Downloaded from http://bjo.bmj.com/ on August 30, 2016 - Published by group.bmj.com Clinical science The height of the posterior staphyloma and corneal hysteresis is associated with the scleral thickness at the staphyloma region in highly myopic normal-tension glaucoma eyes Jong Hyuk Park,1 Kyu-Ryong Choi,2 Chan Yun Kim,1 Sung Soo Kim1 1Department of Ophthalmology, ABSTRACT optic nerve head (ONH) in eyes with high – Institute of Vision Research, Aims To evaluate the characteristics of the posterior myopia.8 10 Yonsei University College of Medicine, Seoul, Republic of segments of eyes with high myopia and normal-tension Recent studies have demonstrated the importance Korea glaucoma (NTG) and identify which ocular factors are of the posterior ocular structures such as the lamina 2Department of Ophthalmology most associated with scleral thickness and posterior cribrosa and sclera in the pathogenesis of glau- – and Institute of Ophthalmology staphyloma height. coma.8 10 The mechanical influence of the peripa- & Optometry, Ewha Womans Methods The study included 45 patients with highly pillary sclera on the lamina cribrosa is considered University School of Medicine, Seoul, Republic of Korea myopic NTG and 38 controls with highly myopic eyes to be important in that scleral deformations affect (≤−6D or axial length ≥26.0 mm). The subfoveal the stiffness and thickness of the sclera and affect Correspondence to retinal, choroidal, scleral thickness and the posterior the ONH biomechanics by exacerbating strain and Professor Sung Soo Kim, staphyloma heights were examined from enhanced depth stress.11 The increased risk of glaucoma in myopic Department of Ophthalmology, College of Medicine, Yonsei imaging spectral-domain optical coherence tomography eyes may be related in part to the mechanical prop- University, 134 Sinchon-dong, and compared between two groups. erties of the sclera. There have been several Seodaemun-gu, Results Highly myopic NTG eyes had thinner subfoveal hypotheses regarding scleral remodelling mechan- Seoul 120-752, Korea; scleral thickness (473.03±43.75 vs 579.46±75.87 mm, isms including narrowing and dissociation of [email protected] p<0.001) and higher posterior staphyloma (97.80 collagen fibres or downregulation of certain extra- m Received 9 June 2015 ±70.10 vs 62.83±32.01 m, p=0.027) than highly cellular matrix components constituting the 12 13 Revised 29 October 2015 myopic, non-glaucomatous eyes. Subfoveal scleral sclera. However, few studies have investigated Accepted 1 November 2015 thickness was significantly correlated with age, axial the association between scleral mechanical changes Published Online First length, corneal hysteresis and the posterior staphyloma and the increased risk of glaucoma in highly 11 December 2015 height of the superior quadrant, the nasal quadrant and myopic eyes. the arithmetic mean of four quadrants in highly myopic Posterior staphyloma is a protrusion of the pos- NTG eyes. Corneal hysteresis (β=2.694, p=0.015), terior shell of the globe, which is considered to be corneal resistance factor (β=−2.916, p=0.010) and the a hallmark of high myopia. The scleral shell of posterior staphyloma height of the nasal quadrant highly myopic eyes has increased elasticity and a (β=−0.463, p=0.017) were significantly associated with tendency to expand. Recent reports showed that the subfoveal scleral thickness in highly myopic NTG eyes. there is a significant difference in subfoveal scleral Conclusion Subfoveal scleral thinning and non-uniform thickness depending on the presence of posterior posterior staphyloma were closely related in highly myopic staphyloma, and the sclera at the posterior pole in NTG eyes. Corneal hysteresis, corneal resistance factor and highly myopic eyes might stretch inhomogen- the nasal posterior staphyloma height were associated eously.14 Mechanical stretching nasally and super- with the scleral thickness. iorly around the fovea most significantly influences subfoveal scleral thinning, and staphyloma in this area may be associated with axial elongation.15 Thus, posterior staphyloma formation is recognised INTRODUCTION as an important risk factor for high myopia-related High myopia is one of the leading causes of visual diseases. disturbance in the world. Asian countries have Therefore, the aim of this study is to evaluate the higher prevalence of severe myopia (≤−6D), which characteristics of the posterior segments of eyes is reported to be 5.5% in Japan,1 3.6% in with high myopia and normal-tension glaucoma Singapore,2 2.8% in China3 and 2.3% in Korea,4 (NTG) and identify which ocular factors are most but it is estimated that 1% of the global population associated with scleral thickness and posterior sta- exhibits high myopia.5 High myopia is associated phyloma height. with an axial elongation of the globe, leading to the stretching and thinning of the posterior ocular PATIENTS AND METHODS tissues and further pathological changes.6 This retrospective study was approved by the Pathological study show that highly myopic eyes Institutional Review Board (IRB) of Ewha Womans have a significantly thinner retina, choroid and University Mokdong Hospital, Seoul, Korea, and 7 To cite: Park JH, Choi K-R, sclera than age-matched controls without myopia. was conducted in accordance with the tenets of the Kim CY, et al. Br J Structural changes in posterior ocular tissues are Declaration of Helsinki. This study investigated 45 Ophthalmol considered to be the foundation of the visual adults with NTG and high myopia and 38 controls – 2016;100:1251 1256. impairments and the glaucomatous changes in the with high myopia. Participants were recruited from Park JH, et al. Br J Ophthalmol 2016;100:1251–1256. doi:10.1136/bjophthalmol-2015-307292 1251 Downloaded from http://bjo.bmj.com/ on August 30, 2016 - Published by group.bmj.com Clinical science Ewha Womans University Mokdong Hospital between October Measurement of posterior ocular tissues thickness 2013 and March 2014. The inclusion criteria were (1) phakic Retinal, choroidal and scleral thicknesses were measured at highly myopic eyes, defined as a spherical equivalent refractive the fovea. Two independent observers ( JHP, So-Yeon Kim) error less than −6.0 D or an axial length longer than 26.0 mm; used the calliper function of the built-in optical coherence (2) no posterior abnormalities such as choroidal neovascularisa- tomography (OCT) software to make the measurement in a tion, macular schisis, macular hole, retinal detachment and (3) blind fashion. Retinal thickness was defined as the vertical best-corrected visual acuity (BCVA) better than 20/40. The distance from the retinal pigment epithelium (RPE) (the exclusion criteria were (1) eyes with media opacities such as outermost hyper-reflective line at the retina–choroidal inter- dense cataracts that prevent detailed fundus observation; (2) face) to the retinal surface. Choroidal thickness was defined aphakic or pseudophakic eyes; (3) eyes with axial lengths longer as the vertical distance from the RPE line to the hyper- than 30.0 mm and (4) eyes undergoing refractive surgery. After reflective line behind the large vessel layers of the choroid, ophthalmic evaluation, the right eye was selected for inclusion which was presumed to be the choroid–sclera interface. Both in cases in which both eyes of the patient were eligible for the retinal and choroidal thicknesses were measured in the hori- study. zontal and vertical sections running through the centre of the NTG was defined as the presence of glaucomatous optic disc fovea, and the arithmetic mean of both two measurements damage, abnormal visual field (VF) test results and intraocular was used in this study. Scleral thickness was defined as the dis- pressure (IOP) ≤21 mm Hg without topical medical treatment. tance from the choroid–sclera interface to the outer scleral Signs of glaucomatous optic disc damage were as follows: border and was measured in eyes whose outer scleral border diffuse or localised neuroretinal rim loss, excavation and/or could be clearly distinguished from fat tissues in the retinal nerve fibre layer (RNFL) defects. An abnormal VF was retro-ocular structures. Subfoveal scleral thickness was defined as a pattern SD outside of the 95% normal confidence defined as the average of three measurements—from the sub- limits or a Glaucoma Hemifield Test result outside normal foveal point and 1000 mm temporal and 1000 mm nasal from limits. At least two consecutive abnormal VF examinations were the subfoveal point. All measurements were performed per- required, with the most recent test performed within 12 months pendicular to the RPE line. of enrolment. The control group was defined as those having IOP ≤21 mm Hg, with no history of increased IOP, the absence of glaucomatous disc appearance and normal VF results. Measurement of the posterior staphyloma height The presence and location of posterior staphyloma was deter- mined by stereoscopic fundus examination using binocular indir- ect ophthalmoscopy. Selection of posterior staphyloma was Examinations performed in eyes with type II staphyloma (classification by The clinical examinations included measurement of BCVA, Curtin16), which involves the macular region, and in eyes in slit-lamp biomicroscopy with or without contact lens, which the curvature of the inner scleral surface was symmetric- Goldmann applanation tonometry, refractive error (spherical ally centred on the fovea in enhanced depth imaging OCT equivalent) by an autorefractometer (Topcon, Tokyo, Japan), (EDI-OCT) images. We excluded