Histologic differences between primary high myopia and secondary high myopia due to congenital glaucoma

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.

Intraocular Amphiregulin antibody and axial elongation in nonhuman primates

Purpose

To examine the effect of intraocularly applied amphiregulin antibody on physiological axial elongation in young nonhuman primates.

Methods

The experimental study included six male 12-months-old macaque nonhuman primates (body weight:2.46 ± 0.25kg;range:2.20-2.90kg). In the experimental group (n=3 animals), three intravitreal injections of amphiregulin antibody (100μg/50μl) were applied to the left eyes at intervals of 4-6 weeks, and injections of phosphate buffered solution (50μl) were applied to the right eyes. Three other animals were assigned to a blank control group.

Results

During the study period of 23.6 weeks, axial length in the experimental group did not change in the left eyes (18.91 ± 0.37mm to 18.94 ± 0.67mm;P=0.90), while it linearly increased in the right eyes (18.87 ± 0.38mm to 19.24 ± 0.53mm;P=0.056) and in the control group (left eyes:19.15 ± 0.22mm to 19.48 ± 0.22mm;P=0.009; right eyes:19.17 ± 0.15 mm to 19.46 ± 0.23 mm;P=0.024). The interocular difference in axial elongation increased in the experimental group from -0.11 ± 0.12mm at 4 weeks after baseline to -0.34 ± 0.15mm at the study end, while in the control group, the interocular side difference did not change significantly (from 0.01 ± 0.10 mm to 0.03 ± 0.08 mm;P=0.38). The difference in the interocular difference in axial elongation between the two groups was significant at 8 weeks (P=0.01), 15 weeks (P=0.007), and at study end (P=0.02). The interocular difference in axial length correlated with the interocular difference in vitreous cavity length (standardized regression coefficient beta:0.85;P<0.001). The interocular axial length difference was inversely associated with the interocular refractive error difference (beta:-0.49;P<0.001).

Conclusions

Intraocularly applied amphiregulin antibody (100μg) reduced the physiological ocular axial elongation in juvenile nonhuman primates.

Profile of primary childhood glaucoma at a child eye health tertiary facility in Malawi

BACKGROUND

To describe the clinical characteristics and treatment of primary childhood glaucoma at Queen Elizabeth Central Hospital in Blantyre, Malawi.

METHODS

A retrospective case notes review was undertaken of all medical records of patients aged less than 16 years with a diagnosis of primary glaucoma according to the Childhood Glaucoma Research Network Classification (CGRN) who presented from January 2016 to December 2018. The parameters extracted from the case files included age at presentation, sex, type of glaucoma, presenting complaints, laterality of ocular involvement, examination findings and the treatment modality instituted. The Mann-Whitney test was used to investigate factors associated with the intraocular pressure (IOP) in eyes that had a higher presenting IOP value compared to contralateral eyes.

RESULTS

A total of 45 subjects (80 eyes) were identified, 42 with primary congenital glaucoma (PCG) and 3 with juvenile open angle glaucoma (JOAG). The mean age for the population was 2.6 years (S.D ± 3.7) and most of the patients were male, with a male-female ratio of 2:1. The majority of patients had bilateral disease (n = 35, 77.8%) with the commonest presenting complaint being a whitish appearance of the eye (57.5%). The eyes studied had a mean IOP of 30.1 mmHg (CI 27.4-32.9), a mean horizontal corneal diameter (HCD) of 13.6 mm (CI 13.1-14.2) and a mean cup-disc-ratio `(CDR) of 0.73 (CI 0.66-0.79). In addition, 62 eyes (77.5%) had corneal haze on examination. Most patients (n = 59, 73.8%) underwent a combined trabeculotomy - trabeculectomy surgery within the study period. The median presenting IOP was significantly higher with JOAG compared to PCG (P = 0.02).

CONCLUSION

PCG was the most common primary childhood glaucoma at Queen Elizabeth Central Hospital and most patients presented with bilateral eye involvement. Most of the eyes had corneal haze and JOAG was associated with a higher presenting IOP compared to PCG. Further studies to investigate the outcomes of combined trabeculotomy - trabeculectomy surgery in primary childhood glaucoma in Malawi are recommended.

Axial Length Changes Following Surgical Intervention in Children With Primary Congenital Glaucoma

Background

Primary congenital glaucoma (PCG) is a challenging condition to diagnose, treat and effectively monitor. Serial assessment of intraocular pressure (IOP), optic disc cupping, refraction, and axial length (AxL) after surgery are useful to assess disease control. This study aimed to evaluate AxL changes in relation to IOP changes following glaucoma surgery in children with PCG.

Methods

We retrospectively studied AxL changes in children with PCG undergoing surgery. Eyes of children aged ≤ 4 years that did not have prior ocular surgery and that underwent at least one glaucoma surgery during the course of follow-up between June 2014 and July 2018, were included. The effect of change in IOP on change in AxL was estimated using linear mixed effects models.

Results

A total of 105 eyes (of 72 children) with PCG underwent glaucoma surgery representing 26.4% (105/397) eyes. The mean ± SD age of children at baseline was 3.53 ± 4.04 months. At baseline, the mean IOP and AxL were 26.63 ± 9.57 mmHg and 21.67 ± 1.82 mm, respectively. During the course of follow-up post-surgery, the IOP decreased by a mean of 7.25 ± 12.08 mmHg while the AxL increased by a mean of 0.70 ± 1.40 mm. A multivariable mixed effects linear regression revealed that change in AxL was significantly associated with change in IOP (p=0.030) and time since first surgery (p<0.001). A substantial reduction in IOP (≥35 mmHg) was needed at 3 months post-surgery, for AxL to regress.

Conclusion

In children with PCG who undergo glaucoma surgery, change in IOP significantly influences change in AxL. For AxL to regress, a substantial reduction in IOP is needed post-surgery.

Influence of Chronic Ocular Hypertension on Emmetropia: Refractive, Structural and Functional Study in Two Rat Models

Chronic ocular hypertension (OHT) influences on refraction in youth and causes glaucoma in adulthood. However, the origin of the responsible mechanism is unclear. This study analyzes the effect of mild-moderate chronic OHT on refraction and neuroretina (structure and function) in young-adult Long-Evans rats using optical coherence tomography and electroretinography over 24 weeks. Data from 260 eyes were retrospectively analyzed in two cohorts: an ocular normotension (ONT) cohort (<20 mmHg) and an OHT cohort (>20 mmHg), in which OHT was induced either by sclerosing the episcleral veins (ES group) or by injecting microspheres into the anterior chamber. A trend toward emmetropia was found in both cohorts over time, though it was more pronounced in the OHT cohort (p < 0.001), especially in the ES group (p = 0.001) and males. IOP and refraction were negatively correlated at week 24 (p = 0.010). The OHT cohort showed early thickening in outer retinal sectors (p < 0.050) and the retinal nerve fiber layer, which later thinned. Electroretinography demonstrated early supranormal amplitudes and faster latencies that later declined. Chronic OHT accelerates emmetropia in Long–Evans rat eyes towards slowly progressive myopia, with an initial increase in structure and function that reversed over time.

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.

Advances in myopia research anatomical findings in highly myopic eyes

BACKGROUND

The goal of this review is to summarize structural and anatomical changes associated with high myopia.

MAIN TEXT

Axial elongation in myopic eyes is associated with retinal thinning and a reduced density of retinal pigment epithelium (RPE) cells in the equatorial region. Thickness of the retina and choriocapillaris and RPE cell density in the macula are independent of axial length. Choroidal and scleral thickness decrease with longer axial length in the posterior hemisphere of the eye, most marked at the posterior pole. In any eye region, thickness of Bruch's membrane (BM) is independent of axial length. BM opening, as the inner layer of the optic nerve head layers, is shifted in temporal direction in moderately elongated eyes (axial length <26.5 mm). It leads to an overhanging of BM into the intrapapillary compartment at the nasal optic disc side, and to an absence of BM at the temporal disc border. The lack of BM at the temporal disc side is the histological equivalent of parapapillary gamma zone. Gamma zone is defined as the parapapillary region without BM. In highly myopic eyes (axial length >26.5 mm), BM opening enlarges with longer axial length. It leads to a circular gamma zone. In a parallel manner, the peripapillary scleral flange and the lamina cribrosa get longer and thinner with longer axial length in highly myopic eyes. The elongated peripapillary scleral flange forms the equivalent of parapapillary delta zone, and the elongated lamina cribrosa is the equivalent of the myopic secondary macrodisc. The prevalence of BM defects in the macular region increases with longer axial length in highly myopic eyes. Scleral staphylomas are characterized by marked scleral thinning and spatially correlated BM defects, while thickness and density of the choriocapillaris, RPE and BM do not differ markedly between staphylomatous versus non-staphylomatous eyes in the respective regions.

CONCLUSIONS

High axial myopia is associated with a thinning of the sclera and choroid posteriorly and thinning of the retina and RPE density in the equatorial region, while BM thickness is independent of axial length. The histological changes may point towards BM having a role in the process of axial elongation.

Highlights from the 2019 International Myopia Summit on 'controversies in myopia'

Myopia is an emerging public health issue with potentially significant economic and social impact, especially in East Asia. However, many uncertainties about myopia and its clinical management remain. The International Myopia Summit workgroup was convened by the Singapore Eye Research Institute, the WHO Regional Office for the Western Pacific and the International Agency for the Prevention of Blindness in 2019. The aim of this workgroup was to summarise available evidence, identify gaps or unmet needs and provide consensus on future directions for clinical research in myopia. In this review, among the many 'controversies in myopia' discussed, we highlight three main areas of consensus. First, development of interventions for the prevention of axial elongation and pathologic myopia is needed, which may require a multifaceted approach targeting the Bruch's membrane, choroid and/or sclera. Second, clinical myopia management requires co-operation between optometrists and ophthalmologists to provide patients with holistic care and a tailored approach that balances risks and benefits of treatment by using optical and pharmacological interventions. Third, current diagnostic technologies to detect myopic complications may be improved through collaboration between clinicians, researchers and industry. There is an unmet need to develop new imaging modalities for both structural and functional analyses and to establish normative databases for myopic eyes. In conclusion, the workgroup's call to action advocated for a paradigm shift towards a collaborative approach in the holistic clinical management of myopia.

Long-term morphologic fundus and optic nerve head pattern of progressive myopia in congenital glaucoma distinguished by age at first surgery

The purpose of this study was to investigate the preservation of round optic nerve head (ONH) shape in myopic eyes of surgically treated congenital glaucoma patients, with regard to factors associated with intraocular pressure (IOP) elevation-induced peripapillary scleral (PPS) deformation. Using optical coherence tomography (OCT) on the ONH and macula, we identified myopic eyes with round ONH and internally oblique border tissue and those with non-round ONH. We investigated differences in clinical factors between the two groups. We included 51 eyes of 34 patients. Age at first surgery (2.8 vs. 15.2 months, P < 0.001) was significantly different between the two groups. Axial length was also significantly longer (P = 0.004) in the non-round group, but multiple logistic regression analysis revealed age as the only significant factor (P < 0.05) in ONH roundness. Interestingly, the round ONH group also had non-curved fundus morphology and a thick choroid, while the non-round ONH group showed diverse degrees of disc tilt and posterior pole curvature, and a thin choroid. In conclusion, in eyes with congenital glaucoma, age at first surgery, particularly when older than 6 months, was associated with round ONH and emmetropia-like fundus despite high myopia. The findings may indicate two different changes in the posterior sclera and the neural canal in response to the increased IOP.

Retinal Pigment Epithelium Cell Density and Bruch's Membrane Thickness in Secondary versus Primary High Myopia and Emmetropia

To assess differences between secondary high myopia (SHM) due to congenital glaucoma and primary high myopia (PHM) and non-highly myopic eyes (NHM) in the relationships between axial length and Bruch's membrane (BM) thickness and retinal pigment epithelium (RPE) density. The histomorphometric study included human globes enucleated for reasons such as malignant uveal melanoma, end-stage painful secondary angle-closure glaucoma and congenital glaucoma. BM thickness and RPE cell density were measured upon light microscopy. The investigation included 122 eyes (mean axial length: 26.7 ± 3.7 mm; range: 20.0-37.0 mm): 7 eyes with SHM (axial length: 33.7 ± 2.1 mm; range: 31.0-37.0 mm), 56 eyes with PHM (mean axial length: 29.1 ± 2.4 mm; range: 26.0-36.0 mm) and 59 eyes in the NHM-group (axial length: 23.5 ± 1.3 mm; range: 20.0-25.5 mm). In the SHM group, longer axial length was associated with lower RPE cell density at the posterior pole (standardized regression coefficient beta: 0.92; non- standardized regression coefficient B: -2.76; 95% confidence interval (CI): -4.41, -1.10;P = 0.01), at the midpoint posterior pole/equator (beta: -0.87; B: -3.60; 95% CI: -6.48, -0.73;P = 0.03), and at the equator (beta: -0.88; B: -0.95; 95% CI: -1.68, -0.23; P = 0.02), but not at the ora serrata (P = 0.88). In the PHM-group and NHM group, RPE cell density at the posterior pole (P = 0.08) and ora serrata (P = 0.88) was statistically independent of axial length, while at the midpoint posterior pole/equator (P = 0.01) and equator (P < 0.001), RPE cell density decreased with longer axis. BM thickness in the SHM group decreased with longer axial length at the posterior pole (beta: -0.93;B: -0.29; 95% CI: -0.39, -0.14; P = 0.003), midpoint posterior pole/equator (beta: -0.79; B: -0.22; 95% CI: -0.42, -0.02; P = 0.035) and equator (beta: -0.84; B: -0.21; 95% CI: -0.37, -0.06; P = 0.017), while in the PHM-group and NHM-group, BM thickness at any ocular region was not statistically significantly correlated with axial length (all P > 0.05). In the SHM-group, but not in the PHM-group or NHM-group (P = 0.98), lower BM thickness was associated with lower RPE cell density (beta: 0.93; B: 0.09; 95% CI: 0.04, 0.14; P = 0.007), while in the eyes without congenital glaucoma the relationship was not statistically significant. In SHM in contrast to PHM, BM thickness and RPE cell density decrease in a parallel manner with longer axial length. The findings fit with the notion of BM being a primary driver in the process of axial elongation in PHM as compared to SHM.

Prevalence of myopic macular degeneration worldwide: a systematic review and meta-analysis

PURPOSE

To investigate the prevalence of myopic macular degeneration (MMD) in the global population.

METHODS

All published literature of population-based studies on MMD prevalence worldwide were searched and only those with clear definitions to diagnose and classify MMD lesions by standardised grading methods were selected. Meta-analysis methods were used to calculate the pooled prevalence of MMD and its 95% CI in a random-effects model. The prevalence of MMD lesions would also be reported, together with the subgroup analysis of age, region and gender. Correlation between MMD prevalence and spherical equivalent levels and axial length were also evaluated.

RESULTS

12 studies with 58 558 subjects were included in this meta-analysis. The pooled prevalence of MMD in the world population was 2.1% (95% CI: 1.3% to 3.3%). In the subgroup analysis, people with the following characteristics were at higher risk of developing MMD: female, urban life, living in Asia, older age, longer axial length and severer myopia.

CONCLUSIONS

MMD is a serious public health concern worldwide, particularly in subjects who are women, subjects living in urban areas, subjects living in Asia, and subjects with longer axial lengths and severer myopia. Further studies from other continents/ethnicities are needed for comprehensive estimates of the prevalence of MMD globally.

Choroidal neovascular membrane associated with primary congenital glaucoma and buphthalmos

An 18-year-old man with primary congenital glaucoma and buphthalmos in both eyes presented with unilateral, sudden-onset, painless vision loss. He had previously undergone multiple sectoral ab externo rigid-probe trabeculotomy in both eyes and subsequently Baervelt glaucoma implantion in both eyes, with adequate intraocular pressure control. Examination revealed subfoveal choroidal neovascular membrane (CNVM) and associated hemorrhages in the right eye. He was treated with 3 consecutive, monthly, intravitreal injections of bevacizumab and recovered baseline vision.

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

PURPOSE

To assess dimensions and associations of the peripapillary border tissue of the choroid (PBT-C) and peripapillary scleral flange (PBT-S).

METHODS

The histomorphometric investigation included histological sections of enucleated eyes of Caucasian patients. Using light microscopy, the PBT dimensions were measured.

RESULTS

The study included 85 eyes (85 patients) with an age of 62.0 years (14.1 years) (mean (SD)) (range:37-87 years) and mean axial length of 26.7 mm (3.5 mm) (range:21.0-37.0 mm). Thicker PBT-C thickness (mean: 68.8 μm (35.7 μm)) was associated with shorter axial length (p < 0.001; standardized regression coefficient beta: -0.50), and longer PBT-C length (mean: 531 μm (802 μm)) was correlated with longer axial length (p < 0.001;beta:0.66). PBT-C cross-sectional area (mean 17 050 μm² (10 420 μm² )) 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:83 μm (21 μm)) was correlated with presence of glaucoma (p = 0.02). Optic nerve pia mater thickness (mean:109 μm (44 μm)) increased with glaucoma presence (p = 0.046;beta:0.31) but not with axial length (p = 0.34).

CONCLUSIONS

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.

Myopia: Anatomic Changes and Consequences for Its Etiology

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

Scleral structure and biomechanics

As the eye's main load-bearing connective tissue, the sclera is centrally important to vision. In addition to cooperatively maintaining refractive status with the cornea, the sclera must also provide stable mechanical support to vulnerable internal ocular structures such as the retina and optic nerve head. Moreover, it must achieve this under complex, dynamic loading conditions imposed by eye movements and fluid pressures. Recent years have seen significant advances in our knowledge of scleral biomechanics, its modulation with ageing and disease, and their relationship to the hierarchical structure of the collagen-rich scleral extracellular matrix (ECM) and its resident cells. This review focuses on notable recent structural and biomechanical studies, setting their findings in the context of the wider scleral literature. It reviews recent progress in the development of scattering and bioimaging methods to resolve scleral ECM structure at multiple scales. In vivo and ex vivo experimental methods to characterise scleral biomechanics are explored, along with computational techniques that combine structural and biomechanical data to simulate ocular behaviour and extract tissue material properties. Studies into alterations of scleral structure and biomechanics in myopia and glaucoma are presented, and their results reconciled with associated findings on changes in the ageing eye. Finally, new developments in scleral surgery and emerging minimally invasive therapies are highlighted that could offer new hope in the fight against escalating scleral-related vision disorder worldwide.

Comparison of Diagnostic Power of Optic Nerve Head and Posterior Sclera Configuration Parameters on Myopic Normal Tension Glaucoma

PURPOSE

The aim of this study was to compare the diagnostic power of optic nerve head and posterior scleral configuration parameters obtained with the swept-source optical coherence tomography (SSOCT) on myopic normal-tension glaucoma (NTG).

MATERIALS AND METHODS

A total of 203 eyes of 203 participants with myopia diagnosed at Seoul Saint Mary's Hospital between September 2016 and February 2018 were divided into myopic NTG group (n=113) and nonglaucomatous myopia group (n=90). Established optic nerve head (ONH) parameters such as disc torsion, horizontal tilt, and vertical tilt, and novel parameters representing posterior sclera, were quantified using SSOCT. The posterior sclera was presented with the relative position of the deepest point of the eye (DPE) from the optic disc by measuring the distance, depth, and angle. The mean and the statistical distribution of each index were calculated. Differences in distribution led to another novel marker, absolute misaligned angle, which represents the displaced direction of the ONH from the sclera. The ONH was classified as misaligned when the degree of misalignment was >15 degrees in either direction. The area under the receiver operating characteristic curves and multivariate logistic regression analysis were used to test the diagnostic power in the presence of myopic NTG.

RESULTS

No significant difference was observed with respect to age, sex, refractive error, axial length, and central corneal thickness between the 2 groups. However, 20 (22.22%) of 90 eyes in the nonglaucomatous group showed misalignment, whereas 60 (53.09%) of 113 eyes in the NTG group had misalignment (odds ratio: 3.962, P<0.001). The absolute misaligned angle (0.696) and the horizontal tilt (0.682) were significantly associated with myopic NTG, which significantly exceeded other parameters in area under the receiver operating characteristic curves (both P<0.001). The multivariate logistic regression also showed that the absolute misaligned angle (hazard ratio=1.045, 95% confidence interval=1.023-1.068, P<0.001) and the horizontal tilt (hazard ratio=1.061, 95% confidence interval=1.015-1.109, P=0.009) were associated significantly with the presence of NTG.

CONCLUSIONS

The diagnostic power of absolute misaligned angle and the horizontal tilt angle significantly exceeded other parameters on myopic NTG. These parameters may be associated with a displaced direction of the ONH to the posterior sclera, which can be linked to the altered sclera configuration of myopic NTG subjects.

Ocular size and shape in lens-induced Myopization in young Guinea pigs

Background

Lens-induced myopization in guinea pigs has been used as model for the process of myopization in humans. It has not been explored yet whether the change in globe shape in eyes undergoing myopization is similar in experimental myopia in guinea pigs and in clinical myopia in patients.

Methods

The study included 70 guinea pigs (age:2–3 weeks) equally divided into a study group with lens-induced myopization for 5 weeks, and a control group wearing goggles with no refractive power. The globe diameters were measured using a microcaliper after enucleation.

Results

The horizontal globe diameter (9.19 ± 0.15 mm versus 9.15 ± 0.18 mm; P = 0.25) and vertical globe diameter (9.02 ± 0.11 mm versus 8.99 ± 0.14 mm; P = 0.29) did not differ significantly between the study group and control group. The sagittal diameter was significantly longer in the study group (8.96 ± 0.15 mm versus 8.84 ± 0.14 mm; P = 0.001). While the vertical and horizontal globe diameters were correlated with each other in a ratio of approximately 1:1 (non-standardized regression coefficient B:0.94;95% confidence interval (CI):0.73,1.15), the steepness of the regression lines of the associations of both diameters with the sagittal diameter were flatter (horizontal to sagittal diameter: B: 0.64; 95% CI: 0.44,0.83; vertical to sagittal diameter:B:0.55;95% CI:0.41,0.69). Correspondingly, the ratios of horizontal-to-sagittal globe diameter and of vertical-to-sagittal globe diameter decreased (P < 0.001) with longer sagittal diameter.

Conclusions

For each mm axial elongation in young guinea pigs the horizontal globe diameter increased by 0.64 mm (95%CI:0.44,0.83) and the vertical diameter by 0.55 mm (95% CI:0.41,0.69), indicating that the globe enlargement occurred predominantly in the sagittal direction. Axial elongation in guinea pigs led to a similar relative change in ocular shape as in humans.

Amphiregulin and ocular axial length

PURPOSE

To assess the potential role of amphiregulin as messenger molecule in ocular axial elongation.

METHODS

The experimental study included guinea pigs (total n = 78) (age: 3-4 weeks) which underwent bilateral lens-induced myopization and received 15 days later three intraocular injections in weekly intervals of amphiregulin antibody (doses:5 μg, 10 μg, 20 μg) into their right eyes, and three phosphate-buffered saline injections into their left eyes; and guinea pigs without lens-induced myopization and which received three unilateral intraocular injections of amphiregulin antibody (dose: 20 μg) or amphiregulin (doses: 1 ng; 10 ng; 20 ng) into their right eyes, and three phosphate-buffered saline injections into their left eyes. Seven days later, the animals were sacrificed. Intravitally, we performed biometry, and histology and immunohistochemistry post-mortem.

RESULTS

In animals with bilateral lens-induced myopization, the right eyes receiving amphiregulin antibody showed reduced axial elongation in a dose-dependent manner (dose: 5 μg: side difference: 0.14 ± 0.05 mm;10 μg: 0.22 ± 0.06 mm; 20 μg: 0.32 ± 0.06 mm; p < 0.001), thicker sclera (all p < 0.05) and higher cell density in the retinal nuclear layers and retinal pigment epithelium (RPE) (all p < 0.05). In animals without lens-induced myopia, the right eyes with amphiregulin antibody application (20 μg) showed reduced axial elongation (p = 0.04), and the right eyes with amphiregulin injections experienced increased (p = 0.02) axial elongation in a dose-dependent manner (1 ng: 0.04 ± 0.06 mm; 10 ng: 0.10 ± 0.05 mm; 20 ng: 0.11 ± 0.06 mm). Eyes with lens-induced axial elongation as compared to eyes without lens-induced axial elongation revealed an increased visualization of amphiregulin upon immunohistochemistry and higher expression of mRNA of endogenous amphiregulin and epidermal growth factor receptor, in particular in the outer part of the retinal inner nuclear layer and in the RPE.

CONCLUSION

Amphiregulin may be associated with axial elongation in young guinea pigs.

Bruch's Membrane Thickness and Retinal Pigment Epithelium Cell Density in Experimental Axial Elongation

To assess anatomical changes in eyes with progressive myopia, we morphometrically examined the eyes of guinea pigs with lens-induced axial elongation. Starting at an age of 3-4 weeks, guinea pigs in the experimental group (n = 20 animals) developed unilateral lens-induced axial elongation by wearing goggles for 5 weeks compared to a control group of 20 animals without intervention (axial length:8.91 ± 0.08 mm versus 8.74 ± 0.07 mm; P < 0.001). Five weeks after baseline, the animals were sacrificed, and the eyes enucleated. As measured histomorphometrically, Bruch's membrane thickness was not significantly correlated with axial length in either group at the ora serrata (P = 0.41), equator (P = 0.41), midpoint between equator and posterior pole (MBEPP) (P = 0.13) or posterior pole (P = 0.89). Retinal pigment epithelium (RPE) cell density decreased with longer axial length at the MBEPP (P = 0.04; regression coefficient beta = -0.33) and posterior pole (P = 0.01; beta = -0.40). Additionally, the thickness of the retina and sclera decreased with longer axial length at the MBEPP (P = 0.01; beta = -0.42 and P < 0.001; beta = -0.64, respectively) and posterior pole (P < 0.001; beta = -0.51 and P < 0.001; beta = -0.45, respectively). Choroidal thickness decreased at the posterior pole (P < 0.001; beta = -0.51). Experimental axial elongation was associated with a thinning of the retina, choroid and sclera and a decrease in RPE cell density, most markedly at the posterior pole. Bruch's membrane thickness was not related to axial elongation.

Corrugated Bruch's membrane in high myopia

PURPOSE

To assess the appearance of Bruch's membrane (BM) in axially elongated eyes.

METHODS

The light-microscopical investigation included histological anterior-posterior sections of human eyes. Using a light microscope, we assessed whether BM in the posterior segment was straight or locally corrugated. Corrugation of BM was defined as an elevation of BM with a height >20 μm over a basis of 50 μm without collateral proliferations of retinal pigment epithelium or choroidal swelling.

RESULTS

The investigation included 85 eyes (age: 62.0 ± 14.1 years; axial length: 26.7 ± 3.5 mm). In multivariate analysis, the presence of a corrugated BM, detected in eight eyes (9.4%), was strongly associated with the presence of macular BM defects [p = 0.001; odds ratio (OR): 418; 95% confidence interval (CI): 1 215 000], but not with axial length (p = 0.54). Bruch's membrane (BM) corrugation was detected in seven (54%) of 13 eyes with macular BM defects. The single eye with BM corrugation and without macular BM defect showed the corrugated BM located in the parapapillary region at the peripheral end of a large parapapillary gamma zone.

CONCLUSION

Bruch's membrane (BM) corrugation can be present in the vicinity of macular BM defects in highly myopic eyes, perhaps due to differences in the tension within BM in various regions at the margin of the BM defect. Bruch's membrane (BM) corrugation may also develop at the papillary end of BM in eyes with a large parapapillary gamma zone, potentially due to a disinsertion of BM at the end of the peripapillary choroidal border tissue of Jacoby. The observation of BM corrugation may help elucidating the aetiology of axial myopia.

Three Dimensional Evaluation of Posterior Pole and Optic Nerve Head in Tilted Disc

For over a century, tilted disc syndrome (TDS) has been defined vaguely. The lack of consensus of the terminology arises from the lack of understanding of the pathogenesis of this condition. Also, myopic discs with temporal crescents or peripapillary atrophy (PPA) are histologically indistinguishable from TDS. Therefore, we examined the morphological background of the extreme ONH appearances such as the myopic tilted disc and the TDS by analyzing the posterior segment of the eye from a three-dimensional (3D) perspective. 107 eyes of 107 subjects were classified into 3 groups with respect to the optic disc torsion degrees: (1) mild torsion (0–30 degrees; 35 eyes) and (2) moderate torsion (30–60 degrees; 35 eyes) and (3) severe torsion (60–90 degrees; 37 eyes). SSOCT images were analyzed in coronal view, which supplements anterior-posterior depth (z axis in Cartesian coordinates). The amount of optic disc torsion was significantly correlated with Disc-DPE angle and Fovea-Disc depth (r = 0.548, P < 0.001 and r = 0.544, P < 0.001). In conclusion, we describe specific types of posterior sclera configuration that corresponds to the increasing degree of optic disc torsion, even in the extreme ONH appearances such as the myopic tilted disc and the TDS. These findings suggest that the optic disc appearance is determined by the configuration of the posterior sclera.

Three-Dimensional Evaluation of Posterior Pole and Optic Nerve Head in Myopes with Glaucoma

The degree of myopia is represented by a global index, such as refractive error or axial length. However, the progression of myopia mainly develops in the posterior eyeball. Therefore, it is reasonable to assume that the evaluation of myopia should be confined to the posterior segment, where most of the growth and lengthening occurs. Swept source optical coherence tomography software can reconstruct the scans to the coronal view of the posterior pole, which provides additional anterior-posterior depth (z axis in the Cartesian coordinates) that is not provided with the common fundus photograph. We deduced that the parameter of deepest point of the eyeball (DPE) as a surrogate for posterior pole configuration. Between myopes with and without normal tension glaucoma (NTG) with similar axial length, myopes with NTG had deeper and more distant location of the DPE from the optic disc. The difference of the DPE position between the myopes with and without NTG may have implications for the larger optic disc tilt and torsion characteristic of myopes with NTG. Furthermore, these data suggest that myopes with NTG go through excessive posterior scleral remodeling, which may result in vulnerable optic nerve head.

Corneal profile in primary congenital glaucoma

PURPOSE

To investigate biomechanical and ultrastructural corneal parameters and ocular biometrics in the affected eyes of patients with unilateral primary congenital glaucoma (PCG) as compared to unaffected fellow eyes and age-matched healthy controls.

METHODS

A total of 12 patients with treated unilateral PCG and 10 normal subjects were evaluated. LENSTAR was performed to determine biometric parameters; the ocular response analyser was employed to determine biomechanical properties and slit-scanning confocal microscopy was used for evaluation of corneal ultrastucture.

RESULTS

Axial length was significantly higher and mean keratometry in affected eyes was significantly flatter in affected eyes as compared to fellow eyes and normal controls (p < 0.05), and a negative correlation was present between axial length and mean keratometry (p < 0.05). Mean aqueous depth and anterior chamber depth were increased in affected eyes as compared to fellow eyes and normal controls (p < 0.05). There was no significant difference in central corneal thickness (CCT) among affected eyes, fellow eyes and normal controls. Corneal hysteresis (CH) was significantly reduced in affected eyes (p < 0.05) and corneal resistance factor (CRF) was also reduced in the affected eyes as compared to fellow eyes and normal controls, although not statistically significant. Mean endothelial cell density was reduced in the affected eyes compared to fellow eyes and normal controls (p < 0.05).

CONCLUSION

Corneal biometrics, biomechanical parameters and ultrastructural features are altered in eyes affected with PCG despite clinically normal and clear corneas. These findings should be considered in the preoperative assessment of intraocular or corneal surgery in these patients.

[Secondary diseases in high myopia]

BACKGROUND

Eyes with high myopia (axial length ≥ 26.5 mm) do not just have a different size. Due to morphological and structural changes there is a considerably increased risk for many different secondary diseases.

OBJECTIVE

Determination of the incidence and mortality in high myopia, discussion of effects and clinical signs, presentation of treatment recommendations and counselling.

MATERIAL AND METHODS

A systematic search of the literature was carried out and a discussion on basic principles and epidemiological investigations is presented.

RESULTS

Findings due to high myopia are not in a closed state but undergo continuous changes. Choroidal neovascularization (adjusted prevalence 2.5-5%), staphyloma, foveoschisis and peripheral retinal degeneration are examples of problems contributing to the increased rate of visual impairment and blindness related to myopia. High myopia is associated with a clearly increased risk of retinal detachment after lens surgery (hazard ratio 6.1) and particularly more frequently in younger people. The associated primary open-angle glaucoma (odds ratio 2.46) is often recognized too late due to relatively low values of intraocular pressure.

CONCLUSION

Understanding of atrophic areas and staphyloma has benefited from recent advances in imaging (e.g. magnetic resonance imaging, optical coherence tomography and wide-field imaging) that complement and explain histological findings. Knowledge of the associated risk profile is of major clinical relevance.

Bruch´s membrane thickness in relationship to axial length

PURPOSE

To assess a potential role of Bruch´s membrane (BM) in the biomechanics of the eye, we measured its thickness and the density of retinal pigment epithelium (RPE) cells in various ocular regions in eyes of varying axial length.

METHODS

Human globes, enucleated because of an ocular tumor or end-stage glaucoma were prepared for histological examination. Using light microscopy, the histological slides were histomorphometrically examined applying a digitized image analysis system.

RESULTS

The study included 104 eyes with a mean axial length of 27.9±3.2 mm (range:22.6mm-36.5mm). In eyes without congenital glaucoma, BM was significantly thickest (P<0.001) at the ora serrata, followed by the posterior pole, the midpoint between equator and posterior pole (MBEPP), and finally the equator. BM thickness was not significantly correlated with axial length (ora serrata: P = 0.93; equator:P = 0.31; MBEPP:P = 0.15; posterior pole:P = 0.35). RPE cell density in the pre-equatorial region (P = 0.02; regression coefficient r = -0.24) and in the retro-equatorial region (P = 0.03; r = -0.22) decreased with longer axial length, while RPE cell density at the ora serrata (P = 0.35), the MBEPP (P = 0.06; r = -0.19) and the posterior pole (P = 0.38) was not significantly correlated with axial length. Highly myopic eyes with congenital glaucoma showed a tendency towards lower BM thickness and lower RPE cell density at all locations.

CONCLUSIONS

BM thickness, in contrast to scleral and choroidal thickness, was independent of axial length in eyes without congenital glaucoma. In association with an axial elongation associated decrease in the RPE cell density in the midperiphery, the findings support the notion of a biomechanical role BM may play in the process of emmetropization/myopization.

Prevalence of myopic retinopathy in rural Central India

PURPOSE

The aim of this study was to determine the prevalence of myopic retinopathy (MR) in rural Central India.

METHODS

The population-based Central India Eye and Medical Study included 4711 subjects (aged 30+ years). The participants underwent a detailed eye examination, including fundus photography. Myopic retinopathy was defined according to the Pathologic Myopia Study Group.

RESULTS

Readable fundus photographs were available on 4561 (96.8%) subjects (8846 eyes). Myopic retinopathy was present in 15 (0.17 ± 0.04%; 95% confidence interval (CI):0.08%, 0.26%) eyes of 11 (0.24 ± 0.07%; 95%CI: 0.01, 0.04) individuals. Myopic retinopathy occurred only in eyes with an axial length of >26 mm. Eyes with MR had significantly larger optic discs than eyes without MR (3.69 ± 1.22 mm² versus 2.52 ± 0.77 mm² ; p < 0.001). In binary regression analysis, higher prevalence of MR was associated with longer axial length (p < 0.001; odds ratio (OR): 19.6; 95%CI: 4.6, 82.9), higher prevalence of open-angle glaucoma (p = 0.02; OR: 16.1; 95%CI: 1.51, 170), lower best-corrected visual acuity (expressed in logMAR) (=0.03; OR: 0.06; 95%CI: 0.004, 0.75) and female gender (p = 0.002). If level of education was added to the model, educational level was not significantly associated with MR (p = 0.17; OR: 0.53; 95%CI: 0.22, 1.31). If gender was dropped from the model, higher prevalence of MR was associated with lower educational level (p = 0.04; OR: 0.44; 95%CI: 0.20, 0.97).

CONCLUSIONS

Prevalence of MR in rural Central India was low (11/4561 or 0.2%), and correlated with a 16 times higher risk of open-angle glaucoma, after adjusting for axial length and gender. If gender was excluded from the analysis, higher prevalence of MR was associated with lower educational level. This latter finding distinguishes adult MR from today's school children myopia which is strongly associated with higher educational level.

The Location of the Deepest Point of the Eyeball Determines the Optic Disc Configuration

Tilted and rotated appearances are hallmarks of the myopic optic disc. As the eyeball grows axially, the posterior pole elongates not only globally but in a localized manner as well. In this process, the optic disc is pulled towards the deepest point of the elongated eyeball, which might result in a change in optic disc configuration. Thus, we hypothesized that analyzing the variation of posterior pole contour can play a major role in understanding optic disc configuration in myopic subjects. By analyzing consecutive images of swept source OCT coronal sections at the posterior pole, the deepest interface between Bruch's membrane and the choroid could be identified as the deepest point of the eyeball (DPE). The location and the properties of the DPE differed significantly between the 125 eyes of non-glaucomatous myopic group and the 40 eyes of non-glaucomatous emmetropic group classified based on 24 mm axial length. The results suggested that the larger disc to DPE angle and the larger disc to DPE depth strongly predicts the optic disc torsion degree and the optic disc tilt. Our findings suggest that identifying the posterior pole profile plays a major role in understanding the optic disc alterations found in myopic subjects.

Structural and biomechanical corneal differences between patients suffering from primary congenital glaucoma and healthy volunteers

PURPOSE

To determine whether a set of ocular morphometric and biomechanical variables are able to discriminate between healthy volunteers and patients suffering from primary congenital glaucoma (PCG).

METHODS

Case-control study in which 66 patients with PCG and 94 age-matched healthy subjects were evaluated using ocular response analyser (ORA) to record corneal biomechanical properties. Topographic corneal variables were obtained using the Pentacam in both groups. To determine the ability to discern between both groups, a multivariate binary logistic model was constructed. The outcome was the diagnosis of PCG and the predictors; the corneal variables analysed along with their first-term interactions. Sensitivity and specificity of this model along with the area under the receiver characteristic operating curve (AUC of ROC) were determined.

RESULTS

The best model to discriminate between both groups included the following predictors: corneal hysteresis (CH), corneal resistance factor (CRF), posterior maximum elevation (PME), anterior maximum elevation (AME) and central corneal thickness (CCT). This model, for a cut-point of 50%, presents a sensitivity of 86.67%, a specificity of 86.89% and an AUC of the ROC curve of 93.16% [95% confidence interval (CI): 88.97-97.35]. The adjusted odds ratios of those predictors which showed a significant discriminating capacity were as follows: for CH, 0.27 (95% confidence interval: 0.15-0.46); for CRF, 2.13 (95% CI: 1.33-3.40); for PME, 1.06 (95% CI: 1.01-1.12); and for AME, 1.35 (95% CI: 1.10-1.66).

CONCLUSION

Corneal hysteresis (CH), CRF, PME and AME are able to discern between patients with PCG and healthy controls. This fact suggests that there are structural and biomechanical differences between these groups.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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