Macular SD-OCT Outcome Measures: Comparison of Local Structure-Function Relationships and Dynamic Range

Glaucoma Macular SD-OCT Outcome Measures: Comparison of Local Structure-Function Relationships and Dynamic Range Arezoo Miraftabi, 1,2 Navid Amini, 1 Esteban Morales, 1 Sharon Henry, 1 Fei Yu, 1,3 Abdolmonem Afifi, 3 Anne L. Coleman, 1 Joseph Caprioli, 1 and Kouros Nouri-Mahdavi 1 Glaucoma Division, Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California, United States 2 Eye Research Center, Rasoul Akram Hospital, Iran University of Medical Sciences, Tehran, Iran Department of Biostatistics, Jonathan and Karin Fielding School of Public Health, University of California, Los Angeles, Los Angeles, California, United States Correspondence: Kouros Nouri- Mahdavi, 100 Stein Plaza, Los An- geles, CA, 90095, USA; nouri-mahdavi@jsei.ucla.edu. Submitted: March 28, 2016 Accepted: July 14, 2016 Citation: Miraftabi A, Amini N, Morales E, et al. Macular SD-OCT outcome measures: comparison of local struc- ture-function relationships and dy- namic range. Invest Ophthalmol Vis Sci. 2016;57:4815–4823. DOI:10.1167/iovs.16-19648 P URPOSE . We tested the hypothesis that the macular ganglion cell layer (GCL) thickness demonstrates a stronger structure-function (SF) relationship and extends the useful range of macular measurements compared with combined macular inner layer or full thickness. M ETHODS . Ninety-eight glaucomatous eyes and eight normal eyes with macular spectral domain optical coherence tomography (SD-OCT) volume scans and 10-2 visual fields were enrolled. Inner plexiform layer (IPL), GCL, macular retinal nerve fiber layer (mRNFL), ganglion cell-inner plexiform layer (GCIPL), ganglion cell complex (GCC), and full thickness (FT) measurements were calculated for 8 3 8 arrays of 38 superpixels. Main outcome measures were local structure- function relationships between macular superpixels and corresponding sensitivities on 10-2 fields after adjusting for ganglion cell displacement, dynamic range of measurements, and the change point (total deviation value where macular parameters reached measurement floor). R ESULTS . Median (interquartile range [IQR]) mean deviation was 7.2 (11.6 to 3.2) dB in glaucoma eyes. Strength of SF relationships was highest for GCIPL, GCL, GCC, and IPL (q ¼ 0.635, 0.627, 0.621, and 0.577, respectively; P 0.046 for comparisons against GCIPL). Highest SF correlations coincided with the peak of GCL thickness, where the dynamic range was widest for FT (81.1 lm), followed by GCC (65.7 lm), GCIPL (54.9 lm), GCL (35.2 lm), mRNFL (27.5 lm), and IPL (20.9 lm). Change points were similar for all macular parameters (7.8 to 8.9 dB). C ONCLUSIONS . GCIPL, GCL, and GCC demonstrated comparable SF relationships while FT, GCC, and GCIPL had the widest dynamic range. Measurement of GCL did not extend the range of useful structural measurements. Measuring GCL does not provide any advantage for detection of progression with current SD-OCT technology. Keywords: macular imaging, SD-OCT, dynamic range, structure-function dentification of glaucoma progression is a pivotal task in day- to-day management of glaucoma, to which various structural and functional measures have been applied. The advent of spectral-domain optical coherence tomography (SD-OCT) has provided the glaucoma research community with a powerful tool for detecting early glaucoma or its progression. Many reports have highlighted the potential role of retinal nerve fiber layer (RNFL), 1,2 although more research is needed to better understand its limitations and the appropriate circumstances for its application. Some recent investigations have demon- strated the utility and added value of macular SD-OCT imaging for detecting glaucoma, but its role remains less well defined with respect to progression. 3–10 Thanks to development of segmentation algorithms applied to SD-OCT imaging, various inner macular parameters are now available to investigators and clinicians. 3,11,12 These include single layer measurements such as ganglion cell (GCL), inner plexiform (IPL), or retinal nerve fiber layer, combination of inner retinal layers such as the ganglion cell-inner plexiform layer (GCIPL) and the ganglion cell complex (GCC), which includes the combined I thickness of the GCIPL and macular RNFL (mRNFL), or the full retinal thickness. The comparative utility of these various thickness parameters for detection of glaucoma progression is unknown. To this aim, the strength of the corresponding structure-function relationships and the comparative dynamic range of these parameters need to be compared. Another issue of interest is the point of change on structure-function plots at which each parameter reaches its measurement floor. We hypothesized that the macular GCL has a stronger correlation with central visual field sensitivities and may extend the range of useful structural measurements compared with other individual or combined inner retinal layers and may be a better outcome measure for detection of glaucoma progression. To this aim, this study was carried out to compare: (1) localized structure-function relationships between GCL and other macular thickness measurements, (2) the dynamic range of macular structural parameters, and (3) the change point for these parameters (i.e., the approximate threshold sensitivity beyond which the structural measures do not provide much additional information). iovs.arvojournals.org j ISSN: 1552-5783 This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.