Peripapillary Tissue Research Articles

Effect of Eye Globe and Optic Nerve Morphologies on Gaze-Induced Optic Nerve Head Deformations.

The purpose of this study was to investigate the effect of globe and optic nerve (ON) morphologies and tissue stiffnesses on gaze-induced optic nerve head deformations using parametric finite element modeling and a design of experiment (DOE) approach. A custom software was developed to generate finite element models of the eye using 10 morphological parameters: dural radius, scleral, choroidal, retinal, pial and peripapillary border tissue thicknesses, prelaminar tissue depth, lamina cribrosa (LC) depth, ON radius, and ON tortuosity. A central composite face-centered design (1045 models) was used to predict the effects of each morphological factor and their interactions on LC strains induced by 13 degrees of adduction. Subsequently, a further DOE analysis (1045 models) was conducted to study the effects and potential interactions between the top five morphological parameters identified from the initial DOE study and five critical tissue stiffnesses. In the DOE analysis of 10 morphological parameters, the 5 most significant factors were ON tortuosity, dural radius, ON radius, scleral thickness, and LC depth. Further DOE analysis incorporating biomechanical parameters highlighted the importance of dural and LC stiffness. A larger dural radius and stiffer dura increased LC strains but the other main factors had the opposite effects. Notably, the significant interactions were found between dural radius with dural stiffness, ON radius, and ON tortuosity. This study highlights the significant impact of morphological factors on LC deformations during eye movements, with key morphological effects being more pronounced than tissue stiffnesses.

Relationship between the structure and microcirculation of the optic disc region and myopic traction maculopathy in highly myopic eyes

PurposeTo explore the characteristics and influencing factors structural and microcirculatory of optic disc and peripapillary tissue in eyes with myopia traction maculopathy (MTM).MethodsThere were 100 eyes from 77 patients in this study. We used 1:1 matching axial length in myopic eyes. Patients were divided into two groups according to the presence or absence of MTM. Fundus structure parameters were obtained by swept source optical coherence tomography (SS-OCT), and the optic disc microcirculation parameters were obtained by OCT angiography (OCTA).ResultsMTM group were older (P = 0.001) and had poorer Best-corrected Visual Acuity (BCVA) (P = 0.011), the optic disc-fovea distance (DFD) was longer (P < 0.019), optic disc tilt was greater (P < 0.001), area of peripapillary atrophy (PPA) was larger (P < 0.001), and PPA/optical disc area (ONH) was higher (P < 0.001). The peripapillary scleral thickness (PST) was lower in the MTM group (P < 0.001). The mean peripapillary choroidal thickness (PCT) (P < 0.001) and PCT in the 10 orientations were significantly lower in the MTM group than in the NMTM group (all P < 0.01). Vascular density in the nasosuperior (NS) region of the optic disc was significantly lower in the MTM group (P = 0.037). The generalized estimating equation suggested that PPA area (P = 0.028), mean PCT (P = 0.008), superior PCT (P = 0.027), inferonasal PCT (P = 0.040), temporoinferior PCT (P = 0.013), and PST (P = 0.046) correlated with MTM. Age, axial length, optic disc tilt, PPA area, mean PCT, and optic disc central zone (0–2 mm) vascular density (all P < 0.05) were significantly correlated with PST.ConclusionsThe enlarged PPA area and thinner PCT and PST in eyes with MTM are more significant. Lower PST in high myopia was related to abnormalities of PCT and microcirculation.Trial registrationClinical Trial Registration number: ChiCTR2100046590

Morphology of Serous Retinal Detachment in Morning Glory Optic Disc Anomaly in a Patient before and after Treatment with Systemic Carboanhydrase Inhibitors

Morning glory optic disc anomaly (MGODA) is a rare congenital defect of the optic nerve head. The optic nerve is enlarged, and its conical excavation is filled with glial tissue. It may be associated with cerebral malformations and ocular complications, whereas serous retinal detachment occurs in 38% of affected patients. Surgical treatment of detachment showed poor visual outcome in the past and conservative treatment options are scarce. A woman with MGODA presented in our clinic with sudden vision loss due to serous retinal detachment. She denied any previous ophthalmological problems and her past medical history was unremarkable. Vision testing showed normal visual acuity in her left eye and finger counting in her right eye. Slit lamp examination was unremarkable. Fundus examination of the right eye showed retinal detachment without holes or traction membranes and an enlarged optic disc with raised peripapillary tissue and glial tissue in the center of the optic disc. Due to the pathognomonic otpic disc finding, we diagnosed MGODA complicated by a serous retinal detachment. We treated the patient with systemic carboanhydrase inhibitors and documented the initial clinical findings as well as the course of disease under treatment by optical coherent tomography (OCT), fundus autofluorescence imaging (FAF), and visual field testing. During follow-up, we detected noticeable subretinal fluid regression and improvement in visual acuity. The application of oral carboanhydrase inhibitors appears to be a valid therapeutic option in patients with MGODA-associated serous macular detachment. OCT and FAF imaging are useful modalities for documentation of subretinal fluid regression and structural changes in the peripapillary region.

Changes in Optic Nerve Head and Retinal Morphology During Spaceflight and Acute Fluid Shift Reversal

Countermeasures that reverse the headward fluid shift experienced in weightlessness have the potential to mitigate spaceflight-associated neuro-ocular syndrome. This study investigated whether use of the countermeasure lower-body negative pressure during spaceflight was associated with changes in ocular structure. To determine whether changes to the optic nerve head and retina during spaceflight can be mitigated by brief in-flight application of 25-mm Hg lower-body negative pressure. In the National Aeronautics and Space Administration's "Fluid Shifts Study," a prospective cohort study, optical coherence tomography scans of the optic nerve head and macula were obtained from US and international crew members before flight, in-flight, and up to 180 days after return to Earth. In-flight scans were obtained both under normal weightless conditions and 10 to 20 minutes into lower-body negative pressure exposure. Preflight and postflight data were collected in the seated, supine, and head-down tilt postures. Crew members completed 6- to 12-month missions that took place on the International Space Station. Data were analyzed from 2016 to 2021. Spaceflight and lower-body negative pressure. Changes in minimum rim width, optic cup volume, Bruch membrane opening height, peripapillary total retinal thickness, and macular thickness. Mean (SD) flight duration for the 14 crew members (mean [SD] age, 45 [6] years; 11 male crew members [79%]) was 214 (72) days. Ocular changes on flight day 150, as compared with preflight seated, included an increase in minimum rim width (33.8 μm; 95% CI, 27.9-39.7 μm; P < .001), decrease in cup volume (0.038 mm3; 95% CI, 0.030-0.046 mm3; P < .001), posterior displacement of Bruch membrane opening (-9.0 μm; 95% CI, -15.7 to -2.2 μm; P = .009), and decrease in macular thickness (fovea to 500 μm, 5.1 μm; 95% CI, 3.5-6.8 μm; P < .001). Brief exposure to lower-body negative pressure did not affect these parameters. Results of this cohort study suggest that peripapillary tissue thickening, decreased cup volume, and mild central macular thinning were associated with long-duration spaceflight. Acute exposure to 25-mm Hg lower-body negative pressure did not alter optic nerve head or retinal morphology, suggesting that longer durations of a fluid shift reversal may be needed to mitigate spaceflight-induced changes and/or other factors are involved.

Paired Optic Nerve Microvasculature and Nailfold Capillary Measurements in Primary Open-Angle Glaucoma.

PurposeTo assess microvascular beds in the optic nerve head (ONH), peripapillary tissue, and the nailfold in patients with primary open-angle glaucoma (POAG) versus controls.MethodsPatients with POAG (n = 22) and controls (n = 12) underwent swept-source optical coherence tomography angiography of ophthalmic microvasculature and nailfold video capillaroscopy of the hand. The main outcomes were vessel density (VD) and blood flow of the ONH, the peripapillary and the nailfold microvasculatures.ResultsPatients with POAG were younger than controls (63.5 ± 9.4 vs. 69.9 ± 6.5 years, P = 0.03). Deep ONH VD and blood flow were lower in patients with POAG than controls (39.1% ± 3.5% vs. 43.8% ± 5.7%; 37.8% ± 5.3% vs. 46.0% ± 7.8%, respectively, P < 0.02 for both); similar results were observed with peripapillary VD (37.9 ± 2.6%, 43.4 ± 7.6%, respectively, P = 0.03). Nailfold capillary density and blood flow were lower in patients with POAG than controls (8.8 ± 1.0 vs. 9.8 ± 0.9 capillaries/mm; 19.9 ± 9.4 vs. 33.7 ± 9.8 pL/s, respectively; P < 0.009 for both). After adjusting for age and gender, deep ONH VD and blood flow, peripapillary VD, and nailfold capillary blood flow were lower in POAG than controls (β = −0.04, −0.07, −0.05, −13.19, respectively, P ≤ 0.046 for all). Among all participants, there were positive correlations between deep ONH and nailfold capillary blood flow (Pearson's correlation coefficient r = 0.42, P = 0.02), peripapillary and nailfold capillary density (r = 0.43, P = 0.03), and peripapillary and nailfold capillary blood flow (r = 0.49, P = 0.01).ConclusionsPatients with POAG demonstrated morphologic and hemodynamic alterations in both ophthalmic and nailfold microvascular beds compared to controls.Translational RelevanceThe concomitant abnormalities in nailfold capillaries and relevant ocular vascular beds in POAG suggest that the microvasculature may be a target for POAG treatment.

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

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

Longitudinal Observation of Border Tissue Configuration During Axial Elongation in Childhood.

PurposeTo investigate the change of border tissue configuration during axial elongation in childhood.MethodsFifty-four subjects (108 eyes; age range, 29.3–132.5 months) who had undergone a series of swept-source optical coherence tomography scans at intervals of 6 months or longer were classified into stable axial length (AXL) eyes (n = 55; AXL change of ≤0.36 mm) and elongating AXL eyes (n = 53; AXL change of >0.36 mm). The angle between the Bruch's membrane opening (BMO) reference plane and the border tissue of Elschnig was defined as the border tissue angle (BTA). The border tissue angle, BMO distance (BMOD) and minimum rim width (MRW) were measured in the temporal and nasal regions.ResultsDuring 15.6 ± 7.2 months of follow-up, the AXL significantly increased from 22.8 ± 1.3 mm to 23.3 ± 1.4 mm (P < 0.001). Changes of border tissue angle and AXL showed a significant correlation only in the temporal region of elongating AXL eyes (r = –0.409; P = 0.002), but not in stable AXL eyes. Both BMOD and nasal MRW significantly increased from 1482.5 ± 153.0 to 1506.1 ± 154.6 µm and from 310.6 ± 83.2 to 324.6 ± 95.6 µm, respectively (all Ps < 0.001). The changes of BMOD and nasal MRW showed a significant positive correlation with changes of AXL in elongating AXL eyes but not in stable AXL eyes.ConclusionsDuring the axial elongation in childhood, temporal border tissue configuration change, BMO enlargement, and nasal peripapillary tissue elevation showed a significant correlation with changes in the AXL.

IOP-induced regional displacements in the optic nerve head and correlation with peripapillary sclera thickness

Mechanical insult induced by intraocular pressure (IOP) is likely a driving force in the disease process of glaucoma. This study aimed to evaluate regional displacements in human optic nerve head (ONH) and peripapillary tissue (PPT) in response to acute IOP elevations, and their correlations with morphological characteristics of the posterior eye. Cross-sectional (2D) images of the ONH and PPT in 14 globes of 14 human donors were acquired with high-frequency ultrasound during whole globe inflation from 5 to 30 mm Hg. High-frequency ultrasound has a spatial resolution of tens of micrometers and is capable of imaging through the ONH and PPT thickness. Tissue displacements were calculated using a correlation-based speckle tracking algorithm for a dense matrix of kernels covering the 2D imaging plane. The ONH was manually segmented in the ultrasound B-mode images acquired at 5 mmHg based on echogenicity. The lamina cribrosa (LC) boundaries were visible in eight of the fourteen eyes and the LC region was segmented using a semi-automated superpixel-based method. The ONH had larger radial displacement than the PPT in all tested eyes and the difference increased with increasing IOP. A significant negative correlation was found between ONH-PPT displacement difference and PPT thickness (p < 0.05), while no significant correlations were found between ONH-PPT displacement difference and other morphological parameters including PPT radius of curvature, scleral canal size, LC thickness and anterior LC surface depth. Within the ONH, the radial displacement decreased in the region anterior to and across LC but not in the region posterior to LC. Finite element models using simplified geometry and material properties confirmed the role of LC in reducing the overall ONH radial displacements, but did not predict the displacement gradient change observed experimentally. These results suggested that a thinner PPT may be associated with a larger relative posterior motion of the ONH with respect to the surrounding PPT and the LC may play a major role in preventing excessive posterior displacement of ONH during acute IOP elevations.

Role of radially aligned scleral collagen fibers in optic nerve head biomechanics

Collagen fibers organized circumferentially around the canal in the peripapillary sclera are thought to provide biomechanical support to the sensitive tissues within the optic nerve head (ONH). Recent studies have demonstrated the existence of a family of fibers in the innermost sclera organized radially from the scleral canal. Our goal was to determine the role of these radial fibers in the sensitivity of scleral canal biomechanics to acute increases in intraocular pressure (IOP). Following the same general approach of previous parametric sensitivity studies, we created nonlinear generic finite element models of a posterior pole with various combinations of radial and circumferential fibers at an IOP of 0 mmHg. We then simulated the effects of normal and elevated IOP levels (15 and 30 mmHg). We monitored four IOP-induced geometric changes: peripapillary sclera stretch, scleral canal displacement, lamina cribrosa displacement, and scleral canal expansion. In addition, we examined the radial (maximum tension) and through-thickness (maximum compression) strains within the ONH tissues. Our models predicted that: 1) radial fibers reduced the posterior displacement of the lamina, especially at elevated IOP; 2) radial fibers reduced IOP-induced radial strain within the peripapillary sclera and retinal tissue; and 3) a combination of radial and circumferential fibers maintained strains within the ONH at a level similar to those conferred by circumferential fibers alone. In conclusion, radial fibers provide support for the posterior globe, additional to that provided by circumferential fibers. Most importantly, a combination of both fiber families can better protect ONH tissues from excessive IOP-induced deformation than either alone.

This issue of Acta

This issue of Acta

Three-Dimensional Inflation Response of Porcine Optic Nerve Head Using High-Frequency Ultrasound Elastography.

Characterization of the biomechanical behavior of the optic nerve head (ONH) in response to intraocular pressure (IOP) elevation is important for understanding glaucoma susceptibility. In this study, we aimed to develop and validate a three-dimensional (3D) ultrasound elastographic technique to obtain mapping and visualization of the 3D distributive displacements and strains of the ONH and surrounding peripapillary tissue (PPT) during whole globe inflation from 15 to 30 mmHg. 3D scans of the posterior eye around the ONH were acquired through full tissue thickness with a high-frequency ultrasound system (50 MHz). A 3D cross-correlation-based speckle-tracking algorithm was used to compute tissue displacements at ∼30,000 kernels distributed within the region of interest (ROI), and the components of the strain tensors were calculated at each kernel by using least square estimation of the displacement gradients. The accuracy of displacement calculation was evaluated using simulated rigid-body translation on ultrasound radiofrequency (RF) data obtained from a porcine posterior eye. The accuracy of strain calculation was evaluated using finite element (FE) models. Three porcine eyes were tested showing that ONH deformation was heterogeneous with localized high strains. Substantial radial (i.e., through-thickness) compression was observed in the anterior ONH and out-of-plane (i.e., perpendicular to the surface of the shell) shear was shown to concentrate in the vicinity of ONH/PPT border. These preliminary results demonstrated the feasibility of this technique to achieve comprehensive 3D evaluation of the mechanical responses of the posterior eye, which may provide mechanistic insights into the regional susceptibility in glaucoma.

Length and width of the peripapillary scleral flange in relation to axial length

AbstractPurposeThe peripapillary scleral flange is the continuation of the posterior sclera after separating from the optic nerve dura mater and serves as the biomechanical anchor for the lamina cribrosa from which it is separated by the peripapillary border tissue of Elschnig. In view of its biomechanical importance for the optic nerve head, we determined the dimensions of the peripapillary scleral flange and its associations with axial length.MethodsThe study included human globes which had been enucleated due to malignant melanomas or end‐stage secondary angle closure glaucoma. Histologic slides were histomorphometrically examined.ResultsThe study included 202 eyes of patients with a mean age of 61.7 ± 13.7 years (range: 24–89 years) and a mean axial length of 24.9 ± 2.5 mm (range: 20.0–35.0 mm). The mean thickness of the peripapillary scleral flange was 0.37 ± 0.10 mm (median: 0.38 mm; range: 0.10–0.76 mm), and a mean length of 0.54 ± 0.43 mm (range: 0.05–2.14 mm). Peripapillary scleral flange thickness was inversely correlated with longer peripapillary scleral flange length (p = 0.001; standardized regression coefficient β: −0.46) and longer axial length (p = 0.001; β = −0.23). Correspondingly, peripapillary scleral flange length increased with longer axial length (p &lt; 0.001; β = 0.49).ConclusionsAxial elongation is associated with a marked elongation and corresponding thinning of the peripapillary scleral flange. With the PSF being the biomechanical anchor of the lamina cribrosa, the findings may be of interest for the biomechanics of the optic nerve head in axial myopia.

Compression of the Choroid by Horizontal Duction.

The optic nerve becomes tethered in adduction in most people, which deforms the disc. We investigated the effect of horizontal ocular duction and subject age on choroidal volume at the macular side of the optic disc. In 25 younger (18-33 years) and 15 older (50-73 years) normal subjects, the disc and the peripapillary choroid were imaged with optical coherence tomography (OCT) in central gaze and 35° adduction and abduction. The choroid temporal to the optic disc underlying the region between the Bruch's membrane opening and fovea was segmented into regions that were multiples of the disc radius for determination of local choroidal thickness. Regional volume changes from central gaze were determined in adduction and abduction. In adduction, regional choroidal volume decreased by 42.4 ± 3.4 nanoliters (nL) (standard error of the mean) in younger (P < 0.0001) and 6.2 ± 2.6 nL in older (P < 0.02) subjects. Relative volume reduction in adduction was 7.5% ± 0.6% in younger (P < 0.001) and 1.3% ± 0.6% in older (P < 0.02) subjects. Volume reduction was greatest near the disc and significant up to three disc radii from it in younger and 1 radius in older subjects but was insignificant in abduction. Horizontal duction compresses the temporal peripapillary choroid, more in adduction than in abduction and more in younger than older subjects. This reflects duction-related peripapillary tissue deformation probably related, at least in part, to optic nerve tethering in adduction.

Peripapillary border tissue of the choroid and peripapillary scleral flange in human eyes.

To assess dimensions and associations of the peripapillary border tissue of the choroid (PBT-C) and peripapillary scleral flange (PBT-S). The histomorphometric investigation included histological sections of enucleated eyes of Caucasian patients. Using light microscopy, the PBT dimensions were measured. The study included 85 eyes (85 patients) with an age of 62.0years (14.1years) (mean (SD)) (range:37-87years) and mean axial length of 26.7mm (3.5mm) (range:21.0-37.0mm). Thicker PBT-C thickness (mean: 68.8μm (35.7μm)) was associated with shorter axial length (p<0.001; standardized regression coefficient beta: -0.50), and longer PBT-C length (mean: 531μm (802μm)) was correlated with longer axial length (p<0.001;beta:0.66). PBT-C cross-sectional area (mean 17050μm2 (10420μm2 )) was not significantly associated with axial length (p=0.37). Decreasing with longer axial length (p<0.001;beta:0.64), the angle between PBT-C and Bruch's membrane was approximately 90° in non-highly myopic eyes without overhanging Bruch's membrane (BM), it ranged between 100° and 180° in eyes with BM overhanging into the intrapapillary region, and it was close to 0° in eyes with parapapillary gamma zone. Thicker thickness of PBT-S (mean:83μm (21μm)) was correlated with presence of glaucoma (p=0.02). Optic nerve pia mater thickness (mean:109μm (44μm)) increased with glaucoma presence (p=0.046;beta:0.31) but not with axial length (p=0.34). Peripapillary border tissue of the choroid (PBT-C) and PBT-S as continuation of the optic nerve pia mater are distinct structures, with PBT-C remodelling during myopic axial elongation and PBT-S being mostly independent of axial elongation. PBT-C and PBT-S may be of importance for the optic nerve head biomechanics and PBT-C for separation of the choroidal space from the intrapapillary compartment.

Custom Optical Coherence Tomography Parameters for Distinguishing Papilledema from Pseudopapilledema.

Causes of papilledema can be life-threatening; however, distinguishing papilledema from pseudopapilledema is often challenging. The conventional optical coherence tomography (OCT) scan for assessing the optic nerve often fails to detect mild papilledema. Our study suggests that parameters derived from volumetric OCT scans can provide additional useful information for detecting papilledema. Optical coherence tomography analysis of the optic nerve commonly measures retinal nerve fiber layer thickness (RNFLT) along a 1.73-mm-radius scan path. This conventional scan, however, often fails to detect mild papilledema. The purpose of this study was to evaluate additional OCT-derived measures of the optic nerve head (ONH) and peripapillary retina for differentiating papilledema (all grades and mild) from pseudopapilledema. Cirrus OCT ONH volume scans were acquired from 21 papilledema (15 mild papilledema), 27 pseudopapilledema, and 42 control subjects. Raw scan data were exported, and total retinal thickness within Bruch's membrane opening (BMO) plus RNFLT and total retinal thickness at the following eccentricities were calculated using custom algorithms: BMO to 250, 250 to 500, 500 to 1000, and 1000 to 1500 μm. Minimum rim width was calculated, and BMO height was measured from a 4-mm Bruch's membrane reference plane centered on the BMO. Retinal nerve fiber layer thickness from BMO to 250 μm, minimum rim width, and BMO height had significantly greater areas under the receiver operating characteristic curve than did conventional RNFLT for differentiating mild papilledema from pseudopapilledema (P < .0001) and greater sensitivities at 95% specificity. Using cutoff values at 95% specificity, custom parameters detected 10 mild papilledema patients, and conventional RNFLT detected only 1. Bruch's membrane opening heights above the reference plane were observed in papilledema only, although many papilledema cases had a neutral or negative BMO height. Using OCT volumetric data, additional parameters describing peripapillary tissue thickness, neuroretinal rim thickness, and ONH position can be calculated and provide valuable measures for differentiating mild papilledema from pseudopapilledema.

Mechanical Deformation of Human Optic Nerve Head and Peripapillary Tissue in Response to Acute IOP Elevation.

PurposeTo measure the deformation of the human optic nerve head (ONH) and peripapillary tissue (PPT) in response to acute intraocular pressure (IOP) elevation.MethodsThe ONH and PPT of 14 human donor globes were imaged with high-frequency ultrasonography during inflation testing from 5 to 30 mm Hg. A correlation-based speckle tracking algorithm was used to compute tissue displacements, and the through-thickness, in-plane, and shear strains were calculated by using least-squares strain estimation methods. The ONH and PPT were segmented along the anterior-posterior direction and the nasal-temporal direction. Regional displacements and strains were analyzed and compared.ResultsThe ONH displaced more posteriorly than the PPT in response to an acute IOP increase. Scleral canal expansion was minimal but correlated with ONH posterior displacement at all IOP levels. Through-thickness compression was concentrated in the anterior of both the ONH and the PPT. Shear was concentrated in the vicinity of the canal with higher shear in the peripheral ONH than the central ONH and higher shear in the PPT near the scleral canal than that further away from the canal.ConclusionsHigh-resolution ultrasound speckle tracking showed a displacement mismatch between the ONH and the PPT, larger compressive strains in the direction of IOP loading in the anterior ONH and PPT, and higher shear strains in the periphery of ONH in response to acute IOP elevation in the human eye. These findings delineate the deformation patterns within and around the ONH and may help understand IOP-associated optic nerve damage.

Comparison of peripapillary choroidal thickness between healthy subjects and patients with Parkinson's disease.

PurposeTo study peripapillary choroidal thickness (PPCT) in healthy subjects using swept-source optical coherence tomography (SS-OCT), and to evaluate PPCT differences between Parkinson´s disease (PD) patients, and age- and sex-matched healthy controls.DesignCase-control studyMethods80 healthy subjects and 40 PD patients were consecutively recruited in this single institution study. The healthy subjects were divided into two populations: a teaching population (n = 40, used to establish choroidal zones) and a validating population (n = 40, used to compare measurements with PD patients). An optic disc 6.0×6.0 mm three-dimensional scan was obtained using Deep Range Imaging (DRI) OCT Triton. A 26×26 cube-grid centered on the optic disc was generated to automatically measure choroidal thickness. Five concentric choroidal zones were established and used to compare PPCT between healthy and PD patients.ResultsPPCT was significantly thicker in PD patients compared with controls in all four concentric zones evaluated (p≤0.0001). PPCT followed a similar pattern in controls and PD; it was thicker in the temporosuperior region, followed by the superior, temporal, nasal, and inferior regions.ConclusionPD patients presented with an increased PPCT in all zones surrounding the optic disc compared with healthy subjects. The peripapillary choroidal tissue showed a concentric pattern, with the thickness increasing with increasing distance from the optic nerve. SS-OCT could be useful for evaluating choroidal thinning in clinical practice.

Predictions of Optic Nerve Traction Forces and Peripapillary Tissue Stresses Following Horizontal Eye Movements.

To use finite element (FE) analysis to predict the optic nerve sheath traction forces that act on the optic nerve head (ONH) following horizontal eye movements, and the resulting stress levels in the peripapillary connective tissues of the ONH (Bruch's membrane [BM] and sclera). An FE model of a healthy eye was reconstructed in primary gaze position that included details from the orbital and ONH tissues. Optic nerve sheath traction forces and peripapillary tissue stresses in both adduction and abduction (13°) were computed using FE analysis. Our models predicted that, following eye movements, the ONH was sheared in the transverse plane due to the pulling action of the optic nerve. The optic nerve sheath traction forces were 90 mN in abduction and 150 mN in adduction. Peripapillary tissue stresses were concentrated in the nasal and temporal quadrants. In adduction, scleral stresses were highest in the temporal region, and BM stresses were slightly higher in the nasal region. This trend was reversed in abduction. Following eye movements, our models predicted high optic nerve sheath traction forces of the same order of magnitude as extraocular muscle forces. Optic nerve traction resulted in significant peripapillary stresses, and thus may have a role to play in the development of peripapillary zones, glaucoma, and myopia.

In Vivo Evaluation of the Biomechanical Properties of Optic Nerve and Peripapillary Structures by Ultrasonic Shear Wave Elastography in Glaucoma.

BackgroundPrimary open-angle glaucoma is a multifactorial serious disease characterized by progressive retinal ganglion cell death and loss of visual field.ObjectivesThe purposes of this study were to investigate shear wave elastography (SWE) use in the evaluation of the optic nerve (ON) and peripapillary structures, and to compare the findings between glaucomatous and control eyes.Patients and MethodsA case-controlled study, including 21 patients with primary open-angle glaucoma and 21 age-matched control subjects, was carried out. All of the participants had comprehensive ophthalmological exams that included corneal biomechanical measurements with ocular response analyzer. In vivo evaluation of the biomechanical properties of the ON and peripapillary structures were performed with SWE in all participants. The Kolmogorov–Smirnov test was used to analyze the normal distribution of data. Differences of parameters in ophthalmologic data and stiffness values of patients with and without glaucoma were evaluated using the Mann-Whitney U test.ResultsThere were no statistically significant differences between the glaucoma and control groups in terms of age (P > 0.05) and gender (P > 0.05). Corneal hysteresis was lower in the glaucoma group (P < 0.05). Corneal compensated intraocular pressure and Goldmann correlated intraocular pressure were higher in the glaucoma group (P < 0.0001 for both). The mean stiffness of the ON and peripapillary structures were significantly higher in glaucoma patients for each measured region (P < 0.05).ConclusionThe study evaluated the biomechanical properties of the ON and peripapillary structures in vivo with SWE in glaucoma. We observed stiffer ON and peripapillary tissue in glaucomatous eyes, indicating that SWE claims new perspectives in the evaluation of ON and peripapillary structures in glaucoma disease.

OPTIC DISK PIT MORPHOLOGY AND RETINAL DETACHMENT

The pathogenesis of optic nerve head pits and associated retinal detachment, and the most effective surgical intervention when visual loss develops, remains unclear. The morphology of the optic disk in patients with pits was investigated with optical coherence tomography. For those who underwent surgical treatment for pit-associated retinal detachment, the efficacy of treatment by vitrectomy and separation of the posterior hyaloid, with and without additional peeling of peripapillary tissue, was assessed. On optical coherence tomography imaging, 14 of 18 pits (78%) demonstrated a localized pit-like invagination, whereas 3 (17%) had disks with a generally excavated structure. For 16 of 18 pits (89%), there was evidence of condensed vitreous or glial tissue seen extending from the pit or inside the optic disk. Nine eyes with retinal detachment underwent vitrectomy, posterior hyaloid separation, and endolaser. The retinal detachment completely resolved in 6 of 6 cases where the surgeon additionally peeled the fibrous tissue from the pit and 2 of 3 cases where this was not performed. Spectral domain optical coherence tomography demonstrates the varying morphology of optic pit anatomy. Condensed vitreous strands or glial tissue in the optic nerve pit may also contribute to retinal detachment development.