Gamma Zone of Myopia
Dr. Swati Mishra, Dr. Sarang Lambat, Dr. Vinay Nangia
Suraj Eye Institute, Nagpur, India
Introduction :
Using the EDI-OCT technology, recent clinical studies have demonstrated that in some medium myopic eyes, the end of Bruch’s membrane did not touch the optic disc border.(1) This region without Bruch’s membrane is called the gamma zone. It is characterized by the absence of Bruch’s membrane, retinal pigment epithelium, deep retinal layers, choriocapillaris, and Sattler’s layer of medium-sized choroidal vessels. (2)
Recent histological investigations revealed, that this peripapillary region showed an additional feature a markedly elongated and thinned peripapillary scleral flange and a widening of the peripapillary orbital cerebrospinal fluid space.(3)
Case details
A boy, 9 years of age, came for glass prescription. His Best corrected visual acuity (BCVA) was 6/9 in both eyes with a correction of -8.50 (DS) in right eye (RE) and -7.00 (DS) in left eye (LE). Anterior segment examination was normal. Posterior segment examination showed minimal peripapillary tessellation with gamma zone. His axial length was 25.74 mm and 25.44 mm in RE and LE respectively.
Discussion
Multiple studies agree that there is an association between the axial length and width of gamma zone.(3,4,5) However, the size of gamma zone significantly increased with axial length in a nonlinear manner.On its outer border, the gamma zone is in contact either with the peripapillary beta zone, if a beta zone is present, or with the peripapillary alpha zone. (3)
Gamma zone is also associated with more marked optic disc rotation around the vertical axis and around the horizontal axis, longer horizontal optic disc diameter, longer disc–fovea distance, higher degree of fundus tessellation , and thinner subfoveal choroidal thickness.(4) It has been observed that there is a correlation between development of PPA and progressive tilting of the optic disc in children with myopic shift, demonstrating that PPA might be caused by globe elongation. Hence increase in the width of PPA in this boy could indicate an increase in axial length and progressive myopia, underlying the need for regular retinal evaluation.
References :
1.Na JH Moon BG Sung KR Lee Y Kook MS.. Characterization of peripapillary atrophy using spectral domain optical coherence tomography. Korean J Ophthalmol . 2010; 24: 353–359 DOI: 10.3341/kjo.2010.24.6.353
2.Jonas JB, Ohno-Matsui K, Spaide RF, et al. Macular Bruch’s membrane defects and axial length: association with gamma zone and delta zone in parapapillary region. Invest Ophthalmol Vis Sci. 2013; 54: 1295–1302 DOI: 10.1167/iovs.12-11352
3.Yin Guo; Li Juan Liu; Ping Tang; Yi Feng; Yan Yun Lv; Min Wu; Liang Xu; Jost B. Jonas: Parapapillary Gamma Zone and Progression of Myopia in School Children: The Beijing Children Eye Study. Investigative Ophthalmology & Visual Science March 2018, Vol.59, 1609-1616. DOI: 10.1167/iovs.17-21665
4.Jost B. Jonas, Shefali B. Jonas, Rahul A. Jonas, Leonhard Holbach, Yi Dai, Xinghuai Sun, and Songhomitra Panda-Jonas: Parapapillary Atrophy: Histological Gamma Zone and Delta Zone. PLoS ONE 7(10): e47237. DOI: 10.1371/journal.pone.0047237
5.Jost B. Jonas; Ya Xing Wang; Qi Zhang; Yuan Yuan Fan; Liang Xu, Wen Bin Wei; Rahul A. Jonas: Parapapillary Gamma Zone and Axial Elongation–Associated Optic Disc Rotation: The Beijing Eye Study. Investigative Ophthalmology & Visual Science February 2016, Vol.57, 396-402. DOI: 10.1167/iovs.15-18263