Eye (2013) 27, 410–417 & 2013 Macmillan Publishers Limited All rights reserved 0950-222X/13 www.nature.com/eye CLINICAL STUDY Scleral thickness in M Hayashi, Y Ito, A Takahashi, K Kawano and H Terasaki highly myopic eyes measured by enhanced depth imaging optical coherence tomography Abstract Purpose The purpose of this study was to thickness was the average relative posterior determine the subfoveal scleral thickness in staphyloma height (F ¼ 16.0, Po0.001). The highly myopic eyes by enhanced depth scleral thickness was not significantly imaging spectral-domain optical coherence different between eyes with and without tomography (EDI-OCT) and to identify the myopic retinochoroidal pathologies (P40.05). ocular parameters significantly associated Conclusion Posterior staphyloma formation with the scleral thickness. was a key factor associated with a posterior Methods The subfoveal scleral thickness of scleral thinning in highly myopic eyes. myopic eyes (Z À 8 diopters (D) or axial Eye (2013) 27, 410–417; doi:10.1038/eye.2012.289; length Z26.5 mm) was examined by EDI- published online 11 January 2013 OCT. The correlations between the thickness and the best-corrected visual acuity (BCVA), Keywords: scleral thickness; high myopia; refractive error, axial length (AL), the optical coherence tomography (OCT); posterior Department of subfoveal retinal thickness, choroidal staphyloma; myopic complication Ophthalmology, Nagoya thickness, and posterior staphyloma height University Graduate School of Medicine, Showa-ku, 2 mm from the fovea were investigated. Nagoya, Japan Results A total of 75 eyes of 54 patients Introduction (21 men, 33 women; mean age, 62.3±11.3 Myopia is prevalent worldwide,1–7 especially Correspondence: years; mean AL, 30.2±1.68 mm) were studied. among Asians.8,9 This is important because eyes Y Ito, Department of Eighteen eyes had no pathological Ophthalmology, Nagoya with high myopia develop pathological myopia, retinochoroidal lesions, and 57 eyes had University Graduate School which is a major cause of secondary retinochoroidal lesion, that is, myopic schisis, of Medicine, 65 Tsuruma- blindness.10–13 The visual impairments are cho, Showa-ku, Nagoya choroidal neovascularization, and other caused by pathological changes of the retina 466-8550, Japan retinochoroidal pathologies. The mean Tel: þ 81 52 744 2275; and choroid that frequently develop in eyes subfoveal scleral thickness was Fax: þ 81 52 744 2278. with high myopia. In addition to the 284.0±70.4 lm, and the thickness was E-mail: yasu@med. retinochoroidal changes, it has been shown that nagoya-u.ac.jp significantly correlated negatively with the the sclera is thinner with a loss of tissue, and the absolute value of the nasal and overall scleral thinning is accompanied by a narrowing Received: 1 October 2012 average posterior staphyloma height (Po0.05 Accepted in revised form: and dissociation of the collagen fiber bundles and P 0.01, respectively). The subfoveal 30 November 2012 o and a reduction in the diameter of the collagen Published online: 11 January scleral thickness was also significantly fibrils in mammalian myopia models14–16 and 2013 correlated negatively with the relative value human myopic eyes.17,18 of the superior, nasal, and overall average There have been several suggestions for the This work was presented at posterior staphyloma height (Po0.05, cause of the scleral thinning, for example, a the 50th annual meeting of P 0.01, and P 0.001, respectively). Stepwise Japanese Retina and o o downregulation of the production of certain 19,20 Vitreous Society at Tokyo analyses showed that the factor most extracellular matrix components, a Japan on 3 December 2011 significantly associated with the scleral downregulation of glycosaminoglycan16,21 and Scleral thickness in highly myopic eyes measured by OCT M Hayashi et al 411 proteoglycan syntheses,22,23 a degradation of collagen Data analyses enzymes such as MMP-2,24,25 FGF-2,26 and We obtained six radial scans that were centered on the TGF-b,19,20,27 acting as retinoscleral signaling. However, fovea within a 5 Â 301 (73 eyes) or 5 Â 201 (2 eyes) the precise mechanisms causing the scleral changes rectangle to encompass the macula with the Spectralis have not been definitively determined. HRA þ OCT (version 5.1, then later version 5.3; With the advancement of optical coherence Heidelberg Engineering) using the enhanced depth tomography (OCT), many studies on the morphology imaging technique. To perform EDI-OCT, the OCT device of the choroid have been published in the past 4 was positioned close to the eye to obtain an inverted years.28–37 In our earlier study on the choroid of highly image,28 and a more recent EDI procedure that is built myopic eyes, we detected a thinner sclera by spectral- into the Heidelberg software was selected at the domain OCT because both the retina and choroid were beginning of the scanning procedure. A total of 100 very thin.38 This meant that we should be able to images were averaged to improve the signal-to-noise investigate the morphology of the sclera in highly ratio. myopic eyes. A posterior staphyloma led to a tilting of the scleral Thus, the purpose of this study was to measure the OCT images in many eyes. Therefore, we selected the one scleral thickness at the fovea using enhanced depth scan out of the six radial scans that was most imaging spectral-domain optical coherence tomography perpendicular to the sclera to measure the subfoveal (EDI-OCT) in highly myopic eyes and to examine ocular scleral thickness. The scleral thickness was measured parameters correlated with the thickness. using the caliper tool in the OCT software, and the thickness was measured from the outer scleral border to the choroid/sclera interface in eyes whose outer scleral Materials and methods border could be clearly distinguished from the fat tissue We reviewed the medical records of patients with high in the retrobulbar orbit (Figure 1). myopia who were examined in the Department of The height or depth of the posterior staphyloma was Ophthalmology of the Nagoya University Hospital. also measured in the superior, inferior, nasal, and These eyes were the fellow eyes or eyes that had myopic temporal quadrants as reported.32,34 Briefly, the posterior pathologies. The definition of high myopia was a staphyloma height was measured as the horizontal refractive error Z À 8.0 diopters (D) or an axial length distance from the subfoveal retinal pigment epithelium (AL) Z26.5 mm. Eyes with media opacities such as dense (RPE) to the RPE 2 mm from the fovea in the four cataracts that prevented light from penetrating the media quadrants. The absolute and relative heights of the were excluded. None of the patients had undergone staphyloma were calculated and the relative height was refractive surgery. recorded as a negative value and the absolute height was recorded as a positive value in eyes where the peripheral RPE was located posterior to the subfoveal RPE Examinations (Figure 2). The choroidal and retinal thicknesses at the fovea were The clinical examinations to diagnose pathologic also measured in the same image. However, the retinal myopia included measurement of the best-corrected thickness was measured only in eyes without visual acuity (BCVA), AL by partial coherence retinochoroidal lesions, for example, mCNV or interferometry (IOL Master; Carl Zeiss Meditec, Dublin, retinoschisis, which made the retina and choroid too CA, USA), refractive error (spherical equivalent) by an thick to measure. The choroidal thickness was measured autorefractometer (Topcon, Tokyo, Japan), slit-lamp from the outer border of the hyperreflective line biomicroscopy with or without contact lens, and indirect corresponding to the RPE to the inner sclera border. Eyes ophthalmoscopy. The BCVA was measured with a with a CNV were not measured. Japanese standard decimal visual acuity chart, and the The measurements obtained from the OCT images decimal VAs were converted to the logarithm of the were performed by an experienced ophthalmologist minimum angle of resolution (logMAR) units for (MH) who was masked to the other parameters of statistical analyses. Fundus color photographs and OCT the eye. images were taken of all eyes. Digital fluorescein angiography (FA) and indocyanine green angiography (ICGA; HRA2, version2.0; Heidelberg Engineering, Statement of ethics Heidelberg, Germany) were performed in eyes with a subretinal hemorrhage or suspicious choroidal The protocol for this retrospective study was approved neovascularization (CNV). by the institutional review board of Nagoya University Eye Scleral thickness in highly myopic eyes measured by OCT M Hayashi et al 412 Figure 1 Fundus photographs and optical coherence tomographic findings in a highly myopic eye. (a) Fundus photograph of the right eye of a 57-year-old man. This eye was phakic and the refraction was À 18.5 diopters. The axial length was 32.24 mm. (b) Six radial enhanced depth imaging optical coherence tomography images. The outer scleral border can be clearly seen. Top of the images was most perpendicular to the sclera, and the subfoveal scleral thickness is 278 mm. School of Medicine, and the procedures used conformed Statistical analyses to the tenets of the Declaration of Helsinki. Statistical analyses were performed with one-way analysis of variance (ANOVA), analysis of covariance Reproducibility of scleral thickness measurements (ANCOVA), single regression analysis, and stepwise To evaluate the reproducibility of the technique, three of regression analysis (PASW statistics version 18.0; SPSS the authors (MH, AT, and KK) independently measured Inc. and IBM Company, Chicago, IL, USA). The the scleral thickness of 30 eyes selected at random. In comparison of the subfoveal scleral thickness among the addition, one of the authors (MH) who obtained all groups of eyes with and without retinochoroidal lesions measurements from the OCT images measured the was performed by ANCOVA after adjustments were scleral thickness of 30 eyes 3 times at more than 1-month made for the differences in the age of the patients.