COMMENTARY

Seeking New Optical Coherence Tomography Targets for Tracking Glaucoma Progression

Shuchi B. Patel, MD

Disclosures

November 14, 2016

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

Miraftabi A, Amini N, Morales E, et al
Invest Ophthalmol Vis Sci. 2016;57:4815-4823

Study Summary

Spectral domain optical coherence tomography (SD-OCT) has been a beneficial instrument for detecting and monitoring glaucoma. To date, the retinal nerve fiber layer (RNFL) measurement concentric to the optic nerve has been the most commonly used parameter in this process.

More recently, however, it has been suggested that macular measurements provide accurate diagnosis of glaucoma, although their utility in monitoring progression has yet to be established. In addition, the thickness measurement of individual or combined layers that best correlates with function, as determined by visual field evaluation, is also currently unknown.

Miraftabi and colleagues tested the hypothesis that the macular ganglion cell layer (GCL) has a stronger structure/function relationship and extends the useful range of macular measurements, compared with combined macular inner layer or full thickness. They analyzed 98 glaucomatous eyes and eight normal eyes with SD-OCT volume scans and 10-2 visual fields. Inner plexiform layer (IPL), GCL, macular RNFL, ganglion cell/inner plexiform layer (GCIPL), ganglion cell complex (GCC), and full thickness measurements were calculated.

The main outcome measures were local structure/function relationships between macular superpixels and corresponding sensitivities on 10-2 fields, dynamic range of measurements (the difference between the smallest and largest observed thickness values for macular SD-OCT thickness parameters), and the change point (total deviation value where macular parameters reached measurement floor). For patients with perimetric glaucoma, three OCT scans (quality factor ≥ 15) were obtained, one of which was chosen at random. For all other patients, only one scan was obtained. In addition, 10-2 visual fields were obtained, and the central 18° corresponding to the macula and the central 24 superpixels on SD-OCT were correlated.

The structure/function relationship was highest for GCIPL, GCL, GCC, and IPL, in that order. The highest structure/function correlations coincided with the peak of GCL thickness, where the dynamic range was widest for full thickness, followed by GCC, GCIPL, GCL, macular RNFL, and IPL. Change points were similar for all macular parameters.

The hypothesis that GCL would offer the most useful measurement, in terms of strongest structure/function relationship and dynamic range, was therefore proven incorrect. The authors concluded that measuring GCL independently with current SD-OCT technology did not provide any advantage for detecting glaucoma progression.

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