November 2018
Volume 59, Issue 13
Open Access
Letters to the Editor  |   November 2018
Author Response: Challenges to the Common Clinical Paradigm for Diagnosis of Glaucomatous Damage With OCT and Visual Fields
Author Affiliations & Notes
  • Donald C. Hood
    Departments of Psychology and Ophthalmology, Columbia University, New York, New York, United States
  • Carlos Gustavo De Moraes
    Ophthalmology, Columbia University Medical Center, New York, New York, United States.
Investigative Ophthalmology & Visual Science November 2018, Vol.59, 5524. doi:10.1167/iovs.18-25796
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      Donald C. Hood, Carlos Gustavo De Moraes; Author Response: Challenges to the Common Clinical Paradigm for Diagnosis of Glaucomatous Damage With OCT and Visual Fields. Invest. Ophthalmol. Vis. Sci. 2018;59(13):5524. doi: 10.1167/iovs.18-25796.

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      © ARVO (1962-2015); The Authors (2016-present)

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In our Perspective (“Challenges to the Common Clinical Paradigm for Diagnosis of Glaucomatous Damage With OCT and Visual Fields”),1 we pointed out that early glaucomatous damage typically includes the macular/central ±8°. Thus, to detect and understand glaucomatous damage, clinicians should perform a 10–2, as well as a 24–2, visual field, and an optical coherence tomography (OCT) scan that includes the macula, as well as one that includes the disc. In addition, we argued that structural (OCT) and functional (visual fields) measures typically agree if one compares the abnormal regions seen on deviation/probability plots. 
In his letter to the editor, Dennis Mock2 addresses the latter point and nicely details some of the technical issues to keep in mind when comparing visual field and OCT measures. However, from the perspective of the clinic, a simple topographical comparison, as we have previously described,35 will suffice. That is, one does not need to do more than make a qualitative comparison, although this comparison can be quantified without taking into consideration the corrections/issues he describes.5 
Concerning his technical points, we agree in general for the need to be specific about physical units used in structure-function comparison, as well as the assumptions of the underlying model implied. We have the following two general thoughts. First, he assumes that “The light sensitivity is generally accepted to be proportional to the corresponding underlying quantity of retinal ganglion cells (RGC).” In addition to his reference of Malik et al.,6 others, including us, have also argued for a linear relationship between RGC axon loss and visual sensitivity.710 Thus, there is considerable evidence to support this assumption. However, there is both theoretical and empirical evidence that suggest the relationship may not be nonlinear in the macula.6,11,12 Further, mean deviation values should not be used for quantitative comparisons of function with structure, as it is a geometric average, and violates the linear assumption above. The anti-logs of these values should be averaged, as previously pointed out. For example, see Figure 6 in Hood and Kardon10 for an illustration of the logic. Finally, Mock correctly raises the issue of how to best normalize baseline conditions. However, this is a complex issue, and the alternatives too complex, to address fully in this format. 
References
Hood DC, De Moraes CG. Challenges to the common clinical paradigm for diagnosis of glaucomatous damage with OCT and visual fields. Invest Ophthalmol Vis Sci. 2018; 59: 788–791.
Mock DC. Letter to the editor: challenges to the common clinical paradigm for diagnosis of glaucomatous damage with OCT and visual fields. Invest Ophthalmol Vis Sci. 2018; 59: 5522–5523.
Hood DC, Raza AS, de Moraes CGV, Liebmann JM, Ritch R. Glaucomatous damage of the macula. Prog Retin Eye Res. 2013: 32: 1–21.
Hood DC. Improving our understanding, and detection, of glaucomatous damage: an approach based upon optical coherence tomography (OCT). Prog Retin Eye Res. 2017; 57: 46–75.
Hood DC, De Moraes CG. Four questions for every clinician diagnosing and monitoring glaucoma. J Glaucoma. 2018; 27: 657–664.
Malik R, Swanson WH, Garway-Heath DF. ‘Structure-function relationship' in glaucoma: past thinking and current concepts. Clin Exp Ophthalmol. 2012; 40: 369–380.
Garway-Heath DF, Viswanathan A, Westcott M, Kamal D, Fitzke FW, Hitchings RA. Relationship between perimetric light sensitivity and optic disk neuroretinal rim area. In: Wall M, Wild JM, eds. Perimetry Update 1998/1999. The Hague: Kugler Publications; 1999: 381–389.
Hood DC, Greenstein VC, Odel JG, et al. Visual field defects and multifocal visual evoked potentials: evidence for a linear relationship. Arch Ophthalmol. 2002; 120: 1672–1681.
Garway-Heath DF. Comparison of structural and functional methods. In: Weinreb RN, Greve EL, eds. Glaucoma Diagnosis. Structure and Function. The Hague: Kugler Publications; 2004: 135–143.
Hood DC, Kardon RH. A framework for comparing structural and functional measures of glaucomatous damage. Prog Retin Eye Res. 2007; 26: 688–710.
Swanson WH, Felius J, Pan F. Perimetric defects and ganglion cell damage: interpreting linear relations using a two-stage neural model. Invest Ophthalmol Vis Sci. 2004; 45: 466–472.
Raza AS, Cho JS, de Moraes CGV, et al. Retinal ganglion cell layer thickness and local visual field sensitivity in glaucoma. Arch Ophthalmol. 2011; 129: 1529–1536.
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