https://doi.org/10.1167/tvst.8.1.22 Article Interocular Symmetry of Fixation, Optic Disc, and Corneal Astigmatism in Bilateral High Myopia: The Shanghai High Myopia Study Xiangjia Zhu1,*, Wenwen He2,*,YuDu3, Keke Zhang4, and Yi Lu5 1 Department of Ophthalmology, Eye and Ear, Nose, and Throat Hospital, Funan University, Shanghai, China 2 Eye Institute, Eye and Ear, Nose, and Throat Hospital of Fudan University, 83 Fenyang Road, Shanghai, People’s Republic of China 3 NHC Key Laboratory of Myopia, Fudan University, 83 Fenyang Road, Shanghai, People’s Republic of China 4 Key Laboratory of Myopia, Chinese Academy of Medical Sciences, 83 Fenyang Road, Shanghai, People’s Republic of China 5 Shanghai Key Laboratory of Visual Impairment and Restoration, Shanghai, People’s Republic of China Correspondence: Yi Lu, Eye Insti- Purpose: We investigate the interocular symmetry of fixation, optic disc, and corneal tute, Eye and Ear, Nose, and Throat astigmatism in bilateral high myopia, and evaluate the predictive relationships Hospital, Fudan University, 83 Fe- between them. nyang Rd, Shanghai 200031, Peo- ple’s Republic of China. e-mail: Methods: We enrolled 202 cases with bilateral high myopia. Fixation, in terms of the [email protected] bivariate contour ellipse area (BCEA), was evaluated with the Macular Integrity Assessment microperimetry. Optic disc features, including orientation, tilt, and Received: 10 August 2018 rotation, were evaluated with ultrawide-field retinal photographs. Corneal topography Accepted: 12 December 2018 was performed with Pentacam. Interocular symmetry of fixation, optic disc, and Published: 13 February 2019 corneal astigmatism was assessed, and the predictive relationships between these Keywords: high myopia; interocu- parameters were investigated. lar symmetry; fixation; optic disc; Results: Axial length differences between the two eyes were: 0to 1 mm, 67.8%; 1 corneal astigmatism to 2 mm, 20.3%; 2 to 3 mm, 9.4%; and .3 mm, 2.5%. Axial length, 95% BCEA, and Citation: Zhu X, He W, Du Y, Zhang magnitude of corneal astigmatism showed good interocular symmetry, whereas the K, Lu Y. Interocular symmetry of optic disc tilt, rotation, and axis of corneal astigmatism (mirror axes) showed less fixation, optic disc, and corneal symmetry (all P , 0.05). No interocular symmetry was observed in the direction of the astigmatism in bilateral high myo- fixation ellipse. In both eyes, the corneal steep meridian more often was consistent pia: the Shanghai High Myopia with the optic disc orientation than inconsistent (right eye [OD], P , 0.001; left eye Study. Trans Vis Sci Tech. 2019;8(1): [OS], P ¼ 0.029). 22, https://doi.org/10.1167/ tvst.8.1.22 Conclusions: As different parameters presented different degrees of symmetry, Copyright 2019 The Authors cautions are needed when including both eyes or only one lateral eye in cases of bilateral high myopia for clinical investigations. The optic disc orientation, to some extent, may indicate the steep meridian of the cornea. Translational Relevance: Our study provided evidences for selection of eye laterality in clinical investigations of highly myopic eyes. Several studies have investigated variations in Introduction optic disc features, such as tilt, rotation, and para- papillary atrophy, in highly myopic eyes.2,6–9 Most High myopia is a major worldwide concern today, have been focused on the relationships between the 1–3 especially in East Asia. With elongation of the morphologic changes in the optic disc and the risk of eyeball, mechanical stretching of the posterior pole glaucoma.7,9 Similar to the optic disc, corneas of may cause degenerative changes in the retina and highly myopic eyes also show great interindividual variations in the position and shape of the optic disc, variability in their shapes and biomechanical fea- which consequently lead to functional changes in tures.10,11 highly myopic eyes.2,4,5 Previously, we identified an axial length–dependent 1 TVST j 2019 j Vol. 8 j No. 1 j Article 22 This work is licensed under a Creative Commons Attribution 4.0 International License. Downloaded from tvst.arvojournals.org on 09/30/2021 Zhu et al. reduction in fixation stability of highly myopic eyes and postoperative follow-ups. This investigation is a using the Macular Integrity Assessment (MAIA) subproject of the Shanghai High Myopia Study. microperimetry system (Centervue, Padova, Italy).12 Individuals with bilateral axial lengths .26 mm were The bivariate contour ellipse area (BCEA), which selected for this study; excluded were those whose eyes represents the area of the ellipse containing most of the had severe myopic fundus pathologies, such as fixation positions registered during the measurement choroidal neovascularization, macular hole, or severe procedure, was used to evaluate fixation stability.12,13 macular atrophy, a history of other anterior segment We also noted that the fixation ellipse angle, defined as ocular diseases, trauma, or a systemic condition that the orientation of the longest fixation ellipse diameter, affected their visual performance. Ultimately, 202 varied even more greatly in these eyes. subjects were eligible for this study. The institutional Such great variations in these anatomical or review board of the EENT Hospital of Fudan functional parameters of highly myopic eyes may University approved the study protocol. All proce- inevitably increase the interocular asymmetry in dures were performed in accordance with the tenets of patients with bilateral high myopia. We normally the Declaration of Helsinki. All participants were expect eyes and visual systems to behave somewhat informed of the study objectives, and each signed an symmetrically, and accordingly, we include both eyes informed consent form to participate in this study. of patients for many clinical investigations. However, This study was registered at www.clinicaltrials.gov this may not be correct, especially in highly myopic (accession number NCT03062085). eyes, which show great structural viability due to abnormal elongation of the eyeballs. Studies have Preoperative and Postoperative reported a consistent pattern of asymmetry between Examinations our eyes. The Sydney Childhood Eye Study found only a low level of interocular correlation in the Preoperative examinations included assessment of thickness of the retinal nerve fiber layer (RNFL), with visual acuity, tonometry, measurement of axial length differences of up to 17 lm between the two eyes of (IOLMaster 500, Version 7.7; Carl Zeiss AG, Jena, normal children.14 A study of healthy adults also Germany), funduscopy, B scans, and macular scans confirmed that the RNFL is thicker in right eyes.15 with optical coherence tomography (OCT; Zeiss Thus, it also may be meaningful to investigate the Cirrus HD-OCT 5000; Carl Zeiss AG). Corneal interocular asymmetry of anatomical or functional topography was performed with the Pentacam system parameters, such as fixation, optic disc, and corneal (Pentacam HR, Oculus Optikgera¨te GmbH, Wetzlar, astigmatism, in bilateral highly myopic cases. Germany), and the steep meridian of the anterior Additionally, we assume that if the eyeball is an corneal astigmatism was recorded. Follow-up includ- ideal optical system, certain kinds of predictive ed assessment of visual acuity, manifest refraction, relationships may exist between the cornea astigmatism tonometry, funduscopy, retinal photography, MAIA median and optic disc orientation or the direction of microperimetry, and an OCT macular scan. the macular fixation ellipse, to maintain the coordina- tion of eye function. A previous study showed that an Fixation Assessment abnormally shaped optic disc can be correlated with Fixation was assessed using the MAIA micro- abnormal corneal astigmatism and that the steep perimetry system. The patients were asked to stare at meridian of corneal astigmatism may reflect the the fixation stimulus, which consisted of a red circle 10 orientation of the longest disc diameter. Therefore, with a diameter of 18. The eye trackers within the we also investigated the predictive relationships MAIA system detected fixation loss as a misalign- between fixation, optic disc, and corneal astigmatism. ment of the directions of the central fixation stimulus and gaze, and recorded the points of fixation. The Methods device then automatically calculated two parameters of fixation: the BCEA, which refers to the area (in The Shanghai High Myopia Study is a hospital- degrees squared, deg2) of the ellipse containing most based prospective cohort study that continuously of the fixation positions registered during the includes highly myopic patients scheduled for cataract measurement procedure, and the fixation ellipse surgery in the Eye and Ear, Nose, and Throat (EENT) angle, the orientation of the longest ellipse diameter. Hospital of Fudan University since October 2015. All BCEA normally is calculated by considering 63% or subjects underwent detailed preoperative examinations 95% of the fixation points. Because these two 2 TVST j 2019 j Vol. 8 j No. 1 j Article 22 Downloaded from tvst.arvojournals.org on 09/30/2021 Zhu et al. Figure 1. Flow chart of the study. AL, axial length. parameters are similar, only 95% BCEA was used for angle and steep meridian of corneal astigmatism. further analysis in this study. Figure 1 displays the flow chart of the study. Measurements of Optic Disc Tilt and Statistical Analysis Rotation The agreement between two observers on the optic Ultrawide-field retinal images were obtained with a disc orientation,