Macular Optical Coherence Tomography—From Diagnosis to Prognostication

Abstract

The article by Mohammadzadeh and coauthors 1 investigates longitudinal trend-based assessment of optical coherence tomography (OCT) macular thickness measures, specifically the ganglion cell and inner plexiform layers (GCIPL; Cirrus OCT; Carl Zeiss Meditec). The association between imaging assessed macular thickness and glaucoma was first proposed and then demonstrated by Zeimer and colleagues. [2][3][4] This concept was heretical, in that glaucoma was thought by many to affect first the periphery and then the macula only late in the disease process. The proposal was that glaucoma would be detectable in the macula, perhaps more easily so than in or around the optic disc, as approximately 50% of retinal ganglion cells reside in the macula and because retinal ganglion cell bodies are about 10-to 20-fold the diameter of their 1 μm-thick axons.Zeimer and coauthors used a prototype 2,3 and then a commercial (Talia) 4 retinal thickness analyzer, which projected a slit laser beam onto the retina. The distance between the anterior and posterior borders of the beam could be quantitated and retinal thickness derived from these measurements. Depth resolution was approximately 50 μm, making the macula an attractive target for the retinal thickness analyzer, as opposed to the disc and peripapillary tissues.A short time after the feasibility article by Zeimer et al 2 was published, OCT was invented. With OCT's higher axial resolution at approximately 10 μm at that time, interest for glaucoma diagnosis was directed mainly to the circumpapillary retinal nerve fiber layer (cpRNFL) and optic nerve head (ONH) parameters. Our group assumed (always a bad idea) that the cpRNFL would be a better area to scan for glaucoma damage than the ONH or macula.