Spark ImageWise 29 – Glaucoma

The Hidden Gamma Zone

Dr Shreya Jaiswal, Dr Sarang Lambat, Dr Prabhat Nangia, Dr Vinay Nangia 
Suraj Eye Institute, 559 New Colony, Nagpur 

Case Description
A female 48 years of age came for a regular examination. Her best corrected visual acuity was 6/6, N6 in both eyes. Autorefractometer reading showed a value of -12.25 DS +2.50 DC at 5 degrees in the right eye and -5.00 DS +0.75 DC at 5 degrees in the left eye. Her intraocular pressure was 16 mmHg in both eye. Her axial length of right eye was 26.14 mm and left eye was 24.31 mm. Central corneal thickness was 518 microns in right eye and 488 microns in the left eye. 

Figure 1 shows colour fundus photograph of left eye with presence of a healthy disc with well defined margins (yellow arrowhead) and a vertical cup to disc ratio of 0.3:1 and choroidal tessellations around the disc. The macula appears healthy. 
Figure 2 shows infrared image of the same eye where presence of a tilted disc is seen with presence of a parapapillary atrophy inferonasally (red arrowheads). The disc margin is denoted by the red dot. 
Figure 3 shows photograph of an SD-OCT with line scan passing through the disc, where we can see presence of a Gamma zone (area between the edge of the Bruch’s membrane (yellow arrow head) ending and the margin of the optic disc (red arrowhead).

Discussion

The gamma zone ( which is the space and area between the Bruch’s membrane margin and the margin of the optic disc) starts developing at different ages in different individuals with  different axial lengths. Multiple parameters in the growth of the axial length may be involved, as well as the interplay of the peripapillary tissues. In early stages, on clinical examination of the optic disc and or on the colour photograph, it is often difficult to identify the presence of the gamma zone and its margin may often appear to be the clinical margin of the optic disc.  When the gamma zone becomes more evolved with hyper reflectivity of the  sclera and development of the scleral flange it also becomes more easily identifiable on the colour photo. However on the infrared image, an early gamma zone is seen easily and of course on the EDI image of the optic disc. Gamma zone is known to be associated with moderate and high myopia and longer axial length. Presence of gamma zone has implications in clinical assessment of the optic disc  in glaucoma, because the origin of the blood vessels, the shape of the cup and the neuroretinal rim and the intraoptic disc morphometric correlations are  significantly altered. In addition  the presence of a gamma zone  has a correlation also with  reduced vision in myopes. 

ReadWise

  1. Jonas JB, Jonas SB, Jonas RA, Holbach L, Dai Y, Sun X, Panda-Jonas S. Parapapillary atrophy: histological gamma zone and delta zone. PloS one. 2012 Oct 18;7(10):e47237. DOI – https://doi.org/10.1371/journal.pone.0047237
  2. Guo Y, Liu LJ, Tang P, Feng Y, Lv YY, Wu M, Xu L, Jonas JB. Parapapillary gamma zone and progression of myopia in school children: The Beijing Children Eye Study. Investigative ophthalmology & visual science. 2018 Mar 1;59(3):1609-16.DOI:https://doi.org/10.1167/iovs.17-21665
  3. Kim HR, Weinreb RN, Zangwill LM, Suh MH. Characteristics of focal gamma zone parapapillary atrophy. Investigative ophthalmology & visual science. 2020 Mar 9;61(3):17-. DOI:https://doi.org/10.1167/iovs.61.3.17
  4. Jonas JB, Ohno-Matsui K, Spaide RF, Holbach L, Panda-Jonas S. Macular Bruch’s membrane defects and axial length: association with gamma zone and delta zone in peripapillary region. Investigative ophthalmology & visual science. 2013 Feb 1;54(2):1295-302. DOI :https://doi.org/10.1167/iovs.12-11352

Correspondence 

Dr Vinay Nangia
MS, FRCS, FRCOphth
Director 
Suraj Eye Institute
Nagpur
Email –education@surajeye.org

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