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Editors Selection IGR 17-4
Clinical Examination Methods: OCT: Early Glaucoma Detection
Comment by Jin Wook Jeoung on:
74140 Vertical Macular Asymmetry Measures Derived From SD-OCT for Detection of Early Glaucoma, Sharifipour F; Morales E; Lee JW et al., Investigative Ophthalmology and Visual Science, 2017; 58: 4310–4317
The distribution of retinal ganglion cell axons and cell bodies is highly symmetric between the superior and inferior hemi-field of the retina in normal eyes.1 It is well known that glaucomatous visual field loss is commonly asymmetric across the horizontal meridian.2, 3 Likewise, glaucomatous changes of the retinal layers are often asymmetric between the upper and lower hemifields, especially in the early stages of glaucoma.4
Sharifipour et al.5 tested the hypothesis that biomarkers of vertical macular thickness asymmetry based on ganglion cell-inner plexiform layer (GCIPL) measurements can improve discrimination of early glaucoma from normal subjects. This study demonstrated that macular vertical thickness asymmetry measures did not perform better than sectoral or minimum GCIPL thickness for detection of early glaucoma. A combination of sectoral GCIPL thickness and the best local vertical asymmetry parameter significantly improved the diagnostic performance of macular images.
The asymmetry analysis in this study was based on the following assumptions: 1) inter-hemispheric anatomic symmetry is preserved in normal healthy eye; 2) glaucoma often shows asymmetric features at initial diagnosis and during progression. From this background, the authors propose a novel and simple index, termed as 'asymmetry index', for quantitative evaluation of vertical macular asymmetry.
Some points need to be considered when interpreting the results of this study. First, temporal raphe varies among individuals, which highlights the importance of customized algorithm to increase its glaucoma diagnostic performance and clinical utility. Second, considering the current macular OCT images were not precisely designed to measure vertical asymmetry across the horizontal raphe, further studies would be needed using higher resolution OCT images and automated algorithms for measuring global and local macular asymmetry. It would be interesting to know if further examinations including various stages of glaucoma can make the present data more relevant.
References
- Asrani S, Rosdahl JA, Allingham RR. Novel software strategy for glaucoma diagnosis: asymmetry analysis of retinal thickness. Arch Ophthalmol 2011;129(9):1205-11.
- Duggan C, Sommer A, Auer C, Burkhard K. Automated differential threshold perimetry for detecting glaucomatous visual field loss. Am J Ophthalmol 1985;100(3):420-3.
- Asman P, Heijl A. Glaucoma Hemifield Test. Automated visual field evaluation. Arch Ophthalmol 1992;110(6):812-9.
- Um TW, Sung KR, Wollstein G, et al. Asymmetry in hemifield macular thickness as an early indicator of glaucomatous change. Invest Ophthalmol Vis Sci 2012;53(3):1139-44.
- Sharifipour F, Morales E, Lee JW, et al. Vertical Macular Asymmetry Measures Derived From SD-OCT for Detection of Early Glaucoma. Invest Ophthalmol Vis Sci 2017;58(10):4310-7.
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