median AL was 18.69 mm. The prevalence of myopia was 62.47%, and one-third of the myopic eyes were highly myopic. The presence of fundus tessellations was higher in myopic eyes than non-myopic eyes (42.54% vs. 6.21%). The cutoff value for the presence of tessellations was -3.52 D for RE and 19.38 mm for AL. In myopic eyes, there were significant differences between grade 1 and grade 3 fundus tessellations on RE (-5.57 ± 2.97 D vs. -8.13 ± 3.51 D) and AL (19.66 ± 0.55 mm vs. 20.60 ± 1.06 mm). Beta-peripapillary atrophy (β-PPA) was found in 48.10% of myopic eyes and 6.83% of non-myopic eyes. The presence of β-PPA is associated with the presence of fundus tessellations, AL, and RE. The presence of β-PPA was higher in grade 3 than grade 1 fundus tessellations (94.4% vs. 76%).

Conclusions

More than half of adult rhesus macaques in southwest China are myopic, and one-third of the myopic ones are highly myopic. Similar to humans, tessellated fundi and β-PPA are the characteristic signs of myopic rhesus macaques. Adult rhesus macaques are optimal animal models for research on the pathogenesis of myopia.

Translational Relevance

This study not only provides a reference for the refractive state and AL in myopic rhesus macaques but also indicates that adult rhesus macaques with spontaneous myopia are optimal animal models for research on the pathogenesis of myopia.

Hemisphere opposite to central retinal vascular trunk deviation is earlier affected by glaucomatous damage in primary angle-closure glaucoma

PURPOSE

The purpose of the study was to investigate whether the position of the central retinal vascular trunk (CRVT), as a surrogate for lamina cribrosa (LC) offset, is associated with the dominant hemisphere of visual field defect in primary angle-closure glaucoma (PACG) eyes.

METHODS

Central retinal vascular trunk deviation was measured from Bruch's membrane opening (BMO) centre, which was delineated by OCT imaging, using the horizontal midline as a reference. The dominant hemisphere developing visual field defect was defined as three connected abnormal points (having a p-value < 5% probability of being normal) appearing in only one hemisphere or each point of the hemisphere having a statistically worse value compared with its mirrored point in the opposite hemisphere on pattern deviation plots.

RESULTS

One hundred five (80%) of 132 eyes with PACG had dominant hemisphere of visual field defect initially: 70 eyes (67%) in the superior and 35 eyes (33%) in the inferior hemisphere. The CRVT was located superiorly in the dominant superior visual field defect group (p < 0.001). A logistic regression analysis revealed that superior deviation of the CRVT was the only factor associated with dominant superior visual field defect (p < 0.001). Externally oblique border (EOB) presence was associated with larger BMO (p = 0.005) and angular deviation of CRVT (p = 0.002).

CONCLUSIONS

Central retinal vascular trunk deviation was associated with the dominant hemisphere of visual field defect in PACG eyes. This finding implies that the LC position relative to the BMO centre (LC/BMO offset) may incur structural vulnerability in the optic nerve head of PACG eyes.

Anatomic Peculiarities Associated with Axial Elongation of the Myopic Eye

PURPOSE

To describe anatomical peculiarities associated with axial elongation in the human myopic eye.

METHODS

Reviewing the results of previous histomorphometrical investigations of enucleated human globes, as well as reviewing findings obtained in population-based studies and hospital-based clinical investigations of myopic patients and non-myopic individuals.

RESULTS

Myopic axial elongation is associated with a change from a mostly spherical eye shape to a prolate ellipsoid form. It is combined with choroidal and scleral thinning, most pronounced at the posterior pole and less pronounced in the fundus midperiphery. In the fundus midperiphery, the retina and density of the retinal pigment epithelium (RPE) and photoreceptors decrease with a longer axial length, while in the macular region, retinal thickness, RPE cell density, and choriocapillaris thickness are not related to axial length. With axial elongation, a parapapillary gamma zone develops, leading to an enlargement of the optic disc-fovea distance and a decrease in angle kappa. Axial elongation is also correlated with an increase in the surface and volume of Bruch's membrane (BM), while BM thickness remains unchanged. Axial elongation causes moderately myopic eyes to show a shift of BM opening to the foveal direction so that the horizontal disc diameter becomes shorter (with a consequent vertical ovalization of the optic disc shape), a temporal gamma zone develops, and the optic nerve exit takes an oblique course. Features of high myopia are an enlargement of the RPE opening (myopic parapapillary beta zone) and BM opening (secondary macrodisc), elongation and thinning of the lamina cribrosa, peripapillary scleral flange (parapapillary delta zone) and peripapillary choroidal border tissue, secondary BM defects in the macular region, myopic maculoschisis, macular neovascularization, and cobblestones in the fundus periphery.

CONCLUSIONS

These features combined may be explained by a growth in BM in the fundus midperiphery leading to axial elongation.

Parapapillary gamma zone enlargement in a 10-year follow-up: the Beijing Eye Study 2001-2011

PURPOSE

To assess prevalence and associated factors of parapapillary gamma zone enlargement (GZE).

METHODS

Using fundus photographs and optical coherence tomographic images of participants of the population-based Beijing Eye Study, we examined gamma zone changes in a 10-year follow-up.

RESULTS

The study included 89 highly myopic eyes (61 participants; age: 65.0 ± 9.8 years) and 86 randomly selected non-highly myopic eyes. GZE prevalence was significantly higher in highly myopic eyes than non-highly myopic eyes (75/89; 84%; 95% CI: 77, 92 versus 18/86; 21%; 95% CI:12, 30; p < 0.001). None of the eyes showed a reduction in gamma zone size. Higher prevalence of segmental GZE without enlargement of Bruch's membrane opening (BMO) (mean: 26/175; 14.9%; 95% CI: 9.5, 20.2) was associated with optic disc size reduction (OR: 43.3; 95% CI: 10.9, 172; p < 0.001), disc-fovea distance elongation (OR: 15.4; 95% CI: 3.12, 76.4; p = 0.001) and lower prevalence of high axial myopia (OR: 0.08; 95% CI: 0.01, 0.44; p = 0.001). Higher prevalence of circular GZE (mean: 38/175; 21.7%; 95% CI: 16, 28) was correlated with optic disc enlargement (OR: 4.30; 95% CI: 1.58, 11.7; p = 0.004), and higher prevalence of myopic maculopathy progression (OR: 4.04; 95% CI: 1.60, 10.2; p = 0.003), or alternatively, higher prevalence of high myopia (OR: 4.44; 95% CI: 1.76, 11.2; p = 0.002). Circular GZE or BMO enlargement was associated with lower prevalence of macular BM defect enlargement (p = 0.035). GZE occurred perpendicular to the orientation of myopic lacquer cracks in 12 out of 17 (71%; 95% CI: 46, 95) eyes with lacquer cracks. Segmental GZE occurred in 49 (89%) out of 55 eyes in the same direction as shortening of the disc diameter developed.

CONCLUSIONS

The observations support the possibility of a posterior myopic axial elongation-associated BMO shift, leading to a segmental GZE in non-highly myopic eyes, followed by a circular GZE in highly myopic eyes. Large gamma zone might be protective against macular Bruch's membrane defects.

Comparative analysis of OCT-defined parapapillary beta and gamma zones between primary open angle glaucoma and primary angle closure glaucoma

The ophthalmoscopic beta zone of parapapillary atrophy has recently been proposed to divide into a gamma zone and a (new) beta zone based on OCT imaging. The present study was undertaken to compare the microstructural characteristics of parapapillary gamma and beta zones and their influencing factors between primary open angle glaucoma (POAG) and primary angle closure glaucoma (PACG). Seventy-three PACG patients that had no evidence of an acute attack and 78 POAG patients were enrolled. Patients were matched by propensity scores for age and visual field mean defect (MD) value. The area and angular extent of both zones were measured. In multivariate analysis, a larger beta zone was correlated with older age, severe MD value and longer axial length. A larger gamma zone was correlated with longer axial length. Older age and severe MD value were correlated with the concentric shape of beta zone. Comparing the PACG and POAG groups that adjusted for age and MD value, gamma zone was larger and more prevalent in the POAG group, while beta zone showed no significant difference. Taken separately, MD value was associated with the area and shape of beta zone in the PACG group. Axial length was associated with the temporal shape of beta zone in the POAG group. These data indicated that OCT-defined parapapillary beta and gamma zones exhibited different characteristics in two types of glaucoma. Clinically, the size of parapapillary beta zone may serve as a better indicator of glaucoma severity in eyes with PACG than that in POAG.

Advances in OCT Imaging in Myopia and Pathologic Myopia

Advances in imaging with optical coherence tomography (OCT) and optical coherence tomography angiography (OCTA) technology, including the development of swept source OCT/OCTA, widefield or ultra-widefield systems, have greatly improved the understanding, diagnosis, and treatment of myopia and myopia-related complications. Anterior segment OCT is useful for imaging the anterior segment of myopes, providing the basis for implantable collamer lens optimization, or detecting intraocular lens decentration in high myopic patients. OCT has enhanced imaging of vitreous properties, and measurement of choroidal thickness in myopic eyes. Widefield OCT systems have greatly improved the visualization of peripheral retinal lesions and have enabled the evaluation of wide staphyloma and ocular curvature. Based on OCT imaging, a new classification system and guidelines for the management of myopic traction maculopathy have been proposed; different dome-shaped macula morphologies have been described; and myopia-related abnormalities in the optic nerve and peripapillary region have been demonstrated. OCTA can quantitatively evaluate the retinal microvasculature and choriocapillaris, which is useful for the early detection of myopic choroidal neovascularization and the evaluation of anti-vascular endothelial growth factor therapy in these patients. In addition, the application of artificial intelligence in OCT/OCTA imaging in myopia has achieved promising results.

Characteristics of the Optic Nerve Head in Myopic Eyes Using Swept-Source Optical Coherence Tomography

Purpose

To investigate the characteristics of the optic nerve head (ONH) in myopia using swept-source optical coherence tomography (SS-OCT).

Methods

Participants were divided into three groups according to the axial length (AL). The optic disc morphology, retinal nerve fiber layer (RNFL) thickness, and radial peripapillary capillary (RPC) vessel density (VD), optic disc tilt, rotation, Bruch's membrane opening distance (BMOD), border length (BL), border tissue angle, focal lamina cribrosa (LC) defects, β- and γ-zone peripapillary atrophy (PPA), microvasculature dropout (MvD), choroidal thickness (CT), and the choroidal vascularity index (CVI) were compared. Linear regression analysis evaluated relationships between spherical equivalent, AL, and ONH parameters.

Results

One hundred five, 98, and 118 eyes were included in groups 1, 2, and 3, respectively. With AL increasing, the mean, superior and temporal CT, central mean and temporal, pericentral mean, inferior and nasal RPC VD, and temporal CVI decreased, whereas the mean and temporal RNFL thickness, optic disc, RIM and β-PPA area, presence and area of γ-PPA, BMOD and BL increased. Compared to other groups, group 3 depicted a larger cup area, more focal LC defect and total and juxtapapillary MvD; a lower central superior, inferior and nasal, pericentral superior, and temporal RPC VD. Group 1 demonstrated more tilted disc, larger inferior and nasal CT, mean, superior, inferior, and nasal CVI.

Conclusions

Myopia eyes have larger ONH changes, PPAs, regional RNFL, and MvD, but smaller regional CTs, RPC VD, and CVIs. SS-OCT may be useful in detecting ONH variations during myopia.

Change of peripapillary retinal nerve fiber layer and choroidal thickness during 4-year myopic progress: Boramae Myopia Cohort Study Report 4

AIMS

To investigate the longitudinal changes of peripapillary retinal nerve fibre layer (RNFL) and choroidal thickness during myopic axial elongation.

METHODS

Peripapillary RNFL and choroidal thickness were prospectively evaluated by spectral-domain optical coherence tomography (SD-OCT) in 46 eyes of 23 myopic children over the course of 4 years. Using serial OCT images acquired based on a fixed scan circle in the glaucoma progression analysis mode, general and sectoral RNFL thicknesses were acquired at the same position and the angular location of the peak was measured. The peripapillary choroidal thickness likewise was measured at eight positions in serial OCT images.

RESULTS

The mean age at the baseline was 9.6±1.7 years. The mean axial length increased from 24.80±1.28 mm to 25.64±1.35 mm. The global peripapillary RNFL thickness was 98.54±12.06 µm at baseline. The global and sectoral RNFL thicknesses did not change during the 4 years. The angular location of RNFL peaks was also stable and was located in the superotemporal (64.18±10.85°) and inferotemporal (293.98±11.62°) sectors. The global peripapillary choroidal thickness was 145.40±28.67 µm at the baseline. The global and sectoral choroidal thicknesses did not change during the 4 years.

CONCLUSIONS

The peripapillary RNFL and choroidal thicknesses as well as the locations of the RNFL peaks had been preserved, during the 4-year follow-up on myopic children, when traced and measured from the same location.

Optic disc morphology and peripapillary atrophic changes in diabetic children and adults without diabetic retinopathy or visual impairment

PURPOSE

To investigate the changes in optic disc morphology and peripapillary atrophy (PPA) in diabetic children and adults without diabetic retinopathy (DR) or visual impairment (VI).

METHODS

This cross-sectional study included two groups of subjects. One group included 91 children with type 1 diabetes mellitus (T1DM) and 86 healthy children, and the other group included 444 adults with T2DM and 442 healthy controls. The optic disc parameters including major and minor axis lengths, optic disc ovality (ODO), optic disc tilt, optic disc area and β-PPA area were analysed in all subjects. Optic disc rotation and the Bergmeister papilla were analysed only in children. Patients with diabetes and healthy controls were compared in each group of the study population.

RESULTS

In both groups, patients with diabetes and healthy controls were matched for age, sex and axial length (AL). Among the children, β-PPA area was significantly smaller in those with diabetes (0.29 ± 0.43 mm² ) than in the healthy controls (0.46 ± 0.58 mm² , p < 0.05). Multiple linear regression analysis showed that diagnosis of DM was negatively associated with β-PPA area. Longer AL and higher body mass index (BMI) were positively associated with β-PPA area. Among adults, ODO was significantly larger in those with diabetes (1.14 ± 0.09) than in healthy controls (1.12 ± 0.06, p < 0.05). Multiple linear regression analysis showed that the BMI and DM were potential risk factors affecting ODO.

CONCLUSION

Hyperglycaemia had different effects on the optic disc in children and adults. Unlike in healthy controls, hyperglycaemia had an impact on the peripapillary tissue in children and on optic disc shape in adults before DR and VI development.

Decreasing myopic lacquer crack and widening parapapillary gamma zone: case report

Background

Myopic axial elongation may be due to an equatorial enlargement of Bruch’s membrane (BM), leading to a prolate eye shape and increasing strain with BM and the retinal pigment epithelium (RPE) layer at the posterior pole. The increased BM strain may cause an enlargement of Bruch’s membrane opening (BMO) of the optic nerve head, with the subsequent development and enlargement of parapapillary gamma zone as BM-free parapapillary zone. The increased strain within BM and RPE may also cause lacquer cracks (LCs) as linear breaks in the RPE and / or BM. Studies suggested that a more marked gamma zone enlargement is associated with lower prevalence of LCs or macular BM defects. Here report on the disappearance of a LC during a 10-year follow-up of a highly myopic eye, concurrent with a marked increase in gamma zone.

Case presentation

A 56-year-old woman showed in her right eye (axial length measured 30.69 mm) a LC, vertically oval optic disc, and parapapillary gamma zone in 2001. When re-examined in 2006, gamma zone had enlarged, while the LC was no longer detectable. In 2011, the LC was not visible neither upon ophthalmoscopy and or upon optical coherence tomography (OCT), while gamma zone had further enlarged. The gamma zone enlargement occurred in a direction perpendicular to the direction of the former LC.

Conclusions

The observation suggest that a LC can decrease in width, in temporal association with an enlargement of gamma zone. It fits with the notion that an enlargement of the BMO (i.e., enlarging gamma zone) may lead to a relaxation of the BM strain and subsequently to a decrease in the width of the LC.

Offset of openings in optic nerve head canal at level of Bruch's membrane, anterior sclera, and lamina cribrosa

We compared the central retinal vascular trunk (CRVT) position, as a surrogate of lamina cribrosa (LC) offset, with the anterior scleral opening (ASCO) offset from the Bruch’s membrane opening (BMO). Based on the BMO-centered radial scans, the BMO and ASCO margins were demarcated, and each center was determined as the center of the best-fitted ellipse for each margin. The ASCO/BMO offset was defined as the offset between each center. Angular deviations and the extent of ASCO and CRVT offsets from the BMO center were compared directly. Incomplete demarcation of ASCO was found in 20%, which was associated with a larger BMO area and a larger ASCO offset from the BMO. The angular deviation of ASCO offset was associated with that of CRVT offset and that of the longest externally oblique border. The ASCO offset was smaller than the CRVT offset, and, unlike the CRVT offset, it was rarely deviated to the inferior side. The complete ASCO margin might not be demarcatable when determined on BMO-centered radial scans in the presence of an offset. Also, the ASCO, which reflects only the superficial scleral layer, might not reflect the LC position, because the LC might be shifted further from the ASCO.

Central retinal vascular trunk deviation in unilateral normal-tension glaucoma

Purpose

To investigate whether the position of the central retinal vascular trunk (CRVT), as a surrogate of lamina cribrosa (LC) offset, was associated with the presence of glaucoma in normal-tension glaucoma (NTG) patients.

Methods

The position of the CRVT was measured as the deviation from the center of the Bruch’s membrane opening (BMO), as delineated by spectral-domain optical coherence tomography imaging. The offset index was calculated as the distance of the CRVT from the BMO center relative to that of the BMO margin. The angular deviation of CRVT was measured with the horizontal nasal midline as 0° and the superior location as a positive value. The offset index and angular deviation were compared between glaucoma and fellow control eyes within individuals.

Results

NTG eyes had higher baseline intraocular pressure (P = 0.001), a larger β-zone parapapillary atrophy area (P = 0.013), and a larger offset index (P<0.001). In a generalized linear mixed-effects model, larger offset index was the only risk factor of NTG diagnosis (OR = 31.625, P<0.001). A generalized estimating equation regression model revealed that the offset index was larger in the NTG eyes than in the control eyes for all ranges of axial length, while it was the smallest for the axial length of 23.4 mm (all P<0.001).

Conclusions

The offset index was larger in the unilateral NTG eyes, which fact is suggestive of the potential role of LC/BMO offset as a loco-regional susceptibility factor.

Commentary review on peripapillary morphological characteristics in high myopia eyes with glaucoma: diagnostic challenges and strategies

The incidences of open angle glaucoma (OAG) and high myopia are increasing concomitantly. Considering the aging population and concurrent rapid increase in the number of individuals with myopia, the risk of visual defects caused by highly myopic OAG is likely to increase dramatically over the next few decades. However, precise screening and diagnosis of OAG is challenging because of the tilt and rotation of the optic disc, as well as extensive β-zone parapapillary atrophy in highly myopic eyes. Recent advances in optical coherence tomography (OCT) and OCT angiography (OCTA) technologies imply that both modalities are promising tools for the detection of highly myopic OAG. Notably, the diagnosis of OAG remains to be determined with the longitudinal changes of functional damages (e.g. visual field defect, visual electrophysiological changes). We herein describe some aspects of microvascular and microstructural pathology in patients with highly myopic OAG and proposes a framework for the development of novel diagnostic and therapeutic strategies.

Angular Location of Retinal Nerve Fiber Layer Defect: Association With Myopia and Open-Angle Glaucoma

Purpose

To compare retinal nerve fiber layer (RNFL) defects' angle measurements determined from the center of the optic disc and Bruch's membrane opening (BMO), as a function of myopia and open-angle glaucoma (OAG) subtypes.

Methods

In total, 118 patients with OAG were grouped by axial length (AL; high myopia, AL >26 mm; mild to moderate myopia, 24 ≤ AL ≤26 mm; nonmyopia, AL <24 mm) and OAG subtype (normal-tension glaucoma [NTG], high-tension glaucoma [HTG]). The disc and BMO centers were determined by a merged image of red-free fundus photography and spectral-domain optical coherence tomography. The angular location of the RNFL defect close to the fovea (angle α) was measured from the disc center and BMO center, respectively (angle αdisc and angle αBMO). The difference between angle αdisc and αBMO (Δα), as well as the RNFL defect width (angle γ), was evaluated.

Results

Angle αdisc was smaller in myopic eyes and correlated significantly with AL (P = 0.001), whereas it did not differ among OAG subgroups. Angle αBMO and angle γ were not different in the myopic and OAG subgroups. The Δ α was larger for eyes with higher degree of myopia and had significant correlation with AL (P < 0.001) and was larger in NTG eyes than in HTG eyes (P = 0.023).

Conclusions

The angular location of the RNFL defect measured from the disc center, but not from the BMO center, was closer to the fovea for glaucomatous eyes with higher values of AL. The present study may facilitate understanding of the characteristic locational pattern of the RNFL defect in myopic glaucomatous eyes.

Retinal applications of swept source optical coherence tomography (OCT) and optical coherence tomography angiography (OCTA)

The advent of optical coherence tomography (OCT) revolutionized both clinical assessment and research of vitreoretinal conditions. Since then, extraordinary advances have been made in this imaging technology, including the relatively recent development of swept-source OCT (SS-OCT). SS-OCT enables a fast scan rate and utilizes a tunable swept laser, thus enabling the incorporation of longer wavelengths than conventional spectral-domain devices. These features enable imaging of larger areas with reduced motion artifact, and a better visualization of the choroidal vasculature, respectively. Building on the principles of OCT, swept-source OCT has also been applied to OCT angiography (SS-OCTA), thus enabling a non-invasive in depth-resolved imaging of the retinal and choroidal microvasculature. Despite their advantages, the widespread use of SS-OCT and SS-OCTA remains relatively limited. In this review, we summarize the technical details, advantages and limitations of SS-OCT and SS-OCTA, with a particular emphasis on their relevance for the study of retinal conditions. Additionally, we comprehensively review relevant studies performed to date to the study of retinal health and disease, and highlight current gaps in knowledge and opportunities to take advantage of swept source technology to improve our current understanding of many medical and surgical chorioretinal conditions. We anticipate that SS-OCT and SS-OCTA will continue to evolve rapidly, contributing to a paradigm shift to more widespread adoption of new imaging technology to clinical practice.

Optic nerve head anatomy in myopia and glaucoma, including parapapillary zones alpha, beta, gamma and delta: Histology and clinical features

The optic nerve head can morphologically be differentiated into the optic disc with the lamina cribrosa as its basis, and the parapapillary region with zones alpha (irregular pigmentation due to irregularities of the retinal pigment epithelium (RPE) and peripheral location), beta zone (complete RPE loss while Bruch's membrane (BM) is present), gamma zone (absence of BM), and delta zone (elongated and thinned peripapillary scleral flange) within gamma zone and located at the peripapillary ring. Alpha zone is present in almost all eyes. Beta zone is associated with glaucoma and may develop due to a IOP rise-dependent parapapillary up-piling of RPE. Gamma zone may develop due to a shift of the non-enlarged BM opening (BMO) in moderate myopia, while in highly myopic eyes, the BMO enlarges and a circular gamma zone and delta zone develop. The ophthalmoscopic shape and size of the optic disc is markedly influenced by a myopic shift of BMO, usually into the temporal direction, leading to a BM overhanging into the intrapapillary compartment at the nasal disc border, a secondary lack of BM in the temporal parapapillary region (leading to gamma zone in non-highly myopic eyes), and an ocular optic nerve canal running obliquely from centrally posteriorly to nasally anteriorly. In highly myopic eyes (cut-off for high myopia at approximately -8 diopters or an axial length of 26.5 mm), the optic disc area enlarges, the lamina cribrosa thus enlarges in area and decreases in thickness, and the BMO increases, leading to a circular gamma zone and delta zone in highly myopic eyes.

Short foveo-disc distance in situs inversus of optic disc

Situs inversus of optic disc (SIOD) is thought to be a congenital optic disc abnormality that is caused by dysversion of optic nerve insertion. SIOD, however, has many additional features that cannot be explained by abnormal optic-nerve-insertion directionality. In this study, we measured the distance between the fovea and disc in 22 eyes of 15 SIOD patients. For comparison, two control eyes were matched with each SIOD eye by age and axial length. The vertical distance between the temporal vascular arcades also was measured. The foveo-disc distance was shorter in the SIOD eyes than in the control eyes, while the inter-arcade distance did not differ. Further, we measured the circumpapillary retinal nerve fiber layer thickness, which showed nasal crowding of two humps in the SIOD eyes. This nasal crowding disappeared when we shifted the circle scan by the mean difference (465 μm) of the foveal-disc distance between the two groups. Our findings suggest that the optic disc was located closer to the fovea than it would have been normally. Thus, SIOD might reflect incomplete expansion of the posterior pole in the direction of the fovea-disc axis.

Relationship between Three-Dimensional Magnetic Resonance Imaging Eyeball Shape and Optic Nerve Head Morphology

PURPOSE

To determine if the 3-dimensional (3D) eyeball shape is associated with the positions of the central retinal vascular trunk (CRVT) and the externally oblique border (EOB) in the optic nerve head (ONH).

DESIGN

Prospective, cross-sectional study.

PARTICIPANTS

Fifty-six subjects (112 eyes) with a diagnosis of glaucoma or glaucoma suspect.

METHODS

The eyeball shape on 3D magnetic resonance imaging (MRI) scans was classified according to the dimension of the longest diameter: axial dimension (prolate sphere), group 1; horizontal dimension (horizontally oblate sphere), group 2; and vertical dimension (vertically oblate sphere), group 3. The deviation of the CRVT, as a surrogate of lamina cribrosa (LC) shift, was measured from the center of the Bruch's membrane opening (BMO) demarcated by OCT imaging, with the horizontal midline as 0° and the superior location as a positive value. The angular location of the longest EOB was also measured.

MAIN OUTCOME MEASURE

Positions of CRVT and EOB according to the 3D eyeball shape.

RESULTS

Among 112 eyes, 54 (48%) had a prolate shape (group 1), 23 (21%) had a horizontally oblate shape (group 2), and 35 (31%) had a vertically oblate shape (group 3). The angular deviation of the CRVT differed among the groups: to the nasal side in group 1, to the temporal side in group 2, and along the vertical meridian in group 3. In cases of asymmetric eyeball shape, the CRVT was deviated toward the undergrown side from the overgrown side, regardless of grouping. The angular location of the longest EOB was in the direction opposite to the CRVT position (P < 0.001). A generalized estimating equation analysis revealed that the temporal location of the CRVT was associated with older age (P = 0.001), nasal location of the longest EOB (P < 0.001), and oblate shape of the eyeball (P < 0.001, group 2; P = 0.007, group 3).

CONCLUSIONS

The position of the CRVT and EOB were associated with the 3D eyeball shape. Considering that infant ONH morphology is highly uniform, various modes of eyeball expansion during growth can result in diverse directionalities of offset between the LC and the BMO in adults.

Characteristics of Focal Gamma Zone Parapapillary Atrophy

Purpose

The purpose of this study was to investigate the characteristics of focal γ-zone parapapillary atrophy (focal γPPA) in patients with primary open-angle glaucoma (POAG) using spectral-domain optical coherence tomography (SD-OCT).

Methods

Three groups of POAG eyes (n = 214) were defined according to the circumferential extent of Bruch's membrane (BM) within the β-zone PPA, as follows: (1) no γPPA (intact BM; n = 81), (2) conventional γPPA (γPPA involving the fovea-BM-opening axis; n = 89), and (3) focal γPPA (γPPA not involving the fovea-BM-opening axis; n = 44). Clinical and ocular characteristics, including age, axial length (AXL), and focal lamina cribrosa (LC) defects were compared among the three groups.

Results

The focal γPPA group was significantly older (60.6 ± 11.0 years) and had shorter AXL (24.10 ± 1.34 mm) than those of the conventional γPPA group (46.2 ± 13.8 years and 26.53 ± 1.61 mm, respectively; P < 0.001). These values of the focal γPPA group were similar to those of the no γPPA group (23.73 ± 0.97 mm for AXL and 64.0 ± 13.0 years for age). The focal γPPA group had a significantly higher prevalence of focal LC defects than did the other two groups (70.5% [31/44] for the focal γPPA group versus 46.1% [41/89] for the conventional γPPA group versus 37.0% [30/81] for the no γPPA group; P = 0.002).

Conclusions

Focal γPPA was differentiated from conventional γPPA by older age and shorter AXL. Further, focal γPPA was frequently accompanied by focal LC defects. Longitudinal studies elucidating whether focal LC defects and focal γPPA share common pathogenesis are warranted.

Hemisphere opposite to vascular trunk deviation is earlier affected by glaucomatous damage in myopic high-tension glaucoma

PURPOSE

To investigate whether the position of the central vascular trunk, as a surrogate of lamina cribrosa (LC) shift, is associated with the initial hemisphere of visual field defect in myopic high-tension glaucoma (HTG) eyes.

METHODS

The deviation of the central vascular trunk was measured from the center of the Bruch's membrane opening (BMO), which was delineated by OCT imaging. The angular deviation was measured with the horizontal nasal midline as 0° and the superior location as a positive value. The initial hemisphere developing visual field defect was defined as three connected abnormal points (having a P value with less than 0.5% probability of being normal) appearing in only one hemisphere in pattern deviation plots. If those points were observed in both hemispheres initially, the eye was classified as bi-hemispheric visual field defect.

RESULTS

Initially, 36 eyes (44%) had superior visual field defects, 27 (33%) inferior visual field defects, and 18 (22%) bi-hemispheric visual field defects. After a mean follow-up of 5 years, the number of bi-hemispheric visual field defects had increased to 34 (42%). A logistic regression analysis revealed that inferior deviation of vascular trunk was the only factor associated with initial inferior visual field defect (P = 0.001), while initial bi-hemispheric visual field defects were associated with worse mean deviation at initial visits (P<0.001). A conditional inference tree analysis showed that both the angular deviation (P<0.001) and initial mean deviation (P = 0.025) determined the initial hemispheres developing visual field defect.

CONCLUSIONS

Although both hemispheres were involved as glaucoma progression, the axons on the side counter to the vascular trunk deviation were damaged earlier in HTG. This finding implies the LC shift could add additional stress to axons exposed to high intraocular pressure.

Parapapillary atrophy and changes in the optic nerve head and posterior pole in high myopia

We investigated the relationship between microstructure of β-parapapillary atrophy (β-PPA) and morphologic features of optic nerve head (ONH) and posterior pole in highly myopic eyes. Eighty-nine highly myopic eyes were included in this study. Bruch’s membrane opening (BMO) area, lamina cribrosa (LC) thickness, anterior laminar depth, peripapillary and subfoveal choroidal thickness (CT), macular Bruch’s membrane (BM) length, and width of β-PPA with and without Bruch’s membrane (PPA_+BM and PPA_−BM) were evaluated. The mean age and axial length of the included subjects were 26.88 ± 2.44 years and 27.03 ± 0.88 mm, respectively. The width of PPA_−BM was larger with increasing BMO area (P = 0.001), whereas the BMO area was not associated with the width of PPA_+BM. The large PPA_+BM was significantly related to a thinner LC (P = 0.003), deeper anterior lamina surface (P < 0.001), longer macular BM length (P = 0.008), and thinner temporal peripapillary CT (P = 0.034). We found that the morphologic features of the ONH and posterior pole in highly myopic eyes were different based on the microstructure of β-PPA. Whether these features are linked to the development of glaucoma in myopic eyes should be investigated in future studies.

Association of macular thickness with parapapillary atrophy in myopic eyes

Background

To investigate whether macular structure could be affected by axial elongation and to determine the association between macular intraretinal thickness and the microstructure of β-zone parapapillary atrophy (PPA) in myopic eyes.

Methods

The study recruited 113 healthy myopic subjects (113 eyes). Images of the macula, subfoveal choroid, and optic nerve head were acquired using spectral-domain optical coherence tomography (SD-OCT). An automatic segmentation algorithm was used to segment the macular images into 7 intraretinal layers. PPA widths with and without Bruch’s membrane (PPA_+BM and PPA_-BM, respectively) were evaluated. Linear regression analysis was performed to evaluate the association between macular intraretinal thickness and axial length and the microstructure of PPA.

Results

An increase in axial length was associated with a decrease in whole macular thickness of the peripheral region and an increase in whole macular thickness of the central region. Thickness alterations of the macular intraretinal layers were most apparent in the peripheral region. A significant correlation was found between PPA_-BM width and macular intraretinal layer thickness, whereas no significant correlation was found between PPA_+BM width and macular intraretinal layer thickness. Moreover, both PPA_+BM and PPA_-BM widths significantly correlated with subfoveal choroidal thickness.

Conclusions

Macular intraretinal layer thickness may be affected by PPA_-BM width. These findings indicate that the microstructure of PPA should be considered when evaluating the macula in patient with myopia and glaucoma.

Nasalization of Central Retinal Vessel Trunk Predicts Rapid Progression of Central Visual Field in Open-Angle Glaucoma

Central visual field (CVF) loss is important in maintaining vision-related quality of life in eyes with open-angle glaucoma (OAG). The present study investigated whether nasalized location of central retinal vessel trunk (CRVT) at baseline is associated with rapid rate of CVF loss in early-stage OAG eyes. This study included 76 OAG eyes with high nasalization CRVT [HNL] group and 75 OAG eyes with low nasalization CRVT [LNL] group matched for glaucoma severity at baseline that showed progressive visual field (VF) loss. The rates of mean threshold changes at various regions were compared in the two groups using a linear mixed model. Clinical variables associated with rapid rate of CVF progression were also identified using a linear mixed model. The rate of CVF loss in the central 10° was significantly higher in the HNL group than that in the LNL group (-0.452 dB/year vs. -0.291 dB/year, P < 0.001). The average and inferior hemi-macular ganglion cell inner plexiform layer (GCIPL) progression rates were significantly faster in the HNL group than in the LNL group (P < 0.05). Nasalized location of CRVT was an independent predictor of a more rapid VF loss in the central 10° region (P < 0.05).

Case report: what gives the myopic tilted disc an oval appearance?

Background

Myopic tilted disc, observed as an oval disc, has been alleged to be a funduscopic en-face manifestation of excessive optic nerve head (ONH) sloping or tilting. Here, we report the case of a myopic child showing a developing oval disc in fundus photos during axial elongation, but without progressive tilting in spectral-domain optical coherence tomography (SD-OCT) images.

Case presentation

By merging B-scan SD-OCT images of the ONH and macula, the curvature of the posterior pole, including both the fovea and ONH, was reconstructed and compared before and after 2 years of axial elongation. Despite the marked increase of disc ovality, the posterior polar curvature was rarely changed. The preponderance of optic disc change was induced by the shift of the temporal disc margin in the nasal direction. This shifting alone imitated an increase of tilt angle but one that was still far smaller than the required degree of tilt for ONH-tilt-based disc ovality. To clarify, we calculated the required extent of axial elongation to obtain a substantial degree of ONH tilt when considering the adjacency of the fovea and the ONH. Without a focal increase of posterior polar curvature, which is to say posterior staphyloma, such change is not possible until the axial length increases extraordinarily.

Conclusion

The most prominent change in the development of myopic tilted disc, which change gives it an oval appearance and imitates a tilt when measured, is actually not a tilt but rather a shift of the temporal disc margin.

Position of Central Vascular Trunk and Shape of Optic Nerve Head in Newborns

Purpose

To investigate the baseline position of the central vascular trunk (CVT) and the characteristics of the optic nerve head (ONH) in newborns.

Methods

CVT position was evaluated based on fundus images obtained from newborns who had undergone eye-screening examinations. It was then graded according to the optic disc area as follows: grade 1, within central 4%; grade 2, within central 9%; grade 3, within central 16%; grade 4, within central 25%; grade 5, outside central 25% of optic disc area. The direction of the CVT position was determined in cases of grade 2 or more as superior, inferior, nasal, and temporal, relative to the optic disc center. The ovality index and the vertical cup-to-disc ratio were determined as well.

Results

In 1000 fundus images from 1000 newborns, 87.1% showed grade 1 (95% confidence interval 84.7-88.8), and 10.7% showed grade 2. The most common CVT direction was central (87.1%, grade 1), followed by nasal (11.0%) and inferior (1.2%). The ovality index was 1.28 ± 0.09 (range, 1.01-1.61). The ONH shape was vertically oval and highly uniform. The average vertical cup-to-disc ratio was 0.29 ± 0.13 (range, 0.00-0.67).

Conclusions

The CVT of newborns was located in the central area of the ONH in most cases. The shape of the optic disc was vertically oval, and very similar among the newborns. Considering the high variability of ONH morphology and the diverse location of the CVT in adults, our result suggests that the shape of the ONH and the CVT position might change during eyeball growth.

Morphological features of parapapillary beta zone and gamma zone in chronic primary angle-closure glaucoma

PURPOSE

To investigate the morphological features of parapapillary beta zone and gamma zone and their associated factors in eyes with chronic primary angle-closure glaucoma (CACG).

METHODS

The observational cross-sectional study included 65 CACG eyes and 65 non-myopic control eyes. On enhanced depth imaging of optical coherent tomography images, the area of parapapillary beta zone and gamma zone, and the peripapillary choroidal thickness at 6 sectors were measured. The optic disc ovality index and Bruch's membrane opening (BMO) shape were further calculated.

RESULTS

Beta zone was present in 103 (79.2%) eyes and gamma zone in 29 (22.3%) eyes. Compared to control eyes, CACG was associated with larger parapapillary beta zone, female gender, and older age (P < 0.01). No significant difference was observed in axial length and peripapillary choroidal thickness between both groups (P > 0.05). In multivariate analysis, beta zone area was positively associated with older age and higher prevalence of CACG (P < 0.01), while a larger gamma zone area was associated with a smaller disc ovality index and a higher BMO ovality ratio (P < 0.01). The peripapillary choroidal thickness at six sectors was decreased with older age (P < 0.01).

CONCLUSIONS

In mainly non-myopic subjects with or without CACG, larger parapapillary beta zone was correlated with older age and presence of glaucoma, while a larger parapapillary gamma zone was correlated with disc ovality but not with glaucoma. Parapapillary beta zone and gamma zone may play different roles in physiological and glaucomatous changes around optic nerve head.