Bruch´s membrane thickness in relationship to axial length
BruchÂs membrane thickness in relationship to axial length
Hai Xia Bai 1 2
Ying Mao 1 2
Ling Shen 1 2
Xiao Lin Xu 1 2
Fei Gao 1 2
Zhi Bao Zhang 1 2
Bin Li 1 2
Jost B. Jonas 0 2
0 Department of Ophthalmology, Medical Faculty Mannheim, Heidelberg University , Mannheim , Germany
1 Beijing Institute of Ophthalmology, Beijing Tongren Eye Center, Beijing Tongren Hospital, Capital Medical University, Beijing Ophthalmology & Visual Sciences Key Laboratory , Beijing , China , 2 Department of Ophthalmology, The 2nd Affiliated Hospital, Harbin Medical University , Harbin, Heilong-jiang , China
2 Editor: James Fielding Hejtmancik, National Eye Institute , UNITED STATES
Purpose To assess a potential role of BruchÂs 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.
Data Availability Statement: All relevant data are
within the paper and its Supporting Information
Funding: The authors received no specific funding
for this work.
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.
secreting neuroprotective factor and/or
antiangiogenic factor; Patent number: 20120263794),
and Patent application with University of
Heidelberg (Heidelberg, Germany) (Title: Agents for
use in the therapeutic or prophylactic treatment of
myopia or hyperopia; European Patent Number: 3
070 101). This does not alter our adherence to
PLOS ONE policies on sharing data and materials.
BruchÂs membrane (BM) forms the border between the intravitreal cavity with the vitreous
body and retina on its inner side and the choroid on its outer side [
]. It is formed by the
retinal pigment epithelium (RPE) and consists of the basal membrane of the latter, two
collagenous layers separated from each other by an elastic layer in its center, and the basal membrane
of the choriocapillaris on its outer side. Together with the RPE, BM participates in forming the
blood retina barrier, separating the retina with its almost fluid-free interstitial space from the
spongy choroid with fenestrated choriocapillaris vessel walls and pronounced interstitial fluid.
Recent studies on the emmetropization of the eye have suggested that BM, in addition to
having a function in separating the retinal and vitreal compartment from the choroidal space,
could play a biomechanical role in the process of emmetropization and myopization [2±9].
Since the biomechanical characteristics of a tissue strongly depend on its thickness, we
measured the thickness of BM in different locations of human enucleated eyes. We also assessed
the density of the RPE cells since the latter produce the BM.
The histomorphometric investigation included human globes which had been enucleated due
to uveal melanomas or end-stage painful glaucoma. The Medical Ethics Committee of the
Beijing Tongren Hospital approved the study protocol according to the Declaration of Helsinki.
The necessity of a written informed consent by the patients was waived since the eyes had been
enucleated up to 50 years before the study was started. As inclusion criterion, all histological
slides examined in the study had to run through the center of the cornea, the optic disc and
through the posterior pole. Exclusion criteria were tissue changes attributable to the
underlying diseases and which prevented a thickness measurement of BM.
After processing the enucleated eyes were prepared in a standardized manner for light
microscopical examination. It included fixation in a solution of 4% formaldehyde for at least
24 hours, measurement of the sagittal globe diameter, sectioning of the eyes, and staining of
the slides with hematoxycilin eosin or by the Periodic-Acid-Shiff (PAS) method. The slides
were histomorphometrically examined using a digitized image analysis system (Moticam 2006
(2.0M pixel USB2.0) and Motic Digital Medical Image Analysis System, Motic China group,
Co. Ltd. Xiamen, China). We measured the thickness of BM (defined as the distance between
the basal membrane of the RPE on its inner side to the basal membrane of the choriocapillaris
on its outer side), the thickness of the choroid and the thickness of the sclera at the ora serrata,
the equator, the midpoint between the equator and the posterior pole (MBEPP), and at the
posterior pole (Fig 1). Scleral thickness was additionally determined in the pars plana region.
At each measurement region, four measurements at slightly different points were obtained
and the mean of these measurements was taken for further statistical analysis. For the
assessment of the density of the RPE cells, we used the same digitized image analysis system, and we
counted the number of RPE cells on BruchÂs membrane for a length of 480 μm in the region
just posterior to the ora serrata, the region just anterior to the equator, the region just posterior
to the equator, at the MBEPP, and at the posterior pole. The methods have been described in
detail recently [4±8,10].
A statistical analysis program (SPSS, version 22.0, IBM-SPSS, Chicago, IL, USA) was used
for the statistical analysis. In a first step, we calculated the mean values ± standard deviations
of the outcome parameters at each measurement location. Using a two-tailed student-t-test for
paired samples, we then compared in a second step the BM thickness measurements and RPE
density values between the various locations of measurement. Finally, in linear regression
analysis, we performed a univariate analysis, followed by a multivariate analysis, to test associations
2 / 12
Fig 1. Histo-photograph showing thickness measurements of BruchÂs membrane (in μm); Black arrows: BruchÂs membrane; Red arrow:
Choriocapillaris vessel; Green Arrow: Large choroidal vessel.
between BM thickness or the RPE cell count with axial length and other parameters. All
P-values were 2-sided and considered statistically significant when less than 0.05.
The study included 104 globes of 104 patients (51 women) with a mean age of 35.7 ± 18.4 years
(median: 35 years; range:1±81 years) and a mean axial length of 27.9 ± 3.2 mm (median: 27.5
mm; range: 22.6mm±36.5mm). Reasons for enucleation were uveal melanoma in 34 patients
and end-stage painful glaucoma in 70 patients, among them five patients with congenital
glaucoma. Axial length was longer than 26.0 mm in 64 eyes.
In the eyes without congenital glaucoma, BM thickness was significantly the thickest
(P<0.001) at the ora serrata, followed by the posterior pole, the MBEPP, and the equator
(Table 1) (Fig 2). In the eyes without congenital glaucoma, BM thickness was not significantly
correlated with axial length, neither at the ora serrata (P = 0.93), the equator (P = 0.31), the
3 / 12
P-Value (1): Statistical significance of the difference between the non-highly myopic group and the highly myopic group without congenital glaucoma
P-Value (2): Statistical significance of the difference between the congenital glaucoma group and the remaining eyes
MBEPP (P = 0.15) nor the posterior pole (P = 0.35) (Fig 3). Correspondingly, the non-highly
myopic group and the highly myopic group without congenital glaucoma did not differ
significantly (P>0.15) in BM thickness (Table 1). BM thickness showed a tendency towards thinner
measurements in the group of eyes with secondary high myopia due to congenital glaucoma
as compared to both other groups (Table 1). The differences were however not statistically
BM thickness increased significantly with older age when measured at the ora serrata
(P = 0.01; r = 0.25) and at the equator (P<0.001; r = 0.43), while BM thickness measured at the
MBEPP (P = 0.20) or at the posterior pole (P = 0.17) was not significantly associated with age
4 / 12
Fig 2. Graph showing the distribution of BruchÂs membrane thickness at various ocular locations in enucleated
human eyes with globes with congenital glaucoma excluded.
BM thickness measurements obtained at any location did not differ between the
glaucomatous group and the non-glaucomatous group (P>0.30).
In the eyes without congenital glaucoma, RPE cell density measured 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 in the ora serrata region
(P = 0.35), at the MBEPP (P = 0.06; r = -0.19) and at the posterior pole (P = 0.38) was not
significantly correlated with axial length (Figs 5 and 6). RPE density at the posterior pole showed
a tendency to be lower in the eyes with secondary high myopia due to congenital glaucoma
(24.8 ± 3.3 cells / 480μm section length) than in the eyes with primary high myopia (27.0 ± 3.5
cells / 480μm section length) and the non-highly myopic eyes (27.0 ± 3.0 cells / 480μm section
length) (Table 1) (Fig 6). The differences were however not statistically significant (P = 0.20).
The thickness of the choroid decreased significantly with longer axial length for choroidal
thickness measurements obtained at the equator (P = 0.006; r = -0.27), at the MBEPP
5 / 12
Fig 3. Graph showing the distribution of BruchÂs membrane thickness at the posterior pole versus axial length
in enucleated human eyes without congenital glaucoma.
(P<0.001; r = -0.35) and at the posterior pole (P<0.001; r = -0.39). The association was most
marked for the choroidal measurements taken at the posterior pole. There was no difference
if the highly myopic eyes with congenital glaucoma were included or excluded from the
analysis. Scleral thickness measured at the ora serrata (P<0.001; r = -0.51), the equator (P<0.001;
r = -0.13), the MBEPP (P = 0.02; r = -0.23) and at the posterior pole (P<0.001; r = -0.60)
decreased with longer axial length, most marked at the posterior pole (Fig 7). Again, there was
no difference if the highly myopic eyes with congenital glaucoma were included or excluded
from the analysis.
In this histomorphometric study on human eyes, the thickness of BM was not related with
axial length in eyes without congenital glaucoma. The density of the RPE cells decreased with
longer axial length in the pre-equatorial and retro-equatorial region, while at the posterior
pole, as was the thickness of BM, the RPE cell density was not significantly correlated with
axial length. In contrast, thickness of choroid and of the sclera markedly decreased with longer
axial length, most marked at the posterior pole.
6 / 12
Fig 4. Graph showing the distribution of BruchÂs membrane thickness at the equator versus age in enucleated
human eyes (Equation of the regression line: BruchÂs membrane thickness at the Equator (μm) = 0.008 x Age
(Years) + 1.45).
These findings obtained on Chinese eyes confirmed the results of a previous investigation
on Western European eyes, in which as in the present study, BM thickness was not related
with axial length in eyes without congenital glaucoma, and in which the RPE cell density
decreased in the retro-equatorial region with elongating axial length [
]. In eyes with
congenital glaucoma examined previously, BM thickness showed a marginally significant inverse
association with axial length, while the present study only showed a tendency towards a
thinner BM in the highly myopic eyes with congenital glaucoma .
The findings obtained in the present study and in the previous investigation on different
study populations cannot fully be compared with results obtained in other studies, since BM
thickness has not intensively been examined yet, except for in a relatively few studies on BM
thickness in relation to age-related macular degeneration [11±17]. In all these latter studies,
BM thickness was not compared with axial length.
The BM thickness measurements obtained in the present study were thinner than in the
previous study in which BM thickness was measured with the help of a millimeter scale aligned
with the ocular of the light microscope [
]. The values of the present study were also slightly
thinner than the measurements of BM thickness Ramrattan and colleagues obtained with
7 / 12
Fig 5. Graph showing the distribution of the retinal pigment epithelium cell density at the posterior pole versus
axial length in enucleated human eyes without congenital glaucoma (Equation of the regression line: RPE Cell
density (Cells / 480μm Section Length)) = -0.15 x Axial Length (mm) + 25.6).
values ranging between 2 and 5 μm [
]. Reason for the discrepancy between both studies
might have been that RamrattanÂs study in contrast to our investigation also included eyes
with age-related macular degeneration.
The finding that BM thickness, in contrast to choroidal thickness and scleral thickness, did
not decrease with increasing axial length fitted with the hypothesis that BM might play a role
in the process of emmetropization [
]. The latter, taking place after the end of the second year
of life, has been defined as the adjustment of the length of the optical axis in relationship to the
refractive power of cornea and lens. The hypothesis was based on findings that after a spherical
eye growth with active increase in scleral volume till the end of the second year of life, the
dimensions of cornea and lens remain mostly constant while the globe elongates axially to
bring the foveola into the optical focus. That axial elongation was accompanied by a thinning
of the choroid and sclera, leading to a re-arrangement of the available choroidal and scleral
tissue without a major active increase in tissue volume [
]. Thinning of the choroid and
sclera was most marked at the posterior pole. In contrast to the choroidal and scleral thinning,
retinal thickness in the macular region did not decrease with longer axial length, parallel to the
observation that best corrected visual acuity was independent of axial length if eyes with
myopic maculopathy were excluded [
]. There was however a thinning of the retina in the
8 / 12
Fig 6. Graph showing the distribution of the retinal pigment epithelium cell density at the posterior pole (cells /
480μm section length) in enucleated human eyes, stratified by high myopia and presence of congenital
midperiphery collateral to a decrease in the density of the RPE cells in the same region, as has
also been found in the present study [
]. Other studies had suggested that the detection of a
defocus of the image on the retina is perceived in the retro-equatorial region [21±24]. Since
BM thickness was independent of axial elongation as found in the present study and the
previous investigation on an ethnically different study population, it has been postulated that axial
elongation occurred by a production of new BM in the retro-equatorial region. It could explain
the axial elongation-associated thinning of the retina and decrease in the density of the RPE
cells in that region. It could also explain that the length of BM in the macular region, the
density of the RPE cells at the posterior pole (as also shown in the present study), the macular
retinal thickness, and correspondingly, best corrected visual acuity, were independent of axial
length. The axial elongation-related increase in the optic disc-fovea distance occurred by the
development and enlargement of parapapillary gamma zone without BM [
]. Fitting with the
hypothesis of BM playing a role in axial elongation, a recent experimental study on guinea pigs
with lens-induced myopization showed that an intravitreally applied antibody of amphiregulin
was associated with a dosage-dependent decrease in axial elongation [
]. Amphiregulin is a
member of the epithelial growth factor family, and the RPE has receptors for epidermal growth
factor and amphiregulin [
9 / 12
Fig 7. Scatterplot showing the association between scleral thickness at the posterior pole and axial length in
enucleated human eyes (Equation of the regression line: Scleral thickness at Posterior Pole (μm) = -34.6 x
Axial Length (mm) + 1688).
If the results of the present study are discussed, potential limitations should be taken into
account. First, the measurements were influenced by the post mortem tissue swelling and
fixation induced tissue shrinkage. Since BM does not contain blood vessels and may not show a
marked edema, it might have been unlikely however, that preparation-associated tissue
changes had markedly changed BM thickness. Second, the study material consisted of sagittal
sections through the pupil and the optic nerve, while serial sections of the eyes were not
available. Third, the investigation consisted of eyes with tumors or end-stage glaucoma so that it
has remained unclear whether the results can be transferred onto normal human eyes. Fourth,
the group of eyes with congenital glaucoma was rather small with 5 globes included, so that the
statistical power for analysis of the data of these eyes was limited.
In conclusion, 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/
10 / 12
S1 Datafile. S1 datafile containing microdata of the study.
Conceptualization: Hai Xia Bai, Bin Li, Jost B. Jonas.
Data curation: Hai Xia Bai, Ying Mao, Ling Shen, Xiao Lin Xu, Fei Gao, Zhi Bao Zhang, Bin
Li, Jost B. Jonas.
Formal analysis: Hai Xia Bai, Ying Mao, Ling Shen, Xiao Lin Xu, Fei Gao, Zhi Bao Zhang, Jost
Funding acquisition: Bin Li.
Investigation: Hai Xia Bai, Ying Mao, Ling Shen, Xiao Lin Xu, Fei Gao, Zhi Bao Zhang.
Methodology: Hai Xia Bai, Ying Mao, Ling Shen, Xiao Lin Xu, Fei Gao, Zhi Bao Zhang, Bin
Li, Jost B. Jonas.
Project administration: Hai Xia Bai, Bin Li.
Resources: Bin Li.
Supervision: Bin Li, Jost B. Jonas. Validation: Hai Xia Bai, Ying Mao, Ling Shen, Xiao Lin Xu, Fei Gao, Zhi Bao Zhang, Bin Li, Jost B. Jonas.
Writing ± original draft: Hai Xia Bai, Jost B. Jonas.
Writing ± review & editing: Hai Xia Bai, Ying Mao, Ling Shen, Xiao Lin Xu, Fei Gao, Zhi Bao
Zhang, Bin Li, Jost B. Jonas.
11 / 12
1. Curcio CA , Johnson M . Structure, function and pathology of BruchÂs membrane . In: Ryan SJ , Schachat AP , Wilkinson CP , Hinton DR , Sadda SR , Wiedemann P . Retina 5th edition . Saunders Co., 2012; Chapter 20 .
2. Jonas JB , Ohno-Matsui K , Jiang WJ , Panda-Jonas S. BruchÂs membrane and the mechanism of myopization. A new theory . Retina . 2017 Jan 12 . doi: 10 .1097/IAE.0000000000001464. [Epub ahead of print]. PMID: 28085774
3. Jonas JB , Wang YX , Zhang Q , Liu Y , Xu L , Wei WB . Macular BruchÂs membrane length and axial length . The Beijing Eye Study. PloS One 2015 ; 10 :e0136833. https://doi.org/10.1371/journal.pone. 0136833 PMID: 26317992
4. Shen L , You QS , Xu X , Gao F , Zhang Z , Li B , et al. Scleral and choroidal volume in relation to axial length in infants with retinoblastoma versus adults with malignant melanomas or end-stage glaucoma . Graefes Arch Clin Exp Ophthalmol 2016 ; 254 : 1779 ± 1786 . https://doi.org/10.1007/s00417-016 -3345-7 PMID: 27116210
5. Shen L , You QS , Xu X , Gao F , Zhang Z , Li B , et al. Scleral and choroidal thickness in secondary high axial myopia . Retina 2016 ; 36 : 1579 ± 1585 . https://doi.org/10.1097/IAE.0000000000000947 PMID: 26735565
6. Jonas JB , Holbach L , Panda-Jonas S . Histologic differences between primary high myopia and secondary high myopia due to congenital glaucoma . Acta Ophthalmol 2016 ; 94 : 147 ± 153 . https://doi.org/10. 1111/aos.12937 PMID: 26695106
7. Jonas JB , Xu L , Wei WB , Pan Z , Yang H , Holbach L , et al. Retinal thickness and axial length . Invest Ophthalmol Vis Sci 2016 ; 57 : 1791 ± 1797 . https://doi.org/10.1167/iovs.15-18529 PMID: 27074383
8. Jonas JB , Ohno-Matsui K , Holbach L , Panda-Jonas S . Retinal pigment epithelium cell density in relationship to axial length in human eyes . Acta Ophthalmol 2017 ; 95 :e22± e28 . https://doi.org/10.1111/aos. 13188 PMID: 27545271
9. Jiang WJ , Song HX , Li SY , Guo B , Wu JF , Li GP , et al. Amphiregulin antibody and reduction of axial elongation in experimental myopia . EBioMedicine 2017 ; 17 : 134 ± 144 . https://doi.org/10.1016/j.ebiom. 2017 . 02 .021 PMID: 28256400
10. Jonas JB , Holbach L , Panda-Jonas S. BruchÂs membrane thickness in high myopia . Acta Ophthalmol 2014 ; 92 :e470± 474 . https://doi.org/10.1111/aos.12372 PMID: 24612938
11. Newsome DA , Huh W , Green WR . Bruch's membrane age-related changes vary by region . Curr Eye Res 1987 ; 6 : 1211 ± 1221 . PMID: 3677781
12. Pauleikhoff D , Harper CA , Marshall J , Bird AC . Aging changes in Bruch's membrane: a histochemical and morphological study . Ophthalmology 1990 ; 97 : 171 ± 178 . PMID: 1691475
13. Ramrattan RS , van der Schaft TL , Mooy CM , de Bruijn WC , Mulder PG , de Jong PT. Morphometric analysis of Bruch's membrane, the choriocapillaris, and the choroid in aging . Invest Ophthalmol Vis Sci 1994 ; 35 : 2857 ± 2864 . PMID: 8188481
14. Guymer R , Luthert P , Bird A . Changes in Bruch's membrane and related structures with age . Prog Retin Eye Res 1999 ; 18 : 59 ± 90 . PMID: 9920499
15. Okubo A , Rosa RH Jr, Bunce CV , Alexander RA , Fan JT , Bird AC , et al. The relationships of age changes in retinal pigment epithelium and Bruch's membrane . Invest Ophthalmol Vis Sci 1999 ; 40 : 443 ± 449 . PMID: 9950604
16. Dithmar S , Curcio CA , Le NA , Brown S , Grossniklaus HE , et al. Ultrastructural changes in Bruch's membrane of apolipoprotein E-deficient mice . Invest Ophthalmol Vis Sci 2000 ; 41 : 2035 ± 2042 . PMID: 10892840
17. Chong NH , Keonin J , Luthert PJ , Frennesson CI , Weingeist DM , Wolf RL , et al. Decreased thickness and integrity of the macular elastic layer of Bruch's membrane correspond to the distribution of lesions associated with age-related macular degeneration . Am J Pathol 2005 ; 166 : 241 ± 251 . https://doi.org/10. 1016/S0002- 9440 ( 10 ) 62248 - 1 PMID: 15632016
18. Heine L. BeitraÈge zur Anatomie des myopischen Auges . Arch Augenheilk 1899 ; 38 : 277 ± 290 .
19. Vurgese S , Panda-Jonas S , Jonas JB . Sclera thickness in human globes and its relations to age, axial length and glaucoma . PLoS One 2012 ; 7 : e29692 .
20. Shao L , Xu L , Wei WB , Chen CX , Du KF , Li XP , et al. Visual acuity and subfoveal choroidal thickness . The Beijing Eye Study. Am J Ophthalmol 2014 ; 158 : 702 ± 709 .e1 https://doi.org/10.1016/j.ajo. 2014 . 05 . 023 PMID: 24878308
21. Benavente-PeÂrez A , Nour A , Troilo D. Axial eye growth and refractive error development can be modified by exposing the peripheral retina to relative myopic or hyperopic defocus . Invest Ophthalmol Vis Sci 2014 ; 55 : 6765 ± 6773 . https://doi.org/10.1167/iovs.14-14524 PMID: 25190657
22. Berntsen DA , Barr CD , Mutti DO , Zadnik K. Peripheral defocus and myopia progression in myopic children randomly assigned to wear single vision and progressive addition lenses . Invest Ophthalmol Vis Sci 2013 ; 54 : 5761 ± 5770 . https://doi.org/10.1167/iovs.13-11904 PMID: 23838771
23. Hasebe S , Jun J , Varnas SR . Myopia control with positively aspherized progressive addition lenses: a 2-year, multicenter, randomized, controlled trial . Invest Ophthalmol Vis Sci 2014 ; 55 : 7177 ± 7788 . https://doi.org/10.1167/iovs.12-11462 PMID: 25270192
24. Smith EL 3rd, Hung LF , Huang J , Blasdel TL , Humbird TL , Bockhorst KH . Effects of optical defocus on refractive development in monkeys: evidence for local, regionally selective mechanisms . Invest Ophthalmol Vis Sci 2010 ; 51 : 3864 ± 3873 . https://doi.org/10.1167/iovs.09-4969 PMID: 20220051
25. Jonas RA , Wang YX , Yang H , Li JJ , Xu L , Panda-Jonas S , et al. Optic discÐfovea distance, axial length and parapapillary zones . The Beijing Eye Study 2011 . PloS One 2015 ; 10 :e0138701. https://doi.org/10. 1371/journal.pone. 0138701 PMID: 26390438
26. Yan F , Hui YN , Li YJ , Guo CM , Meng H . Epidermal growth factor receptor in cultured human retinal pigment epithelial cells . Ophthalmologica 2007 ; 221 : 244 ± 250 . https://doi.org/10.1159/000101926 PMID: 17579290