Macular OCT is useful for examining the RGCs and axons, the cells that are affected by glaucoma. The currently available devices differ in the areas sampled as well as the layers that they assess.
This article was reviewed by Jullia A. Rosdahl, MD, PhD
Jullia A. Rosdahl, MD, PhD, demonstrated the importance of the technology for her patients, describing the case of a 69-year-old Caucasian man who she last saw five years earlier, and who did not want treatment at that time. After another physician recommended treatment, he returned for a second opinion for his normal tension glaucoma.
The patient had visual acuities of 20/25 in both eyes and intraocular pressures of 13 mm Hg in both eyes (untreated). He had a paracentral visual field (VF) defect that had not worsened measurably over the five years. Progressive retinal nerve fiber layer (RNFL) thinning was seen on the OCT maps and corresponded to the VF defect. The glaucoma appeared to have progressed. The patient was skeptical.
Dr. Rosdahl is associate professor of ophthalmology, Duke University, Department of Ophthalmology, Chapel Hill, NC.
Macular OCT showed inferior thinning and, she pointed out, progression analysis showed two characteristic arcuate-shaped areas of progression. With this information, the patient was convinced of his progressive disease and agreed to treatment.
Preserving the RGCs
Most of the retinal ganglion cells (RCGs) are in the macula, in the inner three layers of the retina (retinal nerve fiber layer, ganglion cell layer, inner plexiform layer). These layers are collectively termed the ganglion cell complex and account for 40% of the macular thickness.
Once the RGCs are affected, blindness ensues. Measurement of the RCGs is useful to assess glaucoma because the RCGs numbers in the macula are relatively consistent amongst the population, Dr. Rosdahl explained.
More RCGs are present in the central retina than in the peripheral retina. Therefore, the numbers of RCGs sampled during automated VF testing varies considerably between the periphery and central tissues, with VF points in the periphery representing smaller numbers of RGCs than VF points centrally.
Dr. Rosdahl noted that the devices appear to be more helpful in patients with a mean deviation better than -10 decibels on automated VF testing.
This is not a cut-off, though, as she showed an example where the macular OCT scans helped in a patient who could no longer perform automated VF testing.