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

Heterogenous thinning of peripapillary tissues occurs early during high myopia development in juvenile tree shrews

Myopia is an independent risk factor for glaucoma, but the link between both conditions remains unknown. Both conditions induce connective tissue remodeling at the optic nerve head (ONH), including the peripapillary tissues. The purpose of this study was to investigate the thickness changes of the peripapillary tissues during experimental high myopia development in juvenile tree shrews. Six juvenile tree shrews experienced binocular normal vision, while nine received monocular -10D lens treatment starting at 24 days of visual experience (DVE) to induce high myopia in one eye and the other eye served as control. Daily refractive and biometric measurements and weekly optical coherence tomography scans of the ONH were obtained for five weeks. Peripapillary sclera (Scl), choroid-retinal pigment epithelium complex (Ch-RPE), retinal nerve fiber layer (RNFL), and remaining retinal layers (RRL) were auto-segmented using a deep learning algorithm after nonlinear distortion correction. Peripapillary thickness values were quantified from 3D reconstructed segmentations. All lens-treated eyes developed high myopia (-9.8 ± 1.5 D), significantly different (P < 0.001) from normal (0.69 ± 0.45 D) and control eyes (0.76 ± 1.44 D). Myopic eyes showed significant thinning of all peripapillary tissues compared to both, normal and control eyes (P < 0.001). At the experimental end point, the relative thinning from baseline was heterogeneous across tissues and significantly more pronounced in the Scl (-8.95 ± 3.1%) and Ch-RPE (-16.8 ± 5.8%) when compared to the RNFL (-5.5 ± 1.6%) and RRL (-6.7 ± 1.8%). Furthermore, while axial length increased significantly throughout the five weeks of lens wear, significant peripapillary tissue thinning occurred only during the first week of the experiment (until a refraction of -2.5 ± 1.9 D was reached) and ceased thereafter. A sectorial analysis revealed no clear pattern. In conclusion, our data show that in juvenile tree shrews, experimental high myopia induces significant and heterogeneous thinning of the peripapillary tissues, where the retina seems to be protected from profound thickness changes as seen in Ch-RPE and Scl. Peripapillary tissue thinning occurs early during high myopia development despite continued progression of axial elongation. The observed heterogeneous thinning may contribute to the increased risk for pathological optic nerve head remodeling and glaucoma later in life.

Reduction of experimental ocular axial elongation by neuregulin-1 antibody

Background

Since the mechanisms underlying myopic axial elongation have remained unclear, we examined the effect of neuregulin-1 (NRG-1), an epidermal growth factor family member, on myopic axial elongation.

Methods

The guinea pigs aged two to three weeks were subjected to bilateral negative lens-induced axial elongation and received weekly intravitreal injections into their right eyes of NRG-1 antibody (doses: 5 μg, n = 8; 10 μg, n = 8, 20 μg, n = 9) or of NRG-1 (doses: 0.05 μg, n = 8; 0.01 μg, n = 9; 0.2 μg, n = 8), underwent only bilateral negative lens-induced axial elongation (myopia control group, n = 10), or underwent no intervention (control group, n = 10). The contralateral eyes received corresponding intravitreal phosphate-buffered solution injections. One week after the last injection, the guinea pigs were sacrificed, the eyeballs were removed, the thicknesses of the retina and sclera were histologically examined, the expression of NRG-1 and downstream signal transduction pathway members (ERK1/2 and PI3K/AKT) and the mRNA expression of NRG-1 in the retina was assessed.

Results

The inter-eye difference in axial length at study end increased (p < 0.001) from the normal control group (-0.02 ± 0.09 mm) and the myopia control group (-0.01 ± 0.09 mm) to the low-dose NRG-1 antibody group (-0.11 ± 0.05 mm), medium-dose NRG-1 antibody group (-0.17 ± 0.07 mm), and high-dose NRG-1 antibody group (-0.28 ± 0.06 mm). The relative expression of NRG-1, ERK1/2, and PI3K/AKT in the retina decreased in a dose-dependent manner from the myopia control group to the NRG-1 antibody groups and the normal control group. The relative NRG-1 mRNA expression in the retina was higher (p < 0.01) in the myopic control group than in the NRG-1 antibody groups and normal control group. Scleral and retinal thickness decreased from the normal control group to the NRG-1 antibody groups to the myopic control group. After intraocular injection of NRG-1 protein, there was a slight dose-dependent increase in the difference in axial length between the right and left eye, however not statistically significantly, from the normal control group (-0.02 ± 0.09 mm) to the high-dose NRG-1 protein group (0.03 ± 0.03 mm; p = 0.12).

Conclusion

Intravitreal NRG-1 antibody application was dose-dependently and time-dependently associated with a reduction in negative lens-induced axial elongation in young guinea pigs.

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.

IMI-Nonpathological Human Ocular Tissue Changes With Axial Myopia

Purpose

To describe nonpathological myopia-related characteristics of the human eye.

Methods

Based on histomorphometric and clinical studies, qualitative and quantitative findings associated with myopic axial elongation are presented.

Results

In axial myopia, the eye changes from a spherical shape to a prolate ellipsoid, photoreceptor, and retinal pigment epithelium cell density and total retinal thickness decrease, most marked in the retroequatorial region, followed by the equator. The choroid and sclera are thin, most markedly at the posterior pole and least markedly at the ora serrata. The sclera undergoes alterations in fibroblast activity, changes in extracellular matrix content, and remodeling. Bruch's membrane (BM) thickness is unrelated to axial length, although the BM volume increases. In moderate myopia, the BM opening shifts, usually toward the fovea, leading to the BM overhanging into the nasal intrapapillary compartment. Subsequently, the BM is absent in the temporal region (such as parapapillary gamma zone), the optic disc takes on a vertically oval shape, the fovea-optic disc distance elongates without macular BM elongation, the angle kappa reduces, and the papillomacular retinal vessels and nerve fibers straighten and stretch. In high myopia, the BM opening and the optic disc enlarge, the lamina cribrosa, the peripapillary scleral flange (such as parapapillary delta zone) and the peripapillary choroidal border tissue lengthen and thin, and a circular gamma and delta zone develop.

Conclusions

A thorough characterization of ocular changes in nonpathological myopia are of importance to better understand the mechanisms of myopic axial elongation, pathological structural changes, and psychophysical sequelae of myopia on visual function.

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

Purpose

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

Methods

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

Results

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

Conclusions

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

Anatomic Peculiarities Associated with Axial Elongation of the Myopic Eye

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Photoreceptor density in relation to axial length and retinal location in human eyes

The purpose of the study was to examine the density of retinal photoreceptors and retinal pigment epithelium (RPE) cells in relation to myopic axial elongation in human eyes. Using light microscopy, we assessed the density of photoreceptors and RPE cells at the ora serrata, equator, and midperiphery (equator/posterior pole midpoint), and the RPE cell density additionally at the posterior pole, in enucleated human globes. The study included 78 eyes (mean age: 59.2 ± 15.6 years; range: 32-85 years) with a mean axial length of 27.3 ± 3.6 mm (range: 21.5-37.0 mm). Close to the ora serrata, at the equator and midperiphery, photoreceptor and RPE cell density was 246 ± 183, 605 ± 299 and 1089 ± 441 photoreceptors/mm and 56.1 ± 13.7, 45.2 ± 15.1, and 48.8 ± 15.6 RPE cells/mm, respectively. Densities of both cell types in all three regions were positively correlated with each other (all P < 0.001) and decreased with longer axial length (all P < 0.001) and longer distance between the ora serrata and the posterior pole (all P < 0.001), most marked at the midperiphery and least marked close to the ora serrata. The PRE cell density at the posterior pole was not significantly (P = 0.35) related to axial length. The photoreceptor density at the ora serrata (beta:- 0.33) and equator (beta: - 0.27) and RPE cell density at the ora serrata (beta: - 0.27) decreased additionally with the presence of glaucoma. The findings suggest that the axial elongation-related decrease in photoreceptor and RPE cell density is most marked at the midperiphery, followed by the equator and finally the ora serrata region. It suggests that the axial elongation-related enlargement of the eye wall predominantly takes place in the retro-equatorial region, followed by the equatorial region.

Epiregulin, epigen and betacellulin antibodies and axial elongation in young guinea pigs with lens-induced myopization

Background

To examine an effect of intravitreally applied antibodies against epidermal growth factor family members, namely epiregulin, epigen and betacellulin, on ocular axial elongation.

Methods

The experimental study included 30 guinea pigs (age:3–4 weeks) which underwent bilateral lens-induced myopization and received three intraocular injections of 20 µg of epiregulin antibody, epigen antibody and betacellulin antibody in weekly intervals into their right eyes, and of phosphate-buffered saline into their left eyes. Seven days after the last injection, the animals were sacrificed. Axial length was measured by sonographic biometry.

Results

At baseline, right eyes and left eyes did not differ (all P > 0.10) in axial length in neither group, nor did the interocular difference in axial length vary between the groups (P = 0.19). During the study period, right and left eyes elongated (P < 0.001) from 8.08 ± 0.07 mm to 8.59 ± 0.06 mm and from 8.08 ± 0.07 mm to 8.66 ± 0.07 mm, respectively. The interocular difference (left eye minus right eye) in axial elongation increased significantly in all three groups (epiregulin-antibody:from 0.03 ± 0.06 mm at one week after baseline to 0.16 ± 0.08 mm at three weeks after baseline;P = 0.001); epigen-antibody group:from -0.01 ± 0.06 mm to 0.06 ± 0.08 mm;P = 0.02; betacellulin antibody group:from -0.05 ± 0.05 mm to 0.02 ± 0.04 mm;P = 0.004). Correspondingly, interocular difference in axial length increased from -0.02 ± 0.04 mm to 0.13 ± 0.06 mm in the epiregulin-antibody group (P < 0.001), and from 0.01 ± 0.05 mm to 0.07 ± 0.05 mm in the epigen-antibody group (P = 0.045). In the betacellulin-antibody group the increase (0.01 ± 0.04 mm to 0.03 ± 0.03 mm) was not significant (P = 0.24).

Conclusions

The EGF family members epiregulin, epigen and betacellulin may be associated with axial elongation in young guinea pigs, with the effect decreasing from epiregulin to epigen and to betacellulin.

Histopathology of myopic cobblestones

PURPOSE

To search for the histological correlate of peripheral 'cobblestones' in highly myopic eyes.

METHODS

The histomorphometric investigation included histologic sections of enucleated eyes of Caucasian patients. Using light microscopy, we measured the thickness of the retina, Bruch's membrane (BM) and choriocapillaris.

RESULTS

The study included 50 eyes (mean age:60.6 ± 18.7 years;axial length:26.5 ± 3.8 mm), with cobblestone regions detected in 7 eyes. BM thickness and choriocapillaris thickness in the cobblestone region were thinner (1.1 ± 0.2 µm versus 2.4 ± 0.8 µm; p < 0.001 and 1.6 ± 0.5 µm versus 2.6 ± 1.9 µm; p = 0.02, respectively), and just outside of the cobblestone region they were thicker (3.3 ± 0.6 µm versus 2.4 ± 0.8 µm; p = 0.005 and 5.7 ± 1.6 µm versus 2.6 ± 1.9 µm; p = 0.002, respectively) than in corresponding regions of eyes without cobblestones. Within the group of eyes with cobblestones, BM thickness (1.1 ± 0.2 mm versus 3.3 ± 0.6 mm; p < 0.001), choriocapillaris thickness (1.6 ± 0.5 mm versus 5.7 ± 1.6 mm; p < 0.001) and choriocapillaris density (48±15 µm/300 µm versus 159 ± 66 µm/300 µm;PP=0.002) were significantly lower in the cobblestone region than just outside of the cobblestone region. The cobblestone regions were characterized by firm adhesion of disorganized retina with thinned BM, few retinal pigment epithelium (RPE) islands within cobblestone regions, and absence of regional scleral or overall choroidal thinning. BM was mono-layered within, and double-layered outside of cobblestone regions, with the inner layer missing within the cobblestone region (except for the RPE islands).

CONCLUSIONS

Peripheral cobblestone regions in highly myopic eyes are characterized by marked BM thinning with absence of an inner BM layer, almost complete RPE absence, choriocapillaris thinning and firm connection of a disorganized retina to BM. These findings may help elucidating the process of axial elongation in myopic eyes.

In vivo Imaging of Retina and Choroid in Guinea Pigs

Purpose: To evaluate the feasibility of in-vivo imaging of the retina and choroid using spectral domain optical coherence tomography (OCT) in guinea pigs. Methods: The study included 19 pigmented guinea pigs (age: 3-4 weeks) which underwent sonographic axial length measurements and OCT imaging. At study end, the animals were sacrificed and histomorphometric examinations of the retina and choroid were performed. We assessed the reproducibility of the OCT measurements and compared in-vivo measurements to histomorphometric data. Results: The mean thickness of the retina and choroid near the optic nerve head was 175.6 ± 25.8 and 63.4 ± 16.5 μm, respectively, and mean Bruch's membrane opening (BMO) diameter was 831 ± 121 μm. The intra-observer comparison of measurements of retinal thickness (intraclass correlation coefficient (ICC) = 0.92, 95% CI: 0.86-0.96; P < 0.001), choroidal thickness (ICC = 0.92, 95% CI: 0.86-0.96; P < 0.001), and BMO diameter (ICC = 0.92, 95% CI: 0.86-0.96; P < 0.001) showed a high correlation. A high agreement was present also for the inter-observer reproducibility of the measurements of retinal thickness (Pearson correlation coefficient (R) = 0.98; P < 0.001), choroidal thickness (R = 0.96; P < 0.001), and BMO diameter (R = 0.98; P < 0.001). The Bland-Altman plots showed that 2.6% (1/38), 5.3% (2/38), and 7.9% (3/38) of the measurement points of retinal thickness, choroidal thickness and BMO diameter, respectively, were located outside of the 95% limits of agreement. The OCT-based thickness measurements of retina and choroid were significantly higher than those measured by histomorphometry (both P-values <0.01). Conclusion: OCT-based in-vivo morphometric imaging of the retina and choroid in guinea pigs is feasible with an acceptable intra-observer repeatability and inter-observer reproducibility.

Visually guided chick ocular length and structural thickness variations assessed by swept-source optical coherence tomography

Chicks are an excellent model for studying myopia. To study the change of the ocular structures in chicks, ultrasound is mostly used. However, it suffers from limited spatial resolution. In this study, we investigated the axial length (AL) and the thickness of different ocular structures in chicks' eye undergoing visually induced changes using a swept-source optical coherence tomography (SS-OCT) system in vivo. Two groups of chicks wore a translucent plastic goggle (n = 6) over the right eye to induce form-deprivation myopia. Following 12 days of form deprivation, goggles were removed in one group of chicks (n = 3), and they were allowed to experience 5 days of unrestricted vision (recovery). Goggles remained in place for a total of 17 days for the remaining 3 chicks. A separate group of 3 chicks were untreated and served as normal control. Ocular dimensions were measured in control, myopic, and recovered eyes using an SS-OCT system. We found myopic chick eyes had significantly thicker AL, lens thickness (LT), anterior chamber depth (ACD), and vitreous chamber depth (VCD), but significantly thinner retina thickness (RT) and choroid thickness (ChT) compared to the control eyes. Following 5 days of recovery, the cornea thickness (CT), retina pigment epithelium thickness (RPET), and ChT were significantly thicker, while the ACD and LT became significantly thinner compared to that of myopic eyes. SS-OCT can serve as a promising tool to provide measurements of the entire ocular structures, for evaluating the change of thickness and depth of different ocular structures in chicks in vivo. The change of AL in the myopic and recovered chick eyes can be attributed to the thickness alterations of different ocular structures. Altogether, this work demonstrated the feasibility of SS-OCT in chick myopic research and exhibited new insights into the changes of ocular structures in chicks experiencing myopia after unrestricted vision recovery.

Location of Parapapillary Gamma Zone and Vertical Fovea Location. The Beijing Eye Study 2011

Purpose

To assess the spatial relationship between the locations of the parapapillary gamma zone and the fovea.

Methods

In a non-glaucomatous subgroup of the population-based Beijing Eye Study population, we measured the mean angle between the optic disc–fovea line and the horizontal (disc–fovea angle), the vertical distance of the fovea from the horizontal through the optic disc center (fovea vertical distance), and the location and width of the widest part of parapapillary gamma zone.

Results

The study included 203 individuals (203 eyes; mean axial length, 24.4 ± 1.5 mm; range, 22.03–28.87 mm). The widest gamma zone part was located most often temporal horizontally (51.7%), then inferiorly (43.8%), superiorly (2.5%), and nasally (2.0%). The disc–fovea angle (mean, 7.50° ± 4.00°; range, –6.30° to –23.25°) was significantly higher (P = 0.003; i.e., fovea located more inferiorly) in eyes with the widest gamma zone inferiorly (8.46° ± 4.37°) than in eyes with the widest gamma zone temporally (6.71° ± 3.46°) and in eyes with the widest gamma zone temporally, superiorly, or nasally combined (6.75° ± 3.53°; P = 0.003). The fovea vertical distance (mean, 0.65 ± 0.33 mm; range, –0.20 to 1.67 mm) was longer (P = 0.001; i.e., fovea located more inferiorly) in eyes with the widest gamma zone inferiorly (0.73 ± 0.33 mm) than in eyes with the widest gamma zone temporally (0.58 ± 0.30 mm) and in eyes with a temporal, superior, or nasal gamma zone combined (0.58 ± 0.31 mm; P = 0.001). The fovea vertical distance increased (multivariate analysis) with the widest gamma zone location inferiorly (β = 0.25; P = 0.001) and wider width of the gamma zone (β = 0.19; P = 0.01).

Conclusions

An inferior fovea location is associated with a wider inferior gamma zone and vice versa, supporting the notion of an inferior shifting of Bruch's membrane as the cause for an inferior gamma zone.

Genotype-phenotype correlation and interaction of 4q25, 15q14 and MIPEP variants with myopia in southern Chinese population

BACKGROUND/AIMS

To determine the association and interaction of genome-wide association study-reported variants for Asian populations with myopia and ocular biometric parameters in southern Chinese population.

METHODS

Totally, 1462 unrelated Han Chinese subjects were recruited with complete ophthalmic examinations, including 1196 myopia and 266 control subjects. A total of nine variants were selected for TaqMan genotyping. The genetic association, joint additive effect and genotype-phenotype correlation were investigated.

RESULTS

The 4q25 variant rs10034228 (p=0.002, OR=0.56) and MIPEP variant rs9318086 (p=0.004, OR=1.62) were found to be significantly associated with myopia as well as different severity of myopia. Moreover, 15q14 variant rs524952 (p=0.015, OR=1.49) also showed mild association with myopia and high myopia. However, there was no significant association of CTNND2, vasoactive intestinal peptide receptor 2 and syntrophin beta 1 variants with myopia. Joint additive analysis revealed that the subjects carrying 6 risk alleles of the 3 associated variants were 10-fold higher risk predisposed to high myopia. Genotype-phenotype correlation analysis revealed that high myopia subjects carrying 4q25 rs10034228 T allele showed thicker central corneal thickness, whereas high myopia subjects carrying 15q14 rs524952 A allele were associated with longer axial length and larger curvature ratio.

CONCLUSION

This study revealed significant association of 4q25, 15q14 and MIPEP variants with myopia and different severity of myopia in southern Chinese population, joint additively enhancing 10-fold of risk predisposing to high myopia. The correlation of these associated variants with axial length and corneal parameters suggests their contribution to the refractive status in high myopia subjects.

Intraocular epidermal growth factor concentration, axial length, and high axial myopia

Purpose

Various molecules such as dopamine have been found to be associated with axial elongation in experimental studies. Here, we examined whether intraocular EGF is associated with axial length in myopic patients.

Methods

The hospital-based investigation included patients of European descent without optic nerve, retinal, or macular diseases except for myopic maculopathy. Using aqueous humor samples collected during surgery, the EGF concentration was examined applying a cytometric bead array. High myopia was defined by an axial length of ≥ 27.0 mm.

Results

The study included a non-highly myopic group of 11 patients (mean age, 72.9 ± 10.8 years; mean axial length, 24.3 ± 1.1 mm) and a highly myopic group of three patients (age, 81.11 ± 12.3 years; axial length, 29.5 ± 1.3 mm), with one of them having pathologic myopic maculopathy. In multivariable linear regression analysis, higher EGF concentration was correlated with the highly myopic versus non-highly myopic group (beta, 1.24; non-standardized correlation coefficient B, 6.24; 95% confidence interval (CI), 0.10,12.4;P = 0.047) after adjusting for axial length. The amount of intraocular EGF was significantly higher in the highly myopic group than in the non-highly myopic group (89.1 ± 40.8 pg versus 34.1 ± 13.2 pg; P = 0.005), and it was highest in the eye with myopic maculopathy (135 pg).

Conclusions

The intraocular amount of EGF is higher in highly myopic versus non-highly myopic eyes.

IMI 2021 Yearly Digest

Purpose

The International Myopia Institute (IMI) Yearly Digest highlights new research considered to be of importance since the publication of the first series of IMI white papers.

Methods

A literature search was conducted for articles on myopia between 2019 and mid-2020 to inform definitions and classifications, experimental models, genetics, interventions, clinical trials, and clinical management. Conference abstracts from key meetings in the same period were also considered.

Results

One thousand articles on myopia have been published between 2019 and mid-2020. Key advances include the use of the definition of premyopia in studies currently under way to test interventions in myopia, new definitions in the field of pathologic myopia, the role of new pharmacologic treatments in experimental models such as intraocular pressure-lowering latanoprost, a large meta-analysis of refractive error identifying 336 new genetic loci, new clinical interventions such as the defocus incorporated multisegment spectacles and combination therapy with low-dose atropine and orthokeratology (OK), normative standards in refractive error, the ethical dilemma of a placebo control group when myopia control treatments are established, reporting the physical metric of myopia reduction versus a percentage reduction, comparison of the risk of pediatric OK wear with risk of vision impairment in myopia, the justification of preventing myopic and axial length increase versus quality of life, and future vision loss.

Conclusions

Large amounts of research in myopia have been published since the IMI 2019 white papers were released. The yearly digest serves to highlight the latest research and advances in myopia.

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.

Histology of myopic posterior scleral staphylomas

PURPOSE

Since histomorphometric descriptions of posterior scleral staphylomas, although forming a major part of myopic maculopathy, have been scarce so far, we histomorphometrically examined scleral staphylomas in enucleated human eyes.

METHODS

Using light microscopy, we histomorphometrically examined sagittal histological sections of human globes enucleated due to malignant choroidal melanomas or secondary angle-closure glaucoma.

RESULTS

Out of 246 globes included into the study, posterior scleral staphylomas were detected in 10 eyes (mean length: 31.4 ± 3.0 mm; range: 28.0-37.0 mm). In the staphylomatous region in the study group as compared with the corresponding region of a control group adjusted for age and axial length, scleral thickness was significantly lower (109 ± 25 µm versus 319 ± 161 µm; p = 0.001). The study group in the staphylomatous region as compared to the highly myopic control group in the corresponding region did not differ significantly in retinal pigment epithelium (RPE) cell density (19.6 ± 4.9 cells/300 µm versus 21.1 ± 5.7 cells/300 µm; p = 0.84) and RPE height (8.2 ± 2.8 µm versus 6.1 ± 2.5 µm; p = 0.13), Bruch's membrane (BM) thickness (3.5 ± 1.3 µm versus 4.2 ± 2.3 µm; p = 0.40) and choriocapillaris thickness (5.3 ± 2.8 µm versus 4.4 ± 2.8 µm; p = 0.49) and density (164 ± 99 µm versus 226 ± 38 µm; p = 0.13). All staphylomatous regions showed a localized BM defect.

CONCLUSIONS

Marked scleral thinning and spatially correlated BM defects histologically characterized myopic scleral staphylomas, while thickness and density of the choriocapillaris and RPE and BM thickness did not differ significantly between staphylomatous versus non-staphylomatous eyes in the respective regions. These findings support the notion that a locally reduced scleral resistance against a backward pushing BM led to a local scleral outpouching. The outpouching-associated increase in curvature length may stretch BM with the sequel of a localized BM rupture.

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.

Blockade of epidermal growth factor and its receptor and axial elongation in experimental myopia

To examine the influence of epidermal growth factor (EGF) and its receptor (EGFR) on axial ocular elongation, we intraocularly injected an EGF antibody and an EGFR antibody into young guinea pigs with lens-induced axial elongation (myopization). Mean axial elongation was reduced in the eyes injected with the EGF/EGFR-antibody compared with the contralateral control eyes injected with PBS (phosphate-buffered solution) (0.43 ± 0.13 mm vs 0.53 ± 0.13 mm; P < .001). The intereye difference in axial length increased (P = .005) as the doses of the EGF antibody and EGFR antibody increased. As a corollary, the thickness of the retina at the posterior pole was dose-dependently increased in the injected eyes compared to the contralateral control eyes. Immunohistochemical staining for EGF and the relative mRNA expression of EGF and EGFR were the highest in eyes not injected with the EGF antibody or EGFR antibody and decreased (P < .05) as the dose of EGF antibody or EGFR antibody increased. In an in vitro study, EGF had a stimulating effect and the EGF antibody had an inhibitory effect on the proliferation and migration of RPE cells. The findings showed that the intravitreal application of an EGF antibody and EGFR antibody is associated with a dose-dependent reduction in lens-induced axial elongation in young guinea pigs. The EGFR family may play a role in axial elongation of the eye and in the development of myopia.

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.

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.