Glaucoma
The Foveal Position Relative to the Optic Disc and the Retinal Nerve Fiber Layer Thickness Profile in Myopia Jin A Choi,1 Jung-Sub Kim,2 Hae-Young Lopilly Park,3 Hana Park,3 and Chan Kee Park3 1
St. Vincent’s Hospital, Department of Ophthalmology, College of Medicine, Catholic University of Korea, Seoul, Republic of Korea B & VIIT Eye Center, Seoul, Republic of Korea 3Seoul St. Mary’s Hospital, Department of Ophthalmology, College of Medicine, Catholic University of Korea, Seoul, Republic of Korea 2
Correspondence: Chan Kee Park, Department of Ophthalmology and Visual Science, Seoul St. Mary’s, Hospital, College of Medicine, Catholic University of Korea, #505 Banpodong, Seocho-ku, Seoul, 137-701, Republic of Korea; [email protected]. Submitted: November 13, 2013 Accepted: January 17, 2014 Citation: Choi JA, Kim J-S, Park H-YL, Park H, Park CK. The foveal position relative to the optic disc and the retinal nerve fiber layer thickness profile in myopia. Invest Ophthalmol Vis Sci. 2014;55:1419–1426. DOI: 10.1167/iovs.13-13604.
PURPOSE. To evaluate retinal nerve fiber layer (RNFL) thickness profiles according to the foveal position relative to the optic disc in myopia METHODS. In 164 eyes of 164 healthy myopic subjects, the disc–foveal angle was defined as the angle between a horizontal line through the disc center and the line connecting the fovea and disc center in fundus photographs overlaid on Cirrus-HD optical coherence tomography (OCT) images. The quadrant/clock-hour based peripapillary RNFL thickness and differences between the inferior and superior (I-S) quadrant RNFL thicknesses were measured with OCT. RNFL thickness profiles were determined according to the disc–foveal angle and axial length (AL). RESULTS. As the disc–foveal angle increased (i.e., the fovea becomes more inferior to the optic disc), the superior RNFL decreased significantly (P ¼ 0.003), whereas the inferior RNFL and IS difference increased (P ¼ 0.010 and P < 0.001, respectively). As the AL increased, the average and temporal RNFLs increased significantly (P ¼ 0.013 and P < 0.001, respectively), and I-S difference was not affected (P ¼ 0.231). The disc–foveal angle was significantly decreased with the distance between the fovea and the optic disc (P ¼ 0.033). In multiple linear regression analysis, the disc–foveal angle was found to be a significant factor related to I-S differences, superior and inferior RNFL (all, P < 0.05) after adjusting for age, disc area, and AL. CONCLUSIONS. The intrinsic foveal position relative to the optic disc was an essential determinant of normal RNFL thickness in myopia. In particular, it was associated with the vertical asymmetry of RNFL distribution. Keywords: disc–foveal angle, retinal nerve fiber layer, RNFL distribution, myopia
K
nowledge of the normal retinal nerve fiber layer (RNFL) thickness profile is important because an evaluation of RNFL thickness is crucial in detecting and following glaucoma patients.1 New imaging devices such as optical coherence tomography (OCT) using Fourier/spectral domain technology enable precise measurements of the RNFL thickness with good sensitivity and specificity for the detection of glaucomatous damage.2 However, considerable variation in the RNFL thickness profile exists in the normal population.3,4 Known factors determining normal RNFL distribution are age, ethnicity, axial length (AL), and optic disc area.5 Another issue is that the fovea is normally positioned below the optic nerve head, which might cause asymmetry in the distribution of the RNFL between the superior and inferior retina.6,7 The fovea is located 6.38 6 3.08 vertically below the optic disc in healthy individuals, and considerable interindividual variation exists in the range of the normal disc–foveal angle.8–11 This anatomical variation in the relative foveal position among individuals is considered one of the sources of variability in the structure-function correspondence in glaucomatous eyes.12,13 In this regard, it is believed that the foveal position relative to the optic disc affects the RNFL distribution. However, the normal RNFL thickness profiles Copyright 2014 The Association for Research in Vision and Ophthalmology, Inc. www.iovs.org j ISSN: 1552-5783
associated with the foveal position relative to the optic disc have not yet been elucidated. Myopia is an increasing public health concern due to its high prevalence and increasing severity, particularly among the Asian population.14 During myopic axial elongation, the posterior sclera undergoes dynamic changes which are reflected in the posterior pole parameters (i.e., optic disc morphology, peripapillary atrophy (PPA), and the position of fovea in relationship to the optic disc), as shown in previous studies.15,16 Therefore, it is important to evaluate the effect of the relative foveal position on RNFL distribution in relationship to the AL because myopia also affects the normal RNFL distribution. Therefore, this study investigated the clinical characteristics and RNFL thickness profiles associated with the intrinsic foveal position relative to the optic disc in a healthy myopic population.
MATERIALS
AND
METHODS
Study Samples The medical records of all consecutive patients with myopia who underwent preoperative examination for refractive 1419
Disc-Foveal Angle and RNFL Thickness surgery (LASIK or surface ablation, including laser epithelial keratomileusis [LASEK], epi-LASIK, or phakic intraocular lens insertion), between September and October, 2012 at the B & VIIT Eye Center, Republic of Korea, patient charts were reviewed retrospectively. This study was performed according to the tenets of the Declaration of Helsinki, and the study protocol was approved by the institutional review/ethics boards of the Catholic University, Seoul St. Mary’s Hospital. All subjects underwent a full ophthalmic examination, which included measuring the visual acuity (VA) and refraction, the intraocular pressure (IOP) using Goldmann applanation tonometry, AL using laser interference biometry (IOL Master; Carl Zeiss Meditec, Dublin, California), a dilated fundus examination, stereodisc photometry, and retinal photography using digital retinal cameras (CR-1 Mark II; Cannon, Tokyo, Japan) after maximum pupil dilatation and standard perimetry (24-2 Swedish interactive threshold algorithm, SAP, Humphrey field analyzer II; Carl Zeiss Meditec) and OCT (Cirrus highdefinition (HD)-OCT; Carl Zeiss Meditec). Inclusion criteria were a healthy optic nerve head without glaucomatous damage (i.e., no disc hemorrhage, thinning, or neural rim notching) and absence of any glaucomatous visual field (VF) defects. A glaucomatous VF change was defined as the consistent presence of a cluster of 3 or more points on the pattern deviation plot with a probability of occurring in
The Foveal Position Relative to the Optic Disc and the Retinal Nerve Fiber Layer Thickness Profile in Myopia Jin A Choi,1 Jung-Sub Kim,2 Hae-Young Lopilly Park,3 Hana Park,3 and Chan Kee Park3 1
St. Vincent’s Hospital, Department of Ophthalmology, College of Medicine, Catholic University of Korea, Seoul, Republic of Korea B & VIIT Eye Center, Seoul, Republic of Korea 3Seoul St. Mary’s Hospital, Department of Ophthalmology, College of Medicine, Catholic University of Korea, Seoul, Republic of Korea 2
Correspondence: Chan Kee Park, Department of Ophthalmology and Visual Science, Seoul St. Mary’s, Hospital, College of Medicine, Catholic University of Korea, #505 Banpodong, Seocho-ku, Seoul, 137-701, Republic of Korea; [email protected]. Submitted: November 13, 2013 Accepted: January 17, 2014 Citation: Choi JA, Kim J-S, Park H-YL, Park H, Park CK. The foveal position relative to the optic disc and the retinal nerve fiber layer thickness profile in myopia. Invest Ophthalmol Vis Sci. 2014;55:1419–1426. DOI: 10.1167/iovs.13-13604.
PURPOSE. To evaluate retinal nerve fiber layer (RNFL) thickness profiles according to the foveal position relative to the optic disc in myopia METHODS. In 164 eyes of 164 healthy myopic subjects, the disc–foveal angle was defined as the angle between a horizontal line through the disc center and the line connecting the fovea and disc center in fundus photographs overlaid on Cirrus-HD optical coherence tomography (OCT) images. The quadrant/clock-hour based peripapillary RNFL thickness and differences between the inferior and superior (I-S) quadrant RNFL thicknesses were measured with OCT. RNFL thickness profiles were determined according to the disc–foveal angle and axial length (AL). RESULTS. As the disc–foveal angle increased (i.e., the fovea becomes more inferior to the optic disc), the superior RNFL decreased significantly (P ¼ 0.003), whereas the inferior RNFL and IS difference increased (P ¼ 0.010 and P < 0.001, respectively). As the AL increased, the average and temporal RNFLs increased significantly (P ¼ 0.013 and P < 0.001, respectively), and I-S difference was not affected (P ¼ 0.231). The disc–foveal angle was significantly decreased with the distance between the fovea and the optic disc (P ¼ 0.033). In multiple linear regression analysis, the disc–foveal angle was found to be a significant factor related to I-S differences, superior and inferior RNFL (all, P < 0.05) after adjusting for age, disc area, and AL. CONCLUSIONS. The intrinsic foveal position relative to the optic disc was an essential determinant of normal RNFL thickness in myopia. In particular, it was associated with the vertical asymmetry of RNFL distribution. Keywords: disc–foveal angle, retinal nerve fiber layer, RNFL distribution, myopia
K
nowledge of the normal retinal nerve fiber layer (RNFL) thickness profile is important because an evaluation of RNFL thickness is crucial in detecting and following glaucoma patients.1 New imaging devices such as optical coherence tomography (OCT) using Fourier/spectral domain technology enable precise measurements of the RNFL thickness with good sensitivity and specificity for the detection of glaucomatous damage.2 However, considerable variation in the RNFL thickness profile exists in the normal population.3,4 Known factors determining normal RNFL distribution are age, ethnicity, axial length (AL), and optic disc area.5 Another issue is that the fovea is normally positioned below the optic nerve head, which might cause asymmetry in the distribution of the RNFL between the superior and inferior retina.6,7 The fovea is located 6.38 6 3.08 vertically below the optic disc in healthy individuals, and considerable interindividual variation exists in the range of the normal disc–foveal angle.8–11 This anatomical variation in the relative foveal position among individuals is considered one of the sources of variability in the structure-function correspondence in glaucomatous eyes.12,13 In this regard, it is believed that the foveal position relative to the optic disc affects the RNFL distribution. However, the normal RNFL thickness profiles Copyright 2014 The Association for Research in Vision and Ophthalmology, Inc. www.iovs.org j ISSN: 1552-5783
associated with the foveal position relative to the optic disc have not yet been elucidated. Myopia is an increasing public health concern due to its high prevalence and increasing severity, particularly among the Asian population.14 During myopic axial elongation, the posterior sclera undergoes dynamic changes which are reflected in the posterior pole parameters (i.e., optic disc morphology, peripapillary atrophy (PPA), and the position of fovea in relationship to the optic disc), as shown in previous studies.15,16 Therefore, it is important to evaluate the effect of the relative foveal position on RNFL distribution in relationship to the AL because myopia also affects the normal RNFL distribution. Therefore, this study investigated the clinical characteristics and RNFL thickness profiles associated with the intrinsic foveal position relative to the optic disc in a healthy myopic population.
MATERIALS
AND
METHODS
Study Samples The medical records of all consecutive patients with myopia who underwent preoperative examination for refractive 1419
Disc-Foveal Angle and RNFL Thickness surgery (LASIK or surface ablation, including laser epithelial keratomileusis [LASEK], epi-LASIK, or phakic intraocular lens insertion), between September and October, 2012 at the B & VIIT Eye Center, Republic of Korea, patient charts were reviewed retrospectively. This study was performed according to the tenets of the Declaration of Helsinki, and the study protocol was approved by the institutional review/ethics boards of the Catholic University, Seoul St. Mary’s Hospital. All subjects underwent a full ophthalmic examination, which included measuring the visual acuity (VA) and refraction, the intraocular pressure (IOP) using Goldmann applanation tonometry, AL using laser interference biometry (IOL Master; Carl Zeiss Meditec, Dublin, California), a dilated fundus examination, stereodisc photometry, and retinal photography using digital retinal cameras (CR-1 Mark II; Cannon, Tokyo, Japan) after maximum pupil dilatation and standard perimetry (24-2 Swedish interactive threshold algorithm, SAP, Humphrey field analyzer II; Carl Zeiss Meditec) and OCT (Cirrus highdefinition (HD)-OCT; Carl Zeiss Meditec). Inclusion criteria were a healthy optic nerve head without glaucomatous damage (i.e., no disc hemorrhage, thinning, or neural rim notching) and absence of any glaucomatous visual field (VF) defects. A glaucomatous VF change was defined as the consistent presence of a cluster of 3 or more points on the pattern deviation plot with a probability of occurring in
