Determinants of lamina cribrosa depth in healthy Asian eyes: the Singapore Epidemiology Eye Study

Ciliary muscle traction during accommodation is able to induce optic nerve head deformation

OBJECTIVES

To use finite element (FE) modeling and in vivo optical coherence tomography (OCT) imaging to explore the effect of ciliary muscle traction on optic nerve head (ONH) deformation during accommodation.

METHODS

We developed a FE model to mimic the ciliary muscle traction during accommodation, and varied the stiffness of the sclera, choroid, Bruch's membrane (BM), prelaminar neural tissue and lamina cribrosa (LC) to assess their effects on accommodation-induced ONH strains. To validate the FE model, OCT images of the right eyes' ONHs from 20 subjects (25 ± 1.5 years, range: 24-28 years) were taken for an accommodative stimulus of 6-diopters (6D) and a relaxed state of 0D. Based on OCT images, the accommodation-induced ONH effective strains, choroidal thickness and BM opening (BMO) changes were measured.

RESULTS

Our FE model predicted that the ciliary muscle pulling force could be transmitted to the ONH through the choroid and BM. The LC strain caused by the ciliary muscle pulling (0.0177) is comparable to that induced by an IOP elevation of 45 mmHg (0.0173). The accommodation-induced LC strain increased with stiffer choroid and BM. Three-dimensional strain tracking showed that the LC strains under 6D and 0D accommodation were 0.057 ± 0.033 and 0.023 ± 0.014 (p < 0.05). The reduction in choroidal thickness and the enlargement in BMO were observed during accommodation.

CONCLUSIONS

Our study showed that during accommodation, ciliary muscle traction could induce large ONH deformations and that stiffer choroid and BM increased the pulling force transmitted to the ONH, thereby leading to higher LC strains.

Factors Associated With Lamina Cribrosa Microvasculature Determined Through Swept-Source Optical Coherence Tomography Angiography

PRCIS

The lamina cribrosa (LC) microvasculature reduction was associated with the posterior deformation of LC, as well as the functional deterioration, in all spectrums of open angle glaucoma.

OBJECTIVE

To investigate the factors associated with the lamina cribrosa vessel density (LCVD) determined through swept-source optical coherence tomography angiography.

MATERIALS AND METHODS

The optic nerve head (ONH) scan was obtained using swept-source optical coherence tomography angiography (PLEX Elite 9000; Carl Zeiss Meditec, Inc.). The lamina cribrosa curvature index (LCCI) was assessed using seven horizontal B-scan images across the ONH. The LCVD was calculated from the segmented layer at the level of LC. Primary open angle glaucoma (POAG) eyes were categorized into 2 groups according to the visual field mean deviation (VF MD; mild to moderate [≥ -12 dB] and advanced [< -12 dB]). The factors associated with the LCVD were evaluated using linear regression analysis.

RESULTS

A total of 127 POAG and 43 healthy eyes were included. POAG eyes showed a significantly thinner circumpapillary retinal nerve fiber layer and macular ganglion cell inner plexiform layer, lower LCVD, and greater LCCI compared with healthy eyes (all P < 0.05). In the mild to moderate group, lower LCVD was associated with worse VF MD, thinner circumpapillary retinal nerve fiber layer and macular ganglion cell inner plexiform layer, and greater LCCI (all P < 0.05). In the advanced group, the LCVD was associated with VF MD and LCCI (both P < 0.05). A greater LCVD was correlated with a greater LCCI in the healthy group ( P = 0.045).

CONCLUSIONS

Reduced LCVD was associated with an increased LCCI in all spectrums of POAG. LC deformation may affect the ONH microvasculature in glaucoma.

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

Purpose

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.

Methods

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.

Results

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.

Conclusions

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.

Lamina Cribrosa Configurations in Highly Myopic and Non-Highly Myopic Eyes: The Beijing Eye Study

Purpose

The purpose of this study was to examine characteristics of lamina cribrosa (LC) configuration in highly myopic (HM) eyes.

Methods

Participants from the Beijing Eye Study 2011, free of optic nerve or retinal diseases, were randomly selected to examine LC depth (LCD) and LC tilt (LCT) using three-dimensional optical coherent tomography images of the optic nerve head (ONH). LCD and LCT were measured as the distance and angle between the LC plane with two reference planes, including the Bruch's membrane opening (BMO) plane and the peripapillary sclera (PPS) plane, respectively. Each parameter was measured in both horizontal and vertical B-scans.

Results

The study included 685 individuals (685 eyes) aged 59.6 ± 7.7 years, including 72 HM eyes and 613 non-HM eyes. LCD measurements showed no significant differences between HM eyes and non-HM eyes in both horizontal (LCD-BMO = 421.83 ± 107.86 µm for HM eyes vs. 447.24 ± 104.94 µm for non-HM eyes, P = 0.18; and LCD-PPS = 406.39 ± 127.69 µm vs. 394.00 ± 101.64 µm, P = 1.00) and vertical directions (LCD-BMO = 435.78 ± 101.29 µm vs. 450.97 ± 106.54 µm, P = 0.70; and LCD-PPS = 401.62 ± 109.9 µm vs. 379.85 ± 110.35 µm, P = 0.35). However, the LCT was significantly more negative (tilted) in HM eyes than in non-HM eyes horizontally (LCT-BMO = -4.38 ± 5.94 degrees vs. -0.04 ± 5.86 degrees, P < 0.001; and LCT-PPS = -3.16 ± 5.23 degrees vs. -0.94 ± 4.71 degrees, P = 0.003), but not vertically (P = 1.00).

Conclusions

Although LCD did not differ significantly between HM and non-HM eyes, LCT was more negative in HM eyes, suggesting that the temporal or inferior side of the LC was closer to the reference plane. These findings provide insights into morphological and structural changes in the LC and ONH between HM and non-HM eyes.

Effects of Deep Optic Nerve Head Structures on Bruch's Membrane Opening- Minimum Rim Width and Peripapillary Retinal Nerve Fiber Layer

PURPOSE

To explore the effects of deep optic nerve head (ONH) structures on Bruch's membrane opening (BMO)-minimum rim width (MRW) and peripapillary retinal nerve fiber layer thickness (pRNFLT) in healthy eyes.

DESIGN

Prospective cross-sectional study.

METHODS

Two hundred five healthy eyes of 141 subjects (mean ± standard deviation of age and axial length (AXL): 46.9 ± 10.0 years and 24.79 ± 1.15 mm) were enrolled. Best fit multivariable linear mixed models identified factors associated with BMO-MRW and pRNFLT. Explanatory variables included age, gender, AXL, BMO and anterior scleral canal opening (ASCO) area and ovality, magnitude of BMO and ASCO shift, peripapillary choroidal thickness, lamina cribrosa (LC) parameters, prelaminar thickness, and peripapillary scleral (PPS) angle.

RESULTS

Thinner BMO-MRW was associated with older age, smaller ASCO/BMO offset magnitude, larger BMO area, thinner prelaminar thickness, deeper LC, and thinner pRNFLT (P = .011, <.001, .004, <.001, <.001, <.001 respectively). Thinner pRNFLT was associated with shorter AXL, smaller ASCO area, a more posteriorly bowed PPS, shallower LC and thinner BMO-MRW. (P = .030, .002, .035, .012, <.001 respectively) CONCLUSIONS: BMO-MRW and pRNFLT were influenced by several deep ONH structures such as BMO and ASCO position shift, BMO or ASCO area, prelaminar thickness, PPS bowing and LC depth in addition to patient characteristics such as age and AXL. The degree and/or direction of associations varied between deep ONH structures and BMO-MRW or pRNFLT. Despite both BMO-MRW and pRNFLT being surrogate parameters for RGC loss, a complex relationship with ONH deep-layer morphology was indicated.

Clinical Characteristics and Associated Factors to the Development of Glaucoma in Eyes With Myopic Optic Neuropathy

PURPOSE

To observe the development of glaucoma in myopic eyes with and without myopic optic neuropathy (MON) and analyze associated factors to the development of typical glaucomatous damage.

DESIGN

A prospective, observational, cohort study.

METHODS

A total of 233 myopic eyes with no definite evidence of glaucomatous damage were included. Myopic patients without any retinal nerve fiber layer (RNFL) or visual field (VF) abnormalities were classified as myopic eyes without MON. Myopic patients with decreased RNFL at the superonasal (SN) or nasal area, and with corresponding VF defects either in the temporal or inferotemporal (IT) region were classified as myopic eyes with MON. Myopic eyes that developed glaucoma were defined by the presence of glaucomatous VF in the SN region including defects in Bjerrum area, or a new localized RNFL defect in the IT region. Disc morphological features and optic nerve head (ONH) parameters of two groups were compared.

RESULTS

Myopic eyes with MON had a thinner average peripapillary RNFL thickness (P < 0.001), worse MD of the VF (P = 0.031), a higher percentage of IT VF defects (P < 0.001), smaller torsion degree (P = 0.047), and greater LCD (P = 0.022). Myopic eyes with MON who developed glaucoma had a thinner average peripapillary RNFL thickness (P = 0.009), greater PPA area (P = 0.049), greater LCD (P < 0.001), and thinner LCT (P < 0.001). Thinner baseline temporal RNFL thickness (HR, 0.956; 95% CI, 0.928-0.986; P = 0.004), greater baseline LCD (HR, 1.003; 95% CI, 1.000-1.005; P = 0.022), and greater PPA area (HR, 1.000; 95% CI, 1.000-1.003; P = 0.050) were significantly associated factors with glaucoma development.

CONCLUSIONS

Myopic eyes with MON have a greater risk to develop glaucoma compared to myopic eyes without MON. Structural weakness due to myopia, especially at the temporal side of the ONH and the peripapillary sclera, increases the risk of glaucoma in myopic eyes with MON.

Parapapillary gamma zone associated with increased peripapillary scleral bowing: the Beijing Eye Study 2011

AIMS

To investigate the association between the backward configuration of the peripapillary sclera (PPS), measured as PPS angle (PPSA), and presence and extent of parapapillary gamma zone.

METHODS

Out of the population-based Beijing Eye Study 2011, we randomly selected individuals free of optic nerve and retinal diseases. With Spectralis optical coherence tomography, we measured gamma zone (zone free of Bruch's membrane (BM)) and determined the PPSA, defined as the angle between the anterior scleral surface lines from both sides of the optic nerve head (ONH).

RESULTS

The study included 678 individuals with age of 59.5±7.6 years (range: 50-90) and axial length of 23.5±1.3 mm (20.9-29.2). Gamma zone was more prevalent in eyes with larger PPSA (p=0.006) after adjustment for axial length (p<0.001) and BM opening area (p<0.001). Gamma zone width was positively associated with PPSA, axial length and BM opening area (all p<0.001) in multivariable analysis. Circular gamma zone was accompanied with larger PPSA as compared with focal gamma zone (19.9°±7.2° vs 6.3°±5.3°, p<0.001). Focal temporal gamma and focal inferior gamma had similar mean PPSA (p=0.69). However, the horizontal PPSA was significantly larger than the vertical PPSA in inferior gamma (6.9°±6.3° vs 4.7°±6.6°; p=0.005), while they were comparable in temporal gamma (6.1°±5.8° vs 6.3°±6.4°; p=0.073).

CONCLUSIONS

A more backward bowing of the PPS was linearly and spatially associated with the presence, size and extent of gamma zone. It suggested that the BM and the sclera were closely related in participating the biomechanical behaviour of the ONH.

Comparison of lamina cribrosa depth shallowing after trabeculectomy between primary open-angle glaucoma and exfoliation glaucoma

The lamina cribrosa (LC) becomes shallower as intraocular pressure (IOP) decreases after trabeculectomy. The LC in eyes with exfoliation syndrome has distinctive properties in the connective tissue and extracellular matrix, but how these affect the changes in LC depth in response to IOP reduction after trabeculectomy is unknown. We analyzed pre- and postoperative spectral-domain optical coherence tomography of exfoliation glaucoma (XFG) and primary open-angle glaucoma (POAG) patients who underwent trabeculectomy and investigated whether LC depth differed between XFG and POAG eyes after trabeculectomy. In total, 30 XFG eyes and 30 visual field mean deviation-matched POAG eyes were included. LC depth was determined at an average of 3.9 months after trabeculectomy. Postoperatively, the LC depth became shallower and the BMO-MRW became thicker in both XFG and POAG eyes. XFG eyes showed lesser amount of LC depth shallowing than POAG eyes. Greater preoperative LC depth, lower postoperative IOP, and absence of XFG were all associated with a greater degree of postoperative LC depth shallowing. These findings suggest that the LC of XFG eyes may inherently possess the distinctive properties of the connective tissue and extracellular matrix contained within it, which could affect the LC response to the reduction in IOP after trabeculectomy.

Asian Race and Primary Open-Angle Glaucoma: Where Do We Stand?

Primary open-angle glaucoma (POAG) is an optic neuropathy characterized by irreversible retinal ganglion cell damage and visual field loss. The global POAG prevalence is estimated to be 3.05%, and near term is expected to significantly rise, especially within aging Asian populations. Primary angle-closure glaucoma disproportionately affects Asians, with up to four times greater prevalence of normal-tension glaucoma reported compared with high-tension glaucoma. Estimates for overall POAG prevalence in Asian populations vary, with Chinese and Indian populations representing the majority of future cases. Structural characteristics associated with glaucoma progression including the optic nerve head, retina, and cornea are distinct in Asians, serving as intermediates between African and European descent populations. Patterns in IOP suggest some similarities between races, with a significant inverse relationship between age and IOP only in Asian populations. Genetic differences have been suggested to play a role in these differences, however, a clear genetic pattern is yet to be established. POAG pathogenesis differs between Asians and other ethnicities, and it may differ within the broad classification of the Asian race. Greater awareness and further research are needed to improve treatment plans and outcomes for the increasingly high prevalence of normal tension glaucoma within aging Asian populations.

Predicting the development of normal tension glaucoma and related risk factors in normal tension glaucoma suspects

This study investigated the predicted risk factors for the development of normal-tension glaucoma (NTG) in NTG suspects. A total of 684 eyes of 379 NTG suspects who were followed-up for at least 5 years were included in the study. NTG suspects were those having (1) intraocular pressure within normal range, (2) suspicious optic disc (neuroretinal rim thinning) or enlarged cup-to-disc ratio (≥ 0.6), but without definite localized retinal nerve fiber layer (RNFL) defects on red-free disc/fundus photographs, and (3) normal visual field (VF). Demographic, systemic, and ocular characteristics were determined at the time of the first visit via detailed history-taking and examination of past medical records. Various ocular parameters were assess using spectral-domain optical coherence tomography and Heidelberg retinal tomography. Conversion to NTG was defined either by the presence of a new localized RNFL defect at the superotemporal or inferotemporal region on disc/fundus red-free photographs, or presence of a glaucomatous VF defect on pattern standard deviation plots on two consecutive tests. Hazard ratios were calculated with the Cox proportional hazard model. In total, 86 (12.6%) of the 684 NTG suspects converted to NTG during the follow-up period of 69.39 ± 7.77 months. Significant (P < 0.05, Cox regression) risk factors included medication for systemic hypertension, longer axial length, worse baseline VF parameters, thinner baseline peripapillary RNFL, greater disc torsion, and lamina cribrosa (LC) thickness < 180.5 μm (using a cut-off value obtained by regression analysis). Significant (P < 0.05, Cox regression) risk factors in the non-myopic NTG suspects included medication for systemic hypertension and a LC thinner than the cut-off value. Significant (P < 0.05, Cox regression) risk factors in the myopic NTG suspects included greater disc torsion. The results indicated that 12.6% of NTG suspects converted to NTG during the 5–6-year follow-up period. NTG suspects taking medication for systemic hypertension, disc torsion of the optic disc in the inferotemporal direction, and thinner LC of the optic nerve head at baseline were at greater risk of NTG conversion. Related baseline risk factors were different between myopic and non-myopic NTG suspects.